432 research outputs found
Pattern Diversity Characterization of Reconfigurable Antenna Arrays for Next Generation Wireless Systems
The use of multi-antenna technology in wireless radio communications has attracted tremendous attention due to its potential to increase data rates without requiring additional bandwidth and transmission power. This has been driven by the burgeoning demand for high data rates and the need for instantaneous and ubiquitous access to information. It is therefore no surprise that current and future generation wireless standards such as LTE and WiMAX have adopted the use of adaptive multi-antenna systems also known as adaptive Multiple Input and Multiple Output (MIMO) as their de facto transmission technology. In this thesis work, we focus on the design of a smart wireless antenna system, and the study of relevant techniques that enable us to reap the benefits of their deployment in small wireless devices with MIMO capability. Specifically, we employ a new class of adaptive antenna systems known as Reconfigurable Antenna Systems (RAS) for portable devices. These antennas are capable of dynamically changing their electrical and radiation characteristics to suit the conditions of the wireless channel. The changing radiation patterns lead to pattern diversity gains that improve system performance. This is in contrast to conventional non-reconfigurable arrays which depend on signal processing techniques such as antenna grouping and beamforming to achieve performance gains. However, despite the demonstrable system-level performance benefits of RAS in adaptive MIMO, few of these antennas have been adopted and integrated in state-of-the-art wireless standards. Their usage has been partly inhibited by the prohibitive costs of implementation and operation in a real wireless infrastructure. As part of this thesis research effort we attempt to integrate these new antennas into a cost-effective real wireless MIMO testbed for use in current generation technologies. The solution integration is carried-out through the use of readily available software-defined radio frameworks. We first design, analyze and characterize the pattern diversity in RAS antenna arrays that resonate at frequencies suitable for 4G applications. We then study the benefits of pattern diversity obtained from RAS arrays over conventional space diversity approaches such as antenna grouping and beamforming. This dissertation also presents low-complexity adaptive physical layer models and algorithms to exploit the benefits of RAS array integration in MIMO wireless systems. We implement these algorithms in software-defined radio frameworks, experimentally test, and benchmark them against other established approaches in literature. And finally, integrate and test these RAS array design prototypes as part of the MIMO wireless system that leverages a state-of-the-art wireless base station and mobile terminals.Ph.D., Electrical Engineering -- Drexel University, 201
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Space-time-frequency methods for interference-limited communication systems
textTraditionally, noise in communication systems has been modeled as an additive, white Gaussian noise process with independent, identically distributed samples. Although this model accurately reflects thermal noise present in communication system electronics, it fails to capture the statistics of interference and other sources of noise, e.g. in unlicensed communication bands. Modern communication system designers must take into account interference and non-Gaussian noise to maximize efficiencies and capacities of current and future communication networks. In this work, I develop new multi-dimensional signal processing methods to improve performance of communication systems in three applications areas: (i) underwater acoustic, (ii) powerline, and (iii) multi-antenna cellular. In underwater acoustic communications, I address impairments caused by strong, time-varying and Doppler-spread reverberations (self-interference) using adaptive space-time signal processing methods. I apply these methods to array receivers with a large number of elements. In powerline communications, I address impairments caused by non-Gaussian noise arising from devices sharing the powerline. I develop and apply a cyclic adaptive modulation and coding scheme and a factor-graph-based impulsive noise mitigation method to improve signal quality and boost link throughput and robustness. In cellular communications, I develop a low-latency, high-throughput space-time-frequency processing framework used for large scale (up to 128 antenna) MIMO. This framework is used in the world's first 100-antenna MIMO system and processes up to 492 Gbps raw baseband samples in the uplink and downlink directions. My methods prove that multi-dimensional processing methods can be applied to increase communication system performance without sacrificing real-time requirements.Electrical and Computer Engineerin
Index modulation for next generation wireless communications.
Doctoral Degree. University of KwaZulu-Natal, Durban.A multicarrier index modulation technique in the form of quadrature spatial modulation (QSM)
orthogonal frequency division multiplexing (QSM-OFDM) is proposed, in which transmit antenna
indices are employed to transmit additional bits. Monte Carlo simulation results demonstrates a 5 dB
gain in signal-to-noise ratio (SNR) over other OFDM schemes. Furthermore, an analysis of the
receiver computational complexity is presented.
A low-complexity near-ML detector for space-time block coded (STBC) spatial modulation
(STBC-SM) with cyclic structure (STBC-CSM), which demonstrate near-ML error performance and
yields significant reduction in computational complexity is proposed. In addition, the union-bound
theoretical framework to quantify the average bit-error probability (ABEP) of STBC-CSM is
formulated and validates the Monte Carlo simulation results.
The application of media-based modulation (MBM), to STBC-SM and STBC-CSM employing radio
frequency (RF) mirrors, in the form of MBSTBC-SM and MBSTBC-CSM is proposed to improve
the error performance. Numerical results of the proposed schemes demonstrate significant
improvement in error performance when compared with STBC-CSM and STBC-SM. In addition, the
analytical framework of the union-bound on the ABEP of MBSTBC-SM and MBSTBC-CSM for the
ML detector is formulated and agrees well with Monte Carlo simulations. Furthermore, a
low-complexity near-ML detector for MBSTBC-SM and MBSTBC-CSM is proposed, and achieves a
near-ML error performance. Monte Carlo simulation results demonstrate a trade-off between the
error performance and the resolution of the detector that is employed.
Finally, the application of MBM, an index modulated system to spatial modulation, in the form of
spatial MBM (SMBM) is investigated. SMBM employs RF mirrors located around the transmit
antenna units to create distinct channel paths to the receiver. This thesis presents an easy to evaluate
theoretical bound for the error performance of SMBM, which is validated by Monte Carlo simulation
results. Lastly, two low-complexity suboptimal mirror activation pattern (MAP) optimization
techniques are proposed, which improve the error performance of SMBM significantly
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