885 research outputs found
Throughput analysis of ALOHA with cooperative diversity
Cooperative transmissions emulate multi-antenna systems and can improve the quality of signal reception. In this paper, we propose and analyze a cross layer random access scheme, C-ALOHA, that enables cooperative transmissions in
the context of ALOHA system. Our analysis shows that over a fading channel C-ALOHA can improve the throughput by 30%, as compared to standard ALOHA protocol
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
CSMA Local Area Networking under Dynamic Altruism
In this paper, we consider medium access control of local area networks
(LANs) under limited-information conditions as befits a distributed system.
Rather than assuming "by rule" conformance to a protocol designed to regulate
packet-flow rates (e.g., CSMA windowing), we begin with a non-cooperative game
framework and build a dynamic altruism term into the net utility. The effects
of altruism are analyzed at Nash equilibrium for both the ALOHA and CSMA
frameworks in the quasistationary (fictitious play) regime. We consider either
power or throughput based costs of networking, and the cases of identical or
heterogeneous (independent) users/players. In a numerical study we consider
diverse players, and we see that the effects of altruism for similar players
can be beneficial in the presence of significant congestion, but excessive
altruism may lead to underuse of the channel when demand is low
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