Closed-Form Rate Outage Probability for OFDMA Multi-Hop Broadband Wireless Networks under Nakagami-m Channels

Abstract: Rate outage probability is an important performance metric to measure the level of quality of service (QoS) in the 4th Generation (4G) broadband access networks. Thus, in this paper, we calculate a closed form expression of the rate outage probability for a given user in a down-link multi-hop OFDMA-based system encountered as a result of links channel variations. The channel random behavior on different subcarriers allocated to a given user is assumed to follow independent non-identical Nakagami-m distributions. Besides the rate outage probability formulas for single hop and multi-hop networks, we also derive a novel closed form formulas for the moment generating function, probability distribution function (pdf), and the cumulative distribution function (cdf) of a product of independent non-identical Gamma distributed random variables (RVs). These RVs are functions of the attainable signal-to-noise power ratio (SNR) on the allocated group of subcarriers. For single-hop scenario, inspired by the rate outage probability closed formula, we formulate an optimization problem in which we allocate subcarriers to users such that the total transmission rate is maximized while catering for fairness for all users. In the proposed formulation, fairness is considered by guaranteeing a minimum rate outage probability for each admitted user