Joint scale-lag diversity in wideband mobile direct sequence spread spectrum systems

Abstract

Abstract-We consider the effect of mobility on a wideband direct sequence spread spectrum (DSSS) communication system, and study a scale-lag Rake receiver capable of leveraging the diversity that results from mobility. A wideband signal has a large bandwidth-to-center frequency ratio, such that the typical narrowband Doppler spread assumptions do not apply to mobile channels. Instead, we assume a more general temporal scaling phenomenon, i.e., a dilation of the transmitted signal's time support. Based on a uniform ring of scatterers model, we determine that the wideband scattering function, which quantifies the average scale spreading, has a "bathtub-shaped" scale profile. We compare the performances of a scale-lag Rake and a frequency-lag Rake, each capable of leveraging the diversity that results from mobility. Such analysis applies, for example, to ultra-wideband (UWB) radio frequency channels and underwater wideband acoustic channels.Index Terms-Mobile wireless communication, scale-lag diversity, spread spectrum, wideband systems.

Cooperative Communication over Multi-Scale and Multi-Lag Wireless Channels

“…Due to the nature of wideband propagation, such wideband multi-scale and multilag channels exhibit some fundamental differences compared to the so-called narrowband channels. In particular, these multi-scale, multi-lag channel descriptions offer improved modeling of LTV wideband channels over multi-Doppler-shift, multi-lag models [10][11][12]. Orthogonal Frequency Division Multiplexing (OFDM) technology has been introduced and examined for wideband LTV channels.…”

“…For wideband channels, on the other hand, each propagation path experiences a distinct Doppler scale, hence the term, multi-scale, multi-lag channel. For both types of wideband and narrowband time-varying channels, so-called canonical channel models have been proposed [8][9][10][11], limiting the number of channel coefficients required to represent the channel.…”

“…For wideband time-varying channels a canonical model has been proposed in [9][10][11], which is also dubbed as the scale-lag canonical model. This model has been adopted for direct sequence spread spectrum (DSSS) communication systems [11] to develop a scale-lag RAKE receiver to collect the diversity inherent in the multi-scale multi-lag channel.…”

“…For wideband time-varying channels a canonical model has been proposed in [9][10][11], which is also dubbed as the scale-lag canonical model. This model has been adopted for direct sequence spread spectrum (DSSS) communication systems [11] to develop a scale-lag RAKE receiver to collect the diversity inherent in the multi-scale multi-lag channel. In addition, this model has spurred the use of wavelet signaling due to the fact that when the wavelets are "matched" to the scale-lag model, the receiver structure is greatly simplified -the signals corresponding to different scale-lag branches of the model are orthogonal when a single wavelet pulse is transmitted.…”

“…This scale-lag diversity is better described by the wavelet transform than the conventional time-frequency representation for the narrowband linear time-varying (LTV) system, and is so called the wideband LTV representation [10,11]. Wideband LTV representation has been proven and verified for many applications in terms of high data rate wireless communications [14][15][16][17], high-speed underwater acoustic communications [18][19][20], vehicle-to-vehicle (V2V) wideband communication systems [21,22], and radar/sonar systems [23].…”