Bi-code channel access with robust medium access control for ad hoc networking

Traditionally, ad hoc networks operate on a contention based common channel, which brings problems with increasing traffic. Also, some potential capacity is wasted, because to avoid collisions, all the neighboring nodes of the transmitting one are blocked from transmitting. With CDMA (code division multiple access), it is possible to make multiple simultaneous and co-located successful transmissions and thus increase capacity within the limits of multiple access interference (MAI). In this paper, a cross-layered design approach is taken and bi-code channel access (BCCA) method and its dedicated MAC (BC-MAC) are proposed for ad hoc networking. In BCCA, two channels (spreading codes) are tracked at the receiver. One is used as a receiver based CDMA-channel for robust data transmission, and the other, without forgetting the fundamental idea of ad hoc networking, as a common access channel. With BCCA collisions (incoming transmissions with same code) are rare, so, simple medium access control (MAC) methods can be used to gain performance. It is shown that BC-MAC clearly outperforms commonly used methods in studied cases and still is easy to implement, robust for design parameters under different conditions, while maintaining the original idea of ad hoc networking. Most of the improvements arise with high traffic load, which is crucial especially in the military environment, where typically no extra bandwidth is available.