Partial Parallel Interference Cancellation Research Articles

Analysis of Multiuser Detectors and Performance improvement in DS-CDMA system using Multistage Multiuser Detection Techniques

The Direct Sequence Code Division Multiple Access (DS-CDMA) system faces several disruptions, this is most crucial of which is the Multi Access Interference (MAI) caused by its users. The efficiency of the system gradually declines as every quantity rises, and the MAI rises, especially in faded environments. This work proposes a multiple-phase multiuser identification approach called Differencing Partial Parallel Interference Cancellation (DPPIC), which improves the overall efficiency. The methods known as Differencing Parallel Interference Cancellation (DPIC) and Partial Parallel Interference Cancellation (PPIC) are combined in this methodology. Current solutions for Parallel Interference Cancellation (PIC) and PPIC have enhanced overall effectiveness; however, this has come at the expense of increasing the complexity of computation. As the variety of consecutive stages grows, the MAI falls. Using the DPIC approach may reduce the computational burden without improving system functionality. The use of the Partial Differencing Parallel Interference Cancellation (PDPIC) technique can enhance system performance while lowering the level of complexity. According to the simulation findings, Bit Error Rate (BER) vs normalized signal strength (i.e., Eb / N0) performs more effectively for the suggested DPPIC approach than for PIC, the PPIC, and PDPIC.

Generalized Receiver with Parallel Interference Cancellation for Multiuser Detection

Parallel interference cancellation is considered as a simple yet effective multiuser detector for direct -sequence code-division multiple-access (DS-CDMA) systems. However, system performance be deteriorated due to unreliable interference cancellation in the early stages. Thus, a detector with the partial parallel interfere-nce cancellation in which the partial cancellation factors are introduced to control the interference cancellation level has been developed as a remedy. Although the partial cancellation factors are crucial, complete solutions for their optimal values are not available. In this paper, we consider a two-stage decoupled generalized receiver with the partial parallel interference cancellation. Using the minimum bit error rate (BER) criterion, we derive a complete set of optimal partial cancellation factors. This includes the optimal partial cancellation factors for pe-riodic and aperiodic spreading codes in channels with the additive white Gaussian noise and multipath chann-els. Simulation results demonstrate that the considered theoretical optimal partial cancellation factors agree clo-sely with empirical ones. The proposed two-stage generalized receiver with the partial parallel interference can-cellation using the derived optimal partial cancellation factors outperforms not only a two-stage, but also a three-stage conventional generalized receiver with the full parallel interference cancellation.

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.

Interference and Complexity Reduction in Multi-stage Multi-user Detection in DS-CDMA

Multi-stage parallel interference cancellation (PIC) technique gives good performance compared to successive interference cancellation (SIC) method, but biased decision statistic and complexity problems are raised due to imperfect estimation of multiple access interference (MAI) as number of stages increases. partial parallel interference cancellation (PPIC) technique is proposed to cancel the interference partially stage by stage to overcome biased problem. The complexity reduction for PIC detection is based on the convergence nature of interference cancellation which is called the difference PIC (D-PIC) detection technique. In this paper we combine (PPIC and DPIC) these two techniques and propose a multi-stage multi-user (PD-PIC) detector for performance improvement and complexity reduction compared to conventional PIC detector. The performance is degraded as the number of users increases in each technique.

Partial PIC-MRC Receiver Design for Single Carrier Block Transmission System over Multipath Fading Channels

Single carrier block transmission (SCBT) system has become one of the most popular modulation systems due to its low peak-to-average power ratio (PAPR), and it is gradually considered to be used for uplink wireless communication systems. In this paper, a low complexity partial parallel interference cancellation (PIC) with maximum ratio combining (MRC) technology is proposed to use for receiver to combat the intersymbol interference (ISI) problem over multipath fading channel. With the aid of MRC scheme, the proposed partial PIC technique can effectively perform the interference cancellation and acquire the benefit of time diversity gain. Finally, the proposed system can be extended to use for multiple antenna systems to provide excellent performance. Simulation results reveal that the proposed low complexity partial PIC-MRC SIMO system can provide robust performance and outperform the conventional PIC and the iterative frequency domain decision feedback equalizer (FD-DFE) systems over multipath fading channel environment.

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.

EFFECT OF IMPERFECT POWER CONTROL ON PARALLEL INTERFERENCE CANCELLATION FOR CDMA

This paper presents a study of the effect of imperfect power control on the performance of a Partial Parallel Interference Cancellation (PPIC) multiuser receiver. We show that the PPIC receiver can absorb the effect of imperfect power control to a great extent compared with other types of receivers. Additionally, the effect of imperfect power control on the optimum weights of the PPIC receiver is considered. It is found that imperfect power control causes the receiver to become more susceptible to performance degradation as a result of deviation from optimal weights.

A Detection Algorithm Combined Frequency Domain Equalization with Partial Parallel Interference Cancellation Based on Energy-Ordering

针对频率选择性信道下的DS-CDMA系统,该文提出了一种联合MMSE(最小均方误差)频域均衡与基于能量排序的部分并行干扰删除(MMSE-EOPPIC)的多用户检测算法。该算法首先采用基于重叠剪切法的MMSE频域均衡代替Rake接收机对各用户的数据信息进行初始估计,然后在干扰删除的每个迭代级根据用户能量由强到弱的顺序依次对用户进行部分干扰删除;为了提高每个迭代级检测的可靠性,该文将当前级已经检测出的能量较强用户的硬判决值用于重构当前级能量较弱用户的多址干扰(MAI)。仿真结果表明MMSE-EOPPIC检测算法可以有效提高系统的比特误码率性能。

Signal Processing by Generalized Receiver in DS-CDMA Wireless Communication Systems with Optimal Combining and Partial Cancellation

Symbol error rate (SER) of quadrature subbranch hybrid selection/maximal-ratio combining (HS/MRC) scheme for 1-D modulations in Rayleigh fading under employment of the generalized receiver (GR), which is constructed based on the generalized approach to signal processing (GASP) in noise, is investigated. diversity input branches are split into in-phase and quadrature subbranches. -ary pulse amplitude modulation, including coherent binary phase-shift keying (BPSK), with quadrature subbranch HS/MRC is investigated. GR SER performance for quadrature HS/MRC and HS/MRC schemes is investigated and compared with the conventional HS/MRC receiver. Comparison shows that the GR with quadrature subbranch HS/MRC and HS/MRC schemes outperforms the traditional HS/MRC receiver. Procedure of partial cancellation factor (PCF) selection for the first stage of hard-decision partial parallel interference cancellation (PPIC) using GR employed by direct-sequence code-division multiple access (DS-CDMA) systems under multipath fading channel in the case of periodic code scenario is proposed. Optimal PCF range is derived based on Price's theorem. Simulation confirms that the bit error rate (BER) performance is very close to potentially achieved one and surpasses the BER performance of real PCF for DS-CDMA systems discussed in the literature.

Signal Processing by Generalized Receiver in DS-CDMA Wireless Communication Systems with Frequency-Selective Channels

The generalized receiver (GR) based on a generalized approach to signal processing (GASP) in noise is investigated in a direct-sequence code-division multiple access (DS-CDMA) wireless communication system with frequency-selective channels. We consider four avenues: linear equalization with finite impulse response (FIR) beamforming filters; channel estimation and spatially correlation; optimal combining; and partial cancellation. We investigate the GR with simple linear equalization and FIR beamforming filters. Numerical results and simulation show that the GR with FIR beamforming filters surpasses in performance the optimum infinite impulse response beamforming filters with conventional receivers, and can closely approach the performance of GR with infinite impulse response beamforming filters. Channel estimation errors are taken into consideration so that DS-CDMA wireless communication system performance will not be degraded under practical channel estimation. GR takes an estimation error of a maximum likelihood (ML) multiple-input multiple-output (MIMO) channel estimation and GR spatially correlation into account in computation of minimum mean square error (MMSE) and log-likelihood ratio (LLR) of each coded bit. The symbol error rate (SER) performance of DS-CDMA employing GR with a quadrature sub-branch hybrid selection/maximal-ratio combining (HS/MRC) scheme for 1-D modulations in Rayleigh fading is obtained and compared with that of conventional HS/MRC receivers. Procedure of selecting a partial cancelation factor (PCF) for the first stage of a hard-decision partial parallel interference cancellation (PPIC) of the GR employed in DS-CDMA wireless communication system is proposed. A range of optimal PCFs is derived based on the Price’s theorem. Computer simulation results show superiority in bit error rate (BER) performance that is very close to that potentially achieved and surpasses the BER performance of the real PCF for DS-CDMA systems discussed in literature.

Adaptive parallel interference cancellation for CDMA systems—A weight selection and filtering scheme

Parallel interference cancellation (PIC) is a well-known multiuser detection algorithm in direct-sequence code-division multiple-access (DS-CDMA) systems. It is typically implemented with a multi-stage architecture. One problem associated with the PIC is that unreliable interference cancellation may occur in the early stages and the system performance may be degraded. Thus, the partial PIC detector was developed to control the cancellation level by use of interference cancellation factors. Partial PIC can be implemented with an adaptive form, in which optimal weights are derived using the least mean square (LMS) algorithm. In this paper, we propose an algorithm improving the conventional adaptive partial PIC. The main idea is to reduce the number of active weights in the LMS algorithm, and to perform weight post-filtering such that the resultant excess mean square error can be reduced. We also analyze the performance of the proposed algorithm and derive the bit error rate of the second stage output. Simulation results verify that the proposed algorithm outperforms the conventional partial PIC, and derived analytical results are accurate.

Variance-reduced partial parallel interference cancellation for MC-CDMA uplink systems

In this paper, we present an improved version of partial parallel interference cancellation (PPIC), called variancereduced PPIC (VRPPIC), for multicarrier code division multiple access uplink systems. The VRPPIC detector is a combination of the PPIC receiver and a new bit estimator, where a simplified realization is derived for the main PPIC operations and soft decisions from PPIC are linearly combined by the bit estimator using appropriate weighting factors (derived from the PPIC weighting factors) to reduce the conditional variance of the final signal estimate. Also, we derive an optimal weighting factor (OWF) selection algorithm for VRPPIC based on minimizing a monotonically increasing conditional variance function. The derived OWFs for all the interference cancellation stages are equal and can easily be obtained from a linear function of the number of active users. Simulation results show that VRPPIC with the proposed OWFs significantly outperforms VRPPIC (or PPIC) with randomly selected weighting factors in multipath Rayleigh fading channels.

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 of a Novel Adaptive Multistage Full Parallel Interference Canceller for CDMA Systems

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 direct-sequence 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.

Performance analysis of an adaptive two-stage PIC CDMA receiver in AWGN channels

Parallel interference cancellation (PIC) is considered a simple yet effective multiuser detector for direct-sequence code-division multiple-access (DS-CDMA) systems. However, its performance may deteriorate due to unreliable interference cancellation in the early stages. Thus, a partial PIC detector, in which partial cancellation factors (PCFs) are introduced to control the interference cancellation level, has been developed as a remedy. Recently, an interesting adaptive multistage PIC algorithm was proposed. In this scheme, coefficients combining the channel responses and optimal PCFs are blindly trained with the least mean square (LMS) algorithm. The algorithm is simple to implement, inherently applicable to time-varying environments, and superior to the non-adaptive type of partial PICs. Despite its various advantages, its performance has not been theoretically analyzed yet. The contribution of this paper is to fill the gap by analyzing an adaptive two-stage PIC in AWGN channels. We explicitly derive the analytical results for optimal weights, weight-error means, and weight-error variances. Based on these results, we finally derive the output bit error rate (BER) for each user. Simulation results indicate that our analytical results highly agree with empirical ones.

Suboptimal Search Algorithm in Conjunction With Polynomial-Expanded Linear Multiuser Detector for FDD WCDMA Mobile Uplink

A suboptimum search algorithm that considers the users' power profile in conjunction with a primary stage of polynomial-expanded (PE) linear multiuser detector for mobile uplink is proposed to suppress interference level. The initial stage is improved by mathematical analysis using two new ideas based on the Rayleigh-Ritz and Gershgorin theorems for both synchronous and asynchronous users. The performance of the PE structure is further enhanced by a new suboptimum search algorithm as the second stage. The structure of the search algorithm is based on starting from a point close to the optimum search and performing sequential steps to modify it. The proposed structures of the PE method and the suboptimum search algorithm are well suited together and make them collaboratively work without encountering a high level of complexity, since they use similar information as the correlation matrix. The power profile of the users is also considered in the suboptimum search algorithm, which led to more than a 50% reduction of the complexity, while keeping the performance almost the same. The performance of the final structure is carried out by means of computer simulations, and it has been compared to a partial parallel interference cancellation method with optimized partial coefficients. One of the main features of the structure proposed in this paper is that it performs its operations on the canonical formulation of the system, which makes it highly suitable for a broad range of systems such as multicarrier code division multiple access and multiinput multioutput.

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

In this letter, we present a simple method of selecting the partial cancellation factor (PCF) for the first stage of a hard-decision partial parallel interference cancellation detector for direct-sequence code-division multiple access (DS-CDMA) systems. Using Price's theorem, we derive a range of the optimal PCF, where the lower and upper boundary values can be explicitly calculated from the processing gain and the number of users of the DS-CDMA system. Computer simulation results show that, using the average of these two boundary values as the PCF for the first stage, the bit error rate performance closely approximates that of the real optimal PCF.

Efficient statistical parallel interference cancellation for DS-CDMA in Rayleigh fading channels

We present a reduced-complexity parallel interference cancellation (PIC) technique, in which PIC is performed only on "unreliable" bits (blocks). We term our technique statistical PIC (STPIC), since the decision to employ PIC for any user signal is based upon received signal statistics. Here we propose two different methods: one is bitwise (instantaneous) STPIC (ISTPIC), in which IC is performed only on the bits whose absolute log likelihood ratio (LLR) is below a pre-selected threshold; the other method is block STPIC (BSTPIC), in which IC is performed only on the blocks whose average signal-to-noise-plus-interference ratio (SNIR) is below a pre-selected threshold. Both LLR and SNIR statistics reduce to quantities simple to obtain. We show that STPIC can achieve performance equivalent to conventional full PIC (FPIC) and other partial PIC techniques in flat Rayleigh fading channels, but with reduced computational complexity. We also show our proposed ISTPIC can achieve performance better than FPIC in good channel conditions (e.g., AWGN), still with reduced computational complexity. The ISTPIC performance gain over conventional FPIC is larger in conditions of larger loading factor where efficient IC techniques are more likely to be needed

Improved partial parallel multistage detection for V-BLAST systems

An improved partial parallel interference cancellation (PIC) detection method for V-BLAST is proposed. During every PIC stage, the substreams are detected in an ascending order of error performance from the previous stage to mitigate error propagation caused by the wrong cancellations. Simulation results are presented to show the performance improvements.

Fuzzy adaptive partial parallel multistage detection for MIMO systems

Vertical Bell Laboratories Layered Space-Time (V-BLAST) detection followed by a full parallel interference cancellation (full PIC) or a constant-weight partial parallel interference cancellation (CW-PPIC) scheme has been proposed. However, its performance degrades when the received power of the antenna is unbalanced and/or the system is heavily loaded. Therefore, V-BLAST is proposed, followed by fuzzy adaptive partial parallel multistage detection for MIMO systems. The simulation results show that the error probability of this proposed method is better than that of V-BLAST followed by full PIC or CW-PPIC schemes.