Two dimensional cross-layer optimization for packet transmission over fading channel

In this paper a single-input-single-output wireless data transmission system with adaptive modulation and coding over correlated fading channel is considered, where run-time power adjustment is not available. Higher layer data packets are enqueued into a finite size buffer space before being released into the time-varying wireless channel. Without fixing the physical layer error probability, the objective is to minimize the average joint packet loss rate due to both erroneous transmission and buffer overflow. Two optimization techniques are incorporated to achieve the best solution. The first is policy domain optimization that formulates the data rate adaptation design as classical Markov decision problem. The second is channel domain optimization that appropriately partitions the channel variation based on particular fading environment and carried traffic pattern. The derived policy domain analytical model can precisely map any policy design into various QoS performance metrics with finite buffer setup. We then propose a tractable suboptimization framework to produce different two-dimensional suboptimal solutions with scalable complexity-optimality tradeoff for practical implementations.

I. Introduction

WITH rapid development of wireless broadband applications, recently, cross-layer protocol design has emerged to be a practical yet necessary research subject. The main challenges of MAC-PHY cross-layer design for wireless communications are twofold. At the physical layer, on one side, multi-path propagation leads to a wireless fading channel over which signals are distorted and attenuated randomly before reception. At the MAC layer, on the other side, the limited buffer space is significantly vacated or exhausted from time to time, due to bursty arrivals from upper layers. These facts impose severe obstacles for providing quality-of-service (QoS) to upper layer applications. In this paper, we address the cross-layer optimization issues by jointly considering adaptive transmission scheduling and wireless fading channel partitioning, to achieve better performance gain. The major contributions of this work are summarized as follows: 1) This work proposes an advanced algorithm for adaptive modulation and coding (AMC)-enabled multirate transmission scheduling, where run-time power adjustment is not available. 2) This work develops an analytical model of the proposed algorithm for evaluating various QoS performance metrics. 3) Combined with previous research, this work proposes a new method for cross-layer performance optimization. 4) Based on the optimal solution, this work introduces a tractable design framework that generates a set of suboptimal schemes with scalable complexity-optimality tradeoff, for practical implementation.