629 research outputs found
EVEREST IST - 2002 - 00185 : D23 : final report
Deliverable pĂşblic del projecte europeu EVERESTThis deliverable constitutes the final report of the project IST-2002-001858 EVEREST. After its successful completion, the project presents this document that firstly summarizes the context, goal and the approach objective of the project. Then it presents a concise summary of the major goals and results, as well as highlights the most valuable lessons derived form the project work. A list of deliverables and publications is included in the annex.Postprint (published version
Robust header compression over IEEE 802 networks
Tese de mestrado. Redes e Serviços de Comunicação. Faculdade de Engenharia. Universidade do Porto, INESC Porto. 200
Streaming Video Performance and Enhancements in Resource-Constrained Wireless Networks
Streaming video is an increasingly popular application in wireless networks. The concept of a live streaming video yields several enticing possibilities: real-time video conferencing, television broadcasting, pay-per-view movie streaming, and more. These ideas have already been explored via the internet and have met with mixed success, largely due to the shortcomings of the underlying network. Taking streaming video to wireless networks, then, poses several significant challenges. Wireless networks are inherently more susceptible to failures and data corruption due to their unstable communications medium. This volatility suggests serious drawbacks for any implementation of streaming video. Video frame errors, jitter, and even complete sync loss are entirely conceivable in a wireless environment. Many of these issues have been undertaken and several approaches to mediation or even solution of these problems are underway. This thesis proposes to use advanced simulation techniques to properly exhaustively permute many vital parameters within a UMTS network and uncover, if they exist, bottlenecks in UMTS performance under considerable network load. This is accomplished via a described testing plan with simulation environment. Additionally this thesis proposes a new UDP-like transport layer specially optimized for streaming media over resource-constrained networks, tested to work with significant improvements under the UMTS cellular networking system. Finally this thesis provides several innovative new methods in the furtherance of the field of streaming media research in resourceconstrained and cellular environments. Overall this thesis makes several important contributes to an exciting and ever-growing field of active research and discussion
Error resilient packet switched H.264 video telephony over third generation networks.
Real-time video communication over wireless networks is a challenging problem because
wireless channels suffer from fading, additive noise and interference, which translate
into packet loss and delay. Since modern video encoders deliver video packets with
decoding dependencies, packet loss and delay can significantly degrade the video quality
at the receiver. Many error resilience mechanisms have been proposed to combat packet
loss in wireless networks, but only a few were specifically designed for packet switched
video telephony over Third Generation (3G) networks.
The first part of the thesis presents an error resilience technique for packet switched
video telephony that combines application layer Forward Error Correction (FEC) with
rateless codes, Reference Picture Selection (RPS) and cross layer optimization. Rateless
codes have lower encoding and decoding computational complexity compared to traditional
error correcting codes. One can use them on complexity constrained hand-held
devices. Also, their redundancy does not need to be fixed in advance and any number of
encoded symbols can be generated on the fly. Reference picture selection is used to limit
the effect of spatio-temporal error propagation. Limiting the effect of spatio-temporal
error propagation results in better video quality. Cross layer optimization is used to
minimize the data loss at the application layer when data is lost at the data link layer.
Experimental results on a High Speed Packet Access (HSPA) network simulator for
H.264 compressed standard video sequences show that the proposed technique achieves
significant Peak Signal to Noise Ratio (PSNR) and Percentage Degraded Video Duration
(PDVD) improvements over a state of the art error resilience technique known as
Interactive Error Control (IEC), which is a combination of Error Tracking and feedback
based Reference Picture Selection. The improvement is obtained at a cost of higher
end-to-end delay.
The proposed technique is improved by making the FEC (Rateless code) redundancy
channel adaptive. Automatic Repeat Request (ARQ) is used to adjust the redundancy
of the Rateless codes according to the channel conditions. Experimental results show
that the channel adaptive scheme achieves significant PSNR and PDVD improvements
over the static scheme for a simulated Long Term Evolution (LTE) network.
In the third part of the thesis, the performance of the previous two schemes is
improved by making the transmitter predict when rateless decoding will fail. In this
case, reference picture selection is invoked early and transmission of encoded symbols
for that source block is aborted. Simulations for an LTE network show that this results
in video quality improvement and bandwidth savings.
In the last part of the thesis, the performance of the adaptive technique is improved
by exploiting the history of the wireless channel. In a Rayleigh fading wireless channel,
the RLC-PDU losses are correlated under certain conditions. This correlation is
exploited to adjust the redundancy of the Rateless code and results in higher Rateless
code decoding success rate and higher video quality. Simulations for an LTE network
show that the improvement was significant when the packet loss rate in the two wireless
links was 10%.
To facilitate the implementation of the proposed error resilience techniques in practical
scenarios, RTP/UDP/IP level packetization schemes are also proposed for each
error resilience technique.
Compared to existing work, the proposed error resilience techniques provide better
video quality. Also, more emphasis is given to implementation issues in 3G networks
Prediction of RoHCv1 and RoHCv2 compressor utilities for VoIP
Modern cellular networks utilising the long–term evolution (LTE) and the coming 5G set of standards face an ever–increasing demand for low–latency mobile data from connected devices. Header compression is employed to minimise the overhead for IP–based cellular network traffic, thereby decreasing the overall bandwidth usage and, subsequently, transmission delays. Here, we employ machine learning approaches for the prediction of Robust Header Compression version 1’s and version 2’s compression utility for VoIP transmissions, which allows the compression to dynamically adapt to varying channel conditions. We evaluate various regression models employing r2 and mean square error scores next to complexity (number of coefficients) based on an RTP specific training data set and separately captured live VoIP audio calls. We find that the proposed weighted Ridge regression model explains about at least 50 % of the observed results and the accuracy score may be as high as 94 % for some of the VoIP transmissions
Wireless Video Telephony Performance Enhancements: Towards Applied Network Engineering Approach
The aim of this network engineering research is to improve video transmission performance (such as end-to-end delay) in video telephony applications in cellular network scenarios. There exists a definite need for quality-of-service (QoS) and guaranteed throughput when using streaming media. However, in wireless environments where resources are precious, this is often not possible, especially with a large user base that is communicating simultaneously. Not only does traffic load pose a problem, but also the inherent instability of the radio links makes the task considerably more difficult. This presents the need for a new method for undertaking the task of wireless streaming media in resource-constrained cellular environments. Introduced and studied here is the effectiveness of a new transport-layer method based on UDP-lite, which is shown to significantly improve the performance of streaming media over noisy wireless networks in the Universal Mobile Telecommunications System (UMTS) cellular environment
Adaptive header compression techniques for mobile multimedia networks
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Robust error detection methods for H.264/AVC videos
The 3rd generation of mobile systems is mainly focused on enabling multimedia
services such as video streaming, video call and conferencing. In order to achieve
this, the Universal Mobile Telecommunications System (UMTS), is the standard that
has been developed by the 3rd Generation Partnership ect (3GPP) in Europe,
including the baseline profile of H.264/AVC in the specification. With the union of
both technologies a great improvement on video transmission over mobile networks,
and even modification of the user habits towards the use of the mobile phone is expected.
Nevertheless, video transmission has always been related to wired networks
and unfortunately the migration to wireless networks is not as easy as it seems.
In real time applications the delay is a critical constraint. Usually, transmission
protocols without delivery warranties, like the User Network Protocol (UDP) for IP
based networks, are used. This works under the assumption that in real time applications
dropped packets are preferable to delayed packets. Moreover, in UMTS the
network needs to be treated in a different way, thus the wireless channel is a prone
error channel due to its high time variance. Typically, when transmitting video, the
receiver checks whether the information packet is corrupted (by means of a checksum)
or if its temporal mark exceeds the specified delay. This approach is suboptimal, due to the fact that
perhaps the video information is not damaged and could still be used.
Instead, residual redundancy on the video stream can be used to locate the errors
in the corrupted packet, increasing the granularity of the typical upper-layer checksum
error detection. Based on this, the amount of information previous to the error
detection can be decoded as usually.
The aim of this thesis is to combine some of the more effective methods concretely, Syntax check, Watermarking and Checksum schemes have
been reformulated, combined and simulated
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