Improving the performance of the FPBA algorithm using random transmitter power levels

To enhance the throughput of the framed pseudo-Bayesian ALOHA (FPBA) algorithm used for reservation in wireless ATM, a scheme is described in which multiple power levels are used at the transmitters. One of the simultaneously sent packets can often be successfully received due to the power capture effect. The authors consider a capture model in which the transmitter captures the channel only if its signal-to-interference ratio is above some threshold when received at the central station. Rayleigh fading, shadowing and path loss all contribute to the capture effect in conjunction with the new physically induced random transmission power levels. Throughput equations of the algorithm are derived and the performance of the algorithm waiting time and throughput in the presence of the wireless channel is illustrated. Results show significant improvement in the throughput and low stable access delay for a wide range of traffic conditions

Slotted Aloha for Networked Base Stations

We study multiple base station, multi-access systems in which the user-base station adjacency is induced by geographical proximity. At each slot, each user transmits (is active) with a certain probability, independently of other users, and is heard by all base stations within the distance $r$. Both the users and base stations are placed uniformly at random over the (unit) area. We first consider a non-cooperative decoding where base stations work in isolation, but a user is decoded as soon as one of its nearby base stations reads a clean signal from it. We find the decoding probability and quantify the gains introduced by multiple base stations. Specifically, the peak throughput increases linearly with the number of base stations $m$ and is roughly $m/4$ larger than the throughput of a single-base station that uses standard slotted Aloha. Next, we propose a cooperative decoding, where the mutually close base stations inform each other whenever they decode a user inside their coverage overlap. At each base station, the messages received from the nearby stations help resolve collisions by the interference cancellation mechanism. Building from our exact formulas for the non-cooperative case, we provide a heuristic formula for the cooperative decoding probability that reflects well the actual performance. Finally, we demonstrate by simulation significant gains of cooperation with respect to the non-cooperative decoding.Comment: conference; submitted on Dec 15, 201

Mobile Radio Slotted ALOHA with Capture, Diversity and Retransmission Control in the Presence of Shadowing

this paper, the capture performance of a random access scheme in the presence of Rayleigh fading, shadowing and diversity is studied. The conditional throughput Cn , i.e., the average number of packets which are correctly received per slot, given the number of colliding packets, n, is computed, as well as its limit as n ! 1. Some different diversity schemes are compared. Also, retransmission control is considered as a means to enhance the system performance. The stability of the controlled system is directly proved. Finally, the effect of long-term attenuations on the system performance and stability is discussed

Modern Random Access for Satellite Communications

The present PhD dissertation focuses on modern random access (RA) techniques. In the first part an slot- and frame-asynchronous RA scheme adopting replicas, successive interference cancellation and combining techniques is presented and its performance analysed. The comparison of both slot-synchronous and asynchronous RA at higher layer, follows. Next, the optimization procedure, for slot-synchronous RA with irregular repetitions, is extended to the Rayleigh block fading channel. Finally, random access with multiple receivers is considered.Comment: PhD Thesis, 196 page