Poster Abstract: BurstMAC — Low Idle Overhead and High Throughput in One MAC Protocol

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 [5], 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. CSMA protocols 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, TDMA protocols such as LMAC can handle high loads without collision, but have low throughput and significant overhead in idle mode [2]. BurstMAC closes this gap by combining low idle overhead with high throughput under load. We present the ideas behind BurstMAC and report initial performance results. I. PROTOCOL OVERVIEW To achieve the above behavior, BurstMAC combines several techniques which will be outlined in the following. To provide high throughput under load, BurstMAC uses efficient time scheduling and multiple radio channels. However, the control overhead is strictly dependent on the amount of traffic. In idle situations, the overhead comes close to that of a few clearchannel assessments. 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 messages without collision on the control channel in frame c. Secondly, the node receives data on radio channel c during the data section, coordinating multiple senders to receive data without collisions. FRAME 1 FRAME 2 FRAME 31 FRAME 32 1 round = 32 frames