Multistage Partial Parallel Interference Cancellation Research Articles

Multi-Stage Partial Parallel Interference Cancellation Algorithm for MUSA Systems

Multi-User Shared Access is a non-orthogonal multiple access scheme of 5G,which has a high computational complexity and a large time delay due to the usage of successive interference cancellation detection algorithm. This paper proposes a multi-stage partial parallel interference cancellation detection algorithm, which does not require repeated ordering and repeated matrix inversion. In the first stage of detection, the bits of these users with good channel conditions will be outputted, and the influence of multiple access interference on users with bad channel conditions in the second stage will be decreased. Theoretical analysis and simulation results show that the symbol error rate of the proposed algorithm is slightly better than that of the two-stage MMSE-PIC, and the complexity is reduced. In the meanwhile, the computational complexity is significantly reduced without SER performance degradation when compared with MMSE-SIC algorithm.

On the Selection of Partial Cancellation Factors for a Two-Stage Hard-Decision PPIC Scheme in DS-CDMA Systems

In this paper, we present a simple method of selecting the partial cancellation factors (PCFs) for a two-stage, hard-decision, partial parallel interference cancellation (PPIC) detector for direct-sequence code-division multiple access (DS-CDMA) systems. Using Price's theorem, we derive a range of the optimal PCF for each PPIC stage in multipath fading environments, where the lower and upper bounds can be explicitly calculated from the processing gain and the number of active users of the DS-CDMA system considered. Computer simulation results show that, using the average of the lower and upper bounds as the PCF for each PPIC stage, the bit error rate (BER) performance closely approximates that of the real optimal PCFs. Moreover, a multistage PPIC detector using the proposed PCFs in the first two stages achieves its BER performance limit with fewer stages. That is, the proposed PCF selection method reduces the complexity of a PPIC detector and provides the same BER performance. This makes the proposed PCFs attractive for use in PPIC receivers in DS-CDMA systems.

PIC receiver implementations for the asynchronous UMTS scenarios

In this paper, three different implementations of a multistage partial parallel interference cancellation (PIC) receiver for the asynchronous UMTS signal are presented and compared. The proposed structures take into account the scrambling and channelization codes employed in UMTS and two of them are advanced structures specifically designed to attempt to remove completely the multiuser interference thanks to the addition of specific data buffers for this scenario. The advanced structures proposed outperform the direct implementation of the PIC receiver derived from synchronous CDMA scenarios by taking into account the whole set of interference terms. Also, no windowing is necessary at the receiver and no framing transmission is required.

Performance and Optimization of Multistage Partial Parallel Interference Cancellation for Wideband CDMA Systems in Multipath Fading Channels

In this paper, a closed-form bit error rate (BER) of hard-decision multistage partial parallel interference cancellation (PPIC) having perfect and imperfect channel estimation for complex spreading code-division multiple access (CDMA) over multipath Rayleigh channels was derived. The effects of receiving BER, power ratio of pilot to data channels, multiple-access interference (MAI) and multipath interference, additive white Gaussian noise, and other factors affecting channel estimation error are analyzed. The expression determining the optimal interference cancellation weight at path level for PPIC is first derived. Then, the oscillatory behavior of user-level-optimized PIC and the convergence of perfect channel estimation PIC and path-level-optimized PIC are validated. Results indicate that all factors determining the optimal weight certainly affect the BER performance of PPIC and that the lower BER limit of multistage PPIC depends on the adjustable factors, which include power ratio, observation length, and signal-to-noise ratio, and an unchangeable factor, i.e., number of users. In addition, the variance of MAI for complex spreading sequence is obtained, and the analytical expression can also be employed to predict the performance of multicode CDMA

Analytical Performance Analysis of the Linear Multistage Partial PIC Receiver for DS-CDMA Systems

In this letter, we derive a recursive expression for the decision statistic of a linear multistage partial parallel interference cancellation (PIC) receiver for direct-sequence code-division multiple-access systems that allow us to present two closed-form expressions (exact and approximate) for the bit-error probability of this receiver. The bit-error rate is computed in terms of the number of PIC stages, set of cancellation parameters, crosscorrelation between the users' codes, amplitude of the users' signals, and noise power.

Fuzzy-based adaptive partial parallel interference canceller for CDMA communication systems over fading channels

The authors propose a fuzzy inference system (FIS) for the multistage partial parallel interference cancellation (PIC) multiuser detectors in a direct-sequence code-division multiple-access (DS-CDMA) communication system. The multistage PIC scheme is an effective method for the multiuser detection in the DS-CDMA systems, but the performance still suffers degradations in the near–far situations. The partial PIC (PPIC), which tries to reduce the cancellation error due to the wrong interference estimations in the earlier stages, outperforms the conventional PIC (CPIC) when the system load is high. In the paper, an adaptive fuzzy inference mechanism is proposed to generate the adequate cancellation weights for the multistage PPIC by using the measured SNR and signals' amplitudes, which reveal the reliability of the received signals. Simulation results show that the proposed fuzzy-based PPIC (FB-PPIC) detector is more robust over the fading channels and is more near–far resistant than both the CPIC and constant weight PPIC (CW-PPIC) schemes.