Wideband MIMO Channel Research Articles

Two-Cylinder and Multi-Ring GBSSM for Realizing and Modeling of Vehicle-to-Vehicle Wideband MIMO Channels

A new geometry-based stochastic scattering model (GBSSM) for wideband multiple-input–multiple-output vehicle-to-vehicle (V2V) channels is proposed in this paper. The proposed GBSSM with cross-polarized antennas combines three-dimensional two cylinders to model the stationary scatterers and two-dimensional multirings to imitate the moving scatterers. The channel realization by using the channel matrix in this paper is much more straightforward and concise to study the channel characteristics compared with the too complicated analytical solutions available so far. Because V2V propagation channels are nonstationary, the time-varying channel properties and parameters are further investigated based on the proposed GBSSM and realized channels, which can be used in the link and system-level simulations in V2V radio systems.

A Non-Stationary Geometry-Based Street Scattering Model for Vehicle-to-Vehicle Wideband MIMO Channels

In this paper, a non-stationary geometry-based street scattering model for wideband multi-input multi-output vehicle-to-vehicle fading channels is proposed. It is assumed that the static scatterers on the both roadsides are uniformly distributed on time-varying ellipses, and the mobile scatterers are uniformly distributed in time-varying segments of the road. Both the relatively low- and high- speed mobile scatterers are under consideration, and the velocity distributions of the low- and high- speed moving scatterers are assumed to follow exponential and mixed Gaussian, respectively. In this work, we extend the proposed narrowband model to wideband and also introduce the carrier frequency and bandwidth into the model. In order to avoid complicated procedure in deriving the analytical expressions of the channel parameters and functions, the channel is realized first, then the channel properties and parameters are investigated.

Mobile-to-Mobile Wideband MIMO Channel Realization by Using a Two-Ring Geometry-Based Stochastic Scattering Model

In this paper, a geometry-based stochastic scattering model (GBSSM) for wideband multiple-input multiple-output mobile-to-mobile (M2M) isotropic scattering fading channels is proposed. The model is based on a two-ring scattering model which can be applied for the line-of-sight (LOS) and non-LOS scenarios by considering the single- and double-bounced components. The target of developing the GBSSM is to realize the channel in typical environments for future internet-of-thing networks such as shopping malls, logistics centers and so on to be used in the link and system level simulations in M2M new radio systems. The channel realization in this paper is more straight forward and concise to study the channel characteristics compare with the too complicated analytical solutions available so far.

Blind Recursive Subspace-Based Identification of Time-Varying Wideband MIMO Channels

We present a blind recursive algorithm for tracking rapidly time-varying wireless channels in precoded multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. Subspace-based tracking is normally considered for slowly time-varying channels only. Due to the frequency correlation of the wireless channels, the proposed scheme can collect data not only from the time but from the frequency domain as well to speed up the update of the required second-order statistics. After each such update, the subspace information is recomputed using the orthogonal iteration, and then, a new channel estimate is obtained. We also investigate choices of precoder in terms of the tradeoff between the symbol recovery capability and the channel estimation performance and demonstrate the convergence properties of our approach. The proposed algorithm is evaluated in a Third-Generation Partnership Project (3GPP) Spatial Channel Model suburban macro scenario, in which a mobile station is allowed to move in any direction with a speed up to 100 km/h, corresponding to a maximum Doppler shift of about 230 Hz in this case. Numerical experiments show that the normalized mean square error of the channel estimates converges to a level of -30 dB within less than five OFDM symbols when the signal-to-noise ratio (SNR) (per symbol) is ≥ 20 dB.

Performance Evaluation of Closed-Loop Spatial Multiplexing Codebook Based on Indoor MIMO Channel Measurement

Closed-loop MIMO technique standardized in LTE can support different layer transmissions through precoding operation to match the channel multiplexing capability. However, the performance of the limited size codebook still needs to be evaluated in real channel environment for further insights. Based on the wideband MIMO channel measurement in a typical indoor scenario, capacity loss (CL) of the limited size codebook relative to perfect precoding is studied first in two extreme channel conditions. The results show that current codebook design for single layer transmission is nearly capacity lossless, and the CL will increase with the number of transmitted layers. Furthermore, the capacity improvement of better codebook selection criterions is very limited compared to CL. Then we define the maximum capacity boost achieved by frequency domain layer adaption (FDLA) and investigate its sensitivity to SNR and channel condition. To survey the effect of frequency domain channel variation on MIMO-OFDM system, we define a function to measure the fluctuation levels of the key channel metrics within a subband and reveal the inherent relationship between them. Finally, a capacity floor resulted as the feedback interval increases in frequency domain.

Statistical Analysis of Polarized Wide-Band MIMO Channels in an Indoor Environment

In this paper, a 2x2 and a 4x4 indoor MIMO measurement campaign at a (2 -5) GHz is presented. A statistical analysis to study the effects of a 2x2 and a 4x4 MIMO on the channel capacity with their respective received fixed signal to noise ratios were analyzed both in the LOS and in NLOS scenarios. Furthermore, investigations were carried out on all the possible wide band antenna polarizations in order to ascertain which mode of propagation yields a highly decorrelated spatial channel. The three received signal to noise ratios namely 10dB, 20dB and 30dB were used to model various received signal powers. It was found that copolar configurations HH and VV yielded the maximum capacity values both in the LOS and in NLOS respectively. Finally, a validity test was conducted and it was realized that the empirical distribution is similar and within the theoretical (i.i.d) distribution.

Performance Analysis of MIMO Schemes in Residential Home Environment via Wideband MIMO Propagation Measurement

This paper illustrates a large-scale MIMO propagation channel measurement in a real life environment and evaluates throughput performance of various MIMO schemes in that environment. For that purpose, 4 × 4 MIMO transceivers and a novel spatial scanner are fabricated for wideband MIMO channel measurements in the 5GHz band. A total of more than 50, 000 spatial samples in an area of 150m2, which includes a bedroom, a Japanese room, a hallway, and the living and dining areas, are taken in a real residential home environment. Statistical properties of the propagation channel and throughput performance of various MIMO schemes are evaluated by using measured data. Propagation measurement results show large dynamic channel variations occurring in a real environment in which statistical properties of the channel, such as frequency correlation and spatial correlation are not stationary any more, and become functions of the SNR. Furthermore, evaluation of throughput shows that although MIMO schemes outperform the SISO system in most areas, open loop systems perform badly in the far areas with low SNR. Paying for the cost of CSI or partial CSI at Tx, closed loop and hybrid systems have superior performance compared to other schemes, especially in reasonable SNR areas ranging from 10dB to 30dB. Spatial correlation, which is common in Japanese wooden residences, is also found to be a dominant factor causing throughput degradation of the open loop MIMO schemes.

Reduced-complexity cluster modeling for time-variant wideband MIMO channels

This paper presents a reduced-complexity cluster modeling method for channel models that are based on the 3GPP and similar channel models to simulate the time variation of spatially correlated wideband MIMO channels. The main novelty is that, when modeling the time-variant wideband MIMO channels, instead of tracking the changes in the angles of arrival (AoAs) of all the multi-path components (MPCs) defined, we only track the change in the centre AoA for each of the clusters. Hence for moderate angle spreads (ASs) of clusters and a constant uniform distribution of the offsets of the MPCs within each cluster, tracking the time-variant centre AoAs of the clusters allows us to develop a computationally efficient approximation method to calculate the instantaneous channel matrix and spatial correlation matrix for time-variant wideband MIMO channels. The development of this approximation method includes two stages: firstly, we evaluate the approximation method for simulating wideband MIMO channels with time-invariant AoAs in terms of the centre angles and scatterer distributions of clusters; secondly, on the basis of the validation at stage one, we develop the approximation method for the wideband MIMO channels with time-variant AoAs, and evaluate this approximation method by the extended correlation matrix distance (CMD) metric. We use the extended CMD metric to compare the CMDs predicted by the approximate and exact calculation under different time-variant scenarios. The simulation results show that the approximation method works well when the velocity of the movement is up to 50 m/s and provided the ASs of the clusters are within 10 ∘.

Large-Scale Characteristics of 5.25 GHz Based on Wideband MIMO Channel Measurements

Based on the channel measurements at 5.25 GHz in the hotspot area, empirical path loss (PL) models are developed and discussed for the IMT-Advanced system design. The measured scenarios include indoor line-of-sight (LOS), non-LOS, outdoor LOS/obstructed LOS, and outdoor-to-indoor propagations. The PL exponent, intercept, and standard deviation of shadow fading are obtained by using the least square method in each scenario. Moreover, the floor attenuation factor and penetration loss are determined from the cross-floor measurement and outdoor-to-indoor measurement, respectively.

도심 환경을 고려한 마이크로파 대역 MIMO 전파 채널 측정 시스템에 관한 연구

본 논문은 국내 도심 환경을 고려한 마이크로파 대역 다중 안테나 전파 채널 특성을 연구하기 위한 광대역 MIMO 채널 측정 시스템 구축과 성능 확인을 위한 시험 측정을 기술하였다. 차세대 이동 통신을 고려하여 채널 측정 시스템은 고속의 스위칭 방식과 100 MHz의 광대역 채널 대역폭을 지원하도록 설계되었으며, <TEX>$4{\times}4$</TEX> MIMO 채널 측정을 지원한다. 시스템 성능 확인 및 교정을 위한 시험 측정을 분당 빌딩 밀집 지역에서 실시하였다. 3.7 GHz와 8 GHz의 도심 LOS 구간의 시험 측정 데이터를 분석한 결과, 3.7 GHz 및 8 GHz 대역에서의 광대역경로 손실 지수는 각각 1.79와 1.76으로 측정되었으며, 평균 RMS 지연 확산은 각각 200 ns과 42 ns로 측정되었다. 시험 측정 결과, 본 MIMO 채널 측정 시스템은 실외 도심 환경에서 커버리지와 신호대 잡음비 및 채널 용량 등의 마이크로파 대역 전파 특성 연구에 적합함을 확인하였다. In this paper, the development of wideband MIMO channel sounder and a pilot measurement result is described for research on the multi antenna radio propagation characteristics considering urban environment at microwave frequencies. We developed <TEX>$4{\times}4$</TEX> MIMO(BW:100 MHz) channel sounder using the high speed switching mechanism and periodic pseudo random binary signals method considering next generation mobile communication system. A pilot measurement campaign at the urban area of Bundang is presented for confirmation of system performance. From the analysis of measurement data, wideband path loss exponent of 3.7 and 8 GHz band is 1.79 and 1.76. Average RMS delay spread is 200 ns and 42 ns respectively. From the experiment results, operation of this measurement system is confirmed considering research for a coverage, SNR and channel capacity in urban environment at microwave frequencies.

Reduced-Complexity Time-Domain Equalization for Turbo-MIMO Systems

A reduced-complexity time-domain equalization scheme for wideband turbo-multiple-input multiple-output (turbo-MIMO) systems is presented. This scheme, called iterative trellis search equalization, is based on a modified version of the M-Bahl-Cocke-Jelinek-Raviv (M-BCJR) algorithm, applied to a suitably chosen trellis representation of the wideband MIMO channel process. Exploiting the properties of quadrature amplitude modulation (QAM) signal constellations with block-partitionable labels, this modified M-BCJR algorithm has complexity per bit that is independent of the constellation size, and polynomial in the number of transmit antennas and channel memory. Results from computer simulations show that the new scheme successfully mitigates intersymbol interference even if only a very small fraction of trellis state transitions is considered. It is also demonstrated that asynchronous transmission of the spatially multiplexed symbol streams can result in considerable performance improvement compared to synchronous MIMO systems.

An Experimental Investigation of Wideband MIMO Channel Characteristics Based on Outdoor Non-LOS Measurements at 1.8 GHz

This paper presents an experimental investigation of the wideband MIMO channel characteristics in an outdoor nonline-of-sight environment. Our wideband MIMO testbed is a true array system with four transmitting antennas and eight receiving antennas, which operates at a carrier frequency of 1.8 GHz with a bandwidth of 2.5 MHz. The measurements are conducted at the J. J. Pickle Research Campus at the University of Texas at Austin. From the measured data, the matrix channel complex impulse responses and multipath delay profiles are extracted. Statistical descriptions of the elements in the channel matrices and the frequency correlation functions are also presented. Based on the measured data, the channel capacities are computed and the Kronecker model results are evaluated for arrays of different sizes. It shows that the Kronecker model underestimates the channel capacities due to higher correlation matrices for arrays of larger sizes in outdoor environments

On the performance of recursive space–frequency codes and iterative decoding in wideband OFDM‐MIMO systems: simulated and measured results

AbstractIn this paper, we study the performance of a bandwidth efficient space–frequency turbo encoding scheme over wideband channels. Results are presented for simulated wideband MIMO channels consisting of two transmit antennas and up to two receive antennas. In addition, wideband channel measurements undertaken with practical multi‐element antenna structures at both the access point (AP) and mobile terminal (MT) are presented. Analysis is in terms of channel capacity, 10% channel outage capacity and space–frequency iterative decoding for an lEEE802.11a physical layer complaint modem. It is shown when operating with a spectral efficiency of 1.2 bits/s/Hz, the iterative decoded space–time codes comes within approximately 4.7 dB of 10% outage capacity over Rayleigh fading wideband channels with two transmit and two receive antennas. Over measured channels the iterative decoding scheme performs within 7.7 dB 10% of outage capacity. Losses due to channel state information estimation are also investigated. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Modeling of Wide-Band MIMO Radio Channels Based on NLoS Indoor Measurements

In this paper, we first verify a previously proposed Kronecker-structure-based narrow-band model for nonline-of-sight (NLoS) indoor multiple-input-multiple-output (MIMO) radio channels based on 5.2-GHz indoor MIMO channel measurements. It is observed that, for the narrow-band case, the measured channel coefficients are complex Gaussian distributed and, consequently, we focus on a statistical description using the first- and second-order moments of MIMO radio channels. It is shown that the MIMO channel covariance matrix can be well approximated by the Kronecker product of the covariance matrices, seen from the transmitter and receiver, respectively. A narrow-band model for NLoS indoor MIMO channels is thus verified by these results. As for the wide-band case, it is observed that the average power-delay profile of each element of the channel impulse response matrix fits the exponential decay curve and that the Kronecker structure of the second-order moments can be extended to each channel tap. A wide-band MIMO channel model is then proposed, combining a simple COST 259 single-input-single-output channel model and the Kronecker structure. Monte Carlo simulations are used to generate indoor MIMO channel realizations according to the models discussed. The results are compared with the measured data using the channel capacity and good agreement is found.

COFDM performance evaluation in outdoor MIMO channels using space∕polarisation-time processing techniques

Outdoor physical layer performance results are presented for a proposed 4G coded orthogonal frequency division multiplexing (COFDM) system. The transceiver employs space-time processing and results are obtained using measured wideband MIMO channels. Gains as high as 10.5 dB are observed using 2Tx and 2Rx antennas for 1/2 rate coded QPSK at a packet error rate (PER) of 10/sup -2/. Additionally, results are compared for spatial and polarisation diversity.