Scalable Sporadic Medium Access for Complex Propagation Environments

Supporting networks with a large number of nodes in infrastructure-poor and complex propagation environments is an important challenge for military and civilian applications. A major problem when using classical approaches, such as code division multiple access (CDMA), is maintaining inter-link coordination while mitigating multi-user interference (MUI). By contrast, loosely synchronous (LS) codes have perfect code orthogonality within a window of inter-link delays at a cost of the number of available spreading codes. Since sporadic communications naturally involves a low probability of transmission, we investigate the potential for LS code reuse to effectively support more users. We study this problem by simulating inter-user channels using a high-fidelity physics-based model. We focus our study of the channel on the low-VHF band, which has improved penetration and channel coherence in complex environments. We perform initial characterization of different levels of code reuse, synchronization and coordination. Of particular interest is a purely random (uncoordinated) spreading code assignment. The results illustrate good performance of a scalable medium access scheme.