Extending 60 GHz UWB coverage to medium distances under NLOS conditions

Ultra-wideband (UWB) communications can be achieved under non-line-of-sight (NLOS) propagation conditions at distances over 100 m using a single carefully designed and located microwave reflector in conjunction with a multi-carrier modulation technique such as orthogonal frequency-division multiplexing (OFDM) that is less sensitive to multipath effects than single-carrier modulation. One key factor in achieving high data throughputs is the average intensity levels of the reflected signals that are produced by using high-gain antennas and reflectors. A second key factor is the proper design of a reflector to minimize delays spreads and provide adequate signal strengths. A third key factor is the application of a suitable technique to recover defective OFDM subcarriers. In order to firmly ground performance predictions on experimental measurements, precise frequency response measurements of reflected signals were carried out in a 1 GHz band centered around 60.1 GHz. 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 from various levels of distortion resulting in the lack of availability of some OFDM subchannels for UWB 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 delay spread was short (18.1 ns). The signal-amplitude metric was used for the selection of OFDM subcarriers.