  Contention Resolution Diversity Slotted ALOHA (CRDSA) and its burst degree
optimizations (CRDSA++, IRSA) make use of MAC burst repetitions and
Interference Cancellation (IC) making possible to reach throughput values as
high as $T \simeq 0.8$ in practical implementations, whereas for the
traditional slotted ALOHA $T \simeq 0.37$. However, these new techniques
introduce a frame-based access to the channel that limits the performance in
terms of throughput and packet delivery delay. In this paper, a new technique
named Sliding Window CRDSA (SW-CRDSA) and its counterpart for irregular
repetitions (SW-IRSA) are introduced in order to exploit the advantages of MAC
burst repetition and Interference Cancellation (IC) with an unframed access
scheme. Numerical results are also provided in order to validate the statement
of better performance.
