A Model of the IEEE 802.11 DCF in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a throughput analysis of the IEEE 802.11 protocol at the data link layer in non-saturated traffic conditions taking into account the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture become important in terms of the actual observed throughput in typical network conditions whereby traffic is mainly unsaturated, specially in an environment of high interference. We extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel, along with a state characterizing the system when there are no packets to be transmitted in the buffer of a station.Comment: Accepted for oral presentation to IEEE Globecom 2007, Washington D.C., November 200

Оцінка впливу завад на швидкість передачі інформації у пакетних мережах передачі даних

Наводяться розрахунки впливу типу модуляції та енергетичних співвідношень у каналі передачі даних на швидкість передачі даних та оптимізація довжини пакету даних при передачі у каналах зв’язку при дії завад. Показано, що для оптимізації швидкості передачі даних потрібно використовувати адаптивний підхід управління МАС рівнем, що повинно передбачати аналіз характеристик середи передачі даних, та мати можливість динамічно міняти різні параметри МАС-рівня у залежності від змін середовища.Calculations over of modulation type influencing and energy relation in data channel on speed of information transfer data and optimization of package length of data are brought at a transmission in the communications channel at the action of noise. It is shown that for optimization of data rate it is necessary to take adaptive approach of MAC-level management, that must foresee the analysis of communication environment descriptions of data, and to be in a position dynamically to change the different parameters of МАС-level depending on changing of environment

Throughput Analysis of CSMA Wireless Networks with Finite Offered-load

This paper proposes an approximate method, equivalent access intensity (EAI), for the throughput analysis of CSMA wireless networks in which links have finite offered-load and their MAC-layer transmit buffers may be empty from time to time. Different from prior works that mainly considered the saturated network, we take into account in our analysis the impacts of empty transmit buffers on the interactions and dependencies among links in the network that is more common in practice. It is known that the empty transmit buffer incurs extra waiting time for a link to compete for the channel airtime usage, since when it has no packet waiting for transmission, the link will not perform channel competition. The basic idea behind EAI is that this extra waiting time can be mapped to an equivalent "longer" backoff countdown time for the unsaturated link, yielding a lower link access intensity that is defined as the mean packet transmission time divided by the mean backoff countdown time. That is, we can compute the "equivalent access intensity" of an unsaturated link to incorporate the effects of the empty transmit buffer on its behavior of channel competition. Then, prior saturated ideal CSMA network (ICN) model can be adopted for link throughput computation. Specifically, we propose an iterative algorithm, "Compute-and-Compare", to identify which links are unsaturated under current offered-load and protocol settings, compute their "equivalent access intensities" and calculate link throughputs. Simulation shows that our algorithm has high accuracy under various offered-load and protocol settings. We believe the ability to identify unsaturated links and compute links throughputs as established in this paper will serve an important first step toward the design and optimization of general CSMA wireless networks with offered-load control.Comment: 6 pages. arXiv admin note: text overlap with arXiv:1007.5255 by other author

Performance evaluation of self-similar models for traffic on IEEE 802.11 networks - study of case for the QRD network

Este artículo evalúa el desempeño de modelos de tráfico fractal o autosimilar en redes IEEE 802.11. Este estudio está enfocado en la red “Quindio Región Digital” (QRD). La evaluación del desempeño de los modelos de tráfico se realiza en tres etapas. En la primera etapa, se obtienen las características estadísticas del tráfico actual en la red QRD. En la segunda etapa, se seleccionan los modelos de tráfico más adecuados a las características actuales de la red QRD como operación fuera de saturación y gestión de tráfico heterogéneo. En la tercera etapa, se definine una métrica de rendimiento que se utiliza para evaluar los patrones de tráfico a través de la simulación.This paper evaluates the performance of fractal or self-similar traffic models in IEEE 802.11 networks. This study is focused on the “Quindio Región Digital” (QRD) network. Performance evaluation of the traffic models is performed in three stages. In the first stage, we obtain the statistical characteristics of the current traffic on the QRD network. In the second stage, the most suitable traffic models are selected for the current characteristics of the QRD network such as outof-saturation operation and management of heterogeneous traffic. In the third stage, we define a performance metric that is used to evaluate the traffic patterns through simulation

Investigating the validity of IEEE 802.11 MAC modeling hypotheses

As WLANs employing IEEE 802.11 have become pervasive, many analytic models for predicting their performance have been developed in recent years. Due to the complicated nature of the 802.11 MAC operation, approximations must be made to enable tractable mathematical models. In this article, through simulation we investigate the veracity of the approximations shared by many models that have been developed starting with the fundamental hypotheses in Bianchipsilas (1998 and 2000) seminal papers. We find that even for small numbers of station these assumptions that hold true for saturated stations (those that always have a packet to send) and for unsaturated stations with small buffers. However, despite their widespread adoption, we find that the commonly adopted assumptions that are used to incorporate station buffers are not appropriate. This raises questions about the predictive power of models based on these hypotheses

Unsaturated Throughput Analysis of IEEE 802.11 in Presence of Non Ideal Transmission Channel and Capture Effects

In this paper, we provide a throughput analysis of the IEEE 802.11 protocol at the data link layer in non-saturated traffic conditions taking into account the impact of both transmission channel and capture effects in Rayleigh fading environment. The impact of both non-ideal channel and capture become important in terms of the actual observed throughput in typical network conditions whereby traffic is mainly unsaturated, especially in an environment of high interference. We extend the multi-dimensional Markovian state transition model characterizing the behavior at the MAC layer by including transmission states that account for packet transmission failures due to errors caused by propagation through the channel, along with a state characterizing the system when there are no packets to be transmitted in the buffer of a station. Finally, we derive a linear model of the throughput along with its interval of validity. Simulation results closely match the theoretical derivations confirming the effectiveness of the proposed model.Comment: To appear on IEEE Transactions on Wireless Communications, 200