New Modified Turbo Decoder for Embedded Local Content in Single-Frequency Networks

Current DVB-SH systems rely on hierarchical modulation to insert local content into the complementary ground component. The local content is inserted as a low priority bit stream, while the global content will be transmitted as a high-priority bit stream. At the receiver, the standard approach of extracting the local content from the received signal first requires detection of the global content. Subsequently, one can extract the local content by subtracting the coded and modulated form (restored version) of the detected global content from the received signal. In this paper, we propose a different approach to remove the global content from the received signal. In our new approach, a hybrid signal is designed to represent the turbo-coded global content, which contains decoded bits from the turbo decoder representing systematic bits, and detected bits from the received signal prior to the turbo decoder representing parity bits. This technique would relieve the receiver from performing coding and modulation on the detected global content so as to ensure a less computational burden and a smaller latency than the current technology. The obvious tradeoff between complexity and performance would imply higher bit error rates arising from our proposed system. Therefore, to mitigate the bit-error-rate performance degradation, we propose modifying the turbo decoder so that the systematic bit streams and the parity bit streams will be decoded differently with respect to their corresponding signal-to-noise ratios. Monte Carlo simulation results demonstrate that our proposed new scheme can achieve better computational efficiency and less latency in the slight sacrifice of error performance.