Modified turbo decoder for local content in single-frequency networks

DVB-SH systems rely on hierarchical modulation to insert local content in the complementary ground component. The local content is inserted as a low priority (LP) bit stream, while the global content will be transmitted as a high-priority (HP) bit stream. At the receiver, the standard approach of extracting the local content from the received signal requires to detect the global content first. Henceforth, one can remove the global content by subtracting the coded and modulated signal of the detected stream from the received signal. In this paper, we propose and investigate a different approach of removing the global content from the received signal. In our new approach, a hybrid signal is designed, which contains (i) detected bits from the turbo decoder as systematic bits, and (ii) detected bits from the received signal prior to the turbo decoder as parity bits. This technique would relieve the receiver from performing coding and modulation on the detected global content so as to ensure less computational burden and a smaller latency than the current technology. The obvious tradeoff between complexity and performance would imply high bit error rates. Therefore, to mitigate the bit-error-rate performance degradation, we propose to modify 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 less computational complexity and latency in the slight sacrifice of error performance.