On the Interaction Between Joint Tx/Rx IQI and Channel Estimation Errors in DVB-T Systems

Digital video broadcasting terrestrial (DVB-T) systems use hierarchical modulation, which involve a “high-priority” and a “low-priority” (LP) bit stream. An inherent weakness of this scheme is the severe performance degradation of the less protected LP stream. In addition, the presence of inphase quadrature imbalance (IQI) at both transmitter/receiver front end may significantly reduce the detection accuracy. Here, we propose an improved receiver design for OFDM-based DVB-T systems confronting the effects of both imperfect channel estimation and IQI. First, we propose a specific pilot-symbol arrangement inside the OFDM symbol that facilitates derivation of the posterior distribution of the perfect channel conditioned on its maximum-likelihood (ML) estimate. The latter posterior distribution plays an important role toward an improved receiver design for taking into account channel estimation errors in the presence of IQI at the receiver side. Second, we derive the formulation of an improved and efficient detector under channel estimation errors when IQI is also present only at the receiver side. Third, we generalize our proposed improved detector for the case where IQI is present at both transmitter and receiver sides. The proposed approach is able to reduce the impact of channel uncertainty on the receiver's performance in the presence of IQI. Our results are compared to those achieved by the conventional mismatched ML detector, which uses the imperfect channel as perfect channel and to those obtained by the detector based on the expectation-maximization algorithm. Numerical results over a realistic COST 207 channel model show that significant performance improvement is achieved for bit error rate of the LP stream in the considered DVB-T system.