| Uplink multiple access capability of an ultra-wideband (UWB) network is studied. The multiple access method is based on a phenomenon of multiple delay capture [1] and enabled by time reversal (TiR) technique. Multiple delay capture is an efficient random multiple access method that can be viewed as a time-of-arrival division multiple access with low chance of signal collision. Obviously, the key to this multiple access is to effectively separate the signals arriving at different time within a given time frame. Multipath could prevent the arrived signals from being separated. DS/SS is typically bound with multiple delay capture, where spreading/de-spreading processing actually helps separate the signals at the base station. However, this type of multiple access would not function well in severe multipath environments because of high probability of collision.
The UWB signaling is typically of low duty cycle, but at much higher data rates compared to the narrow band scenarios, the UWB multipath is relatively severer. In this paper a multiple input single output (MISO) TiR technique is considered to shorten the UWB channel impulse response (CIR). TiR takes advantage of rich scattering environments to achieve signal focusing both temporally and spatially. A pre-filter whose impulse response is time reversed version of the CIR is placed at the transmitter, resulting in an equivalent CIR with sharp profile. Furthermore, signal focusing can be enhanced by using MISO at the transmitter.
With MISO TiR, a resulted waveform observed at the base station contains very low-duty-cycle main lobes and low side lobes, which is in favor of multiple delay capture. Probability of main lobe collision will be analyzed and indoor measurement data will be used to generate results.
References
[1] D. Davis and S.A. Gronemeyer, “Performance of slotted ALOHA random access with delay capture and randomized time of arrival,” IEEE Trans. Commun., vol. COM-28, pp. 703–710, May 1980. |
| R&D Engineer II, The Center for Manufacturing Research, TTU, TN.
Received the MS in 1990 and the Ph.D. in 1996, all in EE.
Research area: wireless communications
Recent work: UWB transceiver, time reversal, millimeter-wave radio. |