Abstract
To account for nonstationarity, channel characterization and system design methods that employ the non-wide-sense stationary uncorrelated scattering (non-WSSUS) assumption are desirable. Furthermore, the inadequacy of the Doppler shift operator to properly account for the frequency shift in wideband channel implies that the time-frequency characterization methods that employ the Doppler shift operator are not appropriate for most wideband channels. In this article, the statistical time-scale domain characterization of the non-WSSUS wideband channel is presented. This approach employs the time scaling operator in order to account for frequency spreading, and also emphasizes on the nonstationarity of the wideband channel. The non-WSSUS statistical assumption termed local-sense stationary uncorrelated scattering (LSSUS) is presented and employed in characterizing the nonstationary property of the time-varying wideband channel. The LSSUS channel model is then parameterized to provide useful coherence and stationarity/nonstationarity parameters for optimal system design. Some application relevance of the developed model in terms of channel capacity and diversity techniques are discussed. Measurement and simulation results show that the assumption of ergodic capacity and the performance of various diversity techniques depend on the degree of channel stationarity/nonstationarity. It is shown that the quantification of this degree of stationarity through the channel parameters can provide a way of tracking channel variation and allowing for adaptive application of diversity techniques and the channel capacity.
Highlights
Time-varying channels are often modeled as stationary random processes using the concept of the wide-sense stationary uncorrelated scattering (WSSUS) assumption [1]
The assumption of the statistical stationarity of the time-varying channel allows for the definition of some channel parameters that are employed in system designs
(1) How can the time-varying non-WSSUS wideband channel be characterized in the time-scale domain? (2) What are the necessary parameters and information that can be obtained from the non-WSSUS model? (3) How can such information be used in system design in order to optimize performance? To address these questions, we present the non-WSSUS time-scale domain characterization method for time-varying wideband channel which employs the assumption that the channel statistics are locally stationary
Summary
Time-varying channels are often modeled as stationary random processes using the concept of the wide-sense stationary uncorrelated scattering (WSSUS) assumption [1]. We present the non-WSSUS time-scale domain characterization method for time-varying wideband channel which employs the assumption that the channel statistics are locally stationary. This method is considered appropriate for wideband nonstationary channels. A method of characterizing the non-WSSUS wideband channels using a statistical concept termed LSSUS assumption is presented in the time-scale domain. The closed-form expression for the LSSUS channel is derived bearing in mind that the stationarity/nonstationarity interval is dependent on the properties of the transmit signal and the wireless channel We note that this LSSUS closed-form expression can be applied to most channels, but in terms of merit, it is more appropriate for the characterization of the wideband channels like acoustic, sonic, UWB channels, and other emerging systems operating at high fractional bandwidths; in which case the concept of time scaling is more suitable than Doppler shift. One of the popular statistical properties used in channel characterization is the mean and the ACF [1]
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