Transmitter precoding and code-sharing techniques using block transmission system
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Date
2009
Authors
Nayef Khatib, Mutamed Turki
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Abstract
Recently, mobile communications services are penetrating into our society at an
explosive growth rate. All of the current cellular communication systems have
adopted digital technology. Nowadays, the demands for various wideband services
such as high-speed Internet access and video/high-quality image transmission, is
increasing. The third-generation mobile communication system has been designed to
support wideband services with the same quality as the fixed networks. The wireless
communications systems are expected to play more roles in providing portable
access to future information services. The demand for new services to support
Internet and advanced video applications presents key technical challenges, i.e.,
multimedia access requires high-bandwidth and low-latency network connections to
many users, mobility requires adaptation to time varying channel conditions and
portability imposes severe constraints on receiver size and power consumption.
Physical limitations on wireless channels impose huge challenges to reliable
communication. Bandwidth limitations, propagation loss, noise and interference
make the wireless channel a narrow pipe that does not readily accommodate rapid
flow of data. Thus, researches aim to design systems that are suitable to operate in
such channels, in order to have high performance quality of service. Also, The
mobility of the communication systems require further investigations to reduce the
complexity and the power consumption of the receiver.
This thesis presents new techniques that improve the performance of the
communication system used for transmission of digital data over time varying
channels such as high frequency mobile channels. All the techniques described
through this thesis are classified as block transmission systems, which are type of
linear equalization to minimize the effect of intersymbol interference (ISI). The data
are transmitted in the form of blocks of data symbols. Successive blocks of data are
separated either by blocks of training signals or blocks of no signal. Transmission of
data signals in blocks considerably reduces the complexity of the receiver and also
helps in reducing error propagation effects. The appropriate length of each data block
depends on the channel parameters expected and the allowed complexity.
The first system described in this thesis is the precoding system. This system aims to
reduce the complexity of the receiver by moving the equalization which usually done
in the receiver to the transmitter. No other processing is needed at the receiver except
a threshold testing. On the other hand, this precoding technique results in a 2 dB
enhancement in the system performance in comparison with the normal Block Linear
Equalizer (BLE) where all the equalization is done at the receiver.
In the second system, a sharing strategy was applied on the precoding system in
order to increase the performance of the system. The equalization is divided so that
75% of the process is done at the transmitter, while 25% is completed at the receiver.
This makes the system more immune toward additive noise, and results in 2 dB
enhancement more than the precoder, and 4 dB more than BLE. Because of the extra
guard band in the transmitted block, it is named sharing system with guard band.
The third system is the sharing system without guardband. It is also depends on the
idea of dividing the equalization process between the transmitter and the receiver, but
it is applied on the BLE. The sharing ratio is 25% at the transmitter, and 75% at the
receiver. There is no extra guard bands in this system, so, it needs less bandwidth in
comparison with the precoding and the other sharing system. The bit error rate
performance of this system is the same as the precoding system.
Description
PhD
Keywords
Electrical engineering , Transmitter precoding , Code-sharing techniques , Block transmission system