Title page for ETD etd-01242006-083415


Document Type Master's Dissertation
Author Marx, Frans Engelbertius
Email fmarx@worldonline.co.za
URN etd-01242006-083415
Document Title DSSS Communication Link Employing Complex Spreading Sequences
Degree MEng (Electronic Engineering)
Department Electrical, Electronic and Computer Engineering
Supervisor
Advisor Name Title
Prof L P Linde
Keywords
  • Multi-Dimensional Direct Sequence Spread Spectrum
  • Families of Complex
Date 2005-08-26
Availability unrestricted
Abstract
The present explosion in digital communications and multi-user wireless cellular networks has urged

a demand for more effective modulation methods, utilizing the available frequency spectrum more

efficiently. To accommodate a large number of users sharing the same available frequency band,

one requirement is the availability of large families of spreading sequences with excellent AC and

CC properties. Another requirement is the availability of sets of orthogonal basis functions to

extend capacity by exploiting all available degrees of freedom (e.g., temporal, frequency and spatial

dimesions), or by employing orthogonal multi-code operation in parallel, such as used in the latest

3GPP and 3GPP2 Wide-band Code Division Multiple Access (WCDMA) modulation standards

by employing sets of orthogonal Walsh codes to improve the overall data throughput capacity.

The generic Direct Sequence Spread Spectrum (DSSS) transmitter developed in this dissertation

has originally been designed and implemented to investigate the practicality and usefulness of

complex spreading sequences, and secondly, to verify the concept of non-linearly interpolated

root-of-unity (NLI-RU) filtering. It was found that both concepts have a large potential for application

in point-to-point, and particularly micro-cellular Wireless Local Area Networks (WLANs) and

Wireless-Local-Loop (WLL) environments. Since then, several novel concepts and subsystems have

been added to the original system, some of which have been patented both locally and abroad, and are

outlined below. Consequently, the ultimate goal of this research project was to apply the principles

of the generic DSSS transmitter and receiver developed in this study in the implementation of a

WLL radio-frequency (RF)-link, and particularly towards the establishment of affordable wireless

multimedia services in rural areas. The extended coverage at exceptionally low power emission

levels offered by the new design will be particularly useful in rural applications. The proposed

WLL concept can for example also be utilized to add a unique mobility feature to for example

existing Private Automatic Branch Exchanges (PABXs). The proposed system will in addition

offer superior teletraffic capacity compared to existing micro-cellular technologies, e.g., the Digital

European Cordless Telephony (DECT) system, which has been consider by Telkom for employment

in rural areas. The latter is a rather outdated interim standard offering much lower spectral efficiency

and capacity than competitive CDMA-solutions, such as the concept analyzed in this dissertation,

which is based on the use of unique large families of spectrally well confined (i.e., band-limited)

constant envelope (CE) complex spreading sequences (CSS) with superior correlation properties. The

CE characteristic of the new spreading sequences furthermore facilitates the design of systems with

superior power efficiency and exceptionally robust performance characteristics (much less spectral

re-growth) compared to existing 2G and 3G modulation standards, in the presence of non-linear power

amplification. This feature allows for a system with larger coverage for a given performance level and

limited peak power, or alternatively, longer battery life for a given maximum communication distance

and performance level, within a specified fixed spreading bandwidth. In addition, the possibility to

extend the concept to orthogonal multi-code operation provides for comparable capacity to present

3G modulation standards, while still preserving superior power efficiency characteristics in non-linear

power amplification. Conventional spread spectrum communication systems employ binary spreading

sequences, such as Gold or Kasami sequences. The practical implementation of such a system

is relatively simple. The design and implementation of a spread-spectrum communication system

employing complex spreading sequences is however considerable more complex and has not been

previously presented, nor been implemented in hardware. The design of appropriate code lock loops

for CSS has led to a unique design with 3dB performance advantage compared to similar loops

designed for binary spreading sequences. The theoretical analysis and simulation of such a system

will be presented, with the primary focus on an efficient hardware implementation of all new concepts

proposed, in the form of a WLL RF-link demonstrator.

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  00front.pdf 540.52 Kb 00:02:30 00:01:17 00:01:07 00:00:33 00:00:02
  01part1.pdf 115.77 Kb 00:00:32 00:00:16 00:00:14 00:00:07 < 00:00:01
  02part2.pdf 795.40 Kb 00:03:40 00:01:53 00:01:39 00:00:49 00:00:04
  03part3.pdf 645.71 Kb 00:02:59 00:01:32 00:01:20 00:00:40 00:00:03
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  05part5.pdf 769.83 Kb 00:03:33 00:01:49 00:01:36 00:00:48 00:00:04
  06back.pdf 436.40 Kb 00:02:01 00:01:02 00:00:54 00:00:27 00:00:02

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