Cross-Layer Design for Packet Data Transmission in Maximum Ratio Transmission Systems with Imperfect CSI and Co-Channel Interference

Introduction

With the enormous growth in demand for multimedia services, wireless communications has become the bottleneck in end-to-end wired-wireless networks because radio resources are very scarce and expensive. In addition, the transmission of high data rate demanding services faces fundamental limitations due to impairments inflicted by multipath fading channels. Hence, achieving high data rates with reliable transmission over error-prone mobile radio channels is a major challenge for a mobile radio system design. Recently, being an efficient solution, the so-called cross-layer design paradigm has been proposed where a set of parameters across multiple layers of the protocol stack are exchanged. With this strategy, the overall system performance can be enhanced while keeping the Quality of Service (QoS) satisfactory.

In this chapter, we will investigate a cross-layer design that jointly considers Adaptive Modulation (AM) at the physical layer and Truncated-Automatic Repeat Request (T-ARQ) at the data link layer. As signal traversing from transmitter to receiver may experience reflection, diffraction, and scattering, it can be severely degraded. Instead of circumventing the time-varying effects of the wireless channel, we can exploit these rapid fluctuations to improve spectral efficiency. Specifically, adaptive modulation is deployed by changing to an appropriate modulation constellation, i.e., selecting suitable signal constellation size in accordance with the variation of the end-to-end received Signal-to-Noise Ratio (SNR) (Webb & Steele, 1995; Goldsmith & Chua, 1997, 1998; Alouini, et al., 1999; Alouini & Goldsmith, 2000). However, applying pure adaptive modulation cannot maximize spectral efficiency since the number of available signal constellations is limited. The ARQ scheme at the data link layer is often used to enhance transmission reliability by retransmitting packets detected being in error. Due to the finite buffer size and stringent delay constraints for multimedia services, the maximum number of retransmissions should be limited by using T-ARQ (Malkamaki & Leib, 2000). Under a predefined threshold, e.g., packet lost rate and delay, a cross-layer design combining AM and T-ARQ has gained great attention in the research community (see e.g., Liu, et al., 2004a, 2004b; Maaref & Aïssa, 2004a, 2004b, 2005; Qi, et al., 2010; Wu & Ci, 2006; and references therein).

Multiple-Input Multiple-Output (MIMO) systems, where multiple antennas are deployed at transceivers to significantly improve the system performance compared to its single antenna counterpart, can be subcategorized into spatial multiplexing gain, spatial diversity gain, and opportunistic beamforming transmission. The cross-layer design combining AM at the physical layer and ARQ at the data link layer has been well investigated for Orthogonal Space-Time Block Coding (OSTBC) to exploit the spatial diversity of MIMO systems. In particular, Maaref and Aïssa (2004a, 2004b) have presented the performance of cross-layer design for OSTBC transmission over Rayleigh and Nakagami-m fading channels, respectively. Taking into account the antenna correlation and rank-deficient channel effects, the cross-layer design has been investigated for Nakagami-m fading (Qi, et al., 2010). It has been shown that the packet error rate performance of the cross-layer design is significantly degraded by antenna correlation. More importantly, the keyhole fading makes the fluctuating behavior in the system performance of the cross-layer design less severe compared to the non-keyhole Nakagami-m case. Taking channel estimation errors into consideration, Maaref and Aïssa (2005) have shown that the average spectral efficiency of the cross-layer design can deteriorate by as much as 2.5 bits/s/Hz.