A Differential Detection Technique for Local Services in DAB Single Frequency Networks

Digital Audio Broadcasting (DAB) is a widely used terrestrial audio broadcast transmission system. DAB employs Orthogonal Frequency-Division Multiplexing which allows the operation in a Single Frequency Network (SFN). SFNs are beneficial for the distribution of services in large areas, but do not support local services, i.e. different services from different transmitters, without distortion. However, some audio service providers rely on local services. A Local Service Insertion technique for DAB SFNs that supports existing receivers was developed, tested and presented in a field trial in Braunschweig, Germany. The results showed some co-channel interference between local services for existing receivers that use conventional differential detection (CDD). In this paper, we investigate an iterative decision-directed differential detection technique with channel equalization to combat the remaining co-channel interference. An increase in robustness against co-channel interference of about 3 dB is found in comparison to CDD.

I. Introduction

Digital Audio Broadcasting (DAB) is a digital terrestrial audio broadcast standard [1] that is being deployed in a number of countries around the world to deliver digital audio and data to fixed, portable, and mobile receivers. A key aspect in the development was the focus on the efficient use of spectrum. Therefore, Orthogonal Frequency-Division Multiplexing (OFDM) was chosen as it allows for Single Frequency Networks (SFNs). An SFN contains multiple transmitters that send identical signals synchronized in time and frequency. The signals from different transmitters are mutually supportive and result in an SFN gain [2]. Thus, SFNs are well suited for network-wide global services. In contrast, local services intended for parts of the network will waste network capacity in SFNs. Therefore, it might be useful to distribute local services in multi-frequency networks (MFNs) which cover the intended regions separately. Unfortunately, MFNs require a significant amount of valuable frequency spectrum, require higher power as they lack the SFN gain, and for systems like DAB/DAB+ a complete multiplex with multiple services needs to be filled for commercial reasons.