Novel Layer-2 transmission strategies for 5G systems

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In this project, one of the major issues related to the interaction between Layer 1 and Layer 2 of communication systems will be addressed. In particular, new strategies relating hybrid ARQ (HARQ) and adaptive modulation and coding (AMC) will be designed and analyzed. The supporting company, InterDigital, wants to remedy the major weakness of these two fundamental mechanisms of modern communication systems which is caused by a lack of exchange of information regarding the state of the channel and the state of the decoder. While AMC is meant to adjust the transmission parameters to the time-varying channel, HARQ is a "safety net" which deals with residual errors and does not take advantage of the CSI acquired during the retransmissions. Having practically no parameters to adjust, HARQ is very robust but helps very little to improve the throughput. Therefore, while AMC and HARQ have significantly contributed to the success of modern wireless communication systems, in their current form they are not ready to meet 5G systems requirements of lower latency (< 1ms), high reliability (99.999%) and particularly, the improved spectral efficiency. Thus, to address this need of Interdigital, new transmission strategies exploiting the results of previous theoretical studied will be proposed for practical codes and modulations. These new strategies will target transmission scenarios similar to those used in 4G and others that are expected for 5G systems. Exploiting the ideas of i) variable-length (or variable-bandwidth) transmission ii) multi-packet transmission and iii) adaptation based on the decoder state information accumulated throughout the HARQ cycle, transmission strategies where AMC and HARQ exploit jointly the CSI and rich signaling feedback to improve the throughput of the HARQ-based transmissions will be proposed and analyzed.