WIP: BurstMAC — A MAC Protocol with Low Idle Overhead and High Throughput

Many sensor network applications feature bursty traffic patterns: after long periods of idle time with almost no network traffic, large amounts of data have to be transmitted reliably and in a timely manner. One example is volcano monitoring [8], where precious high-volume data is generated by rare volcanic eruptions. Unfortunately, existing MAC protocols do not sufficiently support such applications with bursty traffic patterns. Protocols design for low data rates such as WiseMAC or SCP-MAP have very low overhead in idle situations, but have high overhead and low throughput under high load due to collisions. In contrast, scheduled protocols such as LMAC can handle high loads without collision, but have low throughput and significant overhead in idle mode [4]. We devise a new MAC protocol, BurstMAC, that closes this gap by combining low idle overhead with high throughput under load. It achieves radio duty cycles of < 1% in an idle network and uses up to 71% of the available bandwidth during traffic bursts without any collisions. 1 I. PROTOCOL OVERVIEW BurstMAC combines a number of techniques to combine high throughput under load with low idle overhead. Most notably, scheduling and the use of multiple radio channels enable high throughput, while cooperative transmissions and techniques to eliminate preambles guarantee low idle overhead. In this section, we present the key ideas behind BurstMAC and outline the basic protocol structure A. Collision-free Communication To avoid collisions, BurstMAC operates in synchronous rounds. The sink node is used as time reference for synchronization. Each node synchronizes to the average time of all nodes which are closer to the time reference than itself. Each round consists of 32 frames. Every frame contains a control section and a data section as depicted in Fig. 1. To maximize throughput and to allow for collision-free communication during the data section, BurstMAC uses 32 interference-free data channels and one control channel. The control section is used for time synchronization, to broadcast other information to all network neighbors, and to assign color ids to nodes. As a result of the latter, each node is assigned a color id c ∈ 1..32 that is unique within two hops. The color id c is used for two purposes. Firstly, the control section of frame c is reserved for the node with color id c, which allows a node to send control 1The work presented in this work-in-progress paper was partially supported by the Swiss National Science Foundation under grant number 5005-67322 (NCCR-MICS) FRAME 1 FRAME 2 FRAME 31 FRAME 32 1 round = 32 frames