Iterative Multiuser Detection Research Articles

Progressive Pattern Interleaver with Multi-Carrier Modulation Schemes and Iterative Multi-User Detection in IoT 6G Environments with Multipath Channels.

Sixth-generation (6G) wireless networks demand a more efficient implementation of non-orthogonal multiple access (NOMA) schemes for severe multipath fading environments to serve multiple users. Using non-orthogonal multiple access (NOMA) schemes in IoT 6G networks is a promising solution to allow multiple users to share the same spectral and temporal resource, increasing spectral efficiency and improving the network's capacity. In this work, we have evaluated the performance of a novel progressive pattern interleaver (PPI) employed to distinguish the users in interleaved division multiple access (IDMA) schemes, suggested by 3GPP guidelines as a NOMA scheme, with two multi-carrier modulation schemes known as single-carrier frequency-division multiple access (SC-FDMA) and orthogonal frequency-division multiplexing (OFDM), resulting in SC-FDMA-IDMA and OFDM-IDMA schemes. Both schemes are multi-carrier schemes with orthogonal sub-carriers to deal against inter-symbol interference (ISI) and orthogonal interleavers for the simultaneous access of multiple users. It has been suggested through simulation outcomes that PPI performance is adequate with SC-FDMA-IDMA and OFDM-IDMA schemes in terms of bit error rate (BER) under multipath channel conditions. Moreover, regarding bandwidth requirement and the implementation complexity of the transmitted interleaver structure, PPI is superior to the conventional random interleaver (RI).

Progressive pattern orthogonal interleaver set for interleave division multiple access based, non orthogonal multiple access schemes: Beyond 5G perspective

Abstract This communication suggests an orthogonal interleaver set for interleave division multiple access (IDMA) based non orthogonal multiple access (NOMA) schemes from beyond 5G viewpoint to support enormous increase in user count. The method generates an orthogonal interleaver set by providing two mother interleavers as seed to generate other users’ interleaving patterns progressively. The key feature of the proposed scheme is that it reduces implementation complexity and memory requirement at the base station, while implementing iterative multiuser detection (MUD), which most of the interlaever designs suggested in literature do not consider. It provides additional security to the user data due to progressively changing mother interleavers’ pattern along with the conventional purpose of providing unique identity for individual users in the system. The proposed orthogonal interleaver set is tested through simulations under multiple IDMA system configurations. It has been observed that it preserves the bit error rate (BER) performance of the IDMA scheme along with the optimal implementation complexity and minimal information exchange requirement between base station and mobile station to share the interleaver design.

Bitwise Early Termination of Multiuser Detection for IDMA Systems

This letter presents an early termination scheme for iterative multiuser detection in interleave division multiple access (IDMA) systems. Instead of handling an entire frame as a whole, each bit in the frame is separately considered. If further iterations are found to be dispensable in determining a bit, the estimate of the bit is immediately finalized, and all the calculations associated with the bit are bypassed afterward, diminishing the computational complexity. To confirm the dispensability, all log-likelihood ratios (LLRs) associated with a bit are examined. Once their magnitudes exceed a threshold, their statistical measures are unlikely to change even after a few more iterations, implying that further iterations are unnecessary. As a countermeasure for infrequent behaviors deviating from such an expectation, the signs of the LLRs in two consecutive iterations are compared. If they all match, the bitwise procedure is terminated. For the remaining bits not fulfilling the criterion, the procedure continues as usual. As a result, in the realm of practical signal-to-noise ratios, a significant number of iterations and operations can be discarded while sustaining the near-optimal error rate.

Achievable Rate Region for Iterative Multi-User Detection via Low-Cost Gaussian Approximation

We establish a multiuser extrinsic information transfer (EXIT) chart area theorem for the interleave-division multiple access (IDMA) scheme, a special form of superposition coding, in multiple access channels (MACs). A low-cost multi-user detection (MUD) based on the Gaussian approximation (GA) is assumed. The evolution of mean-square errors (MSE) of the GA-based MUD during iterative processing is studied. We show that the $K$ -dimensional tuples formed by the MSEs of $K$ users constitute a conservative vector field. The achievable rate is a potential function of this conservative field, so it is the integral along any path in the field with value of the achievable rate solely determined by the two path terminals. Optimized error correcting codes can be found given the integration paths in the MSE fields by matching EXIT type functions. The above findings imply that i) low-cost GA detection can provide MAC capacity-approaching performance, ii) the sum-rate capacity can be achieved independently of the integration path in the MSE fields; and iii) the integration path determining achievable rate tuples of all users can be an extra degree of freedom for code design.

Iterative Multiuser Detection and Decoding for Sparse Code Multiple Access Combined With Spectrally Efficient Frequency Division Multiplexing

Sparse code multiple access (SCMA) combined with spectrally efficient frequency division multiplexing (SEFDM) is a wireless air-interface technology with dual non-orthogonal characteristic which can meet the high spectral efficiency requirement of the future Internet of Things (IoT). In this paper, an iterative multiuser detection/decoder (IMUDD) method for SCMA-SEFDM is proposed, which performs soft information iteration in a turbo style. IMUDD can effectively achieve the multiple-access interference (MAI), inter-symbol interference (ISI) and inter-carrier interference (ICI) cancellation through an external iteration and three internal iterative processes. At each iteration, extrinsic information is extracted from detection and decoding stages, then it is used as a priori information in the next iteration. Furthermore, to reduce the computational complexity of IMUDD scheme, a logarithm domain IMUDD is adopted and analyzed. The simulation results show that IMUDD has a noticeable performance improvement compared to the traditional turbo structured receivers over the multipath fading channel or the additive white Gaussian noise (AWGN) channel.

Uplink Transmit Power Control for Single-Carrier Grouped FDMA with Iterative Multiuser Detection

We consider an uplink power allocation scheme for single-carrier frequency-division multiple access (FDMA) with iterative multiuser detection, called single-carrier grouped FDMA (SC-GFDMA). SC-GFDMA is a non-orthogonal scheme in which several users share a single time-frequency resource. Hence, the uplink signal of a user can be regarded as both a signal and a source of interference. The signal power of each user should be sufficiently high to ensure reliable signal detection and sufficiently low to suppress inter-user interference. That is, the transmit power of each user should be adjusted appropriately to achieve high spectral efficiency. In this context, a power control method for an uplink SC-GFDMA system is proposed by analyzing the signal-to-interference-plus-noise ratios of users sharing each time-frequency resource. In particular, the uplink spectral efficiency is improved by limiting the transmit power of each user according to a criterion derived using a semi-analytic method called signal-to-noise ratio-variance density evolution. Simulation results demonstrate that the proposed method can significantly increase the spectral efficiency of the system, even with a considerably reduced total transmit power.

Rateless Coded Uplink Transmission Design for Multi-User C-RAN.

Cloud radio access network (C-RAN) is a promising technology for the Internet of Things (IoT). In C-RAN, the remote radio head (RRH) and baseband unit (BBU) in the conventional base station are separated, and each BBU is backward centralized into a virtual BBU pool. In this paper, we consider the uplink transmission for the two-user C-RAN with two RRHs under a block fading channel. A novel rateless coded transmission scheme is designed. During each transmission round, each user keeps transmitting to the RRHs using Raptor code until the BBU pool feeds back an acknowledgement (ACK). With the proposed scheme, each user does not require the instant channel state information, which greatly reduces the system overhead. We also design the quantizer at the RRHs and the iterative multi-user detector and decoder at the BBU pool, based on the belief propagation (BP) algorithm. For the Raptor code applied at each user, we optimize the corresponding output node degree profile, based on extrinsic information transfer (EXIT) analysis for the decoding process at the BBU pool. The resulted degree profiles are optimal in an average sense under all possible channel states. The simulation results show that the rateless coded transmission scheme with the optimized degree profiles outperforms the benchmark degree profile in both bit error rate and average system throughput. Moreover, the achieved performance is close to the theoretical limit.

Iterative multiuser detector-decoding for nonbinary LDPC coded multicarrier MFSK systems

This paper investigates an iterative multiuser detection for nonbinary low density parity check (LDPC) coded multicarrier multiple level frequency shift keying system to increase system performance under specific signal-to-noise ratio and data rate. We propose three-level hard-limited detection probabilities over both additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. During multiuser detection (MUD) process, the hard-limited detection probabilities are computed in advanced and stored in tables. By using table looking up, the MUD soft outputs can be computed efficiently. We test the reliability of soft outputs from nonbinary LDPC channel decoder for all users. If the soft output exceeds a reliability threshold, the user is declared as a reliable user. For each symbol, we count the number of reliable users on it, and, use this information to update the soft output of MUD during the iterative multiuser detection and decoding process, which cancel multiple access interference iteratively. Numerical results show that the performances of three-level hard-limited systems outperform two-level hard-limited systems over AWGN channels and Rayleigh fading channels.

Bit-Interleaved Coded SCMA With Iterative Multiuser Detection: Multidimensional Constellations Design

This paper investigates the constellation/codebook design of a promising uplink multiple access technique, sparse code multiple access (SCMA), proposed for the fifth generation mobile networks. The application of bit-interleaved coded modulation with iterative multiuser detection is considered for uplink SCMA over fading channels. Extrinsic information transfer chart is used to aid the analysis and the design of multidimensional constellations, and the design criteria for multidimensional constellations and labelings optimization are thus established. Furthermore, a new and simple approach of multi-stage optimization for the multidimensional constellation design is proposed for SCMA, to improve the bit-error rate performance and alleviate the complexity of turbo multiuser detection. Numerical and simulation results are also provided to demonstrate the performance and verify the efficiency of the proposed scheme, compared with the state of the art.

A Memory-Efficient IDMA Architecture Based on On-the-Fly Despreading

This paper presents a memory-efficient receiver architecture for interleave division multiple access (IDMA). For the iterative multiuser detection, existing IDMA architectures first store all log-likelihood ratios (LLRs) into a memory in an iteration, and then despread them in the following iteration. To store new LLRs in the following iteration without overwriting the previous ones to be despread, the memory needs to be duplicated. The proposed architecture, on the other hand, despreads the LLRs on-the-fly while storing them by immediately processing one LLR per cycle. As a result, the architecture finishes despreading within one iteration and is free of the duplicate memory. Since the hardware complexity and the power consumption of an IDMA receiver are dominated by the memory usage, the proposed architecture is particularly effective in alleviating such measures. Moreover, the proposed architecture mitigates the overall latency slightly, as it is exempted from the additional cycles required to despread in the last iteration. Implementation results demonstrate that the IDMA receivers based on the proposed architecture require 57% bits in memories, occupy only 39% silicon area, and consume only 30% power on average, compared to the latest low-latency architecture.

Polar coded iterative multiuser detection for sparse code multiple access system

Polar coded sparse code multiple access (SCMA) system is conceived in this paper. A simple but new iterative multiuser detection framework is proposed, which consists of a message passing algorithm (MPA) based multiuser detector and a soft-input soft-output (SISO) successive cancellation (SC) polar decoder. In particular, the SISO polar decoding process is realized by a specifically designed soft re-encoder, which is concatenated to the original SC decoder. This soft re-encoder is capable of reconstructing the soft information of the entire polar codeword based on previously detected log-likelihood ratios (LLRs) of information bits. Benefiting from the soft re-encoding algorithm, the resultant iterative detection strategy is able to obtain a salient coding gain. Our simulation results demonstrate that significant improvement in error performance is achieved by the proposed polar-coded SCMA in additive white Gaussian noise (AWGN) channels, where the performance of the conventional SISO belief propagation (BP) polar decoder aided SCMA, the turbo coded SCMA and the low-density parity-check (LDPC) coded SCMA are employed as benchmarks.

Reduced Complexity Detection in MIMO Systems with SC-FDE Modulations and Iterative DFE Receivers

This paper considers a Multiple-Input Multiple-Output (MIMO) system with P transmitting and R receiving antennas and different overall noise characteristics on the different receiver antennas (e.g., due to nonlinear effects at the receiver side). Each communication link employs a Single-Carrier with Frequency-Domain Equalization (SC-FDE) modulation scheme, and the receiver is based on robust iterative frequency-domain multi-user detectors based on the Iterative Block Decision Feedback Equalization (IB-DFE) concept. We present low complexity efficient receivers that can employ low resolution Analog-to-Digital Converters (ADCs) and require the inversion of matrices with reduced dimension when the number of receive antennas is larger than the number of independent data streams. The advantages of the proposed techniques are particularly high for highly unbalanced MIMO systems, such as in the uplink of Base Station (BS) cooperation systems that aim for Single-Frequency Network (SFN) operation or massive MIMO systems with much more antennas at the receiver side.

반복적 다중사용자 검출을 가진 단일 반송파 주파수 분할 다중접속 시스템에서 다단계 변조를 위한 적응형 전력 제어

반복적 다중사용자 검출을 가진 단일 반송파 주파수 분할 다중접속 시스템에서 다단계 변조를 위한 적응형 전력 제어

Spectral-Efficient Band Allocation Scheme for Frequency-Domain Pulse-Shaping-Based SC-FDMA Systems

One major concern of employing frequency-domain pulse shaping (FDPS) to reduce the peak-to-average power ratio of single-carrier frequency-division multiple-access (SC-FDMA) signals is the decrease of system spectral efficiency due to the excess bandwidth wasted in the existing band allocation schemes (BASs). To improve the spectral efficiency of FDPS-based SC-FDMA systems, a novel BAS is proposed, where edge subcarriers for each user are overlapped with those of all its neighbors. However, the spectrum overlapping incurs multiuser interference and degrades the bit error rate (BER) performance. To address this problem, two iterative multiuser detection (MUD) algorithms are proposed based on expectation propagation (EP), termed joint EP (J-EP) and distributed EP (D-EP). Simulation results demonstrate that, aided by either of the EP-based MUD algorithms, the FDPS-based SC-FDMA system with the proposed BAS can work more spectral-efficiently without BER performance degradation compared to those with the existing BASs. In addition, the D-EP algorithm performs nearly the same as J-EP but requires much lower complexity, making it more appealing for large numbers of allocated subcarriers.

Multi-User Detection for Sporadic IDMA Transmission Based on Compressed Sensing

The Internet of Things (IoT) is placing new demands on existing communication systems. The limited orthogonal resources do not meet the demands of massive connectivity of future IoT systems that require efficient multiple access. Interleave-division multiple access (IDMA) is a promising method of improving spectral efficiency and supporting massive connectivity for IoT networks. In a given time, not all sensors signal information to an aggregation node, but each node transmits a short frame on occasion, e.g., time-controlled or event-driven. The sporadic nature of the uplink transmission, low data rates, and massive connectivity in IoT scenarios necessitates minimal control overhead communication schemes. Therefore, sensor activity and data detection should be implemented on the receiver side. However, the current chip-by-chip (CBC) iterative multi-user detection (MUD) assumes that sensor activity is precisely known at the receiver. In this paper, we propose three schemes to solve the MUD problem in a sporadic IDMA uplink transmission system. Firstly, inspired by the observation of sensor sparsity, we incorporate compressed sensing (CS) to MUD in order to jointly perform activity and data detection. Secondly, as CS detection could provide reliable activity detection, we combine CS and CBC and propose a CS-CBC detector. In addition, a CBC-based MUD named CBC-AD is proposed to provide a comparable baseline scheme.

Joint Transmit Power Allocation and Splitting for SWIPT Aided OFDM-IDMA in Wireless Sensor Networks

In this paper, we propose to combine Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) with Simultaneous Wireless Information and Power Transfer (SWIPT), resulting in SWIPT aided OFDM-IDMA scheme for power-limited sensor networks. In the proposed system, the Receive Node (RN) applies Power Splitting (PS) to coordinate the Energy Harvesting (EH) and Information Decoding (ID) process, where the harvested energy is utilized to guarantee the iterative Multi-User Detection (MUD) of IDMA to work under sufficient number of iterations. Our objective is to minimize the total transmit power of Source Node (SN), while satisfying the requirements of both minimum harvested energy and Bit Error Rate (BER) performance from individual receive nodes. We formulate such a problem as a joint power allocation and splitting one, where the iteration number of MUD is also taken into consideration as the key parameter to affect both EH and ID constraints. To solve it, a sub-optimal algorithm is proposed to determine the power profile, PS ratio and iteration number of MUD in an iterative manner. Simulation results verify that the proposed algorithm can provide significant performance improvement.

Design and Analysis of Numerical Interleaver for IDMA Schemes with Iterative Multi-user Detection

Objective: This work provides a comprehensive study of a novel orthogonal interleaver set based on particular numerical equation for generation of user specific interleavers. Methods/Analysis: Performance analysis is done based upon the computer simulations in various scenarios with IDMA system and SC-FDMA-IDMA system, under different channel conditions including Additive White Gaussian Noise (AWGN) and Under Water Acoustic (UWA) channel to compare proposed interleaver with other interleavers in literature. The performance of different interleavers is compared on the basis of bit error rate (BER) results and also by hardware and bandwidth requirements. Findings: Compared to other interleavers discussed in literature, the proposed interleaver set is easy to generate, more-over this work has presented a method which doesn’t require common master random interleaving pattern to develop other interleaving patterns. The analysis confirms that the proposed method of interleaver generation outperforms various other interleavers in terms of BER performance and bandwidth requirement, while providing considerably lower complexity. Applications: Applications of orthogonal interleavers include all non-orthogonal multiple access schemes based on Multi-User Detection (MUD) strategy including Interleave Division Multiple Access (IDMA), Orthogonal Frequency Division Multiplexing-Interleave Division Multiple Access (OFDM-IDMA) and Single Carrier Frequency Division Multiple Access-Interleave Division Multiple Access (SC-FDMA-IDMA) scheme, employing user specific interleavers for user separation.

Differential Characteristics Based Iterative Multiuser Detection for Wireless Sensor Networks.

High throughput, low latency and reliable communication has always been a hot topic for wireless sensor networks (WSNs) in various applications. Multiuser detection is widely used to suppress the bad effect of multiple access interference in WSNs. In this paper, a novel multiuser detection method based on differential characteristics is proposed to suppress multiple access interference. The proposed iterative receive method consists of three stages. Firstly, a differential characteristics function is presented based on the optimal multiuser detection decision function; then on the basis of differential characteristics, a preliminary threshold detection is utilized to find the potential wrongly received bits; after that an error bit corrector is employed to correct the wrong bits. In order to further lower the bit error ratio (BER), the differential characteristics calculation, threshold detection and error bit correction process described above are iteratively executed. Simulation results show that after only a few iterations the proposed multiuser detection method can achieve satisfactory BER performance. Besides, BER and near far resistance performance are much better than traditional suboptimal multiuser detection methods. Furthermore, the proposed iterative multiuser detection method also has a large system capacity.

Investigation on iterative multiuser detection physical layer network coding in two-way relay free-space optical links with turbulences and pointing errors.

Physical layer network coding (PNC) improves the throughput in wireless networks by enabling two nodes to exchange information using a minimum number of time slots. The PNC technique is proposed for two-way relay channel free space optical (TWR-FSO) communications with the aim of maximizing the utilization of network resources. The multipair TWR-FSO is considered in this paper, where a single antenna on each pair seeks to communicate via a common receiver aperture at the relay. Therefore, chip interleaving is adopted as a technique to separate the different transmitted signals at the relay node to perform PNC mapping. Accordingly, this scheme relies on the iterative multiuser technique for detection of users at the receiver. The bit error rate (BER) performance of the proposed system is examined under the combined influences of atmospheric loss, turbulence-induced channel fading, and pointing errors (PEs). By adopting the joint PNC mapping with interleaving and multiuser detection techniques, the BER results show that the proposed scheme can achieve a significant performance improvement against the degrading effects of turbulences and PEs. It is also demonstrated that a larger number of simultaneous users can be supported with this new scheme in establishing a communication link between multiple pairs of nodes in two time slots, thereby improving the channel capacity.

Iterative multiuser detection for high spectral efficiency reverse-link of multibeam satellite via expectation propagation

Iterative multiuser detection for high spectral efficiency reverse-link of multibeam satellite via expectation propagation