无线传感器网络PQ-MAC 协议研究.

Presentation on theme: "无线传感器网络PQ-MAC 协议研究."— Presentation transcript:

1 无线传感器网络PQ-MAC 协议研究

2 摘要：本文提出了PQ-MAC协议---无线传感器网络中为网络提供优质服务质量的基于优先级的介质访问控制协议(MAC)，利用睡眠-唤醒流量调度机制PQ-MAC协议能够最大限度地减少能量消耗，利用不同的信道接入机制，分组调度，队列管理方法，PQ-MAC可以很好的支持QoS。PQ-MAC综合了时分多路(TDMA), 载波侦听多路访问(CSMA)技术的特点。本文提出的协议是一个能量利用效率高，基于优先级的，和QoS兼容的MAC协议。它包含多层次的队列管理，睡眠-唤醒调度，和网络在竞争时期的调度计划。它还保证在规定时间范围内传送高质量的数据包。本文从三个方面比较WSN中PQ-MAC和S-MAC之间的性能优劣：能量消耗，吞吐量，平均等待时间。 仿真结果显示在WSN中PQ-MAC的性能比S-MAC好。

3 名词解释： PQ-MAC：基于优先级的介质访问控制协议(priority-based medium access control (MAC) protocol for providing quality of service) QoS ： 优质网络服务质量(quality of service) TDMA：时分多路(time division multiple access) CSMA ：载波侦听多路访问(carrier-sense multiple access) CP ：竞争时期(contention period)

4 1 绪论

5 1.1绪论 无线传感器网络中对于节点的设计已经被广泛的研究，像体系结构、协议制定，节能、位置设定等，但在多跳无线网络(multi-hop wireless networks)中如何保证提供优质的网络服务(QoS)这方面的内容却没有受到太多的关注。例如，为了保证传送图像和视频时端到端的时延和误码率是在一个可接受的范围内，我们必须小心的处理数据的传输。 A lot of research has been done on some important aspects of WSNs such as architecture and protocol design, energy conservation, and location, less attention has been given to providing certain QoS guarantees in multi-hop wireless networks. For instance, the transmission of imaging and video data requires careful handling in order to ensure that end-to-end delay is within acceptable range and the variation in such delay is acceptable 。

6 1.2 PQ-MAC与S-MAC介绍 本文介绍了两种应用在多跳无线网络(multi-hop wireless networks)中的协议，S-MAC、PQ-MAC。 S-MAC：S-MAC协议是在802.11协议的基础上提出的，是一种典型的基于竞争的MAC协议，设计的目标是减少能量消耗,提供良好的扩展性。其主要实现机制包括周期性侦听与睡眠、串音避免、消息传递和流量自适应侦听。 PQ-MAC：PQ-MAC协议，也就是本文提出的改善在多跳无线网络(multi-hop wireless networks)中提供优质网络服务质量(QoS)的协议，PQ-MAC协议最显著的特点是它为优先分组调度制定了多层次的队列管理系统，在竞争时期(CP)将QoS设定为高优先级，网络传输流量低的时候为了是能量利用效率高，它还提供了睡眠-唤醒交替机制。 The most distinguishable feature of PQ-MAC is that it provides a multi-level queue system for priority packet scheduling, a prioritized CP scheme for QoS, and a sleep wakeup sequence generator for energy efficiency in low traffic.

7 2 PQ-MAC的应用

8 PQ-MAC启动阶段的操作包括：发现邻居(寻找相邻的网络节点)、时隙分配(slot assignment)、全局时钟同步(global time synchronization)。
PQ-MAC has a setup phase that includes the following operations: neighbor discovery, slot assignment, and global time synchronization

9 2.1 PQ-MAC中的时分多路(TDMA)调度机制
PQ-MAC中的时分多路(TDMA)调度机制，这里采用了Z-MAC协议中的DRAND和时隙(time frame (TF))规则，图一显示了TDMA调度机制和TF规则的结合使用。 For TDMA scheduling within PQ-MAC, we use DRAND [6] and the time frame (TF) rule of Z-MAC. Figure 1 shows an example of a TDMA schedule obtained by the TF rule. Fig. 1 the slot scheduling by TF rule

10 2.2 PQ-MAC中的多层次队列管理系统 PQ-MAC中的多层次队列管理系统如图二所示，当接受到一个包后，包分类器将根据所接收到的包的优先级进行分类存储，包调度器从队列中选择优先级最高的包，然后将它传输到下一个节点。 The multiple level queuing system of PQ-MAC is implemented in each node as shown in Fig. 2. A received packet is classified based on its priority and stored in the queue by the packet classifier. The packet scheduler selects a packet in the higher priority queue and transmits it to the next node. Fig. 2 The multi-level queue for priority packet scheduling

11 2.3 PQ-MAC中的超级帧结构 本文为PQ-MAC定义了一个超级帧结构(super frame structure (SFS))，如图三所示。 其中SFS包括两个子帧—数据帧(data frame (DF))和控制帧(control frame (CF))，对于数据帧(DF，每个节点交替的睡眠-唤醒，唤醒的节点向其它节点发送数据包。每个节点的交替睡眠-唤醒调度有控制帧(CF)控制。 In PQ-MAC, we define a super frame structure for synchronized scheduling. As shown in Fig. 3, the super frame (SF) consists of two sub-frames, the data frame (DF) and the control frame (CF). In the DF, each node repeats its current sleep-wake up sequence and transmits data packets. Every node wakes up and exchanges sleep-wake up sequence of its neighbors throughout the CF. The DF consists of N slots and is divided into a series of STFs.

12 Fig. 3 The super frame structure

13 2.4 PQ-MAC时隙 本文将PQ-MAC中的一个时隙定义为向外传送一个数据包所需要的时间，时隙的时间范围必须大于处理发送一个包所需要的时间(Data=contention window + RTS + CTS + DATA + ACK)，时隙的安排如图四所示，当一个节点i要向外发送数据时，必须确认当前他是否拥有该时隙。 In PQ-MAC, we redefine the term “slot” to represent one packet transmission. The span of a time slot TD is chosen such that it is long enough to handle a complete data transmission (contention window + RTS + CTS + DATA + ACK). The slot and the ordered CP are illustrated in Fig. 4. When a node i has data to transmit, it checks whether it is the owner of the current slot.

14 Fig 4 The slot structure and the ordered contention period with each priority

15 2 仿真结果分析

16 本文在5 × 5的网格拓扑网络(5 × 5 mesh topology network)上用NS-2测试了PQ-MAC和S-MAC的性能，两次仿真，本文都是用恒定的比特率(constant bit rate (CBR))和不同的时间间隔(different time intervals)，其中传输层用的是UDP协议，仿真时间持续了1500秒。 仿真结果如图五，六，七所示 We simulated both PQ-MAC and S-MAC in a 5 × 5 mesh topology network using the NS − 2 simulator. In both simulations, we used constant bit rate (CBR) traffic source with different time intervals and UDP as the transport layer protocol. The simulation time was set to 1500 seconds.

17 Table 1 Parameters used in the simulations

18 Fig. 5 The comparison of total energy consumptions between PQ-MAC and S-MAC with different incoming traffic rates.

19 Figure 5 shows the energy consumption between PQMAC and S-MAC with the change in traffic load. It shows that PQ-MAC consumes less energy than S-MAC for all traffic loads. 图五显示在网络流量改变时PQ-MAC 和 S-MAC所需要的能量对比，很明显S-MAC比PQ-MAC高。

20 Fig. 6 The comparison of total throughput between PQ-MAC and SMAC with different incoming traffic rates.

21 Figure 6 shows that the throughput of PQMAC and S-MAC are the same when the traffic is light.
图六显示当网络流量比较低的时候，应用PQ-MAC 和 S-MAC，网络吞吐量区别不大，但当网络流量大时，应用PQ-MAC可以很好的提高网络吞吐量。

22 Fig. 7 The comparison of packet delay between PQ-MAC and S-MAC with different network traffic load.

23 Figure 7 shows packet delays as the traffic load applied to the network increases.
图七显示当网络越来越繁忙的时候，对于改善数据包的延迟到达，应用PQ-MAC的延迟时间明显比S-MAC短。

24 3 总结

25 本文提出的PQ-MAC可以有效的区分每个数据包的优先级，然后根据数据包优先级的不同分别发送数据，本文还和S-MAC作了仿真比较，本文所提出的PQ-MAC在网络流量大情况下的无论是节能技术，还是网络吞吐量方面都比S-MAC性能要好，特别在网络繁忙时利用睡眠-唤醒交替机制可以有效的发送数据。 The proposed scheme effectively separates the medium access of each group of packet transmission according to packet priority. In comparison with S-MAC, our protocol achieves greater power savings under light traffic loads and performs higher throughput under heavier traffic loads by using the sleep-wakeup schedule.