Channel Characterization and Robust Tracking for Diversity Reception over Time-Variant Off-Body Wireless Communication Channels

EURASIP Journal on Advances in Signal Processing, Jul 2010

In the 2.45 GHz band, indoor wireless off-body data communication by a moving person can be problematic due to time-variant signal fading and the consequent variation in channel parameters. Off-body communication specifically suffers from the combined effects of fading, shadowing, and path loss due to time-variant multipath propagation in combination with shadowing by the human body. Measurements are performed to analyze the autocorrelation, coherence time, and power spectral density for a person equipped with a wearable receive system moving at different speeds for different configurations and antenna positions. Diversity reception with multiple textile antennas integrated in the clothing provides a means of improving the reliability of the link. For the dynamic channel estimation, a scheme using hard decision feedback after MRC with adaptive low-pass filtering is demonstrated to be successful in providing robust data detection for long data bursts, in the presence of dramatic channel variation.

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Channel Characterization and Robust Tracking for Diversity Reception over Time-Variant Off-Body Wireless Communication Channels

EURASIP Journal on Advances in Signal Processing Hindawi Publishing Corporation Channel Characterization and Robust Tracking for Diversity Reception over Time-Variant Off-Body Wireless Communication Channels Patrick Van Torre 1 2 Luigi Vallozzi 2 Hendrik Rogier 2 Marc Moeneclaey 0 Jo Verhaevert 1 Markus Rupp 0 Department of Telecommunications and Information Processing (TELIN), Ghent University , St. Pietersnieuwstraat 41, 9000 Ghent , Belgium 1 Hogeschool Gent, INWE Department , Schoonmeersstraat 52, 9000 Gent , Belgium 2 Information Technology Department (INTEC), Ghent University , St. Pietersnieuwstraat 41, 9000 Ghent , Belgium In the 2.45 GHz band, indoor wireless off-body data communication by a moving person can be problematic due to time-variant signal fading and the consequent variation in channel parameters. Off-body communication specifically suffers from the combined effects of fading, shadowing, and path loss due to time-variant multipath propagation in combination with shadowing by the human body. Measurements are performed to analyze the autocorrelation, coherence time, and power spectral density for a person equipped with a wearable receive system moving at different speeds for different configurations and antenna positions. Diversity reception with multiple textile antennas integrated in the clothing provides a means of improving the reliability of the link. For the dynamic channel estimation, a scheme using hard decision feedback after MRC with adaptive low-pass filtering is demonstrated to be successful in providing robust data detection for long data bursts, in the presence of dramatic channel variation. 1. Introduction The safety of rescue workers can be improved by smart textiles that allow a data communication system to be integrated into their garment. Textile antenna systems provide a convenient means for unobtrusive integration that does not disturb the movements of the rescue worker. The structure of the patch antennas used, with a ground plane near the body, limits the radiation exposure of the body and the influence of the body on the radiation pattern of the antenna. Operations are often performed indoors, where dramatic signal fading occurs due to multipath propagation. Given the rapid movements by rescue workers in combination with the multipath fading of the indoor environment and the shadowing by the human body, the channel seen by the multiantenna system varies rapidly in time. Often short bursts are used to counter this problem. However, this introduces a significant overhead caused by the retransmission of the necessary preambles for each burst. The measurements presented in this paper are performed in the same environment where earlier measurements for off-body communication, documented in [ 1, 2 ], indicated Rayleigh-distributed small-scale fading. The rapid fluctuations over larger distance scales are caused by both smallscale fading and shadowing. The cumulative distribution function and level crossing rate in these cases fitted to the Nakagami distribution. Measurements were performed deploying two textile antenna patches integrated in a garment on the human body, using short data bursts and treating the channel as time-invariant. In this paper, a continuous transmission, consisting of a data stream that lasts for much longer than the channel’s coherence time, will be performed. Measurements are presented deploying four wearable antenna patches at the rescue worker and capturing longer time frames, subject to very significant variations of the channel behavior in time. In [ 1, 2 ], no such drastic channel variation occurred during the same received burst. Important parameters of the time-varying off-body communication channel, such as autocorrelation, coherence time, and power spectral density, are determined. The values are shown to be influenced by walking speed as well as antenna location on the body. Measurements are performed for line-of-sight (LoS) and Non line-of-sight (NLoS) situations. Diversity techniques, using multiple antennas, are widely known to combat the effects of fading. At the receiving side, maximal ratio combining (MRC) is used to combine signals from different antennas. To use MRC effectively, an accurate channel estimation is necessary at all times. Channel estimation can be performed using a series of pilot symbols. In previous publications [ 1, 2 ], the transmitted bursts are kept short, allowing the channel to be treated as invariant for the duration of the burst. However, as each separate burst needs to contain a number of pilot symbols, a significant overhead is introduced, limiting the effective data throughput. For the measurements presented, long data bursts containing one million data symbols and lasting over one second are transmitted. During this transmission time, the channel is definitely not invariant when communicating with a walking person; therefore, a robust system of dynamic channel tracking is needed. As we p (...truncated)


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Patrick Van Torre, Luigi Vallozzi. Channel Characterization and Robust Tracking for Diversity Reception over Time-Variant Off-Body Wireless Communication Channels, EURASIP Journal on Advances in Signal Processing, 2010, pp. 978085, Volume 2010, Issue 1, DOI: 10.1155/2010/978085