An Approach to Using Amplitude Probability Distribution for Emission Limits to Protect Digital Radio Receivers Using Error-Correction Codes

New emission limits are needed to protect digital communication systems from radiated interference. Current standard emission limits were developed to protect amplitude- and frequency-modulated analog radio services. However, developments in digital technology require emission limits adapted to protect digital radio communication services. An approach to define emission limits on the amplitude probability distribution (APD) of the envelope of an interference source has been presented earlier. This approach is derived for coherent radio receivers utilizing no error-correction codes. However, since the most important digital radio systems today use error correction, it is necessary to develop the method to handle coded systems as well. This paper proposes a method to define emission limits on the APD of the interference to protect coded communication systems. The method is a further development of previously proposed emission limits derived for an uncoded system, which is modified in accordance with the coding gain.

I. Introduction

Developments within digital radio communications require new radiated emission limit requirements on interference sources to be established. Communication systems today are digital and use error-correction coding. The present emission limits were developed to protect amplitude- and frequency-modulated analog radio signals. These limits are defined as the maximum allowed level of the measured quasi-peak value of the radiated emissions from the interference source. However, the levels measured by the quasi-peak detector are not correlated to the impact of an interference source on a digital radio system. The quasi-peak detector was originally developed to simulate the human perception of electromagnetic interference on amplitude-modulated analog radio signals [1]. Hence, there is a great need for new emission limits [2]. Work on this matter is in progress within the Special Committee on Radio Interference (CISPR) [3]. Two alternative measurement methods have been discussed: the rms-average (rms-AVG) detector and the amplitude probability distribution (APD) measurement function [4].