CN113411908A - Self-organizing wireless broadband network transceiving system based on collision avoidance - Google Patents

Abstract

The invention discloses a self-organizing wireless broadband network transceiving system based on collision avoidance, which comprises a plurality of self-organizing network broadband network transceivers, wherein each self-organizing network broadband network transceiver comprises a main control module, a signal conversion module front-end transformer, a power amplification module, a network interface module and a communication port; the power amplifier module, the front-end transformer of the signal conversion module, the signal conversion module and the main control module are sequentially connected, and the network interface module and the communication port are respectively connected with the main control module; and the plurality of ad hoc network broadband network transceivers are in communication connection. The invention is suitable for the self-organizing wireless broadband network transceiving system, and greatly improves the reliability of data transmission.

Description

Self-organizing wireless broadband network transceiving system based on collision avoidance

Technical Field

The invention relates to the technical field of communication, in particular to a self-organizing wireless broadband network transceiving system based on collision avoidance.

Background

The hidden terminal pair of the wireless network refers to a station pair which is located in the coverage area of the same wireless node but not in the transmission coverage area of the other side, and if the hidden terminal pair sends data to the node at the same time, the data transmission of the hidden terminal pair and the node is collided, so that data transmission errors are caused, and the hidden terminal pair is difficult to check and avoid and is a hidden terminal problem. The two-time handshake access mode cannot solve the problem of hidden terminals, so that the reliability of the self-organizing wireless network using CSMA/CA is poor, and particularly, the problem is more obvious when the method is implemented in a wireless ad hoc network with a multi-hop function, and the requirement of correctly receiving and transmitting network broadband data is difficult to meet.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a self-organizing wireless broadband network transceiving system based on collision avoidance, which comprises a plurality of self-organizing network broadband network transceivers, wherein each self-organizing network broadband network transceiver comprises a main control module, a signal conversion module front-end transformer, a power amplifier module, a network interface module and a communication port; the power amplifier module, the front-end transformer of the signal conversion module, the signal conversion module and the main control module are sequentially connected, and the network interface module and the communication port are respectively connected with the main control module; and the plurality of ad hoc network broadband network transceivers are in communication connection.

A carrier sense multiple access method for collision avoidance based on the collision avoidance-based ad hoc wireless broadband network transceiving system ofclaim 1, comprising the steps of:

an ad hoc network broadband network transceiver is a node, a dynamic and multi-hop routing network is established and maintained in a plurality of nodes through a routing protocol of the ad hoc network, and when a node needs to send data, idle evaluation is carried out on the available state of a channel by an interception mechanism with a fixed time interval; if the channel state is busy, adopting a self-adaptive back-off mechanism to avoid collision until the channel is idle; and if the channel is idle, the node occupies the channel and adopts a four-way handshake mechanism to perform data transmission.

Further, the interception mechanism comprises physical carrier interception and virtual carrier interception, wherein the physical carrier interception is to use a physical layer technology to evaluate an idle channel state and then feed back the channel state to the MAC layer; the virtual carrier sense mechanism realizes the detection of hidden nodes through a network allocation vector of an MAC layer, and the network allocation vector NAV realizes the virtual carrier sense by using a locally maintained NAV variable in a storage medium expectation protocol; the Duration field of RTS, CTS and DATA frame in the protocol stores the estimated transmission time of the frame, which is used to inform all nodes in the communication range of the node of the Duration time of the wireless channel to be occupied, each node maintains a local NAV variable to record the Duration time in the received frame and update the local NAV, the node judges the occupation time of the wireless channel according to the NAV value, when the NAV variable of the node is decreased to 0, the channel is determined to be idle; the channel is idle when both the protocol level and the physical level evaluate the channel as idle.

Further, the adaptive back-off mechanism is:

the backoff duration is generated as shown in the following equation:

BT＝Random()*τ

wherein τ represents a time slot;

the self-adaptive logarithm backoff algorithm adopts a logarithm function taking the number of competition nodes in a network as a variable, and dynamically adjusts the initial value of a competition window and the window backoff amplitude, wherein the adjustment of the competition window comprises the following processes:

firstly, a node monitors a channel before sending data, and enters a backoff stage after the channel is monitored to be continuously idle for a DIFS interval, wherein the initialization value of a contention window is CW₁I.e. by

CW₁＝CW_min*log_an

Step two, after the node enters the backoff stage, calculating the random backoff duration and storing the random backoff duration into a backoff counter, namely

B_i＝INT(CW_I*Random())

Wherein INT is a rounding function;

step three, continuously monitoring the channel, wherein the value of the back-off counter is reduced by 1 when the channel is continuously idle for one time slot, and if the value B of the back-off counter is_iIf the value is reduced to 0, sending data, and entering the step four, otherwise returning to the step three; if the node detects that the channel is busy in the backoff process, B is saved_iUntil the channel continuous idle time length is detected to be DIFS, the third step is executed again;

step four, if the transmission fails and the maximum retransmission times m are not exceeded; the contention window CW is adjusted, i.e.

CW_i+1＝Min(CW_i*log_an，CW_max)，0≤i<m

Returning to the step two to carry out retreat retransmission after the competition window is updated; if the node successfully sends the data or reaches the maximum retransmission times m, updating the contention window and waiting for the next data sending, namely

CW₁＝CW_min*log_an。

Further, the four-way handshake mechanism is as follows:

on the basis of a CSMA/CA handshake access mode, RTS/CTS handshake signals are added, and an ACK control message is added to confirm a link layer; the adopted message exchange sequence is RTS-CTS-DATA-ACK, when a DATA message is sent, a sending node firstly sends an RTS, a receiving node sends back a CTS after receiving the RTS to determine a channel, the sending node starts to send the DATA message DATA after correctly receiving the CTS, and the receiving node sends back an ACK for confirmation after correctly receiving the DATA message to finish the DATA message transmission.

The invention has the beneficial effects that: the node access mechanism disclosed by the invention improves the CSMA/CA handshake access mode, adds RTS/CTS handshake signals, adopts a combination mechanism of physical carrier sense and virtual carrier sense, adds an ACK control message to confirm a link layer, adopts the message exchange sequence of RTS-CTS-DATA-ACK, can effectively avoid the problem of hiding a terminal, is suitable for a self-organizing wireless broadband network transceiving system, and greatly improves the DATA transmission reliability.

Drawings

FIG. 1 is a schematic diagram of an ad hoc network broadband network transceiver;

FIG. 2 is a schematic diagram of a four-way handshake access mechanism;

FIG. 3 is a diagram illustrating a data frame format;

fig. 4 is a schematic diagram of a route discovery process.

Detailed Description

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.

As shown in fig. 1, a self-organizing wireless broadband network transceiving system based on collision avoidance includes a plurality of self-organizing network broadband network transceivers, where the self-organizing network broadband network transceivers include a main control module, a signal conversion module front-end transformer, a power amplifier module, a network interface module, and a communication port; the power amplifier module, the front-end transformer of the signal conversion module, the signal conversion module and the main control module are sequentially connected, and the network interface module and the communication port are respectively connected with the main control module; and the plurality of ad hoc network broadband network transceivers are in communication connection.

A carrier sense multiple access method for collision avoidance based on the collision avoidance-based ad hoc wireless broadband network transceiving system ofclaim 1, comprising the steps of:

an ad hoc network broadband network transceiver is a node, a dynamic and multi-hop routing network is established and maintained in a plurality of nodes through a routing protocol of the ad hoc network, and when a node needs to send data, idle evaluation is carried out on the available state of a channel by an interception mechanism with a fixed time interval; if the channel state is busy, adopting a self-adaptive back-off mechanism to avoid collision until the channel is idle; and if the channel is idle, the node occupies the channel and adopts a four-way handshake mechanism to perform data transmission.

The interception mechanism comprises physical carrier interception and virtual carrier interception, wherein the physical carrier interception is to use a physical layer technology to evaluate the idle channel state and then feed back the channel state to an MAC layer; the virtual carrier sense mechanism realizes the detection of hidden nodes through a network allocation vector of an MAC layer, and the network allocation vector NAV realizes the virtual carrier sense by using a locally maintained NAV variable in a storage medium expectation protocol; the Duration field of RTS, CTS and DATA frame in the protocol stores the estimated transmission time of the frame, which is used to inform all nodes in the communication range of the node of the Duration time of the wireless channel to be occupied, each node maintains a local NAV variable to record the Duration time in the received frame and update the local NAV, the node judges the occupation time of the wireless channel according to the NAV value, when the NAV variable of the node is decreased to 0, the channel is determined to be idle; the channel is idle when both the protocol level and the physical level evaluate the channel as idle.

The self-adaptive back-off mechanism is as follows:

the backoff duration is generated as shown in the following equation:

BT＝Random()*τ

wherein τ represents a time slot;

the self-adaptive logarithm backoff algorithm adopts a logarithm function taking the number of competition nodes in a network as a variable, and dynamically adjusts the initial value of a competition window and the window backoff amplitude, wherein the adjustment of the competition window comprises the following processes:

firstly, a node monitors a channel before sending data, and enters a backoff stage after the channel is monitored to be continuously idle for a DIFS interval, wherein the initialization value of a contention window is CW₁I.e. by

CW₁＝CW_min*log_an

Step two, after the node enters the backoff stage, calculating the random backoff duration and storing the random backoff duration into a backoff counter, namely

B_i＝INT(CW_I*Random())

Wherein INT is a rounding function;

step three, continuously monitoring the channel, wherein the value of the back-off counter is reduced by 1 when the channel is continuously idle for one time slot, and if the value B of the back-off counter is_iIf the value is reduced to 0, sending data, and entering the step four, otherwise returning to the step three; if the node detects that the channel is busy in the backoff process, B is saved_iUntil the channel continuous idle time length is detected to be DIFS, the third step is executed again;

step four, if the transmission fails and the maximum retransmission times m are not exceeded; the contention window CW is adjusted, i.e.

CW_i+1＝Min(CW_i*log_an，CW_max)，0≤i<m

Returning to the step two to carry out retreat retransmission after the competition window is updated; if the node successfully sends the data or reaches the maximum retransmission times m, updating the contention window and waiting for the next data sending, namely

CW₁＝CW_min*log_an。

The four-way handshake mechanism is as follows:

on the basis of a CSMA/CA handshake access mode, RTS/CTS handshake signals are added, and an ACK control message is added to confirm a link layer; the adopted message exchange sequence is RTS-CTS-DATA-ACK, when a DATA message is sent, a sending node firstly sends an RTS, a receiving node sends back a CTS after receiving the RTS to determine a channel, the sending node starts to send the DATA message DATA after correctly receiving the CTS, and the receiving node sends back an ACK for confirmation after correctly receiving the DATA message to finish the DATA message transmission.

Specifically, a collision avoidance-based self-organizing wireless broadband network transceiving system, the basic component unit of which is a broadband network transceiver. The broadband network transceiver carries out real-time dynamic networking according to different scenes and routing protocols to form a system network topological graph.

The broadband network transceiver is composed of units such as a processing unit, a network unit, a communication unit, a power supply unit and the like. The processing unit is composed of a microprocessor and is mainly responsible for realizing a communication protocol and executing related algorithms. The main role of the network element is the maintenance of the network topology and routing information. The communication unit is responsible for the operation of a carrier sense and collision avoidance back-off mechanism, the transmission of wireless data, the transceiving of radio frequency channels and the like. The power supply unit is used for providing power energy for the modules. The mutual cooperation among all modules of the nodes enables the whole self-organizing broadband network to work normally.

Design of wireless communication unit based on collision avoidance

The communication mode adopted by the wireless communication unit disclosed by the invention is a carrier monitoring multiple access mechanism with collision avoidance. The mechanism ensures that two or more self-networking broadband network transceivers are dynamically prevented from generating conflict under the condition of simultaneously competing to access the same channel, and the algorithm is self-adaptively accessed to the network and realizes data transceiving.

The basic idea is that when a node needs to send data, the idle evaluation is first performed on the channel availability status by a listening mechanism at a fixed time interval. If the channel state is busy, the mode of the self-adaptive logarithmic backoff algorithm disclosed by the invention is adopted to avoid collision until the channel is free. When the channel is idle, the network node occupies the channel, and the four-way handshake mechanism disclosed by the invention is adopted, so that the validity of the transmission data is ensured.

Compared with the resource allocation type (such as TDMA and CDMA), the resource competition type communication mode utilizes the spectrum resources more effectively and meets the communication requirement of network nodes dynamically.

Interframe space

In the communication mode adopted by the wireless communication unit disclosed by the invention, after each frame is successfully transmitted, the wireless communication unit needs to randomly wait for a period of idle time before starting the next transmission, and the short period of idle time is called an Inter-frame Spacing (IFS). Collectively define 2 types of IFSs: distributed Inter-frame Spacing (DIFS), Short Inter-frame Spacing (SIFS). The interval size relationship is SIFS < DIFS.

And (4) DIFS: in the collision avoidance mechanism, a node waits for a specific time, i.e., DIFS, before sending data, and it must be ensured that the channel is always idle during this time.

SIFS: the receiving node needs to wait for a time interval of SIFS before sending the ACK, in order to prevent other nodes waiting to access the channel from trying to use the channel, the SIFS being shorter than DIFS.

Request To Send frame (RTS): in the RTS/CTS access mode, a request transmission frame, which is transmitted before transmitting data, is used to reserve a channel.

Clear To Send (CTS): and in the RTS/CTS access mode, a return frame sent by the destination node is used for determining that the channel is idle.

Carrier sensing mechanism

Two carrier sensing mechanisms

The protocol uses two ways to detect the channel: physical carrier sensing and virtual carrier sensing. The former is technical and the latter is protocol. The physical carrier sensing directly evaluates the idle channel state by using a physical layer technology, and then feeds back the channel state to the MAC layer. Hidden nodes cannot be detected by physical carrier sensing.

So to avoid collisions, we also propose virtual carrier sensing. The virtual carrier sensing mechanism is implemented by a network allocation vector of the MAC layer.

Network allocation vector

The NAV is a locally maintained NAV variable used in the storage medium's intended protocol to implement virtual carrier sensing. The Duration field of RTS, CTS and DATA frame in the protocol stores the predicted transmission time of the frame, which is used to inform all nodes in the communication range of the node of the Duration of the wireless channel to be occupied, each node needs to maintain a local NAV variable to record the Duration time in the received frame and update the local NAV in time, the node judges the occupation time of the wireless channel according to the NAV value, and when the NAV variable of the node is decreased to 0, the node virtually judges that the channel is idle, and can access the channel. The ad hoc network system described in this patent comprehensively judges the state of the channel according to the above two carrier sense mechanisms, and only when the protocol level and the physical level both evaluate that the channel is in an idle state, the channel is considered to be idle.

Four-way handshake access mechanism

The node access mechanism disclosed by the invention improves the CSMA/CA handshake access mode, adds RTS/CTS handshake signals and adds an ACK control message to confirm a link layer. The message exchange sequence is RTS-CTS-DATA-ACK, and the problem of hiding the terminal can be avoided in this way. As long as there is a data message to be sent, the sending node will send an RTS first. The RTS is sent in the same way as the message in the two-way handshake, and is also for channel contention. The receiving node, upon receiving the RTS, sends back a CTS to determine the channel. And after correctly receiving the CTS, the sending node starts to send a DATA message DATA. And after the receiving node correctly receives the DATA message, sending back an ACK (acknowledgement character) for confirmation, and completing one successful DATA transmission. The RTS/CTS message includes information on how long it takes to send the next data message. Therefore, other nodes adjacent to the transmitting node and hidden terminals adjacent to the receiving node will not transmit data during this time. This back and forth exchange is necessary to avoid hidden terminal problems.

As shown in fig. 2, in the node access mechanism disclosed in the present invention, a source node needs to determine that a channel is in an idle state before transmitting data, and then waits for a DIFS duration, and if the channel is kept in the idle state all the time in the DIFS duration, the node sends an RTS frame in a broadcast manner. The information contained in the RTS frame mainly includes the source node address, the destination node address, and the like. When the destination node receives the RTS frame, if the channel is idle, a CTS frame is also sent in a broadcast mode, and the CTS frame indicates that the source node is allowed to send data. After receiving the CTS frame, the source node indicates that the channel has been reserved successfully, and may formally transmit data by waiting for an SIFS time. And after the destination node normally receives the data, returning ACK to confirm the reception, and after the source node receives the ACK, indicating that the communication process is successfully completed.

Adaptive backoff mechanism

The back-off time is generated as shown in the equation.

BT＝Random()*τ

In the formula, let τ denote a timeslot, and a node needs to go through a random back-off process before accessing a channel, where the back-off duration is composed of several timeslots, that is, the timeslot is a basic unit of the back-off duration.

Traditional binary exponential backoff algorithm

The IEEE802.11 adopts a binary exponential back-off algorithm, and when a source node detects that a channel is busy before preparing to transmit data, or the channel is in a busy state within a time range of waiting for a DIFS, a random back-off algorithm needs to be executed first when the source node detects that the channel is idle again and wants to continue to transmit data. In the random back-off algorithm, a back-off time (BC) is randomly generated and stored in the back-off Counter BC, and if a non-zero value is already stored in the back-off Counter BC at this time, a new back-off time is not generated.

Random () at [0, CW]The distribution is uniform, namely random values in the interval are represented. Contention Window (CW): the contention window size is the upper selection range limit of BC. Indicating that it is in the minimum contention window CW controlled by the wireless network PHY layer_minWith the maximum contention window CW_maxInteger value in between, i.e. having CW_min≤CW≤CW_max。

In the process of executing the back-off algorithm by the network node, if the duration of monitoring the channel idle reaches one time slot, the value of the back-off counter BC is decreased by 1. If the channel is monitored to be busy, the backoff process is temporarily stopped, the value of the backoff counter BC is temporarily frozen until the channel is detected to become idle again, the backoff process is started again, and the value of the counter BC continues to be decremented. The source node may transmit a data packet only when the counter BC is decremented to 0.

As described above, the CW is reduced to the minimum value whenever the node transmission succeeds, and is expanded to twice the current window when the node transmission fails. The size of the CW directly affects the length of the node back-off time, and the larger the CW is, the longer the node back-off time is, and conversely, the shorter the node back-off time is. After a node successfully transmits, the CW of the node is reduced to the minimum, and other nodes which fail to transmit become larger gradually along with the increase of the retransmission times. Therefore, in subsequent competition, the node which successfully sends the data has more competitive advantage, and other nodes which fail to send the data are starved because the data cannot compete for the channel, namely, there is a capture effect, namely, the algorithm is always favorable for the node which successfully sends the data to compete for the channel again in a short time, and a serious unfairness phenomenon is caused.

Improved adaptive logarithmic backoff algorithm

The backoff algorithm described in most of the research inventions at present is based on binary exponential backoff, and the invention discloses an improved backoff algorithm, namely a self-adaptive logarithmic backoff algorithm.

The adaptive logarithm back-off algorithm mechanism disclosed by the invention introduces an adaptive competition window adjusting factor estimated based on the number of competition nodes in the network, so as to achieve the purpose of dynamically adjusting the back-off window according to the competition condition of the network.

The adaptive logarithm backoff algorithm dynamically adjusts the initial value of the contention window and the window backoff amplitude by using a logarithm function taking the number of contention nodes in the network as a variable, and the adjustment formula of the contention window is described as follows.

1. Before sending data, a node needs to monitor a channel first, and enters a backoff stage after the channel is monitored to be continuously idle for a DIFS interval. Contention window initialization value is CW₁I.e. by

CW₁＝CW_min*log_an

2. After the node enters the back-off phase, a random back-off time (in time slot units) is calculated and stored in a back-off counter, i.e. the node

B_i＝INT(CW_I*Random())

Where INT is the rounding function.

3. Continuously monitoring the channel, wherein the value of the back-off counter is reduced by 1 every time the channel is continuously idle for one time slot, and if the value of the back-off counter is B_iAnd if the value is reduced to 0, sending the data and entering the next step, and otherwise, returning to the previous step. If the node detects that the channel is busy in the backoff process, B needs to be saved_iUntil the channel duration idle duration is detected to be DIFS, and the step is re-executed.

4. If the transmission fails and the maximum retransmission time m is not exceeded; the contention window CW is adjusted, i.e.

CW_i+1＝Min(CW_i*log_an，CW_max)，0≤i<m

And jumping to the step 2 for back-off retransmission after the contention window is updated. If the node successfully sends data or the maximum retransmission time m is reached, the contention window is also updated, and the node waits for the next data transmission, that is, the node sends data again

CW₁＝CW_min*log_an

When the base number a is reasonable in value, the algorithm improves the network throughput and the fairness of the node access channel to a certain extent, which is important for the self-organizing wireless broadband network.

Data frame format design

And a MAC layer: the method comprises the steps of receiving a service data unit (MSDU) from an upper layer, encapsulating the MSDU into a protocol data unit (MPDU) according to different types, adding a signal field parameter set (PYPM) of a PHY layer to the front end of the MPDU to serve as Pure Service Data (PSDU) sent to the PHY, adding a header (PYHD) of the PHY layer, and transmitting the PSDU to a PLCP layer of the PHY layer.

And a PLCP layer: and receiving a service data unit (PSDU) from an upper layer, and carrying out tail bit filling according to the data length in the PYHD to reach the length of N OFDM symbols. According to the frame type in the PYPM, OFDM conforming types with different time lengths are selected. Then, the protocol data unit (PPDU) is formed by blocking, scrambling, coding and modulating and is transmitted to a PMD layer of a PHY layer.

A PMD layer: and receiving a service data unit (PPDU) from an upper layer, and filling different OFDM coincidences in sequence. The synchronization sequence is filled into the first OFDM symbol for frequency offset estimation and compensation.

MPDU frame format

Table 1 MPDU frame format table

The frame sending sequence is that the low bit is before and the high bit is after.

MPDU Frame-Frame Control

The Frame Control occupies 2 bytes, and mainly completes the Control of the Frame type.

Table 2 Frame Control format table

Protocol

Protocol stands for Protocol version.

Table 3 field description table

Type

Type represents a frame Type.

Table 4 field description table

SubType

SubType represents a SubType of a frame.

Table 5 field description table

MoreFrag

More Fragments represent long frame Fragments, whether there are any More frames.

Table 6 field description table

Retry

Retry represents whether it is a retransmission frame.

Table 7 field description table

Protected Frame

Protected Frame represents whether it is a Protected Frame.

Table 8 field description table

MPDU frame Duration

Duration occupies 2 bytes, and mainly completes the recording of the value of network allocation vector NAV, and the sending sequence is low bit ahead.

Table 9 field description table

MPDU frame-Address

Table 10 field description table

Name (R)	Length of	Description of the invention
			Address1receiver	6Byte	Destination MAC address
Address2sender	6Byte	Source MAC address
			Address3filtering	6Byte	Filtering MAC addresses, reservations
Address4Optional	6Byte	Reserving MAC addresses

MPDU frame-Seq-Ctl

The Seq-Ctl, which takes 2 bytes and is used to reassemble frame fragments and discard duplicate frames, consists of a 4-bit fragment number and a 12-bit sequence number. The transmission order is low bit ahead.

Table 11 field description table

MPDU Frame-Frame Body

The Frame Body is a data segment of the Frame Body and is used for transmitting upper layer data.

MPDU frame-FCS

The FCS is a frame check sequence that checks the correctness of the frame by CRC check, and takes 4 bytes. And the receiving end judges that the FCS is wrong, and the frame is discarded. If the frame is correct, the frame is transmitted to the upper layer protocol for processing, and a response frame response is sent. And the sending end waits for the response timeout of the 1, and retransmits the frame.

MPDU control frame format

RTS (request to send)

The RTS frame is used to take control of the medium in order to transmit a data frame.

Table 12 frame format table

Frame Control: type is 2 'b 01, Subtype is 4' b1011, and the rest are default values.

Duration: the RTS frame reserves the medium usage right for the frame exchange procedure, so the RTS sender must calculate how much time is needed after the RTS frame ends.

Address1 receiver (destination Address): a receiving end address;

address2 sender (source Address): a sending end address;

CTS (clear to send)

The CTS frame is used to acknowledge the RTS frame.

Table 13 frame format table

Frame Control: type 2 'b 01, Subtype 4' b1100, and the rest are default values.

Duration: the Duration value of the RTS frame is used as the technical reference of the Duration, the time required for sending the CTS frame and 1 SIFS is subtracted, and the result is put into the Duration of the CTS.

Address1 receiver (destination Address): the address of the receiving end, i.e. the address of the sending end of the RTS.

ACK (response)

The CTS frame is used for MAC and any positive acknowledgement required for data transmission.

Table 14 frame format table

Frame Control: type is 2 'b 01, Subtype is 4' b1101, and the rest are default values.

Duration: the Duration value is determined by the position of the ACK frame in the frame exchange.

If Duration is 0 in the complete data frame and in the last frame segment of a series of frame segments. The data transmitting end sets More Fragments of Frame Control to 0 to indicate that the data transmission has ended. The ACK frame is determined accordingly, and Duration is set to 0.

If More Fragments is 1, it indicates that there is a frame fragment in transmission, and the Duration setting is consistent with the CTS frame method.

Address1 receiver (destination Address): the address of the receiving end, i.e. the address of the transmitting end of the frame to be responded to.

PYPM frame format

The PYPM is parameter information transmitted by the MAC layer frame to the PHY layer, and is used for mode selection of data processing by the PHY layer, including OFDM symbol type, OFDM signal bandwidth, coding and decoding mode, modulation mode, and the like.

Table 15 PYPM frame format table

TMType

TMType represents an OFDM symbol time length type, and occupies 4 bits.

Table 16 field description table

BWType

BWType represents the OFDM signal bandwidth type and occupies 4 bits.

Table 17 field description table

CodeType

The CodeType represents the coding and decoding mode of the PHY layer and occupies 4 bits.

Table 18 field description table

ModulType

The moduletype represents the modulation mode of the PHY layer and occupies 4 bits.

Table 19 field description table

FrameLength

The FrameLength represents the total length of the PHY layer PSDU data, and has a unit of Byte, and occupies 2 bytes.

Table 20 field description table

Name (R)	Data of	Description of the invention
			FrameLength	0～65535	Total length of PYPM + MPDU in bytes

PYHD frame format

The PYHD is a header added by the PHY layer for transmitting the MAC layer frame, and is used for the PHY layer to identify the whole frame data of the current MAC data frame, process the whole frame data, and transmit the whole frame data.

Table 21 PYHD frame format table

Head

MAC- > header of PHY, takes 4 bytes, fixed value 32' h55aaaa 55.

Length

MAC- > PHY data length, takes 4 bytes, the unit is byte.

RF channel waveform system

The system described in the invention is based on OFDM multichannel access technology, can realize high-speed broadband transmission, and can ensure good system performance.

Orthogonal Frequency Division Multiplexing (OFDM), an increasingly mature technique, divides a channel into a number of orthogonal channels, modulates each sub-channel with a sub-carrier, and transmits the sub-carriers in parallel, wherein the signal spectrums of the carriers are orthogonal. In each shared frequency spectrum domain, the frequency spectrum domain can be divided into a plurality of frequency bands with widths according to an OFDM modulation mode.

Table 22 downlink waveform basic parameter table

The physical layer waveform system is supposed to adopt an OFDM communication system. The subcarrier spacing is Δ f-15 KHz. The signal bandwidth is 20MHz, the number of available subcarrier points is 1334, the number of FFT conversion points is 2048, and the sampling rate is 30.72 MHz.

The length of one transmission is 2ms, which comprises a pre-guard time 217us, a post-guard time 100us and valid data 1.683 ms. The pre-protection mainly comprises synchronous clock deviation, clock drift, AGC acquisition time, frequency conversion, power amplifier rising time and the like, and the sum is 217 us. The post-protection is mainly transmission delay, and the transmission delay of 30 kilometers is approximately 100 us.

The OFDM subcarrier spacing is 15KHz, the length of one OFDM symbol is 66.7us, and if a Cyclic Prefix (CP) with a length of 4.7us is used, the total length of one OFDM symbol is 71.4 us. Therefore, a total of 23 OFDM symbols are contained in 1.683 ms. The first OFDM symbol is a frame header used for frame synchronization and coarse frequency offset estimation. Therefore, the OFDM symbols of the effective data are 22.

Routing module design

The nodes in the self-organizing broadband network have equal positions and have the functions of a host and a router respectively. Nodes can be added or deleted in the network at any time according to the network requirements, so that the self-organizing broadband network has a frequently-changed network topology structure.

The routing algorithm disclosed by the invention aims to establish and maintain a dynamic, self-starting and multi-hop routing exclusive network in a plurality of mobile nodes. The algorithm enables the mobile node to quickly obtain a route to a new destination node, and the node only needs to maintain the route to the node within the range of its signal, and route information of nodes farther away does not need to be maintained. Disconnection and transaction of a connection in a network can cause a change in the network topology, and the routing algorithm enables a mobile node to respond to the change in time, so that the algorithm can converge quickly when the network topology changes (for example, a node moves in the network). When a connection is broken, the routing algorithm will inform all affected nodes that will disable the route to the connection.

In the routing protocol of the self-organizing broadband network, a node hop-by-hop forwarding mode is adopted, and a dynamic, self-starting and multi-hop routing exclusive network is established and maintained by utilizing route discovery and route maintenance.

Routing protocol format

The routing protocol is based on routing request packets (RREQ), routing reply packets (RREP) and routing error packets

(RERR) three kinds of messages, and two kinds of messages, namely RREP _ ACK and HELLO, are also included in the RREP message.

RREQ message format

Wherein:

type: the RREQ packet type defaults to 1;

j: a multicast reservation field;

r: multicast repair;

g: a mark field, which is used for checking whether the intermediate node has a route reaching the destination node or not and sending the RREP packet if the intermediate node has the route reaching the destination node;

d: a flag field, which judges whether the RREP is the RREP of the destination node;

reserved: reserving a field;

DestinationAddress: a destination node address;

destinationsequence: a destination node sequence number;

SourceAddress: a source node address;

SourceSequence: a source node sequence number;

ID; a packet number of the message;

HopCount: total number of hops from source node to destination node.

RREP message format

Wherein:

type: the RREQ packet type is defaulted to 2;

r: multicast repair;

a: a flag field for judging whether response is needed;

reserved: reserving a field;

ID; a packet number of the message;

DestinationAddress: a destination node address;

destinationsequence: a destination node sequence number;

SourceAddress: a source node address;

SourceSequence: a source node sequence number;

HopCount: total number of hops from source node to destination node.

TTL: the route validity time.

RERR message format

Type: the RERR packet type defaults to 3;

n: the mark is not deleted;

reserved: reserving a field;

hopcount: the number of unreachable nodes;

ID; a packet number of the message;

unaachable destination address: an unreachable destination node address;

unarchable destination sequence: an unreachable destination node sequence number;

AddUnreactable DestinationAddress: other unreachable destination node addresses;

advanced available Destinationsequence: the destination node sequence number.

HELLO message format

Type: HELLO packet type defaults to 4;

reserved: reserving a field;

HopCount: set to 1, the packet is sent to the neighbor nodes within one hop.

ID; a packet number of the message;

DestinationAddress: a destination node address;

destinationsequence: a destination node sequence number;

SourceAddress: a source node address;

SourceSequence: a source node sequence number;

route discovery

When a source node sends data to a destination node, whether a routing message of the destination node is in a routing table of the source node is checked firstly. If the route reaching the destination node exists, the information is directly sent, otherwise, the path message from the sending node to the receiving node is reestablished. The routing protocol disclosed by the invention realizes the establishment and maintenance of the routing table through the intermediate node. This typically involves establishing both forward and reverse routes. The reverse route is established by the destination node sending an acknowledgement packet to the source node. The forward routing means that the source node broadcasts the RREQ to the adjacent nodes, the adjacent nodes check whether the packet is received or not after receiving the RREQ, and if the packet is received, the packet is discarded, otherwise, the packet is checked whether the packet is not the destination node and the hop number is added with 1. The node receives a plurality of RREQ copies sent by the adjacent nodes, and finds the needed node information through RREQ analysis. After receiving the message sent by the source node, the destination node sends a response message and establishes a reverse path. The routing information, whether forward or reverse, generally includes packets such as source address, destination address, broadcast ID, source sequence number, and time-to-live, as shown in fig. 4.

Due to the frequent change of the topology of the mobile wireless network, the addition or deletion of any node will affect the network, i.e. the disconnection of the old existing link and the generation of a new link.

The route maintenance is to perform link maintenance by sending HELLO messages, and the specific process is as follows: a node periodically broadcasts a "HELLO" message to neighboring nodes. The link is considered to have been broken if a HELLO packet has not been received within the time set by the timeout retransmit register. And (4) repairing the disconnected node, firstly broadcasting a RREQ to the interrupted node, if the unreachable node receives the RREQ, sending a response message RREP to the source node, and then, developing a route reconstruction process for the unreachable intermediate node. If no RREQ is received and no good link is repaired, the node broadcasts RERR information to all adjacent nodes, the information is broadcasted by the interrupting node IP and the adjacent node IP through RERR, other nodes know that the link is disconnected

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (5)

1. A self-organizing wireless broadband network transceiving system based on collision avoidance is characterized by comprising a plurality of self-organizing network broadband network transceivers, wherein each self-organizing network broadband network transceiver comprises a main control module, a signal conversion module front-end transformer, a power amplifier module, a network interface module and a communication port; the power amplifier module, the front-end transformer of the signal conversion module, the signal conversion module and the main control module are sequentially connected, and the network interface module and the communication port are respectively connected with the main control module; and the plurality of ad hoc network broadband network transceivers are in communication connection.

2. A carrier sense multiple access method for collision avoidance of an ad hoc wireless broadband network transceiving system based on collision avoidance according to claim 1, comprising the steps of:

an ad hoc network broadband network transceiver is a node, a dynamic and multi-hop routing network is established and maintained in a plurality of nodes through a routing protocol of the ad hoc network, and when a node needs to send data, idle evaluation is carried out on the available state of a channel by an interception mechanism with a fixed time interval; if the channel state is busy, adopting a self-adaptive back-off mechanism to avoid collision until the channel is idle; and if the channel is idle, the node occupies the channel and adopts a four-way handshake mechanism to perform data transmission.

3. A carrier sense multiple access method for collision avoidance according to claim 2, wherein the sensing mechanism comprises physical carrier sense and virtual carrier sense, the physical carrier sense uses physical layer technology to perform idle channel state estimation and then feeds back the channel state to the MAC layer; the virtual carrier sense mechanism realizes the detection of hidden nodes through a network allocation vector of an MAC layer, and the network allocation vector NAV realizes the virtual carrier sense by using a locally maintained NAV variable in a storage medium expectation protocol; the Duration field of RTS, CTS and DATA frame in the protocol stores the estimated transmission time of the frame, which is used to inform all nodes in the communication range of the node of the Duration time of the wireless channel to be occupied, each node maintains a local NAV variable to record the Duration time in the received frame and update the local NAV, the node judges the occupation time of the wireless channel according to the NAV value, when the NAV variable of the node is decreased to 0, the channel is determined to be idle; the channel is idle when both the protocol level and the physical level evaluate the channel as idle.

4. A carrier sense multiple access method for collision avoidance according to claim 2, wherein the adaptive back-off mechanism is:

the backoff duration is generated as shown in the following equation:

BT＝Random()*τ

wherein τ represents a time slot;

the self-adaptive logarithm backoff algorithm adopts a logarithm function taking the number of competition nodes in a network as a variable, and dynamically adjusts the initial value of a competition window and the window backoff amplitude, wherein the adjustment of the competition window comprises the following processes:

firstly, a node monitors a channel before sending data, and enters a backoff stage after the channel is monitored to be continuously idle for a DIFS interval, wherein the initialization value of a contention window is CW₁I.e. by

CW₁＝CW_min*log_an

Step two, after the node enters the backoff stage, calculating the random backoff duration and storing the random backoff duration into a backoff counter, namely

B_i＝INT(CW_I*Random())

Wherein INT is a rounding function;

step three, continuously monitoring the channel, wherein the value of the back-off counter is reduced by 1 when the channel is continuously idle for one time slot, and if the value B of the back-off counter is_iIf the value is reduced to 0, sending data, and entering the step four, otherwise returning to the step three; if the node detects that the channel is busy in the backoff process, B is saved_iUntil the channel continuous idle time length is detected to be DIFS, the third step is executed again;

step four, if the transmission fails and the maximum retransmission times m are not exceeded; the contention window CW is adjusted, i.e.

CW_i+1＝Min(CW_i*log_an,CW_max)，0≤i<m

Returning to the step two to carry out retreat retransmission after the competition window is updated; if the node successfully sends the data or reaches the maximum retransmission times m, updating the contention window and waiting for the next data sending, namely

CW₁＝CW_min*log_an。

5. A collision avoidance carrier sense multiple access method according to claim 2, wherein the four-way handshake mechanism is:

on the basis of a CSMA/CA handshake access mode, RTS/CTS handshake signals are added, and an ACK control message is added to confirm a link layer; the adopted message exchange sequence is RTS-CTS-DATA-ACK, when a DATA message is sent, a sending node firstly sends an RTS, a receiving node sends back a CTS after receiving the RTS to determine a channel, the sending node starts to send the DATA message DATA after correctly receiving the CTS, and the receiving node sends back an ACK for confirmation after correctly receiving the DATA message to finish the DATA message transmission.

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