Analysis and Optimization of a Frequency-Hopping Ad Hoc Network in Rayleigh Fading

TL;DR

This paper develops a method to optimize frequency-hopping ad hoc networks under Rayleigh fading by jointly tuning system parameters to maximize transmission capacity, considering modulation, coding, and channel effects.

Contribution

It introduces a joint optimization framework for frequency-hopping parameters, modulation index, and coding rate in Rayleigh fading environments, with closed-form outage probability expressions.

Findings

Optimized parameters significantly improve transmission capacity.

Two optimization algorithms demonstrate effective capacity maximization.

Insights into tradeoffs among hopping channels, modulation, and coding are provided.

Abstract

This paper proposes a new method for optimizing frequency-hopping ad hoc networks in the presence of Rayleigh fading. It is assumed that the system uses a capacity-approaching code (e.g., turbo or LDPC) and noncoherent binary continuous-phase frequency-shift keying (CPFSK) modulation. By using transmission capacity as the performance metric, the number of hopping channels, CPFSK modulation index, and code rate are jointly optimized. Mobiles in the network are assumed to be uniformly located within a finite area. Closed-form expressions for outage probability are given for a network characterized by a physical interference channel. The outage probability is first found conditioned on the locations of the mobiles, and then averaged over the spatial distribution of the mobiles. The transmission capacity, which is a measure of the spatial spectral efficiency, is obtained from the outage probability. The transmission capacity is modified to account for the constraints of the CPFSK modulation and capacity-approaching coding. Two optimization methods are proposed for maximizing the transmission capacity. The first is a brute-force method and the second is a gradient-search algorithm. The results obtained from the optimization shed new insight into the fundamental tradeoffs among the number of frequency-hopping channels, the modulation index, and the rate of the error-correcting code.