Abstract
The problem of joint channel estimation, equalization, and multiuser detection for a multiantenna DS/CDMA system operating over a frequency-selective fading channel and adopting long aperiodic spreading codes is considered in this paper. First of all, we present several channel estimation and multiuser data detection schemes suited for multiantenna long-code DS/CDMA systems. Then, a multipass strategy, wherein the data detection and the channel estimation procedures exchange information in a recursive fashion, is introduced and analyzed for the proposed scenario. Remarkably, this strategy provides, at the price of some attendant computational complexity increase, excellent performance even when very short training sequences are transmitted, and thus couples together the conflicting advantages of both trained and blind systems, that is, good performance and no wasted bandwidth, respectively. Space-time coded systems are also considered, and it is shown that the multipass strategy provides excellent results for such systems also. Likewise, it is also shown that excellent performance is achieved also when each user adopts the same spreading code for all of its transmit antennas. The validity of the proposed procedure is corroborated by both simulation results and analytical findings. In particular, it is shown that adopting the multipass strategy results in a remarkable reduction of the channel estimation mean-square error and of the optimal length of the training sequence.
Highlights
Direct-sequence code-division multiple-access (DS/CDMA) techniques are of considerable interest, since they are among the basic technologies for the realization of the air interface of current and future wireless networks [1]
Even though the use of long codes ensures that all the users achieve “on the average” the same performance in a frequency-flat channel with perfect power control, it destroys the bit-interval cyclostationarity properties of the CDMA signals and renders ineffective many of the advanced signal processing techniques that have been developed for blind multiuser detection and adaptive channel estimation in short-code CDMA systems [2, 3]
In this paper the issue of joint channel estimation and multiuser detection for long-code multiple-input multipleoutput (MIMO) DS/CDMA systems operating on frequency-selective channels has been considered
Summary
Direct-sequence code-division multiple-access (DS/CDMA) techniques are of considerable interest, since they are among the basic technologies for the realization of the air interface of current and future wireless networks [1]. Denote by Cnk,tp the following 2NM × (N + 1)Mdimensional matrix, containing properly shifted versions of the kth user spreading code adopted in the pth symbol interval on the ntth transmit antenna:. The above representation, which extends to the multipleantenna scenario the one developed in [8] for single-antenna systems, is extremely powerful; from (11) it is seen that even though aperiodic long codes changing at each symbol interval are adopted, and even though the propagation delay and the channel impulse response are not known, the discrete-time signatures may be deemed as the product of a time-varying, but known, matrix, containing properly shifted versions of the spreading codes, times an unknown, but timeinvariant, vector, which carries information on the channel impulse response and timing offset. Based on the representation in (11), our actual goal is to provide an estimation algorithm for the channel vectors gknt,nr
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