Parallel Interference Cancellation Research Articles

Learning-Based Signal Detection for Wireless OAM-MIMO Systems With Uniform Circular Array Antennas

This paper presents a neural-like network-based signal detection method for orbital angular momentum multiplexing systems with uniform circular array antennas. The signal detection network is derived by unfolding the alternating direction method of multipliers (ADMM), and in addition, a parallel interference cancellation (PIC) function is integrated, which enhances the tolerance to inter-mode interference while keeping the complexity feasible. The number of parameters to be learned in each layer of the network is a linear order of the number of antenna elements. Simulation results show that the ADMM-PIC detector exhibits excellent error performance, which cannot be achieved by a conventional minimum mean square error-based detector.

Secrecy Outage Probability and Fairness of Packet Transmission Time in a NOMA System

In this paper, we analyze the secrecy outage probability (SOP) and the fairness of average packet transmission time for a non-orthogonal multiple access (NOMA) system which consists of a base station (BS) and two legal NOMA users in the presence of an eavesdropper (Eve). In order to extract the superimposed signal, the Eve is considered in two modes, i.e., successive interference cancellation (SIC) mode and parallel interference cancellation (PIC) mode. Accordingly, we analyze the secrecy performance of the considered system by deriving a new exact expression for SOP. Furthermore, the optimal power allocation between two legal users is determined such that the average transmission time from BS to two legitimate users are approximately equal to achieve the fairness of average packet transmission time. Monte Carlo simulations are provided to verify our analytical results.

Residue Effect of Parallel Interference Canceller in Belief Propagation Decoding in Massive MIMO Systems

Residue Effect of Parallel Interference Canceller in Belief Propagation Decoding in Massive MIMO Systems

Filtered OFDM: An Insight Into Intrinsic In-Band Interference and Filter Frequency Response Selectivity

The future mobile networks will face challenges in support of heterogeneous services over a unified physical layer, calling for a waveform with good frequency localization. Filtered orthogonal frequency division multiplexing (f-OFDM), as a representative subband filtered waveform, can be employed to improve the spectrum localization of orthogonal frequency-division multiplexing (OFDM) signal. However, the applied filtering operations will impact the performance in various aspects, especially for narrow subband cases. Unlike existing studies which mainly focus its benefits, this paper investigates two negative consequences inflicted on single subband f-OFDM systems: in-band interference and filter frequency response (FFR) selectivity. The exact-form expression for the in-band interference is derived, and the effect of FFR selectivity is analyzed for both single antenna and multiple antenna cases. The in-band interference-free and nearly-free conditions for f-OFDM systems are studied. A low-complexity block-wise parallel interference cancellation (BwPIC) algorithm and a pre-equalizer are proposed to tackle the two issues caused by the filtering operations, respectively. Numerical results show that narrower subbands suffer more performance degradation compared to wider bands. In addition, the proposed BwPIC algorithm effectively suppresses interference, and pre-equalized f-OFDM (pf-OFDM) considerably outperforms f-OFDM in both single antenna and multi-antenna systems.

A Novel Iterative Receiver Design for CP-Free Transmission Under Frequency-Selective Channels

In this letter, we develop a general iterative receiver based on the minimum mean squared error with parallel interference cancellation (MMSE-PIC) for cyclic prefix (CP)-free transmission. In particular, we consider that the receiver detects several blocks jointly, which allows backward block correction (BC). Additionally, we provide a structure with reduced complexity for Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Chirp Division Multiplexing (OCDM) waveforms. As expected, the results show that our BC-based receiver improves the performance compared with a receiver without BC. Moreover, we show that OCDM outperforms OFDM, and has practically no performance loss compared to CP-OFDM, which motivates the use of OCDM instead of CP-OFDM to decrease latency and increase spectral efficiency.

Multiuser detection for uplink non‐orthogonal multiple access system

Non-orthogonal multiple access (NOMA) makes multiple users to overload the same wireless resources by utilising the superposition coding principle, so that NOMA can improve the system capacity and spectral efficiency. Therefore, NOMA has recently received considerable attention as a promising candidate to address some of the challenges for 5G. Various NOMA schemes including the power-domain NOMA (PD-NOMA) are proposed, and successive interference cancellation (SIC) is applied for detection, which limits the promised performance gain brought by NOMA due to the error propagation. In this study, the authors introduce an iterative interference cancellation (IIC) detection scheme for uplink PD-NOMA system by using parallel interference cancellation (PIC) scheme. The interleave division multiple access is also employed for improving system performance. A new detection scheme based on IIC is proposed, which is called advanced IIC (AIIC). The simulation results show that the bit error rate performance of AIIC is much better than that of SIC, and is close to that of maximum a posteriori. The AIIC can obtain the promised performance gain brought by NOMA.

Semi‐blind MIMO‐OFDM channel estimation using expectation maximisation like techniques

This study deals with semi-blind (SB) channel estimation of multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system using maximum likelihood (ML) technique. For the ML cost optimisation function, new expectation maximisation (EM) algorithms for the channel taps estimation are introduced. Different approximation/simplification approaches are proposed for the algorithm's computational cost reduction. The first approach consists of decomposing the MIMO-OFDM system into parallel multiple-input single-output OFDM systems. The EM algorithm is then applied to estimate the MIMO channel in a parallel way. The second approach takes advantage of the SB context to reduce the EM cost from exponential to linear complexity by reducing the size of the search space. Finally, the last proposed approach uses a parallel interference cancellation technique to decompose the MIMO-OFDM system into several single-input multiple-output OFDM systems. The latter are identified in a parallel scheme and with a reduced complexity. The performance of the proposed approaches are discussed, assessed through numerical experiments and compared with respect to the Cramer Rao Bound and to other EM-based solutions reported in the literature.

Overlapped universal filtered multicarrier system for uplink wireless communication

SummaryUniversal filtered multicarrier (UFMC) is a promising new waveform that eliminates cyclic prefix and performs filtering on a chunk of successive subcarriers. Therefore, it is suitable for applications with requirements on high spectral efficiency and low latency. However, the limited bandwidth may be an obstacle for reliable communication in frequency selective channels. This paper proposes a new transmitter structure for uplink wireless communication system based on UFMC waveform. The basic idea is to allow a user to transmit its information on more than one subband simultaneously, increasing its robustness against frequency selectivity. To eliminate the multiuser interference brought by the overlapped transmission strategy, an iterative receiver with parallel interference cancellation is designed. Rate analysis is provided to reveal the rationale of the proposed scheme. Simulations on the symbol error rate performance are conducted to validate the transceiver design. It is found that the proposed scheme outperforms existing UFMC design without sacrificing any other performance metrics with only moderately increased complexity.

An LDPC-Coded SCMA Receiver With Multi-User Iterative Detection and Decoding

This paper presents the first low-complexity realization of an LDPC-code sparse code multiple access (SCMA) receiver with a high-throughput LDPC decoder and a multi-mode SCMA detector. The minimum mean-square error with parallel interference cancellation (MMSE-PIC) algorithm is adopted in the SCMA detection. The modified user-node operations in the MMSE-PIC-based message-passing detector improve the convergence rate in error performance. The proposed receiver also supports multi-user iterative detection and decoding (MU-IDD) to improve the error rate performance. The proposed receiver supports both $4\times 6$ and $8\times 12$ SCMA systems. The proposed MU LDPC decoder has a 57.1% lower hardware complexity than the direct-mapped design that is achieved through hardware sharing and memory access scheduling. Designed in a 40-nm CMOS technology, the SCMA receiver integrates 10.9M logic gates in an area of $3.382\times 3.382$ mm2. The proposed design achieves a gross throughput of 1.198 Gb/s and 599 Mb/s for $8\times 12$ and $4\times 6$ SCMA systems, respectively, under a practical situation. It dissipates 813 mW at a clock frequency of 300 MHz from a 0.9-V supply.

Iterative multipacket detection with FDE based MAC protocol in vehicular ad hoc networks

Wireless access in vehicular environments (WAVE), is especially designed to support vehicular ad hoc networks (VANETs) requirements, where rapidly changing channel conditions introduces unsynchronized transmissions. In such networks, instead of dealing with interferences in medium access control (MAC) layer or physical layer alone, both layers should be considered to cooperate and complement each other. In this paper, multipacket detection (MPD) technique with frequency domain equalization (FDE) is proposed for VANETs, with cyclically shifted different interleavers for different nodes, to remove interference and reducing the information exchange between nodes. These promising multi-hop wireless networks are used in situations, where temporary network connectivity is needed. Therefore, to improve the communication between vehicles (V2V) and from vehicles to roadside infrastructure (V2I), MPD-FDE with interference cancellation (IC) schemes can be used iteratively to successfully decode and receive even colliding packets. For designing such a protocol, different key aspects are discussed with an emphasis on iterative MPD-FDE. Numerical results with different network nodes, show the MPD-FDE performances for coded and uncoded transmissions with different IC schemes, where successive IC (SIC) is much better than parallel IC (PIC) schemes. It is also shown that the proposed protocol provide reliable detection and excellent throughput improvements, with much less resource consumption compared to multiple random interleavers.

Projected block‐wise PIC detection for communication systems with non‐negativity constraints

Recently, a number of interference cancellation (IC) detectors that exploit some prior information of the system have been proposed. Of particular interest is the projected parallel IC (PPIC) detector that makes use of the non-negativity of the data and the spreading codes in incoherent optical-code-division multiple-access systems to improve the detection performance. In this work, the authors generalise the PPIC detector where more than one user is considered at a time yielding the projected block-wise parallel IC (PBPIC) detector. This detector not only accelerates the convergence speed considerably but also improves the conditions of convergence as well. Various approaches for reducing the complexity of the PBPIC detector are investigated. Simulation results agree well with the authors’ theoretical findings.

Multiuser Interference Cancellation for GFDM With Timing and Frequency Offsets

In uplink multiuser systems, different timing offset (TO) and/or carrier frequency offset (CFO) of multiple users cause multiuser interference (MUI) to a desired user. In this paper, we propose two different MUI cancellation methods, namely weighted parallel interference cancellation (WPIC) and adaptive interference cancellation filter (AICF), for uplink transmission with generalized frequency division multiplexing (GFDM) waveform over Rayleigh fading channel given the existence of TO and CFO of multiple users. The proposed WPIC performs MUI estimation using the detected data symbol of other users and obtains the optimal weight to maximize the signal-to-interference ratio (SIR) of the desired user. We also propose the AICF that aims to maximize the SIR of the desired user. Based on our SIR expression derived in closed-form in the presence of TO and CFO, the AICF is obtained by solving the Rayleigh quotient problem. Lastly, the impact of multiple antennas at the receiver on MUI cancellation is also analyzed to improve reliability. The simulation results show that the proposed WPIC and AICF effectively eliminate MUI and that the AICF can outperform the WPIC in terms of the SIR and spectral efficiency. In addition, the multiple receiver antennas effectively cancel MUI as the number of antennas goes to infinity.

Enhanced Multiuser Superposition Transmission Through Structured Modulation

The fifth-generation (5G) air interface, namely, dynamic multiple access (MA) based on multiuser superposition transmission (MUST) and orthogonal MA (OMA), may require a complicated scheduling and heavy signaling overhead. To address these challenges, we propose a unified MA scheme for future cellular networks, which we refer to as structured MUST (S-MUST). In S-MUST, we apply complex power allocation coefficients (CPACs) over multiuser legacy constellations to generate a composite constellation. In particular, the in-phase ( $I$ ) and quadrature ( $Q$ ) components of the legacy constellation of each user are separately multiplied by those of the CPACs. As such, the CPACs offer an extra degree of freedom for multiplexing users and guarantee fairness in symmetric broadcast channels. This new paradigm of superposition coding allows us to design $IQ$ separation at the user side, which significantly reduces the decoding complexity without degrading performance. Hence, it supports low-complexity frequency-selective scheduling that does not entail dynamical switching between MUST and OMA. We further propose to quantize the CPACs into complex numbers where $I$ and $Q$ components of each quantized coefficient are primes, facilitating parallel interference cancellation at each user via modulo operations; last but not least, we generalize the design of S-MUST to exploit the capabilities of multiantenna base stations. The proposed S-MUST exhibits an improved user fairness with respect to conventional MUST (134% spectral efficiency enhancement) and a lower system complexity compared with dynamically alternating MUST and OMA.

MIMO Underwater Acoustic Communication in Shallow Water with Ice Cover

Although multiple-input multiple-output (MIMO) underwater acoustic (UWA) communication has been intensively investigated in the past years, existing works mainly focus on open-water environment. There is no work reporting MIMO acoustic communication in under-ice environment. This paper presents results from a recent MIMO acoustic communication experiment which was conducted in Bohai Gulf during winter. In this experiment, high frequency MIMO signals centered at 10 kHz were transmitted from a two-element source array to a four-element vertical receiving array at 1 km range. According to the received signal of different array elements, MIMO acoustic communication in under-ice environment suffers less effect from co-channel interference compared with that in open-water environment. In this paper, time reversal followed by a single channel decision feedback equalizer is used to process the experimental data. It is demonstrated that this simple receiver is capable of realizing robust performance using fewer hydrophones (i.e. 2) without the explicit use of complex co-channel interference cancelation algorithms, such as parallel interference cancelation or serial interference cancelation.

Deep Learning Network for Multiuser Detection in Satellite Mobile Communication System.

A multiuser detection (MUD) algorithm based on deep learning network is proposed for the satellite mobile communication system. Due to relative motion between the satellite and users, multiple access interference (MUI) introduced by multipath fading channel reduces system performance. The proposed MUD algorithm based on deep learning network firstly establishes the CINR optimal loss function according to the multiuser access mode and then obtains the best multiuser detection weight through the steepest gradient iteration. Multilayer nonlinear learning obtains interference cancellation sharing weights to achieve maximum signal-to-noise ratio through gradient iteration, which is superior than the traditional serial interference cancellation algorithm and parallel interference cancellation algorithm. Then, the weights with multiuser detection through multilayer network forward learning iteration are obtained with traditional multiuser detecting quality characteristics. The proposed multiuser access detection based on deep learning network algorithm improves the MUD accuracy and reduces the number of traditional multiusers. The performance of the satellite multifading uplink system shows that the proposed deep learning network can provide high precision and better iteration times.

Low‐complexity and full‐diversity parallel interference cancellation for multiuser wireless relaying networks

AbstractIn this paper, the multiuser interference of wireless relaying networks (WRNs) is considered. Two transmission protocols with an interference cancellation scheme are proposed, namely, the concurrentS − R−D‐PICR,D protocol for decode‐and‐forward WRNs and the concurrentS − R − D‐PICD protocol for amplify‐and‐forward WRNs. Unlike the existing protocols, these protocols allow the concurrent transmission in both phases of the transmission, and hence, higher spectral efficiency is offered while maintaining low decoding complexity. The concurrentS − R − D‐PICR,D protocol achieves interference‐free diversity without imposing any condition on the node's antenna number. However and similar to most existing protocols, this protocol requires the channel state information (CSI) of the users‐relay links at the relay. In contrast, the concurrentS − R − D‐PICD protocol achieves a better diversity order, given that the relay's antenna >8, whereas CSI is required only at the destination. Although the diversity's upper bound is not achieved, this protocol uses a simple relay as no CSI or encoding is required at the relay. In addition and unlike the existing protocols, the achievable diversity is determined by both the user's and the destination's antennas, and it is not sacrificed while the number of users is increased. This paper also establishes sufficient conditions for a space‐time block code to achieve the mentioned diversity gain of the proposed protocols.

GPU Accelerated PIC and SIC for OFDM-NOMA

Non-orthogonal multiple access (NOMA) is a candidate multiple access scheme for the fifth-generation (5G) cellular networks. In NOMA systems, all users operate at the same frequency and time, which poses a challenge in the decoding process at the receiver side. In this work, the two most popular receiver structures, successive interference cancellation (SIC) and parallel interference cancellation (PIC) receivers, for NOMA reverse channel are implemented on a graphics processing unit (GPU) and compared. Orthogonal frequency division multiplexing (OFDM) is considered. The high computational complexity of interference cancellation receivers undermines the potential deployment of NOMA systems. GPU acceleration, however, challenges this weakness, and our numerical results show speedups of about from 75–220-times as compared to a multi-thread implementation on a central processing unit (CPU). SIC and PIC multi-thread execution time on different platforms reveals the potential of GPU in wireless communications. Furthermore, the successful decoding rates of the SIC and PIC are evaluated and compared in terms of bit error rate.

Performance Comparison of Adaptive filtering Algorithms for Parallel Interference Cancellation in Asynchronous MC DS-CDMA Systems

The Bit Error Rate (BER) comparison of Adaptive Parallel Interference Cancellation (APIC) algorithms in asynchronous Multicarrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA) system is introduced. The APIC is used to eliminate the Multiple Access Interference (MAI) in MC-DS-CDMA system. The Adaptive filtering algorithms considered are, Normalized Least Mean Squares (NLMS), Variable Step Size Normalized Least Mean Squares (VSS-NLMS), and Generalized Normalized Gradient Descent (GNGD) algorithms. These algorithms are used in coincidence with APIC system for updating cancellation weights. The performance comparison between these algorithms is performed via extensive computer simulations. Simulation results demonstrate that the VSSNLMS algorithm outperforms all other algorithms, the NLMS is modular, while the worst performance is obtained by GNGD.

Improved Uplink NOMA Performance Through Adaptive Weighted Factors Aided PIC and MA Signature

Non-orthogonal multiple access (NOMA) is one innovative technology that provides low latency, high system capacity, high spectrum efficiency, and massive connectivity to solve several challenges suffered by a fifth generation (5G) mobile communication system. NOMA on the uplink with superior research value was widely mentioned at Mobile World Congress and has been released in the latest technical report by the Third Generation Partnership Project (3GPP). However, how to decode all users' signals on the uplink NOMA precisely and in parallel and achieve the separation of the superimposed users' signals is the major challenge. Therefore, an improved uplink NOMA scheme through adaptively weighted factors aided parallel interference cancellation (PIC) algorithm and multiple access (MA) signature is proposed to solve the problem. In this paper, we first briefly discuss the research status of the MA signatures used to separate superimposed users' signals. In addition, we review the existing interference cancellation algorithms used by receivers to decode message signals, which mainly include a successive interference cancellation (SIC) algorithm and the PIC algorithm. And the research value of the PIC algorithm on uplink NOMA is highlighted. Then, we briefly formulate the effect of the bias in decision statistics and adaptive weighted factors aided PIC algorithm is proposed to reduce the biased estimation. Finally, yet important, we comprehensively evaluate the performance of the proposed improving PIC algorithm in terms of bit error rate (BER), computational complexity, sum data rate, and delay estimation errors.

Pilot- and CP-Aided Channel Estimation in MIMO Non-Orthogonal Multi-Carriers

Motivated by 5G application requirements that challenge the use of orthogonal frequency division multiplexing (OFDM), non-orthogonal multi-carriers are being investigated. Unlike OFDM that takes advantage of orthogonal pilot observation, in non-orthogonal waveforms, pilots are contaminated by interference from multiple dimensions, i.e., inter-subsymbol-, inter-carrier-, and inter-antenna-interference, when multiple-input-multiple-output (MIMO) is also part of the transmission. Employing cyclic-prefix (CP) in multi-carrier systems not only protects the signal from inter-symbol-interference but also allows circular interpretations of the channel, which simplifies the estimation and equalization techniques. Nevertheless, the CP information is usually discarded at the receiver side. In this paper, by considering the fact that non-orthogonal waveforms suffer from multiple dimensions of interference, we derive a MIMO linear-minimum-mean-squared-error (LMMSE)-based parallel-interference-cancellation (PIC) method for joint channel estimation and equalization of non-orthogonal waveforms. Unlike the common practice, by properly localizing the pilots in time domain, we also use the pilots’ information from CP. We apply our proposed algorithm to a flexible non-orthogonal waveform known as generalized frequency division multiplexing (GFDM). Taking advantage of block-circularity of GFDM, we investigate the complexity aspects for such CP-aided LMMSE-PIC channel estimation. Through simulation results, we show that using CP information of pilots for GFDM gains up to 2.4-dB better frame error rate performance than an OFDM signal.