Deliverable D2.2c Final Evaluation and Comparison of Channel Coding / Decoding Schemes 3.2 Precoder-aided Iterative Detection Assisted Multilevel Coding and Three-dimensional 3.3 a Simple Rate-1/2 Co-decoding Scheme for Writing on Dirty Paper....................................... 26

This deliverable continues the work presented in the previous deliverables “Preliminary channel coding behaviour and model” (D2.2a) and “Intermediate evaluation and comparison of channel coding/decoding schemes (D2.2b) and present the research and demonstration activities performed on channel coding in months 16-29 of the PHOENIX project. Following the studies on RCPC codes and preliminary evaluations on Low-Density Parity-Check (LDPC) codes, the activity focused in the recent months on the study of LDPC codes and their adaptation in the PHOENIX JSCC framework. Due to the necessity of protecting the transmitted information from packet losses, LDPC codes under iterative message passing decoding algorithm and over channels introducing bursts of erasure, are analysed. LDPC codes are then considered in the framework of a simple co-decoding scheme in a Dirty paper writing scenario, where the transmitted signal is affected by interference known by the transmitter and thermal noise. A novel three-dimensional (3D) EXIT chart for investigating the iterative behaviour of Multilevel Coding (MLC) invoking Multistage Decoding (MSD) is then described in the deliverable. Finally, the integration of the said coding schemes in the PHOENIX demonstration chain is provided and in particular the possibility to perform unequal error protection either at upper system layers, e.g. at application (or content) layer, or at physical layer or at both layers through combined schemes is afforded. The radio link characteristics considered in the demonstration platform are then shortly described. Keyword list: PHOENIX, channel coding, RCPC, LDPC, IRA codes, simulation chain, unequal error protection PHOENIX Deliverable D2.2c 2/51 Executive Summary This deliverable continues the work presented in deliverable ‘Preliminary channel coding behaviour and model’ (D2.2a) and ‘Intermediate evaluation and comparison of channel coding/decoding schemes (D2.2b). The research and demonstration activity performed on channel coding in months 16-29 of the PHOENIX project is thus described in this deliverable. In the first two D2.2 deliverables, convolutional codes and LDPC codes characteristics useful to be exploited in the joint source and channel coding (JSCC) framework under investigation in the PHOENIX project were studied. In particular, Rate Compatible Punctured Convolutional (RCPC) codes and Low Density Parity Check Codes were investigated. Their ability to provide unequal error protection (UEP) and the exploitation of the possibly provided soft information for soft decoding of VLC codes, their ability to adapt to varying channel conditions and to provide good performance with the packet lengths of interest in the PHOENIX project have been analysed, in order to drive the choice for the best candidate schemes in different scenarios. Adaptive space-time block coding was also studied. In this deliverable, after a short review of the previous activity and conclusions on it, an LDPC based scheme is proposed, allowing easily an Unequal Error Protection (UEP) transmission strategy, while keeping a single encoder at the transmitter and a decoder at the receiver. With such approach, to change the code rate it is sufficient to change the puncturing pattern applied to the parity bits and the length of the shortened fraction of systematic bits. The difference with other code families (e.g. with the Rate Compatible Punctured Convolutional Codes, RCPCC) allowing to change the protection level within the same packet, simply changing the puncturing matrix and informing the receiver on which matrix to use along the packet, consists in the fact that with the proposed UEP scheme with using LDPC codes, the channel code rate has to be fixed within the same packet. Both the possibility of using RCPC codes and LDPC codes are thus considered as an option in the project and implemented in the PHOENIX project demonstrator. In the PHOENIX framework, errors typically consist in bit errors or packet losses. For this reason, also the ability of LDPC codes to cope with packet losses, or erasures, has been studied. Low-Density Parity-Check (LDPC) codes under iterative message passing decoding algorithm, over channels introducing bursts of erasure, are described in the deliverable. The burst erasure channel model considered can be seen as an erasure channel based on a hidden Markov chain (HMC-EC). In order to characterize the channel, the expression of mutual information is recalled for any erasure channel with memory and with independent identically distributed (i.i.d.) and equiprobable input symbols. An optimization algorithm is then proposed, which is able to heavily improve LDPC iterative decoder performance. This algorithm can be in principle applied to any given LDPC code. Simulation results relative to both random and IRA / eIRA codes are shown comparing the performance before and after the application of our optimization algorithm. LDPC codes are then considered in the framework of a simple co-decoding scheme for a Dirty Paper writing scenario, where the transmitted signal is affected by interference known by the transmitter and thermal noise. We focused on rate-1/2 codes, suitable for low SNR regions, but the scheme is easily generalizable to different code rates. In particular our approach involves a proper combination of an LDPCC and a vector quantizer based on a convolutional code and directly allows for iterative soft-information exchanges between the respective decoders. We show that it is possible to reach BER performance within 1.2-1.3 dB from the correspondent LDPC code’s in AWGN channels. Moreover, the obtained performance are completely unaffected by the amount of interference. A novel three-dimensional (3D) EXIT chart for investigating the iterative behaviour of Multilevel Coding (MLC) invoking Multistage Decoding (MSD) is then described in the deliverable. The extrinsic information transfer characteristics of both the symbol-to-bit de-mapper used and those of the different-protection constituent decoders suggest that potential improvements can be achieved by appropriately designing the de-mapper. The proposed 3D EXIT chart is then invoked for studying the precoder-aided multilevel coding scheme employing both MSD and Parallel Independent Decoding (PID) for communicating over AWGN and uncorrelated Rayleigh fading channels with the aid of 8PSK modulation. At BER= 5 10 , the precoder was capable of enhancing the achievable 0 b E N / performance by 0.5dB to 2.5dB over AWGN and Rayleigh channels, respectively. The description of the UEP schemes considered can be found in deliverables D2.4b and D2.4c, where they are described due to the UEP strategy choice being performed by the system controller. PHOENIX Deliverable D2.2c 3/51 Finally, the integration of the said coding schemes in the PHOENIX demonstration chain is described. In particular, the possibility to perform unequal error protection either at upper system layers, e.g. at application (or content) layer, or at physical layer ,or at both layers through combined schemes, is afforded. The Content UEP module may be viewed as a plug-in to the source codec and can be realistically driven by the application controller on the basis of the available channel and network state information for adaptation over a wired and wireless links that are then possibly untouched. This ensures backward compatibility with existing networks and established radio access solutions of PHOENIX optimisation solution. On the other side, physical layer UEP has the advantage of the availability of more detailed channel state information and also provides the possibility to protect network headers. The PHOENIX demonstrator allows thus the choice of the protection strategy according to the scenario. A combined approach is also envisaged, where UEP is performed at content level, whereas network headers are more protected than payload at physical layer. A description of the options of the software demonstration platform at radio link level is also provided. For further details on this aspect, the readers are reported to deliverables D2.3c and D2.4c. PHOENIX Deliverable D2.2c 4/51 Executive Summary . 2