Mobile Ad hoc Networks (MANETs) are wireless networks, which consist of a collection of mobile nodes with no fixed infrastructure, where each node acts as a router that participates in forwarding data packets. They are a new paradigm of wireless communications for mobile hosts that are resource-constrained with only limited energy, computing power and memory. Previous studies on MANETs concentrated more on energy conservation in an idealistic environment without taking into consideration, the effects of realistic mobility, interference and fading. The definition of realistic mobility models is one of the most critical and, at the same time, difficult aspects of the simulations of networks designed for real mobile ad hoc environments. The reason for this is that most scenarios for which ad hoc networks are used have features such as dynamicity and extreme uncertainties. Thus use of real life measurements is currently almost impossible and most certainly expensive. Hence the commonly used alternative is to simulate the movement patterns and hence the reproduction of movement traces quite similar to human mobility behavior is extremely important. The synthetic models used for movement pattern generation should reflect the movement of the real mobile devices, which are usually carried by humans, so the movement of such devices is necessarily based on human decisions. Regularity is an important characteristic of human movement patterns. All simulated movement models are suspect because there is no means of accessing to what extent they map reality. However it is not difficult to see that random mobility models such as Random Walk, Random Waypoint (default model used in almost all network simulations), etc., generate movements that are most non-humanlike. Hence we need to focus on more realistic mobility models such as Gauss Markov, Manhattan Grid, Reference Point Group Mobility Model (RPGM), Column, Pursue and other Hybrid mobility models. These models capture certain mobility characteristics that emulate the realistic MANETs movement, such as temporal dependency, spatial dependency and geographic restriction. Also a Rayleigh/Ricean fading channel is introduced to obtain a realistic fading environment. The energy consumed by the data, MAC, ARP and RTR packets using IEEE 802.11 MAC protocol with the various mobility models in fading and non-fading channel conditions are obtained using ns-2 simulations and AWK programs. The realistic movement patterns are generated using three different mobility generators BonnMotion Mobility Generator, Toilers Code and Scengen Mobility Generator. This thesis work performs an in-depth study on th eeffects of realistic mobility and fading on energy consumption, packet delivery ratio and control overhead of MANETs.

High data rate applications are the trend in today's wireless technology. W-CDMA standard was designed to support such high data rates of up to 3.84 Mcps. The main purpose of this research was to analyze the feasibility of a fixed-point implementation of the W-CDMA downlink receiver algorithm on a general-purpose digital signal processor (StarCore SC140 by Motorola). The very large instruction word architecture of SC140 core is utilized to generate optimal implementation, to meet the real time timing requirements of the algorithm. The other main aim of this work was to study and evaluate the performance of the W-CDMA downlink structure with incorporated space-time transmit diversity. The effect of the channel estimation algorithm used was extensively studied too.

In this thesis, we address the statistics of mutual information of amplify-and-forward (AF) multiple-input multiple-output (MIMO) two-hop relay channels, where the source terminal (ST), relay terminal (RT) and destination terminal (DT) are equipped with a number of correlated antennas and there is a line-of-sight (LOS) component (Rician fading) of each link. To the best of our knowledge, deriving analytical expressions for the statistics of mutual information of the relay channel is difficult and still unsolvable. To circumvent the mathematical difficulties, we consider this problem under the large-system regimen in which the numbers of antennas at the transmitter and receiver go to infinity with a fixed ratio. In the large-system regimen, this thesis has made the following contributions: 1) We get the mean and the variance of the mutual information of the concerned relay channel. 2) We show that the mutual information distribution converges to the Gaussian distribution. The analytical results are derived by mean of two powerful tools developed in the context of theoretical physics: emph{saddle-point approximation} and emph{superanalysis}. The derived analytical results are very general and can degenerate to several previously results as special cases. From a degenerated case, we realize that the previous result by Wagner {em et al.} cite{Wag-08} is wrong and thus we provide the corrected result. Finally, Simulation results demonstrate that even for a moderate number of antennas at each end, the proposed analytical results provide undistinguishable results as those obtained by Monte-Carlo results.

Adaptive modulation and diversity combining represent very important adaptive solutions for future generations of wireless communication systems. Indeed, to improve the performance and the efficiency of these systems, these two techniques recently have been used jointly in new schemes named joint adaptive modulation and diversity combining (JAMDC) schemes. Considering the problem of finding lowcomplexity, bandwidth-efficient, and processing-power efficient transmission schemes for a downlink scenario and capitalizing on some of these recently proposed JAMDC schemes, we propose and analyze three fully joint adaptive modulation, diversity combining, and power control (FJAMDC) schemes. More specifically, the modulation constellation size, the number of combined diversity paths, and the needed power level are determined jointly to achieve the highest spectral efficiency with the lowest possible combining complexity, given the fading channel conditions and the required bit error rate (BER) performance. The performance of these three FJAMDC schemes is analyzed in terms of their spectral efficiency, processing power consumption, and error-rate performance. Selected numerical examples show that these schemes considerably increase the spectral efficiency of the existing JAMDC schemes with a slight increase in the average number of combined paths for the low signal to noise ratio range while maintaining compliance with the BER performance and a low radiated power resulting in a substantial decrease in interference to co-existing systems/users.

To achieve cooperative diversity in cognitive radio network, Decode and Forward (DF) protocol is implemented at Cognitive Radios (CRs) using Orthogonal Space Time Block Coding (OSTBC). The 2-hop communication between source and destination is completed with the help of Cognitive Relays (CRs) using Multiple Input Multiple Output (MIMO) technology within the network. To achieve spatial diversity and good code rate Alamouti 2×2 STBC is used for transmission. CR is using the decoding (Decode and Forward (DF)) strategy and without amplifying ability before forwarding data towards destination provide better performance. The main objective of this thesis is to detect Primary User (PU) spectrum availability or non-availability for the use of Secondary Users (SU). The Alamouti STBC encoded data is broadcasted to wireless Rayleigh faded channel through transmitter having two transmitting antennas. The CRs are preferred to place close with PU to detect transmitted signal and because of having decoding capability CRs decode the collected data using Maximum Likelihood (ML) decoding technique then re-encode the decoded data for further transmission towards receiver. The energy of PU signal received at relays is calculated using energy detector used at cognitive controller having authority to make final decision about presence or absence of PU signal within the spectrum by comparing calculated energy of PU received signal with a predefined value. If the calculated signal energy is less than threshold value it is pretended as the absence of PU and in the other case spectrum is assumed as occupied by PU. Decoding PU signal at relays before forwarding towards destination provide better performance in terms of detection probability and decreasing probability of false alarming as the Signal to Noise (SNR) increases. The proposed cooperative spectrum sensing using DF protocol at cognitive relays with Alamouti STBC is implemented and results are validated by MATLAB simulation. / +46 455 38 50 00

In this report, we introduce cooperative spectrum sensing using orthogonal space time block coding (OSTBC) in order to achieve cooperative diversity in the cognitive radios (CRs) network. Transmit diversity or gain is achieved by introducing more than one antenna on the transmitter and receiver side, but in small electronic mobile devices it looks impractical. The signals received from the primary users (PUs) are amplified by the cognitive relays and further forwarded to the cognitive controller where decisions are made on the basis of the information collected from each cognitive relay. The cooperative relaying protocol used here in cognitive relays is based on an amplifying-forward (AF) scheme. Alamouti scheme in OSTBC has been proposed to achieve better detection performance in CR network. The energy detector performance is analyzed over an independent Rayleigh fading channel. In CR network the secondary user (SU) shares PU's frequency band if it fi nds PU is not in its vicinity. The SU starts using the licensed band and leaves the band as soon as it finds the PU is present or going to use the same band. The detection of the spectrum holes by CRs has to be more agile and intelligent. The main objective of the CRs network is to use the free holes without causing any interference to the PUs. The energy detection technique is simple and outperforms other sensing techniques in cooperative cognitive radio networks. The energy detector collects information from different users, compares it with a certain prede fined threshold () value and then makes a fi nal decision. Detection and false alarm probabilities are derived and manipulated using OSTBC on PU and SU through AF protocol in cooperative communication. The performance of the system is analyzed with single and multiple relays and with and without direct path between the PUs and SUs. Maximum ratio (MRC) and selection combining (SC) schemes are used in energy detector and the results are compared with and without direct link between PU and SU. The analysis is performed by placing the relay close to the PUs. Our results are processed and validated by computer simulation.

In wireless Communication, the need of radio spectrum increases nowadays. But in the system we are losing approximately 82-86% of spectrum most of the time due to the absence of Primary User (PU). To overcome this issue Cognitive Radio (CR) is an admirable approach. The concept of cooperative communication needs to be considering because high data rate is the demand for wireless services. Cooperative diversity in the network realized by 3-hop Decode, Amplify and Forward (DAF) and Decode and Forward (DF) and in 2-hop DF and Amplify and Forward (AF) Protocols implemented in cognitive radio communication network using Orthogonal Space Time Block Coding (OSTBC). The communication between end points is accomplished by using Multiple Input and Multiple Output (MIMO) antenna arrangement. During the Propagation, Alamouti Space Time Block Coding is used to accomplish spatial diversity and the encoded data is transmitted through Rayleigh fading channel. CR decodes the transmitted signal using Maximum Likelihood (ML) decoding method. Afterward signal broadcast toward the destination. To check the energy level of signal, energy detection technique applies at the Cognitive Controller (CC). Finally, CC will take ultimate decision for the presence of primary user if the energy level of signal is greater than predefined threshold level, it means PU is present otherwise it is absent. The main objective of this thesis is to analyze the performance of 3-hop and 2-hop communication network using relays. The performance is compared on the bases of two parameters i.e. Bit Error Rate (BER) and Probability of Detection (PD). The results are processed and validated by MATLAB simulation.

High data rate applications are the trend in today's wireless technology. W-CDMA standard was designed to support such high data rates of up to 3.84 Mcps. The main purpose of this research was to analyze the feasibility of a fixed-point implementation of the W-CDMA downlink receiver algorithm on a general-purpose digital signal processor (StarCore SC140 by Motorola). The very large instruction word architecture of SC140 core is utilized to generate optimal implementation, to meet the real time timing requirements of the algorithm. The other main aim of this work was to study and evaluate the performance of the W-CDMA downlink structure with incorporated space-time transmit diversity. The effect of the channel estimation algorithm used was extensively studied too.

In this work wireless communication systems with multiple co-channel signals present at the receiver are considered. One of the major challenges in the development of such systems is the computational complexity required for the detection of the transmitted signals. This thesis addresses this problem and develops reduced complexity algorithms for the detection of multiple co-channel signals in receivers with multiple antennas. The signals are transmitted from either a single user employing multiple transmit antennas, from multiple users or in the most general case by a mixture of the two. The receiver is assumed to be overloaded in that the number of transmitted signals exceeds the number of receive antennas. Joint Maximum Likelihood (JML) is the optimum detection algorithm which has exponential complexity in the number of signals. As a result, detection of the signals of interest at the receiver is challenging and infeasible in most practical systems. The thesis presents a framework for the detection of multiple co-channel signals in overloaded receivers. It proposes receiver structures and two list-based signal detection algorithms that allow for complexity reduction compared to the optimum detector while being able to maintain near optimum performance. Complexity savings are achieved by first employing a linear preprocessor at the receiver to reduce the effect of Co-Channel Interference (CCI) and second, by using a detection algorithm that searches only over a subspace of the transmitted symbols. Both algorithms use iterative processing to extract ordered lists of the most likely transmit symbols. Soft information can be obtained from the detector output list and can then be used by error control decoders. The first algorithm named Parallel Detection with Interference Estimation (PD-IE) considers the Additive White Gaussian Noise (AWGN) channel. It relies on a spatially reduced search over subsets of the transmitted symbols in combination with CCI estimation. Computational complexity under overload is lower than that of JML. Performance results show that PD-IE achieves near optimum performance in receivers with Uniform Circular Array (UCA) and Uniform Linear Array (ULA) antenna geometries. The second algorithm is referred to as List Group Search (LGS) detection. It is applied to overloaded receivers that operate in frequency-flat multipath fading channels. The List Group Search (LGS) detection algorithm forms multiple groups of the transmitted symbols over which an exhaustive search is performed. Simulation results show that LGS detection provides good complexity-performance tradeoffs under overload. A union bound for group-wise and list-based group-wise symbol detectors is also derived. It provides an approximation to the error performance of such detectors without the need for simulation. Moreover, the bound can be used to determine some detection parameters and tradeoffs. Results show that the bound is tight in the high Signal to Interference and Noise Ratio (SINR) region.

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