On the Throughput Allocation for Proportional Fairness in Multirate IEEE 802.11 DCF

This paper presents a modified proportional fairness (PF) criterion suitable for mitigating the \textit{rate anomaly} problem of multirate IEEE 802.11 Wireless LANs employing the mandatory Distributed Coordination Function (DCF) option. Compared to the widely adopted assumption of saturated network, the proposed criterion can be applied to general networks whereby the contending stations are characterized by specific packet arrival rates, $\lambda_s$, and transmission rates $R_d^{s}$. The throughput allocation resulting from the proposed algorithm is able to greatly increase the aggregate throughput of the DCF while ensuring fairness levels among the stations of the same order of the ones available with the classical PF criterion. Put simply, each station is allocated a throughput that depends on a suitable normalization of its packet rate, which, to some extent, measures the frequency by which the station tries to gain access to the channel. Simulation results are presented for some sample scenarios, confirming the effectiveness of the proposed criterion.Comment: Submitted to IEEE CCNC 200

Performance analysis under finite load and improvements for multirate 802.11

Automatic rate adaptation in CSMA/CA wireless networks may cause drastic throughput degradation for high speed bit rate stations (STAs). The CSMA/CA medium access method guarantees equal long-term channel access probability to all hosts when they are saturated. In previous work it has been shown that the saturation throughput of any STA is limited by the saturation throughput of the STA with the lowest bit rate in the same infrastructure. In order to overcome this problem, we ¯rst introduce in this paper a new model for ¯nite load sources with multirate capabilities. We use our model to investigate the throughput degradation outside and inside the saturation regime. We de¯ne a new fairness index based on the channel occupation time to have more suitable de¯nition of fairness in multirate environments. Further, we propose two simple but powerful mechanisms to partly bypass the observed decline in performance and meet the proposed fairness. Finally, we use our model for ¯nite load sources to evaluate our proposed mechanisms in terms of total throughput and MAC layer delay for various network con¯gurations

On the Behavior of the Distributed Coordination Function of IEEE 802.11 with Multirate Capability under General Transmission Conditions

The aim of this paper is threefold. First, it presents a multi-dimensional Markovian state transition model characterizing the behavior of the IEEE 802.11 protocol at the Medium Access Control layer which accounts for packet transmission failures due to channel errors modeling both saturated and non-saturated traffic conditions. Second, it provides a throughput analysis of the IEEE 802.11 protocol at the data link layer in both saturated and non-saturated traffic conditions taking into account the impact of both the physical propagation channel and multirate transmission in Rayleigh fading environment. The general traffic model assumed is M/M/1/K. Finally, it shows that the behavior of the throughput in non-saturated traffic conditions is a linear combination of two system parameters; the payload size and the packet rates, $\lambda^{(s)}$, of each contending station. The validity interval of the proposed model is also derived. Simulation results closely match the theoretical derivations, confirming the effectiveness of the proposed models.Comment: Submitted to IEEE Transactions on Wireless Communications, October 21, 200

A control theoretic approach to achieve proportional fairness in 802.11e EDCA WLANs

This paper considers proportional fairness amongst ACs in an EDCA WLAN for provision of distinct QoS requirements and priority parameters. A detailed theoretical analysis is provided to derive the optimal station attempt probability which leads to a proportional fair allocation of station throughputs. The desirable fairness can be achieved using a centralised adaptive control approach. This approach is based on multivariable statespace control theory and uses the Linear Quadratic Integral (LQI) controller to periodically update CWmin till the optimal fair point of operation. Performance evaluation demonstrates that the control approach has high accuracy performance and fast convergence speed for general network scenarios. To our knowledge this might be the first time that a closed-loop control system is designed for EDCA WLANs to achieve proportional fairness

Aggregation with fragment retransmission for very high-speed WLANs

In upcoming very high-speed WLANs the physical layer (PHY) rate may reach 600 Mbps. To achieve high efficiency at the medium access control (MAC) layer, we identify fundamental properties that must be satisfied by any CSMA/CA based MAC layer and develop a novel scheme called Aggregation with Fragment Retransmission (AFR). In the AFR scheme, multiple packets are aggregated into and transmitted in a single large frame. If errors happen during the transmission, only the corrupted fragments of the large frame are retransmitted. An analytic model is developed to evaluate the throughput and delay performance of AFR over a noisy channel, and to compare AFR with competing schemes in the literature. Optimal frame and fragment sizes are calculated using this model. Transmission delays are minimised by using a zero-waiting mechanism where frames are transmitted immediately once the MAC wins a transmission opportunity. We prove that zero waiting can achieve maximum throughput. As a complement to the theoretical analysis, we investigate by simulations the impact of AFR on the performance of realistic application traffic with diverse requirements. We have implemented the AFR scheme in the NS-2 simulator and present detailed results for TCP, VoIP and HDTV traffic. The AFR scheme described was developed as part of the 802.11n working group work. The analysis presented here is general enough to be extended to the proposed scheme in the upcoming 802.11n standard. Trends indicated by our simulation results should extend to any well-designed aggregation scheme

Resource allocation in networks from a connection-level perspective (Asignación de recursos en redes desde la perspectiva de las conexiones)

En esta tesis, se analizan varios problemas de asignación recursos que surgen en el estudio de los sistemas de telecomunicaciones. En particular, nos centramos en las redes de datos, de los cuales el ejemplo más importante es la Internet global. En este tipo de redes, el recurso escaso que debe ser asignado es la cantidad de ancho de banda de cada conexión curso. Esta asignación realiza en tiempo real por los protocolos subyacentes, que técniamente se encuentran divididos en varios niveles o capas. Desde este punto de vista, la red puede ser pensada como un sistema de control a gran escala, donde cada entidad debe seguir un conjunto dado de leyes de control, a fin de encontrar una asignación adecuada de recursos. Desde el influyente trabajo de Kelly et. al., este problema se ha expresado en términos económicos, dando lugar a la teoría conocida como Network Utility Maximization (maximización de utilidad en redes). Este marco ha demostrado ser una herramienta valiosa para analizar los mecanismos existentes y diseño de protocolos nuevos que mejoran el comportamiento de la red. Proporciona además un vínculo crucial entre el tradicional análisis por capas de los protocolos de red y las técnicas de optimización convexa, dando lugar a lo que se denomina análisis multi-capa de las redes. En este trabajo nos centramos en el análisis de la red desde una perspectiva a nivel de conexiones. En particular, se estudia el desempeño de eficiencia y justicia en la escala de conexiones de varios modelos de asignación de recursos en la red. Este estudio se realiza en varios escenarios: tanto single-path como multi-path (redes con múltiples caminos) así como escenarios cableados e inalámbricos. Se analizan en detalle dos problemas importantes: por un lado, la asignación de los recursos realizada por los protocolos de control de congestión cuando se permiten varias conexiones por usuario. Se identifican algunos problemas del paradigma actual, y se propone un nuevo concepto de \emph{equidad centrada en el usuario}, desarrollando a su vez algoritmos descentralizados que se pueden aplicar en los extremos de la red, y que conducen al sistema a un global adecuado. El segundo problema importante analizado aquí es la asignación de los recursos realizada por los algoritmos de control de congestión cuando trabajan sobre una capa física que permite múltiples velocidades de transmisión como es el caso en las redes inalámbricas. Se demuestra que los algoritmos usuales conducen a ineficiencias importantes desde el punto de vista de las conexiones, y se proponen mecanismos para superar estas ineficiencias y mejorar la asignación de los recursos prestados por dichas redes. A lo largo de este trabajo, se aplican varias herramientas matemáticas, tales como la optimización convexa, la teoría de control y los procesos estocásticos. Por medio de estas herramientas, se construye un modelo del sistema, y se desarrollan leyes de control y algoritmos para lograr el objetivo de desempeño deseado. Como paso final, estos algoritmos fueron probados a través de simulaciones a nivel de paquetes de las redes involucradas, proporcionando la validación de la teoría y la evidencia de que pueden aplicarse en la práctica