Iterative Joint Channel Estimation and Multiuser Detection for DS-CDMA in Frequency-Selective Fading Channels

Abstract

Abstract-An iterative joint channel estimation, symbol detection, phase recovery and interference cancellation structure is proposed for asynchronous code-division multiple-access systems over frequency-selective fading channels. Based on the expectation maximization (EM) algorithm, a recursive channel estimator is developed for blind channel tracking, using a novel stochastic signal processing technique. To perform symbol detection given the phase ambiguities of the resultant EM channel estimates, a noncoherent scheme is developed to compute the a posteriori probabilities (APPs) of data symbols. Moreover, by incorporating the APPs into the proposed recursive channel estimator, phase ambiguity due to the EM channel estimation can be resolved, which enables soft multiple access interference cancellation for multiuser detection. Based on these new signal processing schemes, an iterative structure is proposed for joint channel estimation and multiuser detection over fast fading channels.

LEO Satellite-Enabled Grant-Free Random Access with MIMO-OTFS

“…Additionally, the phase ambiguity problem [4] inevitably arises in ( 9) since both channel and information symbols are unknown in the receiver. Common methods for combating this problem include differential coding or asymmetric constellation [14]. In this work, we adopt the latter approach.…”

“…), (14) where ← − p l,u,l ′ m,i,j is initialized as 1/|A| and updated later. Then, given the conditional PDF of h l,u,l ′ i,j in (7), the message from check nodes e l to variable nodes S is the Bernoulli distribution given by…”

Multiple access interference suppression for CDMA systems via ℓ∞-minimization

“…Many existing robust multiuser detection techniques are based on the MOE criterion [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] . They belong to the class of second-order statistics methods.…”

“…Clearly, the channel estimation accuracy dominates the performance of the detector. However, the blind channel identification [5] , [11] , [12] , [13] requires a large number of samples and a high signal-to-noise ratio (SNR). Moreover, there exists an inherent sign ambiguity for the existing blind channel estimation techniques, which constitutes another limitation of this method.…”