Spelling suggestions: "subject:"5ource/ehannel coding"" "subject:"5ource/achannel coding""
51 |
Utilizing Channel State Information for Enhancement of Wireless Communication SystemsHeidari, Abdorreza January 2007 (has links)
One of the fundamental limitations of mobile radio
communications is their time-varying fading channel. This
thesis addresses the efficient use of channel state information
to improve the communication systems, with a particular
emphasis on practical issues such as compatibility with the
existing wireless systems and low complexity implementation.
The closed-loop transmit diversity technique is used to improve
the performance of the downlink channel in MIMO communication
systems. For example, the WCDMA standard endorsed by 3GPP
adopts a mode of downlink closed-loop scheme based on partial
channel state information known as mode 1 of
3GPP. Channel state information is fed back
from the mobile unit to the base station through a low-rate
uncoded feedback bit stream. In these closed-loop systems,
feedback error and feedback delay, as well as the sub-optimum
reconstruction of the quantized feedback data, are the usual
sources of deficiency.
In this thesis, we address the efficient reconstruction of the
beamforming weights in the presence of the feedback
imperfections, by exploiting the residual redundancies in the
feedback stream. We propose a number of algorithms for
reconstruction of beamforming weights at the base-station, with
the constraint of a constant transmit power. The issue of the
decoding at the receiver is also addressed. In one of the
proposed algorithms, channel fading prediction is utilized to
combat the feedback delay. We introduce the concept of Blind
Antenna Verification which can substitute the conventional
Antenna Weight Verification process without the need for any
training data. The closed-loop mode 1 of 3GPP is used as a
benchmark, and the performance is examined within a WCDMA
simulation framework. It is demonstrated that the proposed
algorithms have substantial gain over the conventional method
at all mobile speeds, and are suitable for the implementation
in practice. The proposed approach is applicable to other
closed-loop schemes as well.
The problem of (long-range) prediction of the fading channel is
also considered, which is a key element for many
fading-compensation techniques. A linear approach, usually used
to model the time evolution of the fading process, does not
perform well for long-range prediction applications. We propose
an adaptive algorithm using a state-space approach for the
fading process based on the sum-sinusoidal model. Also to
enhance the widely-used linear approach, we propose a tracking
method for a multi-step linear predictor. Comparing the two
methods in our simulations shows that the proposed algorithm
significantly outperforms the linear method, for both
stationary and non-stationary fading processes, especially for
long-range predictions. The robust structure, as well as the
reasonable computational complexity, makes the proposed
algorithm appealing for practical applications.
|
52 |
Joint Source-Channel Coding Reliability Function for Single and Multi-Terminal Communication SystemsZhong, Yangfan 15 May 2008 (has links)
Traditionally, source coding (data compression) and channel coding (error protection) are performed separately and sequentially, resulting in what we call a tandem (separate) coding system. In
practical implementations, however, tandem coding might involve a large delay and a high coding/decoding complexity, since one needs to remove the redundancy in the source coding part and then insert certain redundancy in the channel coding part. On the other hand, joint source-channel coding (JSCC), which coordinates source and channel coding or combines them into a single step, may offer substantial improvements over the tandem coding approach.
This thesis deals with the fundamental Shannon-theoretic limits for a variety of communication systems via JSCC. More specifically, we investigate the reliability function (which is the largest rate at which the coding probability of error vanishes exponentially with
increasing blocklength) for JSCC for the following discrete-time communication systems: (i) discrete memoryless systems; (ii) discrete memoryless systems with perfect channel feedback; (iii) discrete memoryless systems with source side information; (iv) discrete systems with Markovian memory; (v) continuous-valued
(particularly Gaussian) memoryless systems; (vi) discrete asymmetric 2-user source-channel systems.
For the above systems, we establish upper and lower bounds for the JSCC reliability function and we analytically compute these bounds. The conditions for which the upper and lower bounds coincide are also provided. We show that the conditions are satisfied for a large class of source-channel systems, and hence exactly determine the reliability function. We next provide a systematic comparison between the JSCC reliability function and the tandem coding reliability function (the reliability function resulting from separate source and channel coding). We show that the JSCC reliability function is substantially larger than the tandem coding
reliability function for most cases. In particular, the JSCC reliability function is close to twice as large as the tandem coding reliability function for many source-channel pairs. This exponent gain provides a theoretical underpinning and justification for JSCC design as opposed to the widely used tandem coding method, since
JSCC will yield a faster exponential rate of decay for the system error probability and thus provides substantial reductions in
complexity and coding/decoding delay for real-world communication systems. / Thesis (Ph.D, Mathematics & Statistics) -- Queen's University, 2008-05-13 22:31:56.425
|
Page generated in 0.0747 seconds