We analyze the performance of dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay systems by considering the source-to-relay and relay-to-destination channels undergo Rayleigh and Rician fading, respectively. Several MIMO techniques and practical relaying scenarios are considered to investigate the effect of such asymmetric fading on the MIMO AF relaying systems. First, we investigate the performance of the optimal single stream beamforming on non-coherent AF MIMO relaying. We use tools of finite-dimensional random matrix theory to statistically characterize the instantaneous signal-to-noise ratio (SNR). The closed-form expressions of the cumulative distribution function, probability density function, and moments of SNR are derived and used to analyze the performance of the system with outage probability, bit error rate (BER), and ergodic capacity. Numerical simulations are carried out to investigate the effects of the Rician factor, rank of the line-of-sight (LoS) component, and the number of antennas at the nodes on the system performance. Additionally, the performance is compared with orthogonal space-time block-coding (OSTBC) based AF MIMO system. Next, we investigate relay selection schemes for non-coherent dual-hop AF relaying with OSTBC over asymmetric fading channels. We propose two relay selection methods as optimal and sub-optimal schemes. The performance of proposed schemes are discussed with respect to the outage probability, BER and the ergodic capacity. Finally, we study the effect of co-channel interference (CCI) and feedback delay on the multi-antenna AF relaying over asymmetric fading channels. Here, transmit beamforming vector is calculated using outdated channel state information due to the feedback delay from relay-to-source, and the relay node experience CCI due to frequency reuse in the cellular network. The performance is investigated using the outage probability, BER and ergodic capacity to analyze the effect of the Rician factor, CCI, feedback delay and number of antennas. All these discussions are useful to evaluate the performance of AF MIMO systems in asymmetric fading channels. Our analysis suggests that having good LoS component increases the performance of the system for multiple-input-single-output (MISO) and single-input-multiple-output (SIMO) scenarios of relay-destination channel. Having good scattering component increases the performance for MIMO cases.

Wireless sensor networks (WSNs) are gaining popularity in different areas of applications like industrial monitoring, military applications, home automation, smart grid applications, body organ monitoring, etc. A WSN is a wireless network comprising of a number of devices, called sensor nodes. A sensor node, usually battery powered, is capable of detecting physical phenomena, such as light, temperature, movement, noise, pressure, humidity, etc. Medium access control (MAC) protocols are in a key role for determining the energy efficiency of a WSN, which is a key design issue for battery operated sensor nodes. Alongside energy efficiency, reliable transmission is also always preferred in communication networks. The IEEE 802.15.4 standard provides low power solutions to the WSN applications by specifying physical and MAC layer functions for low rate wireless personal area networks. In this thesis, Markov chain models are derived to study the throughput and the energy consumption of IEEE 802.15.4 MAC taking into account the packet corruption by both collisions and channel errors. An increase in reliability reduces retransmissions of erroneous packets, which in turn reduces the energy consumption. Therefore, a network with low energy consumption and high reliability is always desired. Wireless radio channel is the medium used for the transmissions in WSNs and it is error prone leading to received data corruption. To mitigate this influence of channel to some extent, forward error correction (FEC) may be employed. FEC provides error correction with the addition of redundant bits to the original message. Various FEC codes are analysed to study the influence of coding on the performance of the IEEE 802.15.4 type networks. Along with the FEC, influence of data frame payload size on performance is also studied. Numerical analyses are carried out and illustrated using Matlab. The results show that the performance of an IEEE 802.15.4 type network can be improved using an appropriate choice of payload size and FEC.

Coordinated Multipoint (CoMP) transmission has been identified as a promising concept to handle the substantial interference in the LTE-Advanced systems and it is one of the key technology components in the future 5G networks. CoMP transmission involves two coordination schemes: joint processing (JP) and coordinated beamforming (CB). The scope of this thesis is limited to JP. In the CoMP JP scheme, each user is coherently served by multiple base stations (BSs) and consequently, the user’s signal strength is enhanced and the interference is mitigated. The coherent joint processing requires sharing data and channel state information (CSI) of all the users among all the BSs, which leads to high backhaul capacity requirement and high signaling cost especially in large-scale networks. Grouping the BSs into smaller coordination clusters within which a user is served by only the BSs in the cluster will significantly reduce the signaling cost and the backhaul burden. In this thesis, optimal BS clustering and beamformer design for CoMP JP in the downlink of a multi-cell network is studied. The unique aspect of the study is that the BS clustering and the beamformer design are carried out jointly by iteratively solving a series of convex sub-problems. The BSs are dynamically grouped into small coordination clusters whereby each user is served by a few BSs that are in a coordination cluster. The joint BS clustering and beamformer design is performed to maximize a network utility function in the form of the weighted sum rate maximization (WSRM). The weighted sum rate maximization (WSRM) problem is formulated from the perspective of sparse optimization framework where sparsity is induced by penalizing the objective function with a power penalty. The WSRM problem is known to be non-convex and NP-hard. Therefore, it is difficult to solve directly. Two solutions are studied; in the first approach, the WSRM problem is solved via weighted minimum mean square error (WMMSE) minimization and the second approach involves approximation of the WSRM problem as a successive second order cone program (SSOCP). In both approaches, the objective function is penalized with a power penalty and the clusters can be adjusted by a single parameter in the problem. The performance evaluation of the proposed algorithms is carried out via simulation and it is shown that the serving sets in the network can be controlled according to the available backhaul capacity by properly selecting a single parameter in the problem. Finally, an algorithm for a fixed number of active links is proposed.

Human Body Communication (HBC) is a novel communication method between devices which use human body as a transmission medium. This idea is mostly based on the concept of wireless biomedical monitoring system. The on-body sensor nodes can monitor vital signs of a human body and use the body as a transmission medium. This technology is convenient for long durations of clinical monitoring with the option of more mobility and freedom for the user. In this thesis, IEEE 802.15.6-2012 physical (PHY) layer for the HBC was simulated. Simulation model is following the standard’s requirements and processes. The human body was taken as a transmission medium and simulations, which follow the HBC standard, have been carried out. For the purpose of simulations, MATLAB is used as a platform to test and run the simulations. The constants and variables used in the simulations are taken from the IEEE 802.15 working group for wireless personal area networks (WPANs). The transmitter model and the receiver model have been taken from the standard, with changes done in it for performing the simulations on the PHY layer only. The simulations were done keeping in mind the dielectric properties of the outer layer of a human body, i.e., the dielectric values for human skin are noted and their corresponding values were used in the mathematical calculations. The work done here presents a transmitter and receiver architecture for the human body communication. The minimum data rate being 164 kbps and the transmitter being designed around the 21 MHz center frequency has achieved some outputs which are worth looking. The channel models used in this simulator are HBC channel and AWGN (additive white Gaussian noise) channel. It was observed that when signal was passed through AWGN channel, noise was added uniformly over the signal, while in the HBC channel signal strength is directly proportional to the transceiver ground sizes. In conclusion, the size of the ground terminals plays a critical role for the signal quality in the HBC simulator. The results in this thesis show that pathloss has certain linearity with the distance. The pathloss is calculated for different parts of the body with higher loss for structure with higher amount of bone, and vice versa. It is observed that in the HBC channel there are four factors with high impact on the system. These are the distances between the transceiver in air and on body while the other two are the sizes of the transceiver grounds. The size of the transmitter ground has been deemed very significant for the HBC from the simulations results. The four factors show high impact on the HBC channel. The signal strength is highly effected with the change in these four characteristics. From the simulation results it is evident that the HBC channel show a 15 to 20 dB deviation when compared to AWGN channel. The Eb⁄N0 for BER level at 10^(-3) for AWGN channel is 10 to 11 dB while for HBC it is around 27 dB showing a significant difference in the results.

In wireless communication systems, there is a need to design efficient schemes in order to overcome the problem of spectrum scarcity. One technology to address the problem of spectrum scarcity is cognitive radio (CR), in which a network entity is able to adapt intelligently to the environment through observation, exploration and learning. When multiple autonomous cognitive radios are searching for spectrum opportunities, they face competition from each other in order to access the available free channel. This will result in reduced throughput which occurs due to collision between cognitive radios, when they try to transmit in the same channel. The purpose of this thesis is to study a smart adaptation scheme for efficient channel access which enable autonomous cognitive radios to improve their overall bandwidth efficiency in a distributed cognitive radio network with the help of spatial reuse. An adaptive persistent strategy with efficient collision detection has been studied in this work for autonomous channel sensing order selection which enable distributed CRs to avoid collision and allow them to improve their overall system efficiency by increasing the average number of successful transmissions, especially, when number of available channels are less than the number of CRs competing to access these free channels. The performance of the studied strategy is compared with random selection of sensing orders. Simulation results are presented, which indicate that the studied strategy with spatial reuse achieves the highest number of successful transmissions in a given time slot as compared to other strategies. Simulation results are also compared for the case with no spatial reuse and the results indicate that it degrades the system efficiency by reducing the average number of successful transmissions in a given time slot.

The benefits of MIMO technology have made it a solution for the present and future wireless networking demands. Increasing the number of antennas is an intuitive approach for boosting the network capacity; however, processing load and implementation limitations put a practical bound on this goal. Recently a solution known as massive MIMO has shown that a very large antenna array at the base station can simplify the processing, in a way that even matched filter (MF) can be used for detection purpose. The ultimate performance of massive MIMO can be achieved only under some optimistic assumptions about the channel and hardware deployment. In practice, there are some restrictions that do not allow the ultimate performance for a massive MIMO system. Under some realistic assumptions, an efficient use of all the resources becomes important in a way that the application of simple algorithms like MF and zero forcing (ZF) becomes questionable. Thus, in this thesis work, more efficient approach based on optimal minimum power beamforming is considered as the benchmark. The idea is to investigate the behavior of this algorithm and the performance differences with respect to some sub-optimal methods when the system dimensions grow large. Two solutions for the minimum power beamforming are reviewed (SOCP and uplink-downlink duality). The solution that is on focus is based on the second order cone programming (SOCP). Intercell interference(ICI) plays a critical role in the SOCP algorithm as it couples the sub-problems at the base stations. Thus, a large dimension approximation for the optimal ICI, using random matrix theory tools, is derived which tackles both of the processing simplification and the backhaul exchange rate reduction goals. This approximation allows derivation of an approximated optimal intercell interference based on the channel statistics that results a procedure for decoupling the subproblems at base stations. The comparison between the SOCP algorithm and the sub-optimal methods is carried out via simulation. The results show that the performance gap with respect to the sub-optimal methods grows when correlation between the antenna elements at the BS side increase. In a network simulation with 7 cell and 28 users, this gap remains significant even with 100 antennas at the BS side. These performance differences justify the application of more complex algorithms like SOCP for a MIMO system with a large antenna array when the practical restrictions are taken into account.

The future demand of increased transmission rate and bandwidth efficiency is of prime concern in the modern wireless communication systems. Faster than Nyquist signaling (FTN) is under the great interest of research to address this issue of high data rate, which is also a major requirement, for the fifth generation (5G) communication networks. The data bits are transmitted at a rate higher than the conventional methods which are bounded by the Nyquist condition and the outputs are compared so as to analyze the benefits. Receiver processing techniques are implemented to achieve the high data rate with improved error performance at the lower decoding complexity. Considering the bandwidth efficiency as a key factor, more data symbols are sent at the given time interval by reducing the time period for signal transmission. This ensures more data being transmitted. In the scenario of perfect Nyquist signaling, pulse designs were based on the principle of orthogonality. The signal pulse form h(t) is orthogonal with respect to shifts by nT, where T is the signaling interval. In the thesis, the time period is reduced to T < 1, which prompt more symbols to be transmitted. The pulses are no longer orthogonal. These non orthogonal FTN signals are accepted as a promising approach for the required solution of increased data rate. FTN comes as a tradeoff between the high data rate achievement and error probability. Reduction of the time factor affirms good data rate but at the same time, cost of high error rate has to be paid. Efficient receiver processing techniques are designed to compensate between these two factors. Main obstacle due to the reduction of time period in FTN signaling is to tackle the unavoidable inter symbol interferences (ISI). Going beyond the Nyquist bound, as a consequence, results high ISI. This necessitates an effective receiver processing to overcome the ISI. Minimum mean square error (MMSE) detection algorithm is employed to equalize the received signals and analyze the performance of the FTN system. Finally, the system portrayal is studied by processing the results under the implementation of turbo coding systems. The bit error rate (BER) characteristics are analyzed under these circumstances. Efficient encoding pattern and decoding algorithm helps in reducing the errors. Analysis of the simulation results show that the turbo code proficiency is improved by increasing the number of iterations. Performance indication is also related to the frame size or the interleaver size and the signal power. In other words, it comes as a trade-off between energy efficiency, bandwidth efficiency, complexity and error rates. Furthermore, for the fair comparison of the performance analysis, transmission rates for turbo coded transmission systems under the conditions of Nyquist signaling and FTN signaling are made equivalent.

A wireless body area network (WBAN) is a collection of miniaturized and energy efficient wireless sensor nodes which monitor human body functions and its surroundings. It has been observed that WBANs perform single application per network, computation and storage capacities are scarce and there is no or limited mobility support. Technically complex WBAN application solutions today, find refuge in processing computationally complex data external to WBANs, i.e., processing sensor data on a conventional PC which is impractical and clumsy. There is a strong need for WBAN platforms which can perform computationally complex tasks on their own having enough resources in terms of computation and memory but still consuming as low power as possible in order to prolong network uptime. In this thesis work, an improved WBAN named multipurpose-BodyNet (MPBodyNet) is implemented. It has enough computational and memory resources and compact software solutions to achieve high performance and fidelity. MPBodyNet is a self-configuring, multipurpose WBAN which can perform multiple applications and user can switch between applications by a mere push of button. It supports mobility and it acts like an agent network to other networks. MP-BodyNet forms a hierarchy where low-capability networks are supported by higher-capacity networks. Hardware used for MP-BodyNet has been designed by WSN-Team at Centre for Wireless Communications, University of Oulu and this thesis proposes two application scenarios. Senior citizen protection mode (SPM) deals with a very hot health care issue for elderly people and patients. An algorithm is proposed and implemented that can detect falls or if the subject/patient has fainted. In SPM, MP-BodyNet can generate alarms in case of emergency and events can be seen on a central server as well as a special alarm is generated to the user’s phone (android app.) which can in turn establish an emergency call automatically. Algorithmic efficiency achieved is 100%. Silent communication mode (SCM) deals with a military hand signal/gesture recognition application. A quite complex pattern recognition algorithm has been proposed with two novelties in it i.e., a sampling process is introduced in the algorithm and the whole algorithmic processing is supposed to be done on the sensor node itself, no processing is supposed to be happening external to the WBAN. Algorithm for SCM is only presented here conceptually after rigorous research about the subject at disposal. It is not implemented in this thesis due to lack of time and is saved for future development. After a gesture would be recognized, an audio message mapped to the gesture will be heard over a headphone.

Full duplex (FD) radios are the next generation wireless paradigm to answer the growing demand of high capacity along with energy and spectrum efficient wireless transceivers. Given the colossal power difference between the transmit and receive signal, self-interference cancellation becomes one of the key challenge in the design of a FD radio. A model of self-interference channel is required to develop a robust cancellation mechanism. One of the key contribution of this thesis is to define the properties of the self-interference channel. Furthermore, an analog baseband cancellation mechanism for FD transceivers is also defined, which can be used as a cancellation stage before the signal goes to digital domain. The self-interference channel was measured using ultra wide-band antennas (UWB). Narrow-band measurement technique i.e., a vector network analyzer (VNA) was used for the channel measurements. Spatial resolution of 4.3 cm was achieved. Measurements were done in variety of locations including an anechoic chamber with different antenna orientation. Antennas were mounted on an old laptop frame. Coherence bandwidth of the self-interference channel was found to be varying between 1 MHz and 10 MHz, effectively making it a frequency selective channel. The average amount of isolation was found to be around 40 dB irrespective of the antennas relative orientation. It was also observed that a major amount of power was transferred because of direct coupling between the antennas and this coupling was due of the frame on which antennas were mounted. Using the defined analog baseband cancellation mechanism, an orthogonal frequency division multiplexing (OFDM) based transceiver was simulated using Matlab. The impact of different bit analog-to-digital converter (ADC), digital-to-analog converter (DAC), different training sequence length for the desired and the self-interference channel, were observed in the simulations. The simulations were performed for both 16 and 64 quadrature amplitude modulation (QAM). Training symbols were used in front of the data frame to estimate both the desired and self-interference channel and also to set the gain of variable gain amplifiers (VGA). The least square algorithm was used for the estimates. The self-interference power was set to −20 dBm and thermal noise floor was set to −81.68 dBm. It was found that a twelve bit ADC along with a sixteen bit DAC would provide a performance within 1.5 dB of theoretical performance.

Nowadays, wireless device users engage in various forms of wireless applications and services. Multiple-Input Multiple-Output (MIMO) system technology, which involves multiple uses of antennas at both the transmitter and the receiver side of wireless channel, can be used to improve the wireless channel capacity without any need for extra spectrum in the rich scattering environment. The MIMO technology is regarded as a fundamental component for this new emerging wireless communication Long Term Evolution (LTE) standard. However, as a result of short distance between the antennas in the small mobile terminals, the total antenna efficiency gets reduced and the mutual coupling that exists between the MIMO antenna elements also becomes very high which lead to high Envelope Correlation Coefficient (ECC). This Master’s thesis aims to study the impact of antenna type on the ECC for a two antenna system in a typical mobile terminal sized device (ground plane) by using different configurations of antenna placement. The mobile antennas are to operate in LTE band 3 (from 1.710 GHz to 1.880 GHz) and LTE band 20 (from 0.791GHz to GHz 0.862 GHz). This thesis has been addressed by first introducing the fundamental theory of antennas. It is followed with description of effect on ground plane due to different mobile antenna structures and as a last part on the basics of LTE and LTE-Advanced components, focusing on the concept of multiple antennas design on mobile terminal. In this thesis, three types of antenna structures have been considered: Planar Inverted-F Antenna (PIFA), monopole and loop antennas. The designs and simulations of the antenna structures have been performed using CST Microwave studio software. The two antenna systems showed better performance when one antenna is located at the bottom of the ground plane with feed at the corner and the second antenna is placed perpendicularly at the top with feed positioned on the same side of the ground plane as the bottom antenna. ECC values of less than 0.2 in LTE band 3 and less than 0.49 in LTE band 20 were obtained. The study shows that good efficiency and low ECC (low mutual coupling) can be achieved from the placement of the MIMO antennas on the ground plane. In consideration to future work, the results in this thesis can serve as helpful information in multi-antenna designs for mobile terminals.