Enhanced lattice reduction algorithm for detection and precoding of MIMO systems with perfect CSI

A unified approach is developed for the study of multi-input, multi-output (MIMO) systems under fast fading with quantized covariance feedback. In such systems, the receiver computes, using perfect channel state information (CSI), the covariance matrices to be adopted by the transmitter corresponding to the current channel realization, and feeds back a quantized version of this information to the transmitter using finite, say Nf, bits per channel realization. Our analysis is based on a geometric framework we developed in a companion paper for manifolds of positive semi-definite (covariance) matrices with various trace and rank constraints. That analysis applies to MIMO systems in a unified manner to optimal as well as various suboptimal precoding methods for obtaining input covariances. These include, for example, the capacity achieving spatio-temporal water-filling strategy, the incorporation of just spatial water-filling and reduced-rank beamforming with power allocation in both cases, as well as MIMO systems with antenna selection. For a given system strategy, including the one that achieves capacity, the gap between the communication rates in the perfect and quantized covariance cases is shown to be O(2-Nf/N), where N is the dimension of the particular Pn manifold used for quantization. This dimension depends on the precoding strategy adopted and strongly determines how quickly the communication rate with quantized covariance feedback approaches that with perfect CSI at the transmitter (CSIT). Our results show how the choice of covariance quantization manifold can be tailored to the available feedback rate in MIMO system design.

In this paper, we design a zero-forcing (ZF) Tomlinson-Harashima precoding (THP) and a minimum mean square error (MMSE) THP for multiuser MIMO relay system with direct link. Based on these precoding structures, we propose the optimal combining weights of the ZF THP and the MMSE THP in half duplex relay system, and the sub-optimal weights of MMSE THP to reduce feedback channel state information (CSI). Through the Monte Carlo simulation, we verify that the optimal weights combining method outperforms the constant weights combining method. In addition, we confirm that the performance of the sub-optimal weights combining method is close to the optimal method, while reducing the feedback CSI simultaneously.

We consider the design of the precoder for a multi-input multi-output (MIMO) communication system equipped with a decision feedback equalizer (DFE) receiver. For such design problems, perfect knowledge of the channel state information (CSI) at both the transmitter and the receiver is usually required. However, in the wireless communications environment, it is often difficult to provide sufficiently timely and accurate feedback of CSI from the receiver to the transmitter for such designs to be practically viable. In this paper, we consider the optimum design of a precoder for a wireless communication link having M transmitter antennas and N receiver antennas (M ≪ N), in which the channels are assumed to be flat fading and may be correlated. We assume that full knowledge of CSI is available at the receiver. At the transmitter however, only the second order statistics of the channels are available. Our goal here is to come up with an efficient design of the optimal precoder for such a MIMO system by minimizing the average arithmetic mean-squared error (MSE) of zero-forcing (ZF) decision feedback detection subject to a constraint on the total transmitting power. Applying some of the properties of the matrix parameters, this non-convex optimization problem can be transformed into a convex geometrical programming problem which can then be efficiently solved using an interior point method. The superior performance of our MIMO system equipped with the optimum precoder is verified by computer simulations.

최근 대용량, 초고속 통신 서비스의 비중이 높아짐에 따라 배열 안테나를 사용하는 MIMO(Multi-Input Multi-Output) 시스템의 활용이 중요하게 평가되고 있다. 하지만 기존의 MIMO 시스템은 다수의 안테나를 사용하기 때문에 안테나의 개수만큼 RF(Radio Frequency) 체인이 요구되며, 이로 인해 복잡도와 전력 소모가 크다는 단점을 가진다. 이러한 기존 MIMO 시스템의 단점을 해결하기 위해서 단일 능동 소자와 다수의 기생 소자를 이용하는 방식의 ESPAR(Electronically Steerable Parasitic Array Radiator) 안테나를 사용하는 빔 공간 MIMO 시스템에 대한 연구가 활발히 진행되고 있다. ESPAR 안테나를 사용하는 빔 공간 MIMO 시스템은 단일 RF 체인으로 구성되어 있기 때문에 기존 MIMO 시스템의 단점을 해결할 수 있다. 본 논문에서는 시스템의 보안성을 향상시키기 위해 QPSK(Quadrature Phase Shift Keying) 변조 방식의 ESPAR 안테나를 사용하는 빔 공간 MIMO 시스템에 비예측성, 비주기성, 구현의 용이성, 민감한 초기조건 등의 특징을 가지고 있는 카오스 통신 알고리즘을 적용하여 QPSK 변조 방식의 ESPAR 안테나를 사용하는 카오스 빔 공간 MIMO 시스템을 구성하고 성능을 평가한다. Recently, utilization of MIMO(Multi-Input Multi-Output) system using array antennas is evaluated significantly according to the extension of high-capacity and high-speed communication services. However, MIMO system has disadvantages such as high-complexity and high-power-consumption, because RF(Radio Frequency) chain is required as antenna number, and several array antenna is used in conventional MIMO system. In order to solve these problems, research about beamspace MIMO system using ESPAR(Electronically Steerable Parasitic Array Radiator) antenna that has single RF chain by using one active antenna and several parasitic elements has been studied actively. Beamspace MIMO system using ESPAR antenna is possible to solve the problems of conventional MIMO system, because this system is composed by single RF chain. In this paper, in order to improve the system security, chaos communication algorithm that has characteristics such as non-periodic, non-predictability, easy implementation and initial condition is applied to QPSK (Quadrature Phase Shift Keying) modulated beamspace MIMO system. We design the chaos QPSK modulated beamspace MIMO system, and evaluate SER performance of this system.

In wireless communication, multiple signals are utilized to receive and send information in the form of signals simultaneously. These signals consume little power and are usually inexpensive, with a high data rate during data transmission. An Multi Input Multi Output (MIMO) system uses numerous antennas to enhance the functionality of the system. Moreover, system intricacy and power utilization are difficult and highly complicated tasks to achieve in an Analog to Digital Converter (ADC) at the receiver side. An infinite number of MIMO channels are used in wireless networks to improve efficiency with Cross Entropy Optimization (CEO). ADC is a serious issue because the data of the accepted signal are completely lost. ADC is used in the MIMO channels to overcome the above issues, but it is very hard to implement and design. So, an efficient way to enhance the estimation of channels in the MIMO system is proposed in this paper with the utilization of the heuristic-based optimization technique. The main task of the implemented channel prediction framework is to predict the channel coefficient of the MIMO system at the transmitter side based on the receiver side error ratio, which is obtained from feedback information using a Hybrid Serial Cascaded Network (HSCN). Then, this multi-scaled cascaded autoencoder is combined with Long Short Term Memory (LSTM) with an attention mechanism. The parameters in the developed Hybrid Serial Cascaded Multi-scale Autoencoder and Attention LSTM are optimized using the developed Hybrid Revised Position-based Wild Horse and Energy Valley Optimizer (RP-WHEVO) algorithm for minimizing the "Root Mean Square Error (RMSE), Bit Error Rate (BER) and Mean Square Error (MSE)" of the estimated channel. Various experiments were carried out to analyze the accomplishment of the developed MIMO model. It was visible from the tests that the developed model enhanced the convergence rate and prediction performance along with a reduction in the computational costs.

Latest communications standards have incorporated wireless multi-input multi-output (MIMO) systems combining the use of space-time coding (STC) and spatial multiplexing (SM) techniques. One of the challenges of such space-time coded multiplexing (STCM) systems is the design of high performance and low complexity detectors at large MIMO dimensions, where existing group-based and direct detection detectors suffer from either performance degradation or high computational cost. In this paper, we present pairwise element-based lattice reduction (ELR)-aided detectors for the STCM systems. By utilizing the symmetric structure of the equivalent channel matrix, the proposed pairwise ELR (PELR)-aided detectors approximately halve the complexity of the original ELR-aided detectors while keeping similar bit-error-rate (BER) performance. They also have a lower BER and similar complexity compared to other state-of-the-art detectors. We demonstrate the better tradeoff between the BER and complexity of our PELR-aided detectors under large MIMO systems with simulations.

The Multi-input multi-output (MIMO) technique is very useful for increasing the transmission reliability, high date rate, robustness and channel capacity in the modern radio communication systems. As many algorithms inspired from the nature have been proposed to evaluate the performance of MIMO system parameters like channel capacity, bit error rate and the best fitness value of channel capacity. But this technique delivers some issues such as increases the cost and complexity of hardware due to increasing number of antennas. To solve this issue, an effective optimal transmit antenna subset selection method is described in this paper with the aid of PSO. For each position of the particle, corresponding fitness function is evaluated and from there global best fitness values are chosen. The implementation of proposed work is done in the working platform MATLAB and the performance of MIMO are evaluated with various selection of transmit antenna subsets. Moreover, Improvement in Channel Capacity and BER with increasing SNR are discussed Hence, with the aid of proposed work, the selection of transmit antenna with the maximum capacity and minimum BER are made and which leads to the reduced hardware complexity and decrease number of antennas in the MIMO system.

Lattice reduction (LR)-aided equalizers have been well studied for multi-input multi-output (MIMO) systems due to their great bit-error-rate (BER) improvement over linear equalizers (LEs) and relatively low complexity. In this paper, we present results on the maximum information rate (denoted as "capacity" hereafter) of MIMO transmission with LR-aided equalizers employed at the receiver. First, we derive the main steps for calculating the capacity with different equalizers. Then, we illustrate the capacity when LR-aided equalizers are adopted. We show that the capacity gap between maximum likelihood equalizer (MLE) and LR-aided LEs is linked to the orthogonality deficiency (od) of the dual of the lattice-reduced channel matrix. Although LR-aided LEs do not guarantee to improve capacity every channel realization, we give the conditions when the ergodic capacity of LR-aided LEs is greater than that of LEs, as well as when their outage diversity is the same as that of MLE. Lastly, we show numerical examples with several state-of-the-art LR algorithms to corroborate the theoretical analysis.

Recently, lattice-reduction (LR) has been proposed to improve the performance of linear and successive interference cancellation (SIC) detectors and precoders in MIMO systems. It is proved that LR-aided linear detectors collect the same diversity order as that exploited by the ML detector but with much lower complexity when perfect channel state information (CSI) is assumed to be available. However, in practice, CSI is always contaminated by channel estimation error and feedback quantization error. In this paper, we proposed MMSE based LR-aided robust linear and SIC detectors and MMSE based LR-aided (robust) linear precoder and (robust) Tomlinson-Harashima precoder (THP) which are capable of improving the BER performance in the context of imperfect CSI. Furthermore, we find that the performance improvement of LR-aided nonlinear method in SIC detectors at receiver is more pronounced than that in THP at transmitter.

The effect of DC offset on multi-input multi-output (MIMO) direct transceivers with adaptive modulation (AM) is discussed in this paper. A variable-rate variable-power (VRVP) AM system with perfect channel state information (P-CSI) at both the transmitter and receiver in a MIMO scenario is considered. The DC offset is modeled as a zero mean complex Gaussian distributed random variable. By this modeling of the DC offset, the analytical expression for degraded bit error rate (BER) is derived. To derive this analytical expression, we establish a reasonable approximation. The good agreement between the analytical and simulation results shows that the approximation is valid and confirms the accuracy of the analytical expressions. Moreover, an approach to improve the degraded BER in these systems is introduced. For this purpose, we introduce a design for AM MIMO systems that takes account of DC offset and its effectiveness is confirmed. Throughput analysis for the AM MIMO system in the presence of DC offset is presented in this paper too. An analytical expression for throughput is derived and approximated to a simpler equation. At last, throughput results are compared to the simulation outcomes.

In a companion paper, we have studied the zero-forcing (ZF) transceiver with decision feedback equalizer (DFE) over slowly time-varying narrowband multiinput multioutput (MIMO) channels. The space-time generalized triangular decomposition (ST-GTD) was used for the design of ZF-DFE transceivers. The space-time geometric mean decomposition (ST-GMD) ZF transceiver minimizes both the arithmetic mean square error (MSE) at the feedback detector and the average uncoded bit error rate (BER) in moderate high signal-to-noise ratio (SNR). This paper addresses the design problem of DFE transceiver without zero-forcing constraint. In the first part, a channel independent temporal precoder is superimposed on the conventional block-wise GMD-based minimum mean square error (MMSE) DFE transceiver to take advantage of the temporal diversity. In the second part, ST-GTD is applied for the design of MMSE DFE transceivers. With accurate channel prediction and space-time powerloading, the proposed ST-GMD MMSE transceiver minimizes the arithmetic MSE at the feedack detector, and maximizes Gaussian mutual information. For practical applications, the ST-GTD MMSE transceiver which does not require channel prediction but shares the same asymptotic BER performance with the ST-GMD MMSE system is also developed. In the convex region, our analysis shows that the proposed MMSE transceivers has better BER performance than the conventional GMD-based MMSE transceiver; the average BERs of the proposed systems are nonincreasing functions of the ST-block size. The superior performance of ST-GMD MMSE transceiver over the ST-GMD ZF transceiver is also verified analytically.

Transmit diversity schemes have been studied for high spectral-efficiency and high bit-rate transmission, such as multi-input multi-output (MIMO) systems. In this paper, a novel dual polarized ceiling-mounted antenna is designed and simulated. In the MIMO systems, forward error correction coding is essential for high quality communications. At the two typical scenes, the single-input single-output system compared with two single polarized antennas and an dual polarized antenna MIMO system is tested. It is shown that the MIMO system have improved throughput level obviously. The dual polarized ceiling-Mounted dual streams MIMO antenna will save much construction cost in the long-term evaluation systems in the future, which can be called the “green” MIMO antenna.

In this contribution, we investigate the performance of dual-polarized multi input multi output (MIMO) multi-carrier interleave division multiple access system (MC-IDMA) over correlated frequency selective channels in the presence of channel state estimation error. In the code division multiple access (CDMA), orthogonal spreading sequence is used as user specific where as in IDMA, user specific interleaving pattern is used. In our considered work, Multi-carrier (MC) is realized by orthogonal frequency division multiplexing (OFDM). The channel is estimated at the mobile stations (MSs) by pilot assisted channel estimation (PACE) technique using minimum mean square error (MMSE) algorithm. Further, the dual-polarized MIMO system considered in our work which is realized with the aid of orthogonal polarizations, replaces two spatially separated uni-polarized antennas, thus resulting in polarization multiplexing. In particular, we evaluate the effects of three types of delay spread on MIMO MC-IDMA system in the context of downlink (DL) communications pertaining to the Standard University Interim (SUI) channel model. In a multi-user environment, users experience multi stream interference (MSI) in addition to the multiple access interference (MAI) and these interferences can degrade the system performance. Furthermore, we consider turbo code as channel encoder for MIMO MC-IDMA system to mitigate the effects of MAI and MSI. It is discerned from the simulation results that dual-polarized MIMO MC-IDMA system is capable of supporting many users and performs better in terms of achievable bit error rate (BER) in the context of DL communications with reduced number of antennas.

Capacity maximizing in massive MIMO with linear precoding for SSF and LSF channel with perfect CSI

This brief presents a lattice reduction (LR) aided precoding processor for 64-QAM 4 × 4 multiple-input-multiple-output systems. The proposed processor is based on a modified Lenstra-Lenstra-Lovasz LR algorithm and the Tomlinson-Harashima precoding (THP) algorithm. This study develops a configurable architecture for high-throughput THP processing or high-performance LR-THP processing. The proposed processor can also change the stage number of the LR algorithm to achieve a tradeoff between performance and throughput. This study designs and implements the precoding processor by using TSMC 90-nm 1P9M CMOS technology. The chip measurement results presented in this study show that the proposed processor achieves 576 Mbit/s in the THP mode or 10-3 bit error rate in the LR-THP mode with 64-QAM modulation at 28.3 dB. The chip occupies a 0.5- mm2 area and consumes 15.4 mW of power at its maximum clock speed of 120 MHz.