a low power HF communication system

Abstract

The HF band of radio frequencies, from 3-30 MHz, is unique in its property that itis refracted by the ionosphere. This property allows long distance radio telecommunicationsaround the world without requiring infrastructure. High frequency (HF)communication has been largely superseded by satellite and cellular technologiesfor day-to-day communications, due to the tight bandwidth constraints and technicaldifficulties inherent in using it. However there is still a need for HF communicationsdevices where existing infrastructure is not available, such as in remote or polar locations,or in emergency situations due to natural disasters.This research is aimed at the development of an asymmetric HF communicationslink, with a battery-powered remote unit that transmits a small amount of data to amains-powered base station. New technologies are identified and evaluated for usein the link, with the aim of reducing the power requirements of the remote unit.Error correction techniques are investigated. Low-density parity check (LDPC) codes,which are powerful codes used for forward error correction, are suggested for usein the link. Quasi-cyclic LDPC codes allow the low-power transmitter unit to use acomputationally simple encoder based on feedback shift registers for generating theLDPC block codes cheaply. Semi-blind LDPC turbo equalisation is a powerful techniquethat can be used at the base station which utilises the structure of the LDPCcode to encode the data stream. This equalises a received signal with a minimalamount of training data required, reducing the duty cycle of the remote unit. Hybridautomatic repeat request (HARQ) techniques are also investigated, which increasethe throughput of a link when data repeats are required. A novel HARQ techniquewas created and proven to increase throughput in links with noise.As the proposed system may be deployed in remote locations, or locations where itmight be difficult or undesirable to erect a proper HF antenna, a selection of buriedantennas are characterised.A design for a remote unit is suggested. This unit was manufactured and used totest the capability of inexpensive, low power hardware to implement the proposedremote unit algorithms.

Date of Award	27 Jan 2012
Original language	English
Awarding Institution	The University of Manchester