Parallel Interference Cancellation Technique 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.

Unsourced Random Access Over Fading Channels via Data Repetition, Permutation, and Scrambling

We focus on an unsourced random access (URA) system for communication over fading channels where the payload of each packet is encoded for error-correction, repeated, permuted, and scrambled. Each packet is also equipped with a preamble that is used for channel estimation and detection of permutation and scrambling sequences utilized for payload encoding. We propose an algorithm to resolve multiple-access preamble transmission, based on the approximate message-passing (AMP), that is capable to support high numbers of active users and achieve low probabilities of miss-detection. We also develop a parallel interference cancellation technique for payload reception that iteratively refines the channel estimates and attempts to minimize the mean squared error (MSE) of the users’ data via selective error-correction decoding. Finally, we derive a detailed system performance analysis that closely matches the obtained numerical results. We demonstrate that the presented system can more than double the number of active users, supported by the state-of-the-art systems. Large gains in terms of the minimal required signal-to-noise ratios (SNR)s are also demonstrated for a wide range of active user numbers.

Semi‐blind MIMO‐OFDM channel estimation using expectation maximisation like techniques

This study deals with semi-blind (SB) channel estimation of multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system using maximum likelihood (ML) technique. For the ML cost optimisation function, new expectation maximisation (EM) algorithms for the channel taps estimation are introduced. Different approximation/simplification approaches are proposed for the algorithm's computational cost reduction. The first approach consists of decomposing the MIMO-OFDM system into parallel multiple-input single-output OFDM systems. The EM algorithm is then applied to estimate the MIMO channel in a parallel way. The second approach takes advantage of the SB context to reduce the EM cost from exponential to linear complexity by reducing the size of the search space. Finally, the last proposed approach uses a parallel interference cancellation technique to decompose the MIMO-OFDM system into several single-input multiple-output OFDM systems. The latter are identified in a parallel scheme and with a reduced complexity. The performance of the proposed approaches are discussed, assessed through numerical experiments and compared with respect to the Cramer Rao Bound and to other EM-based solutions reported in the literature.

MAI Mitigation Using V-BLAST and PIC Based Binary Orthogonal Code Spreaded Multi Antenna MC-CDMA System

In this paper, the reduction of Multiple Access Interference (MAI) in Multi Carrier-Code Division Multiple Access (MC-CDMA) uplink system is analyzed. Simultaneous access over channels by numerous users results in MAI which leads to high Bit Error Rate (BER). Therefore the data received at the receiver is intended to numerous users. As a result, it is necessary to separate the data corresponding to different users efficiently. So in this paper, the Vertical-BELL Laboratories Layered Space-Time (V-BLAST) algorithm with Parallel Interference Cancellation (PIC) technique based MC-CDMA system is proposed. Due to the combination of V-BLAST and PIC in MC-CDMA system the MAI is reduced to a certain extent, which is shown in simulation result. Further the system performance is analyzed using Binary Orthogonal Codes (BOC) as spreading sequence. The result shows that Binary Orthogonal Coded V-BLAST and PIC based System provide better performance than conventional spreading sequence like Walsh Hadamard and Pseudorandom Noise (PN) sequence.

IJARCCE - Computer and Communication Engineering

Orthogonal frequency division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies and developed as a popular scheme for 4G mobile communications. Inter-carrier interference (ICI) is a big challenge for OFDM systems while trying to utilize the full spectrum with zero cyclic prefix. It has been investigated that the ICI in OFDM is almost like the co-channel interference in CDMA and the techniques used there to reduce the interference can be used in OFDM also .The techniques are frequency domain equalizers like Operator perturbation Techniques (OPT) and Serial interference cancellation (SIC) and Parallel interference cancellation technique (PIC) along with Gauss Seidel iterative reduction technique. The aim of this paper is to study the OFDM systems suffering from ICI, due to large Doppler shift associated with high velocity of receiver. The main impact of ICI in an OFDM system is to destroy the orthogonality between subcarrier leads to the introduction of off-diagonal element in the channel matrix, making the traditionally considered diagonal channel matrix inaccurate and increasing the complexity of channel estimation and equalization .In this paper iterative cancellation methods have been studied and compared as they require the inversion of only a small portion of original full matrix and thus the complexity is reduced

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.

Performance and capacity analysis of Poisson photon-counting based Iter-PIC OCDMA systems

In this paper, an iterative parallel interference cancellation (Iter-PIC) technique is developed for optical code-division multiple-access (OCDMA) systems relying on shot-noise limited Poisson photon-counting reception. The novel semi-analytical tool of extrinsic information transfer (EXIT) charts is used for analysing both the bit error rate (BER) performance as well as the channel capacity of these systems and the results are verified by Monte Carlo simulations. The proposed Iter-PIC OCDMA system is capable of achieving two orders of magnitude BER improvements and a 0.1 nats of capacity improvement over the conventional chip-level OCDMA systems at a coding rate of 1/10.

A Projected Parallel Interference Cancellation for Asynchronous Upstream OCDMA-PON

OCDMA is a promising candidate for next generation passive optical networks (NG-PON). OCDMA-PON can potentially provide all customers with a Gb/s-class BW upstream with inherent flexibility. Unfortunately OCDMA suffers from multiple access interference (MAI) and various detection noises. To mitigate MAI, we propose a novel parallel interference cancellation technique for incoherent DS-OCDMA that better exploits the non-negativity of the solution. The proposed PIC scheme incorporates this additional information into its structure. The proposed PIC detector is shown to outperform the conventional correlator detector, the decorrelator detector, the linear parallel interference Cancellation (LPIC) detector and even the linear minimum mean square error (LMMSE) detector.

A novel code-based iterative PIC scheme for multirate CI/MC-CDMA communication

This paper introduces a novel code-based iterative parallel interference cancellation technique (Code-PIC) for the multirate carrier interferometry/multicarrier code division multiple-access (CI/MC-CDMA) system, which supports simultaneous transmission of high and low data rate users. In Code-PIC scheme, multiple-access interference (MAI) for the desired user is estimated based on the projection of subcarrier and subsequent removal of interference from the received signal depending on specific high or low data rate users. Carrier interferometry (CI) codes are used to minimize the cross-correlation between users, which significantly reduces the multiple-access interference (MAI) for the desired user. The effect of MAI in CI/MC-CDMA is reduced by giving proper phase shift to different set of users. Improved estimation of MAI in Code-PIC results in lower residual interference after interference cancellation. Simulation results show that Code-PIC scheme offers improved BER performance over AWGN and Rayleigh fading channels compared to Block-PIC and Sub-PIC with reduced latency and complexity.

Time Reversal Receivers for High Data Rate Acoustic Multiple-Input–Multiple-Output Communication

A low-complexity receiver is proposed for high-frequency underwater acoustic multiple-input-multiple-output (MIMO) channels. The receiver uses time reversal combining followed by a single-channel decision feedback equalizer (DFE) to deal with the intersymbol interference. Periodical MIMO channel estimation is employed to track fast channel fluctuations. Both serial and parallel interference cancellation techniques are integrated with time reversal DFE to address the cochannel interference (CoI) in underwater MIMO systems. Two channel estimation algorithms are also implemented. It was demonstrated through the experiment conducted at Kauai, HI in 2005 that the proposed receiver can deal with the fast-fluctuating, dispersive MIMO channel at the carrier frequency of 37.5 kHz. Parallel interference cancellation combined with matching pursuit channel estimation was shown to provide significant performance improvements, indicating the receiver algorithm can effectively suppress the CoI. Four streams of binary phase-shift keying (BPSK) sequences at an aggregate rate of 16 kb/s and quadrature phase-shift keying (QPSK) sequences at a rate of 32 kb/s were demodulated at low bit error rates. These data rates corresponded to bandwidth efficiencies of 2.29 b/s/Hz or 4.57 b/s/Hz in a dynamic underwater environment, where the source and the receiver were drifting at a 2-km range.

A novel technique to increase the capacity of code division multiple access system using scrambled spreading sequences

A multistage Linear Parallel Interference Cancellation (LPIC) approach is presented to mitigate the effect of multiuser interference in uplink Direct Sequence Code Division Multiple Access (DS CDMA) system. The system is overloaded to accommodate more number of users than the processing gain of the system. The performance of this overloading scheme is evaluated by assigning one set of orthogonal Gold codes to the first N users and another set of orthogonal Gold codes to extra users. Both the sets are overlaid by a common pseudo noise scrambling sequence. This paper proposes a novel technique of using Weighted Linear Parallel Interference Cancellation (WLPIC) for overloaded CDMA system resulting in bandwidth saving, better performance and increase in the speed of interference cancellation. Also this technique considerably reduces the multipleaccess interference, since set-1 users suffer from interference of the set-2 users only, while the set-2 users suffer from interference of the set-1 users. This provides a way for accommodating additional users in the same available bandwidth. Considerable conservation of time is achieved by avoiding the usage of conventional successive Interference Cancellation (IC) for scrambled CDMA system. The empirical results show that this scheme provides 50% overloading with three-stage weighted linear parallel interference cancellation (WLPIC) technique for N = 64 at a Bit Error Rate (BER) of 10-3 and 75% overloading at a BER of 10-2. The three-stage WLPIC scheme clearly outperforms matched filter detector, Conventional LPIC and the twostage WLPIC on Additive White Gaussian Noise (AWGN) channel.

Efficient Detection Algorithms for MIMO Communication Systems

In this paper, two new efficient detection algorithms, Type 1 (T1) with better complexity-performance tradeoff and Type 2 (T2) with lower complexity, are derived from one generalized framework for multiple-input multiple-output (MIMO) communication systems. The proposed generalized detection framework constructed by parallel interference cancellation (PIC), group, and iteration techniques provides three parameters and three sub-algorithms to generate two efficient detection algorithms and conventional BLAST-ordered decision feedback (BODF), grouped, iterative, and B-Chase detection algorithms. Since the group interference suppression (GIS) technique is applied to the proposed detection algorithms, the complexities of the preprocessing (PP) and tree search (TS) can be reduced. In (8,8) system with uncoded 16-QAM inputs, one example of the T1 algorithm can save complexity by 21.2% at the penalty of 0.6 dB loss compared with the B-Chase detector. The T2 algorithm not only reduces complexity by 21.9% but also outperforms the BODF algorithm by 3.1 dB.

OCDMA System with Interference Cancellation Research using Group Information Codes

A parallel interference cancellation technique using reference signal for optical code division multiple access (OCDMA) system is proposed. In the proposed system, we use the code sequences, which is composed of the group information and the selected MPC/OOC code sequences. With the help of the fiber Bragg gratings (FBGs) encoder, we estimate the multiple access interference (MAI) by the group information codes. This new cancellation technique can be realized with simple structure. Considering the effects of the MAI, avalanche photodiode (APD) noise, and thermal noise, we analyze the performance of the proposed MPC/OOC system. The results show that this parallel interference cancellation technique can eliminate the MAI efficiently, improve the bit error probability (BER) performance, and increase the simultaneous users in the system.

Generalized Parallel Interference Cancellation With Near-Optimal Detection Performance

The maximum-likelihood detection (MLD) algorithm is the optimal detection scheme for vertical Bell Laboratories layered space-time (V-BLAST) systems. However, it is generally infeasible to implement the MLD algorithm in practical systems because of its high computational complexity. In this paper, we used two parallel interference cancellation techniques, including precancellation and postcancellation, to simplify the MLD algorithm into a class of computationally efficient suboptimal detection algorithms, herein called the generalized parallel interference cancellation (GPIC) algorithm. Numerical analysis shows that the GPIC algorithm can approximately achieve the MLD performance with considerably low and stable computational complexity. Furthermore, it can be significantly accelerated via parallel processing methods. With near-optimal performance, low and stable complexity, and high running speed, the GPIC algorithm is very suitable for real-time communication systems.

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

Simple Interference Cancellation Technique for Multicarrier DS-CDMA

In this article, we propose a new scheme for multi user detection (MUD) using the parallel interference cancellation (PIC) technique. This technique provides a good complexity, latency, and performance compromise. Among spread-spectrum techniques, the most popular one is the direct sequence-code division multiple access (DS-CDMA), where each active user’s data is modulated (multiplied) by a unique code. This technique is suitable for multicarrier (MC) direct sequence-code division multiple access (DS-CDMA) systems. We offer a new scheme of soft detectors whose performance is superior to that of the other famous suboptimal detectors. On each sub carrier, instead of making hard bit decisions of the other users in the current stage and regenerating and cancelling the interference signal, a weighted sum of the soft outputs of the other users in the current stage is cancelled from the soft output of the desired user. This is the input to the next stage, then at the last stage, the interference cancelled outputs from all the subcarriers are combined (maximal ratio combining) to form the decision statistics. We derived expressions for the bit error rate (BER) on Rayleigh fading channels. Analytical results are found for different stages in the proposed PIC scheme. The simulation results show that the proposed scheme offers good interference cancellation than the other filter receiver. The complexity of this scheme grows linearly with the number of users. Moreover, this scheme is much faster than other receivers such as successive interference cancellation (SIC).

DS-OCDMA receivers based on parallel interference cancellation and hard limiters

In an incoherent direct-sequence optical code-division multiple-access (DS-OCDMA) system, multiple-access interference (MAI) is one of the principal limitations. To mitigate MAI, the parallel interference cancellation (PIC) technique can be used to remove nondesired users' contribution. In this paper, we study four DS-OCDMA receivers based on the PIC technique with hard limiters placed before the nondesired users or before the desired user receiver, or both. We develop, for the ideal synchronous case, the theoretical upper bound of the error probability for the four receivers. Significant performance improvement is obtained by comparison with conventional receivers in the case of optical orthogonal codes. The paper highlights that the number of active users with null error probability is doubled, compared with conventional receivers. Finally, we show that, thanks to their good performances, the PIC structures permit considerably reducing the minimal code length required to have 30 users with bit-error rate <10 -9. So, the hardware constraints are relaxed for realistic application

Parallel multiple access interference cancellation in optical DS-CDMA systems

This paper investigates the Parallel Interference Cancellation technique in Direct Sequence Optical Code Division Multiple Access (ds-ocdma) system. In the proposed system, the estimated interference is removed from the received signal. We have developped a new approach to obtain the analytical expression of error probability in chip synchronous case, for Optical Orthogonal Codes (ooc). We have shown that under specific conditions between codes parameters and users’ number, the interference can be completely neutralized. Simulation results have validated the theoretical analysis. It is shown that the proposed receiver is effective in reducing significantly the effects of Multiple Access Interference (mai) compared to other interference cancellation systems.

Multiuser Detection of DS-CDMA Signals Using Partial Parallel Interference Cancellation in Satellite Communications

Multiuser detection (MUD) using parallel interference cancellation (PIC) technique provides a good complexity, latency, and performance compromise. This technique is suitable for satellite systems using either code-division multiple-access (CDMA) or a combination of time-division multiple-access (TDMA) and CDMA. We offer a new scheme that is a combination of soft and hard PIC detectors whose performance is superior to that of the other famous suboptimal detectors. In soft partial parallel interference cancellation (PPIC), in the first few stages, when the performance is still poor, the accurate knowledge of power and phase cannot be of much use. However, in the following stages, accurate power and phase estimation can improve the performance. This coincides with the time when the decisions are reliable enough to be used for parameter estimation. In our scheme, after a few stages of soft interference cancellation (IC), estimation of the parameters will start. Having these estimates, in the subsequent stages hard IC is performed. The complexity of this scheme grows linearly with the number of users. Moreover, this scheme is much faster than other receivers such as successive interference cancellation (SIC). PIC detectors are usually studied in equal-power case, i.e., a perfect power control scheme is assumed. In this paper, PIC detector in a near-far condition where user signals arrive at the receiver with different power levels is also investigated.

Interleaving scheme for multicarrier CDMA system

In MultiCarrier Code-Division Multiple-Access (MC-CDMA) system, the received signals scattered in the frequency domain are combined to get frequency diversity gain. However, the frequency diversity gain is limited because of correlation between subcarriers. A novel interleaving scheme for MC-CDMA system is proposed in this paper. A circular shifting register is introduced into each subcarrier branch to decrease the correlation between subcarriers. By using interleaving, frequency diversity gain of system is increased. System structure and model with interleaver are discussed. In the case of multiple users, Parallel Interference Cancellation (PIC) technique is also introduced. Computer simulations demonstrate the performance of proposed scheme, and the performance comparison of MC-CDMA with interleaver and conventional MC-CDMA system is shown as well.