Assessment of MISO time reversal for short-range communications in the 5 GHz ISM band

The purpose of this paper is to investigate the performance of Time Reversal (TR) for short-range Multiple-Input Single-Output (MISO) systems in the Industrial, Scientific, and Medical (ISM) 5 GHz band using actual channel measurements. Such a scenario is considered for low cost user equipment applications, where low-complexity schemes like TR will be an potential candidate. The experiment is conducted with 8 transmit antennas and 1 receive antenna per user. The antennas are arranged in compact and distributed configurations, and the channel is measured in both Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) dominated scenarios. We investigate the performance of TR in terms of time compression, spatial focusing, and diversity gain, by analyzing the delay spread, the spatial Peak-to-Average-Leakage power ratio and the diversity gain, respectively. The conclusions that can be drawn from the experiment are: TR with multiple transmit antennas shows better performance compared to the single antenna link in terms of time compres- sion, spatial focusing, and diversity gain, even in realistic short-range communications. Second, a distributed 8 Tx antenna configuration achieves lower delay spread and higher diversity gain than a compact antenna array with the same number of elements. In the situation where practical impairments are taken into consideration, the system delay involving propagation and processing time is found to be a crucial parameter degrading the performance of TR.

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