Abstract
Time reversal (TR) is considered as a promising technique for green and multi-user communications thanks to its time and space focusing properties. TR can be viewed as a precoding scheme which can be combined with orthogonal frequency division multiplexing (OFDM) and easily carried out in a multiple transmit antenna context. This paper analyzes the performance of TR for a multiple-input single-output (MISO) OFDM system and provides a comparison with maximum ratio transmission (MRT) and equal gain transmission (EGT) precoding techniques. The analytical performance of the three precoding techniques is derived by computing the capacity and the bit error rate (BER) as a function of the transmit signal-to-noise ratio (SNR). First, the capacity analysis highlights the ability of the TR system to provide higher bit rates than the MRT system at low SNRs, while the capacity of the MRT system is the highest at high SNRs. From the obtained BER analytical expressions, the diversity exploitation of each system is discussed. In particular, it is shown that the TR system only exploits half the available diversity, while the systems using EGT or MRT exploit the full diversity. Hence, contrary to what is expected from the theoretical capacity analysis, the TR system is shown to underperform the other precoding schemes in terms of BER. To overcome such a drawback, the combination of TR with classical adaptive modulation techniques is studied, allowing the achievable throughput to be increased without destroying the focusing properties of TR. It is then observed that TR takes advantage of adaptive modulations and outperforms the other schemes at low SNRs. In this study, analytical results and closed-form expressions of capacity and BER performance are provided and confirmed through Monte Carlo simulations.
Highlights
Multiple-antenna communications have raised intense academic and industrial interests in the last two decades and have become a key technology in the evolution of wireless systems (LTE, WLAN, WiMAX, etc.)
We propose to lead a complete analysis on the performance of different multiple-input single-output (MISO)-orthogonal frequency division multiplexing (OFDM) systems based on precoding techniques, including the recently experimented Time reversal (TR) approach
It has been highlighted that depending on the precoding schemes, the transmitted signal experiences different equivalent channels, leading to fundamental differences in terms of capacity, signal-to-noise ratio (SNR) gain, and diversity exploitation capability
Summary
Multiple-antenna communications have raised intense academic and industrial interests in the last two decades and have become a key technology in the evolution of wireless systems (LTE, WLAN, WiMAX, etc.). As far as multiple-input single-output (MISO) systems are concerned, only diversity gain can be expected since the spatial multiplexing gain is driven by the size of the smallest antenna array between transmitter and receiver [5]. Time reversal (TR) recently appeared as a strong candidate for MISO transmissions because it relies on a simple preprocessing technique for any number of transmit antennas and involves very simple receivers even considering frequency-selective channels. This technique is different from SVD, MRT, or EGT because of the way of weighting the precoding factors over the frequency dimension as it is further detailed in the paper. The total transmit power is referred to as Pe, and ρ stands for the transmit SNR
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