\gls{HARQ} schemes are employed in mobile communication systems to reduce the residual Frame Error Rate (FER) after channel decoding. If decoding fails, the receiver requests the transmission of additional redundancy about these frames to improve the decoding success. Signaling is carried out over a feedback link from the receiver back to the transmitter. However, errors on the feedback link severely influence the behavior of the HARQ system and may degrade the overall system performance. In this contribution, the impact of HARQ signaling errors on the FER, the average number of HARQ transmissions per frame, and the system throughput is investigated. We derive analytical expressions for all performance measures based on FER simulations of the HARQ system with reliable feedback. The theoretical results are verified by the example of the LTE physical layer, however, they are also applicable to other communication systems. Moreover, target requirements for the maximum tolerable feedback error probabilities are derived which are used to develop design guidelines for HARQ feedback transceivers.

Mobile communication systems as, e.g, UMTS LTE perform rate matching and Hybrid Automatic Repeat reQuest (HARQ) to provide adequate decoding performance over a wide range of channel conditions. In UMTS LTE this is realized by means of a fixed rate convolutional Turbo code and a rate matching scheme based on bit puncturing and bit repetition. A promising alternative to convolutional Turbo codes with simple bit repetition are Rate-Compatible Insertion Convolutional (RCIC) Turbo codes which have proven considerable performance gains in systems without HARQ. Since modern systems conventionally employ HARQ, a novel HARQ scheme for UMTS LTE based on RCIC Turbo codes is presented in this paper. Extensive simulations have demonstrated that the conventional UMTS LTE HARQ scheme is outperformed by our novel HARQ scheme in terms of system throughput.

In this paper, the impact of HARQ signaling errors caused by unreliable feedback on the throughput of communication systems like UMTS LTE is investigated. We derive analytical expressions for the calculation of the average number of transmissions per data frame as well as the system throughput based on a general feedback channel model. In combination with the residual frame error rates (FERs) after channel decoding, measured for a system with error-free feedback, a semi-analytical evaluation of the influence of unreliable feedback information on the system throughput can be carried out for any feedback channel condition. Consequently, time-consuming simulations of the respective system with unreliable feedback can be avoided. The theoretical results are verified by extensive simulations of the UMTS LTE physical layer. They are also applicable to other communication systems.

We propose the combination of orthogonal frequency division multiplexing (OFDM) and turbo decodulation (TDeC) - a multiple turbo process consisting of iterative demodulation and iterative source-channel decoding - for transmission of correlated source codec parameters over wireless frequency-selective broadband fading channels. As OFDM systems split up frequency-selective fading channels into orthogonal flat-fading channels, individual modulation signal constellations sets with different bit mapping rules can be assigned to subcarriers taking into account the iterative reception and decoding process. The superior performance of the proposed OFDM-TDeC system is demonstrated by analyzing the achieved residual bit error rate (BER) and parameter signal-to-noise ratio (SNR).