Adaptive error correction scheme for chirp spread spectrum wireless link

Project team

Victor Malishev, professor
Boris Lavrenko, postgraduate student
Anastasja Lavrenko, postgraduate student
Saint-Petersburg State Electrotechnical University

Introduction

Currently, a great number of various approaches to provide error-free transmission in modern communication systems were designed. The error correction algorithms differ both in implementation complexity and in efficiency, trying their best to correct a transmission error and to increase the throughput of a data link operating in a noisy environment.

When the channel introduces predominately random bit errors, convolutional codes provide a good solution. In burst-error channels, Reed-Solomon codes are among the best codes because errors composed of many consecutive corrupted bits translate into only a few erroneous symbols.

Evaluating adaptive error correction scheme in wireless environments is challenging because repeatable experiments are difficult: urban wireless environment cannot easily be isolated and propagation conditions vary quickly. Rigid error control policies can perform very poorly, because they either introduce too much overhead in “good” environments or are not aggressive enough in “bad” environments.

This project is aimed to carry out the choice and investigation of adaptive error correction scheme for short range wireless data transmission system. It is supposed to research the efficiency of adaptive error control policies in subject to the varying propagation and channel noise, typical for urban and industrial environment.

Implementation of short range (100…1000 meters) wireless link is based on chirp spread spectrum signals in 2.4 GHz ISM band with 60…80 MHz bandwidth. The throughput of a data link is about 500 megabit per second; packet length varies from 64 to 256 byte. Computational power “on board” is strictly limited. However, off-line error correction pre- and post processing is acceptable for some applications. Preliminary experiments in urban and industrial environment shows relatively low random bit error rate and remarkable packet loss rate, demanding development of adaptive error correction scheme with interleaving.

Project stages

The choice of coding scheme and parameters is inseparably connected with adverse propagation conditions. So, the mathematical simulation of coding schemes performance on the assumption of applying of several error models is considered as initial stage of the research. The error models corresponded as varying proportion of the burst and random bit errors is of the main interest of this study. But in spite of being known the common error distribution, constructing the adequate model provided to be a quite complicated task. Thereby it is required to accumulate and review some statistics of the most typical urban noise sources in the field experiments.

The software implementation of selected algorithm supposed to be a consecutive stage. As computational power of examined system is also constrained, such realization should be inspected for computational complexity on each development step.

To make this study complete it is intended to test the system in real working conditions.

Targets

The main purpose of this project is to work out the adaptive error correction scheme for wireless data transmission system that will be robust to variations of radio wave propagation and interference in case of urban or industrial environment.