9,535 research outputs found
Fuzzy Logic Control of Adaptive ARQ for Video Distribution over a Bluetooth Wireless Link
Bluetooth's default automatic repeat request (ARQ) scheme is not suited to video distribution resulting in missed display and decoded deadlines. Adaptive ARQ with active discard of expired packets from the send buffer is an alternative approach. However, even with the addition of cross-layer adaptation to picture-type packet importance, ARQ is not ideal in conditions of a deteriorating RF channel. The paper presents fuzzy logic control of ARQ, based on send buffer fullness and the head-of-line packet's deadline. The advantage of the fuzzy logic approach, which also scales its output according to picture type importance, is that the impact of delay can be directly introduced to the model, causing retransmissions to be reduced compared to all other schemes. The scheme considers both the delay constraints of the video stream and at the same time avoids send buffer overflow. Tests explore a variety of Bluetooth send buffer sizes and channel conditions. For adverse channel conditions and buffer size, the tests show an improvement of at least 4 dB in video quality compared to nonfuzzy schemes. The scheme can be applied to any codec with I-, P-, and (possibly) B-slices by inspection of packet headers without the need for encoder intervention.</jats:p
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
Recommended from our members
Distributed video coding in wireless multimedia sensor network for multimedia broadcasting
Recently the development of Distributed Video Coding (DVC) has provided the promising theory
support to realize the infrastructure of Wireless Multimedia Sensor Network (WMSN), which composed of autonomous hardware for capturing and transmission of quality audio-visual content. The implementation of DVC in WMSN can better solve the problem of energy constraint of the sensor nodes due to the benefit of lower computational encoder in DVC. In this paper, a practical DVC scheme, pixel-domain Wyner-Ziv(PDWZ) video
coding, with slice structure and adaptive rate selection(ARS) is proposed to solve the certain problems when applying DVC into WMSN. Firstly, the proposed slice structure in PDWZ has extended the feasibility of PDWZ to work with any interleaver size used in Slepian-wolf turbo codec for heterogeneous applications. Meanwhile,
based on the slice structure, an adaptive code rate selection has been proposed aiming at reduce the system delay occurred in feedback request. The simulation results clearly showed the enhancement in R-D performance and perceptual quality. It also can be observed that system delay caused by frequent feedback is greatly reduced, which gives a promising support for WMSN with low latency and facilitates the QoS management
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, , 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
- …