Space-time codes (STC) are a class of signaling techniques, offering coding and diversity gains along with improved spectral efficiency. These codes exploit both the spatial and the temporal diversity of the wireless link by combining the design of the error correction code, modulation scheme and array processing. STC are well suited for improving the downlink performance, which is the bottleneck in asymmetric applications such as downstream Internet. Three original contributions to the area of STC are presented in this dissertation. First, the development of analytic tools that determine the fundamental limits on the performance of STC in a variety of channel conditions. For trellis-type STC, transfer function based techniques are applied to derive performance bounds over Rayleigh, Rician and correlated fading environments. For block-type STC, an analytic framework that supports various complex orthogonal designs with arbitrary signal cardinalities and array configurations is developed. In the second part of the dissertation, the Virginia Tech Space-Time Advanced Radio (VT-STAR) is designed, introducing a multi-antenna hardware laboratory test bed, which facilitates characterization of the multiple-input multiple-output (MIMO) channel and validation of various space-time approaches. In the third part of the dissertation, two novel space-time architectures paired with iterative processing principles are proposed. The first scheme extends the suitability of STC to outdoor wireless communications by employing iterative equalization/decoding for time dispersive channels and the second scheme employs iterative interference cancellation/decoding to solve the error propagation problem of Bell-Labs Layered Space-Time Architecture (BLAST). Results show that remarkable energy and spectral efficiencies are achievable by combining concepts drawn from space-time coding, multiuser detection, array processing and iterative decoding.

Space-Time Codes for High Data Rate Wireless Communications

Tables of integrals

Channel models are important tools to evaluate the performance of new concepts in mobile communications. However, there is a tradeoff between complexity and accuracy. In this paper, we extend the popular Wireless World Initiative for New Radio (WINNER) channel model with new features to make it as realistic as possible. Our approach enables more realistic evaluation results at an early stage of algorithm development. The new model supports 3-D propagation, 3-D antenna patterns, time evolving channel traces of arbitrary length, scenario transitions and variable terminal speeds. We validated the model by measurements in a coherent LTE advanced testbed in downtown Berlin, Germany. We then reproduced the same scenario in the model and compared several channel parameters (delay spread, path gain, K-factor, geometry factor and capacity). The results match very well and we can accurately predict the performance for an urban macro-cell setup with commercial high-gain antennas. At the same time, the computational complexity does not increase significantly and we can use all existing WINNER parameter tables. These artificial channels, having equivalent characteristics as measured data, enable virtual field trials long before prototypes are available.

QuaDRiGa: A 3-D Multi-Cell Channel Model With Time Evolution for Enabling Virtual Field Trials

The fifth generation (5G) mobile communication systems will be in use around 2020. The aim of 5G systems is to provide anywhere and anytime connectivity for anyone and anything. Several new technologies are being researched for 5G systems, such as massive multiple-input multiple-output communications, vehicle-to-vehicle communications, high-speed train communications, and millimeter wave communications. Each of these technologies introduces new propagation properties and sets specific requirements on 5G channel modeling. Considering the fact that channel models are indispensable for system design and performance evaluation, accurate and efficient channel models covering various 5G technologies and scenarios are urgently needed. This paper first summarizes the requirements of the 5G channel modeling, and then provides an extensive review of the recent channel measurements and models. Finally, future research directions for channel measurements and modeling are provided.

A Survey of 5G Channel Measurements and Models

High-speed railway (HSR) brings convenience to peoples' lives and is generally considered as one of the most sustainable developments for ground transportation. One of the important parts of HSR construction is the signaling system, which is also called the “operation control system,” where wireless communications play a key role in the transmission of train control data. We discuss in detail the main differences in scientific research for wireless communications between the HSR operation scenarios and the conventional public land mobile scenarios. The latest research progress in wireless channel modeling in viaducts, cuttings, and tunnels scenarios are discussed. The characteristics of nonstationary channel and the line-of-sight (LOS) sparse and LOS multiple-input-multiple-output channels, which are the typical channels in HSR scenarios, are analyzed. Some novel concepts such as composite transportation and key challenging techniques such as train-to-train communication, vacuum maglev train techniques, the security for HSR, and the fifth-generation wireless communications related techniques for future HSR development for safer, more comfortable, and more secure HSR operation are also discussed.

Challenges Toward Wireless Communications for High-Speed Railway

Cooperation diversity schemes have been proposed for cellular networks that permit mobile stations to relay signals to a final destination, thereby increasing the network capacity and coverage. The mobile relays either decode and retransmit the received signal or simply amplify and forward (A & F) the signal. The overall channel from the source to the destination via the relay in A & F systems is "double" Gaussian with properties quite different from a typical cellular channel. Since very little is known about A & F relay fading channels, this paper considers their statistical properties such as the envelope probability density function, autocorrelation, level crossing rate, and system performance characteristics like frequency of outages and average outage durations. We briefly discuss the simulation of these channels and verify our analysis by simulations.

Statistical properties of amplify and forward relay fading channels

A 3-D reference model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) channels is reviewed along with its corresponding first- and second-order channel statistics. To validate the reference model, an experimental MIMO M-to-M channel-sounding campaign was conducted for M-to-M vehicular communication with vehicles that travel along surface streets and expressways in a metropolitan area. To compare the first- and second-order channel statistics that were obtained from the reference model with those obtained from the empirical measurements, a new maximum-likelihood-based stochastic estimator is derived to extract the relevant model parameters from the measured data. The measured data is processed and compared with the analytical results. The close agreement between the analytically and empirically obtained channel statistics confirms the utility of the proposed reference model and the method for estimating the model parameters.

Wideband MIMO Mobile-to-Mobile Channels: Geometry-Based Statistical Modeling With Experimental Verification

Several new "sum-of-sinusoids" models have recently been introduced for the simulation of Rayleigh fading channels. These models are statistical in nature implying that their simulation parameters such as the Doppler frequencies are random. They have been shown to accurately reproduce some of the desired statistical properties of the faded envelope such as the time autocorrelation and the level crossing rate. However, a comparative analysis of these models, hitherto scattered throughout the literature, is not available. This paper compares these models in terms of their complexity and performance. The performance assessment is based upon the variance of the time average statistical properties from their ideal ensemble averages.

Comparative analysis of statistical models for the simulation of Rayleigh faded cellular channels

The BER degradation caused by imperfect channel estimation as well as the adverse effect of jamming on pilot symbols, which are used for the channel estimation (CE), is often neglected while analyzing OFDM und MC-CDMA systems leading to over-optimistic results. Therefore, to provide a more realistic analysis, we analyze the vulnerability of pilot symbol aided CE schemes for OFDM/MC-CDMA systems to narrowband and partial band jamming. We derive closed form BER expressions for studying the effect of imperfect CE for OFDMA/MC-CDMA in the absence of jamming in a frequency selective Rayleigh fading environment. We extend these results via simulations and theory (wherever permitted by mathematical tractability) to account for jamming. Some possible solutions such as the use of boosted pilots and the use of jamming side information, whenever available, to excise the jammed pilots or provide MMSE equalization are proposed to reduce the impact of jamming on the CE.

Analysis of OFDM/MC-CDMA under channel estimation and jamming

By adopting multiple-input multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) technologies, indoor wireless systems could reach data rates up to several hundreds of Mbits/s and achieve spectral efficiencies of several tens of bits/Hz/s, which are unattainable for conventional single-input single-output systems. The enhancements of data rate and spectral efficiency come from the fact that MIMO and OFDM schemes are indeed parallel transmission technologies in the space and frequency domains, respectively. To validate the functionality and feasibility of MIMO and OFDM technologies, we set up a four-transmitter four-receiver OFDM testbed in a typical indoor environment, which achieves a peak data rate of 525 Mbits/s and a spectral efficiency of 19.2 bits/Hz/s. The performances including MIMO channel characteristics, bit-error rate against signal-to-noise ratio curves, the impairments of carrier frequency offset and channel estimation inaccuracy, and an asymmetric MIMO scheme are reported and analyzed in this paper.

http://www.creydos.com/uploads/5/3/4/2/53422083/4x4mimo.pdf

T.G. Pratt

Papers

Statistical properties of amplify and forward relay fading channels

Wideband MIMO Mobile-to-Mobile Channels: Geometry-Based Statistical Modeling With Experimental Verification

Comparative analysis of statistical models for the simulation of Rayleigh faded cellular channels

Analysis of OFDM/MC-CDMA under channel estimation and jamming

A high-speed four-transmitter four-receiver MIMO OFDM testbed: experimental results and analyses