165 research outputs found
Random Access Game and Medium Access Control Design
Motivated partially by a control-theoretic viewpoint, we propose a game-theoretic model, called random access game, for contention control. We characterize Nash equilibria of random access games, study their dynamics, and propose distributed algorithms (strategy evolutions) to achieve Nash equilibria. This provides a general analytical framework that is capable of modeling a large class of system-wide quality-of-service (QoS) models via the specification of per-node utility functions, in which system-wide fairness or service differentiation can be achieved in a distributed manner as long as each node executes a contention resolution algorithm that is designed to achieve the Nash equilibrium. We thus propose a novel medium access method derived from carrier sense multiple access/collision avoidance (CSMA/CA) according to distributed strategy update mechanism achieving the Nash equilibrium of random access game. We present a concrete medium access method that adapts to a continuous contention measure called conditional collision probability, stabilizes the network into a steady state that achieves optimal throughput with targeted fairness (or service differentiation), and can decouple contention control from handling failed transmissions. In addition to guiding medium access control design, the random access game model also provides an analytical framework to understand equilibrium and dynamic properties of different medium access protocols
Multi-Round Contention in Wireless LANs with Multipacket Reception
Multi-packet reception (MPR) has been recognized as a powerful
capacity-enhancement technique for random-access wireless local area networks
(WLANs). As is common with all random access protocols, the wireless channel is
often under-utilized in MPR WLANs. In this paper, we propose a novel
multi-round contention random-access protocol to address this problem. This
work complements the existing random-access methods that are based on
single-round contention. In the proposed scheme, stations are given multiple
chances to contend for the channel until there are a sufficient number of
``winning" stations that can share the MPR channel for data packet
transmission. The key issue here is the identification of the optimal time to
stop the contention process and start data transmission. The solution
corresponds to finding a desired tradeoff between channel utilization and
contention overhead. In this paper, we conduct a rigorous analysis to
characterize the optimal strategy using the theory of optimal stopping. An
interesting result is that the optimal stopping strategy is a simple
threshold-based rule, which stops the contention process as soon as the total
number of winning stations exceeds a certain threshold. Compared with the
conventional single-round contention protocol, the multi-round contention
scheme significantly enhances channel utilization when the MPR capability of
the channel is small to medium. Meanwhile, the scheme automatically falls back
to single-round contention when the MPR capability is very large, in which case
the throughput penalty due to random access is already small even with
single-round contention
On the Asymptotic Validity of the Decoupling Assumption for Analyzing 802.11 MAC Protocol
Performance evaluation of the 802.11 MAC protocol is classically based on the
decoupling assumption, which hypothesizes that the backoff processes at
different nodes are independent. This decoupling assumption results from mean
field convergence and is generally true in transient regime in the asymptotic
sense (when the number of wireless nodes tends to infinity), but, contrary to
widespread belief, may not necessarily hold in stationary regime. The issue is
often related with the existence and uniqueness of a solution to a fixed point
equation; however, it was also recently shown that this condition is not
sufficient; in contrast, a sufficient condition is a global stability property
of the associated ordinary differential equation. In this paper, we give a
simple condition that establishes the asymptotic validity of the decoupling
assumption for the homogeneous case. We also discuss the heterogeneous and the
differentiated service cases and formulate a new ordinary differential
equation. We show that the uniqueness of a solution to the associated fixed
point equation is not sufficient; we exhibit one case where the fixed point
equation has a unique solution but the decoupling assumption is not valid in
the asymptotic sense in stationary regime.Comment: 16 pages, 4 figures, accepted for publication in IEEE Transactions on
Information Theor
Performance evaluation of a medium access control protocol for a distributed ARQ scheme in cooperative wireless networks
A performance evaluation of a medium access control protocol for a distributed ARQ scheme in cooperative wireless networks is presented in this paper. The protocol under evaluation is the Persistent Relay Carrier Sensing Multiple Access protocol (PRCSMA). The protocol was designed to be easily integrated in standard IEEE 802.11 networks in order to increase their performance and to extend coverage. The main goals of this paper are to present and to discuss the performance evaluation of the PRCSMA under different network configurations. Computer simulations demonstrate the robustness of the protocol under different scenarios.Peer ReviewedPostprint (author’s final draft
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