Capacity of large wireless CDMA ad hoc networks with retransmission diversity

In this paper, we consider large wireless CDMA ad hoc networks on which nodes are uniformly distributed in an infinitely large area. The number of nodes per square meter and processing gain trend to infinity with their ratio kept a constant. Nodes access each other through a common CDMA channel without power control. Received power decays with node distance. When a packet is not successfully demodulated at a receiving node, it is retransmitted. A maximum ratio combiner is employed to combine all received data in multiple retransmissions of a packet. A Markov chain property is applied to derive stationary distribution of number of retransmissions, stationary link throughput and packet delay. Then the link (one-hop) transport capacity, optimum link distance achieving link transport capacity, node capacity, and node transport capacity are obtained. The network transport capacity obtained per node considering all traffic demand and scheduling is also obtained. Numerical evaluation points out that if multiple retransmissions are necessary for a packet, the one-hop transport capacity is achieved by delivering the packet to a nearest neighbor node, or otherwise by delivering to a farther determinable node. It is also shown that exploitation of retransmission diversity substantially increases the capacity of an ad hoc wireless network and reduces packet delay.