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 iās 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},
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