Multiple-input multiple-output (MIMO) is a well-known technique for efficiently increasing bandwidth utilization. However, the implementation of the MIMO receiver with a reasonable hardware cost is a big challenge. Most MIMO receivers exploit minimum mean-square error (MMSE), zero-forcing (ZF) and maximum-likelihood (ML) to detect MIMO signals. Among the detectors, the ZF detector is simple detector with low computational complexity, but lower performance compared to ML decoder, which has huge computational complexity. If the K-Best sphere decoding algorithm (SDA) is adopted, the system complexity can be substantially reduced and the performance can approach that of the ML scheme when the value K is sufficiently large. In this paper, a hard-output MIMO detector is implemented using the K-Best SDA for 4¡Ñ4 64-quadrature amplitude modulation (QAM) MIMO detection. The implementation is realized by using a 0.18-£gm CMOS technology. The implementation chip core area is 3.35mm2 with 229K gates, and the decoding throughput is up to 3.12Mb/s with a 25MHz clock rate.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / Wireless communication systems may use training signals for the receiver to learn the fading coefficients of the channel. Obtaining channel state information (CSI) at the receiver is often times necessary for the receiver to correctly detect and demodulate transmitted symbols. The type of training signal, the length of time to spend training, and the frequency of training are all important parameters in these types of systems. In this work, we derive an analytic expression for calculating the optimal training parameters for continuously fading channels. We also provide simulation results showing why this training scheme is considered optimal.

In the past two decades, wireless communication systems have grown with an unprecedented speed from radio paging and cellular telephony to multimedia platforms offering voice and video streaming . One undesired outcome of this expansion is a heavy utilization of the available frequency spectrum. Particular pressure comes from new multimedia applications, which require larger operational bandwidth for their implementations. Conventional coding, modulation and multiplexing techniques are unable to overcome the problem associated with the limited frequency spectrum, and therefore modern wireless systems are improved through the utilization of the space/angle domain. In order to improve capacity and reliability with the space/angular domain, wireless systems require the use of multiple element antennas (MEA) accompanied by appropriate signal processing algorithms. Typically multiple antennas are used to steer the beams of the line of sight (LOS) signal toward desired users and nulls in the direction of undesired users. However, in the case of indoor environments, the presence of reflections, scattering and refraction caused by the environment, it is better to make use of non-line of sight (NLOS) signal propagation. As these types of MEA antenna systems are a relatively new concept in wireless communications, their potential needs be tested experimentally in real world conditions. To achieve this goal, prototype systems capable to implement various modulation, coding and transmission schemes for MEA are required. This thesis investigates the benefits of MEA systems by building and testing such systems in indoor environments. The project area spans across many disciplines including wireless communications, antennas, embedded systems and RF hardware design, and therefore the thesis begins with essential background information. This concerns some fundamental concepts of a wireless communication channel and its information capacity. These are accompanied by ample considerations of signal propagation and adverse effects of reflection, scattering and diffraction. Also included are the signal modulation and coding. Following this background information, the main topic concerning diversity and multiple-input multiple output system that involves the use of multiple element antennas is introduced. This background material sets the reasons for investigating of two types wireless communication systems that include multiple element antennas: antenna diversity and MIMO. Following the literature review, the thesis reports on investigations that realize the thesis aims. The first part of the undertaken investigations concerns an indoor 2×2 MEA diversity system in which MEAs accompany conventional transceivers. In the experiments, Bluetooth transceivers aimed for a short range operation at 2.45 GHz are used, which are both connected to a 2-element antenna array. The connection is made via a switched beamforming network which involves 4-port hybrid circuits. Two ports of these hybrids are used for connecting antennas, while the one of the remaining two is connected to the Tx or Rx transceiver. By switching between these two input ports of the hybrid, two different radiation patterns can be formed, at both Tx and Rx. One Bluetooth transceiver is stationary while the other is made mobile by employing a purpose built mechanical sub-system covering the precise movement within a circle of 3 m. Both the movement and collection of the data as well as the display of the obtained results are accomplished with the in-house developed software run on a micro-controller and computer. Experimentally, it is shown that the proper Tx and Rx mode for a given position, improves the received signal strength. This leads to improved signal to noise ratio (SNR) and thus the quality of signal transmission. The implementation of this concept only requires a signal quality indicator, and simple feedback between the receiver and the transmitter. In the selected transceivers, "RSSI" was the quality indicator used, and is present in many modern wireless transceivers. Also, any signal quality indicator can be used. Although the experiments were performed with respect to the transmit/receive pattern diversity, they can also be easily extended to other forms of antenna diversity such as polarization or field diversity. The undertaken investigations are original in terms of the full proof of benefits of pattern diversity for indoor wireless systems. The second part of the undertaken investigations focuses on the design, development and testing of a full indoor multiple element antenna system. This demonstrator system includes two main modules: the baseband processor (based on a field programmable gate array) and the RF front end. The FPGA signal processing module is designed around the Altera Stratix II S260 chip, which is commercially available. Suitable hardware design is required to accomplish MIMO signal transmission. The RF front end module performing direct conversion between baseband and 2.45 GHz or 5 GHz radio frequency bands uses the commercially available MAX2829 chip. The interface between FPGA and RF front end is a set of analogue to digital (ADC) and digital to analogue (DAC) converters that operate on signals between the FPGA and the RF transmitter/receiver modules. They are capable of handling 12/14 bit signals at up to 125 MSmp/sec. The data rate chosen in these investigations is 3.125 Mbps. In addition to the MAX2829 IC chip, amplifiers, switches and antennas are included in the RF module. The development of this wireless communication system has been accomplished through a number of design, development and testing stages. Most of the research effort concerned FPGA based signal processing because this part of the system is where the information processing takes place. For the MIMO system, the transmitted signal has to be modulated and coded, with efficient utilization of the multiple element antennas in both these processes. The prerequisite to signal demodulation is signal synchronization. In turn, the decoding requires the knowledge of characteristics of the channels that are formed between transmitting and receiving antennas. For an efficient FPGA hardware design, all the numerical operations must occur in fixed point arithmetic. To accomplish all of these functions, suitable baseband signal processing algorithms were developed as part of the thesis work. First, they were written in MATLAB and then transferred to C++ which is closer to the FPGA implementation. Having confirmed their validity, they were hardware deployed. In the investigated MIMO demonstrator, QPSK modulation and the Alamouti coding scheme were selected for modulating and coding of the transmitted signal. The implementation of the hardware baseband module was validated using a purpose developed channel emulator. This emulator was capable of implementing the channel properties from actual measurements and from theoretical models. The applied theoretical models concern the single and double bounce scattering models, as well as a full EM model and include full EM interactions within array antennas formed by wire dipoles. These models produce random characteristics of the complex channel matrix which describes the channel properties for narrow or wideband case. With this channel emulator, investigations were performed with respect to channel estimation. The training and semi-blind channel estimation methods were tested using the developed emulator. To schedule signal transmission as well as to obtain suitable insight into individual processes, two extra modules were developed as part of the thesis project. These are the scheduler and visualisation modules. The scheduling hardware controls data packets for at the transmitter, and oversees the packets being decoded at the receiver module. For the visualization module, specialized hardware buffers and analysis modules are created for data storage. The signals resulting from the encoding and decoding processes are stored in these buffers, synchronized to each other, which allows for synchronous visualization of the signals. The data from these buffers is streamed to a PC via a 100 Mbit Ethernet connection and a soft-core processor (running uClinux) in the baseband board. Using a web browser on the PC, a graphical interface using scalable vector graphics (SVG) is used for interaction with the embedded web server to display and control what the hardware is sending and receiving. Due to latency, only a quasi-real time display on PC is possible, as 10 ms of time domain data takes 60 ms to display. The FPGA hardware performs real-time continuous data transmission and decoding, and the latency is only in the visualization system. Using the developed baseband system it was shown that the proposed semi-blind channel estimation was advantageous over the classical training approach when the channel properties change during packets transmissions. The developed channel emulator, semi-blind channel estimation algorithm and the visualisation software are the original contributions of this thesis. Having established the proper functioning of the FPGA baseband processor, the remaining investigations concerned the development of the RF transceiver module. This task was accomplished using guidelines offered by the MAX chip manufacturer. The challenge concerned its manufacturing in 4-layer board format. This part of the project required the outsourcing of the PCB manufacturing and component assembly to obtain successful production of the RF front-end board. The RF tests undertaken as part of the project verified the operation of this RF hardware. With the successful development of individual baseband and RF modules, the last part of project concerned the integration of them. Because most of the benefits of the 2×2 MIMO system were demonstrated via the use of a channel emulator, this part of the thesis consisted of the results of a number of experiments. Considerable effort was spent for the full integration of the RF and baseband modules to make them ready for real-time operation. Some of the undertaken tasks were new, as they were not required for experiments using only the baseband system and channel emulator. One of the new challenges concerned proper symbol synchronization. Two novel algorithms were proposed and verified. One of these were based on a simple comparison between "I" and "Q" components of the received signal and the other one involving a correlation of the signal to a known training sequence. The last experiment involved the experimental measurements of signals transmitted over air using the testbed. As the number of interfaces was limited only one transmitting and one receiving antenna was connected to the 2×2 baseband system. However, the Alamouti scheme is able to function when only one of the two antenna is connected, and therefore real-time performance in an indoor environment was successfully tested. The presented designs, algorithms and visualisation form a strong platform for other researchers to continue and expand the work done in this project.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / This paper addresses the air-to-ground communication problem, where multiple transmit antennas are used on the aircraft to combat multi-path interference. The channel is assumed to have a line-of-sight component and a single ground reflection. Multiple input multiple output (MIMO) techniques can be used in this situation, to increase the reliability and data rate. In this paper we discuss how the MIMO channel capacity changes, with the aircraft antenna configuration, altitude, velocity, range, and a number of other parameters. For comparison, the MIMO results are compared to systems which have single antennas at the transmitter, at the receiver, or at both ends.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / Adaptive modulation is a communication technique capable of maximizing throughput while guaranteeing a fixed symbol error rate (SER). However, this technique requires instantaneous channel state information at the transmitter. This can be obtained by predicting channel states at the receiver and feeding them back to the transmitter. Existing algorithms used to predict single-input single-output (SISO) channels with recurrent neural networks (RNN) are extended to multiple-input multiple-output (MIMO) channels for use with adaptive modulation and their performance is demonstrated in several examples.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / The accuracy of channel estimation plays a crucial role in the demodulation of data symbols sent across an unknown wireless medium. In this work a new analytical expression for the channel estimation error of a multiple input multiple output (MIMO) system is obtained when the wireless medium is continuously changing in the temporal domain. Numerical examples are provided to illustrate our findings.

Spatial modulation (SM) is a transmission technique proposed for multiple–input multiple– output (MIMO) systems, where only one transmit antenna is active at a time, offering an increase in the spectral efficiency equal to the base–two logarithm of the number of transmit antennas. The activation of only one antenna at each time instance enhances the average bit error ratio (ABER) as inter–channel interference (ICI) is avoided, and reduces hardware complexity, algorithmic complexity and power consumption. Thus, SM is an ideal candidate for large scale MIMO (tens and hundreds of antennas). The analytical ABER performance of SM is studied and different frameworks are proposed in other works. However, these frameworks have various limitations. Therefore, a closed–form analytical bound for the ABER performance of SM over correlated and uncorrelated, Rayleigh, Rician and Nakagami–m channels is proposed in this work. Furthermore, in spite of the low–complexity implementation of SM, there is still potential for further reductions, by limiting the number of possible combinations by exploiting the sphere decoder (SD) principle. However, existing SD algorithms do not consider the basic and fundamental principle of SM, that at any given time, only one antenna is active. Therefore, two modified SD algorithms tailored to SM are proposed. It is shown that the proposed sphere decoder algorithms offer an optimal performance, with a significant reduction of the computational complexity. Finally, the logarithmic increase in spectral efficiency offered by SM and the requirement that the number of antennas must be a power of two would require a large number of antennas. To overcome this limitation, two new MIMO modulation systems generalised spatial modulation (GNSM) and variable generalised spatial modulation (VGSM) are proposed, where the same symbol is transmitted simultaneously from more than one transmit antenna at a time. Transmitting the same data symbol from more than one antenna reduces the number of transmit antennas needed and retains the key advantages of SM. In initial development simple channel models can be used, however, as the system develops it should be tested on more realistic channels, which include the interactions between the environment and antennas. Therefore, a full analysis of the ABER performance of SM over urban channel measurements is carried out. The results using the urban measured channels confirm the theoretical work done in the field of SM. Finally, for the first time, the performance of SM is tested in a practical testbed, whereby the SM principle is validated.

IEEE 802.11n Wireless Local Area Networks (WLANs) employ Multiple-Input-Multiple-Output (MIMO), which significantly boosts the raw data rate at the Physical layer (PHY). But the potential of enhancing Medium Access Control (MAC) layer efficiencies by MIMO is still in its early stage and is the aim of the research in this thesis. Many existing works in this field mainly employ distributed MIMO spatial multiplexing/Multi-User Detection (MUD) technique and stream sharing to enable multiple simultaneous transmissions. Most works require synchronization among multiple transmissions, split the channel, and aim for single-hop networks. In this thesis, a novel Hybrid Carrier Sense (HCS) framework is proposed, mainly at the MAC layer to exploit the power of MIMO. HCS senses the channel availability jointly by the virtual carrier sense and physical carrier sense. HCS does not require synchronization among nodes; each node independently and locally determines when to start its transmission. HCS not only shares the channel, but also exploits the bi-directional handshakes of the wireless transmissions and increases the number of simultaneous stream transmissions. For a network with M antennas in each node, HCS can accommodate 2x(M-1) streams instead of M streams achieved by all other existing works. Moreover, HCS is aimed for multi-hop wireless ad hoc networks, in which the hidden terminal, exposed terminal, and deafness problems greatly degrade network performance. The HCS framework incorporates solutions to these problems. HCS is implemented in an NS2 network simulator and the performance evaluation shows that HCS significantly outperforms MIMO-enabled IEEE 802.11 (in which MIMO is only used for enhancing the raw data rate in the physical layer), resulting in higher aggregate throughput, packet delivery ratio and fairness in multi-hop wireless ad hoc networks. The HCS framework will be in wide use in the future generation of wireless networks and opens up more research possibilities. Some ideas in the HCS framework can be applied not only for MIMO, but also for many other techniques surveyed in this thesis; or we may combine them with HCS to further boost the network performance. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-10-15 21:46:15.983

Design and analysis of random-like codes for various multiple-input and multiple-output communication systems are addressed in this work. Random-like codes have drawn significant interest because they offer capacity-achieving performance. We first consider the analysis and design of low-density parity-check (LDPC) codes for turbo multiuser detection in multipath CDMA channels. We develop techniques for computing the probability density function (pdf) of the extrinsic messages at the output of the soft-input soft-output (SISO) multiuser detectors as a function of the pdf of input extrinsic messages, user spreading codes, channel impulse responses, and signal-to-noise ratios. Using these techniques, we are able to accurately compute the thresholds for LDPC codes and design good irregular LDPC codes. We then apply the tools of density evolution with mixture Gaussian approximations to optimize irregular LDPC codes and to compute minimum operational signal-to-noise ratios for ergodic MIMO OFDM channels. In particular, the optimization is done for various MIMO OFDM system configurations which include different number of antennas, different channel models and different demodulation schemes. We also study the coding-spreading tradeoff in LDPC coded CDMA systems employing multiuser joint decoding. We solve the coding-spreading optimization based on the extrinsic information SNR evolution curves for the SISO multiuser detectors and the SISO LDPC decoders. Both single-cell and multi-cell scenarios will be considered. For each of these cases, we will characterize the extrinsic information for both finite-size systems and the so-called large systems where asymptotic performance results must be evoked. Finally, we consider the design optimization of irregular repeat accumulate (IRA) codes for MIMO communication systems employing iterative receivers. We present the density evolution-based procedure with Gaussian approximation for optimizing the IRA code ensemble. We adopt an approximation method based on linear programming to design an IRA code with the extrinsic information transfer (EXIT) chart matched to that of the soft MIMO demodulator.

The scarce and overpopulated radio spectrum is going to present a major barrier to the growth and development of future wireless networks. As such, spectrum sharing seems to be inevitable to accommodate the exploding demand for high data rate applications. A major challenge to realizing the potential advantages of spectrum sharing is interference management. This thesis deals with interference management techniques in noncooperative networks. In specific, interference alignment is used as a powerful technique for interference management. We use the degrees of freedom (DoF) as the figure of merit to evaluate the performance improvement due to the interference management schemes. This dissertation is organized in two parts. In the first part, we consider the K-user multiple input multiple output (MIMO) Gaussian interference channel (IC) with M antennas at each transmitter and N antennas at each receiver. This channel models the interaction between K transmitter-receiver pairs sharing the same spectrum for data communication. It is assumed that the channel coefficients are constant and are available at all nodes prior to data transmission. A new cooperative upper-bound on the DoF of this channel is developed which outperforms the known bounds. Also, a new achievable transmission scheme is provided based on the idea of interference alignment. It is shown that the achievable DoF meets the upper-bound when the number of users is greater than a certain threshold, and thus it reveals the channel DoF. In the second part, we consider communication over MIMO interference and X channels in a fast fading environment. It is assumed that the transmitters obtain the channel state information (CSI) after a finite delay which is greater than the coherence time of the channel. In other words, the CSI at the transmitters becomes outdated prior to being exploited for the current transmission. New transmission schemes are proposed which exploit the knowledge of the past CSI at the transmitters to retrospectively align interference in the subsequent channel uses. The proposed transmission schemes offer DoF gain compared to having no CSI at transmitters. The achievable DoF results are the best known results for these channels. Simple cooperative upper-bounds are developed to prove the tightness of our achievable results for some network configurations.