We consider the problem of multiuser detection for DSCDMA in doubly-selective (timeand frequency-selective) channels, and propose a time-varying multiuser detector (TVMUD) to solve this problem. Using a basis expansion model (BEM) to model the doubly-selective channel and the TVMUD, we derive a closed-form expression for the BEM coefficients of the TV-MUD as a function of the BEM coefficients o...

We propose channel estimation and direct equalization techniques for transmission over doubly selective channels. The doubly selective channel is approximated using the basis expansion model (BEM). Linear and decision feedback equalizers implemented by time-varying finite impulse response (FIR) filtersmay then be used to equalize the doubly selective channel, where the time-varying FIR filters ...

In this paper, we propose a serial equalizer for doubly-selective channels. We use a Basis Expansion Model (BEM) Finite Impulse Response (FIR) to model the doubly-selective channel and to design the serial equalizer. In contrast to our previous works, we decrease the modeling error of the BEM FIR by fitting the BEM FIR to the true doubly-selective channel over a time-window that is independent ...

High data rates give rise to frequency-selective propagation, whereas carrier frequency-offsets and mobility-induced Doppler shifts introduce time-selectivity in wireless links. To mitigate the resulting timeand frequency-selective (or doubly selective) channels, optimal training sequences have been designed only for special cases: pilot symbol assisted modulation (PSAM) for time-selective chan...

This paper considers block transmissions over single-antenna doubly selective channels that obey a complexexponential basis expansion model. We consider the noncoherent case, when the channel fading coefficients are not known at both transmitter and receiver. We characterize the spectral efficiency of the channel when the inputs are chosen from continuous distributions. Then, we study several p...

Most transmission schemes for MIMO channels assume (i) a block fading channel without delay spread and (ii) availability of channel state information at the receiver. Here, we extend the space-time motrir modulation (STMMj scheme and the iterative demodulation algorithm that we introduced previously to unknown, doubly selective MlMO channels, i.e., delayDoppler-spread MlMO channels that are unk...

Orthogonal Frequency Division Multiplexing based on Offset Quadrature Amplitude Modulation (OFDM/OQAM) systems are highly sensitive to Carrier Frequency Offset (CFO), especially in doubly selective fading channels. In this paper, by modeling the doubly selective channel with Basis Expansion Model (BEM), we prove the cyclostationarity of the received OFDM/OQAM signal in the presence of CFO. A bl...

In this paper, we propose a time-varying (TV) finite impulse response (FIR) equalizer for doubly-selective (timeand frequencyselective) channels. We use the basis expansion model (BEM) to approximate the doubly-selective channel and to design the TV FIR equalizer. This structure allows us to turn a large design problem into an equivalent small design problem, containing only the BEM coefficient...

In this paper, a pilot assisted minimum mean square error multiuser channel estimation algorithm is proposed for quasi-synchronous CDMA systems. The doubly selective multiuser fading channel is represented as a time-varying chip-spaced tapped delay line filter with correlated filter taps. The multiuser channel tap coefficients at pilot symbol positions are estimated under the MMSE criterion wit...