64 research outputs found
On transmitter power control for cellular mobile radio networks
Master'sMASTER OF ENGINEERIN
Near far resistant detection for CDMA personal communication systems.
The growth of Personal Communications, the keyword of the 90s, has already the signs of a technological revolution. The foundations of this revolution are currently set through the standardization of the Universal Mobile Telecommunication System (UMTS), a communication system with synergistic terrestrial and satellite segments. The main characteristic of the UMTS radio interface, is the provision of ISDN services. Services with higher than voice data rates require more spectrum, thus techniques that utilize spectrum as efficiently as possible are currently at the forefront of the research community interests. Two of the most spectrally efficient multiple access technologies, namely. Code Division Multiple Access (CDMA) and Time Division Multiple Access (TDMA) concentrate the efforts of the European telecommunity.This thesis addresses problems and. proposes solutions for CDMA systems that must comply with the UMTS requirements. Prompted by Viterbi's call for further extending the potential of CDMA through signal processing at the receiving end, we propose new Minimum Mean Square Error receiver architectures. MMSE detection schemes offer significant advantages compared to the conventional correlation based receivers as they are NEar FAr Resistant (NEFAR) over a wide range of interfering power levels. The NEFAR characteristic of these detectors reduces considerably the requirements of the power control loops currently found in commercial CDMA systems. MMSE detectors are also found, to have significant performance gains over other well established interference cancellation techniques like the decorrelating detector, especially in heavily loaded system conditions. The implementation architecture of MMSE receivers can be either Multiple-Input Multiple Output (MIMO) or Single-Input Single-Output. The later offers not only complexity that is comparable to the conventional detector, but also has the inherent advantage of employing adaptive algorithms which can be used to provide both the dispreading and the interference cancellation function, without the knowledge of the codes of interfering users. Furthermore, in multipath fading channels, adaptive MMSE detectors can exploit the multipath diversity acting as RAKE combiners. The later ability is distinctive to MMSE based receivers, and it is achieved in an autonomous fashion, without the knowledge of the multipath intensity profile. The communicator achieves its performance objectives by the synergy of the signal processor and the channel decoder. According to the propositions of this thesis, the form of the signal processor needs to be changed, in order to exploit the horizons of spread spectrum signaling. However, maximum likelihood channel decoding algorithms need not change. It is the way that these algorithms are utilized that needs to be revis ed. In this respect, we identify three major utilization scenarios and an attempt is made to quantify which of the three best matches the requirements of a UMTS oriented CDMA radio interface. Based on our findings, channel coding can be used as a mapping technique from the information bit to a more ''intelligent" chip, matching the ''intelligence" of the signal processor
Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems
Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER
Optimality of binary power-control in a single cell via majorization
This paper considers the optimum single cell power-control maximizing the
aggregate (uplink) communication rate of the cell when there are peak power
constraints at mobile users, and a low-complexity data decoder (without
successive decoding) at the base station. It is shown, via the theory of
majorization, that the optimum power allocation is binary, which means links
are either "on" or "off". By exploiting further structure of the optimum binary
power allocation, a simple polynomial-time algorithm for finding the optimum
transmission power allocation is proposed, together with a reduced complexity
near-optimal heuristic algorithm. Sufficient conditions under which
channel-state aware time-division-multiple-access (TDMA) maximizes the
aggregate communication rate are established. Finally, a numerical study is
performed to compare and contrast the performance achieved by the optimum
binary power-control policy with other sub-optimum policies and the throughput
capacity achievable via successive decoding. It is observed that two dominant
modes of communication arise, wideband or TDMA, and that successive decoding
achieves better sum-rates only under near-perfect interference cancellation
efficiency.Comment: 24 pages, 11 figure
Multi-carrier CDMA using convolutional coding and interference cancellation
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN016251 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Interference characterization and suppression for multiuser direct-sequence spread-spectrum system
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (p. 175-184).In this thesis we investigate efficient modulation and detection techniques for the uplink (i.e. transmission from mobile to base station) of a DS-CDMA network. Specifically, the thesis contains three parts. In the first part, we focus on the mobile transmitter. In particular, we evaluate and compare the spectral efficiency of two promising variable rate DS-CDMA transmission techniques, multicode (MCD) and variable-spreading-gain (VSG), under the presence of multiple-access (user-to-user) interferences (MAI) and multipath interferences. The uniqueness of our study is that in bit-error-rate evaluation, instead of approximating the interference as Gaussian noise (which has been done in most of the previous studies), we incorporate both power and distribution of interferences into consideration. We show where the Gaussian assumption may give misleading answers and how our results in these cases are different from those obtained in the past. In part two and three of the thesis, we focus on the base station receiver. Specifically, we present effective joint detection techniques that have good performance-complexity tradeoff. Part two of the thesis introduces a class of novel multistage parallel interference cancellation algorithms based on stage-by-stage minimum mean-squared error (MMSE) optimization. We show that this scheme is capable of achieving significantly better performance than other algorithms with similar complexity. Part three of the thesis presents a low-complexity dual-mode multiuser detector that dynamically switches its detection mode between the matched-filter receiver and the decorrelator. We show that this detector is capable of achieving the performance of a decorrelator but with significant savings in processing power and complexity.by Mingxi Fan.Ph.D
On the performance and capacity of space-time block coded multicarrier CDMA communication systems
Ph.DDOCTOR OF PHILOSOPH
Power control in multimedia CDMA cellular networks.
Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.Wireless mobile communication is witnessing a rapid growth in, and demand
for, improved technology and range of information types and services. Further,
third generation cellular networks are expected to provide mobile users with
ubiquitous wireless access to a global backbone architecture that carries a wide
variety of electronic services. We examine the topic of power control and
models that arc suitable for modem third generation wireless networks. CDMA
technology is proving to be a promising and attractive approach for spectrally
efficient, economical and high quality digital communications wireless
networks. This thesis addresses the challenge of integrating heterogeneous
transmitting sources with a broad range of Quality of Service characteristics in
the cellular COMA networks. Provided the right power control can be devised,
COMA offers the potential of extracting gain from the statistical multiplexing of
such sources. A distributed power control algorithm is proposed which is
required to update the transmitted power of the mobiles in each of the service
classes locally. and enhance the performance of the system significantly.
Algorithms for pragmatic issues like power level quantization and truncation of
power are derived and incorporated into the proposed distributed power control
algorithm
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