Simple Zero-forcing Research Articles

Delay Alignment Modulation: Enabling Equalization-Free Single-Carrier Communication

This letter proposes a novel broadband transmission technology, termed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">delay alignment modulation</i> (DAM), which enables the low-complexity equalization-free single-carrier communication, yet without suffering from inter-symbol interference (ISI). The key idea of DAM is to deliberately introduce appropriate delays for information-bearing symbols at the transmitter side, so that after propagating over the time-dispersive channel, all multi-path signal components will arrive at the receiver simultaneously and constructively. We first show that by applying DAM for the basic multiple-input single-output (MISO) communication system, an ISI-free additive white Gaussian noise (AWGN) system can be obtained with the simple zero-forcing (ZF) beamforming. Furthermore, the more general DAM schemes are studied with the ISI-maximal-ratio transmission (MRT) and the ISI-minimum mean-square error (MMSE) beamforming. Simulation results are provided to show that when the channel is sparse and/or the antenna dimension is large, DAM not only resolves the notorious practical issues suffered by orthogonal frequency-division multiplexing (OFDM), such as high peak-to-average-power ratio (PAPR) and vulnerability to carrier frequency offset (CFO), but also achieves higher spectral efficiency due to the saving of guard interval overhead.

Design and Analysis of LoS-MIMO Systems With Uniform Circular Arrays

We consider the design of a uniform circular array (UCA) system under array misalignment over line-of-sight (LoS) channels. UCAs have been considered as useful array structures since their LoS channels can be diagonalized without the channel state information at the transmitter (Tx). However, such a characteristic holds only when transceiver arrays are perfectly aligned. To overcome this difficulty, we propose an optimal design method and transceiver architectures for UCA systems under array misalignment that achieve channel capacity without knowledge of misalignment angles. To this end, we first verify that the singular values of the misaligned UCA system are independent of tilting and center-shift and small relative array rotation, but fluctuate with the Radii Product to Distance Ratio (RPDR). Using the result, we present an optimal design method for UCA systems that performs an one-dimensional search for the RPDR to maximize channel capacity, and we show that a simple zero-forcing (ZF) receiver can achieve the maximum channel capacity because of the channel characteristic at the optimal design criteria. Additionally, we propose a low-complexity precoding scheme for UCA systems in which the optimal design criteria cannot be fulfilled. The simulation results demonstrate the validity of the proposed design method and transceiver architectures.

Optimality of Linear MIMO Detection for 5G Systems via 1-Opt Local Search

Multiple input multiple output (MIMO) symbol detection problem belongs to non-deterministic polynomial acceptable hard combinatorial optimization (CO) class. One of the key trials in design of MIMO scheme is to develop a low complexity detection algorithm without much compromise in performance. Detection approaches proposed in the literature can be split into non-linear and linear algorithms. Vertical Bell-Labs Layered Space Time (V-BLAST) and Sphere Decoder (SD) are non-linear methods used for extracting transmitted data; whereas, Zero-Forcing (ZF) and Minimum Mean Square Error (MMSE) detections are comparatively in complex and effectual linear techniques. In this work, the heuristic 1-Opt local search method used for solving computationally hard combinatorial optimization problems is applied to the ZF and MMSE detection algorithms. First, simple MIMO decoding using ZF and MMSE is accomplished to find the estimated symbol then the transmitted symbol is calculated using the heuristic 1-opt approach by means of the estimated symbol. Simulation results demonstrate that 1-opt search when applied to the ZF and MMSE displays better bit error rate (BER) performance than the simple ZF and MMSE detectors. It is also verified through simulations that the proposed 1-Opt based detectors display better BER performance as compared to the complex nonlinear VBLAST and SD at considerably reduced complexity. Hence, the proposed detectors are appropriate for effective hardware implementations.

COMMUNICATION SYSTEMS FOR HIGH SPEED FLYING DEVICES WITH REPETITION CODES

Communication systems for devices moving at high speed are suffering from error-floor due to the Doppler effect. This paper proposes a simple narrowband communication systems for high speed flying devices for critical applications such as missile and drone. To make the system simple, we consider Repetition codes and slight increase of the number of pilot symbols such that the system can predict accurately the fast-changing channel due to time-selective fading. The equalizer in this paper is designed according to the addition of the pilot symbols so that the system works at a maximum speed of 450 km/h to make successful operation for missile and drone before they are taken down by the enemy. Computer simulations are used to evaluate the performance of the proposed communication systems. The operating frequency is industrial, scientific, and medical (ISM) band, where binary phase shift keying (BPSK) modulations are used with Repetition codes being the channel coding. The bit error rate (BER) performance is evaluated under additive white Gaussian noise (AWGN) and Rayleigh fading channels. The results confirm that excellent BER performances are obtained having error-floor less than 10????4 making many applications, including image transmission, are possible, which are great for high speed flying devices even with Repetition codes and simple zero forcing (ZF) equalizer. The results of this study are expected to help the development of future communication systems for missile, drone, and airplane applications.

Error Rate Analysis of ZF and MMSE Decoders for Massive Multi Cell MIMO Systems in Impulsive Noise Channels

In wireless channels, Non-Gaussian noise is one of the most common noise models that is observed. This type of noise has a severe impact on wireless systems with linear and multiuser detection devices. In this paper, We study the performance of zero forcing (ZF) and minimum mean square error (MMSE) ZF detection methods in Impulsive multi-cell MIMO channels. We start by showing the Bit Error Rate performance in non-Gaussian channels for ZF Detection, then we extend the derivations for MMSE ZF system. We clearly show the lower and upper bound derivations and verify it through simulations. The sum rate analysis for this case is also examined. Finally, we address the ZF matrix inversion complexity problem, and propose a simple ZF algorithm that does not necessitate the matrix inversion. We then investigate the convergence of such a detector and look at the Symbol Error rate SER performance through simulation again.

Interference Channels With Coordinated Multipoint Transmission: Degrees of Freedom, Message Assignment, and Fractional Reuse

Coordinated multipoint (CoMP) transmission is an infrastructural enhancement under consideration for next generation wireless networks. In this paper, the capacity gain achieved through CoMP transmission is studied in various models of wireless networks that have practical significance. The capacity gain is analyzed through the degrees of freedom (DoF) criterion. The DoF available for communication provides an analytically tractable way to characterize the capacity of interference channels. The considered channel model has $K$ transmitter/receiver pairs, and each receiver is interested in one unique message from a set of $K$ independent messages. Each message can be available at more than one transmitter. The maximum number of transmitters at which each message can be available, is defined as the cooperation order $M$ . For fully connected interference channels, it is shown that the asymptotic per user DoF, as $K$ goes to infinity, remains at ${1}/{2}$ as $M$ is increased from 1 to 2. Furthermore, the same negative result is shown to hold for all $M\geq 2$ for any message assignment that satisfies a local cooperation constraint. On the other hand, when the assumption of full connectivity is relaxed to local connectivity, and each transmitter is connected only to its own receiver as well as $L$ neighboring receivers, it is shown that local cooperation is optimal. The asymptotic per user DoF is shown to be at least max $\left\{{1}/{2},{2M}/(2M+L)\right\}$ for locally connected channels, and is shown to be ${2M}/(2M+1)$ for the special case of Wyner's asymmetric model where $L=1$ . An interesting feature of the proposed achievability scheme is that it relies on simple zero-forcing transmit beams and does not require symbol extensions. Also, to achieve the optimal per user DoF for Wyner's model, messages are assigned to transmitters in an asymmetric fashion unlike traditional assignments where message $i$ has to be available at transmitter $i$ . It is also worth noting that some receivers have to be inactive, and fractional reuse is needed to achieve equal DoF for all users.

Characterization of Implemented Algorithm for MIMO Spatial Multiplexing in Reverberation Chamber

Previously, the throughput for a single-input multiple-output (SIMO) system was successfully tested in a reverberation chamber (RC), and the results were in good agreement with a model based on the ideal threshold receiver. In the present communication, we measure the throughput of a 2 × 2 open loop multiple-input multiple-output (MIMO) system with full spatial multiplexing (i.e., two data streams), and we compare the results with an extended throughput model taking the spatial multiplexing into account. The measured throughput is found to be in agreement with the simulated one of a simple zero-forcing (ZF) receiver. The throughput degradations due to correlation and power imbalance (caused by different embedded radiation efficiencies of antennas) are studied and referred to as a throughput multiplexing efficiency. These can, to a large extent, be explained by the ZF algorithm. The results show clearly that the rich isotropic multipath (RIMP) environment generated by an RC can be used to study how effective different MIMO algorithms are when there is correlation and efficiency imbalance between the antenna elements.

Performance Evaluation of DWT-OFDM and FFT-OFDM for Multicarrier Communications Systems using Time Domain Zero Forcing Equalization

Other than the conventional fast Fourier transform (FFT) for multicarrier modulation, a new approach for multicarrier modulation (MCM) has been known. Meanwhile, multicarrier modulation involves dividing the broadband channel into many orthogonal but overlapping narrowband carriers. In an OFDM modulation based multicarrier system using the FFT, a cyclic prefix (CP) is inserted after each symbol frame to combat the effects of inter symbol interference (ISI). By inserting the CP, which results in spectral inefficiency OFDM schemes trades up to 25% of the transmit bandwidth. A new MCM approach that is void of the expense is the wavelet transform-based systems. These systems also have very suppressed side-lobes and exhibit improved BER performance. In wavelet based systems, the latest challenge in its implementation is in the channel estimation. In this work we have studied the performance of the FFT based OFDM system against wavelet transform (WT) based multicarrier system using a simple zero forcing (ZF) equalization in time domain. The studied system shows some improved BER performance.

Beamforming techniques for enabling spatial-reuse in MCCA 802.11s networks

We address the problem of co-channel interference (CCI) in wireless mesh networks based on the IEEE802.11s extension. The carrier sensing mechanism deployed in those networks insufficiently addresses the CCI problem, causing the hidden and exposed node problems; consequently degrading the throughput and latency. In this paper, we show how beamforming techniques can be implemented on top of the IEEE802.11s medium access control protocol and, using the information readily available, cancel the interference to mitigate this inefficiency of carrier sense and improve the spatial-reuse gain. In addition, we propose the signal-to-jamming-noise ratio (SJNR) beamformer and show that it significantly improves the spatial-reuse gain compared to the simple zero-forcing (ZF) beamformer and the basic IEEE802.11s access scheme. We derive the ergodic capacity of the ZF beamformer and the basic IEEE802.11s access scheme and simulate the performance of the various schemes. We show that improvements of up to 85% are achieved as function of the scenario simulated and the beamforming technique used and that the SJNR scheme outperforms the standard ZF beamformer.

높은 안테나 상관도를 갖는 다중입출력 공간 다중화 시스템을 위한 통계적 프리코딩 기법

다중입출력 공간 다중화 시스템은 송수신 안테나 간 상관도가 있는 채널에서 심각한 성능 열화를 겪는다. 본 논문에서는 ML (maximum likelihood) 수신기를 결합한 다중입출력 무선통신 환경을 위해, 송신단에서 채널상관 행렬 정보만을 활용한 새로운 통계적 프리코딩 기법을 소개한다. 우리는 다차원 심볼 성상의 최소 유클리디언 거리를 최대화하는 두 가지 간단한 형식의 (closed-form solution) 프리코더, 회전 변환 및 파워 로딩 기법을 제안한다. 또한, 제안한 기법을 선형 zero-forcing (ZF) 수신기에 확장 적용하여 성능을 향상시키는 방법을 고안한다. 실험 결과를 통해 제안하는 기법은 ML 수신기 및 ZF 수신기에서 기존의 기법에 비하여 각각 2dB 및 8dB의 비트 에러율 성능 이득을 제공함을 확인할 수 있다. It has been shown that the performance of multiple-input multiple-output (MIMO) spatial multiplexing systems is significantly degraded when spatial correlation exists between transmit and receive antenna pairs. In this paper, we investigate designs of a new statistical precoder for spatial multiplexing systems with maximum likelihood (ML) receiver which requires only correlation statistics at the transmitter. Two kinds of closed-form solution precoders based on rotation and power allocation are proposed by means of maximizing the minimum E tlidean distance of joint symbol constellations. In addition, we extend our results to linear receivers for correlated channels. We provide a method which yields the same profits from the proposed precoders based on a simple zero-forcing (ZF) receiver. The simulation shows that 2dB and 8dB gains are achieved for ML and ZF systems with two transmit antennas, respectively, compared to the conventional systems.

Distributed spatial-temporal precoding with limited feedback in MIMO multi-relay systems

Precoding techniques can be introduced into multi-relay systems due to the similarity between cooperative communication systems and traditional multi-input–multi-output (MIMO) systems. In this paper, a channel state information (CSI) feedback scheme based on the zero-forcing (ZF) relaying protocol is proposed at first, where the information of relaying channel and noise related to each relay node can be compressed into two positive real parameters. Then, based on the proposed feedback scheme, the singular-vector-based local temporal precoder is presented at the source node through two continuous transmitted vectors, which is termed as distributed spatial–temporal precoding (DSTP). Moreover, various spatial data rates can be conveniently supported by DSTP. Based on the analysis on DSTP, it is better that the number of data streams is not larger than the number of antennas equipped at the source node. The unitary DSTP with the proposed feedback scheme outperforms not only the close-loop direct transmission but also the simple ZF relaying method. Copyright © 2010 John Wiley & Sons, Ltd.

An Analysis of the EIC Method for OFDM/OQAM Systems

OFDM/OQAM is a multi-carrier modulation scheme that, differently from conventional OFDM, does not require any guard interval. Indeed, the interference that results from a transmission over time and/or frequency selective channels can be partly contained if the pulse shape has been appropriately selected. Nevertheless, for certain transmission conditions, a simple zero-forcing (ZF) equalization is not enough to cancel this interference. In this paper, we propose an Equalization with Interference Cancellation (EIC) to counteract the performance floor that characterizes OFDM/OQAM systems using a simple ZF equalization. The basic principle rests on an accurate computation of the interference term taking into account the channel and the prototype filter coefficients. The simulation results illustrate the efficiency of the EIC method.