Securing UWB Communications under NLOS Indoor Propagation Conditions

Ultra-wideband (UWB) communications can be achieved under non-line-of-sight (NLOS) propagation conditions using carefully selected and located microwave scatterers together with a multi-carrier modulation technique such as orthogonal frequency-division multiplexing (OFDM). One key factor in achieving high data throughputs is the average signal intensity of the scattered signals that may be achieved by using one or multiple scatterers. Precise scattered signal measurements carried out in a 1 GHz band centered around 29.5 GHz with single or multiple scatterers have led to the conclusion that there exists an approximate relationship of proportionality between the average received signal intensity expressed in dB and the sum of scatterer cross section per unit length. Measurements of the frequency response of NLOS indoor propagation channels were performed for three different laterally-positioned receive antenna locations and used for single-input multiple output (SIMO) studies. Based on these measurements, OFDM data transmission streams were simulated. It was determined that individual subchannels of the OFDM data transmission stream suffered distortions to various degrees resulting in the unsuitability of some subchannels for data transmission. Using the technique of post-discrete Fourier transform (post-DFT) multiple subcarrier selection (MSCS), it was found that data throughputs comparable to those achievable under quasi-perfect propagation conditions could be obtained in NLOS indoor channels provided that the sum of the scatterer cross sections was of sufficient magnitude. Signal-level and error-rate metrics were used for the selection of OFDM subcarriers.