MIMO Receiver Research Articles

Front-End Design for Compact MIMO Receivers: A Communication Theory Perspective

The front-end is a crucial component in modern wireless communication systems. For SISO systems minimizing the front-end noise factor is optimal, and this also applies to MIMO systems with i.i.d. noise. However, for compact MIMO receivers that may exhibit spatially correlated noise, e.g., through antenna mutual coupling, the optimal design procedure is not clear. In this paper we develop MIMO low-noise design principles from a communication theory perspective by deriving generalizations of SNR and noise factor from various MIMO communication schemes. As one result, we are able to derive optimal matching networks for a bank of uncoupled amplifiers.

LTE uplink MIMO receiver with low complexity interference cancellation

In LTE/LTE-A uplink receiver, frequency domain equalizers (FDE) are adopted to achieve good performance. However, in multi-tap channels, the residual inter-symbol and inter-antenna interference still exist after FDE and degrade the performance. Conventional interference cancellation schemes can minimize this interference by using frequency domain interference cancellation. However, those schemes have high complexity and large feedback latency, especially when adopting a large number of iterations. These result in low throughput and require a large amount of resource in software defined radio implementation. In this paper, we propose a novel low complexity interference cancellation scheme to minimize the residual interference in LTE/LTE-A uplink. Our proposed scheme can bring about 2 dB gains in different channels, but only adds up to 7.2 % complexity to the receiver. The scheme is further implemented on Xilinx FPGA. Compared to other conventional interference cancellation schemes, our scheme has less complexity, less data to store, and shorter feedback latency.

Receive Combiner Bank for MIMO System under Multi-User Cochannel Interference

The MIMO system with receive combiner bank (MIMO-RCB), in which a bank of receive combiners is added before the decoding (or detecting) unit of the MIMO receiver, is proposed to increase the received SINR for the scenario where there is multi-user cochannel interference. The proposed MMSE combining, which aims to maximize one component of the received SINR for each receive branch, is used on each receive combiner of MIMO-RCB. We show by both analytic results and simulation results that MIMO-RCB with the proposed receive combining provides a gain of at least 2 for the received SINR, and this implies that the performance of the MIMO system can be enhanced by MIMO-RCB with the proposed receive combining.

Matrix Inversion Algorithm: Applications in High Speed MIMO LTE Receiver

Matrix inversion algorithm acting an important role in MIMO wireless communication.In this paper, we presenta matrix inversion algorithm and it’s applications in the high speed MIMO LTE receiver which is based on floating point DSP. Matrix operations are the most costly computational module within MIMO receivers but a matrix inversion algorithm is very easy to compute and significantly reduce the computational module cost. We will demonstrate the MIMO LTE applications for reducing the module cost by square matrix inversion algorithms.

Optimal Low Noise Single Front-End MIMO Receiver System with Parasitic Antenna Element

Optimal Low Noise Single Front-End MIMO Receiver System with Parasitic Antenna Element

Channel estimation for nonlinear MIMO receiver with square envelope detection

SUMMARYTwo practical channel estimation schemes, the moment‐based first‐and‐second moments and the simplified maximum likelihood estimators, are proposed for the MIMO/on–off keying system with square envelope detection applied for wireless sensor networks. Here, both the channel response and noise power are estimated simultaneously in comparison with other approaches in which the noise quantity is assumed to be known at the receiver. Hence, the developed estimators are more practical than those estimators without noise power estimation. Simulation results reveal that the system with both proposed schemes can achieve an excellent BER performance in a wide signal‐to‐noise ratio (SNR) range. More specifically, we observed that the simplified maximum likelihood estimator performed as well as the moment‐based first‐and‐second moments estimator for SNR greater than 7.5 dB, yet had much more decline at low SNRs. This study also investigated the effects of the numbers of receive antennas and transmit antennas on the system performance. Simulation results demonstrated that, at the BER of 10−3, the 5 × 5 system had an improvement of 7 dB in SNR compared with the 3 × 3 system. Copyright © 2011 John Wiley & Sons, Ltd.

A comparison of iterative MIMO receivers under channel uncertainty

ABSTRACTThis work investigates iterative architectures for coded transmission over multiple input multiple output channels in the presence of channel uncertainty. Robust receivers that are less sensitive to the uncertainty are designed. The nature of iterative algorithms is especially suited to iterative decoding and channel estimation (ID&CE), which is a widely accepted means of dealing with imperfections in channel state information. ID&CE re‐estimates the channel in each iteration to deal with the uncertainty. The derived robust algorithm can be combined with ID&CE to yield significant performance gains as demonstrated by the simulation results. Copyright © 2011 John Wiley & Sons, Ltd.

Simplified Quantisation in a Reduced-Lattice MIMO Decoder

Symbol detection in a lattice-reduction aided MIMO receiver depends upon appropriate quantisation in the reduced lattice and this has previously been achieved using a shift-and-scale method. This paper describes a novel parity-based method that avoids the need to perform inversion of the reduction matrix and simplifies the computation involved in symbol estimation in MIMO receivers using QAM and PAM modulation schemes. The new algorithm is shown to be functionally identical to the shift-and-scale method.

Design and simulation of a flexible beamforming interface for MIMO receivers using a Butler labyrinth

This article focuses on the design and simulation of a new component for analog beamforming based on the Butler labyrinth. The proposed component enables the analysis of four-antenna beamforming in systems with two receive channels. The problem was to design a component that would enable simulation of a MIMO receiver with an accurate account of the analog beam-former effects on the digital signal processing level. The entire process is described—from layout design to the final DSP level integration and simulation. The performance of the simulated Butler component is compared to that of an ideal, theoretical one. The differences in the results indicate the importance of taking into account the effects of the layout level design on the DSP simulation level. The new component proves valuable for the bottom-up approach in the design and simulation of a wireless system. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.

A Comparison of MIMO Detection Algorithms with Channel Coding in Frequency Selective Fading Channel Environments

Recent works on MIMO receiver design were mainly focused on sphere decoding, which provides a trade-off between the performance and complexity by suitably choosing the “radius” or the number of candidates in the search space. Meanwhile, another approach, called poly-diagonalization and trellis detection, has been proposed to compromise the complexity and performance. In this paper, we compare various MIMO receiver algorithms in terms of both performance and complexity. The performance is evaluated in a frequency selective fading channel environment on the basis of orthogonal frequency division multiplexing with channel coding, for which the generation of soft decision values is crucial. The simulations show that the poly-diagonalization approach matches the performance of sphere decoding at similar computational complexity.

Low Complexity, Quasi-Optimal MIMO Detectors for Iterative Receivers

We propose a novel family of Soft-Input Soft-Output detectors for iterative, point-to-point, MIMO receivers. Compared to the optimal Maximum A Posteriori receiver, low complexity is achieved restricting the detector search to small subsets of the entire QAM hyper-symbol constellation, through simple criteria. These criteria are applied to an improved version of the non-iterative Layered ORthogonal lattice Detector. We show that, notwithstanding the suboptimal low-complexity implementation, this detector approaches the EXtrinsic Information Transfer of the MAP detector. Therefore, when included in an iterative receiver it delivers the same performance. Furthermore, the deterministic complexity and highly parallelizable structure of the proposed detector are well suited for HDL and ASIC implementation. To focus on a specific setting, we consider the indoor MIMO wireless LAN 802.11n standard, taking into account errors in Channel Estimation and a frequency selective, spatially correlated channel model.

Energy Efficient Hardware Architecture of LU Triangularization for MIMO Receiver

An energy-efficient hardware architecture of complex-valued matrix lower-upper (LU) triangularization for multi-input-multi-output (MIMO) receivers is presented in this paper. In the LU triangularization process, Gaussian elimination operation is expressed as a series of vector-scalar products, where basic common computations can be precomputed and shared to reduce computational complexity. Our computation-sharing-based architecture was implemented using a 0.25-μm CMOS process, and the hardware can perform LU triangularization from 2 × 2 to 8 × 8 matrices. Numerical results show that the proposed architecture has considerable energy savings over conventional matrix triangularization schemes.

Nonlinear MIMO: affordable MIMO technology for wireless sensor networks

We consider a sensor network, where an access point (AP) communicates with many sensor nodes (SN), which are simple, cheap, low-complexity and low-power communication nodes. Such systems typically use nonlinear modulation and detection, due to their low power consumption. Increasing their performance by means of multiple antennas at the AP and the SNs has not been considered, since this would violate the stringent power and cost constraints at the SN. We consider SNs with MIMO receivers that perform a nonlinear operation on the complex-valued received signal (amplitude or phase detection). These receivers enjoy the low-cost, low-power, low-complexity characteristics that are crucial for a sensor network. Such nonlinear MIMO systems are first introduced and studied here. They bring the high-rate, high-performance world of MIMO systems and the low-cost, low-complexity world of sensor networks together. We only consider the single-user MIMO system between the AP and one SN, and study the fundamental limits of such systems. We compute achievable rates under perfect and noisy CSI at the SN, and observe that these systems also achieve spatial multiplexing gain, albeit different to legacy linear MIMO systems. We quantify and analyze these gains using numerical means, and give insight into the effect of the nonlinearity on the information theoretic limits of nonlinear MIMO systems.

MIMO transmission and reception techniques using three-element ESPAR antennas

A novel scheme for spatially multiplexing two BPSK signals using a 3-element ESPAR (electronically steerable parasitic array radiator) antenna was reported in. In this paper we first optimize the set of loads controlling the parasitic elements within the transmission mode by maximizing the outage capacity. We also propose different reception techniques for spatially demultiplexing real and complex signals (using the same set of loads). The proposed transmission and reception schemes are evaluated in an indoor peer-to-peer mobile ad-hoc channel via simulations, where each ad-hoc node is equipped with a 3-element ESPAR terminal.

MIMO Receiver Using Reduced Complexity Sequence Estimation With Channel Estimation and Tracking

A sequence-based multiple-input-multiple-output receiver incorporating channel estimation and tracking for a frequency selective fading environment is developed. It employs near-maximum likelihood sequence estimation using the partitioned Viterbi algorithm and offers linearly increasing complexity with the number of transmit antennas. The receiver implements channel estimation and tracking using a vector-polynomial-based generalized recursive least squares algorithm. The resulting integrated receiver can operate in a continuously time-varying Rayleigh or Rician fading environment. Simulation results show that it offers a good tradeoff between complexity and performance. Further complexity reduction can be achieved using tentative decisions as reference signals to the estimator and a reduced complexity form of the estimator.

Joint Least Squares Estimation of Frequency, DC Offset, I-Q Imbalance, and Channel in MIMO Receivers

Multiple-input-multiple-output (MIMO) receivers with direct-conversion radio-frequency (RF) architecture are investigated in this paper. Direct conversion is a low-cost RF design that requires fewer external components in chip implementation. Nevertheless, it introduces extra RF impairments such as I-Q imbalance and dc offset in addition to frequency offset that is commonly encountered in all RF architectures. This paper proposes to do the joint least squares (LS) estimation of frequency, dc offset, I-Q imbalance, and a channel in MIMO receivers to improve performance; frequency-dependent and frequency-independent I-Q imbalances are included. Previously, RF impairments were separately estimated in MIMO receivers, which leads to inferior performance. In particular, a receiver architecture that facilitates the joint estimation of the frequency, the dc offset, the I-Q imbalance, and the channel is proposed. The LS criterion is then applied to obtain the joint estimators, with a special training-sequence design to reduce complexity. Simplified estimators on the frequency and dc offset are also proposed with almost no loss in performance. Finally, the estimators are shown through analysis to be unbiased and approach the Cramer-Rao lower bound (CRLB) for signal-to-noise ratios (SNRs) of interest. The analysis is verified by computer simulations.

Improved Fractional Fourier Transform Based Receiver for Spatial Multiplexed MIMO Antenna Systems

In this work the performance of a Fractional Fourier transform (FrFT) based Minimum Mean Squared Error receiver for MIMO systems with space time processing over Rayleigh faded channels is presented. The proposed receiver called Optimum FrFT based MIMO receiver (OFMR) shows improved performance outperforming the simple MMSE receiver in Rayleigh faded channel.

Using Parasitic Elements for Implementing the Rotating Antenna for MIMO Receivers

We consider a new concept of a multiple-input-multiple-output (MIMO) receiver which uses one active receiving antenna and multiple parasitic elements. The parasitic elements give the possibility of creating a directive antenna beam which is rotated 360 degrees around within the duration of a symbol period. The received signal which is accessed at the antenna connector of the active antenna is expanded in frequency bandwidth compared to the transmitted signal. We show that each sub-band of the received signal consists of linearly independent combinations of the transmitted signals, and thus we have obtained a MIMO receiver. We give a few examples on how to implement this receiver and also explain the effects of sampling the wave-field at discrete angular directions.

Phased array antennas in MIMO receiver

In this paper, a computer simulation of a MIMO system comprising phased array antennas (PAA) in all receiving branches is presented. In order to examine the system performance under relatively realistic conditions, a ray-tracing simulator was applied to generate a baseband channel impulse response matrix H. A bit error rate (BER) of two systems utilizing different detection methods: V-BLAST and simple matrix inversion was examined in order to determine phased array antennas applicability. Results of an attempt to determine relationship between BER and properties of particular matrix H realization are also provided.

Implementable wireless access for B3G networks. II. MIMO receiver architectures [Topics in Radio Communications

This article presents a comprehensive overview of the research conducted within Mobile VCE's Core Wireless Access Research Programme, a key focus of which has naturally been on MIMO transceivers. The article, the second of four, provides a follow on from the first article, which dealt with MIMO channels and comprises a compilation of material that has been presented in detail elsewhere (see references within the article). In Part I MIMO channel measurements, analysis, and modeling were presented, which were then utilized to develop compact and distributed antenna arrays. This article reports parallel activities into low-complexity MIMO single-user space-time coding techniques, as well as SISO and MIMO multi-user CDMA-based transceivers for B3G systems. Also, overall B3G system designs have been suggested for beamformed multilayer CDMA-based networks