US20110316716A1 - Low power wireless parking meter and parking meter network - Google Patents

Abstract

A parking meter and parking meter network is described as well as a method of operating the parking meter and parking meter network. The parking meter network includes a gateway that transmits a first beacon message that is received at the parking meter. The parking meter synchronizes an internal timer based on the receiving of the first beacon message, and then goes to sleep for a period of time. The gateway transmits a second beacon message and the parking meter wakes up at the expiration of the sleep period using the synchronized internal time and receives the second beacon message.

Description

TECHNICAL FIELD
• The present disclosure relates generally to parking meters, and more particularly to low power wireless parking meters and a system of low power wireless parking meters.
BACKGROUND
• Cities may deploy thousands of single-space parking meters throughout their jurisdiction. The management of such a deployment is labor intensive. Costs of overhead can be larger than necessary due to the normal inefficiencies in managing large distributed systems.
• Wireless parking meters have been devised that enable the parking meter to communicate with enforcement officers or backend parking meter management systems to make parking enforcement, as well as management of the parking meters, more efficient. Networked parking meters have used cellular networks for communication, or other network communication such as WiFi (802.11a/b/g/n) protocols. While these communication protocols may provide network connectivity to the meter, their power requirements do not make them ideally suited to their use in battery powered parking meters. In addition the costs for a commercial cellular data plan required for each module may become prohibitive.
• Some wireless parking meters may use a low power communication protocol such as ZigBee or SSIPCO for the wireless communication. However, while these communication protocols are designed for low powered devices, they may have unnecessary overhead for use in a battery powered single space parking meter.
• The use of wireless systems have disadvantages when used in battery powered parking meters, which may include, for example, shorter operation time due to increased power consumption, and communication latency when communicating with a backend system. The power consumption and communication latency may be affected by the communication protocol used.
• Current wireless battery powered meters do not provide a power efficient means for allowing a backend parking management system to initiate communication with the parking meter in a manner that provides low latency and low power consumption.
SUMMARY
• In accordance with an embodiment of the present disclosure there is provided a method of operating a wireless parking meter network. The method comprises transmitting from a gateway a first beacon message; receiving at a parking meter the first beacon message; synchronizing an internal timer of the parking meter based on receiving the first beacon message; placing the parking meter in a sleep mode for a period of time (sleep period); transmitting from the gateway a second beacon message; placing the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer; and receiving at the parking meter the second beacon message.
• In accordance with a further embodiment of the present disclosure there is provided a method of operating a wireless parking meter in a parking meter network. The method comprises receiving at the parking meter a first beacon message from the parking meter network; synchronizing an internal timer of the parking meter based on receiving the first beacon message; placing the parking meter in a sleep mode for a period of time (sleep period); placing the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer; and receiving at the parking meter a second beacon message from the parking meter network.
• In accordance with a still further embodiment of the present disclosure there is provided a parking meter for use in a parking meter network. The parking meter comprises a parking meter mechanism; a radio board for receiving messages; a processor executing instructions; and a memory storing instructions executed by the processor. The executed instructions provide in the parking meter a radio board module operable to receive a beacon message; and, a device module that is operable to synchronize an internal timer of the parking meter based on receiving the beacon message, place the parking meter in a sleep mode for a period of time (sleep period), and place the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer.
• In accordance with yet a further embodiment of the present disclosure there is provided a parking meter network. The parking meter network comprises a gateway for transmitting beacon messages; and a parking meter. The parking meter comprises a parking meter mechanism; a radio board for receiving messages including the beacon messages and transmitting messages; a processor executing instructions; and a memory storing instructions executed by the processor. The executed instructions provide in the parking meter a radio board module that is operable to receive a beacon message; and, a device module that is operable to synchronize an internal timer of the parking meter based on receiving the beacon message, place the parking meter in a sleep mode for a period of time (sleep period), and place the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer.
BRIEF DESCRIPTION OF THE DRAWINGS
• Embodiments of the present disclosure will be described with reference to the Figures in which:
• FIG. 1 is a diagram showing an illustrative parking meter network in accordance with the present disclosure;
• FIG. 2 is a diagram showing an illustrative sub-system of a parking meter network in accordance with the present disclosure;
• FIG. 3 depicts in a timing diagram the timing of a device communicating using frequency hopping in accordance with the present disclosure;
• FIG. 4 is a diagram showing illustrative communication paths of components in a parking meter network in accordance with the present disclosure;
• FIG. 5 is a diagram showing two illustrative sub-systems of a parking meter network in accordance with the present disclosure;
• FIG. 6 is a diagram showing illustrative components of a parking meter in accordance with the present disclosure;
• FIG. 7 is a diagram showing illustrative components of a parking meter in accordance with the present disclosure;
• FIG. 8 is a flow diagram showing an illustrative method of a gateway registering a repeater in accordance with the present disclosure;
• FIG. 9 is a flow diagram showing an illustrative method of a repeater registering with a gateway in accordance with the present disclosure;
• FIG. 10 is a flow diagram showing an illustrative method of initializing a parking meter in accordance with the present disclosure;
• FIG. 11 is a message flow diagram showing illustrative messages for processing an event at a parking meter in accordance with the present disclosure;
• FIG. 12 is a message flow diagram showing illustrative messages for a backend system communicating with a parking meter in accordance with the present disclosure;
• FIG. 13 is a message flow diagram showing illustrative messages for processing a credit card payment at a parking meter in accordance with the present disclosure; and
• FIG. 14 is a message flow diagram showing illustrative messages for processing a parking meter payment received at a backend system in accordance with the present disclosure.
DETAILED DESCRIPTION
• FIG. 1 is a diagram showing an illustrative parkingmeter network system100 in accordance with the present disclosure. A parkingmeter network system100 is depicted that comprises twosub-systems104 and106. As further described herein thesub-systems104,106 provide wireless communication between battery powered parking meters and a back-end system110.FIG. 1 depicts a singleillustrative parking meter120; however it is understood that multiple parking meters will typically be present in the parkingmeter network systems100. Thesub-systems104,106 have a communication coverage range in which they may communicate with wireless parking meters. The communication range of the sub-systems may overlap as depicted inFIG. 1, in which bothsub-systems104,106 can communicate withparking meter120. The range of the twosub-systems104,106 is depicted as being 200 meters. However as is well understood the range of wireless communication may be affected by various factors, including for example the location of obstacles and other electromagnetic signals. As such the communication ranges described herein are to be understood as illustrative. Furthermore the communication ranges may be changed by adjusting the power of the transmitter in order to obtain the desired communication coverage.
• Thesub-systems104,106 are arranged in an area wherewireless parking meters120 are deployed, for example alongcity streets102, or parking lots. Thesub-systems104,106 may be connected to a back-end system110 through various communication means, for example, through a wired or wireless internet connection or a cellular network. Regardless of the specific connection, it is understood that thesub-systems104,106 are considered to be connected to the back-end system110 generally through anetwork108.
• The back-end system110 may be a computer or server running software that allows theparking meter network100 to be managed. As is will be understood, the computer or server includes at least one processor for executing instructions stored in a memory. As is further understood, the computer or server may comprise multiple processors and memory units. Furthermore the implementation of the backend system may be distributed across multiple computers or servers that may be located in the same or different areas and are operatively coupled together. The back-end system110 may provide auditing of the parkingmeter network system100, including, for example, determining the usage ofvarious parking meters120 to help determine parking patterns. The back-end system110 may also provide enforcement information such as locations of high activity, or whereparking meters120 have expired. The back-end system110 may also provide maintenance information such as which meters are jammed or require a battery to be replaced. This information may be sent to enforcement officials or maintenance personnel. The information may also be used in planning parking regulations.
• As described further herein, the back-end system110 may also be used to co-ordinate payment atparking meters120. For example theparking meters120 and parkingmeter network system100 as described herein may be used to facilitate the use of a credit card at aparking meter120 for making payment, or may facilitate the use of alternative methods of payment, such as the use of a cell phone, SMS text messages, or over the Internet or using an Internet, or other communication network, enabled device.
• As shown inFIG. 1, the communication range ofsub-systems104,106 may overlap. This may be advantageous for providing more reliable communication with theparking meter120, since aparking meter120 may be able to communicate withmultiple sub-systems104,106. In order to avoid the communication signals of the two sub-systems from interfering with each other, the parkingmeter network system100 uses spread spectrum techniques, such as frequency hopping, to communicate with themeters120.
• Eachsub-system104,106 communicates withmeters120 using frequency hopping. Eachsub-system104,106 is provided with a channel set that determines the frequency channels it will communicate on. The channel set provided to thesub-systems104,106 may be a pseudo-random order list of frequencies as the channel set. Each channel set is orthogonal to the other channel sets, as such adjacent sub-systems are able to communicate withparking meters120 without interfering with the communication ofadjacent sub-systems104,106.
• Although only twosub-systems104,106 are depicted, as many sub-systems may be used as is required to provide sufficient coverage of the area in which wireless parking meters are deployed.
• FIG. 2 is a diagram showing anillustrative sub-system104 of a parking meter network in accordance with the present disclosure. It is understood that thesub-system104 described with reference toFIG. 2 would be similar to additional sub-systems used in theparking meter network100; however the additional sub-systems would use different channel sets.
• Thesub-system104 comprises agateway205, a plurality ofrepeaters210,211,212,213,214,215, and a plurality ofwireless parking meters120 deployed about acity street102. Also depicted inFIG. 2 arewireless parking meters222 which are not in communication with thesub-system104. Theseparking meters222 could be in communication with another sub-system (not shown).
• Thegateway205 acts as a link between thewireless parking meters120 and theback end system110 ofFIG. 1. The repeaters210-215 repeat messages they receive, either from thegateway205 or fromparking meters120. The communication range of thedevices205,210-215 and120 is typically the same range. Arepeater215 is depicted as having a communication range of 100 meters. As a result, it will be placed within 100 meters of thegateway205, which will result in the 200 meter communication range of thesub-system104, depicted inFIG. 1, since aparking meter120 will be able to communicate with therepeater215 from a distance of 100 meters, and the repeater can communicate with thegateway205 from a distance of 100 meters.
• Although it is possible to use multiple repeaters210-215 to pass a message from aparking meter120 to thegateway205, in order to achieve a low latency for communication only a single repeater is used when communicating between a parking meter and thegateway205. That is, a message may be passed from aparking meter120 to arepeater215 to thegateway205. However, it is not passed from theparking meter120 to therepeater215 then to anotherrepeater214 and finally to thegateway205. This restriction is made in order to maintain a low latency for communication. It is understood that in situations where a higher communication latency is acceptable this restriction may be relaxed.
• As described further herein, messages are passed between thegateway205 and theparking meters120. The repeaters210-215 forward messages either to theparking meters120 from thegateway205, or to thegateway205 from theparking meters120 if theparking meters120 are out of communication range of thegateway205. In order to minimize the system requirements of the repeaters, for example the amount of memory required for storage and/or the processing power of its processor, they do not store messages and only forward messages on.
• As set forth above, thesub-systems104,106, or more particularly the gateways, repeaters and parking meters of the sub-systems, use the spread spectrum technique of frequency hopping for communication. The carrier frequency used to communicate between devices of the sub-systems of the parking meter network can change many times per second. A communication system that uses a single channel is less robust than a communication system that changes channels. As required by the FCC, each channel cannot be used more than 400 ms in a 10 second window. Also, all channels must be used equally by the system and by every device within the system. To satisfy these requirements, at least 25 channels should be used and all sub-system devices should channel hop.
• FIG. 3 depicts in a timing diagram the timing of a communication device communicating using frequency hopping. Thedwell time302 is the time the communication device spends communicating on each channel. The blankinginterval304 is the unusable time that occurs between channel changes. As described herein a beacon message may be transmitted at the beginning of each frequency hop. The time between transmitting beacons is the sum of the dwell time and the blanking interval and is depicted as thebeacon interval306 inFIG. 3. Thedwell time302, blankinginterval304 and thebeacon interval306 are constant as is illustrated inFIG. 3. The parking meter system dwell time may be for example 400 ms. The parking meter system blanking interval may be for example 500 uSec.
• A channel set is an ordered list of channels, also referred to as frequencies, a radio of a sub-system device will cycle through as part of its frequency hopping. In the parking meter network system there may be, for example, 16 channel sets, each consisting of the same 25 channels in different pseudo-random orders. The channel sets can be created orthogonally, for example by having sequences of channels in different directions so that the channels could only overlap once per channel set cycle, to minimize the amount of interference between radios using different channel sets. The number of channel sets is not bound by a firm system requirement. Sixteen (16) channel sets may be sufficient for a parking meter network system application. However, the number of channels sets may be varied depending on the requirements of the parking meter system. Also, the above has described the 16 channel sets as using the same 25 channels in differing orders, It is possible for the parking meter network system to use more channels than 25; however each channel set would still comprise an ordered list of 25 channels, or the number of channels used in a channel set.
• The specific channel set used by agateway205 can be configured during installation of thegateway205. Thegateway205 may then forward the channel set it is configured to use for communicating to a repeater when it joins the parking meter system via a Network Initialization Vector (NIV). The NIV includes the channel set indicating the frequencies, and their order used by thegateway205. The NIV may also be received by parking meters in order to determine the channel to use in order to communicate with the gateway.
• Whengateway205 hops to the next frequency in the channel set it transmits a beacon message that includes the NIV of thegateway205. This beacon message may be used by theparking meters120 and the repeaters210-215 in order to synchronize their communication timing and frequency hopping timing. The communication timing may provide a time window for a sub-system device to use when communicating with other sub-system devices. The beacon message may also be used by themeters120 and repeaters210-215 in order to determine the channel set used by thegateway205, through the NIV.
• In order to initially receive a beacon message a repeater orparking meter120 may scan through all of the frequencies used in the collection of channel sets of the parking network system to detect if a beacon message is being broadcast. These frequencies may be pre-programmed into the repeaters and parking meters. The parking meter or repeater may listen on each frequency for a given period of time to detect a beacon message, for example the dwell time of 400 ms before switching to another frequency. It is possible to detect beacon messages being transmitted in different ways. For example, instead of dwelling on each frequency for the illustrative dwell time of 400 ms, the parking meter or repeater may dwell on each frequency only long enough in order to detect if a beacon is being transmitted, and if a beacon is detected the receiver or parking meter may remain on the frequency until the beacon has been received. Alternatively, if the channel sets all comprise the same frequencies, a repeater or parking meter may dwell on a single frequency for an entire channel set cycle. The time may be, for example, [dwell time (500 ms)+blanking interval (500 us)]×number of frequencies in channel set (25). This method may be used even if there is only a single frequency which is common to all channel set. This may be extended in order to listen to a first frequency for the channel set cycle to for example detect beacons from gateways using a first set of channel sets with the first frequency in common, followed by detecting beacons on a second frequency common to a second set of channel set used by gateways in the parking meter network system. Regardless of the technique used, once a beacon message is detected, the repeater or parking meter is able to determine the channel set used by thegateway205 from the NIV included in the beacon message and no longer needs to hop through all of the frequencies used by the parking meter network.
• Each repeater210-215 registers with thegateway205. The number of repeaters that may register with thegateway205 may vary depending on the requirements of the system, however as described herein, thegateway205 is able to register up to 6 repeaters. When a repeater registers with agateway205 it uses the gateway's channel set described in the gateway's NIV for communications. Once a repeater registers with a gateway it begins to send beacon messages as well. As described further herein the timing of the sending of beacon messages may occur in a predetermined manner; and only a single repeater of the possibly 6 registered repeaters broadcasts a beacon message after the gateway's beacon message. This may be coordinated by having the gateway broadcast a beacon message including a short system ID assigned to the repeater that is to repeat or forward the beacon message.
• Unlike repeaters210-215, eachparking meter120 may communicate with different sub-systems comprising agateway205 and any registered repeaters. Eachparking meter120 determines the best communication path to agateway205 and uses that path for its communications. If the determined best path is broken or unavailable, the parking meter is able to select and use a different path, either to communicate with the same gateway, or a different gateway. In order for thebackend system110 ofFIG. 1 to communicate withindividual parking meters120, each parking meter is provided with a unique identifier. The unique identifier may be a 32 bit number.
• FIG. 4 is a diagram showing illustrative communication paths of components in a parking meter network system in accordance with the present disclosure. Eachparking meter120 is able to determine the link quality of messages it receives. For example a radio of theparking meter120 may provide a measure of the quality through a link quality indicator (LQI). During the initialization of aparking meter120, theparking meter120 scans all available frequencies to determine all available communication paths to gateways. This is done by receiving beacon messages from gateways and/or repeaters. Aparking meter120 associates a LQI value with each beacon message it receives. Each beacon message indicates a possible communication path from the parking meter to a gateway. The path may either be direct or through a repeater. Once the parking meter has received all beacon messages, they are ordered from highest LQI to lowest LQI. The parking meter will then use the highest quality communication path available for its subsequent communication.
• With reference toFIG. 4,parking meter120 has three communication paths available for communicating with thegateway205. The first path is a direct path to thegateway205 with an LQI of 60. The second path is throughrepeater215 and has an LQI of 10. The third path is throughrepeater214 and has an LQI of 30. Theparking meter120 would preferably use the direct path to the gateway for communication. If this communication path is unusable, for example multiple messages sent from the parking meter to the gateway are not acknowledged, theparking meter120 will attempt to use the next best communication path, in the example ofFIG. 4 this would be throughrepeater214. If this link is unusable, for example messages sent through therepeater214 are not acknowledged by thegateway205, the parking meter would use the next best path, which would be throughrepeater215. The example ofFIG. 4 depicts only asingle gateway205, however theparking meters120 are not registered with aparticular gateway205, and as such it is possible to use a communication path to another gateway, as described below with reference toFIG. 5.
• FIG. 5 is a diagram showing two illustrative sub-systems of a parking meter network in accordance with the present disclosure.FIG. 5 depicts twosub-systems104,106, each with agateway205,405 respectively.Parking meter120 is within communication range of bothgateways205,405 of thesub-systems104,106. This communication may either be direct or through a repeater (not shown). When theparking meter120 is initialized it will determine all possible communication paths, not just the communication paths to a single sub system. As such if communication is lost with the highest quality path, for example withgateway205, theparking meter120 will use the next highest quality link, even if that is through a different sub-system, in this case throughgateway405.
• FIG. 6 is a diagram showing illustrative components of aparking meter120 in accordance with the present disclosure. The components of theelectronic parking meter120 may be selected to operate from a 3.3 volt power supply (not shown) in order to contribute to the energy efficiency of theparking meter120.
• Theelectronic parking meter120 includes amicrocontroller530, which may be used to control its operations. Themicrocontroller530 comprises a number of components that populate a printed circuit board (PCB) (not shown). It has been found to be particularly advantageous to have all of the components located on one side, the front side, of the PCB so that there is sufficient space on the backside of the PCB for a battery pack (not shown).
• Themicrocontroller530 comprises a processor (CPU)531 associated with aflash memory532 and a random access memory (RAM)533. CPU531 may be a Texas Instruments—MSP430F449 processor or any other type of similar processor operating at 3.3 volts. Theflash memory532 is a rewritable memory in which is stored theelectronic parking meter120 software and operating parameters, as well as radio control components as described further with reference toFIG. 6. TheRAM533 may be a fast read-write memory for the temporary storage of variables and the like during software processing.
• Themicrocontroller530 clocking system is basically controlled by a 32.768 kHzcrystal clock534, which drives frequency locked loop (FLL)535 to provide an output having a frequency of 7.3 MHz, the operating frequency for the CPU531. However, in addition theclock534 drives abasic timer536 that may be used as an internal timer to periodically wake-up the CPU531 from a low power or sleep mode as well as to control the CPU531 to produce a real time clock which may be used to provide parking meter functionality, such as when to apply particular rate schedules. In this particular embodiment, the basic timer provides a 64 Hz output signal. A further 3.58MHz crystal clock537, which is normally powered off, is also adapted to be coupled toFLL535.Clock537 is powered up, when required, to provide an appropriate clock for a card reader to be described below. In this situation,clock534 continues to be coupled tobasic timer536 to provide the 64 Hz signal.
• Themicrocontroller530 may include atemperature sensor538, which measures the actual temperature of the environment of the microcontroller531 of theparking meter120. Thetemperature sensor538 may be polled periodically to log the temperature of the meter. The temperature may be logged inflash memory532. The temperature reading may be used for a number of purposes such as to adjust a real time clock, to modify the operation of LCD's, to compensate for battery power level fluctuation due to temperature change and to compensate coin sensors in a coin chute.
• Theparking meter120 has input andoutput interfaces539 that may include a number of devices. A standard input device forparking meters120 is acoin chute540, which receives coins inserted into a coin slot in themeter120 housing and which, using coin sensors541, recognizes the coins. One form of coin chute is described in U.S. Pat. No. 6,227,343 issued on May 8, 2001, which is incorporated in its entirety herein by reference. Thecoin chute540 is normally in the sleep mode, however CPU531 under the control of thebasic timer536, periodically polls the coils in the coin sensors541 to determine if a coin is dropping through thechute540.Coin chute540 may be modified from the chute described in the above patent regarding the hardware for processing information. Rather than include a processor within the coin chute, thepresent coin chute540 performs an analog to digital conversion to digitize the information generated by the coin sensors541; the digitized information is transmitted to CPU531 through the I/O539 where it is processed to determine the time purchased by a user. The coin transaction information may also be stored in the electrical erasable programmable read only memory (EEPROM)542. This audit information may therefore remain with thechute540 if it is removed for maintenance or for insertion into another parking meter.
• Thechute540 can further include anRF communications port543 that is accessed by inserting an antenna into the coin slot of the coin chute640 to achieve high speed wireless communications with themeter120 CPU631.
• An optional input device for theparking meter120 is acard reader545 for asmart card546 that is ISO 7816 compliant. The standard operating voltage forsmart cards540 is 1.8, 3 or 5 volts. Since the power supply (not shown) output voltage is 3.3 volts, the ISO 7816interface547 is used to step up the supply voltage to 5 volts or step down the voltage to 1.8 or 3 volts. As with thecoin chute540, thecard reader545 is normally in the sleep mode consuming insignificant amounts of power. However, in the case of thecard reader545, a mechanical switch causes an interrupt when acard546 is inserted into thereader545. CPU531 thus interrogates thecard reader545 through ISO 7816interface547 to determine the operating voltage of the card and than starts the routine for payment bysmart card546.
• With the addition of aSAM socket548, theparking meter120 is able to validate the money on thecard546 and decode information through decryption algorithms and keys, which are stored on theSAM548. Using aSAM548, themeter120 will be able to accept higher level card systems, may take money off of the card and store it in theSAM548 itself or inmemory532. This money data may then be taken from theSAM548 or thememory532 through an audit.
• Card reader545 purchase interfaces fall into two standard groups. The first is a buttonless approach. Acard546 is inserted into thecard reader545 and after thecard546 is identified and read, parking time is incremented automatically on theparking meter120, i.e. the longer a card is left in thereader545 the greater the amount of time has been purchased. Thus a user has to watch the time increment on themeter120 and then remove thecard546 when the desired amount of time is reached. In the second approach, thecard546 is identified and read in the same manner as the first, however in this case the user must manually increment the time desired on themeter120. This is accomplished by having the user push abutton550. Thus the time increments with every push of thebutton550, allowing the user greater control.
• Thecard reader545 may also include a credit card reader for reading credit card transactions. The parking meter network described herein provides a low latency and low power communication protocol that enables battery powered parking meters to communicate with a back-end system to process credit card transactions.
• In addition to the parking meter mechanism components described above, theparking meter120 includes anRF radio board560 for communicating with thegateway205, or repeaters210-215. Theradio board560 may include aradio module562 that includes a radio transceiver566 for transmitting and receiving RF signals, amicrocontroller564 for controlling the transceiver566, a plurality of oscillators570,572 for providing the required timing signals and anantenna568 for sending and receiving the RF signals. Theantenna568 may form part of theRF radio board560, or it may be connected to the RF radio board, for example by a wire or cable which may allow the antenna to be placed in the parking meter in a location that maximizes the transmission of the signals, and so reduce the power requirements of the parking meter.
• TheRF radio board560 may be connected to the parking meter mechanism through an expansion port or other type of connection. The expansion port may connect the microcontroller of the RF radio board with the microcontroller of the parking meter mechanism. The parking meter mechanism may control the operation of the RF radio board by sending commands to the microcontroller of the RF radio board over an SPI Bus. Theradio board560 is described in relation to a parking meter, however substantially similar radio boards may be included in other devices of the parking meter network system, including the gateways and repeaters.
• Themicrocontroller564 andtransceiver568 may be separate components or may be provided in a single package. In one embodiment themicrocontroller564 and thetransceiver568 are provided in a single package and is a CC1110F16RSP sold by Texas Instruments. The RF radio board may transmit/receive in the industrial, scientific and medical (ISM) band in the 902-928 MHz frequency range. This is often referred to as a 900 MHz system. Although the 900 MHz band is described, it is understood that a different band may be required in certain jurisdictions, such as the 2.4 GHz band.
• FIG. 7 is a diagram showing illustrative components of a radio device in accordance with the present disclosure. The radio device may include gateways, repeaters and/or parking meters. The components ofFIG. 7 may be implemented within the hardware of thedevice600. The components may be implemented using instructions stored in memory of the device. These instructions may include software code, firmware, hardware or a combination thereof. Thedevice600 refers generically to a gateway repeater or parking meter. Thedevice600 comprises a radio module which may be implemented in part or in whole by theRF radio board560 described with reference toFIG. 6, and a device module which may be implemented in part or in whole by the device components, including a microprocessor and memory. For example, when the device is a parking meter the device module may comprise the parking meter mechanism502 described with reference toFIG. 5, including operating instructions stored in the memory and executed by the microprocessor to provide the parking meter functionality. The device module of a repeater and gateway may only include a microprocessor and memory. It is understood that the repeaters and gateways may comprise additional components if it is desirable for them to perform additional tasks.
• The microcontroller of theradio board560, or other components implementing the radio module, may provide, by the execution of instructions stored in memory, anSPI driver605. TheSPI driver605 allows the device to control the radio board, its microprocessor or its transceiver, by issuing commands that are implemented by theSPI driver605. The radio board may be a slave device to the microcontroller of the device. TheSPI driver605 provides a means for getting command/control and data packets into and out of the microcontroller of the radio board.
• The microcontroller of the device may provide, by the execution of instructions stored in memory, a protocol or software stack to allow the device to perform the required tasks. The software stack may comprise adevice software stack610 and aradio control stack612. Thedevice software stack610 may be specific to the type of device, for example a repeater, gateway or parking meter. Theradio control stack612, which is common to the devices, may provide basic functionality for controlling the radio board to the device software stack.
• Theradio control stack612 may comprise anSPI protocol layer614 for implementing the synchronous serial protocol (SPI based) that allows for communications between the microcontroller of the device and the microcontroller of radio board. This protocol may also support configuring network and device parameters over the SPI interface. These parameters may include, for example, RF channel, Network ID, Device ID, etc.
• Theradio control stack612 may also comprise an RF MACFrequency hopper layer616 for implementing the frequency hopping MAC layer that upper layers of theradio control stack612 can utilize to transport RF messages over the parking meter network. The RF MAC Frequency hopper provides hopping and synchronizing of the parking meter network to the hop sequence and timing of the network.
• Theradio control stack612 may also comprise asynchronizer layer618 for providing a timing scheme to keep the various components of the parking meter network within a tight and manageable time frame. This allows all devices to synchronize as quickly as possible, while conserving power. In addition, thesynchronizer layer618 may implement a method of duty cycling that puts all devices to sleep in a systematic way to limit the power consumption.
• Theradio control stack612 may also comprise an RF protocol layer which includes a highlevel RF protocol622 and a low-level RF driver620. The high level RF protocol implements parking meter network functions such as discovering sub-systems, joining sub-systems, verifying a path to a gateway, finding a path to a gateway, etc.
• Theradio control stack612 may also comprise anAES security layer624 for providing encryption and decryption of information sent over the parking meter network. This may be used since the parking meter network may allow credit card payments to be made at the parking meter, and as such the communication should be encrypted.
• Components of the device stack have been described with reference toFIG. 7. Although various components have been described to provide the functionality of devices of the parking meter network system, it is understood that the components are one possible illustrative embodiment. The functionality may be implemented in devices using more or fewer components that provide different functionality from the components described inFIG. 7.
• The devices of the parking meter network, namely the gateways, repeaters and parking meters, may transmit messages that are formatted in packets. The data field of each packet, depending on the message type, is divided into message information and message data. Some messages will not have any message data. All packets may use sync words to establish the start of packets, a length byte defining the length of the packet and a 16-bit CRC for providing error detection/correction. The length of the preamble sync word, length field and CRC may not be included in the length field value of the message as their length is constant and known for a particular message packet.
• Beacon messages will have a preamble of approximately 200 bytes. This length allows any device to scan though all frequencies to find the channel the transmitting device is on. A non-beacon message may have a shorter preamble, for example 4 bytes. The beacon message is a broadcast message sent by the gateway and repeaters. It allows devices to synchronize to the frequency hopping and timing of the communication. An LQI value is used by meters to determine the best route to the gateway.
• The communication protocol used by parking meter system may use different message types. The message type of a message may be indicated by a particular field within the message packet. Illustrative message types may include:
• • Beacon message sent from either a gateway or repeater. The beacon message may include data such as the NIV of the gateway.
  • Meter Transaction messages sent from the meter to the gateway when a transaction, such as a credit card transaction, occurs.
  • Gateway to Meter messages sent from the gateway to the meter to deliver information, for example from a backend system
  • Meter Transaction Acceptance messages sent from the gateway to the meter indicating the acceptance of a transaction, such as the acceptance of a credit card transaction
  • Gateway to Repeater messages may be used to send information from the gateway to a repeater
  • Gateway Transaction messages may be sent from a gateway to a backend system
  • Meter to Gateway messages may be sent from the meter to the gateway to send information about the meter to the gateway
  • Meter Status Request messages sent from gateways to meters to request the meter to send its status to the gateway
  • Repeater to Gateway messages may be used to send information from the repeaters to gateways
  • Meter Status messages may be sent from the meter to the gateway in response to the meter status request message
  • Ping messages may be sent by devices to other devices in order to test connectivity with the other devices
  • Ping Acknowledge messages may be sent from devices in response to a ping message
  • Repeater Status Request messages may be sent from gateways to repeaters to request the status of the repeater
  • Repeater Status messages may be sent from the repeaters to the gateways in response to a repeater status request message
  • Repeater messages may be sent from a repeater to either a gateway or meter and may be forwarding a message received at the repeater
  • Join Request messages may be sent from a repeater to a gateway to request being registered with a gateway
  • Join Acceptance messages may be sent from gateways to repeaters once the repeater has been registered with the gateway. The join acceptance may include a short system ID assigned to the repeater by the gateway
  • Join Denial messages may be sent from gateways to repeaters indicating that the repeater was not registered with the gateway
  • Meter Acknowledgement messages may be sent from a meter to acknowledge receiving a message sent from a gateway, and possibly forwarded by a repeater
  • Gateway Acknowledgement messages may be sent from a gateway to acknowledge receiving a message from a meter, and possibly forwarded by a repeater
  • Repeater Acknowledgement messages may be sent from a repeater to acknowledge receiving a message from a gateway
  • AMA Acknowledge messages may be sent from a meter to a gateway to acknowledge receiving the AMA message alert.
• As described above a gateway may broadcast beacon messages using the RF radio board of the device. A gateway's beacon message may be used by repeaters and parking meters to synchronize to the gateway. The parking meters and repeaters may synchronize to both the communication time, for example the timing window of when to send messages, as well as the frequency hopping timing, for example when to hop to the next channel frequency. Once a device is synchronized with the gateway it may use an internal timer to maintain close synchronization, reducing the time spent trying to resynchronize and so reduce power consumption. Each time the device receives a gateway beacon message, or more particularly receives the end of the gateway beacon message, an internal timer is reset. In repeaters the timer is set so that the repeater attempts to detect the next beacon message at the beginning of the next frequency hop performed by the gateway. In parking meters, the timer may be set to a multiple of the frequency hop time. The meter may go into a sleep mode while waiting for the internal timer to expire. Once the timer expires the meter may wake up and attempt to resynchronize with the beacon message. The use of the internal timer allows the device to go into a low powered sleep mode and wake up within a limited time shift error of the expected beacon message. This allows for fast resynchronization and lowers the use of power.
• If a meter is not within range of a gateway it will synchronize with a repeater. The meter may follow the same scheme as if synchronized with a gateway; however, it will synchronize with the repeater beacon not the gateway beacon. As described above, repeaters are registered to a single gateway. A repeater will broadcast a repeater beacon message after the gateway beacon message. In an illustrative embodiment each repeater registered with the gateway does not transmit its beacon message after each gateway beacon. Rather, only one of the repeaters registered with the gateway broadcasts its beacon after the gateway beacon. The repeaters registered with a gateway broadcast their beacon messages in a round robin fashion based on a short system ID assigned to it by the gateway when registered. Although a repeater does not broadcast a beacon at each frequency hop, it will resynchronize with the gateway with every gateway beacon the gateway sends out. Doing so allows the repeaters to maintain a close synchronization with the gateway as well as to determine if the gateway is sending an asynchronous message alert (AMA) notification to a parking meter as this message will be embedded in the gateway's beacon as described further herein. Repeaters will forward any AMA notifications from the gateway to all meters within range.
• The use of the beacon message to synchronize parking meters with either the gateway or repeater allows the parking meter to receive messages from the backend system asynchronously with an acceptably low latency, while maintaining low power consumption. This may be used advantageously to allow for the display of parking time purchased via a cell phone or other device. The ability to communicate asynchronously with parking meters in a low latency and low power manner may also provide additional or alternative benefits, which may include, for example, controlling or altering parking rates of parking meters remotely, requesting information from parking meters or repeaters as well as other possible benefits.
• Parking meters do not need to be linked to a single gateway sub system. They may be able to hop from one sub system to another. When first synchronizing (initialization synchronization), the parking meter may determine if it is within range of a gateway by detecting gateway beacon messages. The parking meter may also try to detect beacon messages from as many repeaters and gateways as possible. The ID address, LQI and channel set of these repeaters and gateways will be stored by the parking meter. The parking meter may select the best possible route to the gateway once this is complete. This selection may be based on the LQI determined during the initialization synchronization. If this link is ever broken the next best route will be used. This aides in providing a low latency response at the meter as well as low power consumption.
• Repeaters of the illustrative subsystem depicted inFIG. 2 send a beacon once for every six gateway beacon messages they receive. This is desirable to prevent beacon messages from colliding with one another. Repeaters will send beacons based upon the short system ID Address assigned to them by the gateway when the repeater registers with the gateway. For example, a repeater with an assigned short system ID of 1 may transmit a beacon message following the gateway's beacon message. Following the gateway's next beacon message the repeater with the short system ID of 1 does not transmit a beacon message, rather a repeater with a short system ID of 2 may transmit the beacon message. The gateway may control which repeater sends the beacon message by including the short system ID of the repeater that is to transmit the beacon in the beacon message. All of the repeaters will receive the beacon message; however, only the repeater with the assigned short system ID matching that in the beacon message retransmits the beacon message.
• Gateways, repeaters, and meters may receive a unique 32-bit address during manufacturing. On each sub system the gateway may always be assigned a short system address of zero. The repeaters can be assigned a short system address of 1-6, or the maximum number of repeaters allowed to be registered with a single gateway, by the gateway when they initially register with the sub-system. Once a gateway has allowed six repeaters to register with it all other repeater requests to join the sub system may be denied. Gateways and repeaters will not process messages for other networks. Each subsystem has a unique Network ID that the gateways and repeaters use for identifying messages for their particular subsystem. Assigning a short address to the gateway and repeaters may be done to reduce the number of bytes necessary to transmit/receive over the radio, which can help save power. Because meters may be able to hop between subsystems they use their entire 32-bit address in communications.
• In the parking meter network, the source of a message, for example the gateway or the parking meter, is notified of message delivery by an acknowledgement message from the message destination. Repeaters do not acknowledge messages they receive and forward, they will only forward acknowledgements. If a parking meter sends a message and it does not receive an acknowledgement from the gateway, either directly or via a repeater, the parking meter will resend the message. The scenarios below highlight different parking meter message transmission possibilities.
• Normal Message Completion
• • 1. Parking meter sends a ‘Meter to Gateway’ message to gateway.
  • 2. gateway sends an acknowledgement message to parking meter.
  • 3. Parking meter receives acknowledgement message.
• Normal Message Completion with Repeater
• • 1. Parking meter sends a ‘Meter to Gateway’ message to repeater.
  • 2. Repeater receives and forwards the message to the gateway.
  • 3. Gateway sends an acknowledgement to repeater.
  • 4. Repeater receives and forwards the acknowledgement message to parking meter.
  • 5. Parking meter receives acknowledgement message.
• Retry Mode 1
• • 1. Parking meter sends a ‘Meter to Gateway’ message to gateway.
  • 2. Parking meter did not receive an acknowledgement message.
    • a. Parking meter did not receive the acknowledgement message or
    • b. Gateway did not receive the message
  • 3. Parking meter retries sending the message.
  • 4. If the 3^rdretry of sending the message fails then retry mode 2 is used.
• Retry Mode 2—Try Another Route
• • 1. Parking meter selects a new route from stored data during initialization synchronization. If another route does not exist to a sub-system then retry mode 3 is used.
  • 2. Parking meter sends a ‘Meter to Gateway’ message to gateway using newly selected route.
  • 3. Parking meter did not receive an acknowledgement message.
    • a. Parking meter did not receive the acknowledgement message or
    • b. Gateway did not receive the message
  • 4. Parking meter retries sending the message.
  • 5. If the 3^rdretry fails then repeat retry mode 2.
• Retry Mode 3—Find a New Network
• • 1. Parking meter goes through the initialization synchronization routine to identify all possible routes. The routes may have changed since the previous initialization.
  • 2. Parking meter messaging routine is restarted and the message is attempted to be sent again.
• The above message transmission scenarios are for messages that originate at a parking meter. The use of the beacon message may be used to provide asynchronous communication between the back-end system and the parking meter. That is, the back-end system may send a message to a particular parking meter. The back-end system sends the message information to a particular gateway, for example the backend may send the message information to the last gateway that received a message from the parking meter. The gateway constructs an Asynchronous Message Alert (AMA) beacon message, which is a beacon message with the parking meter ID of the parking meter the backend system is trying to communicate with, as well as an indication that the beacons message is an AMA beacon message in it. By embedding the AMA in the beacon all parking meters can be notified that a message is pending, including the intended parking meter. Because a parking meter can hop from one system to another, not directly linked, all Gateways in a particular area may send out the AMA. For example, the back-end system may determine that there are three gateways that are in possible communication with the intended parking meter. The gateways send out the AMA beacon message; which all repeaters registered with these gateways will then forward to the parking meters within range.
• Gateways can continue to send the AMA beacon message until one of the gateways receives an AMA acknowledgement message from the intended parking meter indicating that the meter has received the AMA beacon message and is ready to receive the AMA message. This gateway may then indicate to the back-end system that the AMA beacon message has been received and no longer needs transmitting and the actual message may be transmitted. The backend may then indicate to the other possible gateways that were broadcasting the AMA beacon message to stop broadcasting the AMA beacon message.
• After receiving the AMA beacon message indicating a gateway message is waiting for it, a parking meter will send an AMA acknowledgement message to the gateway to indicate recognition of the message in waiting. The gateway may then send the AMA message to the meter. Once the AMA message is received the meter will reply with an AMA acknowledgement indicating that the message was received.
• Gateways may include a single meter ID in an AMA beacon message. As such, if the backend has multiple AMA to send to different parking meters, the backend queues the AMA messages and disperses them to the appropriate gateway or gateways. The gateway then sends an AMA beacon message for the first parking meter in the queue which will acknowledge the AMA beacon message and receive the AMA message from the queue. The AMA message is acknowledged by the parking meter. The backend system will disperse the next AMA message to the gateway.
• The back end may maintain a database of all parking meters in the parking meter system along with the gateway and/or repeater path(s) that have been associated with any traffic to and/or from those devices.
• The indication that a beacon message is an AMA beacon will consist of AMA byte (0x01) in an Alert field and 4 destination address bytes of the parking meter ID of the message packet.
• The system described above for sending a message from the backend to a specific parking meter may be extended to act as a broadcast message alert (BMA). By placing a broadcast byte (0x10) in the Alert field of a beacon message, the parking meter network can be notified that the beacons sent out contain a system wide broadcast. The broadcast data is held in the 4 address bytes, since the message does not require the field to be used for a particular parking meter's ID. The broadcast message may be time based, for example it may be sent out for a specified length of time and then stopped.
• The AMA and BMA messages may be used to provide additional features to parking meters, such as “congestion parking”. Congestion parking allows the city to dynamically adjust the pricing paid by parkers in a city based on the traffic patterns, time of day, in an effort to for example, relieve congestion of cars on the street, and or increase the revenue stream generated from the parking meter network. The AMA message may be used to provide congestion parking to a single parking meter, while the BMA message may provide congestion parking to all parking meters in the parking meter system or all parking meters in a specific region or area of the City; i.e. downtown. The region or area of the city may be controlled by the sub-system the parking meter is communicating with. Gateways of sub-systems may broadcast a BMA beacon message, which will be received by all parking meters in that area. The backend system may maintain the geographic location of the gateways of the parking meter system. The backend system may also maintain the location of individual parking meters. Alternatively, the region or area of the parking meter may be inferred from the location of the gateway it is communicating with.
• A complete rate profile describing the parking rates on a parking meter may be about 2000 bytes. It may not be practical to send a complete new profile each time it is desired to adjust the parking rates of the parking meters. Rather than sending a complete rate profile, a rate multiplier or a rate index number may be sent, for example in a BMA beacon message, in order to change the rate of all parking meters in an area or region, or an AMA message in order to change the rate of a single parking meter.
• Sending a rate multiplier to the parking meter, whether individually using an AMA message or in a group using a BMA beacon message, may include sending a 3 digit number representing a decimal number with two decimal places. This allows the parking meter rate to both be increased and decreased. With the rate normally set at 1.00, the range of rate multiplier numbers may be from 0.00 thru to 9.99. Thus if the rate for a group of meters was normally $2/hr, sending a multiplier of 1.50 to it will cause its current effective rate to be $3/hr. So there are 999 possible rate multiplier numbers to choose from, which provide a large range of control of the parking rates. It will be appreciated that the multiplier may have fewer or more digits depending on the desired granularity of control over the parking meter rates.
• Parking meters may support different rates, although commonly only one rate is defined in a given rate profile. The additional rates may be used to define “congestive parking” rates which escalate in price at some scaling factor. The AMA or BMA message may send the rate index number to specify which rate, for example number 1 thru 8, to use.
• How quickly the parking meters are required or desired to react to congestive parking rate changes may affect the AMA latency configurations on the meters. The latency settings of the AMA determines how quickly an individual meter can respond to a remote command to change its rate or multiplier, or more generally, how quickly the parking meter can respond or receive an AMA message. The shorter the latency setting is, the more power that is used by the parking meter. The AMA latency setting may be determined by the frequency at which a parking meter makes a resynchronization with the parking meter network, since the parking meter resynchronizes with the beacon message which include the AMA indicator indicating that an AMA message is waiting. This rate may be controlled by the parking meter network using AMA or BMA messages.
• The communication protocol used by the devices attempts to mitigate possible collisions. While not all collisions will be avoidable, a majority may be prevented with a good communication timing protocol. Like their beacon messages which are scheduled in a round robin manner to be broadcast after a gateway beacon message, all repeater communication transmission times may be scheduled to occur in specific time slots so as to prevent collisions. This schedule may be based on the repeater's short Network ID address given to it by the gateway when the repeater joined the system. Likewise all meters will have a scheduled time slot in which to transmit messages as well as a time slot to retry sending messages. These slots may be based upon the unique 32-bit ID address assigned to the parking meter during manufacturing. A parking meter's time slot or retry time slot may be based upon its parking meter ID address. Because each parking meter ID address is unique the full set of time slots may never overlap completely. Additionally, or alternatively, to further reduce the possibility of collisions, all communication devices of the parking meter system may perform a clear channel assessment (CCA) before transmitting to ensure the channel is open.
• The synchronizing of the meters and repeaters with the gateway's beacon message helps to provide a tight synchronization time frame so that the meters and repeaters may transmit in the correct time slot and help mitigate the number of possible collisions.
• FIG. 8 is a flow diagram showing an illustrative method of a gateway registering a repeater in accordance with the present disclosure. As descried above, a gateway can limit the number of repeaters that may communicate with it. Themethod700 begins when the gateway receives a join request message from a repeater (702). The join request message includes the identifier of the repeater (repeater ID). The gateway uses the repeater ID from the join request message to determine if the repeater is already registered with the gateway (704), for example the repeater ID received in the join request message matches a repeater ID of a repeater registered with the gateway. The gateway maintains a list of the repeater IDs of the repeaters that have been registered with it already. If the gateway determines that the repeater has already been registered (Yes at704), it sends a join acceptance message to the repeater (706). The join acceptance message includes a short system ID the gateway assigns to the repeater, which may be for example a number from 1 to the maximum number of repeaters that can be registered with a gateway. The short system ID is used by the repeater to coordinate the communication timing with the gateway. Each repeater uses the short system ID to determine the time slots it uses for sending messages including its repeaters beacon message. If the gateway determines that the repeater has not already been registered (No at704), for example the list of registered repeaters does not contain the repeater's ID, the gateway then determines if there is a spot for the repeater to register with the gateway. The gateway determines if there is spot by checking if the number of registered repeaters is equal to the maximum number of repeaters that can be registered with the gateway at one time (708). If there is a spot available for the repeater (No at708) the gateway registers the repeater's ID (709), increasing the number of repeaters that are registered with the gateway (710), and sends an acceptance message to the repeater (706) including the short system ID assigned to the repeater by the gateway. If the gateway has already registered the maximum number of repeaters (Yes at708) it sends a join denial message to the repeater indicating that the repeater was not registered with the gateway (712). Once the gateway has sent either a join acceptance message or a join denial message to the repeater the registration process ends. The gateway may inform the backend system that the repeater has been registered with it.
• FIG. 9 is a flow diagram showing an illustrative method of a repeater registering with a gateway in accordance with the present disclosure. Themethod800 begins with the repeater detecting beacon messages from gateways (802). The repeater may scan through the different frequencies used by the parking meter network and determines if a gateway is broadcasting a beacon message on the frequency. The repeater receives any beacon messages it detects. The repeater assigns each received beacon message a link quality index (LQI) value that represents the quality of the communication channels. Each beacon message sent by a gateway and received by the repeater includes the gateway's network initialization vector (NIV) indicating the channel set used by the gateway. The repeater receives the beacon messages and orders them based on the LQI of the beacon message. The repeater then sends a join request message to the gateway with the highest LQI value (804). The gateway processes the join request message, for example, as described above with reference toFIG. 8, and sends a response message. The repeater receives a response message from the gateway (806) and determines if the response message is either an acceptance message or a denial message (808). If the response message is an acceptance message (Yes at808) the repeater sets the gateway as its communication point in the parking meter network (810). The repeater uses the channel set described by the gateway's NIV for subsequent communications. If the received response message is not an acceptance message, the repeater sends a join request to the gateway with the next highest LQI (812) and receives a response message from the gateway (806), and continues processing the message as previously described. Although not depicted in the illustrative method ofFIG. 9, if the repeater reaches the end of the gateway list without being registered, it may start the method over again, to possibly identify new or additional gateways.
• FIG. 10 is a flow diagram showing an illustrative method of initializing a parking meter in accordance with the present disclosure. Themethod900 begins with the parking meter identifying the gateways and repeaters that are within communication range. The meter detects beacon messages from the gateways and repeaters (902) and records the network ID, LQI and NIV of the beacon messages and orders the discovered communication pathways from the highest LQI to the lowest (904). The parking meter may detect the beacon messages in a similar manner as described above for repeaters. The parking meter sets the route with the highest LQI as the route to use for communicating with the parking meter network (906).
• The methods described above with reference toFIGS. 8,9 and10 may be implemented in various hardware or software combinations. For example, the methods may be implemented in the device modules of different devices in the parking meter system. For example, the method of registering a repeater at a gateway described with reference toFIG. 8, may be implemented in thedevice software stack610 of the device module of a gateway device, or alternatively it may be implemented in different components of the device. Similarly the method used by a repeater to register with a gateway described with reference toFIG. 9 may be implemented in thedevice software stack610 of the device module of a repeater device. The parking meter initialization method may be implemented in thedevice software stack610 of the device module of a parking meter.
• FIG. 11 is a message flow diagram showing illustrative messages for a parking meter communicating with a backend system though a gateway in accordance with the present disclosure. Thegateway205 periodically sends a beacon message (1102) which is received byparking meters120. The beacon message is sent each time the gateway hops to a new frequency. The parking meter resynchronizes with the beacon message sent from the gateway, or the repeater if the parking meter is communicating with a repeater. Once the parking meter resynchronizes with the beacon message, it can go into a low power sleep mode. In the illustrative scenario ofFIG. 11, theparking meter120 receives a parking meter event for example a coin is inserted into the parking meter, which places the parking meter into a wake up mode and processes the parking meter event. The processing of the parking meter event may cause the parking meter to send a message to the gateway. The parking meter waits for its particular time slot to send the meter message to the gateway. Once the parking meter's time slot arrives the meter sends a meter message to the gateway (1104). The gateway receives the parking meter message and sends an acknowledgement message back to the parking meter (1106). The parking meter receives the acknowledgement from the gateway and processes it. Once the acknowledgement has been processed the parking meter may return to the low powered sleep mode. Alternatively, the parking meter may stay awake or in a more active mode awaiting a response to the message or data that was sent to the gateway, and possibly processed by the backend. Once the gateway receives the meter message from the meter, the gateway may send the message on to the backend system (1108) which may process the information. The backend system may send a response message to the parking meter through the gateway. In such a case the parking meter remains in an awake mode to receive the response message. If the backend has a message or response destined for a particular parking meter, it can determine the fastest or lowest latency path by looking at the received message packet from the parking which will show the IDs of the gateway and any repeaters used by the parking meter to communicate with the backend system. This path data may be maintained and updated in a backend database associated with each parking meter.
• FIG. 12 is a message flow diagram showing illustrative messages for a backend system communicating with a parking meter in accordance with the present disclosure. A backend system may send asynchronous messages to parking meters. The backend system sends the message information to a gateway. The message information may include the unique ID of the parking meter the message is intended for (1202). The gateway receives the information and creates and queues an Asynchronous Message Alert (AMA) message. Alternatively the backend system may create the AMA message and send it to the gateway and the gateway will queue the AMA message and generate the AMA beacon message. The AMA beacon message may be a beacon message with an Alert bit set and including the parking meter's ID the AMA message is intended for. The gateway sends the AMA beacon and the parking meter receives the AMA beacon message when it resynchronizes with the AMA beacon message (1204). If the address of the AMA beacon message matches that of the parking meter, the parking meter sends an AMA acknowledgement message (1206) indicating that the gateway can send the AMA message. Once the AMA acknowledgement is received by the gateway, the gateway sends the AMA message (1208) to the parking meter. The parking meter receives the message and sends an AMA message acknowledgement (1210) to the gateway indicating that it has received the message information. The gateway may send a message back to the backend system indicating that the message has been delivered to the meter.
• FIG. 13 is a message flow diagram showing illustrative messages for processing a credit card payment at a parking meter in accordance with the present disclosure. The parking meter periodically resynchronizes with the beacon message (1302) of the gateway, or a repeater, as described above. The parking meter wakes when a credit card event occurs, for example when a credit card is inserted or swiped at a meter. The parking meter processes the credit card event, for example by determining the amount of time to be purchased and encrypting the credit card information for transmission to the gateway. The parking meter waits for its transmission time slot and once it occurs, the parking meter sends a parking meter transaction message (1304), including the credit card transaction information, to the gateway, and then waits for the acknowledgement message (1306) from the gateway indicating that the transaction message has been received by the gateway. Once the acknowledgement message has been received the parking meter stays awake or in a more active mode awaiting a response to the credit card transaction data just sent to the backend system. The gateway sends the credit card transaction to the backend system (1308). The backend system receives the credit card transaction information and processes it, resulting in the transaction being either approved or denied. Regardless of the results of the processing of the transaction, the transaction processing response is sent from the backend system to the gateway (1310). Once received from the backend the gateway sends the results of the transaction processing (1312), which in the illustrative example ofFIG. 13 is a transaction approval message to the parking meter. The parking meter sends an acknowledgement (1314) back to the gateway and processes the transaction message. This may result in the parking meter approving the purchase of time, or declining the purchase of time. Once the parking meter finishes processing the message, it may return to a low power sleep mode.
• The meter initiated messaging and the AMA messaging may also be used at parking meters to process credit card transaction. The AMA method may be desirable to use if the processing of the credit card transaction by the backend system takes a long period of time. The AMA technique allows the parking meter to go to sleep until the transaction processing result is ready from the backend, which can be indicated to the parking meter using an AMA beacon message. Although the AMA messaging may be used, it may cause an undesirable amount of time to pass before the transaction is completed since the parking meter goes to sleep. To mitigate this, upon going to sleep while waiting for a transaction response, the parking meter may modify the resynchronization frequency to resynchronize with each channel hop, and so detect and receive the AMA message as quickly as possible using the AMA messaging technique,
• Although the AMA message may be used, it is possible for the parking meter to remain in the awake state waiting for the transaction processing result from the backend system, as depicted inFIG. 13. This type of processing may be desirable to use when the time required to process the transaction request by the backend system is low, and the lowest latency time is desirable, since it can provide the transaction processing response as soon as it is available from the backend system. The short processing time will help the parking meter to consume little power
• FIG. 14 is a message flow diagram showing illustrative messages for processing a parking meter payment received at a backend system in accordance with the present disclosure. The AMA beacon message may also be used to provide additional payment options. For example, payments that originate at the backend system may be made. These payment options may include for example, paying using a cell phone, text messaging, or over the Internet or using an Internet, or other communication network, enabled device. These payment options are initiated by a person wishing to purchase time at a particular parking meter. The purchaser contacts the backend system in some manner (1402), for example using a cell phone and indicates the meter ID for the parking meter time is being purchased at. The backend system may then process the payment request and send the results of the transaction to the parking meter using an AMA message (1404). The backend system sends the transaction response to the gateway which sends an AMA beacon message (1406) for the particular parking meter. Once the parking meter receives the AMA beacon message when synching with the gateway, the parking meter sends an AMA acknowledgement to the gateway (1408). The gateway subsequently sends the transaction information, depicted as a transaction approval message, to the parking meter (1412). Depending on if the transaction was approved or denied the transaction information may indicate the amount of time purchased and the parking meter may display the amount of time purchased. The parking meter receives the transaction information and sends an acknowledgement to the transaction message (1414). The parking meter may return to a low power sleep state.

Claims (48)

1. A method of operating a wireless parking meter network comprising:

transmitting from a gateway a first beacon message;

receiving at a parking meter the first beacon message;

synchronizing an internal timer of the parking meter based on receiving the first beacon message;

placing the parking meter in a sleep mode for a period of time (sleep period);

transmitting from the gateway a second beacon message;

placing the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer; and

receiving at the parking meter the second beacon message.

2. The method ofclaim 1, further comprising:

re-synchronizing the internal timer of the parking meter based on receiving the second beacon message.

3. The method ofclaim 1, further comprising:

determining the start of a transmission time slot of the parking meter for transmitting messages to the gateway, the start determined using the synchronized internal timer and occurring a length of time after the transmission of beacon messages including the first and second beacon messages; and

transmitting from the parking meter a message to the gateway in the transmission time slot.

4. (canceled)

5. The method ofclaim 1, wherein placing the parking meter in the sleep mode for the sleep period comprises:

setting the length of time of the sleep period based on an expected length of time between the gateway transmitting the first and second beacon messages, the expected length of time is determined based on a known rate at which the gateway transmits beacon messages and the number of beacon messages that are to be transmitted by the gateway between the parking meter receiving the first and second beacon messages.

6-10. (canceled)

11. The method ofclaim 1, further comprising attempting to register a repeater at the gateway comprising:

receiving at the gateway the join request message from the repeater, the join request message including a repeater ID uniquely identifying the repeater;

determining using the repeater ID if the repeater is currently registered with the gateway;

determining if the maximum number of repeaters have already been registered with the gateway;

registering the repeater with the gateway by assigning a short system ID to the repeater when the maximum number of repeaters are not registered with the gateway and the repeater is not currently registered with the gateway;

determining the short system ID assigned to the repeater when the repeater is currently registered with the gateway;

sending from the gateway to the repeater the join acceptance message including the short system ID assigned to the repeater when the repeater is registered with the gateway; and

sending from the gateway to the repeater join denial message when the repeater is not registered with the gateway.

12-15. (canceled)

16. The method ofclaim 11, wherein transmitting from the gateway the first beacon message comprises:

selecting one of the short system IDs of repeaters registered with the gateway; and

transmitting the first beacon message including the selected short system ID; and

wherein the method further comprises:

determining at the repeater if the first beacon message includes the short system ID of the repeater; and

retransmitting the first beacon message when the first beacon message includes the short system ID of the repeater.

17-19. (canceled)

20. The method of claim19, wherein the spread spectrum technique for transmission of messages, including the first and second beacon messages, in the parking meter network, wherein the spread spectrum technique uses frequency hopping and comprises:

transmitting from the gateway the first beacon message on a first communication frequency comprising:

transmitting the first beacon message including a network initialization vector (NIV) specifying the frequencies used by the gateway for communications, the NIV indicating an order of the frequencies used by the gateway, the NIV including the first frequency and the second frequency;

transmitting from the gateway the second beacon message on a second communication frequency, wherein the gateway transmits beacon messages, including the first and second beacon messages, as the first message after hopping to another communication frequency; and

transmitting from a second gateway a beacon message including a second NIV specifying a second order of frequencies used by the second gateway for communications, the second order of frequencies orthogonal to the order of frequencies specified in the NIV.

21-24. (canceled)

25. The method ofclaim 1, further comprising:

transmitting from the parking meter a message to the gateway;

receiving at the gateway a message from the parking meter;

sending the message to a backend server using a network connection;

maintaining the parking meter in the wakeup mode after transmitting the message to the gateway;

processing the message at the backend server;

sending a response message back to the gateway using the network connection, the response message based on the processing of the message;

transmitting the response message from the gateway to the parking meter;

receiving at the parking meter the response message from the gateway; and

placing the parking meter in the sleep mode.

26-28. (canceled)

29. The method ofclaim 25, wherein the message is a credit card transaction message, and the response message is either a transaction approval message or a transaction declined message.

30. The method ofclaim 1, further comprising:

initiating communication with an intended parking meter comprising:

transmitting from the gateway a beacon message including:

an indication that the beacon message is an asynchronous message alert (AMA) beacon message; and

a unique parking meter identification (ID) of the intended parking meter; and

receiving at the intended parking meter the AMA beacon message.

31. (canceled)

32. The method ofclaim 30, further comprising:

sending to the gateway an AMA acknowledgement message acknowledging receiving the AMA beacon message at the intended parking meter;

maintaining the intended parking meter in the wakeup mode;

receiving at the gateway the AMA acknowledgement message;

transmitting from the gateway an AMA message to the intended parking meter;

receiving at the intended parking meter the AMA message; and

transmitting from the intended parking meter an AMA message acknowledgement message acknowledging receiving the AMA message;

receiving at the gateway the AMA message acknowledgement message.

33. (canceled)

34. The method ofclaim 32, further comprising:

receiving an event at a backend server;

processing the event at the backend server;

generating the AMA message based on the processing of the event; and

sending to the gateway the generated AMA message and a unique parking meter identification (ID) of the intended parking meter.

35. The method ofclaim 34, wherein:

receiving at the backend server the event comprises receiving a transaction request for purchasing parking at the intended parking meter comprising one of:

receiving the transaction request from a telephone;

receiving the transaction request from a mobile phone;

receiving the transaction request as a text message;

receiving the transaction request from an Internet enabled device; and

receiving the transaction request over a communication network;

processing the event comprises processing the transaction request; and

generating the AMA message comprises generating the AMA message including: the result of processing the transaction request.

36. (canceled)

37. The method ofclaim 32, further comprising:

placing the AMA message in an AMA message queue of pending AMA messages at the gateway;

processing the pending AMA messages in the queue; and

transmitting from the gateway an AMA message to the intended parking meter.

38. The method ofclaim 30, further comprising:

controlling the parking rate of the intended parking meter using the AMA message comprising:

transmitting to the intended parking meter in the AMA message either:

a rate multiplier comprising a decimal number indicating a multiplication factor to be applied to a base parking rate of the intended parking meter; or

a rate index comprising an index indicating one of a plurality of pre-programmed parking rates to be applied as the parking rate of the intended parking meter; and

receiving the AMA message at the intended parking meter and applying either the rate multiplier or the rate index received in the AMA message to the parking rate of the intended parking meter.

39. (canceled)

40. The method ofclaim 1, further comprising:

initiating communication with a plurality of intended parking meters comprising:

transmitting from the gateway a beacon message including:

an indication that the beacon message is a broadcast message alert (BMA) beacon message; and

BMA information for the intended parking meters; and

receiving at a subset of the plurality of intended parking meters the BMA beacon message.

41-44. (canceled)

45. A method of operating a wireless parking meter in a parking meter network, the method comprising:

receiving at the parking meter first beacon message from the parking meter network;

synchronizing an internal timer of the parking meter based on receiving the first beacon message;

placing the parking meter in a sleep mode for a period of time (sleep period);

placing the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer; and

receiving at the parking meter a second beacon message from the parking meter network.

46. The method ofclaim 45, further comprising:

re-synchronizing the internal timer of the parking meter based on receiving the second beacon message.

47. The method ofclaim 45, further comprising:

determining at the parking meter the start of a transmission time slot of the parking meter for transmitting messages to a gateway of the parking meter network, the start determined using the synchronized internal timer and occurring a length of time after the transmission of beacon messages including the first and second beacon messages comprising:

determining a time slot from a plurality of time slots of the parking meter network to use as the transmission time slot of the parking meter; and

determining the time at which the transmission time slot will start based on the number of the time slot in the parking meter network, the length of the time slots and the length of the beacon messages; and

transmitting from the parking meter a message to the gateway in the transmission time slot.

48. (canceled)

49. The method ofclaim 45, wherein placing the parking meter in the sleep mode for the sleep period comprises:

setting the length of time of the sleep period based on an expected length of time between receiving the first and second beacon messages, the expected length of time is determined based on a known rate at which the parking meter network transmits beacon messages and the number of beacon messages that are to be transmitted by the parking meter network between the parking meter receiving the first and second beacon messages.

50-56. (canceled)

57. The method ofclaim 45, further comprising:

transmitting from the parking meter a message, including parking meter information, to the parking meter network;

maintaining the parking meter in the wakeup mode after transmitting the message to the parking meter network;

receiving at the parking meter a response message from the parking meter network; and

placing the parking meter in the sleep mode.

58-59. (canceled)

60. The method ofclaim 57, wherein the message is a credit card transaction message, and the response message is either a transaction approval message or a transaction declined message.

61. The method ofclaim 45, further comprising:

receiving at the parking meter an asynchronous message alert (AMA) beacon message comprising:

an indication that the beacon message is an AMA beacon message;

a unique parking meter identification (ID) of the parking meter;

sending to the parking meter network an AMA acknowledgement message acknowledging receiving the AMA beacon message at the parking meter;

maintaining the parking meter in the wakeup mode;

receiving at the parking meter an AMA message; and

transmitting from the parking meter an AMA message acknowledgement message acknowledging receiving the AMA message.

62-63. (canceled)

64. The method ofclaim 61, further comprising:

controlling the parking rate of the parking meter using the AMA message comprising:

receiving at the parking meter in the AMA message either:

a rate multiplier comprising a decimal number indicating a multiplication factor to be applied to a base parking rate of the intended parking meter; or

a rate index comprising an index indicating one of a plurality of pre-programmed parking rates to be applied as the parking rate of the intended parking meter; and

applying either the rate multiplier or the rate index received in the AMA message to the parking rate of the parking meter.

65. (canceled)

66. The method ofclaim 45, further comprising:

receiving at the parking meter a broadcast message alert (BMA) beacon message from the parking meter networking including:

an indication that the beacon message is a broadcast message alert (BMA) beacon message; and

BMA information for the parking meter; and

receiving at the parking meter the BMA beacon message.

67-68. (canceled)

69. The method ofclaim 45, further comprising

initializing the parking meter including:

detecting a beacon message indicating a communication link;

assigning a link quality indicator (LQI) value to the communication link based on the detected beacon message;

detecting additional beacon messages, each beacon message indicating an additional communication link;

assigning an LQI value to each additional communication link;

ordering the communication links based on their LQI values; and

setting the communication link with the best LQI value as the link to use when sending messages from the parking meter.

70. (canceled)

71. A parking meter for use in a parking meter network comprising:

a parking meter mechanism;

a radio board for receiving messages;

a processor executing instructions; and

a memory storing instructions executed by the processor; the executed instructions providing in the parking meter:

a radio board module operable to receive a beacon message;

a device module operable to:

synchronize an internal timer of the parking meter based on receiving the beacon message,

place the parking meter in a sleep mode for a period of time (sleep period); and

place the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer.

72-94. (canceled)

95. A parking meter network comprising:

a gateway for transmitting beacon messages; and

a parking meter comprising:

a parking meter mechanism;

a radio board for receiving messages including the beacon messages and transmitting messages;

a processor executing instructions; and

a memory storing instructions executed by the processor; the executed instructions providing in the parking meter:

a radio board module operable to receive a beacon message;

a device module operable to:

synchronize an internal timer of the parking meter based on receiving the beacon message,

place the parking meter in a sleep mode for a period of time (sleep period); and

place the parking meter in a wakeup mode at the expiration of the sleep period using the synchronized internal timer.

96-102. (canceled)

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