CN101409660A - Channel access control method for wireless sensor network - Google Patents

Abstract

The invention discloses a method for controlling channel access of a wireless sensor network. A base station node and each sensor node adopt a time frame structure with different lengths of time frame, so that the sensor nodes can reserve different time slots by dispatching to carry out data packet transmission, thereby not only reducing collision probability of forwarding data packets among sensor nodes in a high-density monitoring area and improving the utilization rate of wireless channel, but also effectively avoiding overhearing in the wireless sensor network and frequent status switching of a transceiver; therefore, the sensor nodes can be in dormancy status as fully as possible during idle transmission so as to greatly reduce energy consumption under the high-loading network condition and have good energy efficiency. A path reserve mechanism can reserve a multi-hop time slot in advance along data packet forwarding direction in time slot reservation phase, according to the time frame synchronizing characteristics of the sensor nodes on a forwarding path, thereby effectively avoiding end-to-end transmission delay of single data packet caused by intermittent transmission of data packets on the forwarding path.

Description

A kind of channel access control method of wireless sensor network

Technical field

The present invention relates to a kind of wireless sensor network technology, especially relate to a kind of channel access control method of wireless sensor network.

Background technology

Wireless sensor network is an emerging technology, can be widely used in fields such as environmental monitoring, intelligent space, medical system and robot development.In wireless sensor network, channel access control (MAC, Medium AccessControl) agreement is the occupation mode of decision wireless channel, distributes the limited communication resource and ensure one of key network agreement of wireless sensor network efficient communication between sensor node.Sensor node is owing to be subjected to the restriction of cost and volume, usually adopt the powered battery of finite energy, yet, when the supplying cell of sensor node exhausts, because sensor node One's name is legion in the wireless sensor network, sensor node is deployed in the monitored area again usually at random, and operational environment is relatively more abominable usually, for sensor node charging or to change battery unrealistic, and most applied environment requires wireless sensor network continuous operation for a long time.Therefore, save energy to greatest extent, prolong the key issue that will solve that network life becomes wireless sensor network, in addition, as environmental monitoring etc., low delay also is important performance factor in a lot of the application.

Existing application roughly can be divided into two big classes in the MAC of wireless sensor network agreement: based on the MAC agreement of competition with based on the MAC agreement of dispatching.

MAC agreement realization based on competition is simple relatively, and sensor node Maintenance free, and all sensor node shared state information are competed wireless channel each other relatively independently, therefore can provide good expandability.But along with the increase of wireless sensor network data rate, this MAC consultation based on competition makes and produces very high data collision, the idle monitoring and cross-talk in the data transmission procedure, thereby causes very big energy dissipation.S-MAC (Self-organizing MAC) agreement of self adaptation sleep is on 802.11 MAC agreement bases, propose at the saving energy requirement of wireless sensor network one typically based on the MAC agreement of competition, it mainly adopts the periodically low duty ratio working method of monitoring/sleep, the consistent through consultation sleep scheduling mechanism of neighbor node forms virtual cluster, reduces the free time of sensor node and monitors; Utilize physical vlan carrier sense mechanism and RTS/CTS (Request To Send, request transmission/Clear To Send, clear to send) communication mechanism to avoid data collision and cross-talk.Yet because the duty ratio of each sensor node is all identical in the S-MAC agreement, this fixing duty ratio can not be adjusted accordingly along with the changes in flow rate of wireless sensor network, use higher duty ratio in order to satisfy the highest communication load, this will cause causing very big energy dissipation under the situation of low discharge load, and will increase the time-delay that data transmit.

Based on the MAC agreement of scheduling, sensor node is preengage different time slots by scheduling and is carried out transfer of data, can effectively reduce the generation of data collision, and can make sensor node be in sleep state as far as possible in the crack at one's leisure, has good efficiency.Yet this MAC agreement based on scheduling needs relatively stricter time synchronized, can bring very big administration overhead, and is also relatively poor to the dynamic topological structure adaptability of wireless sensor network, and data forwarding has bigger time-delay.TRAMA (Traffic-Adaptive Medium Access) agreement is based on one of MAC agreement of scheduling, it will be divided into insert at random and distribute access two parts dispatching cycle, finish the distribution of time slot based on the distributed election algorithm of each sensor node flow information, can reach certain throughput and fairness, the data collision that can effectively avoid concealed terminal to cause.But the time-delay of the data of TRAMA agreement is bigger, calculates frequent complexity and requires to have point-device clock synchronization.

In addition, existing MAC agreement major part all only is adapted to the lower traditional wireless sensor network of single application and offered load, can not satisfy support use as merging several data collection and event monitoring etc., requirement can be supported the high amount of traffic amount and the wireless sensor network of low delay service can be provided.

Summary of the invention

Technical problem to be solved by this invention provides a kind of channel access control method that has the wireless sensor network of low-energy-consumption under high-load network.

The present invention solves the problems of the technologies described above the technical scheme that is adopted: a kind of channel access control method of wireless sensor network, wireless sensor network comprises a plurality of base-station nodes that are deployed in the sensor node of monitored area and receive the packet that includes Monitoring Data of described sensor node transmission, described base-station node and each sensor node adopt the time frame structure with differing time frames length, described base-station node is chosen frame length when basic according to input parameter, and with described when basic frame length carry out the whole network broadcasting; Each sensor node is according to local nodes density and described frame length when frame length is chosen oneself real work when basic; Frame structure comprises time slot reservation stage and data transfer phase when described.

Between described sensor node of described time slot reservation stage, adopt single-hop time slot reservation mechanism reservation time slot.

Between described sensor node of described time slot reservation stage, adopt path booking-mechanism reservation multi-hop time slot.

Frame length is the described integral multiple of frame length when basic during described real work.

Described input parameter comprises that the node density of wireless sensor network, data produce average speed and maximum burst speed; Described node density is the interior neighbor node number of the double bounce of each sensor node; Described local nodes density comprises the interior neighbor node number of double bounce of interior neighbor node number of the double bounce of oneself and the hop neighbor node of oneself.

Described sensor node is provided with the time slot allocation mode field of the long duration for described data transfer phase in position, the corresponding transmission time slot of each mode bit of described time slot allocation mode field, whether indicate described transmission time slot to be preengage, described sensor node selects idle transmission time slot to carry out time slot reservation by described time slot allocation mode field; Described sensor node is provided with a receiving scheduling table, information in the described receiving scheduling table comprises the numbering and the length of data package of the transmission time slot of source node address, reservation, and described sensor node receives packet according to the information in the described receiving scheduling table at corresponding transmission time slot.

The duration in frame length time slot corresponding reservation stage poor when frame length and described real work when the duration of described data transfer phase is described real work.

The detailed process of described single-hop time slot reservation mechanism reservation time slot is: in the described time slot reservation stage, sending node is checked the time slot allocation mode field of oneself and is selected minimum idle transmission time slot by CSMA/CA (CarrierSense Multi-Access/Collision Avoidance, csma/conflict is avoided) machine-processed competitive channel sends a RTS (Request To Send who includes the numbering of this free time transmission time slot to destination node, request sends) request package, destination node is checked the time slot allocation mode field of oneself after receiving the RTS request package, check whether corresponding transmission time slot is preengage, if do not preengage, then destination node is to CTS (Clear ToSend of sending node feedback, clear to send) feedback packet, simultaneously, destination node is provided with the mode bit of this transmission time slot correspondence and adds a respective entries in the receiving scheduling table of oneself, if preengage, then destination node is not fed back any information; When sending node was not received the CTS feedback packet, sending node time slot allocation mode field according to oneself before the time slot reservation stage finishes continued the next idle transmission time slot of reservation.

The detailed process of described path booking-mechanism reservation multi-hop time slot is: in the described time slot reservation stage, be provided with in packet waiting for transmission and indicate to seek quickness the fast incident generation flag bit of transmitting; Sending node is checked the time slot allocation mode field of oneself and is selected minimum idle transmission time slot by CSMA/CA (Carrier SenseMulti-Access/Collision Avoidance, csma/conflict is avoided) next-hop node of machine-processed competitive channel on the path send a RTS request package that includes the numbering of this free time transmission time slot and be provided with the incident generation flag bit that the speed of indicating to seek quickness transmits, destination node is checked the time slot allocation mode field of oneself after receiving the RTS request package, check whether corresponding transmission time slot is preengage, if do not preengage, then destination node is provided with the CTS feedback packet of the fast incident generation flag bit of transmitting of seeking quickness of indicating to one of sending node feedback, and utilizes incidentally mechanism incidentally own information of preengaging the transmission time slot with bigger numbering to next-hop node in the CTS feedback packet; Receive the same incidentally machine-processed destination node reservation time slot that continues to oneself of all the other node utilizations of CTS feedback packet on the path, till preengaging transmission time slot or the end of time slot reservation stage with maximum numbering.

When definition has different real work frame length and each other two sensor nodes of neighbours be boundary node, these two boundary nodes are designated as i and j respectively, the frame length and the duration in time slot corresponding reservation stage are designated as L respectively during the real work of boundary node i_iAnd R_i, the duration in frame length and time slot corresponding reservation stage is designated as L respectively during the real work of boundary node j_jAnd R_j, L wherein_i＜L_j, boundary node i prolongs (L with the time slot allocation mode field of oneself_j-L_i) position, enter time slot reservation simultaneously during the stage at boundary node i and boundary node j, boundary node i and boundary node j reserve in advance respectively and lay oneself open to data transfer phase in oneself the current dispatching cycle and the other side's node will be in the time slot in time slot reservation stage, boundary node i adopt littler competition window preferential send a reservation first to (R_j-R_i) broadcast packet of individual time slot, boundary node j sends a reservation (L_i-R_j+ 1) to (L_i-R_j+ R_i) broadcast packet of individual time slot, the time slot reservation of next dispatching cycle that enters oneself as boundary node i is during the stage, and boundary node i and boundary node j are moved to the left L with the time slot allocation mode field of oneself respectively_iPosition and (L_i-R_j+ R_i) the new time slot allocation mode field of being used as oneself again behind the position carries out time slot reservation; The time slot reservation of next dispatching cycle that enters oneself as boundary node j is during the stage, and boundary node i and boundary node j adopt and enter identical mode of oneself time slot reservation stage of next dispatching cycle with boundary node i and obtain the new time slot allocation mode field of oneself.

Compared with prior art, the invention has the advantages that base-station node and each sensor node adopt the time frame structure with differing time frames length, sensor node can be preengage the transmission that different time slots carries out packet by scheduling like this, not only reduced the collision probability that packet is transmitted between the inner sensor node of high density monitored area, improved the utilance of wireless channel, and avoid occurring in the wireless sensor network cross-talk and the frequent state exchange of transceiver effectively, make sensor node be in sleep state as far as possible at idle transmission time slot, greatly reduce the waste of energy under the network condition of high capacity, have good efficiency; The path booking-mechanism can be according to the time frame synchronizing characteristics of forward-path upper sensor node, preengage the multi-hop time slot in the time slot reservation stage in advance along the packet routing direction, effectively avoided individual data to wrap in the transmission delay end to end that the Data transmission band comes because of intermittence on the forward-path; The boundary node of time frame adopts the method for each different time frame structure dispatching mode of fusion, make boundary node all be in wake-up states in the time slot reservation stage of differing time frames structure, avoided the time frame overlapping phenomenon that causes because of the time frame structure that uses differing time frames length effectively, thereby avoided data collision, can make simultaneously packet change the time frame structural region that another uses differing time frames length fast over to, effectively reduce the transmission delay of packet from a time frame structural region; In addition, the multi-hop communication transmission application that the present invention is particularly suitable for extensive high capacity and requirement provides low energy consumption, hangs down the wireless sensor network of time delay service.

Description of drawings

Fig. 1 be two have differing time frames length the time frame structure the circulation schematic diagram;

Average sleep rate under different data transmission rates compares schematic diagram to Fig. 2 with existing S-MAC and T-MAC agreement for sensor node adopts the inventive method;

The whole network energy consumption under different data transmission rates compares schematic diagram to Fig. 3 with existing S-MAC and T-MAC agreement for sensor node adopts the inventive method;

Network throughput under different data transmission rates compares schematic diagram to Fig. 4 with existing S-MAC and T-MAC agreement for sensor node adopts the inventive method;

Fig. 5 for sensor node adopt the inventive method with existing S-MAC and T-MAC agreement the transmission delay comparison end to end of the packet under different data transmission rates schematic diagram.

Embodiment

Embodiment describes in further detail the present invention below in conjunction with accompanying drawing.

In wireless sensor network, generally include a plurality of sensor nodes and base-station node, sensor node is deployed in monitors in the monitored area whether event occurs, when sensor node monitors certain incident when taking place, send the Monitoring Data that monitors to base-station node with the form of packet by channel access control method.In channel access control method of the present invention, base-station node and each sensor node adopt the time frame structure with differing time frames length, the time frame structure also claim dispatching cycle, base-station node is chosen suitable frame length when basic according to input parameter, and frame length carries out the whole network broadcasting when basic; Each sensor node frame length when frame length is chosen oneself real work according to local nodes density with when basic.The integral multiple of frame length when frame length is basic during real work.In this specific embodiment, input parameter comprises that the node density of wireless sensor network, data produce average speed and maximum burst speed; Node density is the interior neighbor node number of the double bounce of each sensor node; Local nodes density comprises the interior neighbor node number of double bounce of interior neighbor node number of the double bounce of oneself and the hop neighbor node of oneself.Base-station node can obtain the two-hop neighbor node number of frame length correspondence when basic by neighbor node number in the double bounce of each sensor node.

The present invention is the same with existing MAC agreement based on scheduling, with the time frame structure (dispatching cycle) be divided into time slot reservation and two stages of transfer of data, in the time slot reservation stage, mainly adopted single-hop time slot reservation mechanism reservation single-hop time slot, be to adopt CSMA/CA mechanism competitive channel between the sensor node, and hold consultation with destination node and preengage time slot by sending the RTS/CTS bag.The collision probability that packet is transmitted between the inner sensor node of high density monitored area can be reduced by CSMA/CA mechanism, the utilance of wireless channel can be improved; Simultaneously avoided effectively occurring the frequent state exchange of cross-talk, data collision and transceiver in the wireless sensor network, greatly reduced the waste of energy under the high-load network condition.

At the establishment stage of wireless sensor network, each sensor node will be carried out following step after starting in proper order: frame length negotiation and global clock are synchronous when neighbours' discovery, this locality.In the wireless sensor network running, unless network topology structure generation great change, each sensor node does not repeat above-mentioned steps.

After starting, a sensor node at first begins a simple neighbor discovery process, own current hop neighbor tabulation is sent to the hop neighbor of oneself by periodic broadcast Ping message bag, in emulation experiment, sensor node can select 1 second to be that the cycle Random Access Channel sends Ping message bag, continue 15 seconds time, by this process, one hop neighbor obtains the two-hop neighbor node number of oneself and sends to base-station node, the neighbor node number is a node density in the double bounce of each sensor node that base-station node receives, and node density is chosen basic time frame length L as base-station node_BasicOne of input parameter.Basic time frame length L_BasicAnd has a basic time frame length L_BasicBasic frame time slot corresponding reservation stage duration R_BasicWith B synchronizing cycle_SynchValue, all will calculate according to the deployment scenario of wireless sensor network and actual application demand at the network initial stage of setting up and choose, and the result will be carried out the whole network broadcasting by base-station node.

Basic time frame length L of the present invention_BasicSpan can be by formula L_Basic-R_Basic〉=P_RateN_Basic^(1-α)L_Basict_SlotAnd L_Basic-R_Basic≤ P_Maxrate[N_Basic(1+ β)]^(1-α)L_Basict_SlotDetermine, obtain basic time frame length L_BasicSpan be:$\frac{R_{\mathrm{basic}}}{R_{\mathrm{basic}}-P_{\mathrm{rate}}{N_{\mathrm{basic}}}^{(1-\mathrm{\α})}{t}_{\mathrm{slot}}}\≤L_{\mathrm{basic}}\≤\frac{R_{\mathrm{basic}}}{R_{\mathrm{basic}}-P_{\max \mathrm{rate}}{\left[N_{\mathrm{basic}}(1+\mathrm{\β})\right]}^{(1-\mathrm{\α})}{t}_{\mathrm{slot}}}.$Wherein, P_RateFor data produce average speed, P_MaxrateBe maximum burst speed; t_SlotBe the duration of each slot, slot is the least unit of dispatching cycle; α is the sync rates that all the sensors node carries out the transmission time slot application simultaneously in the double bounce, and node density is big more, and can to carry out the sensor node of transmission time slot application simultaneously many more; β is for selecting a certain node density float factor of frame structure when identical; N_BasicThe two-hop neighbor node number of frame length correspondence when basic, N_Basic=∑ P_iM_i, M_i≤ M_Average, M_AverageBe the average nodal density that base-station node is tried to achieve according to neighbor node number in the double bounce of each sensor node of the whole network that receives, P_iThe expression node density is M_iThe node number account for the proportion of total node number.

Basic frame time slot corresponding reservation stage duration R_BasicThe size requirements of value satisfies sensor node has the sufficient time to (L_Basic-R_Basic) individual transmission time slot preengages application, i.e. R_BasicK₁≤ L_Basic-R_Basic, K₁Be an achievable request times of transmission time slot,${\mathrm{<figure-callout\; label="K"\; filenames="A20081012024300161.png"\; state="\{\{state\}\}">K</figure-callout>}}_1=\frac{t_{\mathrm{slot}}}{t_{\mathrm{request}}}=\frac{t_{\mathrm{slot}}}{t_{\mathrm{DIFS}}+t_{\mathrm{backoff}}+t_{\mathrm{RTS}}+t_{\mathrm{CTS}}+t_{\mathrm{SIFS}}},$Wherein, t_RequestFor finishing needed total time of time slot reservation one time; t_DIFSShortest time interval for distributed coordination DFS; t_BackoffBe average back off time; t_RTSFor sending the required transmitting time of RTS request package; t_CTSFor sending the required transmitting time of CTS feedback packet; t_SIFSThe shortest interFrameGap for distributed coordination DFS.Controlling packet (being RTS request package or CTS feedback packet) can be set to 15 bytes in concrete emulation experiment, communication bandwidth is set to 100Kbps, the duration t of each slot_SlotBe set to 50ms, then t_RTS=t_CTS=15 * 8/100Kbps=1.2ms; Shortest time is t at interval_DIFS=0.6ms, average back off time t_Backoff=3ms, the shortest interFrameGap t_SIFS=0.2ms, thus K can be obtained₁=8.Notice when the sensor node of feedback CTS feedback packet has packet to send, can utilize incidentally mechanism to carry time slot reservation information, thereby can further increase K in the CTS feedback packet₁Value.

B synchronizing cycle of basic frame correspondence_SynchBy formula B_Synch=δ_Clock/ (N_Basicγ_Drift) calculate, wherein, δ_ClockThe clock skew accepted that expression is maximum, γ_DriftThe clock skew rate of expression sensor node, N_BasicThe two-hop neighbor node number of frame length correspondence when basic, N_Basic=∑ P_iM_i, M_i≤ M_Average, M_AverageBe the average nodal density that base-station node is tried to achieve according to neighbor node number in the double bounce of each sensor node of the whole network that receives, P_iThe expression node density is M_iThe node number account for the proportion of total node number.

Frame length differed bigger when frame length may be with oneself the real work of neighbor node when considering the real work of sensor node, frame length when frame length consult to be revised oneself real work when each sensor node carried out this locality after neighbor discovery process, frame structure when final frame length when determining own real work, promptly final definite oneself real work.Suppose that the interior neighbor node number of double bounce that sensor node i obtains is M_i, if

Wherein β is for selecting a certain node density float factor of frame structure when identical, N_BasicThe two-hop neighbor node number of frame length correspondence when basic, then sensor node i finally selects

F frame structure during as oneself real work, symbol "

" for rounding symbol downwards, otherwise, the final selection

F frame structure during as oneself real work, symbol "" be the symbol that rounds up, when and frame structure information when final definite real work of neighbor node broadcasting oneself periodically, this information that neighbor node will be received are recorded in oneself neighbours in the frame structure table.If when certain sensor node found to have the neighbor node more than three or three to select when longer frame structure nF, frame structure changed to nF and upgrades broadcasting during then the real work of oneself; When if frame structure is identical when finding not have the real work of neighbor node and oneself selection, the frame structure during real work of the neighbor node that frame structure was the most close when frame structure changed to own selected real work during then with oneself real work, and upgrade broadcasting equally.Frame structure NF (N=1 in the time of all will finally determining to get well oneself real work through all sensor nodes of the whole network after a plurality of dispatching cycles, 2, ...), and have final when determining good own real work the actual frame time slot corresponding of frame structure to preengage the stage duration be NR_Basic(N=1,2 ...).

Global clock can directly adopt the global clock synchronization mechanism of existing any maturation synchronously, and the clock of the sensor node that the whole network is all is adjusted into the unified identical time.

After frame length was consulted when this locality, sensor node i had finally determined the real work time frame length L of oneself_iPreengage the duration R in stage with the actual frame time slot corresponding of oneself_iEach sensor node is provided with the time slot allocation mode field of the long duration for data transfer phase in position in the present invention, the corresponding transmission time slot of each mode bit of time slot allocation mode field, whether indicate this transmission time slot to be preengage, sensor node selects idle transmission time slot to carry out time slot reservation by this time slot allocation mode field; The duration in frame length and time slot corresponding reservation stage was poor when the duration of data transfer phase was the real work of sensor node, was (L as the duration of the data transfer phase of sensor node i_i-R_i).In addition, each sensor node is provided with a receiving scheduling table, information spinner in the receiving scheduling table will comprise the numbering of the transmission time slot of source node address, reservation, the length of data package of forwarding, and sensor node carries out the reception of packet at the respective transmissions time slot according to the information in this receiving scheduling table.

In the time slot reservation stage, detailed process by single-hop time slot reservation mechanism reservation time slot is: suppose that sensor node i has packet to send to sensor node j, sensor node i at first checks the time slot allocation mode field of oneself, select minimum unappropriated idle transmission time slot to send a RTS request package that includes the numbering of this free time transmission time slot to sensor node j by CSMA/CA mechanism competitive channel, sensor node j is after receiving this RTS request package, check the time slot allocation mode field of oneself equally, check whether corresponding transmission time slot is preengage, if do not preengage, then to CTS feedback packet of sensor node i feedback, simultaneously, destination node is provided with the mode bit of this transmission time slot correspondence and adds a respective entries in the receiving scheduling table of oneself; If this time slot is preengage, then sensor node j does not feed back any information; Sensor node i is if confiscate the CTS feedback packet, and then the time slot allocation mode field according to oneself continues the next unappropriated idle transmission time slot of reservation before the time slot reservation stage finishes.When the neighbor node of sensor node i and sensing node j is received RTS request package or CTS feedback packet, the corresponding mode bit of time slot allocation mode field of oneself can be set according to the transmission time slot of being preengage in RTS request package or the CTS feedback packet, indicate this transmission time slot to be preengage by neighbor node.Like this, at data transfer phase, sensor node can carry out data packet transmission in the transmission time slot of reservation separately, the time frame structure (dispatching cycle) in unappropriated idle transmission time slot then all be in sleep state.

In the time slot reservation stage, the present invention also can adopt the additive method except that single-hop time slot reservation mechanism to preengage time slot.For avoiding individual data to wrap in the transmission delay end to end that the Data transmission band comes because of intermittence on the forward-path, the present invention proposes the path booking-mechanism, according to the time frame synchronizing characteristics of forward-path upper sensor node, be that individual data is preengage the multi-hop time slot in advance along the packet routing direction in the time slot reservation stage.Detailed process by path booking-mechanism reservation multi-hop time slot is: at first increase by the incident generation flag bit that speed transmits of indicating to seek quickness in packet waiting for transmission, suppose that sensor node i monitors certain incident and takes place, sensor node i will check the time slot allocation mode field of oneself and select minimum idle transmission time slot to send a RTS request package that includes the numbering of this free time transmission time slot and be provided with the incident generation flag bit that the speed of indicating to seek quickness transmits by the next-hop node of CSMA/CA mechanism competitive channel on the path, suppose that sensor node j receives this RTS request package, if the corresponding state position in the time slot allocation mode field of sensor node j is unoccupied, the CTS feedback packet that one of feedback is provided with equally the incident generation flag bit that the speed of indicating to seek quickness transmits is given sensor node i, and utilizes that incidentally mechanism is incidentally own in the CTS feedback packet has the information of the transmission time slot of bigger numbering to the next-hop node reservation; Receive on the path CTS feedback packet that is provided with the event flag position the same incidentally mechanism of all the other node utilizations continue to preengage time slot to own destination node, till preengaging transmission time slot or the end of time slot reservation stage with maximum numbering, such data wrap in the actual frame circulation can be effectively reduced the time-delay that packet is transmitted by continuous forward pass multi-hop.Through behind the data transfer phase of this actual frame, the sensor node of receiving the packet that is provided with the event flag position at last will be adopted in the next time slot reservation stage and carry out the path reservation in a like fashion, thereby can apace packet be forwarded to base-station node.Incidentally the mechanism information of destination node oneself to next-hop node reservation transmission time slot that has been destination node to sending node feedback CTS feedback packet the time in the CTS feedback packet has incidentally been saved the next-hop node transmission RTS request package process of destination node to oneself.

Owing to used time frame structure (dispatching cycle) in the present invention with differing time frames length, in the wireless sensor network of a multi-hop, use the sensor node of differing time frames length intersection can be in the scheduling of differing time frames structure, the overlapping phenomenon of time frame occurs.Suppose sensor node i and sensor node j neighbours each other, the duration in frame length and time slot corresponding reservation stage respectively is respectively during the real work of sensor node i and sensor node j: L_i, R_i, L_j, R_j, and L_i＜L_jThe time frame structure of sensor node i and sensor node j circulates as shown in Figure 1, as can be seen from Figure 1 sensor node i time slot reservation during the stage sensor node j but may be in data transfer phase, this will cause data collision and the sensor node i can't be to sensor node j reservation time slot.In order to solve the overlapping problem of bringing of time frame, the present invention has adopted following method: when definition has different real work frame length and each other two sensor nodes of neighbours be boundary node, be that sensor node i and sensor node j among Fig. 1 is boundary node, boundary node i and boundary node j will merge the scheduling mode of frame structure when different, be that boundary node i and boundary node j also will be in wake-up states at the other side's time slot reservation in the stage, for selecting shorter real work time frame length L_iBoundary node i oneself time slot allocation mode field is prolonged (L_j-L_i) position, the time slot allocation mode field of boundary node i can identify the real work time frame length L of boundary node j simultaneously like this_jThe time slot reservation situation.As Fig. 1, boundary node i and boundary node j enter time slot reservation during the stage simultaneously, and boundary node i and boundary node j will reserve in advance respectively and lay oneself open to data transfer phase in oneself the current dispatching cycle and the other side's node will be in the time slot in time slot reservation stage; Boundary node i adopts one of the preferential transmission of littler competition window to preengage first to (R_j-R_i) broadcast packet of individual time slot, boundary node j sends a reservation (L_i-R_j+ 1) to (L_i-R_j+ R_i) broadcast packet of individual time slot.The time slot reservation of next dispatching cycle that enters oneself as boundary node i is during the stage, and boundary node i and boundary node j are moved to the left L with the time slot allocation mode field of oneself respectively_iPosition and (L_i-R_j+ R_i) the new time slot allocation mode field of being used as oneself again behind the position carries out time slot reservation.The time slot reservation of next dispatching cycle that enters oneself as boundary node j is during the stage, and boundary node i and boundary node j adopt and enter identical mode of oneself time slot reservation stage of next dispatching cycle with boundary node i and obtain the new time slot allocation mode field of oneself.If boundary node i will carry out clock synchronization in certain dispatching cycle, then boundary node j adopts in a like fashion synchronous time slot is reserved out.The data collision phenomenon that this method can avoid the time frame overlapping region to produce, simultaneously boundary node i and boundary node j can carry out the normal time slot application that is not interrupted, make packet can be from one the time frame structure (dispatching cycle) zone transmit fast frame length when entering another and using different real work the time frame structure the zone, effectively reduce transmission delay.Littler competition window is used to avoid data collision and the free time section of one section Random Access Channel being provided with.

To compare on the performance such as transmission delay end to end at energy consumption, network throughput and packet T-MAC (Timeout-MAC) agreement of the S-MAC of channel access control method of the present invention and existing self adaptation sleep and adaptive energy by emulation experiment below.

In emulation experiment, 44 sensor nodes are disposed at random in the monitored area of 250m * 250m, and base-station node is deployed in the centre of right margin.In emulation experiment, do not consider the dynamic routing algorithm of data forwarding, and directly adopt fixing route; In the experimental situation simulation parameter be provided with as shown in table 1.

Table 1 simulation parameter is provided with table

Communication bandwidth	100Kbps
		Controlling packet (RTS/CTS) size	15bytes
The packet size	250bytes
		Transmission range	20m
Data produce average speed	0.7(pkts/s)
		Maximum burst speed	2(pkts/s)
The duration t of each slotslot	50ms
		Competition window time slot size slot	300us
Minimum competition window	4
		Maximum contention window	16

Fig. 2 has provided the comparison of method of the present invention average sleep rate under different data transmission rates with existing S-MAC and T-MAC agreement, as can be seen from Figure 2 this method provides longer sleep chance than S-MAC and T-MAC agreement, single-hop time slot reservation mechanism of this method and path booking-mechanism have been avoided cross-talk and idle generation of monitoring effectively, sensor node active state and dormant conversion have been reduced, make sensor node be in the more sleep state, effect is more obvious under the network of high capacity.But under the network of low load, because the duty ratio of this method is 20%, and the duty ratio of S-MAC agreement is 10%, and the duty ratio of T-MAC agreement is lower, causes the sleep rate of this method under low laod network condition lower.

Fig. 3 has provided the comparison of method of the present invention energy consumption of the whole network under different data transmission rates with existing S-MAC and T-MAC agreement, as can be seen from Figure 3, increase along with offered load, this method is compared with the T-MAC agreement with S-MAC, have better energy-saving effect, but the T-MAC agreement has better efficiency under the situation of low load.

Fig. 4 has provided the comparison that method of the present invention and existing S-MAC and T-MAC agreement change in different data transmission rate lower network throughputs, as can be seen from Figure 4 this method has higher network throughput, this is owing to introduced the time frame structure of differing time frames length, the integral multiple of frame length when frame length is basic during real work, and adopt based on the mode of scheduling with the time frame structure be divided into time slot reservation and two stages of transfer of data, fully preengage idle transmission time slot at the sensor node that the time slot reservation stage has packet to send, can effectively improve the utilance of channel, increase network throughput.

Three sensor nodes in picked at random Far Left zone in the emulation experiment environment, suppose that these three sensor nodes monitor all that event occurs, Fig. 5 has shown under the heterogeneous networks load, method of the present invention and existing S-MAC and T-MAC agreement are under different data transmission rates, and the data that three sensor nodes choosing produce are to the comparison of the end-to-end average delay of base-station node.Compare S-MAC and T-MAC agreement as can see from Figure 5 and since among the present invention each dispatching cycle (instant frame structure) all be that packet is preengage a plurality of time slots in advance, therefore, can provide the data packet transmission service of stable more low delay.

Claims (10)

1, a kind of channel access control method of wireless sensor network, wireless sensor network comprises a plurality of base-station nodes that are deployed in the sensor node of monitored area and receive the packet that includes Monitoring Data of described sensor node transmission, it is characterized in that described base-station node and each sensor node adopt the time frame structure with differing time frames length, described base-station node is chosen frame length when basic according to input parameter, and with described when basic frame length carry out the whole network broadcasting; Each sensor node is according to local nodes density and described frame length when frame length is chosen oneself real work when basic; Frame structure comprises time slot reservation stage and data transfer phase when described.

2, the channel access control method of a kind of wireless sensor network according to claim 1 is characterized in that adopting single-hop time slot reservation mechanism reservation time slot between described sensor node of described time slot reservation stage.

3, the channel access control method of a kind of wireless sensor network according to claim 1 is characterized in that adopting path booking-mechanism reservation multi-hop time slot between described sensor node of described time slot reservation stage.

4, the channel access control method of a kind of wireless sensor network according to claim 1, frame length is the described integral multiple of frame length when basic when it is characterized in that described real work.

5, the channel access control method of a kind of wireless sensor network according to claim 1 is characterized in that described input parameter comprises that the node density of wireless sensor network, data produce average speed and maximum burst speed; Described node density is the interior neighbor node number of the double bounce of each sensor node; Described local nodes density comprises the interior neighbor node number of double bounce of interior neighbor node number of the double bounce of oneself and the hop neighbor node of oneself.

6, according to the channel access control method of claim 2 or 3 described a kind of wireless sensor networks, it is characterized in that described sensor node is provided with the time slot allocation mode field of the long duration for described data transfer phase in position, the corresponding transmission time slot of each mode bit of described time slot allocation mode field, whether indicate described transmission time slot to be preengage, described sensor node selects idle transmission time slot to carry out time slot reservation by described time slot allocation mode field; Described sensor node is provided with a receiving scheduling table, information in the described receiving scheduling table comprises the numbering and the length of data package of the transmission time slot of source node address, reservation, and described sensor node receives packet according to the information in the described receiving scheduling table at corresponding transmission time slot.

The duration in frame length time slot corresponding reservation stage poor when frame length and described real work when 7, the channel access control method of a kind of wireless sensor network according to claim 6, the duration that it is characterized in that described data transfer phase are described real work.

8, the channel access control method of a kind of wireless sensor network according to claim 7, the detailed process that it is characterized in that described single-hop time slot reservation mechanism reservation time slot is: in the described time slot reservation stage, sending node is checked the time slot allocation mode field of oneself and is selected minimum idle transmission time slot to send a RTS request package that includes the numbering of this free time transmission time slot by CSMA/CA mechanism competitive channel to destination node, destination node is checked the time slot allocation mode field of oneself after receiving the RTS request package, check whether corresponding transmission time slot is preengage, if do not preengage, then destination node is to CTS feedback packet of sending node feedback, simultaneously, destination node is provided with the mode bit of this transmission time slot correspondence and adds a respective entries in the receiving scheduling table of oneself, if preengage, then destination node is not fed back any information; When sending node was not received the CTS feedback packet, sending node time slot allocation mode field according to oneself before the time slot reservation stage finishes continued the next idle transmission time slot of reservation.

9, the channel access control method of a kind of wireless sensor network according to claim 7, the detailed process that it is characterized in that described path booking-mechanism reservation multi-hop time slot is: in the described time slot reservation stage, be provided with in packet waiting for transmission and indicate to seek quickness the fast incident generation flag bit of transmitting; Sending node is checked the time slot allocation mode field of oneself and is selected minimum idle transmission time slot to send a RTS request package that includes the numbering of this free time transmission time slot and be provided with the incident generation flag bit that the speed of indicating to seek quickness transmits by the next-hop node of CSMA/CA mechanism competitive channel on the path, destination node is checked the time slot allocation mode field of oneself after receiving the RTS request package, check whether corresponding transmission time slot is preengage, if do not preengage, then destination node is provided with the CTS feedback packet of the fast incident generation flag bit of transmitting of seeking quickness of indicating to one of sending node feedback, and utilizes incidentally mechanism incidentally own information of preengaging the transmission time slot with bigger numbering to next-hop node in the CTS feedback packet; Receive the same incidentally machine-processed destination node reservation time slot that continues to oneself of all the other node utilizations of CTS feedback packet on the path, till preengaging transmission time slot or the end of time slot reservation stage with maximum numbering.

10, the channel access control method of a kind of wireless sensor network according to claim 7, it is characterized in that defining when having different real work frame length and each other two sensor nodes of neighbours be boundary node, these two boundary nodes are designated as i and j respectively, and the duration in frame length and time slot corresponding reservation stage is designated as L respectively during the real work of boundary node i_iAnd R_i, the duration in frame length and time slot corresponding reservation stage is designated as L respectively during the real work of boundary node j_jAnd R_j, L wherein_i＜L_j, boundary node i prolongs (L with the time slot allocation mode field of oneself_j-L_i) position, enter time slot reservation simultaneously during the stage at boundary node i and boundary node j, boundary node i and boundary node j reserve in advance respectively and lay oneself open to data transfer phase in oneself the current dispatching cycle and the other side's node will be in the time slot in time slot reservation stage, boundary node i adopt littler competition window preferential send a reservation first to (R_j-R_i) broadcast packet of individual time slot, boundary node j sends a reservation (L_i-R_j+ 1) to (L_i-R_j+ R_i) broadcast packet of individual time slot, the time slot reservation of next dispatching cycle that enters oneself as boundary node i is during the stage, and boundary node i and boundary node j are moved to the left L with the time slot allocation mode field of oneself respectively_iPosition and (L_i-R_j+ R_i) the new time slot allocation mode field of being used as oneself again behind the position carries out time slot reservation; The time slot reservation of next dispatching cycle that enters oneself as boundary node j is during the stage, and boundary node i and boundary node j adopt and enter identical mode of oneself time slot reservation stage of next dispatching cycle with boundary node i and obtain the new time slot allocation mode field of oneself.

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