WO2015184854A1

WO2015184854A1 - Method for implementing mac layer access, and sensor node

Info

Publication number: WO2015184854A1
Application number: PCT/CN2015/072592
Authority: WO
Inventors: 袁斌; 郭阳; 刘静; 李明; 王新兵
Original assignee: 中兴通讯股份有限公司
Priority date: 2014-11-14
Filing date: 2015-02-09
Publication date: 2015-12-10
Also published as: CN105656806A

Abstract

A method for implementing MAC layer access, and a sensor node. The method comprises: a sensor node determines an initial value of a backoff counter according to the number of data packets temporarily stored in a current data queue; and in a process of backoff counting, the sensor node monitors a channel and updates the value of the backoff counter according to the state of the channel until the value of the backoff counter is 0, and the sensor node sends the data packet.

Description

Method for implementing MAC layer access and sensor node

Technical field

The present invention relates to a wireless body area network technology, and more particularly to a method and a sensor node for implementing media access control (MAC) layer access.

Background technique

In the context of today's big data era, a series of big data-based applications have brought new challenges and opportunities to engineering, business and medical. In this data revolution, with the rapid development of wireless communication and semiconductor technology, wireless sensors for human physiological information collection have become increasingly compact and practical, which has led to explosive growth in human physiological information collected by wireless sensors. . These massive amounts of unstructured data present new challenges for wireless body area networks consisting of a variety of sensors suitable for the human body.

The wireless body area network usually consists of a variety of medical sensor nodes (Nodes) and a central node (Hub) distributed throughout the body and in the body. It is a short-distance low-range monitoring for body surface or in vivo biological signs information and some wireless applications. Power consumption wireless communication network. The composition of a typical wireless body area network is shown in Figure 1. The wireless body area network mainly has the following three characteristics: First, the communication distance between nodes is short (near the body surface), and the network topology is mostly a star topology; second, the sensor for medical applications is usually wearable or needs to be implanted in the body. The sensor, considering the comfort of the human body and the difficulty of implanting in the body, the wireless body area network has strict requirements on the size and power consumption of the sensor; thirdly, the business generated by each sensor node, especially the emergency service, should be timely Reliably transferred to the Hub.

The main power consumption of the sensor node lies in the transceiver of the radio frequency module and the MAC. The power consumption of the central node is relatively large due to the need to aggregate and communicate with the external gateway or remote control center. In a distributed network in which a plurality of sensor nodes share a channel in a wireless body area network, a common access mode of the MAC layer is carrier (Media Sense Multiple Access)/Clash Avoidance (CA). Collision Avoidance), as understood by the basic principles of CSMA/CA, inevitably creates conflicts and retransmissions, which will result in more energy consumption. The CSMA/CA specified in IEEE 802.15.6, although different competition window values (CW) are used for different user priority services, the backoff rule is still the same as the original CSMA/CA. This means that when the number of nodes increases, the probability of collision when transmitting data packets will be greatly increased, in order to ensure reliable and efficient transmission of physiological information collected by each sensor node as much as possible, and prolong the lifetime of the wireless body area network, The low-power, low-latency MAC layer access method needs to be applied.

In the application of the invention number "201310141601.X" and the invention name is "a real-time task scheduling medical body network MAC access method", the disclosed MAC access scheme needs to use a conflict resolution queue and a data transmission queue. The queue also introduces mini-slots and data slots to transmit access requests and collision-free data, respectively. Although this scheme can dynamically adjust the transmission order of nodes in the network to improve the quality of service according to the actual situation of nodes and networks, it also inevitably increases the complexity of the MAC layer protocol, which is difficult to implement in practical applications.

In the wireless body area network, especially in the body area network used in the medical field, the transmission of emergency services is an important measure. In the related art, an appropriate amount of small idle time slots are inserted in the super frame for emergency. The scheme of transmission of services, although the number of these idle slots can be given some reference by statistical law, in practice, some unnecessary time slot waste will be generated, which will reduce the throughput of the whole network; In the medical scenario, the frequency of emergency services is usually not too high, so this method is not very practical.

In the IEEE 802.15.6 protocol, when transmitting a data packet, the sensor node first selects a corresponding contention window CW according to the user priority of the corresponding data packet, and then randomly selects a number from [1, CW] as the value of the backoff counter. Perform a backoff count. In the backoff counter, the sensor node listens to the channel: if the channel state is idle, the backoff counter is decremented by one; if the channel state is busy, the value of the backoff counter is locked until the channel state is idle again, the backoff counter The value of the value continues to be decremented by 1 from the value that was just locked. Until the value of the backoff counter is decremented to zero, the sensor node begins to send packets. Although the static CSMA/CA access protocol is relatively simple to implement, for the wireless body area network (WBAN), the sampling rate and data format (such as heart rate and blood pressure information) of different sensor nodes are not the same, so For different nodes, the data arrival rate often differs greatly; due to medical application requirements, the sampling rate of the same sensor node has a slight change in the data sampling rate when the human body is in different physiological states, for example, in the electrocardiogram (ECG). During monitoring, in the event of a suspicious emergency, the sampling rate is increased to provide more detailed information, that is, the packet arrival rate for the same node is different at different times.

In the MAC layer access method implemented by the existing CSMA/CA access protocol, there is a lack of a policy for dynamically adjusting the number of packets sent according to the length of the data packet buffered in the data queue of each sensor node. Therefore, the sensor nodes with more data packets cannot be timely. Access channel. In addition, when a sensor node obtains the channel usage right, since the number of data packets sent by the node is a fixed value, the sensor nodes with many data packets cannot be adjusted in real time to satisfy the transmission of more data packets, which is disadvantageous for high efficiency. The use of time slot resources wastes unnecessary control overhead.

Summary of the invention

In order to solve the above technical problem, an embodiment of the present invention provides a method for implementing MAC layer access and a sensor node, which can adjust the number of packets sent by a data packet in real time, and efficiently utilize time slot resources, thereby avoiding unnecessary waste of control overhead.

A method for implementing media access control MAC layer access includes:

The sensor node determines an initial value of the backoff counter based on the number of data packets buffered in the current data queue;

In the backoff counting process, the sensor node listens to the channel and updates the value of the backoff counter according to the channel condition until the value of the backoff counter is 0, and the sensor node sends the data packet.

Optionally, the determining the initial value of the backoff counter includes:

Before the sensor node sends the data packet, randomly select a value from the contention window [1, CW] as an initial value of the backoff counter;

Difference threshold number CW CW _max contention window value set in advance is equal to the current data packet buffer queue value of L _now.

Alternatively, the number of L _now, the current data packet buffer queue is greater than or equal to the threshold value CW _max, the value of the contention window CW value of said threshold value CW _max.

Optionally, the value of the backoff counter is 0, and the sending, by the sensor node, the data packet includes:

Starting the backoff counter and starting the backoff count;

The sensor node listens to the channel, and if the channel is idle, the value of the backoff counter is decremented by one; If the channel is busy, the value of the backoff counter is locked until the channel is idle again, and the value that is locked from the backoff counter continues to be counted down by one;

Until the backoff counter value is reduced to 0, the sensor node sends a data packet in the data queue; wherein the number of data packets sent by the sensor node is randomly selected from [1, L _now ].

A sensor node includes a preprocessing module and a processing module;

The pre-processing module is configured to: determine an initial value of the back-off counter based on the number of data packets buffered in the current data queue;

The processing module is configured to: start the backoff counter, and during the backoff counting process, listen to the channel and update the value of the backoff counter according to the channel condition until the value of the backoff counter is 0, and send the data packet.

Optionally, the pre-processing module is configured to:

Before the processing module sends the data packet, a value is randomly selected from the contention window [1, CW] as an initial value of the backoff counter; wherein the contention window value CW is equal to the preset threshold CW _max and the cache packet in the current data queue. The difference between the number of L _now .

Optionally, when the number of cached packets L _now in the current data queue is greater than or equal to the threshold CW _max , the contention window value CW takes the threshold CW _max .

Optionally, the processing module is configured to:

Starting the backoff counter and starting the backoff count;

Listening to the channel, if the channel is idle, the backoff counter is decremented by one; if the channel is busy, the value of the backoff counter is locked until the channel is idle again, and the value that is locked from the backoff counter continues to be decremented by one. Counting process

Until the backoff counter value is reduced to 0, the data packet in the data queue is sent; wherein the number of transmitted data packets is randomly selected from [1, L _now ].

Embodiments of the present invention also provide a computer readable storage medium storing program instructions that can be implemented when the program instructions are executed.

The technical solution provided by the embodiment of the present invention makes the sensor node better in the shared channel. According to different data traffic in each node queue, the number of packets is dynamically adjusted, and the number of packets sent by the data packet is adjusted in real time, so that sensor nodes with more data packets can access the channel in time, and the time slot resources are utilized efficiently. The waste of unnecessary control overhead is avoided, thereby improving the throughput of the entire network and reducing the transmission delay.

Moreover, before the packet is sent, the backoff duration used by the backoff process is related to the queue length, and the time that the sensor node occupies the channel is also related to the queue length. This makes the data transmission collision probability between the sensor node and the central node smaller, the delay is lower, and the interaction power consumption is lower. Communication is more efficient and at the same time more convenient to implement in real systems.

BRIEF abstract

The drawings described herein are intended to provide a further understanding of the invention, and are intended to be a part of the invention. In the drawing:

1 is a schematic diagram of the composition of a wireless body area network of the related art;

2 is a flowchart of a method for implementing MAC layer access according to an embodiment of the present invention;

3 is a schematic structural diagram of a sensor node according to an embodiment of the present invention;

4 is a schematic diagram of comparison of throughput performance indicators of a whole network throughput of a sensor node at different arrival rates when the method of the related art and the method of the embodiment of the present invention are respectively used;

FIG. 5 is a schematic diagram showing a comparison of delay simulation performance indexes of data packets of sensor nodes at different arrival rates when the method of the related art and the method of the embodiment of the present invention are respectively used.

Preferred embodiment of the invention

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the case of no conflict, the features in the embodiments and the embodiments in the present application may be arbitrarily combined with each other.

In order to achieve low power consumption and low latency, the MAC layer access method should minimize the collision and retransmission caused by multiple sensor nodes transmitting packets in the shared channel, thereby improving the throughput of the entire network. At the same time reduce energy consumption to extend network survival time. In addition, the MAC layer protocol should not be designed to be too complicated, otherwise it will be difficult to implement in practical applications.

The inventors found that since the sensors in the medical scene are mostly periodically sampled, the data arrival rate is Relatively stable for a while. When the sensor node's packet arrival rate is large, the probability that the sensor node occupies the channel should be greater, and vice versa. Only such a dynamically adjusted MAC layer access method will increase the throughput of the entire body area network and a smaller transmission delay.

2 is a flowchart of a method for implementing MAC layer access according to an embodiment of the present invention. As shown in FIG. 2, the method includes:

Step 200: The sensor node determines an initial value of the backoff counter based on the number of cached packets in the current data queue.

This step includes: randomly selecting a value from the contention window [1, CW] as the initial value of the backoff counter before the sensor node sends the packet. Here, unlike the CSMA/CA method in IEEE 802.15.6, the contention window value CW in the embodiment of the present invention is not a fixed value, but is determined by the formula (1) based on the current queue length of the sensor node:

CW=CW _max -L _now (1)

In formula (1), according to the relevant protocol, CW _max is a preset threshold, and L _now is the number of cache packets in the current data queue.

In particular, when the number of cached packets in the current data queue, L _{now, is} greater than or equal to the threshold CW _max , it indicates that the sensor node has too much data packet accumulation at this time, or the packet traffic of other sensor nodes is also large, therefore, this is The value of the competition window value CW is the threshold CW _max , which ensures the fairness between the nodes.

Step 201: In the backoff counting process, the sensor node listens to the channel and updates the value of the backoff counter according to the channel condition until the value of the backoff counter is 0, and the sensing node sends the data packet.

In this step, the determined backoff counter is started and the backoff count is started. At this time, the sensor node starts to listen to the channel: if the channel is idle, the backoff counter is decremented by one; if the channel is busy, then the value of the backoff counter is locked until Listening to the channel idle again, and continuing to count down by 1 from the value that the backoff counter is locked;

Until the backoff counter value is reduced to 0, the sensor node starts to send the data packet in the data queue. At this time, the number of data packets sent by the sensor node is randomly selected from [1, L _now ].

In the method of the embodiment of the present invention, the backoff counter duration is related to the queue length. When the data packet is accumulated, the value selected by the contention window value CW becomes smaller, and therefore, the backoff time is correspondingly Become smaller. In this way, nodes with more data packets are enabled to access the channel in time. In addition, when a sensor node obtains channel usage rights, the number of transmitted data packets is also related to the current data queue length. The number of data packets sent by the sensor node is not a fixed value, but a random selection of 1 to the current data queue. An integer value between the total number of data packets. If the selected integer is greater than a preset threshold, the number of currently transmitted data packets is set to the threshold, so that the sensor nodes with more data packets only have Larger ones may send more packets, not necessarily, so this is also a manifestation of fairness. At the same time, this is also very beneficial for efficient use of time slot resources, avoiding unnecessary control overhead.

The technical solution provided by the embodiment of the invention enables the sensor node to dynamically adjust the number of packets sent according to different data traffic in each node queue in the shared channel, so that the sensor nodes with more data packets can be connected in time. Incoming channels, thereby increasing overall network throughput and reducing transmission delay. Moreover, the time that the sensor node occupies the channel is also related to the queue length. This makes the data transmission collision probability between the sensor node and the central node smaller, the delay is lower, and the interaction power consumption is lower. Communication is more efficient and at the same time more convenient to implement in real systems.

3 is a schematic structural diagram of a sensor node according to an embodiment of the present invention. As shown in FIG. 3, at least a preprocessing module and a processing module are included, where

The pre-processing module is configured to determine an initial value of the backoff counter based on the number of cached packets in the current data queue;

The processing module is configured to start the backoff counter. During the backoff counting process, the sensor node listens to the channel and updates the value of the backoff counter according to the channel condition until the value of the backoff counter is 0, and the sensing node sends the data packet. The number of data packets sent by the sensor node is randomly selected from [1, L _now ].

Among them, the preprocessing module is set to:

Before the sensor node sends the packet, a value is randomly selected from the contention window [1, CW] as the initial value of the backoff counter; wherein the contention window value CW is a preset threshold CW _max and the number of cached packets in the current data queue L _now The difference.

Particularly, when the number of L _now the current buffer data packet queue is greater than or equal to the threshold value CW _max, the value of the contention window CW value of CW _max.

Among them, the processing module is set to:

Start the backoff counter and start the backoff count;

Listening channel, if the channel is idle, the backoff counter is decremented by one; if the channel is busy, the value of the backoff counter is locked, until the channel is idle again, and the value of the backoff counter is locked and the counting process is decremented by one;

FIG. 4 is a schematic diagram showing comparison of the throughput performance of the whole network throughput (Throughput) of the sensor node at different arrival rates when the method of the related art and the method of the embodiment of the present invention are respectively used, as shown in FIG. 4, curve 43 The CSMA/CA mode for fixed backoff-fix transmission (Fix Backoff–Fix Transmission) is the whole network throughput simulation result curve under the original CSMA/CA protocol condition; curve 42 is the backoff based on real-time queue length. - Full-network throughput simulation result curve under CSMA/CA mode of Queue Backoff-Fix Transmission; curve 41 is backoff based on real-time queue length - number of packets based on real-time queue length (Queu Backoff– The Queue Transmission is a simulation result of the whole network throughput under the condition of the method of the embodiment of the present invention.

Assume that the Sensor node sends a packet to the central node to test the performance of each indicator. In the fixed delivery strategy, that is, the fixed backoff—the number of fixed packets and the backoff based on the length of the real-time queue—the number of fixed packets is one, and the number of transmitted packets is one; considering the actual application, it is impossible to send a sensor node once. A large number of data packets, so in the policy of the real-time queue length based on the real-time queue length based on the real-time queue length, the maximum number of packets to be sent is a positive integer value. .

Within the entire simulation duration shown in Figure 4, assume that the defined throughput is the correct rate of reception for the entire network.

It is also assumed that the delay of the data packet is: the time interval from the generation of the data packet to the correct reception by the central node. For the simulation scenario shown in Figure 4, the simulation of the network's receiving accuracy rate Throughput and the average delay of the data packet is simulated. The simulation performance curve is shown in Figure 4. Figure 4 shows:

In the case of low arrival rate, ie λ<1/68 (packet/time slot), under the three CSMA/CA strategies, the reception correct rate Throughput is approximately 1, that is, the data packets generated by the sensor node can be The central node receives correctly;

In the case of a medium arrival rate, i.e., 1/68 < λ < 1/32 (packet/time slot), the reception correct rate Throughput performance is: curve 41 > curve 42 > curve 43, and, at this time, curve 43 is displayed. The performance drops sharply, the performance shown by curve 42 decreases, but the reception accuracy rate Throughput is still greater than 0.9, while the performance shown by privilege 41 is almost unchanged, still staying near 1;

In the case of a high arrival rate, i.e., 1/32 < λ < 1/20 (packet/time slot), the performance shown by curve 42 appears to deteriorate sharply, while the performance shown by curve 41 shows a slight decrease, but still greater than 0.9. .

In Figure 4, the three modes, curve 41, curve 42 and curve 43, show the correct rate of reception. The throughput is consistent at low arrival rates because the sensor node's own data queue is low at low arrival rates. There is no accumulation. At this time, the CSMA/CA strategy based on the queue length is reverted to the existing static CSMA/CA strategy, so the performance of the three is consistent. However, as the arrival rate increases, the curve 42 shows better performance than the curve 43, because the former's backoff counting process is based on the real-time queue length. The longer the queue length, the shorter the backoff count and the faster access. channel. It can be seen from the simulation results shown in FIG. 4 that the curve 41 shows the best performance because the real-time queue length-based backoff based on the real-time queue length is not only in the back-off counting process. The display is based on the real-time queue length, and the number of packets sent by the node is also based on the real-time queue length. The sensor node with the long data queue can not only access the channel faster, but also can send each time after successfully accessing the channel. More packets, so that packets are transmitted as soon as possible. It can be seen that the dynamic CSMA/CA method based on the real-time queue length in the embodiment of the present invention improves the receiving accuracy of the network.

The delay performance of the network corresponds to the receiving accuracy of the Throughput performance. When the receiving accuracy rate is reduced, all packets will not be delivered to the central node in time, accumulating in the data queue of the sensor node, resulting in delay. Increase. FIG. 5 is a schematic diagram showing a comparison of delay performance simulation indexes of data packets of sensor nodes at different arrival rates when the method of the related art and the method of the embodiment of the present invention are respectively used, as shown in FIG. 5, curve 53 is Fixed backoff—Fix Backoff–Fix Transmission CSMA/CA mode, which is the delay simulation result curve under the original CSMA/CA protocol condition; curve 42 is based on real-time queue length Time-delay simulation result curve under CSMA/CA mode of Queue Backoff–Fix Transmission; curve 41 is backoff based on real-time queue length—the number of packets based on real-time queue length (Queu Backoff – Queue Transmission) is the time delay simulation result curve under the condition of the method of the present invention. From the simulation curve shown in FIG. 5, it is not difficult to see by those skilled in the art that the dynamic CSMA/CA method based on the real-time queue length reduces the packet delay compared with the related art.

Therefore, the performance of the dynamic CSMA/CA mode based on the real-time queue length of the embodiment of the present invention is superior to the original static CSMA/CA strategy.

The above is only an alternative embodiment of the present invention and is not intended to limit the scope of the present invention.

One of ordinary skill in the art will appreciate that all or a portion of the steps of the above-described embodiments can be implemented using a computer program flow, which can be stored in a computer readable storage medium, such as on a corresponding hardware platform (eg, The system, device, device, device, etc. are executed, and when executed, include one or a combination of the steps of the method embodiments.

Alternatively, all or part of the steps of the above embodiments may also be implemented by using an integrated circuit. These steps may be separately fabricated into individual integrated circuit modules, or multiple modules or steps may be fabricated into a single integrated circuit module. achieve. Thus, the invention is not limited to any specific combination of hardware and software.

The devices/function modules/functional units in the above embodiments may be implemented by a general-purpose computing device, which may be centralized on a single computing device or distributed over a network of multiple computing devices.

When each device/function module/functional unit in the above embodiment is implemented in the form of a software function module and sold or used as a stand-alone product, it can be stored in a computer readable storage medium. The above mentioned computer readable storage medium may be a read only memory, a magnetic disk or an optical disk or the like.

Industrial applicability

Claims

A method for implementing media access control MAC layer access includes:

The sensor node determines an initial value of the backoff counter based on the number of data packets buffered in the current data queue;

In the backoff counting process, the sensor node listens to the channel and updates the value of the backoff counter according to the channel condition until the value of the backoff counter is 0, and the sensor node sends the data packet.
The method of claim 1 wherein said determining an initial value of the backoff counter comprises:

Before the sensor node sends the data packet, randomly select a value from the contention window [1, CW] as an initial value of the backoff counter;

Difference threshold number CW CW max contention window value set in advance is equal to the current data packet buffer queue value of L now.
According to the method as claimed in claim 2, wherein the number L now the current data packet buffer queue is greater than or equal to the threshold value CW max, the value of the contention window CW value of said threshold value CW max.
The method according to any one of claims 1 to 3, wherein the value of the backoff counter is 0, and the sending, by the sensor node, the data packet comprises:

Starting the backoff counter and starting the backoff count;

The sensor node listens to the channel, and if the channel is idle, the value of the backoff counter is decremented by one; if the channel is busy, the value of the backoff counter is locked until the channel is idle again, and the backoff counter is locked The value continues to be counted down by 1;

Until the backoff counter value is reduced to 0, the sensor node sends a data packet in the data queue; wherein the number of data packets sent by the sensor node is randomly selected from [1, L now ].
A sensor node includes a preprocessing module and a processing module;

The pre-processing module is configured to: based on the number of data packets buffered in the current data queue, Determining an initial value of the backoff counter;

The processing module is configured to: start the backoff counter, and during the backoff counting process, listen to the channel and update the value of the backoff counter according to the channel condition until the value of the backoff counter is 0, and send the data packet.
The sensor node of claim 5 wherein said pre-processing module is configured to:

Before the processing module sends the data packet, a value is randomly selected from the contention window [1, CW] as an initial value of the backoff counter; wherein the contention window value CW is equal to the preset threshold CW max and the cache packet in the current data queue. the difference between the number of L now.
When the sensor node according to claim 6, wherein the number L now in the current data packet buffer queue is greater than or equal to the threshold value CW max, the value of the contention window CW value of said threshold value CW max.
The sensor node according to any one of claims 5 to 7, wherein the processing module is configured to:

Starting the backoff counter and starting the backoff count;

Listening to the channel, if the channel is idle, the backoff counter is decremented by one; if the channel is busy, the value of the backoff counter is locked until the channel is idle again, and the value that is locked from the backoff counter continues to be decremented by one. Counting process

Until the backoff counter value is reduced to 0, the data packet in the data queue is sent; wherein the number of transmitted data packets is randomly selected from [1, L now ].
A computer readable storage medium storing program instructions that, when executed, can implement the method of any of claims 1-4.