• crdsa
• genetic optimization
• M2M
• random access

In recent years a sudden interest in random access (RA) has risen, driven by the increasing number of applications in which a multitude of (typically small) terminals transmit without coordination bursty messages towards the network infrastructure (e.g. machine-to-machine, device-to-device, SCADA, monitoring, measuring, and automated reporting). Such interest has led to recent work on protocols that exploit iterative successive interference cancellation (I-SIC) at the demodulator side to greatly enhance the random access performances. Content Resolution Diversity Slotted ALOHA (CRDSA) is a time-slotted synchronous RA protocol that implement I-SIC at the receiver and thus benefit from power unbalance of the transmitting users. In this thesis, the optimization of the CRDSA protocol throughput is studied by devising an appropriate transmit power distribution for the terminals. This optimization is carried out by simulation due to the extreme complexity of an analytical approach initially analyzed. After validating the proposed simulator, an optimized power distribution is found through genetic algorithm (GA) based optimization and Monte Carlo simulation tools. The proposed optimized distribution provides a throughput gain of up to 100% over a fixed transmit power and 10% over the uniform distribution which was already proven to be optimal in the spread-spectrum random access schemes with I-SIC (E-SSA). To overcome the higher peak terminal power requirement of CRDSA compared to E-SSA a multi-frequency slotted (MF-CRDSA) and unslotted (MF-ACRDA) variants of CRDSA have been investigated and shown to provide attractive performance. Finally, the addition of (light) direct-sequence spreading on top of (MF-)CRDSA and (MF-)ACRDA has been analyzed as possible enhancements to the current CRDSA physical layer. It has been shown that the inclusion of a moderate spreading provides a lower packet loss ratio (PLR) floor under low load conditions than conventional CRDSA and ACRDA. The combination of these techniques has been analyzed, simulated and proven to be highly beneficial to reduce the terminal power and energy requirements closing the gap with the E-SSA RA technique.