The rise of machine-to-machine communications has rekindled the interest inrandom access protocols as a support for a massive number of uncoordinatedlytransmitting devices. The legacy ALOHA approach is developed under a collisionmodel, where slots containing collided packets are considered as waste.However, if the common receiver (e.g., base station) is capable to store thecollision slots and use them in a transmission recovery process based onsuccessive interference cancellation, the design space for access protocols isradically expanded. We present the paradigm of coded random access, in whichthe structure of the access protocol can be mapped to a structure of anerasure-correcting code defined on graph. This opens the possibility to usecoding theory and tools for designing efficient random access protocols,offering markedly better performance than ALOHA. Several instances of codedrandom access protocols are described, as well as a case study on how toupgrade a legacy ALOHA system using the ideas of coded random access.
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