Transport Capacity and Space-Time-Spectrum Efficiency of Large Wireless CDMA Ad Hoc Networks

In this paper, we study the transport capacity in packet-meters per slot per node and the space time spectrum efficiency in bit-meters per Hz per second per square meter for large wireless CDMA ad hoc networks, considering optimization of MAC and routing protocols and fixed physical layer. The node density and processing gain tend to infinity with their ratio kept a constant. The limiting network consists of infinitely dense, sender uniformly distributed, mutually independent, and memoryless Gaussian channels on the entire 2-D plane. The MMSE receiver, decorrelator, and matched filter are employed in packet demodulation. Retransmission diversity gain for packets of multiple transmissions is considered. Markov chain property is applied to derivation of steady link throughput and link packet delay. The transport capacity, space time spectrum efficiency, packet delay, and average number of hops with an arbitrary source-destination distribution are obtained all in closed form. While multiuser detection gain vanishes in low and high network load regimes, retransmission diversity gain 10log10m dB in SIR for a packet of m transmissions is independent of network load. As the network load tends to infinity, retransmission diversity, if exploited, endows the network with a constant or increasing space time spectrum efficiency; otherwise vanishing.