1,122 research outputs found
Performance Enhancements for Asynchronous Random Access Protocols over Satellite
In this paper, a novel enhancement of the well known
ALOHA random access mechanism is presented which largely extends the achievable throughput compared to traditional ALOHA and provides significantly lower packet loss rates. The novel mechanism, called Contention Resolution - ALOHA (CRA), is based on transmitting multiple replicas of a packet in an unslotted ALOHA system and applying interference cancellation techniques. In this paper the methodology for this new random access technique is presented, also w.r.t. existing Interference Cancellation (IC) techniques. Moreover numerical results for performance comparison with state of the art random access mechanisms, such as Contention Resolution Diversity Slotted ALOHA (CRDSA) are provided. Finally the benefit of taking strong forward error correcting codes for the performance of CRA is shown
Open-Loop Spatial Multiplexing and Diversity Communications in Ad Hoc Networks
This paper investigates the performance of open-loop multi-antenna
point-to-point links in ad hoc networks with slotted ALOHA medium access
control (MAC). We consider spatial multiplexing transmission with linear
maximum ratio combining and zero forcing receivers, as well as orthogonal space
time block coded transmission. New closed-form expressions are derived for the
outage probability, throughput and transmission capacity. Our results
demonstrate that both the best performing scheme and the optimum number of
transmit antennas depend on different network parameters, such as the node
intensity and the signal-to-interference-and-noise ratio operating value. We
then compare the performance to a network consisting of single-antenna devices
and an idealized fully centrally coordinated MAC. These results show that
multi-antenna schemes with a simple decentralized slotted ALOHA MAC can
outperform even idealized single-antenna networks in various practical
scenarios.Comment: 51 pages, 19 figures, submitted to IEEE Transactions on Information
Theor
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 . 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 and is roughly
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
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