The Capacity of Ad hoc Networks under Random Packet Losses

We consider the problem of determining asymptotic bounds on the capacity of a random ad hoc network. Previous approaches assumed a link layer model in which if a transmitter-receiver pair can communicate with each other, i.e., the Signal to Interference and Noise Ratio (SINR) is above a certain threshold, then every transmitted packet is received error-free by the receiver thereby. Using this model, the per node capacity of the network was shown to be $\Theta(\frac{1}{\sqrt{n\log{n}}})$. In reality, for any finite link SINR, there is a non-zero probability of erroneous reception of the packet. We show that in a large network, as the packet travels an asymptotically large number of hops from source to destination, the cumulative impact of packet losses over intermediate links results in a per-node throughput of only $O(\frac{1}{n})$. We then propose a new scheduling scheme to counter this effect. The proposed scheme provides tight guarantees on end-to-end packet loss probability, and improves the per-node throughput to $\Omega(\frac{1}{\sqrt{n} ({\log{n}})^{{\frac{\alpha{{+2}}}{2(\alpha-2)}}})$} where $\alpha>2$ is the path loss exponent.