962 research outputs found
On Frame Asynchronous Coded Slotted ALOHA: Asymptotic, Finite Length, and Delay Analysis
We consider a frame asynchronous coded slotted ALOHA (FA-CSA) system for
uncoordinated multiple access, where users join the system on a slot-by-slot
basis according to a Poisson random process and, in contrast to standard frame
synchronous CSA (FS-CSA), users are not frame-synchronized. We analyze the
performance of FA-CSA in terms of packet loss rate and delay. In particular, we
derive the (approximate) density evolution that characterizes the asymptotic
performance of FA-CSA when the frame length goes to infinity. We show that, if
the receiver can monitor the system before anyone starts transmitting, a
boundary effect similar to that of spatially-coupled codes occurs, which
greatly improves the iterative decoding threshold. Furthermore, we derive tight
approximations of the error floor (EF) for the finite frame length regime,
based on the probability of occurrence of the most frequent stopping sets. We
show that, in general, FA-CSA provides better performance in both the EF and
waterfall regions as compared to FS-CSA. Moreover, FA-CSA exhibits better delay
properties than FS-CSA.Comment: 13 pages, 12 figures. arXiv admin note: substantial text overlap with
arXiv:1604.0629
High-Throughput Random Access via Codes on Graphs
Recently, contention resolution diversity slotted ALOHA (CRDSA) has been
introduced as a simple but effective improvement to slotted ALOHA. It relies on
MAC burst repetitions and on interference cancellation to increase the
normalized throughput of a classic slotted ALOHA access scheme. CRDSA allows
achieving a larger throughput than slotted ALOHA, at the price of an increased
average transmitted power. A way to trade-off the increment of the average
transmitted power and the improvement of the throughput is presented in this
paper. Specifically, it is proposed to divide each MAC burst in k sub-bursts,
and to encode them via a (n,k) erasure correcting code. The n encoded
sub-bursts are transmitted over the MAC channel, according to specific
time/frequency-hopping patterns. Whenever n-e>=k sub-bursts (of the same burst)
are received without collisions, erasure decoding allows recovering the
remaining e sub-bursts (which were lost due to collisions). An interference
cancellation process can then take place, removing in e slots the interference
caused by the e recovered sub-bursts, possibly allowing the correct decoding of
sub-bursts related to other bursts. The process is thus iterated as for the
CRDSA case.Comment: Presented at the Future Network and MobileSummit 2010 Conference,
Florence (Italy), June 201
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