A-MAC: Efficient Medium Access for cluster-based wireless sensor networks

In wireless sensor networks, many applications are based on a two-tier architecture. In a typical two-tier architecture, nodes are grouped into clusters and communicate with a cluster head (CH); the CH then transmits compressed data to the base station (BS). In this paper, we mainly focus on the communication between CHs and the BS. The communication between the CH-BS could be accomplished with traditional medium access control (MAC) protocols such as time division multiple access (TDMA) or carrier sensing multiple access (CSMA). While protocols such as TDMA work well in some situations, they do not work well when the number of clusters is large and the traffic load between the CH-BS is low. In this paper, we propose a new MAC protocol (called A-MAC) for the CH-BS communication that is more efficient than traditional MAC protocols. A-MAC takes only 1/N (N is the number of clusters in the network) of the time spent by TDMA to transmit the same number of packets. We save time by having packets transmitted in parallel and then resolving the collisions (instead of avoiding them). Specifically, we deploy N relay nodes around the BS and have all CHs send their packets to the BS at the same time. When the BS detects a collision, it asks the relay nodes to transmit what was heard. The BS then resolves the collision after it receives enough information from the relay nodes using a multiple-input and multiple-output (MIMO) algorithm. In this paper, we also investigate methods to allocate time for the intra-clustering communication and the CH-BS communication, as well as where to place the relay nodes to maximize throughput. Our simulation results illustrate that A-MAC outperforms TDMA in terms of throughput and delay.