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

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

In this paper, we provide a saturation throughput analysis of the IEEE 802.11 protocol at the data link layer by including the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture effects, specially in an environment of high interference, become important in terms of the actual observed throughput. As far as the 4-way handshaking mechanism is concerned, 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. This way, any channel model characterizing the physical transmission medium can be accommodated, including AWGN and fading channels. We also extend the Markov model in order to consider the behavior of the contention window when employing the basic 2-way handshaking mechanism. Under the usual assumptions regarding the traffic generated per node and independence of packet collisions, we solve for the stationary probabilities of the Markov chain and develop expressions for the saturation throughput as a function of the number of terminals, packet sizes, raw channel error rates, capture probability, and other key system parameters. The theoretical derivations are then compared to simulation results confirming the effectiveness of the proposed models.Comment: To appear on IEEE Transactions on Communications, 200

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

In this paper, we provide a saturation throughput analysis of the IEEE 802.11 protocol at the data link layer by including the impact of both transmission channel and capture effects in Rayleigh fading environment. Impacts of both non-ideal channel and capture effects, specially in an environment of high interference, become important in terms of the actual observed throughput. As far as the 4-way handshaking mechanism is concerned, 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. This way, any channel model characterizing the physical transmission medium can be accommodated, including AWGN and fading channels. We also extend the Markov model in order to consider the behavior of the contention window when employing the basic 2-way handshaking mechanism. Under the usual assumptions regarding the traffic generated per node and independence of packet collisions, we solve for the stationary probabilities of the Markov chain and develop expressions for the saturation throughput as a function of the number of terminals, packet sizes, raw channel error rates, capture probability, and other key system parameters. The theoretical derivations are then compared to simulation results confirming the effectiveness of the proposed models

Verona storico-religiosa. Testimonianze di una storia millenaria.

Testimonianze di una storia millenaria _ come recita il sottotitolo del volume _ giustificano nella loro articolazione, filologicamente e storicamente fondata, la ricerca a pi\uf9 voci su "Verona storico-religiosa". Saggi di archeologia ed epigrafia, storia antica e architettura templare, ebraismo, cristianesimo riformato e islam, nonch\ue9 sul ruolo della Biblioteca Capitolare della Cattedrale e dei fondi religiosi della Biblioteca Civica e dell'Archivio di Stato di Verona, documentano copiosamente l'assunto delle titolature del libro, illustrato da centinaia di fotografie a colori, parte integrante dell'argomentazione storica. Testimonies of a millenarian history _ as subtitle of volume recites _ justify in their articulation founded on philology and history, the research by many authors upon Verona storico-religiosa (Historico-religious Verona). Studies of Archeology and Epigraphy, ancient history and temple Architecture, Hebraism, Reformed Christianity and Islam, besides on cultural office of Cathedral Chapters Library and on religious founds of Municipal Library and State Archives of Verona plentifully document the task of this monograph, illustrated by 200 of coloured photos, integral part of Historical argumentation

Monogenoidea (Dactylogyridae) em tilápias-do-nilo cultivadas sob diferentes densidades de estocagem em tanques-rede Monogenoidea (Dactylogyridae) in Nile tilapia cultured under different stocking densities in cages

Avaliaram-se a prevalência e a intensidade de infecção por Monogenoidea em tilápias-do-nilo (Oreochromis niloticus) cultivadas sob diferentes densidades de estocagem em tanques-rede de 4m³. O delineamento experimental foi inteiramente ao acaso, com quatro tratamentos - densidades (D) de D1=250, D2=300, D3=350 e D4=400 peixes/m³, três repetições por tratamento, utilizando-se 360 peixes capturados e analisados no período de fevereiro a junho de 2003. Os parâmetros físico-químicos da água foram mensalmente monitorados. Observaram-se prevalências de 52,8; 62,5; 69,4; 83,3; 58,3% e intensidade média parasitária de 112,8; 65,7; 274,0; 97,8; 100,2 de Dactylogyrus sp. (Monogenoidea: Dactylogyridae). Não houve relação da prevalência e intensidade de infecção com a densidade de cultivo, porém foi verificado efeito quadrático (P<0,05) da intensidade parasitária em função do mês. Verificaram-se maior intensidade média de infecção (274) e elevada prevalência (83,3%) nos meses em que a temperatura e a transparência da água oscilaram abaixo dos limites recomendados para o conforto térmico e bem-estar das tilápias.<br>The prevalence and infection intensity of Monogenoidea in Nile tilapia (Oreochromis niloticus) cultivated under different stocking densities in 4m³ cages were evaluated. The experiment was designed in sample random sampling with four treatments - densities (D) of D1=250, D2=300, D3=350, and D4=400 fish/m³- and three repetitions, using 360 fish captured and analyzed during the period from February to June 2003. Physiochemical parameters of the water were monthly monitored. Prevalences of 52.8; 62.5; 69.4; 83.3; and 58.3% and parasitic mean intensities of 112.8; 65.7; 274.0; 97.8; and 100.2 Dactylogyrus sp. (Monogenoidea: Dactylogyridae) were observed. No relationship between the prevalence and infection intensity with the cultivation density was found. However, quadratic effect was verified (P<0.05) related to the parasitic intensity in function of the month. High mean intensity of infection (274) and high prevalence (83.3%) were verified in the months in that the temperature and the transparency of the water oscillated below the recommended limits for the thermal comfort and well-being of tilapia