Uniform Channel Decomposition Research Articles

Multi-task deep learning based hybrid precoding for mmWave massive MIMO system

Due to the different signal-to-noise ratio (SNR) of each subchannel, the bit error rate (BER) of hybrid precoding based on singular value decomposition (SVD) decreases. In this paper, we propose a multi-task learning based precoding network (PN) model to solve the BER loss problem caused by SVD based hybrid precoding under imperfect channel state information (CSI). Specifically, we firstly generate a dataset including imcomplete CSI input channel matrix and corresponding output labels to train the PN model. The output labels are designed based on uniform channel decomposition (UCD) which decomposes the channel into multiple subchannels with same gain, while the vertical-bell layered space-time structure (V-BLAST) signal processing technology is combined to eliminate the inner interference of the subchannels. Then, the PN model is trained to design the analog and digital precoding/combining matrix simultaneous. Simulation results show that the proposed scheme has only negligible gap in spectrum efficiency compared with the fully digital precoding, while achieves better BER performance than SVD based hybrid precoding.

BD-UCD-Based Nonlinear Hybrid Precoding for Millimeter Wave Massive Multiuser MIMO Systems

In this letter, we investigate the downlink hybrid precoding design for time-division duplexing (TDD) millimeter wave (mmWave) massive multiuser MIMO (MU-MIMO) systems, aiming to enhance both the sum spectral efficiency (SSE) and the bit error rate (BER) performance. First, we propose a joint analog precoding and combining design via Gram-Schmidt orthogonalization to maximize the beamforming gain while mitigating the inter-user interference. Then, by exploiting the uplink-downlink duality, we propose a block diagonal uniform channel decomposition (BD-UCD) based digital precoding and combining scheme to further improve the SSE and BER performance. Furthermore, Tomlinson–Harashima precoding (THP) is utilized to eliminate both the inter-user interference and the inter-stream interference. Simulation results demonstrate that the proposed BD-UCD-based nonlinear hybrid precoding scheme performs close to the fully-digital BD-UCD scheme and outperforms the other existing hybrid precoding schemes in terms of SSE and BER performance.

Transceiver Design With UCD-Based Hybrid Beamforming for Millimeter Wave Massive MIMO

Hybrid transceiver designs for millimeter wave massive multiple-input multiple-output systems are feasible candidates to reduce the volume of radio frequency (RF) chains, decomposing the signal processing into the analog and digital domains. The existing schemes heavily depend on the singular value decomposition to obtain subchannels with uneven power gains, causing bit error rate (BER) performance degradation. In this paper, we propose a hybrid transceiver design based on the uniform channel decomposition (UCD), yielding subchannels with identical gains to improve the BER performance. Inspired by the UCD concept, we derive an equivalent optimization problem and propose two schemes, namely, phase-extraction and iterative update, to determine the RF beamformers, yielding an effective baseband channel with the greatest possible geometric mean of singular values. We apply the UCD with a minimum mean squared error criterion to complete the baseband beamforming. Finally, we combine the hybrid UCD beamforming with the vertical-Bell Labs layered space-time and dirty paper coding, to eliminate the inter-subchannel interference. An asymptotic analysis of the scheme performance is also pursued. The simulation results show that the proposed hybrid scheme outperforms the conventional schemes on the transmission BER, which achieves a spectral efficiency close to that of the fully-digital counterpart.

Precoder Design for MIMO Visible Light Communications With Decision-Feedback Receivers

Decision-feedback equalization is considered for point-to-point multiple-input multiple-output visible light communication systems. Based on the geometric mean decomposition (GMD) and uniform channel decomposition (UCD), two precoders under the signal non-negativity and total average power constraints are designed for such systems. The GMD scheme can decompose the channel into multiple parallel sub-channels with equal gains. The UCD scheme further improves performance through power allocation. Simulation results of bit-error-rate and capacity are presented. It is shown that the proposed schemes can outperform conventional linear designs and the UCD scheme performs better than the GMD scheme.

다중 셀 MIMO 하향채널에서의 UCD를 이용한 블록 대각 분해

In this paper, we design non-linear transmitter and receiver using a uniform channel decomposition (UCD) to take account of inter-cell interference in multi-cell downlink systems. The designed UCD scheme brings forth the same SINR for all sub-channels in each cell. It provides great convenience to modulation/coding process and achieves the maximum diversity gain. The simulation results confirm that it exhibits a lower BER than the conventional method.

Joint Transceiver Design for Non-Concurrent MIMO Two-Way AF Relaying

We consider an amplify-and-forward infrastructure non-concurrent two-way relaying (ncTWR) scenario where a base station serves a transmit-only user TUE and a receive-only user RUE. Unlike conventional two-way relaying, the RUE in ncTWR experiences back-propagating interference (BI). Uniform channel decomposition and Tomlinson–Harashima precoding improve the bit error rate (BER) of multiple-antenna–multiple-output (MIMO) systems. Inspired by these techniques, we design a transceiver to reduce BER of both users in MIMO ncTWR. This transceiver cancels BI of the RUE and uses spatial noise whitening filters, designed herein, to uniformly decompose MIMO channels of both TUE and RUE. This letter quantifies the improved BER of the proposed transceiver.

Adaptive Uniform Channel Decomposition in MU-MIMO-OFDM: Application to IEEE 802.11ac

This work considers the design of multiuser MIMO (MU-MIMO) schemes suitable for orthogonal frequency division multiplex (OFDM) systems such as those being currently discussed within IEEE 802.11ac. A general framework is proposed showing that the singular value decomposition (SVD), the geometric mean decomposition (GMD), and the uniform channel decomposition (UCD) are all viable mechanisms on which to lay the design. Nonetheless, some striking differences in terms of performance among these three schemes are uncovered. In particular, a novel adaptive transmission scheme based on the UCD is introduced that enables multiuser MIMO-OFDM gains to be realized, clearly outperforming those obtained using the SVD or GMD counterparts while remaining fully compliant with the latest IEEE 802.11ac specification. Relying on the UCD properties, the proposed technique takes into account the availability of a finite modulation and coding set and restrictions on transmission mode selection defined within the standard, to incorporate an optimisation step in charge of selecting the number of transmitted data streams to each user to maximise the system throughput. Comprehensive simulation results in the context of IEEE 802.11ac confirm the applicability and advantage of the adaptive UCD-based design.

Power Allocation Algorithms for GMD or UCD Based Joint Transceiver Designs

In a downlink multiuser multiple-input multiple-output channel, joint transceiver designs based on geometric mean decomposition and uniform channel decomposition can provide a BER performance enhancement by making all substreams of each user have the same SINR. However, if a user power allocation (uPA) algorithm is not applied in their designs, they actually make the same SINR for all substreams in each user while causes different SINR with one another, and therefore the average BER is dominated by the user with the worst SINR. In this regards, it is possible to enhance BER performance further provided that the uPA algorithm is taken into account under a total power constraint. The objective of this paper is to maximize the worst user’s SINR by applying the uPA algorithm with the total power constraint. Because of proposed uPA algorithms, all substreams across all users can have the same SINR, which leads to minimization of average BER. Simulation results show that joint transceiver designs with proposed uPA algorithms have an SNR gain about 2 dB at the BER of \(10^{-3}\).

Root Mean Square Decomposition for EST-Based Spatial Multiplexing Systems

We consider the transceiver design for multiple-input-multiple-output (MIMO) systems when the channel state information (CSI) is available at the transmitter as well as the receiver. First, we propose an open-loop low-complexity MIMO spatial multiplexing scheme based on the energy spreading transform (EST-SM). The EST-SM can spatially multiplex multiple data streams and iteratively detect the data streams with almost negligible interstream interference at sufficiently high SNR. Then, we propose a closed-loop precoding scheme suitable for the EST-SM called root mean square decomposition (RMSD) scheme. The RMSD precoding scheme combined with the EST-SM decomposes a MIMO channel into multiple subchannels with identical SNRs. This desired property minimizes bit error rate (BER) when different bit allocations on different subchannels, which cause a significant increase in system complexity, are not used. We show that when the EST-SM is used the RMSD scheme is optimal in BER performance and it achieves full diversity. Simulation results show that the RMSD scheme outperforms other existing techniques such as the geometric mean decomposition (GMD) scheme (Jiang , IEEE Trans. Signal Process., vol. 53, no. 10, pp. 3791-3803) and the uniform channel decomposition (UCD) scheme1 (Jiang , IEEE Trans. Signal Process., vol. 53, no. 11, pp. 4283-4294) in BER performance.

Research on UCD Precoding for MIMO System

This article mainly describes a new technique of multiple-input multiple-output (MIMO) communication systems based on the recent communication demand. This technique, by pre-coding CSI (the channel state information) at the transmitter, is based on UCD (Uniform Channel Decomposition) algorithm for MIMO system. By Uniform Channel decomposition of channel matrix, the algorithm can decompose a MIMO downlink channel into multiple identical sub-channels. The power allocation applied to each sub channel in MIMO system is identical, and the MIMO channel’s capacity isn’t reduce when the SNR (Signal Noise Ratio) is low. The simulations show that the UCD scheme has a better performance than GMD (Geometric Mean Decomposition) scheme even without the use of error-correcting codes, and the Symbol Error Rate (SER) of UCD algorithm is lower than GMD’s at the same SNR. Consequently, MIMO system gets a better interference performance by UCD algorithm.

Research on UCD Precoding for MIMO System

This article mainly describes a new technique of multiple-input multiple-output (MIMO) communication systems based on the recent communication demand. This technique, by pre-coding CSI (the channel state information) at the transmitter, is based on UCD (Uniform Channel Decomposition) algorithm for MIMO system. By Uniform Channel decomposition of channel matrix, the algorithm can decompose a MIMO downlink channel into multiple identical sub-channels. The power allocation applied to each sub channel in MIMO system is identical, and the MIMO channel’s capacity isn’t reduce when the SNR (Signal Noise Ratio) is low. The simulations show that the UCD scheme has a better performance than GMD (Geometric Mean Decomposition) scheme even without the use of error-correcting codes, and the Symbol Error Rate (SER) of UCD algorithm is lower than GMD’s at the same SNR. Consequently, MIMO system gets a better interference performance by UCD algorithm.

Robust Uniform Channel Decomposition and Power Allocation for MIMO Systems with Imperfect CSI

In point to point MIMO systems, uniform channel decomposition (UCD) has been proven to be optimal in bit error rate (BER) performance and strictly capacity lossless when perfect channel state information (CSI) are assumed to be available at both the transmitter and the receiver side. However, in practice, CSI can be obtained at the transmitter if there is reciprocity between the forward and reverse channels in time division duplex (TDD) systems or can be conveyed from the receiver to the transmitter via a feedback channel. In any case, channel estimation error is inevitable. In this paper, a novel robust UCD scheme and corresponding optimal robust power allocation are proposed, which are capable of improving the BER performance in the context of imperfect CSI compared with the conventional UCD scheme and the robust precoding scheme proposed by Amir D. Dabbagh and David J. Love. Simulation results show that the MIMO channel capacity of the proposed robust UCD scheme is higher than that of the conventional UCD scheme. By deriving and analyzing the MIMO channel capacity lower bound of the robust UCD scheme, we prove that our proposed robust UCD scheme is capacity lossless in a channel estimation error existing MIMO system.

Low-Complexity MIMO Precoder Design With $ \hbox{LDL}^{H}$ Channel Decomposition

We present a new multiple-input-multiple-output (MIMO) precoding scheme using LDLH channel decomposition. The proposed method is verified to have lower complexity and better bit-error-rate (BER) performance than that of conventional singular-value decomposition (SVD). SVD is commonly used to decompose the MIMO channel into parallel eigenmodes. However, the large variation of the singular values often leads to ill-conditioned channel and degraded error performance. Recently, two SVD-based decomposition schemes that aim to improve such subchannel gain uniformity have been developed. They are geometric mean decomposition (GMD) and uniform channel decomposition (UCD). Albeit the error performance of GMD and UCD is optimized, both of them require relatively higher complexity than that of SVD with power allocation. In this paper, we present a scheme with moderate subchannel gain uniformity while exhibiting the lowest complexity compared with that of SVD, GMD, and UCD. Simulations also show that LDLH can outperform all aforementioned schemes as the channel-estimation errors in the receiver become severe.

Joint MIMO transceiver design based on uniform channel decomposition

A joint MIMO transceiver design is presented based on uniform channel decomposition. This closed-loop MIMO system can run at 400 MHz with a 16-QAM constellation on a Xilinx Virtex-4 FPGA, and can achieve a data throughput of up to 12.8 Gbit/s in an 8×8 MIMO configuration.

Practical robust uniform channel decomposition scheme for CSI mismatch in limited feedback MIMO systems

Uniform channel decomposition (UCD) has been proven to be optimal in bit error rate (BER) performance and strictly capacity lossless when perfect channel state information (CSI) is assumed to be available at both the transmitter and receiver side. In practice, CSI can be obtained by channel estimation at receiver and conveyed to transmitter via a limited-rate feedback channel. In such case, the implementation of traditional UCD by treating the imperfect CSI as perfect CSI cause significant performance degradation due to inevitable channel estimation error and vector quantization error. To overcome this problem, a practical robust UCD scheme was proposed in this paper, which includes two steps, firstly, a matching architecture was proposed to eliminate the mismatch between CSI at receiver (CSIR) and CSI at transmitter (CSIT), secondly, an MMSE based robust UCD scheme considering channel estimation error and vector quantization error as an integral part of the design was derived. Simulation results show that the proposed practical robust UCD scheme is capable of improving the BER performance greatly in the context of channel estimation error and vector quantization error compared with the traditional UCD scheme.

A Transceiver Design Based on Uniform Channel Decomposition and MBER Vector Perturbation

Uniform channel decomposition (UCD), as an improvement of geometric mean decomposition (GMD), is capable of decomposing a multiple-input-multiple-output (MIMO) channel into multiple subchannels having an identical capacity. Vector precoding (VP) is a powerful scheme, which is capable of mitigating multiuser interference (MUI) at the transmitter, provided that the channels of the users are known. In this paper, a novel joint transceiver design based on the UCD and the minimum bit error rate (MBER) VP principles is proposed for MIMO systems, in which the precoding and equalization matrices are calculated by UCD, whereas the perturbation vector is chosen to minimize the system's bit error ratio (BER). This UCD-MBER-VP transceiver design outperforms several state-of-the-art benchmark algorithms in terms of achievable BER performance without imposing an increased computational complexity, particularly for rank-deficient systems.

Transceiver design based on blockwise uniform channel decomposition for coded MIMO systems

In this paper, we investigate the transceiver design for coded multiple-input multiple-output (MIMO) systems assuming channel knowledge at both transmitter and receiver. First we derive an expression of the diversity order of singular value decomposition (SVD) based systems with arbitrary channel coding configurations. Motivated by this analysis, we propose a blockwise design based on uniform channel decomposition (UCD) which utilizes a successive interference cancellation (SIC) receiver. To eliminate error propagation inherent in the SIC structure, the proposed scheme applies the UCD precoder for a pair of subchannels to achieve single-symbol decodable maximum likelihood detection (MLD) instead of the SIC receiver. From the analysis, we demonstrate that the proposed scheme has an enhanced diversity order compared to the SVD scheme by exploiting the feature of the UCD. Also, in the presence of imperfect channel knowledge at the transmitter, we describe an appropriate receive filter design for the proposed scheme. The simulation results show that the proposed transceiver technique outperforms both the SVD scheme and the conventional UCD by about 6 dB in 4 by 4 MIMO systems at the spectral efficiency of 12 bps/Hz.

Block diagonal geometric mean decomposition (BD-GMD) for MIMO broadcast channels

In recent years, the research on multiple-input multiple-output (MIMO) broadcast channels has attracted much interest, especially since the discovery of the broadcast channel capacity achievable through the use of dirty paper coding (DPC). In this paper, we propose a new matrix decomposition, called the block diagonal geometric mean decomposition (BD-GMD), and develop transceiver designs that combine DPC with BD- GMD for MIMO broadcast channels. We also extend the BD- GMD to the block diagonal uniform channel decomposition (BD- UCD) with which the MIMO broadcast channel capacity can be achieved. Our proposed schemes decompose each user's MIMO channel into parallel subchannels with identical SNRs/SINRs, thus equal-rate coding can be applied across the subchannels of each user. Numerical simulations show that the proposed schemes demonstrate superior performance over conventional schemes.

Efficient Closed-Loop Schemes for MIMO-OFDM-Based WLANs

The single-input single-output (SISO) orthogonal frequency-division multiplexing (OFDM) systems for wireless local area networks (WLAN) defined by the IEEE 802.11a standard can support data rates up to 54 Mbps. In this paper, we consider deploying two transmit and two receive antennas to increase the data rate up to 108 Mbps. Applying our recent multiple-input multiple-output (MIMO) transceiver designs, that is, the geometric mean decomposition (GMD) and the uniform channel decomposition (UCD) schemes, we propose simple and efficient closed-loop MIMO-OFDM designs for much improved performance, compared to the standard singular value decomposition (SVD) based schemes as well as the open-loop V-BLAST (vertical Bell Labs layered space-time) based counterparts. In the explicit feedback mode, precoder feedback is needed for the proposed schemes. We show that the overhead of feedback can be made very moderate by using a vector quantization method. In the time-division duplex (TDD) mode where the channel reciprocity is exploited, our schemes turn out to be robust against the mismatch between the uplink and downlink channels. The advantages of our schemes are demonstrated via extensive numerical examples.

Uniform channel decomposition for MIMO communications

Assuming the availability of the channel state information at the transmitter (CSIT) and receiver (CSIR), we consider the joint optimal transceiver design for multi-input multi-output (MIMO) communication systems. Using the geometric mean decomposition (GMD), we propose a transceiver design that can decompose, in a strictly capacity lossless manner, a MIMO channel into multiple subchannels with identical capacities. This uniform channel decomposition (UCD) scheme has two implementation forms. One is the combination of a linear precoder and a minimum mean-squared-error VBLAST (MMSE-VBLAST) detector, which is referred to as UCD-VBLAST, and the other includes a dirty paper (DP) precoder and a linear equalizer followed by a DP decoder, which we refer to as UCD-DP. The UCD scheme can provide much convenience for the modulation/demodulation and coding/decoding procedures due to obviating the need for bit allocation. We also show that UCD can achieve the maximal diversity gain. The simulation results show that the UCD scheme exhibits excellent performance, even without the use of any error correcting codes.