Adaptive differential interference cancellation multiuser detection method for DS-CDMA communications

In DS/CDMA systems, overcoming near/far effects and fading is imperative for satisfactory performance. One way to combat the near/far effect is to use stringent power control, as is done in most of the commercial systems. Another approach is Multi-User Detection (MUD). In addition to mitigating the near/far effect, MUD has the more fundamental potential of raising capacity by canceling Multiple Access Interference (MAI). This paper analyses the convergence behavior and performance of successive interference cancellation (SIC) for CDMA systems. This analysis will be generalized for Parallel Interference Cancellation (PIC) also. In this paper a Hybrid Interference Cancellation (HIC) receiver is designed by combining the successive and Parallel Interference Cancellation algorithms, so that the advantages of both the schemes are utilized effectively. The Hybrid Interference Cancellation scheme results in a simple, faster and reliable receiver. With the help of simulations, it is shown that this hybrid approach outperforms the other Multi-User Detection schemes.

Nonlinear interference cancellation multiuser detection algorithms have less BER and are less complex than linear multiuser detection methods. We present a hybrid switched mode detector that uses existing interference cancellation methods i.e. Parallel Interference Cancellation (PIC) and Successive Interference cancellation (SIC) based on channel conditions. This proposed detector takes decisions based on number of users on the channel and switches either to SIC method or PIC method. The switching mechanism is exploited by performance complexity tradeoff between matched filter detector and nonlinear interference cancellation methods.

Non-orthogonal multiple access (NOMA) has become the key technology in 5G communication. NOMA can achieve multi-user multiplexing in transmit power domain by allocating different power, which can effectively improve the spectral efficiency, but also causes the multiple access interference of the receiver signal. The parallel interference cancellation (PIC) technology is applied to NOMA system in order to solve the problem of high-delay and error propagation in the successive interference cancellation (SIC) algorithm. PIC can effectively compensate for the deficiency of SIC algorithm but it has high complexity. Combined with the advantages of SIC and PIC, a joint interference cancellation (JIC) method is proposed. The performance and complexity of the three algorithms are simulated and analyzed. The results show that JIC can effectively reduce the delay and improve the error propagation problem in the case of low complexity.

This paper presents an adaptive multiuser receivers scheme for MIMO OFDM over Turbo-Equalization for Single-Carrier Transmission. It involves the joint adaptive minimum mean square error multiuser detection and decoding algorithm with prior information of the channel and interference cancelation in the spatial domain. A partially filtered gradient LMS (Adaptive) algorithm is also applied to improve the convergence speed and tracking ability of the adaptive detectors with slight increase in complexity. The proposed technique is analyzed in a slow and fast Rayleigh fading channels in MIMO OFDM systems. The adaptive multiuser detection for MIMO OFDM (AMUD MIMO OFDM) perform as well as the iterative equalization for single-carrier.

This paper investigates the effect of other-cell multiple-access interference (MAI) on some suboptimal multiuser detectors such as decorrelating multiuser detector, parallel interference canceller and adaptive minimum mean-squared error (MMSE) multiuser detector. Based on the Gaussian approximation for other-cell MAI, the bit-error rate (BER) of each detector is derived. Both analytical results and simulations indicate that the performance degradation due to other-cell MAI is significant. It is also observed that the other-cell MAI introduces more errors to multiuser detectors that require prior information on users' signature waveforms.

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.

Semi-blind multiuser detection for the reverse link of a multi-cell code-division multiple-access (CDMA) system is considered. In such a system, although active users are present in the home cell and neighbouring cells, the base station receiver only knows the signal information of the users in its own cell. Three new adaptive semi-blind linear multiuser detectors are proposed, based on a parallel interference cancellation approach. Compared with some known semi-blind detectors, the proposed detectors share a rather simple implementation structure and involve reduced latency for processing, which are of particular importance in a time-varying CDMA system. Numerical results are presented to show that the detection performance of the proposed detectors is superior to that of some existing semi-blind multiuser detectors.

This paper proposes a new application of fuzzy inference mechanism to the interference cancellation in a direct-sequence code-division multiple-access (DS/CDMA) communication system over a non-perfect power control channel. Multistage parallel interference cancellation (PIC) is an effective method to cancel the multiple access interference (MAI) for equal-power channels; nevertheless, there is a significant degradation in performance for non-equal power ones. The effectiveness of interference cancellation is related to the reliability of the tentative decision involved in the interference estimates. We established a fuzzy logic system to adapt the weight of each interference cancellation path. According to the received signal's reliability, the weights of interfering users can be estimated by the fuzzy inference mechanism, so that the error propagation would be minimized. The simulation results show that the proposed adaptive fuzzy PIC scheme is robust to the interference and channel noise and is superior to the conventional PIC and constant weight PIC schemes under a severe near-far environment.

In this paper, we propose an adaptive particle swarm optimization (APSO) based partial parallel interference cancellation scheme for direct-sequence code-decision multiple access (CDMA) communication system over frequency selective fading channels. However, the partial cancellation tries to reduce the cancellation error in parallel interference cancellation schemes due to the wrong interference estimations in the early stages. Thus, in order to reduce the computational complexity and improve the performacne of the CDMA system, particle swarm optimization (PSO), which has the ability of solution to complex combinatorial optimization problem, is employed in searching the optimal weight for multiple access interference cancellation. Experiments have been carried out on the method can improved on the multiuser detection in CDMA system, the simulation results show that APSO detector can achieve the global optimization in fast convergence rate, and also show that the proposed detector is obviously superior to convenentional receiver and multiuser detectors based on some optimum algorithm in terms of the multiple access interfere and the mitigation of near-far effect.

In this paper, anew iterative interference cancellation multiuser detection (MUD) method is proposed for overloaded multiple-input multiple-output (MIMO) coded orthogonal frequency division multiplexing (OFDM) systems. In the first iteration, a channel analyzer and selector are employed, which ensure that non-convergent channels are not used. Then low complexity RAKE reception is applied, and a successive interference cancellation (SIC)-based approach is used such that the strongest user is decoded first. In each iteration, the soft output of the convolutional decoder is fed back to cancel inter-user interference using parallel interference cancellation (PIC). The simulation results show that, this technique can achieve near-optimum bit error rate (BER) performance, and optimum frame error rate (FER) performance, with lower complexity than optimum maximum likelihood (ML) methods at the cost of 4% of channels rejected.

An adaptive multiuser detector (MUD) is proposed for direct-sequence ultra-wideband (DS-UWB) multiple access communication systems to suppress both multiple access interference (MAI) and inter-symbol interference (ISI). In this contribution, considering the MUD from a combination viewpoint, we proposed a MUD based on electromagnetism-like (EM) method, which applied the concept of EM search to Hopfield neural network (EMHNN) for solving optimization problems. We analyze the performance of the EMHNN MUD in multipath fading channel, and compare it with the optimum detector and several suboptimum schemes such as conventional, decorrelator detector (DD), minimum-mean-squared error (MMSE) and HNN MUD. Simulation results will demonstrate that the proposed EMHNN MUD, which alleviates the detrimental effects of the MAI problem, can significantly improve the system performance.

Since code division multiple access systems in multipath environments suffer from multiple access interference (MAI), multiuser detection schemes should be used in the receivers. Parallel interference cancellation (PIC) is a promising method to combat MAI due to its relatively low computational complexity and good performance. It is shown that the complexity of PIC is still high for realistic scenarios in terms of the symbol rate, the number of users, spreading gain, and multipath components. However, two novel methods are introduced to reduce significantly the complexity without sacrificing performance. The first approach, called reduced PIC, takes advantage of the composition of the interference to concentrate interference cancellation only on significant terms. The second approach, called differential PIC, exploits the multistage character of PIC to avoid unnecessary double calculations of certain terms in consecutive stages. It is shown that a combination of both approaches leads to a performance very close to the single-user bound whereas the complexity can be kept on the order of the conventional RAKE receiver.

In this paper, an exact expression has been derived for the outage probability and the total system goodput of multi-user detection (MUD) based on successive interference cancellation (SIC) for multi-user communication system. We consider a single antenna wireless system with n mobile users and a base station. We focus on the uplink direction with perfect channel knowledge (CSIR) at the base station. We consider slow fading channels where packet outage is the primary concern even if capacity achieving coding is applied. To capture the effect of packet outage, we consider the packet outage probability and the total system goodput of the n users. The analytical expressions for packet outage probability and system goodput are very important for cross layer optimizations of multi-user systems with MUD. However, due to the SIC processing in the MUD, the outage probability analysis is not trivial as the outage probability of the n users are coupled together. In this paper, we shall propose an analytical approach to evaluate the exact expressions of the packet outage probabilities and the system goodputs for the n users based on ordered statistics. We consider adaptive SIC where an optimal decoding order for the MUD is found per fading slot. Simulation results and discussions are given to verify the analytical expressions. From the results, the system goodput increases with the average user SNR and the number of the users with diminishing returns at large SNR and number of users.

Direct sequence code-division multiple access (DS-CDMA) schemes improve system capacity and provide integrated wireless services which include voice, data and video communications. Multiuser detection (MUD), a scheme by which the receiver jointly and simultaneously detects all the signals from the users, provides significant improvement in the capacity of the DS-CDMA system. The paper focuses on subtractive interference cancellation detectors, especially PIC detectors, and compares their performance with that of the matched filter detector. Single user and multiuser detection techniques are discussed including optimal and sub-optimal multiuser detectors.

In this paper, the performance of parallel interference cancellation (PIC) multi-user detectors in orthogonal frequency division multiple access (OFDMA) mobile communication systems is investigated. In multi-user systems, the multi-user interference (MUI) degraded the system performance, especially in near-far effect environments. An adaptive weight partial PIC (AWPPIC) scheme is proposed to reduce the MUIs and to improve the bit error rate (BER) performance for uplink OFDMA systems. Simulation results show that under the near far problems for block sub carrier assignment (BCA) scheme, the AWPPIC scheme can improve the BER performance no matter what the system load is.