Multiple Access Interference Suppression Research Articles

Reduction of Complexity Design of SAC OCDMA Systems by Utilizing Diagonal Permutation Shift (DPS) Codes with Single Photodiode (SPD) Detection Technique

In this paper, a diagonal permutation code is presented for spectral amplitude coding optical code division multiple access (SAC-OCDMA) employing a single photodiode (SPD) detection technique. It is characterized by practical code length and ideal in-phase cross correlation (CC) that results in multiple access interference (MAI) suppression. A diagonal permutation shift (DPS) code can be constructed using both prime codes and some matrix operations. In addition, it can be easily implemented as it exists for prime numbers P, which limits the addressing probability of codes to P2. Fiber Bragg gratings (FBGs) are used for code encoding and decoding. Simulation analysis that calibrates with BER, Q-factor, and eye diagram proves that DPS code using SPD technique is able to maintain error free transmission compared to the complementary detection scheme (CDS) technique. It is reported that a reduction of fiber Bragg grating (FBG) sets by 41.6% was achieved for SPD over CDS techniques.

IA-OPD: An Optimized Orthogonal Pulse Design Scheme for Waveform Division Multiple Access UWB Systems

A new design scheme of orthogonal pulses is proposed for waveform division multiple access ultra-wideband (WDMA-UWB) systems. In order to achieve WDMA and to improve user capacity, the proposed method, termed as interference alignment based orthogonal pulse design (IA-OPD), employs combined orthogonal wavelet functions in the pulse design. The combination coefficients are optimized by using interference alignment. Due to the reciprocity between transmitted and local template signals, the iterative process based on maximum signal to interference plus noise ratio (Max-SINR) criterion can be used to solve the optimization problem in interference alignment. Numerical results demonstrate that the optimized orthogonal pulses provide excellent performances in terms of multiple access interference suppression, user capacity and near-far resistance without using any multiuser detection techniques. Thus, the IA-OPD scheme can be used to efficiently design a large number of orthogonal pulses for multiuser WDMA-UWB systems with low computational complexity and simple transceiver structure.

Frequency synchronization for interleaved OFDMA uplink systems

This study presents a novel frequency synchronization scheme for orthogonal frequency division multiple access uplink systems. The proposed approach first estimates the carrier frequency offset (CFO) from the zeros of a backward prediction system. Then, based on the CFO estimates, two types of filters, namely zero-forcing and the linearly constrained minimum variance filters, are developed to suppress multiple access interference (MAI). Computer simulation results show that in addition to having a reduced computational complexity, the proposed algorithm has reliable CFO estimates and possesses at least a 3-dB power gain in MAI suppression over conventional minimum mean square error algorithms for frequency synchronization.

Exploration of Multiple Access Interference Suppression Based on Multi-user Detection.

A multi-user detection algorithm for multiple access interference suppression combined with the minimum mean squared error and an artificial fish swarm algorithm is proposed. By taking advantage of the artificial fish swarm algorithm, the proposed algorithm can quickly converge to the optimal solution. The variation in the minimum mean squared error based test results is assigned to the artificial fish swarm algorithm, which is regarded as the initial state of artificial fish. The simulation results show that the proposed algorithm has a better multi-user capacity performance and lower bit-error rate than the minimum mean squared error detector.

Modified Chirp Waveforms-Based OCC-UWB System With Multiple Interferences Suppression

To improve the performance of the ultra-wideband (UWB) system against multiple interferences existed in wireless personal area network (WPAN), such as narrowband interference (NBI), multiple-access interference (MAI), and multipath interference (MI), we present an orthogonal complementary code (OCC)-based UWB system with modified chirp waveforms. Considering the time–frequency characteristics of the chirp functions and the principle of NBI suppression, we first propose the modified linear and nonlinear chirp function-based flexible UWB pulses to suppress the multiple NBIs. Furthermore, with the implementation of OCC spread modulation, the modified chirp waveform-based UWB system is presented to effectively alleviate the influence of the MAI and MI. Simulation results and analysis validate the efficiency of the modified chirp pulse-based OCC-UWB system in the suppression of NBIs, MAI, and MI.

Efficient DS-UWB MUD Algorithm Using Code Mapping and RVM

A hybrid multiuser detection (MUD) using code mapping and a wrong code recognition based on relevance vector machine (RVM) for direct sequence ultra wide band (DS-UWB) system is developed to cope with the multiple access interference (MAI) and the computational efficiency. A new MAI suppression mechanism is studied in the following steps: firstly, code mapping, an optimal decision function, is constructed and the output candidate code of the matched filter is mapped to a feature space by the function. In the feature space, simulation results show that the error codes caused by MAI and the single user mapped codes can be classified by a threshold which is related to SNR of the receiver. Then, on the base of code mapping, use RVM to distinguish the wrong codes from the right ones and finally correct them. Compared with the traditional MUD approaches, the proposed method can considerably improve the bit error ratio (BER) performance due to its special MAI suppression mechanism. Simulation results also show that the proposed method can approximately achieve the BER performance of optimal multiuser detection (OMD) and the computational complexity approximately equals the matched filter. Moreover, the proposed method is less sensitive to the number of users.

Widely‐linear minimum‐mean‐squared error multiple‐candidate successive interference cancellation for multiple access interference and jamming suppression in direct‐sequence code‐division multiple‐access systems

In this paper, the authors propose a widely-linear (WL) receiver structure for multiple access interference (MAI) and jamming signal (JS) suppression in direct-sequence code-division multiple-access systems. A vector space projection (VSP) scheme is also considered to cancel the JS before detecting the desired signals. They develop a novel multiple-candidate successive interference cancellation (MC-SIC) scheme which processes two consecutive user symbols at one time to process the unreliable estimates and a number of selected points serve as the feedback candidates for interference cancellation, which is effective for alleviating the effect of error propagation in the successive interference cancellation (SIC) algorithm. WL signal processing is then used to enhance the performance of the receiver in non-circular modulation scheme. By bringing together the techniques mentioned above, a novel interference suppression scheme is proposed which combines the WL MC-SIC minimum-mean-squared error (MMSE) algorithm with the VSP scheme to suppress MAI and JS simultaneously. Simulations for binary phase shift keying modulation scenarios show that the proposed structure achieves a better MAI suppression performance compared with previously reported SIC MMSE receivers at lower complexity and a superior JS suppression performance.

The Kalman Filtering Blind Adaptive Multi-user Detector Based on Tracking Algorithm of Signal Subspace

Multi-user detection is an effective method to reduce multiple access interference in code division multiple access (CDMA) systems. This paper discusses a signal subspace based blind adaptive multiuser detector and a Kalman filtering blind adaptive multiuser detector. Combining them together, a new Kalman filtering blind adaptive multiuser detector based on a tracking algorithm of the signal subspace is proposed. Analysis and simulation show that the proposed blind multiuser detector achieves better suppression of multiple access interference and has a higher convergence rate.

Performance Analysis of Multistage Interference Cancellation in THUWB Systems Using Adaptive Differential Evolution Algorithm with Novel Mutation and Crossover Strategies

We study the application of differential evolution optimization algorithm to the problem of multiuser detection (MUD) and the suppression of multiple-access interference (MAI) in time-hopping UWB (TH-UWB) system is carried out considering the performance-complexity trade-off. The importance of MUD for achieving high data or low bit error rates in these systems has already been established in several studies. However, the optimum MUD can be characterized as a nondeterministic polynomial-time hard combinatorial optimization problem such that the computational complexity increases exponentially with number of user. In this paper, we proposed modified differential evolution (MDE) optimization algorithm with novel mutation and crossover strategy based MUD is investigated by simulations, when communicating over Saleh---Valenzuela (S---V) channel model. The RAKE detector is used as the first stage to initialize the MDE-based MUD. Then, the MDE algorithm is applied to detect the received data bit by optimizing an objective function incorporating the system of the RAKE detector. The performance evaluation with extensive simulations show that our proposed MDE based MUD can go to convergence rapidly under TH-UWB channel model, the bit error ratio performance is better than of the traditional MUD.

A Method of Constructing Quaternary Periodic Complementary Sequence Sets for Suppression of Multiple Access Interference in CDMA Communication Systems

For suppressing multiple access interference (MAI) in a CDMA communication system, complementary sequence sets are employed as spreading sequences in such system. In this paper, we present a method for constructing a family of quaternary periodic complementary sequence sets, which arises from the conversion of the existing binary periodic complementary sequence sets with odd period of sub-sequences. The period of sub-sequences in the proposed sequence sets is twice as long as the one of the binary sequence sets employed, which is a drawback in the proposed method. Finally, some examples are given in order to illuminate the validity of the new method.

An efficient multiple access interference suppression scheme in asynchronous femtocells

This work considers a code division multiple access (CDMA)-based femtocell system where a fixed set of subscribed users communicate simultaneously to a femtocell access point (FAP) in an asynchronous fashion during the uplink. The main goal of this paper is to present an augmentation protocol for the physical layer of the CDMA2000 femtocell standard with focus on the multiple access interference (MAI) suppression. The above-closed access femtocell uses a unique set of cyclic orthogonal binary codes to eliminate the MAI caused by packet collisions. This property ensures that the time and data rate asynchronicity of active nodes in a femtocell produces a zero MAI situation at the FAP. The work investigates the optimality and the effectiveness of such codes in femtocells from the link bit error rate performance in a practical Rayleigh-fading environment, where Kalman filtering is used at the FAP for the channel estimation. Theoretical findings are verified by simulation evaluations and it is shown numerically a significant improvement in the performance of the proposed scheme when compared with conventional non-cyclic orthogonal codes in a Rayleigh-fading channel in the asynchronous femtocell.

Chip-interleaved optical code division multiple access relying on a photon-counting iterative successive interference canceller for free-space optical channels

In this paper, we design a novel Poisson photon-counting based iterative successive interference cancellation (SIC) scheme for transmission over free-space optical (FSO) channels in the presence of both multiple access interference (MAI) as well as Gamma-Gamma atmospheric turbulence fading, shot-noise and background light. Our simulation results demonstrate that the proposed scheme exhibits a strong MAI suppression capability. Importantly, an order of magnitude of BER improvements may be achieved compared to the conventional chip-level optical code-division multiple-access (OCDMA) photon-counting detector.

A SOA-Based Scheme for MAI Suppression in OCDMA

A noise suppression scheme based on semiconductor optical amplifier (SOA) is investigated in this paper. It aims to inhibit the Multiple-Access interference (MAI) which is the major noise in incoherent optical code division multiple access (OCDMA) system. The saturated SOA is employed as optical limiting amplifier here. The performance of proposed MAI suppression system is analyzed theoretically and experimentally.

Interference cancellation for HNNPSO multiuser detection of UWB systems over multipath fading channel

The problem of multiple access interference (MAI) and inter-symbol interference (ISI) suppression in direct-sequence ultra-wideband (DS-UWB) systems is considered. This paper is dedicated to the application of intelligence computational techniques based on bionics to solve the difficult issue of multiuser detection (MUD) design capable of canceling the so-called MAI to reach low bit error rate (BER) with acceptable computation complexity. We apply the stochastic algorithm that employs a Hopfield neural network (HNN) and particle swarm optimization (PSO) for the MUD problem in DS-UWB system. The use of the HNN embedded PSO (HNNPSO) technique for multiuser detection is a novel ideal, and it leads to efficient techniques that can find a satisfactory solution by maximizing likelihood (ML) function in a small number of iterations. The computer experiments showed that the proposed HNNPSO technique not only can find optimal or close-to-optimal solutions but also obtain both better and more robust results than the existing algorithm reported recently in this literature.

A Blind Two-Stage Receiver for MIMO-CDMA Systems

A blind two-stage multiple-input multiple-output (MIMO) receiver is proposed for code-division multiple access (CDMA) systems utilizing space-time block coding (STBC) over a multipath fading channel. Specifically, in the first stage, a signal-blocked (SB) interference-blocked (IB) detector is first constructed for collection of the desired signals and suppression of multiple access interference (MAI). In the second-stage, a decision-directed scheme is developed to alleviate desired signal cancellation. Computer simulations demonstrate that the proposed blind receiver can achieve a reliable output signal-to-interference-plus-noise ratio (SINR) performance approximating that of the optimal minimum mean squared error (MMSE) receiver and can exhibit the robustness against the finite data sample effect.

New acquisition decision algorithm for multiple access interference suppression in DSSS system

New acquisition decision algorithm for multiple access interference suppression in DSSS system

Blind Multiple Access Interference Suppression Algorithm Based on Relaxed Subgradient Projection for DS/CDMA Systems

A novel blind multiple access interference suppression algorithm based on relaxed parallel subgradient projection is proposed for DS/CDMA systems. The qualification “relaxed” is manifest in two aspects: first, the new expression for updating the interference suppression filter coefficients vector relaxes paralleled projection fields and reduces computation complexity. In addition, the relaxation parameter in the updated process is adaptively determined to guarantee the interference suppression filter coefficients vector falling into fields containing the optimal filter coefficients vector after several iterations. Theoretical analysis and simulation results conclude that this algorithm has a fast convergence speed, steady interference suppression performance, low computation and low bit error rate.

Chip Equalized Adaptive Rake Receiver for DS-CDMA UWB Systems

Conventional Rake receiver is a popular and effective method of utilizing the diversity offered by a DS-CDMA and multipath communication channel. The proposed Rake receiver is useful for suppression of multiple access interference in a multipath channel. The receiver works on chip level equalization on each Rake finger to cancel multi-access interference. Simulation results show that the convergence, diversity gain and bit error probability performance of the proposed receiver is much better than conventional adaptive Rake receiver in multipath channels.

Interference-free code design for MC-CDMA uplink transmissions

In a recent study, solutions have been proposed for completely suppressing the multiple access interference (MAI) arising in the uplink of a quasi-synchronous multicarrier code-division multiple-access network as a consequence of multipath distortions and carrier frequency offsets. This result is achieved by employing exponential orthogonal codes or selecting a particular subset of the Walsh-Hadamard code family without the need for any channel state information at the transmitter side. In the present letter, we revisit this problem and show that MAI suppression can be achieved by following a different line of reasoning which leads to a transmission scheme exhibiting a lower peak-to-average power ratio.

Robust multiuser detection based on variable loading RLS technique

A variable loading recursive least squares (VLRLS) multiuser detection based on the generalized sidelobe canceller is presented to realize the suppression of multiple access interference in code division multiple access (CDMA) systems. In conjunction with a subweight partition approach, the VLRLS detector demonstrates the advantages of insensitivity to dynamic estimate modeling error, less computational load, and more robust to against spreading code mismatches compared to the conventional VLRLS and RLS-based detectors. Simulation results illustrate the effectiveness of the proposed detector.