Chain-type wireless sensor network-oriented hybrid media access control method

Abstract

The present invention relates to wireless network technologies, and particularly to a chain-type wireless sensor network-oriented hybrid media access control (MAC) method. The present invention fully considers features of a chained or linear topology of a wireless sensor network applied in power transmission line monitoring and the like, adopts different access policies at different periods of the network, and proposes a method of time division access control Pipelined TDMA during busy periods and contention access control S-XMAC during idle periods. During busy periods, a pipelined scheduling transmission method is used to avoid the problem of hidden terminals so as to improve transmission reliability and resource utilization. During idle periods, different MAC parameters are set for cluster head members and ordinary cluster members, so that the cluster head members can respond to requests in a more timely manner, and meanwhile, the ordinary cluster members save energy as much as possible, thereby meeting requirements for network real-time quality of the application system while saving energy of the network.

Claims

1. A chain-type wireless sensor network-oriented hybrid media access control method, wherein in a wireless sensor network, if a proportion of cluster heads arid cluster members which simultaneously transmit data reaches a certain value, a time division access control Pipelined TDMA is used, comprising: in every time slot, cluster heads in the network acquire sensor data of all cluster members in subsequent clusters; and cluster heads that acquire sensor data forward acquired sensor data; in the wireless sensor network, if a proportion of cluster heads and cluster members which simultaneously transmit data does not reach a certain value, a contention access control S-XMAC is used, in which wake-up time scheduling is based on position information, comprising: waking up cluster heads and cluster members in order based on geographical positions of cluster heads and cluster members in the network; and the S-XMAC is realized by: each cluster head and cluster member periodically sleeping and waking up by a duty cycle T.sub.duty-cycle; a cluster head waiting to transmit data does not activate a radio frequency to transmit preamble codes, but instead transmits preamble codes containing address information of a transmitting end cluster head and of a destination receiving end cluster head at a time T.sub.preamble ahead of a wake-up time of the destination receiving end cluster head, T.sub.preamble representing the maximum time required for transmitting the preamble codes; after transmission of the preamble codes, the cluster head waiting to transmit data waits for a preamble codes acknowledgment ACK from the destination receiving end cluster head, and repeats transmission of the preamble codes until a preamble codes acknowledgment ACK is received, the cluster head waiting to transmit data will not transmit data until a preamble codes acknowledgment ACK is received; a receiving end cluster head is periodically woken up; if the awoken receiving end cluster head is receiving preamble codes containing address information while awake, the receiving end cluster head judges whether the address information of the destination receiving end cluster head in the preamble codes agrees with the awoken receiving end cluster head address information; if there is a judgment that the address information is in agreement, then the awoken receiving end cluster head sends a preamble codes acknowledgment ACK notifying the transmitting end cluster head to transmit data; if there is not a judgment that the address information is in agreement, then the awoken receiving end cluster head does not send back a preamble codes acknowledgment ACK and goes into dormancy immediately.

2. The chain-type wireless sensor network-oriented hybrid media access control method of claim 1, wherein a subsequent cluster is a cluster head adjacent to a current cluster head in a direction away from a Sink.

3. The chain-type wireless sensor network-oriented hybrid media access control method of claim 1, wherein the cluster heads that acquire data are: in the first time slot, the third cluster heads after every two cluster heads, counting in a direction away from a Sink; in the second time slot, the aggregation of cluster heads adjacent to the cluster heads that acquire data in the first time slot in a direction approaching a Sink; in the third time slot, the aggregation of cluster heads adjacent to the cluster heads that acquire data in the second time slot in a direction approaching a Sink.

4. The chain-type wireless sensor network-oriented hybrid media access control method of claim 1, wherein acquiring sensor data and/or forwarding acquired sensor data require(s) three time slots to complete network transmission scheduling and to prevent data simultaneously transmitted by all cluster members and adjacent clusters from collision with each other.

5. The chain-type wireless sensor network-oriented hybrid media access control method of claim 1, wherein the process of each cluster member transmitting data includes: time slots are secondarily divided into many mini-time slots; mini-time slots are allocated based on address designation algorithm; and cluster members select corresponding mini-time slots in ascending order of addr values to send data; wherein said addr value is: the allocated address addr[1,Ni] of the cluster member when a cluster member is included in the network, Ni being the number of cluster members in the i.sup.th cluster.

6. The chain-type wireless sensor network-oriented hybrid media access control method of claim 1, wherein data forwarding is realized by multiple continuous time slots being allocated to a cluster head, and utilizing the multiple continuous time slots to transmit multiple data packages.

7. The chain-type wireless sensor network-oriented hybrid media access control method of claim 1, wherein each cluster is made to have the same cluster wake-up time in the duty cycle by a cluster head recording the wake-up time of the adjacent cluster in the duty cycle T.sub.duty-cycle.

8. The chain-type wireless sensor network-oriented hybrid media access control method of claim 1, wherein said wake-up time is designed as follows: the wake-up time T.sub.schedule between adjacent cluster heads satisfies the following conditions: wherein, represents the time required by the cluster head for receiving data, including transmission time of the data excluding the preamble codes and dwell time; T.sub.offset.sub._.sub.max represents the maximum clock offset between the transmitting end and the receiving end, determined by the synchronizing cycle and the frequency offset of the cluster head and cluster members; the address ADDRs of the cluster head and cluster members are used to indicate the position information of the cluster head and cluster members, and the wake-up time of the cluster head and cluster members are set as: wherein, T.sub.wake represents the wake-up time of the cluster head or cluster members, T.sub.schedule represents the wake-up time between adjacent cluster heads, T.sub.duty.sub._.sub.cycle represents the duty cycle of the cluster head or cluster members, ADDR represents the address of the cluster head or cluster members, and the symbol >> is a right shift operator.

9. A chain-type wireless sensor network-oriented hybrid media access control method, wherein in a wireless sensor network, if a proportion of cluster heads and cluster members which simultaneously transmit data reaches a certain value, a time division access control Pipelined TDMA is used, comprising: in every time slot, cluster heads in the network acquire sensor data of all cluster members in subsequent clusters; and cluster heads that acquire sensor data forward acquired sensor data; in the wireless sensor network, if a proportion of cluster heads and cluster members which simultaneously transmit data does not reach a certain value, a contention access control S-XMAC is used, in which wake-up time scheduling is based on position information, comprising: waking up cluster heads and cluster members in order based on geographical positions of cluster heads and cluster members in the network; and the maximum time required for transmitting the preamble codes T.sub.preamble is: $T_{\mathrm{preamble}}=\{\begin{array}{cc}{T}_{\mathrm{duty\_cycle}}& \left(T_{\mathrm{duty\_cycle}}2T_{\mathrm{offset\_max}}\right)\\ 2T_{\mathrm{offset\_max}}& \left(T_{\mathrm{duty\_cycle}}>2T_{\mathrm{offset\_max}}\right)\end{array}$ wherein, T.sub.preamble represents the maximum time required for transmitting the preamble codes, T.sub.duty.sub._.sub.cycle represents the duty cycle of the cluster head or cluster members, and T.sub.offset.sub._.sub.max represents the maximum clock offset between the transmitting end and the receiving end.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of a pipelined transmission method;

(2) FIG. 2 is a wake-up time scheduling based on position information in S-XMAC;

(3) FIG. 3 is a comparison between the time for transmitting the preamble codes of X-MAC and that of S-XMAC in the worst situation;

(4) FIG. 4 is a schematic diagram of the running of X-MAC.

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention will be further detailed hereinafter in company with the drawings.

(6) The present invention proposes a chain-type wireless sensor network-oriented hybrid media access control method. The main thought of the method is that different MAC parameters are adopted for the cluster head and cluster members. So that the cluster head can respond to requests in a more timely manner and the ordinary cluster members can save as much energy as possible. Thereby the method meets the requirements for network real-time quality of the applications while reducing energy consumption.

(7) The present invention includes the time division access control Pipelined TDMA during busy periods and the contention access control S-XMAC during idle periods. In the wireless sensor network, the period in which the proportion of cluster heads and cluster members which simultaneously transmit data reaches a certain value (20%) is a busy one; or else it is an idle period.

(8) (1) Time division access control Pipelined TDMA during busy periods includes acquisition within clusters and data forwarding, specifically including the following steps:

(9) Step 1.1: acquisition within clusters. In every time slot, some of the cluster heads in the network acquire the sensor data of all cluster members in subsequent clusters, as shown in FIG. 1. In this stage, it takes only three time slots to complete network transmission scheduling and avoid the problem of hidden terminals by preventing the collision between the data, which are simultaneously transmitted by all cluster members and adjacent clusters. During the step of data acquisition, the cluster members are required to transmit data. The process of the cluster members transmitting data includes: firstly, dividing time slots into many mini-time slots; secondly, mini-time slot allocation based on address designation algorithm; when a cluster member is included in the network, an address addr[1,Ni] within the cluster is allocated, wherein Ni is the number of cluster members in the i.sup.th cluster, and the cluster members select corresponding mini-time slots in ascending order of addr values to send data. The address designation algorithm ensures that the cluster members in one cluster have a unique addr, therefore avoiding collision of data among cluster members.

(10) Said subsequent cluster is the cluster head adjacent to the current cluster head away from the Sink.

(11) Said some of cluster heads in that some of the cluster heads in the network acquire the sensor data of all cluster members in subsequent clusters includes: 1) some of cluster heads in the first time slot are cluster heads that are counted from the third cluster head from the direction away from the Sink of cluster heads and cluster members and after every two cluster heads; 2) some of cluster heads in the second time slot are the aggregation of adjacent cluster heads of the some of cluster heads in the first time slot approaching the Sink; 3) the some of cluster heads in the third time slot are the aggregation of adjacent cluster heads of the some of cluster heads in the second time slot approaching the Sink. The specific definition of the some of cluster heads is: assuming the hop count of clusters is expressed by hop, 1) the some of cluster heads in the first time slot are cluster heads with 3% hop==0; 2) the some of cluster heads in the second time slot are cluster heads with 3% hop==2; 3) the some of cluster heads in the third time slot are cluster heads with 3% hop==1.

(12) Step 12: data forwarding. The cluster heads complete the data forwarding in this stage. Multiple continuous time slots are allocated to a cluster head which utilizes the multiple continuous time slots to transmit multiple data packages. As the principle in the stage of acquisition within clusters, it takes only three time slots to complete data forwarding.

(13) (2) Contention access control during idle periodsS-XMAC: specifically refers to wake-up time scheduling based on position information, and includes the following steps described below:

(14) Step 2.1: each cluster head and cluster member periodically sleep and wake up by duty cycle T.sub.duty-cycle. The cluster head records the wake-up time of the adjacent cluster in duty cycle T.sub.duty-cycle, and the cluster members of each cluster have the same wake-up time, which is called cluster wake-up time, in the duty cycle;

(15) The duty cycle refers to the work cycle of dormancy and wakeup of cluster heads and cluster members, the formal description of which is T.sub.duty.sub._.sub.cycle:
T.sub.duty.sub._.sub.max=wakeup time+dwell time

(16) The cluster wakeup time refers to wake-up time scheduling based on position information. The cluster heads are woken up in order based on the geographical position of the cluster heads and cluster members in the network. The synchronization error between the receiving and transmitting cluster heads and cluster members becomes bigger over time, which may cause the receiving cluster heads and cluster members to be woken up in the same duty cycle before the transmitting cluster heads and cluster members begin to send the preamble codes, thereby leading to communication failure. For the wake-up time scheduling based on position information designed in the present invention, taking the network topology and wakeup scheduling as shown in FIG. 2 as an example, the wake-up time between adjacent cluster heads needs satisfying the conditions below:
T.sub.schedule>+T.sub.offset.sub._.sub.max

(17) wherein, represents the time required by the cluster head for receiving data, including data transmission time and dwell time excluding the preamble codes; T.sub.offset.sub._.sub.max represents the maximum clock offset between the transmitting end and the receiving end, determined by the synchronizing cycle and the frequency offset of the cluster head and cluster members; S-XMAC is not limited to specific synchronization algorithm, the synchronization algorithm can be implemented in other services in the applications such as data acquisition, and no limitations are imposed by the present invention.

(18) The address ADDRs of the cluster head and cluster members are used to indicate the position information of the cluster head and cluster members, and the wake-up time of the cluster head and cluster members are set as:

(19) $T_{\mathrm{wake}}=n{T}_{\mathrm{duty\_cycle}}-\left(\left(\mathrm{ADDR}+1\right)>>1\right)T_{\mathrm{schedule}}$$n=.Math.\frac{\left(\left(\mathrm{ADDR}+1\right)>>1\right)T_{\mathrm{schedule}}}{T_{\mathrm{duty\_cycle}}}.Math.$

(20) Step 2.2: The cluster head of the data to be transmitted does not activate a radio frequency, but it transmits the preamble codes containing the address information of the cluster heads of the transmitting end and the destination receiving end T.sub.preamble ahead of the cluster wake-up time of the destination receiving end instead; as shown in FIG. 3, after transmission of the preamble codes, the cluster head of the data to be transmitted waits for the preamble codes acknowledgment ACK from the cluster head of the destination receiving end. The process is repeated until the ACK is received, then data is transmitted.

(21) The T.sub.preamble refers to the maximum time required for transmitting the preamble codes, as defined below:

(22) $T_{\mathrm{preamble}}=\{\begin{array}{cc}{T}_{\mathrm{duty\_cycle}}& \left(T_{\mathrm{duty\_cycle}}2T_{\mathrm{offset\_max}}\right)\\ 2T_{\mathrm{offset\_max}}& \left(T_{\mathrm{duty\_cycle}}>2T_{\mathrm{offset\_max}}\right)\end{array}$

(23) Step 2.3: the receiving end is periodically when up. If receiving a preamble codes containing the address information of the cluster head while awake, it judges whether the address information of the destination receiving end in the preamble codes agrees with its address information; if so, it sends back an ACK and notifies the transmitting end to transmit data; or else, it does not send back an ACK and goes into a sleep state immediately. The time for the destination receiving end to send back an ACK is as shown in FIG. 4.