118 research outputs found
Optimum Asymptotic Multiuser Efficiency of Pseudo-Orthogonal Randomly Spread CDMA
A -user pseudo-orthogonal (PO) randomly spread CDMA system, equivalent to
transmission over a subset of single-user Gaussian channels, is
introduced. The high signal-to-noise ratio performance of the PO-CDMA is
analyzed by rigorously deriving its asymptotic multiuser efficiency (AME) in
the large system limit. Interestingly, the -optimized PO-CDMA transceiver
scheme yields an AME which is practically equal to 1 for system loads smaller
than 0.1 and lower bounded by 1/4 for increasing loads. As opposed to the
vanishing efficiency of linear multiuser detectors, the derived efficiency is
comparable to the ultimate CDMA efficiency achieved for the intractable optimal
multiuser detector.Comment: WIC 27th Symposium on Information Theory in the Benelux, 200
Design guidelines for spatial modulation
A new class of low-complexity, yet energyefficient Multiple-Input Multiple-Output (MIMO) transmission techniques, namely the family of Spatial Modulation (SM) aided MIMOs (SM-MIMO) has emerged. These systems are capable of exploiting the spatial dimensions (i.e. the antenna indices) as an additional dimension invoked for transmitting information, apart from the traditional Amplitude and Phase Modulation (APM). SM is capable of efficiently operating in diverse MIMO configurations in the context of future communication systems. It constitutes a promising transmission candidate for large-scale MIMO design and for the indoor optical wireless communication whilst relying on a single-Radio Frequency (RF) chain. Moreover, SM may also be viewed as an entirely new hybrid modulation scheme, which is still in its infancy. This paper aims for providing a general survey of the SM design framework as well as of its intrinsic limits. In particular, we focus our attention on the associated transceiver design, on spatial constellation optimization, on link adaptation techniques, on distributed/ cooperative protocol design issues, and on their meritorious variants
Efficient Radio Resource Allocation Schemes and Code Optimizations for High Speed Downlink Packet Access Transmission
An important enhancement on the Wideband Code Division Multiple Access
(WCDMA) air interface of the 3G mobile communications, High Speed Downlink
Packet Access (HSDPA) standard has been launched to realize higher spectral
utilization efficiency. It introduces the features of multicode CDMA transmission
and Adaptive Modulation and Coding (AMC) technique, which makes radio resource
allocation feasible and essential. This thesis studies channel-aware resource
allocation schemes, coupled with fast power adjustment and spreading code optimization
techniques, for the HSDPA standard operating over frequency selective
channel.
A two-group resource allocation scheme is developed in order to achieve a
promising balance between performance enhancement and time efficiency. It only
requires calculating two parameters to specify the allocations of discrete bit rates
and transmitted symbol energies in all channels. The thesis develops the calculation
methods of the two parameters for interference-free and interference-present
channels, respectively. For the interference-present channels, the performance of
two-group allocation can be further enhanced by applying a clustering-based channel
removal scheme.
In order to make the two-group approach more time-efficient, reduction in
matrix inversions in optimum energy calculation is then discussed. When the
Minimum Mean Square Error (MMSE) equalizer is applied, optimum energy allocation
can be calculated by iterating a set of eigenvalues and eigenvectors. By
using the MMSE Successive Interference Cancellation (SIC) receiver, the optimum
energies are calculated recursively combined with an optimum channel ordering
scheme for enhancement in both system performance and time efficiency.
This thesis then studies the signature optimization methods with multipath
channel and examines their system performances when combined with different
resource allocation methods. Two multipath-aware signature optimization methods
are developed by applying iterative optimization techniques, for the system
using MMSE equalizer and MMSE precoder respectively. A PAM system using
complex signature sequences is also examined for improving resource utilization
efficiency, where two receiving schemes are proposed to fully take advantage of
PAM features. In addition by applying a short chip sampling window, a Singular
Value Decomposition (SVD) based interference-free signature design method is
presented
Cyclic Prefix-Free MC-CDMA Arrayed MIMO Communication Systems
The objective of this thesis is to investigate MC-CDMA MIMO systems where
the antenna array geometry is taken into consideration. In most MC-CDMA
systems, cyclic pre xes, which reduce the spectral e¢ ciency, are used. In order
to improve the spectral efficiency, this research study is focused on cyclic pre x-
free MC-CDMA MIMO architectures.
Initially, space-time wireless channel models are developed by considering the
spatio-temporal mechanisms of the radio channel, such as multipath propaga-
tion. The spatio-temporal channel models are based on the concept of the array
manifold vector, which enables the parametric modelling of the channel.
The array manifold vector is extended to the multi-carrier space-time array
(MC-STAR) manifold matrix which enables the use of spatio-temporal signal
processing techniques. Based on the modelling, a new cyclic pre x-free MC-
CDMA arrayed MIMO communication system is proposed and its performance
is compared with a representative existing system. Furthermore, a MUSIC-type
algorithm is then developed for the estimation of the channel parameters of the
received signal.
This proposed cyclic pre x-free MC-CDMA arrayed MIMO system is then
extended to consider the effects of spatial diffusion in the wireless channel. Spatial
diffusion is an important channel impairment which is often ignored and the
failure to consider such effects leads to less than satisfactory performance. A
subspace-based approach is proposed for the estimation of the channel parameters
and spatial spread and reception of the desired signal.
Finally, the problem of joint optimization of the transmit and receive beam-
forming weights in the downlink of a cyclic pre x-free MC-CDMA arrayed MIMO
communication system is investigated. A subcarrier-cooperative approach is used
for the transmit beamforming so that there is greater flexibility in the allocation
of channel symbols. The resulting optimization problem, with a per-antenna
transmit power constraint, is solved by the Lagrange multiplier method and an
iterative algorithm is proposed
Transmitter precoding for multi-antenna multi-user communications
Emerging wireless sensor networks and existing wireless cellular and ad hoc networks motivate the design of low-power receivers. Multi-user interference drastically reduces the energy efficiency of wireless multi-user communications by introducing errors in the bits being detected at the receiver. Interference rejection algorithms and multiple antenna techniques can significantly reduce the bit-error-rate at the receiver. Unfortunately, while interference rejection algorithms burden the receiver with heavy signal processing functionalities, thereby increasing the power consumption at the receiver, the small size of receivers, specifically in sensor networks and in downlink cellular communications, prohibits the use of multiple receive antennas. In a broadcast channel, where a central transmitter is transmitting independent streams to decentralized receivers, it is possible for the transmitter to have a priori knowledge of the interference. Multiple antennas can be used at the transmitter to enhance energy efficiency. In some systems, the transmitter has access to virtually an infinite source of power. A typical example would be the base station transmitter for the downlink of a cellular system. The power consumption at receivers can be reduced if some of the signal processing functionality of the receiver is moved to the transmitter.;In this thesis, we consider a wireless broadcast channel with a transmitter equipped with multiple antennas and having a priori knowledge of interference. Our objective is to minimize the receiver complexity by adding extra signal processing functions to the transmitter. We need to determine the optimal signal that should be transmitted so that interference is completely eliminated, and the benefits that can be obtained by using multiple transmit antennas can be maximized. We investigate the use of linear precoders, linear transformations made on the signal before transmission, for this purpose
A Novel Channel Estimation Technique in MIMO-OFDM Mobile Communication Systems
4G Wireless communication systems have the inherent capability to foster the multimedia services in terms of bandwidth and data rate. These systems have very high integrity compared to the conventional wireless communication systems. It can fully support extended multimedia services with High Definition quality, audio and video files. Wireless internet and other broad band services provided superior quality signal transmission and reception. The degree of freedom enjoyed by the technology in terms of scalability and reliability is highly commendable. Any basic wireless transmitter sends information by varying the phase of the signal. In the receiver end, the desired signal can be decoded by appropriate decoding algorithm. The degradation occurs at the conventional receivers due to lack of Channel State Information. The efficiency of 4G system purely relies on the performance of receiver and is purely dependent on the synchronization of estimated instantaneous channel. In any wireless terminal, channel state information provides the in and around status of the channel. It provides the following parameters of the propagating signal (ie) Scattering, Fading and Attenuation. The dynamic estimation of channel state information can be obtained through Enhanced Least Squares channel estimation algorithm. It is based on Multi Carrier Filter Bank Transmission system. This kind of dynamic estimation can be done with a set of well-known sequence of coded unique bits .For a transmitter the information propagation is initiated in the form of frame bursts. It enhances the throughput of the system to the required level
Energy Efficient Communications in MIMO Wireless Channels: Information Theoretical Limits
ISBN : 978-1466501072This chapter is focused on defining and optimizing an energy-efficiency metric for MIMO systems. This metric, which expresses in bit per Joule, allows one to measure how much information is effectively transferred to the transmitter per unit cost of energy consumed at the transmitter. For a MIMO point-to-point communication (single user MIMO channels) this metric can be useful to determine what power level, precoding scheme, training length, or number of antennas have to be used for obtaining the maximum information that is effectively transferred per unit energy spent. Then, we move from a physical layer-type approach to a cross-layer design of energy-efficient power control by including the effects a queue with finite size at the transmitter. As a last step we study a distributed multiple user scenario (MIMO multiple access channels) where each user selfishly maximizes its energy-efficiency by choosing its best individual power allocation policy. Here, we present the most relevant results in this field in a concise and comprehensible manner
Transmitter based techniques for ISI and MAI mitigation in CDMA-TDD downlink
The third-generation (3G) of mobile communications systems aim to provide enhanced voice,
text and data services to the user. These demands give rise to the complexity and power consumption
of the user equipment (UE) while the objective is smaller, lighter and power efficient
mobiles. This thesis aims to examine ways of reducing the UE receiver’s computational cost
while maintaining a good performance.
One prominent multiple access scheme selected for 3G is code division multiple access. Receiver
based multiuser detection techniques that utilise the knowledge of the downlink channel
by the mobile have been extensively studied in the literature, in order to deal with multiple
access and intersymbol interference. However, these techniques result in high mobile receiver
complexity.
Recently, work has been done on algorithms that transfer the complexity from the UE to the
base station by exploiting the fact that in time division duplex mode the downlink channel can
be known to the transmitter. By linear precoding of the transmitted signal the user equipment
can be simplified to a filter matched to the user’s spreading code. In this thesis the problem
of generic linear precoding is analysed theoretically and a method for analytical calculation
of BER is developed. The most representative of the developed precoding techniques are described
under a common framework, compared and classified as bitwise or blockwise. Bitwise
demonstrate particular advantages in terms of complexity and implementation but lack in performance.
Two novel bitwise algorithms are presented and analysed. They outperform significantly
the existing ones, while maintain a reduced computational cost and realisation simplicity.
The first, named inverse filters, is the Wiener solution of the problem after applying a minimum
mean squared error criterion with power constraints. The second recruits multichannel adaptive
algorithms to achieve the same goal. The base station emulates the actual system in a cell
to converge iteratively to the pre-filters that precode the transmitted signals before transmission.
The advantages and the performance of the proposed techniques, along with a variety of
characteristics are demonstrated by means of Monte Carlo simulations
Transmitter adaptation for CDMA systems.
Kwan Ho-yuet.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.Includes bibliographical references (leaves 84-[87]).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- An Overview on Transmitter Optimization --- p.1Chapter 1.1.1 --- Transmitter Precoding Methods --- p.2Chapter 1.1.2 --- Chip Waveform Optimization --- p.3Chapter 1.1.3 --- Signature Sequence Adaptation --- p.3Chapter 1.2 --- Receiver Optimization --- p.5Chapter 1.3 --- Nonlinear Optimization with Constraints --- p.6Chapter 1.3.1 --- Lagrange Multiplier Methods --- p.6Chapter 1.3.2 --- Penalty Function Methods --- p.7Chapter 1.4 --- Outline of Thesis --- p.8Chapter 2 --- Transmitter Adaptation Scheme for AWGN Channels --- p.10Chapter 2.1 --- Introduction --- p.10Chapter 2.2 --- System Model --- p.12Chapter 2.3 --- Adaptation Algorithm --- p.13Chapter 2.3.1 --- Receiver optimization --- p.14Chapter 2.3.2 --- Single-user transmitter optimization --- p.18Chapter 2.3.3 --- Decentralized transmission scheme --- p.20Chapter 2.4 --- Modification of the sequence adaptation algorithm --- p.25Chapter 2.5 --- Performance Evaluation --- p.28Chapter 2.5.1 --- Performance of the decentralized scheme --- p.28Chapter 2.5.2 --- System Capacity with Target SNR Constraints --- p.29Chapter 2.5.3 --- Performance of modified sequences --- p.31Chapter 2.6 --- Summary --- p.33Chapter 3 --- Transmitter Adaptation Schemes for Rayleigh Fading Channels --- p.34Chapter 3.1 --- Introduction --- p.34Chapter 3.2 --- Sequence Adaptation for MC-CDMA Systems --- p.36Chapter 3.2.1 --- Multi-sequence MC-CDMA systems --- p.36Chapter 3.2.2 --- Single Sequence MC-CDMA systems --- p.41Chapter 3.2.3 --- Performance Evaluation --- p.45Chapter 3.3 --- Sequence Adaptation for Wideband CDMA System in Fading Channels --- p.50Chapter 3.3.1 --- System Model and Algorithm Development --- p.50Chapter 3.3.2 --- Performance Evaluation --- p.56Chapter 3.4 --- Summary --- p.60Chapter 4 --- Practical Issues on Sequence Adaptation --- p.61Chapter 4.1 --- Introduction --- p.61Chapter 4.2 --- Preliminary --- p.62Chapter 4.3 --- Sequence Adaptation Algorithm with Perfect Estimation of SNR --- p.63Chapter 4.4 --- Performance Evaluation --- p.68Chapter 4.4.1 --- Typical Behaviour Analysis --- p.71Chapter 4.4.2 --- Average Performance Analysis --- p.72Chapter 4.5 --- Sequence Adaptation Algorithm with imperfect estimation of pre- vious state SNR --- p.75Chapter 4.6 --- Performance Evaluation --- p.77Chapter 4.7 --- Summary --- p.79Chapter 5 --- Conclusions and Future Works --- p.81Chapter 5.1 --- Conclusions --- p.81Chapter 5.2 --- Future Works --- p.83Bibliography --- p.8
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