Iterative Detection for Orthogonal Precoding in Doubly Selective Channels

TL;DR

This paper investigates general orthogonal precoding in doubly selective channels, demonstrating that iterative detection methods can effectively improve performance, with results showing significant gains over traditional OFDM in high-mobility scenarios.

Contribution

It introduces a general framework for orthogonal precoding detection using iterative interference cancellation and channel estimation, unifying performance analysis for constant modulus sequences.

Findings

OP achieves about 4.8 dB gain over OFDM at BER of 10^{-4}

All constant modulus sequences perform similarly for OP

Coded OP results are the best documented for this architecture

Abstract

Ultra-reliable wireless communication links require the utilization of all diversity sources of a wireless communication channel. Hadani et al. propose a two dimensional discrete symplectic Fourier transform (DSFT) as orthogonal pre-coder for a time-frequency modulation scheme. In this paper we explore \emph{general} orthogonal precoding (OP) and its performance in time- and frequency-selective channels. We show that iterative parallel interference cancellation (PIC) and iterative channel estimation methods can be used for the detection of OP. A scalar signal model for OP transmission is obtained by PIC. Based on this signal model, we can prove that all constant modulus sequences, e.g. the DSFT basis functions or Walsh-Hadamard sequences, lead to the same performance for OP. We validate our receiver structure by numerical link level simulations of a vehicle-to-vehicle communication link with a relative velocity of $0\ldots200\,\text{km/h}$. We demonstrate that OP achieves a gain of about $4.8\,\text{dB}$ if compared to orthogonal frequency division multiplexing at a bit error rate of $10^{-4}$. Our performance results for coded OP are the best results for a fully documented receiver architecture, published so far.