Performance analysis of diversity techniques in wireless communication systems: Cooperative systems with CCI and MIMO-OFDM systems

This Dissertation analyzes the performance of ecient digital commu- nication systems, the performance analysis includes the bit error rate (BER) of dier- ent binary and M-ary modulation schemes, and the average channel capacity (ACC) under dierent adaptive transmission protocols, namely, the simultaneous power and rate adaptation protocol (OPRA), the optimal rate with xed power protocol (ORA), the channel inversion with xed rate protocol (CIFR), and the truncated channel in- version with xed transmit power protocol (CTIFR). In this dissertation, BER and ACC performance of interference-limited dual-hop decode-and-forward (DF) relay- ing cooperative systems with co-channel interference (CCI) at both the relay and destination nodes is analyzed in small-scale multipath Nakagami-m fading channels with arbitrary (integer as well as non-integer) values of m. This channel condition is assumed for both the desired signal as well as co-channel interfering signals. In addition, the practical case of unequal average fading powers between the two hops is assumed in the analysis. The analysis assumes an arbitrary number of indepen- dent and non-identically distributed (i.n.i.d.) interfering signals at both relay (R) and destination (D) nodes. Also, the work extended to the case when the receiver employs the maximum ratio combining (MRC) and the equal gain combining (EGC) schemes to exploit the diversity gain

NLOS mitigation techniques in GNSS receivers based on Level Crossing Rates (LCR) of correlation outputs

Global Navigation Satellite Systems (GNSS) provide navigation services with a highly precise estimation of the position. First military influenced, the use of satellite-based positioning has gained a lot of interest also in civilian tasks nowadays. Because the GNSS performance has been improved over the years, the state-of-the-art GNSS navigation does include indoor positioning and moving autonomously with help of GNSS. The accuracy, which essentially has to be high, can be disturbed by multipath (e.g. diffraction, reflection, refraction or scattering). A possibility to detect multipath, and possibly to avoid those signals in the position solution, is totally necessary. A non-direct signal, namely Non-Light-of-Sight (NLOS), can lead to low accuracy of the positioning. Therefore, this thesis is dealing with the NLOS detection by using the Level Crossing Rate (LCR), which has been used in electronic communication such as Wifi. The thesis is divided in two parts, including a literature review part, following by a simulation of the developed detection technique. All basic knowledge about this work can be extracted from the literature part. In the simulation section, several tests will be provided, done by Matlab simulations. To perform a realistic GNSS signal, a dynamic Galileo Composite Binary Offset Carrier (CBOC) signal was produced

Design and analysis of wireless diversity system

Ph.DDOCTOR OF PHILOSOPH

Multicarrier Frequency Hopping Spread Spectrum Techniques With Quasi-Cyclic Low Density Parity Check Codes Channel Coding

This work presents a new proposed Multicarrier Frequency Hopping Spread Spectrum (MCFH-SS) system employing Quasi-Cyclic Low Density Parity Check (QC-LDPC) codes instead of the conventional LDPC codes. A new technique for constructing the QC-LDPC codes based on row division method is proposed. The new codes offer more flexibility in terms of high girth, multiple code rates and block length. Moreover, a new scheme for channel prediction in MCFH-SS system is proposed. The technique adaptively estimates the channel conditions and eliminates the need for the system to transmit a request message prior to transmitting the packet data. The ready-to-use channel will be occupied with a Pseudonoise (PN) code and use for transmission or else, it will be banned

Error rate performance metrics for digital communications systems.

In this thesis, novel error rate performance metrics and transmission solutions are investigated for delay limited communication systems and for co-channel interference scenarios. The following four research problems in particular were considered. The first research problem is devoted to analysis of the higher order ergodic moments of error rates for digital communication systems with time- unlimited ergodic transmissions and the statistics of the conditional error rates of digital modulations over fading channels are considered. The probability density function and the higher order moments of the conditional error rates are obtained. Non-monotonic behavior of the moments of the conditional bit error rates versus some channel model parameters is observed for a Ricean distributed channel fading amplitude at the detector input. Properties and possible applications of the second central moments are proposed. The second research problem is the non-ergodic error rate analysis and signaling design for communication systems processing a single finite length received sequence. A framework to analyze the error rate properties of non-ergodic transmissions is established. The Bayesian credible intervals are used to estimate the instantaneous bit error rate. A novel degree of ergodicity measure is introduced using the credible interval estimates to quantify the level of ergodicity of the received sequence with respect to the instantaneous bit error rate and to describe the transition of the data detector from the non-ergodic to ergodic zone of operation. The developed non-ergodic analysis is used to define adaptive forward error correction control and adaptive power control policies that can guarantee, with a given probability, the worst case instantaneous bit error rate performance of the detector in its transition fi'om the non-ergodic to ergodic zone of operation. In the third research problem, novel retransmission schemes are developed for delay-limited retransmissions. The proposed scheme relies on a reliable reverse link for the error-free feedback message delivery. Unlike the conventional automatic repeat request schemes, the proposed scheme does not require the use of cyclic redundancy check bits for error detection. In the proposed scheme, random permutations are exploited to locate the bits for retransmission in the predefined window within the packet. The retransmitted bits are combined using the maximal-ratio combining. The complexity-performance trade-offs of the proposed scheme is investigated by mathematical analysis as well as computer simulations. The bit error rate of the proposed scheme is independent of the packet length while the throughput is dependent on the packet length. Three practical techniques suitable for implementation are proposed. The performance of the proposed retransmission scheme was compared to the block repetition code corresponding to a conventional ARQ retransmission strategy. It was shown that, for the same number of retransmissions, and the same packet length, the proposed scheme always outperforms such repetition coding, and, in some scenarios, the performance improvement is found to be significant. Most of our analysis has been done for the case of AWGN channel, however, the case of a slow Rayleigh block fading channel was also investigated. The proposed scheme appears to provide the throughput and the BER reduction gains only for the medium to large SNR values. Finally, the last research problem investigates the link error rate performance with a single co-channel interference. A novel metric to assess whether the standard Gaussian approximation of a single interferer underestimates or overestimates the link bit error rate is derived. This metric is a function of the interference channel fading statistics. However, it is otherwise independent of the statistics of the desired signal. The key step in derivation of the proposed metric is to construct the standard Gaussian approximation of the interference by a non-linear transformation. A closed form expression of the metric is obtained for a Nakagami distributed interference fading amplitude. Numerical results for the case of Nakagami and lognormal distributed interference fading amplitude confirm the validity of the proposed metric. The higher moments, interval estimators and non-linear transformations were investigated to evaluate the error rate performance for different wireless communication scenarios. The synchronization channel is also used jointly with the communication link to form a transmission diversity and subsequently, to improve the error rate performance

Enhancing the bit error rate performance of ultra wideband systems using time-hopping pulse position modulation in multiple access environments

Ultra-Wide Band (UWB) technology is one of the possible solutions for future short-range indoor data communication with uniquely attractive features inviting major advances in wireless communications, networking, radar, imaging, and positioning systems. A major challenge when designing UWB systems is choosing a suitable modulation technique. Data rate, transceiver complexity, and BER performance of the transmitted signal are all related to the employed modulation scheme. Several classical modulation schemes can be used to create UWB signals, some are more efficient than others. These schemes are namely, Pulse Position Modulation (PPM), Pulse Amplitude Modulation (PAM), Binary Phase Shift Keying (BPSK), and On-Off Keying (OOK) are reviewed. In the thesis, the performance of PPM system, combined with Time Hopping Spread Spectrum (THSS) multiple access technique is evaluated in an asynchronous multiple access free space environment. The multiple access interference is first assumed to be a zero mean Gaussian random process to simulate the scenario of a multi user environment. An exact BER calculation is then evaluated based on the characteristic function (CF) method, for Time Hopping-Pulse Position Modulation Ultra Wide Band (TH-PPM UWB) systems with multiple access interference (MAI) in AWGN environment. The resulting analytical expression is then used to assess the accuracy of the MAI Gaussian Approximation (GA) first assumed. The GA is shown to be inaccurate for predicting BERs for medium and large signal-to-noise ratio (SNR) values. Furthermore, the analysis of TH-PPM system is further extended to evaluate the influence of changing and optimising some of the system or signal parameters. It can be shown how the system is greatly sensitive to variations in some signal parameters, like the pulse shape, the time-shift parameter associated with PPM, and the pulse length. In addition, the system performance can be greatly improved by optimising other system parameters like the number of pulses per bit, Ns, and the number of time slots per frame, Nh. All these evaluation are addressed through numerical examples. Then, we can say that, by improving signal or system parameters, the BER performance of the system is greatly enhanced. This is achieved without imposing exact complexity to the transceiver and with moderate computational calculations

High capacity multiuser multiantenna communication techniques

One of the main issues involved in the development of future wireless communication systems is the multiple access technique used to efficiently share the available spectrum among users. In rich multipath environment, spatial dimension can be exploited to meet the increasing number of users and their demands without consuming extra bandwidth and power. Therefore, it is utilized in the multiple-input multiple-output (MIMO) technology to increase the spectral efficiency significantly. However, multiuser MIMO (MU-MIMO) systems are still challenging to be widely adopted in next generation standards. In this thesis, new techniques are proposed to increase the channel and user capacity and improve the error performance of MU-MIMO over Rayleigh fading channel environment. For realistic system design and performance evaluation, channel correlation is considered as one of the main channel impurities due its severe influence on capacity and reliability. Two simple methods called generalized successive coloring technique (GSCT) and generalized iterative coloring technique (GICT) are proposed for accurate generation of correlated Rayleigh fading channels (CRFC). They are designed to overcome the shortcomings of existing methods by avoiding factorization of desired covariance matrix of the Gaussian samples. The superiority of these techniques is demonstrated by extensive simulations of different practical system scenarios. To mitigate the effects of channel correlations, a novel constellation constrained MU-MIMO (CC-MU-MIMO) scheme is proposed using transmit signal design and maximum likelihood joint detection (MLJD) at the receiver. It is designed to maximize the channel capacity and error performance based on principles of maximizing the minimum Euclidean distance (dmin) of composite received signals. Two signal design methods named as unequal power allocation (UPA) and rotation constellation (RC) are utilized to resolve the detection ambiguity caused by correlation. Extensive analysis and simulations demonstrate the effectiveness of considered scheme compared with conventional MU-MIMO. Furthermore, significant gain in SNR is achieved particularly in moderate to high correlations which have direct impact to maintain high user capacity. A new efficient receive antenna selection (RAS) technique referred to as phase difference based selection (PDBS) is proposed for single and multiuser MIMO systems to maximize the capacity over CRFC. It utilizes the received signal constellation to select the subset of antennas with highest (dmin) constellations due to its direct impact on the capacity and BER performance. A low complexity algorithm is designed by employing the Euclidean norm of channel matrix rows with their corresponding phase differences. Capacity analysis and simulation results show that PDBS outperforms norm based selection (NBS) and near to optimal selection (OS) for all correlation and SNR values. This technique provides fast RAS to capture most of the gains promised by multiantenna systems over different channel conditions. Finally, novel group layered MU-MIMO (GL-MU-MIMO) scheme is introduced to exploit the available spectrum for higher user capacity with affordable complexity. It takes the advantages of spatial difference among users and power control at base station to increase the number of users beyond the available number of RF chains. It is achieved by dividing the users into two groups according to their received power, high power group (HPG) and low power group (LPG). Different configurations of low complexity group layered multiuser detection (GL-MUD) and group power allocation ratio (η) are utilized to provide a valuable tradeoff between complexity and overall system performance. Furthermore, RAS diversity is incorporated by using NBS and a new selection algorithm called HPG-PDBS to increase the channel capacity and enhance the error performance. Extensive analysis and simulations demonstrate the superiority of proposed scheme compared with conventional MU-MIMO. By using appropriate value of (η), it shows higher sum rate capacity and substantial increase in the user capacity up to two-fold at target BER and SNR values

Primena tehnika kombinovanja kod bežičnih telekomunikacionih sistema u prisustvu smetnje

Research results shown in this thesis consider selection combining space diversity systems. Weibull fading model is used to describe a desired signal and interference in a wireless telecommunication channel. In an interference-limited environment, like a cellular communication system, the level of cochannel interference is sufficiently high compared to noise so that it can be neglected. In that case, a selection combining receiver can employ different combining algorithms, that can be used to forward the chosen signal to the output of the receiver. After the theoretical basis, which is given at the beginning of the thesis, a detailed analysis of space diversity systems that use different selection algorithms is presented. The system performance is analyzed using one of the proposed criteria: maximal signal-tointerference ratio, maximal desired signal, maximal total signal, and minimal interference. For a system employing each of these algorithms, a detailed analysis of statistical characteristics of first and second order is given using the expressions derived in this thesis. The first focus is on deriving the expressions for probability density function of instantaneous signal-to-interference ratio at the output of selection combining receiver employing each of the previously mentioned algorithms. Based on the derived expressions, numerical results are presented for statistical characteristics of the first order, namely outage probability, average bit error probability, average signal-to-interference ratio and channel capacity. Additionally, for the statistical characteristics of the second order, which are level crossing rate and average fade duration, expressions for joint probability density function of instantaneous signal-tointerference ratio and its time derivative are derived. A new mathematical approach for obtaining analytical expression for probability density function of instantaneous signal-to-interference ratio at the output of selection combining receiver with two branches that uses maximal signal-to-noise ratio algorithm is presented. Considering that mobile terminals are relatively small, the distance between receiving antennas is not large enough to be neglected. Therefore, the correlation between the branches is included in the analysis of statistical characteristics of the first order. Due to easier mathematical manipulation, statistical characteristics of second order do not consider correlation between receiving branches. Numerical results obtained using the expressions derived in this thesis for different decision algorithms are presented graphically. The illustrations show the influence of fading severity, correlation between the desired signals, as well as the interfering ones and balanced and unbalanced inputs for each of mentioned algorithms on outage probability, average bit error probability, average signal-to-interference ratio and channel capacity. The results for second order statistics for dual branch selection diversity system operating in Weibull fading environment were compared for a system that employs two selection algorithms, algorithm based on maximal signal-to-interference ratio, as most frequently used one, and algorithm based on minimal interference, the algorithm that was not exploited in literature. The main contribution of this thesis lies in obtained results for statistical characteristics and performance of the system that uses four proposed algorithms at receiver side. The presented analysis of selection diversity system for given channel conditions can be applied to achieve optimized solutions of wireless system design