Iterative joint detection and decoding based on intereference cancellation

We propose a layered space time (LST) transceiver in a multiuser code division multiple access (CDMA) mobile communication system. In particular, we examine a multiuser iterative receiver with joint detection, channel estimation and decoding in a frequency selective fading channel. The iterative parallel interference canceller (PIC) with statistics combining is used as the multiuser detection scheme and a least mean square (LMS) adaptive algorithm is applied to estimate the multiple input and multiple output (MIMO) frequency selective fading channel. Simulation results are presented to demonstrate the performance of this receiver. It is shown that the performance of the receiver with iterative channel estimation is close to that of the receiver with perfect channel state information (CSI).

This paper introduces four block joint detection (JD) receivers which combining the orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA) techniques, i.e., OFDM-CDMA receiver. The performance of the OFDM-CDMA receiver with orthogonal and non-orthogonal spreading sequences is investigated in mobile radio channels. The sequences considered as spreading codes are orthogonal Walsh-Hadamard, Orthogonal Gold, Gold and maximim length sequences or m - sequences. The JD algorithms for the OFDM- CDMA receiver are Zero Forcing Block Linear Equalizer (ZF- BLE), Minimum Mean Square Error Block Linear Equalizer (MMSE-BLE), with and without decision feedback (DF). Time- domain equalization does not require DFT or FFT operations and can be used to compensate the channel fading effect. Hence for hardware implementation, the time domain interpretation can lead to a more efficient structure when compared with the frequency domain approach. The bit error rate (BER) performance comparisons of different spreading codes and equalizers are shown in the simulations.

The multiuser detection is a signal processing tech- nique which enhances the performance and capacity in DS- CDMA technology. Since its complexity issue was too expensive to handle, there was focus on the suboptimal detectors. In this paper we propose a hybrid method called adaptive differential interference cancellation method (ADIC) which is a hybrid of the differential interference cancellation method and which is then combined in a adaptive way to determine a weight matrix which will map the outcome of the differential interference cancellation method to come out with a better performance. This paper also looks into the computational cost of different methods using the floating point operation (flops) which is a good estimation of the comparative computational cost if not the exact one. I. INTRODUCTION The conventional DS-CDMA match filter detector fails to combat these issues due three prominent drawbacks: unrealis- tic ucorrelated code, near-far problem (even with strict power control (1)), and tough multiple access interference (MAI). Many advanced signal processing approaches have been made to improve the performances of these kinds of detectors. In this paper we will study the different approaches that were made in this field and implement these methods to reach a conclusion about the detection methods. As the name of the topic suggests the focus of our work will be study and propose cost effective better performing multiuser detection method. We will explore Multiuser Detection Techniques in Synchronous CDMA environment. Multi-user detection deals with the development and ap- plication of joint demodulation and interference cancellation cancellation techniques for improved detection of a desired set of digital signals in the presence of multiple access interfer- ence, intersymbol interference and noise. Since veterbi forward dynamic algorithm (2) is used in case of Optimum multiuser detection (3) the complexity grows in with the increase in the number of users. Hence the complexity is immense which increases exponentially with the increase in the number of users. Looking ahead for lower complexity hence lesser cost of implementation, the paper proposes the use of sub-optimal linear detectors (4). The sub-optimal detector the paper next focuses on is Decorrelator type of Detector (5) which is optimal in least squares. This detector out performs the optimal detector in many respects. Then the Minimum Mean Square Error (MMSE) linear detector is proposed which tries to minimize the squared error from the required transformation. It is one of the most popular detectors in use due to its easiness to implement and its lower complexity. But then in the above detection methods the decisions made were based on certain linear transformation criterion and there are missing efforts to check the performance in between the detection process to improvise the transformation method better detection. So then the paper proposes Adaptive multiuser detection. Then the paper focuses on Interference cancellation methods which utilize the feedback to reduce Multiple Access Interference (MAI) in the detected bits. Under the Interference Cancellation umbrella the Successive Interference Cancellation (SIC) (6), (7) method is explored and simulated to observe the results. Then the next method which performs better than SIC and more commonly used in real life, called Parallel Interference Cancellation (PIC) (6), (8) is also implemented. Before going ahead to implement the final proposed detection method, this paper implements Differential Interference Cancellation (DIC) (9) method. And then this paper finally proposes an Inter- ference Cancellation method called the Adaptive Differential Interference Cancellation Multiuser Detection method which is cost effective in comparison to other Interference Cancellation methods as we will require lesser hardware (multipliers as in the SIC or Parallel Interference Cancellation (PIC)) for that matter. More ever since we are using adaptive method the desired BER can be further reduced. This proposed method will be discussed in detail in the following section.

Wavelet-Based Identification of Linear Discrete-Time Systems

Performance analysis of multicell multiuser MIMO MC DS/CDMA system with MMSE user-ordered SIC technique

The analysis and design of relay protocols is a hot issue in 3GPP Long Term Evolution--Advanced. In this paper, we discuss interference cancellation in a multiuser MIMO environment using Amplify-and-Forward (AF), Decode-and-Forward (DF) and De-Modulate-and-Forward (DMF) as relay protocols, and using Thomilson Harashima Precoding and Dirty Paper Coding as precoding techniques, with Zero-Forcing, Minimum Mean Square Error, Successive Interference Cancellation and Ordered Successive Interference Cancellation detection techniques. By using a combination of classical precoding schemes and detection techniques with weighted matrix, we propose a new interference cancellation technique that is capable of cancelling interference. The interference cancellation is managed by AF, DF and DMF relay node protocols and the interference free codeword is transmitted to the selected User Equipment. The proposed algorithm when used with DMF protocol shows best performance, compared to the conventional system or the no-relay system case, it gives best performance. The observation results shows that DMF protocol gives the best results for BER and Throughput performance in a high interference environment.

SummaryThis paper proposes an efficient uplink low‐density parity‐check (LDPC)‐coded multirelay cooperation architecture based on virtual Vertical‐Bell Labs Layered Space–Time (V‐BLAST) processing over a Rayleigh fading channel, where minimum mean square error in combination with a successive interference canceller and belief propagation‐based joint iterative decoder based on the introduced multilayer Tanner graph are effectively designed to detect and decode the corrupted received sequence at the destination. By introducing V‐BLAST transmission to coded multirelay cooperation, relays send their symbol streams simultaneously, which significantly reduce the transmission delay and provide higher transmission efficiency. The theoretical analysis and numerical results show that the proposed LDPC‐coded cooperation scheme outperforms the coded noncooperation under the same code rate and achieves a better compromise, with respect to the performance, signal delay, and encoding complexity associated to the number of relays, than the conventional LDPC‐coded cooperations without V‐BLAST transmission. This performance gain can be credited to the proposed V‐BLAST processing architecture and belief propagation‐based joint iterative decoding by the introduced multilayer Tanner graph at a receiver side. Copyright © 2013 John Wiley & Sons, Ltd.

The transmission scheme of multilayered space-time trellis codes (ML-STTC) achieves tradeoff between diversity gain and multiplexing gain by combining space-time trellis code (STTC) and layered space-time (LST) structure in multiple-input and multiple-output (MIMO) systems. In this paper, iterative minimum mean square error (MMSE) group detection and iterative MMSE interference cancellation (IC) group detection schemes are proposed to improve the performance of ML-STTC. Moreover, the iteration can reduce the influence of the detection order on performance, and compensate for the performance loss of the firstly detected layer instead of power allocation in the iterative MMSE IC group detection scheme.

Being increasingly spectral and energy efficient, massive multiple-input multiple-output (MIMO) is envisaged as a potential technology for fifth generation (5G) wireless communication networks. Radio spectrum has become a scarce resource in wireless communications and consequently imposes excessive cost on the high data rate transmission. Several linear and non linear detection techniques such as Zero-Forcing (ZF), Minimum Mean Square Error (MMSE), and Vertical Bell-Labs Layered Space Time (VBLAST) have been introduced. The purpose of such schemes is to mitigate the signal detection problems which are based on trade-offs between the bit error rate (BER) performance and computational complexities. The challenge in the design of massive-MIMO systems is developing less complex and efficient detection algorithms. The problem in building a receiver for massive-MIMO is to de-correlate the spatial signatures on the receiver antenna array. In this paper, we propose a novel algorithm viz: Hybrid n-Bit Heuristic Assisted-VBLAST (HHAV) to perform an optimum decoding. We have simulated this structure in dynamic Rayleigh fading channel. We have also evaluated the AMP algorithm with two threshold functions which include AMP with ternary distribution (AMPT) and AMP with Gaussian distribution (AMPG). Numerical results confirm that HHAV algorithm performs significantly better than the in vogue aforementioned detection systems as introduced in recent years.

A near maximum likelihood performance modified firefly algorithm for large MIMO detection

In the conventional zero-forcing ordered successive interference cancellation (ZF-OSIC) or minimum mean square error ordered successive interference cancellation (MMSE-OSIC) detection algorithm of vertical Bell-Labs layered space-time (V-BLAST) architecture, there exists an undesirable processing delay due to the calculation of the matrix pseudo-inverse and power reordering in detecting the symbol in each layer. The parallel interference cancellation (PIC) algorithm has a lower processing delay but poorer performance. Based on the features of SIC and PIC algorithms, an integrated PIC and OSIC detection (IPOD) algorithm is proposed which can lower the complexity as well as the processing delay of the whole algorithm with little performance loss. Moreover, there is an alterable parameter in IPOD algorithm which can be changed to obtain different trade off between complexity and performance. Thus, the proposed algorithm is more feasible for practical applications.

Latterly, interference cancellation is a hard issue in cellular systems. Hence we present interference cancellation with an achievable angular channel model based on Coordinated Multi-Point (CoMP) system in our paper. The CoMP schemes are adopted by Long Term Evolution-Advanced (LTE-A) to enhance the LTE downlink data rate, spectral efficiency, average cell throughput etc. This paper inquires about the performance of CoMP and estimates an achievable angular channel model for LTE-A using minimum mean square error (MMSE) receiver which efficiently improves the bit-error-rate (BER) and cell-edge throughput per user.

The structure of an optimum linear precoder for a rotation-invariant performance measure is obtained subject to the constraint of limited input power for a block transmission scheme. It is shown that several known performance measures of a communication system are rotation invariant. The rotation invariant property provides a unified framework for obtaining the structure of an optimum linear precoder for several criteria such as: 1) maximization of minimum distance; 2) maximization of channel capacity; and 3) optimization of different performance measures, such as bit-error rate (BER), mean square error, signal-to-noise ratio of optimum equalizers (linear minimum mean square error, zero-forcing, maximum likelihood (ML), zero forcing-block decision feedback, minimum mean square error-block decision feedback, etc.). This framework provides a method for obtaining the structure of an optimum linear precoder for BER performance measure of the ML equalizer. The structure turns out to be a channel diagonalizing structure after a prerotation of the input constellation. Using this structure, the properties of the optimum precoder that minimize the BER of the ML equalizer for two binary phase-shift keying symbols transmission under input-power constraint are studied.

This paper investigates the placement of training symbols within the data packets of a wireless system in which transmissions are subject to asynchronous interference. The minimum mean square error of the training-based channel estimator is expressed as a function of the Fisher information of the received signal. It is shown that the placement that minimizes the minimum mean square error should be searched for within a set containing half as many elements as the number of training symbols in the packet. Furthermore, a lower bound on the minimum mean square error is derived and analyzed. It is shown that this bound is tight when the power of the interference is high. The placement of the training symbols in two clusters of equal or quasiequal length at the two edges of the data packet minimizes the lower bound for all values of the parameters and, thus, gives the solution of the problem for high values of the interference power. The influence of the training symbols placement on the data transmission performance is also investigated.

This paper investigates the design and analysis of minimum mean square error (MMSE) turbo decision feedback equalization (DFE), with expectation propagation (EP), for single carrier modulations. Classical non iterative DFE structures have substantial advantages at high data rates, even compared to turbo linear equalizers - interference cancellers (LE-IC), hence making turbo DFE-IC schemes an attractive solution. In this paper, we derive an iterative DFE-IC, capitalizing on the use of soft feedback based on expectation propagation, along with the use of prior information for improved filtering and interference cancellation. This DFE-IC significantly outperforms exact turbo LE-IC, especially at high spectral efficiency, and also exhibits various advantages and performance improvements over existing variants of DFE-IC. The proposed scheme can also be self-iterated, as done in the recent trend on EP-based equalizers, and it is shown to be an attractive alternative to linear self-iterated receivers. For time-varying (TV) filter equalizers, an efficient matrix inversion scheme is also proposed, considerably reducing the computational complexity relative to existing methods. Using finite-length and asymptotic analysis on a severely selective channel, the proposed DFE-IC is shown to achieve higher rates than known alternatives, with better waterfall thresholds and faster convergence, while keeping a similar computational complexity.