Analysis of Coding Sequences For Frequency Hop Spread Spectrum

Student: Kian Wei Lee

Supervisor: John Homer

Category: Engineering Thesis Project - Communications

Interference in a wireless radio communication channel has always been a major concern to participating users. Increased traffic within a limited transmission bandwidth degrades the quality of communication severely. Frequency hop spread spectrum (FH-SS) technique is employed to combat interference and to allow simultaneous users to share the finite radio spectrum without interfering with one another significantly.

Bluetooth uses FH-SS for operation in the ISM band (2400 to 2483.5MHz). Devices operating within a Bluetooth piconet will not interfere with one another due to the uniqueness of the hopping sequence used for communication. However, the transmitted signal of a device is subjected to multipath interference where packets of the original sequence can collide with the delayed versions. When two or more piconets operate in close proximity, multiple-access interference is introduced. Packets transmitted from undesired piconets can collide with the packets in an existing piconet. These hop packet collisions can be reduced by proper design of frequency hop sequences.

This thesis is divided into two main parts. Firstly, hop sequences used in Bluetooth communication is analyzed and simulated using MATLAB to obtain the corresponding autocorrelation and cross-correlation characteristics. Secondly, the use of concatenated prime codes to construct hop sequences is analyzed in detail. The design of hop sequences using such codes is simulated to obtain the corresponding autocorrelation and cross-correlation characteristics. A comprehensive analysis on the correlation properties relating to both Bluetooth and concatenated prime code sequences is studied. Different channel frequencies were simulated for both types of sequences to conduct a more accurate comparison. Results show that concatenated prime code sequences generally have lower probability and percentage of hop collisions. However this type of coding sequence also have its disadvantages, despite having shorter computation time and being able to be implemented at a low cost.

Thesis Document (PDF)

Poster Presentation (PDF)