On the Fundamental Relationship Between the Achievable Capacity and Delay in Mobile Wireless Networks

Abstract

In this work, we establish the fundamental relationship between the achievable capacity and delay in mobile wireless networks. Under an i.i.d. mobility model, we first obtain the following upper bound on the achievable capacity given a delay constraint. For a mobile wireless network with n nodes, if the per-bit-averaged mean delay is bounded by $\bar D$, then the upper bound on the per-node capacity is on the order of $\sqrt[3]{{\frac{{\bar D}} {n}}}\log n$. By studying the conditions under which the upper bound is tight, we are able to identify the optimal values of several key scheduling parameters. We then develop a scheduling scheme that can almost achieve the upper bound (up to a logarithmic factor). This suggests that the upper bound is tight. Our scheduling scheme also achieves a provably larger per-node capacity than schemes reported in previous works. In particular, when the delay is bounded by a constant, our scheduling scheme achieves a per-node capacity that is inversely proportional to the cube root of n (up to a logarithmic factor). This implies that, for the i.i.d. mobility model, mobility improves the achievable capacity of static wireless networks, even with constant delays! Finally, the insight drawn from the upper bound allows us to identify limiting factors in existing scheduling schemes. These results present a relatively complete picture of the achievable capacity-delay tradeoffs under different settings.

This work has been partially supported by the NSF grants ANI-0207728, EIA-0130599 and the Indiana 21st Century Fund for Wireless Networks.