Interference Cancelation in Non-Coherent CDMA Systems Using Parallel Iterative Algorithms (original) (raw)
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Interference Cancelation in Coherent CDMA Systems Using Parallel Iterative Algorithms
2007
Least mean square-partial parallel interference cancelation (LMS-PPIC) is a partial interference cancelation using adaptive multistage structure in which the normalized least mean square (NLMS) adaptive algorithm is engaged to obtain the cancelation weights. The performance of the NLMS algorithm is mostly dependent to its step-size. A fixed and non-optimized step-size causes the propagation of error from one stage to the
2002
In direct-sequence code-division multiple-access (DS-CDMA) communication systems, the partial cancellation weight (PCW) in the partial parallel interference cancellation (PPIC) multiuser detection scheme does not give us any idea about the correctness of the bit-decision in the previous stage. Therefore, in this study, we investigate the statistical behavior of the adaptation PCW based on the least mean square (LMS) algorithm in which the adaptation PCW of the last chip in a symbol period reveals the information of the correctness of the bit-decision. Then, an adaptive decision-threshold obtained by maximum a posteriori probability (MAP) detection criterion is proposed to judge the correctness of the bit-decision in the previous stage and the bit-inversion (BI) procedure is proposed to invert the incorrect bit-decision. Furthermore, after BI procedure, a full PIC is performed to cancel the multiple access interference (MAI). Simulation results show that the proposed three-stage BI-based full PIC (BI-FPIC) multiuser detector can reach the performance of single-user-bound over flat fading channels under perfect channel estimation.
Performance of a Novel Adaptive Multistage Full Parallel Interference Canceller for CDMA Systems
IEEE Transactions on Vehicular Technology, 2000
In this paper, we investigate the statistical behavior of the adaptation partial cancellation weight (PCW) in partial parallel interference cancellation (PPIC) schemes based on least mean square (LMS) algorithms in which the adaptation PCW of the last chip in a symbol period reveals the information of the correctness of the bit decision for directsequence code-division multiple-access (DS-CDMA) communication systems. We obtained an adaptive decision threshold using a maximum a posteriori probability (MAP) detection criterion for the PCWs to judge the correctness of the bit decision. A bit-inversion procedure is proposed to invert the incorrect bit decisions. After bit inversion, full PIC is performed to cancel multiple-access interference (MAI). Simulation results show that the proposed three-stage LMS-based adaptive full PIC (AFPIC) multiuser detector reaches the performance of a single user bound over flat fading channels. Moreover, the AFPIC detector effectively cancels MAI over a two-path frequency-selective fading channel.
Selective partial parallel interference cancellation for personal CDMA communications
This paper deals with a cancellation multiuser detector for CDMA communication systems. Proposed receiver is supposed to be used at the end of up-link channel, leading to consider multipath fading phenomena. Proposed receiver approach consists in performing a weighted selective cancellation of the co-channel interfering signals, divided in two different groups according to the received power level: signals exceeding a suitable threshold are considered more reliable and, therefore, cancelled with a higher weight. In comparison with previously proposed cancellation receivers described detector shows remarkable improvement of the resistance to multiple access interference and low computational complexity, linear in the number of users.
Joint iterative interference cancellation and parameter estimation for cdma systems
IEEE Communications Letters, 2000
This letter proposes a unified approach to joint iterative parameter estimation and interference cancellation (IC) for uplink CDMA systems in multipath channels. A unified framework is presented in which the IC problem is formulated as an optimization problem of an IC parameter vector for each stage and user. We also propose detectors based on a least-squares (LS) joint optimization method for estimating the linear receiver filter front-end, the IC, and the channel parameters. Simulations for the uplink of a synchronous DS-CDMA system show that the proposed methods significantly outperform the best known IC schemes.
Reduced and differential parallel interference cancellation for CDMA systems
IEEE Journal on Selected Areas in Communications, 2002
Since code division multiple access systems in multipath environments suffer from multiple access interference (MAI), multiuser detection schemes should be used in the receivers. Parallel interference cancellation (PIC) is a promising method to combat MAI due to its relatively low computational complexity and good performance. It is shown that the complexity of PIC is still high for realistic scenarios in
2010
In this study, we propose a least mean square-partial parallel interference cancellation (LMS-PPIC) method named parallel LMS-PPIC (PLMS-PPIC) in which the normalised least mean square (NLMS) adaptive algorithm with optimised chip time-varying step-size is engaged to obtain the cancellation weights. The former LMS-PPIC method is based on fixed not optimised step-size, which causes propagation of error from one stage to the next one and increases the bit error rate (BER). The unit magnitude of the cancellation weights is the principal property in our step-size optimisation. To avoid computational complexity a small set of NLMS algorithms with different step-sizes are executed. In each iteration the parameter estimate of that NLMS algorithm which the elements magnitudes of its cancellation weight estimate have the best match with unit is chosen. Magnificent decrease in BER is achieved by executing the proposed method. Moreover PLMS-PPIC like former LMS-PPIC method comes to practice only when the channel phases are known. When they are unknown, having only their quarters in (0, 2p), we propose modified versions of LMS-PPIC and PLMS-PPIC to find the channel phases and the cancellation weights simultaneously. Simulation scenarios are given to compare the performance of our methods with that of LMS-PPIC in two cases: balanced channel and unbalanced channel. The results show that in both cases the proposed method outperforms LMS-PPIC, especially for high processing gains.
This paper proposes a unified approach to joint adaptive parameter estimation and interference cancellation (IC) for direct sequence code-division-multiple-access (DS-CDMA) systems in multipath channels. A unified framework is presented in which the IC problem is formulated as an optimization problem with extra degrees of freedom of an IC parameter vector for each stage and user. We propose a joint optimization method for estimating the IC parameter vector, the linear receiver filter front-end, and the channel along with minimum mean squared error (MMSE) expressions for the estimators. Based on the proposed joint optimization approach, we derive low-complexity stochastic gradient (SG) algorithms for estimating the desired parameters. Simulation results for the uplink of a synchronous DS-CDMA system show that the proposed methods significantly outperform the best known IC receivers.