A Low-complexity Channel Shortening Receiver with Diversity Support for Evolved 2G Device

TL;DR

This paper introduces a low-complexity channel shortening receiver for 2G devices with diversity, improving performance and reducing computational complexity by using a mutual information optimized filter and single-stream processing.

Contribution

It proposes a novel MILB-based channel shortener that simplifies diversity processing in 2G receivers while enhancing performance compared to existing methods.

Findings

Superior performance over homomorphic filtering-based methods

Reduced equalization complexity proportional to the number of diversity branches

Effective diversity gain preservation with single-stream processing

Abstract

The second generation (2G) cellular networks are the current workhorse for machine-to-machine (M2M) communications. Diversity in 2G devices can be present both in form of multiple receive branches and blind repetitions. In presence of diversity, intersymbol interference (ISI) equalization and co-channel interference (CCI) suppression are usually very complex. In this paper, we consider the improvements for 2G devices with receive diversity. We derive a low-complexity receiver based on a channel shortening filter, which allows to sum up all diversity branches to a single stream after filtering while keeping the full diversity gain. The summed up stream is subsequently processed by a single stream Max-log-MAP (MLM) equalizer. The channel shortening filter is designed to maximize the mutual information lower bound (MILB) with the Ungerboeck detection model. Its filter coefficients can be obtained mainly by means of discrete-Fourier transforms (DFTs). Compared with the state-of-art homomorphic (HOM) filtering based channel shortener which cooperates with a delayed-decision feedback MLM (DDF-MLM) equalizer, the proposed MILB channel shortener has superior performance. Moreover, the equalization complexity, in terms of real-valued multiplications, is decreased by a factor that equals the number of diversity branches.