Broadband wireless communication systems: Channel modeling and system performance analysis

Wideband channel modeling, which can accurately describe the most important characteristics of wideband mobile fading channels, is essential for the design, evaluation, and optimization of broadband wireless communication systems. In the field of wideband channel modeling, the tradeoff between the prediction accuracy and simulation efficiency has to be taken into account. On one hand, channel models should be as accurate as possible. On the other hand, channel models are supposed to be simple and easy to put into use. There are several commonly used approaches to channel modeling, e.g., measurement-based channel modeling and deterministic channel modeling. Both methods are efficient in capturing the fading behavior of real-world wireless channels. However, the resulting channel models are only valid for the specific environments as those where the measurements were carried out or the ray-tracing scenario was considered. Moreover, these methods are quite time consuming with high computational cost. Alternatively, the geometry-based stochastic channel modeling approach can be employed to model wideband mobile fading channels. The most attractive feature of this method is that the derived channel models are able to predict fading behavior for various propagation environments, and meanwhile they can be easily implemented. Thus, the dissertation will complete the wideband channel modeling task by adopt the geometry-based stochastic approach. In the dissertation, several geometry-based channel models are proposed for both outdoor and indoor propagation scenarios. The significance of the work lies in the fact that it develops channel models under more realistic propagation conditions which have seldom been considered, such as for non-isotropic scattering environxi ments and mobile-to-mobile (M2M) fading channels. In addition, the proposed channel models remove the scarcity that proper geometry-based channel models are missing for indoor environments. The most important statistical properties of the developed channel models including their temporal autocorrelation function (ACF), the two-dimensional (2D) space cross-correlation function (CCF), and the frequency correlation function (FCF) are analyzed. Furthermore, efficient channel simulators with low realization expenditure are obtained. Finally, the validity of the proposed channel models is demonstrated by comparing their analytical channel statistics with the empirical ones measured from real world channels. Besides the work in the field of wideband channel modeling, another part of the dissertation is dedicated to investigate the performance of SISO1 orthogonal frequency division multiplexing (OFDM) broadband communication systems and space-time (ST) coded MIMO2 OFDM broadband communication systems. This work provides a deep insight into the performance of a broadband mobile radio communication system over realistic wideband fading channels. Analytical expressions are derived for bit error probability (BEP) or symbol error rate (SER) of systems. In order to confirm the correctness of the theoretical results as well as to show the usefulness of the wideband channel models in the testing and analysis of a broadband communication system, SISO OFDM systems and space-time coded MIMO OFDM systems are simulated in the dissertation. In order to improve the reliability of digital transmission over broadband wireless radio channels, a differential super-orthogonal space-time trellis code (SOSTTC) is designed for noncoherent communications, where neither the transmitter nor the receiver needs the channel state information (CSI) for decoding. In addition, a new decoding algorithm is proposed. The new algorithm has exactly the same decoding performance as the traditional one. However, it is superior from the standpoint of overall computing complexity

Design and development of mobile channel simulators using digital signal processing techniques

A mobile channel simulator can be constructed either in the time domain using a tapped delay line filter or in the frequency domain using the time variant transfer function of the channel. Transfer function modelling has many advantages over impulse response modelling. Although the transfer function channel model has been envisaged by several researchers as an alternative to the commonly employed tapped delay line model, so far it has not been implemented. In this work, channel simulators for single carrier and multicarrier OFDM system based on time variant transfer function of the channel have been designed and implemented using DSP techniques in SIMULINK. For a single carrier system, the simulator was based on Bello's transfer function channel model. Bello speculated that about 10Βτ(_MAX) frequency domain branches might result in a very good approximation of the channel (where в is the signal bandwidth and τ(_MAX) is the maximum excess delay of the multi-path channel). The simulation results showed that 10Bτ(_MAX) branches gave close agreement with the tapped delay line model(where Be is the coherence bandwidth). This number is π times higher than the previously speculated 10Bτ(_MAX).For multicarrier OFDM system, the simulator was based on the physical (PHY) layer standard for IEEE 802.16-2004 Wireless Metropolitan Area Network (WirelessMAN) and employed measured channel transfer functions at the 2.5 GHz and 3.5 GHz bands in the simulations. The channel was implemented in the frequency domain by carrying out point wise multiplication of the spectrum of OFDM time The simulator was employed to study BER performance of rate 1/2 and rate 3/4 coded systems with QPSK and 16-QAM constellations under a variety of measured channel transfer functions. The performance over the frequency selective channel mainly depended upon the frequency domain fading and the channel coding rate

MIMO and beamforming techniques for reliable off-body communication using textile antennas

Wireless communication systems with textile antennas can be entirely integrated into clothing or garment and do not hinder the user’s movements. Great interest in such an off-body communication system exists in the field of rescue operations, such as firefighting, where the automated communication of vital data between rescue workers or to a base station improves the coordination of the operation and the safety of the rescue workers. To set up a reliable wireless off-body communication link, a number of specific challenges need to be overcome. Persons equipped with wearable antennas constantly change position, orientation, walking pace and body posture. This results in unpredictably variable fading and shadowing on the received signals, producing bit errors, even in case of a high average received signal-to-noise ratio. Fading and shadowing hence dramatically limit the reliability of a communication system with single antennas at both link ends. Using multiple textile antennas, the performance degradation is drastically limited, by means of MIMO and/or beamforming techniques, which mitigate the signal variation and/or produce a higher average signal-to-noise ratio at the receiver, respectively. The research documented in this PhD thesis includes multiple measurement campaigns and their analysis for a diverse number of off-body communication configurations, using MIMO and beamforming techniques with textile antennas. Off-body MIMO techniques are shown to result in a significant improvement of the reliability of the communication, an improvement which further increases when more antennas are used. Channel variation typically of the off-body scenario is tracked with a computationally low-cost system, using adaptive digital low-pass filtering on decision-oriented channel estimation information. Off-body static beamforming techniques are shown to often outperform transmit diversity systems, producing a lower bit error rate at the receiver, provided that receiver diversity is employed to compensate for the channel variation. Finally, a new theoretical model specifically for the off-body MIMO communication channel is presented, allowing an accurate reproduction of bit error rate and channel capacity characteristics as well as the generation of measurement-like random off-body MIMO channel realizations for simulation purposes

Adaptive interference cancelation techniques for multicarrier modulated systems

Current wireline systems and wireless broadcasting systems employ multicarrier modulation (MCM). This includes the high-rate digital subscriber line (HDSL), digital audio broadcasting system (DAB) and the digital terrestrial television broadcasting system (dTTb). Multicarrier modulation is also envisioned for high-speed indoor wireless local area networks (WLAN). Additionally, multicarrier code division multiple access (MC-CDMA), a hybrid of orthogonal frequency division multiplexing (OFDM) and CDMA, is proposed for the downlink (base-to-mobile) of a 3rd generation wireless system as part of the IMT-2000 standardization process. The performance of an MC-CDMA system--similar to a direct sequence CDMA (DS-CDMA) system--is limited by the presence of multiple access interference (MAI) . Downlink communications also suffers from MAI as a result of the multipath channel effect, even if it implements orthogonal code multiplexing. Additionally, transmissions aimed at different mobile users may be assigned different powers in order to increase the system capacity, essentially creating a near-far problem for some users. Due to the MC-CDMA signal structure the conventional decorrelator (based on the inverse of the correlation matrix) is dependent on the channel coefficients, suggesting the use of an adaptive multiuser detector, which can track a time-variant channel. The performance of a blind adaptive multiuser detector for MC-CDMA, based on the bootstrap algorithm, is investigated and compared to the performance of the conventional decorrelator. Additionally, the performance is investigated for different channel conditions. First, for a non-faded flat additive white Gaussian noise (AWGN) channel. Second, for a frequency selective channel with and without correlation between the channel coefficients at the different subcarriers. In general, the mobile terminal suffers from limited available resources such as computing power or battery life and, therefore, cannot accommodate the same level of receiver complexity as the base station. For the downlink, however, the received signal structure is less complex due to the assumed synchronized transmission. Moreover, the mobile receiver is merely required to detect the desired user\u27s data stream. To reduce the complexity, detectors are proposed that do not require knowledge of the active users nor their respective codes, but rather use a combined code to represent all the interfering users at once. The performance of the reduced complexity conventional decorrelator is compared to the performance of an adaptive reduced complexity detector using the bootstrap algorithm. The performance of these detectors is also investigated for the aforementioned channel types. For spectral-efficiency, closely spaced subcarriers are used in a multicarrier modulated system. A resulting drawback is a high sensitivity of the performance to a frequency offset. This results from a Doppler shift, due to mobile movement, as well as from a mismatch between the carrier frequencies at the transmitter and receiver. To mitigate this problem an adaptive decorrelator based frequency offset correction scheme is developed for OFDM and its performance is investigated. Additionally, a blind frequency offset estimation and correction structure is proposed based on a stochastic gradient method. The convergence and statistical properties of this estimator are investigated. A blind adaptive joint multiuser detection and frequency offset correction structure for downlink MC-CDMA is developed. This detector is a combination of the structures for multiuser detection for MC-CDMA and frequency offset correction for OFDM. Moreover, the performance of this detector is investigated and compared to a joint detector based on a minimum mean square error (MMSE) criterion

The Multi-Input Multi-Output (MIMO) Channel Modeling, Simulation and Applications

This thesis mainly focus on the Multi-Input Multi-Output (MIMO) channel modeling, simulation and applications. There are several ways to design a MIMO channel. Most of the examples are given in Chapter 2, where we can design channels based on the environments and also based on other conditions. One of the new MIMO channel designs based on physical and virtual channel design is discussed in Unitary-Independent- Unitary (UIU) channel modeling. For completeness, the different types of capacity are discussed in details. The capacity is very important in wireless communication. By understanding the details behind different capacity, we can improve our transmission efficiently and effectively. The level crossing rate and average duration are discussed.One of the most important topics in MIMO wireless communication is estimation. Without having the right estimation in channel prediction, the performance will not be correct. The channel estimation error on the performance of the Alamouti code was discussed. The design of the transmitter, the channel and the receiver for this system model is shown. The two different types of decoding scheme were shown - the linear combining scheme and the Maximum likelihood (ML) decoder. Once the reader understands the estimation of the MIMO channel, the estimation based on different antenna correlation is discussed. Next, the model for Mobile-to-Mobile (M2M) MIMO communication link is proposed. The old M2M Sum-of-Sinusoids simulation model and the new two ring models are discussed. As the last step, the fading channel modeling using AR model is derived and the effect of ill-conditioning of the Yule-Walker equation is also shown. A number of applications is presented to show how the performance can be evaluated using the proposed model and techniques

Empirical multi-band characterization of propagation with modelling aspects for communictions

Diese Arbeit präsentiert eine empirische Untersuchung der Wellenausbreitung für drahtlose Kommunikation im Millimeterwellen- und sub-THz-Band, wobei als Referenz das bereits bekannte und untersuchte sub-6-GHz-Band verwendet wird. Die großen verfügbaren Bandbreiten in diesen hohen Frequenzbändern erlauben die Verwendung hoher instantaner Bandbreiten zur Erfüllung der wesentlichen Anforderungen zukünftiger Mobilfunktechnologien (5G, “5G and beyond” und 6G). Aufgrund zunehmender Pfad- und Eindringverluste bei zunehmender Trägerfrequenz ist die resultierende Abdeckung dabei jedoch stark reduziert. Die entstehenden Pfadverluste können durch die Verwendung hochdirektiver Funkschnittstellen kompensiert werden, wodurch die resultierende Auflösung im Winkelbereich erhöht wird und die Notwendigkeit einer räumlichen Kenntnis der Systeme mit sich bringt: Woher kommt das Signal? Darüber hinaus erhöhen größere Anwendungsbandbreiten die Auflösung im Zeitbereich, reduzieren das small-scale Fading und ermöglichen die Untersuchung innerhalb von Clustern von Mehrwegekomponenten. Daraus ergibt sich für Kommunikationssysteme ein vorhersagbareres Bild im Winkel-, Zeit- und Polarisationsbereich, welches Eigenschaften sind, die in Kanalmodellen für diese Frequenzen widergespiegelt werden müssen. Aus diesem Grund wurde in der vorliegenden Arbeit eine umfassende Charakterisierung der Wellenausbreitung durch simultane Multibandmessungen in den sub-6 GHz-, Millimeterwellen- und sub-THz-Bändern vorgestellt. Zu Beginn wurde die Eignung des simultanen Multiband-Messverfahrens zur Charakterisierung der Ausbreitung von Grenzwert-Leistungsprofilen und large-scale Parametern bewertet. Anschließend wurden wichtige Wellenausbreitungsaspekte für die Ein- und Multibandkanalmodellierung innerhalb mehrerer Säulen der 5G-Technologie identifiziert und Erweiterungen zu verbreiteten räumlichen Kanalmodellen eingeführt und bewertet, welche die oben genannten Systemaspekte abdecken.This thesis presents an empirical characterization of propagation for wireless communications at mm-waves and sub-THz, taking as a reference the already well known and studied sub-6 GHz band. The large blocks of free spectrum available at these high frequency bands makes them particularly suitable to provide the necessary instantaneous bandwidths to meet the requirements of future wireless technologies (5G, 5G and beyond, and 6G). However, isotropic path-loss and penetration-loss are larger with increasing carrier frequency, hence, coverage is severely reduced. Path-loss can be compensated with the utilization of highly directive radio-interfaces, which increases the resolution in the angular domain. Nonetheless, this emphasizes the need of spatial awareness of systems, making more relevant the question “where does the signal come from?” In addition, larger application bandwidths increase the resolution in the time domain, reducing small-scale fading and allowing to observe inside of clusters of multi-path components (MPCs). Consequently, communication systems have a more deterministic picture of the environment in the angular, time, and polarization domain, characteristics that need to be reflected in channel models for these frequencies. Therefore, in the present work we introduce an extensive characterization of propagation by intensive simultaneous multi-band measurements in the sub-6 GHz, mm-waves, and sub-THz bands. Firstly, the suitability of the simultaneous multi-band measurement procedure to characterize propagation from marginal power profiles and large-scale parameters (LSPs) has been evaluated. Then, key propagation aspects for single and multi-band channel modelling in several verticals of 5G have been identified, and extensions to popular spatial channel models (SCMs) covering the aforementioned system aspects have been introduced and evaluated

Mobile to mobile channel modelling for wireless communications

Wireless communication has been experiencing many recent advances in mobile to mobile (M2M) applications. M2M communication systems differ from conventional fixed to mobile systems by having both transmitter and receiver in low elevation and in motion. This raises the need to come up with new channel models and perform statistical analysis on M2M communication channels looking from a different perspective. This need motivated us to perform the research outlined in this thesis. In reviewing the literature we found that though in general the M2M channel models are sparse, a major gap exists in the non geometrical stochastic based mathematical channel models. In filling this gap, we develop a novel mathematical non geometrical stochastic multiple input multiple output (MIMO) M2M channel model for two dimensional (2D) and three dimensional (3D) scattering environments. This model is based on the underlying physics of free space wave propagation and can be used as a framework for any environment by selecting suitable complex scattering gain functions. In addition, we extend this novel model to multicarrier M2M which is the first multicarrier channel model in the non geometrical stochastic M2M category. Based on our novel M2M channel model, we carry out an extensive analysis in space-time correlation, space-frequency correlation and second order channel statistics. With the choice of suitable parameters, this analysis and channel model can be used for any wireless environment. Thus, we claim that our novel channel model together with the analysis performed in this thesis can be taken as a generalized framework. A significant contribution of our analysis is the consideration of the impact of transmitter and receiver speed to space-time and space-frequency correlation, which is not available in the literature. Using a von Mises-Fisher distribution as the angular power distribution, the usefulness of the derived temporal correlation function is discussed. The simulation results corroborate the fact that both space-time and space-frequency correlations are reduced when transmitter or receiver speed increases. The rate of reduction of space-time correlation in von Mises-Fisher distribution scattering environment is more than in the isotropic environment. Under second order channel statistics, we consider Rice, Rayleigh and Nakagami fading channels in four different non-isotropic scattering environments with angle of departure (AoD) and angle of arrival (AoA) distributions given by (i) separable Truncated Gaussian, (ii) separable von-Mises, (iii) truncated Gaussian bivariate and (iv) truncated Laplacian bivariate distributions. We show that the major second order statistics, namely, the level crossing rate (LCR) and the average fade duration (AFD), in different fading channels can be expressed in terms of known scattering coefficients of the AoD and AoA distributions. As the channel models and their respective measurements provide reliable knowledge of the channel for the design and analysis of M2M systems, the proposed channel model and the corresponding analysis will be useful for the design, testing and performance evaluation of future M2M communication systems