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Power and performance trade-off in DS-CDMA receivers based on adaptive LMS-MMSE multi-user detector.Wang, Qingsheng. January 2003 (has links)
Third generation cellular communication systems based on CDMA techniques have shown great scope for improvement in system capacity. Over the last decade, there has been significant interest in DS-CDMA detectors. The conventional detector, the optimal detector and a number of sub-optimal multi-user detectors (MUD) have been extensively analyzed in the literature. Recently, the reduction of power consumption in DS-CDMA systems has also become another important consideration in both system design and in implementation. In order to support wireless multimedia services, all CDMA-based systems for third generation systems have a large bandwidth and a high data rate, therefore the power consumed by the digital signal processor (DSP) is high. This thesis focuses on power consumption in the adaptive Minimum Mean Square Error (MMSE) detector which is based on the Least Mean Square (LMS) algorithm. This thesis presents a literature survey on MUD and adaptive filter algorithms. A system model of the quantized LMS-MMSE MUD is proposed and its performance is analyzed. The quantization effects in the finite precision LMS-MMSE adaptive MUD including the steady-state weight covariance, mean square error (MSE) and bit error rate (BER) versus wordlength of data and coefficient are investigated when both the data and filter coefficients are quantized. The effects of wordlength size on power consumption are investigated and the tradeoff between the power consumption and performance degradation and the optimal allocation of bits to data and to LMS coefficients under power constraint is presented. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.
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Subspace-based channel estimation for DS/CDMA systems exploiting pulse- shaping information.Gaffar, Mohammed Yusuf Abdul. January 2003 (has links)
Third generation wireless systems have adopted Direct-Sequence/Code-Division Multiple-Access (DS/CDMA) as the multiple access scheme of communication. This system would typically operate in a multipath fading channel. This dissertation only deals with the task of channel estimation at the base station where the multipath delays and attenuations for each user are estimated. This information is used to aid the recovery of data that was transmitted by each user. Subspace-based algorithms are popularly used to perform the task of channel estimation because they have the desirable property of perfectly estimating the channel in a noise-free environment. In this dissertation a new subspace-based channel estimation algorithm for
DS/CDMA systems is presented. The proposed algorithm is based on the Parametric Subspace algorithm by Perros-Meilhac et al. for single-user systems. The main focus of this dissertation is to convert the Parametric Subspace algorithm from a single-user system to a multi-user DS/CDMA system. It has been shown in the literature that by using information of the pulse-shaping filter in the Channel Subspace algorithm, the variance of the channel estimates is decreased. However, this has only been applied to a single-user system. There are several subspace algorithms that have been proposed for DS/CDMA systems. Most of these algorithms sample the received
signal at the chip rate, making it impossible to exploit knowledge of the pulse-shaping filter in the channel estimation algorithm. In this dissertation a new subspace-based channel estimation algorithm is derived for a DS/CDMA system with multiple receive antennas, where the output is oversampled with respect to the chip rate. By oversampling the received signal, knowledge of the pulse-shaping filter is used in the channel estimation algorithm. It is shown that the variance of the channel estimate for the proposed subspace algorithm is less than the Torlak/Xu subspace algorithm that does not exploit information of the pulse-shaping filter. A mathematical expression of the mean square error of estimation for the new algorithm is also derived. It was shown that the analytic expression provides a good approximation of the actual MSE for high SNR. The Parametric Subspace Delay Estimation (PSDE) algorithm was developed by Perros-Meilhac et al. to estimate the multipath delays introduced by the communications channel. The limitation of the PSDE algorithm is that the performance of the algorithm deteriorates as the power of the multipath signals decrease with increasing delay time. This dissertation proposes a modified version of the PSDE algorithm, called the Modified Parametric Subspace Delay Estimation (MPSDE) algorithm, which performs better than the PSDE algorithm in an environment where the power of the multipath signals varies.
The final part of this dissertation discusses the Torlak/Xu channel estimation algorithm and the Bensley/Aazbang delay estimation algorithm. In order to compare the performance of these two subspace algorithms, the Torlak/Xu algorithm is converted to a delay estimation algorithm that is called the Parametric TX algorithm. The performance of the Bensley/Aazbang delay estimation algorithm and the proposed Parametric TX algorithm are compared and it is shown that the Parametric TX algorithm offers the better performance. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.
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Lattice-structure based adaptive MMSE detectors for DS-CDMA systems.Thakadu, Batlhowahela C D. January 2001 (has links)
There has been significant interest in the research community on detectors for DS-CDMA
systems. The conventional detector, which detects users ' data bits, by using a filter matched to the
users' spreading codes, has two major drawbacks. These drawbacks are (1) its capacity is limited
by multiple access interference (MAl) and (2) it suffers from the near-far problem. The remedy to
these problems is to use a multiuser detector, which exploits knowledge of users ' transmission
and channel parameters to mitigate MAl. Such detectors are called multi user detectors (MUD). A
number of these detectors have been proposed in the literature. The first such detector is the
optimal detector proposed by Verdu. Following Verdu's work a number of suboptimal detector
were proposed. These detectors offer better computational complexity at the expense of the bit
error rate performance. Examples of these detectors are the decorrelating detector, the minimum
mean squared error detector (MMSE), the successive interference cancellation and parallel
interference cancellation. In this thesis, we consider the adaptive DS-CDMA MMSE detector,
where lattice-based filter algorithms are employed to suppress MAl. Most of the work in the
literature has considered the implementation of this detector using the Least Mean Square (LMS)
algorithm. The disadvantage of using the LMS algorithm to implement the MMSE detector is that
the LMS algorithm converges very slowly.
The main aims of this thesis are as follows. A review of the literature on MUD is presented. A
lattice based MUD is then proposed and its performance evaluated using both simulation and
analytical methods. The results obtained are compared with those of the LMSMMSE detector.
From the results obtained the adaptive Lattice-MMSE detector is shown to offer good
performance tradeoff between convergence results and BER results. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.
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Design considerations and implementation of a RF front-end for CDMA adaptive array system.Roopram, Kelesh D. January 2000 (has links)
Recent studies have shown that considerable system capacity gains in mobile
communication systems can be obtained by exploiting the use of antenna arrays at the
base station. Unfortunately, these studies make little mention of practical issues
concerning implementation. It is thus one of the objectives of the Centre of Excellence
(CoE) in Radio Access Technologies at the University of Natal to investigate the
development of a widehand CDMA adaptive array transceiver using Alcatel software
radios as the transceiver platforms. Such a transceiver system can be subdivided into
three major sections: RF front-end, signal digitization and baseband processing stages.
Due to the enormity of such an undertaking, the research outlined in this thesis is focused
on (but not isolated to) some aspects of the RF front-end implementation for the proposed
system.
The work in this thesis can be catergorized into two sections. The first section focuses on
the theoretical and practical (or implementation) aspects of antenna arrays and
beamforming. In particular, it is evident that digital (rather than analogue) beamforming
in a multi user environment, is a more viable option from both a cost and implementation
standpoint. The second section evaluates the impact of RF component noise and local
oscillator generated phase noise in a DS-CDMA system. The implementation of a RP
front-end for a BPSK transceiver also forms part of the work in this section. LO phase
noise and Error Vector Magnitude (EVM) measurements are performed on this system to
support relevant theory. By use of the HP89410A phase noise measurement utility and
the phase noise theory developed in this thesis, a quantitative phase noise comparison
between two frequency sources used in the system were made. EVM measurement
results conclusively verified the importance of an LNA in the system. It has also been
shown that the DS-CDMA simulated system exhibits superior performance to the
implemented BPSK system. Furthermore, an EVM troubleshooting methodology is
introduced to identify possible impairments within the BPSK receiver RF front-end.
However, this thesis was written with the intention of bridging the gap between the theoretical and practical implementation aspects of RP wireless communication systems.
It is the author's opinion that this has been achieved to a certain extent. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
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Power control in multimedia CDMA cellular networks.Sharma, Neeru. January 2000 (has links)
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. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
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Space-time multiuser detection of multi-carrier DS-CDMA systems.Whitehead, James Bruce. January 2001 (has links)
Personal wireless communications networks have flourished over the last decade as advances in
digital cellular technology have made them more accessible to the general public. Third
Generation Cellular Communication systems based on code division multiple access (CDMA)
as the multiple access technique, show great scope for improvement in terms of capacity,
through the use of advanced signal processing techniques. Two of the leading areas that
encompass these techniques are space-time processing (smart antennas) and multiuser detection
(MUD). Space-time-MUD (ST-MUD) is a relatively new field that hopes to bring together these
two techniques. The focus of this thesis is ST -MUD in the context of a multi-carrier direct
sequence CDMA (MC-DS-CDMA) communications system, which is one of the adopted
multiple access techniques for the upcoming third generation cellular communications systems.
The concepts of MUD and smart antennas are discussed, and their performance enhancing
capabilities are demonstrated. The use of vector channel models and their role in modelling the
propagation phenomena of the communications channel in terms of the space, time and
frequency domains is also illustrated. A ST-MUD receiver architecture is presented, and the
performance of the architecture with a minimum mean square error (MMSE) decision criterion
is analysed in a frequency selective Rayleigh fading channel. The analysis results are verified
via simulation. Three subspace MUD techniques are adapted for ST -MUD, and the joint space-frequency-
multi path MMSE solution on these subspaces is given. Simulation results are used to
quantify their relative performance. The relevance and applications of the subspace techniques
are elaborated. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.
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Downlink call admission control in mixed service CDMA cellular networks.Ramlakhan, Niven Bhimraj. January 2007 (has links)
Since the ascendance of CDMA (Code Division Multiple Access) as the generally accepted
multiple access technology of choice for next generation networks, the rate of development of
the wireless cellular communication industry has been phenomenal. Next generation wireless
cellular networks offer a myriad of voice, video, data and text based information services for the
future multimedia and information society. This mixed service scenario implies that the same
[mite resource i.e. the air interface must be shared amongst different classes of user, each with a
specific quality of service. With multiple services competing for the same resource and with the
inherent soft capacity nature of CDMA, call admission control becomes a formidable task. The
problem is further compounded by the introduction of priorities between classes. Call admission
control is an essential component of these next generation networks and the open nature of the
current standards, such as UMTS (Universal Mobile Telecommunication System) allow for
vendor implementation of different call admission control policies.
The main area of focus in this dissertation is on a proposed downlink, load-based, mixed service
call admission policy. In a CDMA environment with symmetrical service and equal bandwidths
in each direction, the uplink is commonly considered to be the bottleneck. Based on the
asymmetric nature of the expected traffic in next generation networks the downlink is envisaged
as the future bottleneck. Some of the more common choices for downlink call admission control
include number based as well as power based call admission policies. A load-based call
admission policy has been chosen as the maximum load threshold that can be supported varies
with the state of the system and thus effectively models the behaviour of a soft capacity CDMA
network. This dissertation presents a teletraffic performance analysis model of a load-based call
admission control policy for downlink mixed service CDMA cellular networks.
The performance analysis yields customer oriented grade-of-service parameters such as call
blocking probability which is essential for network planning. In our analysis we incorporate a
Birth-Death Markov queuing model. This mathematical model is verified though computer
simulation. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.
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CDMA performance for a rural telecommunication access.Rasello, Poloko Freddy. January 2005 (has links)
Reviews of possible telecommunication services that can be deployed in the rural areas
are highlighted. These services range from narrowband to broadband. The aim of these
services is to target rural Kwazulu-Natal areas that are without or with limited
telecommunications infrastructure.
Policies that govern telecommunications in South Africa are also reviewed with emphasis
on Universal Service Obligation. The importance of telecommunications infrastructure in
rural areas is also reviewed to the benefit of Kwazulu-Natal.
FDMA, TDMA, CDMA, VSAT, MMDS and MVDS are compared for a possible use in
rural areas. Cost comparison of GSM and CDMA is conducted with emphasis on fade
margin, path loss and penetration rate.
CDMA system design and coverage areas are discussed for rural KwaZulu-Natal. Lastly
bit error rate graphs and power control algorithms are presented for Kwazulu-Natal
scenario. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.
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Game theoretic models for multiple access and resource allocation in wireless networksAkkarajitsakul, Khajonpong 13 December 2012 (has links)
We first present a non-cooperative auction game to solve the bandwidth allocation problem for non-cooperative channel access in a wireless network. The Nash equilibrium is obtained as a solution of the game. To address this problem of bandwidth sharing under unknown information, we further develop a Bayesian auction game model and then Bayesian Nash equilibrium is then obtained. Next, we present a framework based on coalitional game for cooperative channel access for carry-and-forward-based data delivery. Each mobile node helps others to carry and then forward their data. A coalitional game is proposed to find a stable coalition structure for this cooperative data delivery. We next present static and dynamic coalitional games for carry-and-forward-based data delivery when the behavior of each mobile node is unknown by others. In the dynamic game, each mobile node can update its beliefs about other mobile nodes’ types when the static coalitional game is played repeatedly.
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Cochannel interference canceling receivers for TDMA systemsJoung, Jinsoup 05 1900 (has links)
No description available.
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