Turbo Message Passing Based Burst Interference Cancellation for Data Detection in Massive MIMO-OFDM Systems

This paper investigates the fundamental data detection problem with burst interference in massive multiple-input multiple-output orthogonal frequency division multiplexing(MIMO-OFDM) systems. In particular, burst interference may occur only on data symbols but not on pilot symbols, which means that interference information cannot be premeasured. To cancel the burst interference, we first revisit the uplink multi-user system and develop a matrixform system model, where the covariance pattern and the low-rank property of the interference matrix is discussed. Then, we propose a turbo message passing based burst interference cancellation(TMP-BIC) algorithm to solve the data detection problem, where the constellation information of target data is fully exploited to refine its estimate. Furthermore, in the TMP-BIC algorithm, we design one module to cope with the interference matrix by exploiting its lowrank property. Numerical results demonstrate that the proposed algorithm can effectively mitigate the adverse effects of burst interference and approach the interference-free bound.

Dynamic resource allocation for high-speed railway downlink MIMO-OFDM system

The dynamic resource allocation problem in high-speed railway downlink orthogonal frequency-division multiplexing（OFDM） systems with multiple-input multiple-output（MIMO） antennas is investigated.Sub-carriers,antennas,time slots,and power are jointly considered.The problem of multi-dimensional resource allocation is formulated as a mixed-integer nonlinear programming problem.The effect of the moving speed on Doppler shift is analyzed to calculate the inter-carrier interference power.The optimization objective is to maximize the system throughput under the constraint of a total transmitted power that is no greater than a certain threshold.In order to reduce the computational complexity,a suboptimal solution to the optimization problem is obtained by a two-step method.First,sub-carriers,antennas,and time slots are assigned to users under the assumption of equal power allocation.Next,the power allocation problem is solved according to the result of the first-step resource allocation.Simulation results show that the proposed multi-dimensional resource allocation strategy has a significant performance improvement in terms of system throughput compared with the existing one.

Extended Kalman filtering-based channel estimation for space-time coded MIMO-OFDM systems

A space-time coded multiple-input multiple-output orthogonal frequency-division multiplexing （MIMO-OFDM） system is considered as a solution to the future wideband wireless communication system. This paper proposes an extended Kalman filtering-based （EKF-based） channel estimation method for space-time coded MIMO-OFDM systems. The proposed method can exploit pilot symbols and an extended Kalman filter to estimate channel without any prior knowledge of channel statistics. In comparison with the least square （LS） and the least mean square （LMS） methods, the EKF-based approach has a better performance in theory. Computer simulations demonstrate the proposed method outperforms the LS and LMS methods. Therefore it can offer draznatic system performance improvement at a modest cost of computational complexity.

Particle filter for joint frequency offset and channel estimation in MIMO-OFDM systems

A particle filter is proposed to perform joint estimation of the carrier frequency offset （CFO） and the channel in multiple-input multiple-output orthogonal frequency division multiplexing （MIMO-OFDM） wireless communication systems. It marginalizes out the channel parameters from the sampling space in sequential importance sampling （SIS）, and propagates them with the Kalman filter. Then the importance weights of the CFO particles are evaluated according to the imaginary part of the error between measurement and estimation. The varieties of particles are maintained by sequential importance resampling （SIR）. Simulation results demonstrate this algorithm can estimate the CFO and the channel parameters with high accuracy. At the same time, some robustness is kept when the channel model has small variations.

Schemes for synthesizing high-resolution range profile with extended OFDM-MIMO

Two novel schemes are proposed to synthesize high resolution range profile (HRRP) based on co-located multiple-input multiple-output (MIMO) system in the context of the joint radar and communication system. The difference between two schemes is the pattern of selecting pulses, which depends on the demand for the velocity information. The system, a type of frequency diverse array (FDA), takes full advantage of the phase-coded orthogonal frequency division multiplexing (OFDM) signal. Furthermore, the complete discrete form of the phase-coded OFDM echoes is utilized to derive the HRRP processing. The velocity estimation in the second scheme aims to eliminate velocity ambiguity, and high velocity can be retrieved exactly. Meanwhile, the imaging method is investigated with random frequency coding applied to an array. The desired performance of resolving velocity ambiguity and suppressing noise is shown by means of comparisons with previous work. The advantages in the radar imaging and the significance of the work are concluded in the end.

Optimal Multipoint-to-Multipoint Transceiver Design with Massive MIMO Relay Station in OFDM Systems

Based on massive MIMO （ multiple-input multiple-output） （M2M） systems, in order to avoid pilot contamination and improve the performance of rapacity, a pilot training transmission scheme was designed for pilot decontamination by utilizing orthogonal mbearriers of OFDM （ orthogonal frequency division multiplexing） during pilot transmission phase and a joint optimized transceiver design for multi-antenna user pairs was proposed during the data transmission phase. The massive M2M system included a single relay station, multiple paired source nodes and destination nodes. Source nodes precoding matrices and relay station precoding matrix were jointly optimized by maximizing the weighted sum-rate in OFDM systems. After some mathematical manipulation to sum-rate, the cost function of sum.rate was expressed as quadratic optimizing expressions which could be solved by regular convex optlmiTation softwares. Different from existing algorithms, the proposed precoding design was based on massive MIMO OFDM systems with multi-antenna users pairs together pilot decontamination transmission arrangement. Simulations indicate the effectiveness of the proposed optimal precoding system. The proposed scheme not only can reduce pilot contamination, but also can improve performance of bit-error-rate （BER） as wed as sum- rate contrast to existing algorithms. In addition, it shows that the proposed M2M massive MIMO system works steadily when the number of users increases in large scale.

Suboptimal MMSE Channel Estimation with Subspace Tracking for MIMO-OFDM Transmission

A suboptimal minimum mean-squared error estimation （MMSE） is proposed for a dispersive wireless channel in the absence of its .orrelation matrix for multipleinput multiple-output ort,ogonal frequency division multiplexing （MIMO - OFDM） transmission. It utilizes a fast subspace approximation tracking to separate signal subspace with a limited set of channel estimates. The subspace rank is adjusted by pre-set thresholds in different signal-to-noise ratios （SNRs）. The performance comparison among the proposed algorithm, least square based, and the optimal MMSE estimation is shown by numerical simulation under a spatially correlated multi-tap channel scenario. It demonstrates that the approach has better normalized mean square error than recursive least square estimation and yields 3 dB gain over the latter.

ERGODIC CAPACITY FORMULA OF MIMO-OFDM SYSTEMS UNDER CORRELATED FREQUENCY SELECTIVE RAYLEIGH FADING CHANNELS

An explicit formula for the ergodic capacity of Orthogonal Frequency Division Multiplexing (OFDM)-based Multiple-Input Multiple-Output (MIMO) systems under correlated frequency selective Rayleigh channels is derived,by simplifying the channel response matrix in frequency domain into the so-called Kronecker model composed of three kinds of correlations,i.e.multipath tap gain correlation and spatial fading correlations at both transmitter and receiver.The derived formula is very simple and convenient for one to estimate the effects of all three kinds of correlations on MIMO-OFDM capacity.If taps are independent,there is a very simple expression for the ergodic capacity.In case of tap correlation,the capacity formula could be further given in an integral expression.The validity of the new formula is verified and the effects of correlations,delay spread as well as the number of subcarriers on the ergodic capacity are evaluated via Monte Carlo simulations.

Transmit Antenna Selection in MIMO-OFDM System Based on CO-SFBC Schemes

A transmit antenna selection(TAS)multi-input multi-output orthogonal frequency-division multiplexing(MIMO-OFDM)system based on channel-orthogonalized space-frequency block coding(CO-SFBC)schemes was proposed for better performance.Firstly,the principles and criterions for designing CO-STBC/SFBC schemes with angle feedback were proposed,and then the effect of quantization for the feedback angle information within such schemes was discussed.Meanwhile,the TAS scheme was applied to the system to further improve the overall performance.Simulation results show that the combination of the proposed CO-STBC and TAS schemes can significantly improve the system performance,which is much larger than only applying them to systems individually.

A SIMPLIFIED QRD-M SIGNAL DETECTION ALGORITHM FOR MIMO-OFDM SYSTEMS

QR Decompositon with an M-algorithm(QRD-M) has good performance with low complexity,which is considered as a promising technique in Multiple-Input Multiple-Output(MIMO) detections.This paper presented a simplified QRD-M algorithm for MIMO Orthogonal Frequency Division Multiplexing(MIMO-OFDM) systems.In the proposed scheme,each surviving path is expanded only to partial branches in order to carry out a limited tree search.The nodes are expanded on demand and sorted in a distributed manner,based on the novel expansion scheme which can pre-determine the children's ascending order by their local distances.Consequently,the proposed scheme can significantly decrease the complexity compared with conventional QRD-M algorithm.Hence,it is especially attractive to VLSI implementation of the high-throughput MIMO-OFDM systems.Simulation results prove that the proposed scheme can achieve a performance very close to the conventional QRD-M algorithm.

A Virtual Channel-Based Approach to Compensation of I/Q Imbalances in MIMO-OFDM Systems

Multiple-input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) scheme has been considered as the most promising physical-layer architecture for the future wireless systems to provide high-speed communications. However, the performance of the MIMO-OFDM system may be degraded by in-phase/quadrature-phase (I/Q) imbalances caused by component imperfections in the analog front-ends of the transceivers. I/Q imbalances result in inter-carrier interference (ICI) in OFDM systems and cause inaccurate estimate of the channel state information (CSI), which is essential for diversity combining at the MIMO receiver. In this paper, we propose a novel approach to analyzing a MIMO-OFDM wireless communication system with I/Q imbalances over multi-path fading channels. A virtual channel is proposed as the combination of multi-path fading channel effects and I/Q imbalances at the transmitter and receiver. Based on this new approach, the effects of the channel and I/Q imbalances can be jointly estimated, and the influence of channel estimation error due to I/Q imbalances can be greatly reduced. An optimal minimal mean square error (MMSE) estimator and a low-complexity least square (LS) estimator are employed to estimate the joint coefficients of the virtual channel, which are then used to equalize the distorted signals. System performance is theoretically analyzed and verified by simulation experiments under different system configurations. The results show that the proposed method can significantly improve system performance that is close to the ideal case in which I/Q are balanced and the channel state information is known at the receiver.

Power duality for multi-antenna OFDM system in broadcast channel with user scheduling

This paper deals with design and analysis of user scheduling and power allocation for multi-antenna OFDM systems with DPC,ZF-DPC,ZF-BF and TDMA transmit strategies.We consider the general multi-user downlink scheduling problem and power minimization with multi-user rate constraints.According to the channel state,it is shown that there is a power optimal policy which selects a subset of users in each scheduling interval.We present user selection algorithms for DPC,ZF-DPC,ZF-BF and TDMA for multi-antenna OFDM system in broadcast channels,and we also present the practical water-filling solution in this paper.By the selected users with the consideration of fairness,we derive the power optimization algorithm with multi-user rate constraints.We also analyze the power duality of uplink-downlink for the transmit strategies of DPC,ZF-DPC and ZF-BF.Simulation results show that the present user-scheduling algorithm and power minimization algorithm can achieve good power performance,and that the scheduling algorithm can guarantee fairness.

MIMO-OFDM channel estimation method utilizing correlation in time domain for B3G-TDD uplink

This article proposes a simple pilot-aided channel estimation method based on correlation in time domain for multiple-input and multiple-output olthogonal frequency division multiplexing （MIMO-OFDM） systems. Pilot symbols in all transmit antennas are generated from different circular shifting of a certain sequence. Through once correlation, the receiver can obtain time-domain pulse responses for channel fading from all transmit antennas to a certain receive antenna, from which channel estimation in frequency domain can be obtained. Beyond 3G time-division duplex （B3G-TDD） uplink is introduced, and the channel estimation method is used in it. Theoretical analysis and simulation are both carried out. Mean square error （MSE） performance shows that the method can exhibit precise estimation. Complexity analysis proves it requires very low complexity. System simulation result shows that it guarantees the performance of B3G-TDD uplink very well.

A novel differential multiuser detection algorithm for multiuser MIMO-OFDM systems

We propose an efficient low bit error rate(BER) and low complexity multiple-input multiple-output(MIMO) multiuser detection(MUD) method for use with multiuser MIMO orthogonal frequency division multiplexing(OFDM) systems.It is a hybrid method combining a multiuser-interference-cancellation-based decision feedback equalizer using error feedback filter(MIMO MIC DFE-EFF) and a differential algorithm.The proposed method,termed 'MIMO MIC DFE-EFF with a differential algorithm' for short,has a multiuser feedback structure.We describe the schemes of MIMO MIC DFE-EFF and MIMO MIC DFE-EFF with a differential algorithm,and compare their minimum mean square error(MMSE) performance and computational complexity.Simulation results show that a significant performance gain can be achieved by employing the MIMO MIC DFE-EFF detection algorithm in the context of a multiuser MIMO-OFDM system over frequency selective Rayleigh channel.MIMO MIC DFE-EFF with the differential algorithm improves both computational efficiency and BER performance in a multistage structure relative to conventional DFE-EFF,though there is a small reduction in system performance compared with MIMO MIC DFE-EFF without the differential algorithm.

Simple Closed-Loop Method to Compensate Interference Asymmetry in Time-Division Duplex MIMO-OFDM Systems

In wireless communications systems with time-division duplex (TDD) deployment, channel reciprocity and symmetric interference between transmitter and receiver sides are two widely-adopted assumptions for the design of optimal adaptation transmission mode. However, in practice, there is an undesirable but non-negligible effect, namely the asymmetric interference, that makes the assumptions no longer valid. In this paper, a simple closed-loop feedback method of compensating interference asymmetry in TDD multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system is proposed. The system makes the estimated interference at transmit-side be able to track the instantaneous receive-side interference dynamically. The proposed method maintains constant frame error rate (FER) by adopting adaptive modulation coding (AMC) and power loading. The final simulations have verified the effectiveness of the new method.

Performance of Adaptive Subchannel Assignment-Based MIMO/OFDM Systems over Multipath Fading Channels

Adaptive antenna arrays at both the base and mobile stations can further increase system capacity and improve the quality of service of conventional orthogonal frequency division multiplexing （OFDM） systems. Conventional adaptive antenna array-based multiple-input multiple-output （MIMO）/OFDM systems use the sub-carriers characterized by the largest eigenvalue to transmit the OFDM symbols. This paper describes the performance of adaptive subchannel assignment-based MIMO/OFDM systems over multipath fading channels, The system adaptively selects the eigenvectors associated with the relatively large subchannel eigenvalues to generate the antenna array weights at the base and mobile stations and then adaptively assigns the corresponding best subchannels to transmit the OFDM symbols. Simulation results show that the proposed system can achieve better performance than the conventional adaptive antenna arraybased MIMO/OFDM system over multipath fading channels.

Blind Carrier Frequency Offset Estimation via Power Spectrum Analysis in MIMO OFDM Systems

As a generalization of orthogonal frequency-division multiplexing （OFDM） systems, multi-input multi-output （MIMO） OFDM systems are very sensitive to carrier frequency offset （CFO）. This paper proposes a blind CFO estimation method based on power spectrum analysis, which has high bandwidth efficiency and is much less complex. This method can be used to estimate the residual CFO, which is less than half of the subcarrier spacing. The method uses a cosine cost function to get a closed-form CFO estimate. Simulation results illustrate that the method is effective for MIMO OFDM systems.

Diversity analysis of space-time-frequency coded broadband MIMO-OFDM system with correlation across space time and frequency

For the frequency selective and time variant multiple-input multiple-output(MIMO)channel model taking into account transmitting and receiving antenna correlation,the diversity of space-time-frequency coded broadband orthogonal frequency division multiplexing(MIMO-OFDM)system is analyzed.Based on the average pairwise error probability(PEP),the design criterion of space-time-frequency code(STFC)is expanded.For a given STFC,it is found that the achievable diversity order is related to the transmitter and the receiver correlation matrix as well as the time correlation and frequency correlation matrix.The maximum available diversity of STFC over the correlation channel is Lrank(P)rank(Q)rank(RT).The space-time code and space-frequency code are special cases in our approach.Simulation results validate the findings.

Blind carrier frequency offset estimation for constant modulus signaling based OFDM systems: algorithm, identifiability, and performance analysis

Cartier frequency offset （CFO） estimation is critical for orthogonal frequency-division multiplexing （OFDM） based transmissions. In this paper, we present a low-complexity, blind CFO estimator for OFDM systems with constant modulus （CM） signaling. Both single-input single-output （SISO） and multiple-input multiple-output （MIMO） systems are considered. Based on the assumption that the channel keeps constant during estimation, we prove that the CFO can be estimated uniquely and exactly through minimizing the power difference of received data on the same subcarriers between two consecutive OFDM symbols; thus, the identifiability problem is assured. Inspired by the sinusoid-like cost function, curve fitting is utilized to simplify our algorithm. Performance analysis reveals that the proposed estimator is asymptotically unbiased and the mean square error （MSE） exhibits no error floor. We show that this blind scheme can also be applied to a MIMO system. Numerical simulations show that the proposed estimator provides excellent performance compared with existing blind methods.

Robust Precoding Schemes for Multi-User MISO-OFDM Downlink with Limited Time-Domain Feedback

In multi-user multiple-input single-output orthogonal frequency-division multiplexing （MISO-OFDM） downlinks with limited feedback, both linear precoders （LP） and Tomlinson-Harashima precoders （THP） experience performance degradation due to inaccurate channel state information at the transmitter （CSIT）. This analysis treats the downlink channels as random quantities and exploits their second order statistics in robust precoding schemes to correct the errors introduced in the feedback procedure. The time-domain channel vectors are found to reduce the feedback overhead more than the frequency-domain vectors. A compression and restoration method and a codebook design are also given to obtain compact feedback quantities. Simulations show that the robust LP and THP are superior to the previous methods with tradeoffs possible between performance and feedback overhead.