Multistage Interference Cancellation Research Articles

Multistage interference cancellation for cyclic interleaved frequency division multiplexing

AbstractCyclic interleaved frequency division multiplexing (CIFDM), a variant of IFDM, has recently been proposed. While CIFDM employs cyclic interleaving at the transmitter to make multipath components resolvable at the receiver, the current approach of matched filtering followed by multipath combining does not fully exploit the diversity available. This is primarily because the correlation residues among the codes have a significant impact on multipath resolution. As a solution, we introduce a novel multipath successive interference cancellation (SIC) technique for CIFDM, which replaces the conventional matched filtering approach. We have examined the performance of this proposed CIFDM‐SIC technique and compared it with the conventional CIFDM‐matched filter bank and IFDM schemes. Our simulation results clearly demonstrate the superiority of the proposed scheme over the existing ones.

Design and Performance Analysis of Multirate Multicarrier Systems for Dynamic Spectrum Access

In this letter, we analytically study the bit-error-rate (BER) performance of the multirate multicarrier system with a multistage interference cancellation receiver for dynamic spectrum access (DSA) in correlated Rayleigh fading channels. We consider a scheme that incorporates a novel combination of non-contiguous carrier interferometry (NC-CI) codes and NC-binary codes to maintain orthogonality in NC subcarrier allocation for DSA. Simulation corroborates the analysis and demonstrates the superior performance of the proposed system over conventional scheme due to the nice properties of the proposed code design.

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.

Time reversal methods for high frequency multiple-input/multiple-output underwater acoustic communication

As a sound focusing technique, time reversal has been utilized in underwater acoustic communication since the 1990s. Here, we particularly study the usage of time reversal methods to separate sounds from different sound sources for high frequency transmissions (greater than 10 kHz), in addition to sound focusing. The separation of sounds creates multiple parallel acoustic links between multiple transducers and a receiver array, thus, providing increased data rates between the source and receiver for communication purposes. It is referred to as multiple-input/multiple-output (MIMO) acoustic communication. Multiple at-sea experiments have been conducted to demonstrate high frequency MIMO signaling and their communication performance. A number of signal processing techniques have been developed in the time reversal framework to enhance the sound focusing and separation that are needed in high frequency acoustic MIMO communication. For example, multi-stage interference cancellation methods have been devised to suppress the co-channel interference and to ensure the sound separation. In this talk, we will show their effectiveness in the presence of water column variability based on our experimental data. An acoustic communication channel model will also be used to explain the impact of environmental variability.

Modeling and Theoretical Analysis of Multistage Interference Cancellation Scheme

Modeling and Theoretical Analysis of Multistage Interference Cancellation Scheme

Performance analysis of overloaded CDMA system under imperfect synchronization using Parallel/Successive Interference Cancellation

A hybrid Interference cancellation (HIC) technique employing both Parallel and Successive Interference Cancellation (PIC/SIC) is proposed for Overloaded Direct Sequence Code Division Multiple Access (OCDMA) system under imperfect synchronization. Two types of receivers are proposed to efficiently mitigate the multiuser interference (MUI). In type I receiver, the MUI within group-1 users are first cancelled using Parallel Interference Cancellation (PIC). Then the multistage Successive Interference Cancellation (m-SIC) is performed on the resultant output of PIC to efficiently cancel the interference of group-2 users on group-1 users. The type II receiver is designed by performing PIC immediately followed by SIC and this combined process is repeated till a major chunk of multi user interference is cancelled. The BER performance of type II receiver is proved to be better than other cancellation techniques such as PIC, SIC and the proposed type I receiver.

Generalised grouped minimum mean‐squared error‐based multi‐stage interference cancellation scheme for orthogonal frequency division multiple access uplink systems with carrier frequency offsets

In uplink orthogonal frequency division multiple access (OFDMA) systems with carrier frequency offsets (CFOs), there always be a dilemma that high performance and low complexity cannot be obtained simultaneously. In this study, in order to achieve better trade-off between performance and complexity, the authors propose a grouped minimum mean squared error (G-MMSE)-based multi-stage interference cancellation (MIC) scheme. The first stage of the proposed scheme is a G-MMSE detector, where the signal is detected group by group using banks of partial MMSE filters. The signal group can be either user based or subcarrier based. Multiple novel interference cancellation (IC) units are serially concatenated with the G-MMSE detector. Reusing the filters in the G-MMSE detector significantly reduces the computational complexity in the subsequent IC units as shown by the complexity analysis. The performance of the proposed G-MMSE-MIC schemes are evaluated by theoretical analysis and simulation. The results show that the proposed schemes outperform other existing schemes with considerably low complexity.

Pareto Region Characterization for Rate Control in MIMO Interference Systems and Nash Bargaining

In this note, the problem of rate control in multiuser multiple-input multiple-output (MIMO) interference systems is formulated as a multicriteria optimization (MCO) problem. The Pareto rate region of the MCO problem is first characterized by giving a sufficient condition for the convexity of the Pareto rate region. Second, various rate region convexification approaches including a multistage interference cancellation and a full projection (FP)-based interference avoidance scheme are analyzed. An achievable rate region based on FP is also given for MIMO interference systems. Third, Nash bargaining (NB) is applied to transform the MCO problem into a single-objective problem. The characteristics of the NB over MIMO interference systems such as the uniqueness and optimality of different type NB solutions are investigated. A method to determine the optimality of FP- and time-division multiplexing-based NB solutions is presented as well. Finally, the convexity of the rate region and the existence of the FP-based NB solution for MIMO interference systems are examined numerically.

A Tracking System Using a Differential Detector for M-ary Bi-orthogonal Spread Spectrum Communication Systems

As an application of the direct sequence spread spectrum (SS) communication system, there is an M-ary bi-orthogonal SS communication system. In its system, several spreading sequences (bi-orthogonal sequences) are used in a code shift keying basis. Hence, design of the spreading code synchronization system has been an issue in the M-ary bi-orthogonal SS systems. In this paper, the authors focus on a code tracking system using a differential detector and a Delay Lock Loop (DLL). They investigate a tracking performance of their code tracking system by theoretical analysis. In addition, a multi-stage interference canceler is applied to the M-ary bi-orthogonal SS system. As the result, it is shown that the tracking performance of the theoretical analysis is almost the same as that of computer simulations in a multi-user environment. It is also shown that the multi-stage interference canceler is effective in improvement of the BER performance.

The Behaviour of Vertical Bell Laboratories Layered Space-Time Algorithm Combined with Multiuser Detection Schemes in Wireless Communication System

This paper provides the performance analysis of multiuser Vertical Bell Laboratories Layered Space-Time (V-BLAST) system receiver structures for Multiple-input Multiple-Output (MIMO) channel at a base station with assumption of perfect channel estimation and perfect timing delay estimation. In MIMO channels the receivers such as decorrelator, Minimum Mean Square Error (MMSE) and Multistage Parallel Interference Cancellation (MPIC) receiver outperform the conventional receiver. Withal, since the multiple antenna interference led to a strong impact on the performance degradation of a multistage interference cancellation receiver, the performance of MPIC receiver was highly degraded based on system loading.

VLSI Implementation of an Adaptive Multiuser Detector for Multirate WCDMA Systems

A multirate receiver for WCDMA systems based on the adaptive signature method was designed and implemented. We employed an adaptive signature algorithm to consider two well-known multirate schemes, namely, the low rate and the high rate detector for variable spreading factor systems. In monorate scenarios, numerical experimentations showed that the adaptive signature method outperforms the Rake receiver and reaches the performances of the soft 4-stage multistage parallel interference cancellation receiver. In multirate scenarios, the performance comparison of two multirate schemes in floating-point and fixed-point was analyzed. Reusing the existing hardware architecture previously developed for monorate systems, we targeted the hardware implementation of these two multirate schemes on FPGA components.

An Adaptive Multistage Multiuser Detector for MC-CDMA Communication Systems Using Evolutionary Computation Technique

The main targets of multi-carrier direct sequence code division multiple access (MC-DS-CDMA) mobile communication systems are to overcome the multi-path fading influences as well as the near-far effect and to increase its capacity. Many optimal and suboptimal multi-user detection approaches have recently been proposed and analyzed in literature. Unfortunately, most of them share the drawback of requiring a practical solution. Therefore, we have presented an adaptive multistage interference cancellation structure based on the particle swarm optimization (PSO) approach in this paper, and have effectively eliminated the multi-access interference (MAI) and near-far effect, and quickly converges to global optimal solution. Simulation results show that the proposed scheme can outperform some of the existed interference cancellation methods in both the additive white Gaussian noise and the multi-path fading channels.

Performance Analysis of Multistage Interference Cancellation for Asynchronous TH-UWB Systems in Multipath Fading Channels

In this paper, we present an accurate analytical method for an asynchronous time-hopping (TH) ultrawideband (UWB) system using multistage interference cancellation (MIC) in multipath fading channels. To model the asynchronous transmission, we first investigate the chip-asynchronous case and extend the results of chip-asynchronous transmission into completely asynchronous transmission as a more general environment. Specifically, the approximate closed-form expression is derived for numerically calculating the average bit-error probability (BEP) of the MIC receivers, which are based on the hard-decision (HD) and soft-decision (SD) detections, respectively. In performing the analysis, the effect of multiple-access interference (MAI) is modeled as a Gaussian process. The results of an interference cancellation (IC) receiver as a function of the ratio between the two types of processing gain-1) pulse combining gain <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> and 2) pulse spreading gain <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -are analyzed and compared under the constraint that the total processing gain of the system is large and fixed. To build up intuitive knowledge, some remarks on the analytic results are presented to describe the design criterion for the interference suppression. In numerical results, the theoretical analysis is verified via comparison with simulation results in terms of the number of IC stages, the set of cancellation parameters, and the number of users.

Adaptive Duplicated Filters and Interference Canceller for DS-CDMA Systems

A low complexity multiuser detection (MUD) technique, the Adaptive Duplicated Filters and Interference Canceller (ADIC) (patent pending), is proposed in the DS-CDMA context. Of particular interest is the use of adaptive filters block (AFB) dedicated to each user with its respective input signals independent from other users' contributions. The AFBs are mixed with interference canceller block in a cascade arrangement. As shown in this paper, this MUD can outperform the Decision Feedback Soft MultiStage Interference Canceller (DF-Soft-MPIC) MUD with complexity reduction by a factor of 4 to 8 for the data payload throughput from 64 kbps to 384 kbps, respectively. In addition to performance and algorithmic description of the proposed MUD method, a VLSI implementation strategy and hardware resources evaluation are investigated; permitting to estimate the maximum number of users in FPGA devices with respect to WCDMA constraints. The present work proposes a low complexity MUD wherein an interesting trade-off between performance and implementation complexity is described.

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.

A Novel Joint Detection of Frequency Offset and MAI for MC-CDMA Systems

While multicarrier CDMA techniques are used to reduce interference and improve the performance of the system in fading channel, carrier frequency offset and multiple access interference remain major obstacles for a multicarrier CDMA system's performance. In this article we propose a novel joint detection method called modified maximum likelihood multistage parallel interference canceller (M-ML-MPIC) to eliminate the frequency offset and MAI simultaneously. The main idea of our approach is to combine PIC multiuser detection and frequency offset estimation based on a maximum likelihood function with guard interval. We discuss our scheme and report on its performance using a set of simulation experiments.

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

Single-carrier and multi-carrier space–time block coded transmissions over doubly selective fading channels

We propose a multi-stage successive interference cancellation (SIC) receiver for arbitrary linear space-time block codes (STBCs) over general time-frequency selective fading channels with single-carrier (SC) transmissions. The proposed receiver adopts the SIC approach to handle intersymbol interference (ISI) owing to multipath propagation. Simulation results show that the proposed receiver outperforms the OFDM system after a few iterations in the BER range 10 -3 to 10 -5 . We also propose a diversity enhancement space-time signalling scheme for four transmit antennas with an increased diversity order. Simulation results show that the proposed diversity enhancement scheme outperforms the OFDM system even at the first iteration.

An iterative approximate MAP symbol estimator for uncoded synchronous CDMA

This paper proposes an iterative algorithm for multiuser detection in uncoded synchronous code division multiple access communication systems based upon an approximate maximum a posteriori (MAP) formulation. For symbol estimation in the continuous domain, direct use of the a priori symbol distribution in the estimation process is prohibited because it is not differentiable. The proposed algorithm approximates the discrete finite alphabet symbol distribution by a sum of continuous Gaussian distributions centered at the true values of the symbol constellation. This approximation allows the development of a gradient-based iterative MAP estimator that employs the structure of the particular symbol constellation to improve estimation accuracy. Although iterative, the proposed method does not use a tentative solution from another multiuser detector. Simplifications of the proposed algorithm for constant modulus modulation and its special forms for M-ary phase-shift keying are given. Also, an optimum step size is derived to achieve fast convergence. The performance of the proposed algorithm is shown to outperform other well-known multiuser detectors such as minimum mean square error, the decorrelator, and the multistage hard-decision parallel interference canceller, especially for the near/far scenario.

Optimization of Linear Iterative Interference-Cancellation Receivers for CDMA Communications

Iterative methods to solve a linear equation system can be used to derive multistage interference cancellers (ICs) that converge to the decorrelating or the minimum mean-square error linear detectors. The link between linear multistage IC and iterative solution methods is well known; however, the parameters needed for fastest convergence are functions of the eigenvalues of the channel matrix. In this letter, we propose new methods for finding optimal parameters without eigendecomposition.