Turbo packet combining strategies for the MIMO-ISI ARQ channel

Abstract

This paper addresses the issue of efficient turbo packet combining techniques for coded transmission with a Chase-type automatic repeat request (ARQ) protocol operating over a multiple-input-multiple-output (MIMO) channel with intersymbol interference (ISI). First of all, we investigate the outage probability and the outage-based power loss of the MIMO-ISI ARQ channel when optimal maximum a posteriori (MAP) turbo packet combining is used at the receiver. We show that the ARQ delay (i.e., the maximum number of ARQ rounds) does not completely translate into a diversity gain. We then introduce two efficient turbo packet combining algorithms that are inspired by minimum mean square error (MMSE)-based turbo equalization techniques. Both schemes can be viewed as low-complexity versions of the optimal MAP turbo combiner. The first scheme is called signal-level turbo combining and performs packet combining and multiple transmission ISI cancellation jointly at the signal-level. The second scheme, called symbol-level turbo combining, allows ARQ rounds to be separately turbo equalized, while combining is performed at the filter output. We conduct a complexity analysis where we demonstrate that both algorithms have almost the same computational cost as the conventional log-likelihood ratio (LLR)-level combiner. Simulation results show that both proposed techniques outperform LLR-level combining, while for some representative MIMO configurations, signal-level combining has better ISI cancellation capability and achievable diversity order than that of symbol-level combining.Index Terms-Automatic repeat request (ARQ) mechanisms, multiple-input-multiple-output (MIMO), intersymbol interference (ISI), outage probability, turbo equalization, minimum mean square error (MMSE).

Turbo packet combining for broadband MIMO relay communication

“…It presents an extension of the turbo packet combining methods initially proposed for conventional broadband ARQ systems [16], [17] to relay communications.…”

Low complexity frequency domain hybrid-ARQ chase combining for broadband MIMO CDMA systems

“…We introduce two packet combining where all ARQ rounds are used jointly to decode the data packet. The first packet combining scheme, referred to as chip-level packet combining scheme, is an extension of the combining approach introduced in [11,13] to the case of multi-antenna multi-code CDMA systems. In this combining scheme, we exploit the fact that both the CP chip-word and data packet are retransmitted at each ARQ round.…”

Turbo packet combining for broadband space-time BICM hybrid-ARQ systems with co-channel interference

“…The diversitymultiplexing-delay tradeoff has then been characterized in the case of block-fading MIMO ARQ channels, i.e., multiple fading blocks are allowed within the same ARQ round [25]. In [26], the outage probability of MIMO-ISI ARQ channels has been evaluated under the assumptions of short-term static channel dynamic 2 , and Chase-type ARQ [27], i.e., the data packet is entirely retransmitted. It has been shown that, as in the flat fading case, ARQ presents an important source of diversity, but its influence becomes only minimal when the 1 In non-ergodic, i.e., block fading quasi-static channels, the outage probability is a meaningful measure that provides a lower bound on the block error probability.…”

“…[28], [29], [30], [31], [32], [33], [34], [35], [36]). Turbo combining techniques, where decoding is iteratively performed through the exchange of soft information between the soft-input-soft-output (SISO) packet combiner and the SISO decoder, have been proposed for the MIMO-ISI ARQ channel using unconditional minimum mean square error (MMSE)-aided combining [37], [26]. These approaches have then been extended to broadband MIMO code division multiple access (CDMA) systems with ARQ [38].…”