On the Order Optimality of Large-scale Underwater Networks

TL;DR

This paper derives capacity scaling laws for large underwater acoustic networks considering frequency-dependent attenuation, showing how power and bandwidth limitations affect throughput and demonstrating the order optimality of simple multi-hop schemes.

Contribution

It provides the first comprehensive analysis of capacity scaling laws in underwater networks with frequency scaling and identifies regimes where simple schemes are order-optimal.

Findings

Extended networks are highly power-limited with throughput inversely proportional to attenuation.

In dense networks, throughput is limited by bandwidth, power, or both, depending on path-loss regimes.

Nearest-neighbor multi-hop transmission is order-optimal across various regimes.

Abstract

Capacity scaling laws are analyzed in an underwater acoustic network with $n$ regularly located nodes on a square, in which both bandwidth and received signal power can be limited significantly. A narrow-band model is assumed where the carrier frequency is allowed to scale as a function of $n$. In the network, we characterize an attenuation parameter that depends on the frequency scaling as well as the transmission distance. Cut-set upper bounds on the throughput scaling are then derived in both extended and dense networks having unit node density and unit area, respectively. It is first analyzed that under extended networks, the upper bound is inversely proportional to the attenuation parameter, thus resulting in a highly power-limited network. Interestingly, it is seen that the upper bound for extended networks is intrinsically related to the attenuation parameter but not the spreading factor. On the other hand, in dense networks, we show that there exists either a bandwidth or power limitation, or both, according to the path-loss attenuation regimes, thus yielding the upper bound that has three fundamentally different operating regimes. Furthermore, we describe an achievable scheme based on the simple nearest-neighbor multi-hop (MH) transmission. We show that under extended networks, the MH scheme is order-optimal for all the operating regimes. An achievability result is also presented in dense networks, where the operating regimes that guarantee the order optimality are identified. It thus turns out that frequency scaling is instrumental towards achieving the order optimality in the regimes. Finally, these scaling results are extended to a random network realization. As a result, vital information for fundamental limits of a variety of underwater network scenarios is provided by showing capacity scaling laws.