= ALOHA with Collision Resolution (ALOHA-CR): Theory and Software Defined Radio Implementation =
Authors: X. Liu, J.Kountouriotis, A.P. Petropulu, K.R. Dandekar
== Abstract ==
A cross-layer scheme, namely ALOHA With Collision Resolution (ALOHA-CR), is proposed for
high throughput wireless communications in a cellular scenario. Transmission occurs in a time-slotted
ALOHA-type fashion with a caveat: simultaneous transmissions of two users can be successful. The
wireless channel is assumed to be flat fading and constant over the duration of one time slot. A user i
with a non-empty queue transmits a packet with some probability p in the beginning of each time slot,
after waiting for a random time interval. If more than two users transmit in the same slot, the collision
cannot be resolved, the packets are discarded and the users are asked to retransmit at a later time. If only
one user transmits, the transmitted packet is recovered with some probability, depending on the state
of the channel. If two users transmit, the collision can be separated and the packets recovered by first
oversampling the collision signal and then exploiting independent information about the two users that
is contained in the signal polyphase components. The properties of the user delays i’s are determined
so that the probability of user separation is maximized. The ALOHA-CR throughput is derived under
the infinite backlog assumption, i.e., the network users always have data in their queues, and also under
the assumption of finite backlog. In the infinite backlog assumption, the optimal contention probability
is calculated, which maximizes the system throughput. In the finite backlog assumption, the region of
contention probability is determined based on the packet arrival rate. Queuing delay of network users
are also derived. The performance of ALOHA-CR is demonstrated on a WARP testbed containing five
software defined radio nodes. The testbed results indicate ALOHA-CR leads to significant increase in
throughput and reduction of service delays.
{{{
{Liu:2010,
Author = {X. Liu, J. Kountouriotis, A.P. Petropulu, K.R. Dandekar},
Title = {ALOHA With Collision Resolution (ALOHA-CR): Theory and Software Defined Radio Implementation},
Year = {2010}}
magazine title = {{IEEE Transactions on Signal Processing}},
month = aug,
year = {2010},
}}}