Using frequency-orthogonal pseudonoise (FOPN) sounding sequences to identify signals from multiple transmit antennas in mobile double-directional and relay channel sounding systems

A method previously reported by the authors for identifying simultaneous signals from different Tx antennas is applied for double-directional channel sounding between a channel sounder base station (CSBS) and a channel sounder mobile station (CSMS), as well as for single input single output (SISO) channel sounding on relay channels in urban microcell-type Tx/Rx scenarios. Using this method, multiple-orthogonal signals are produced from one pseudo-noise code by using it to modulate RF carriers at pre-calculated offset frequencies. The frequency spectra of the resulting signals are interleaved and they occupy the same overall frequency band, but the spectral lines from different transmitters are separable using Fourier analysis of signals sampled at the CSMS receiver output. In theory, any arbitrary number of links from different transmitters can be measured simultaneously using this method. However, in practice, Doppler spreads limit the number of simultaneous soundings that can be made with acceptable isolation among resulting impulse response estimates. Herein, examples are given of results from double-directional channel sounding using a linear array of 4 Tx antennas at the CSBS and of relay channel sounding with one Tx antenna at the CSBS and one Tx antenna at a channel sounder relay station (CSRS).