A UWB Radio Network Using Multiple Delay Capture Enabled by Time Reversal

An uplink multiple-access method for a centralized ultra-wideband (UWB) radio network is studied. The multiple-access method is based on a phenomenon of multiple delay capture and is enabled by time reversal technique. Multiple delay capture is a random multiple-access method that can be viewed as a time-of-arrival (TOA) division multiple-access. When received signals are of low duty cycle, the chance of collision is low, and the base station is able to communicate with different users simultaneously. At much higher data rate compared to the narrow band scenarios, the delay spread of a UWB channel is relatively large, and the multipath-distorted signal may not be of low duty cycle. To improve the multiple-access efficiency, time reversal in conjunction with transmitter-side antenna array is considered to shorten the UWB channel impulse response (CIR). Time reversal takes advantage of rich scattering environments to achieve signal focusing, while the antenna array further enhances signal focusing. Our focus in this paper will be on evaluating the collision-free probabilities using both analysis and simulation. A lower bound is derived and it is actually a good estimate of the probability that all received signals are collision-free. Finally, quantitative results are provided, showing that the normalized system throughput increases fast as the number of users increases