It is therefore suitable for delivering data that must arrive without delay. It uses Session Description Protocol SDP 22 to carry all descriptive information associated with the streaming session. Figure 2 shows an overview diagram of a typical wireless streaming multimedia system. It can be viewed as a set of protocols, working in concert to deliver wireless video and audio.
It comprises three major subsystems, that is, content creation subsystem, multimedia distribution subsystem and multimedia terminal subsystem. Each major subsystem is divided into mandatory features that are needed to guarantee interoperability in the network and optional features that will lead to better performance and user experience in a deployed system.
All the mandatory features and most of the optional features are defined in a formal international standard. In the next section, we use PacketVideo's technologies as an example to highlight some of the most challenging issues in the deployment of a wireless multimedia streaming system. PacketVideo has developed technologies specifically for wireless multimedia applications For content creation, a number of signal processing functions such as source noise prefiltering, scene change detection and rate control are critical for achieving good quality of the compressed video.
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Among others, rate control is a central piece for video codecs to achieve consistent good quality across the whole sequence under the channel bandwidth and buffer constraints. One of the challenges in rate control for wireless multimedia applications is to be able to handle video sequences of varying characteristics in a simple and coherent way.
Most existing rate control solutions suffer from two fundamental problems, that is, stationarity assumption, which results in constant bit allocation among GOPs Group of Pictures , and model parameter misestimation. Although these prior solutions may work fine for some standard test sequences that are usually simple and more stationary, they typically have problems when dealing with more complex sequences.
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In particular, an R—mad rate vs. It also provides the functionality of proactively adjusting the actual frame rate in return for higher image quality in a more deterministic way, as opposed to the passive random bursty frame dropping experienced in many prior methods. On average, the PSNR gain is 0. Note that when a frame is skipped, the previous encoded frame is used in the PSNR calculation based on the fact that the decoder displays the previous encoded frame instead.
As a result, the skipped frames can usually be easily identified, for example, those points with lower than 25 dB PSNR value. Bit errors in the received bitstream are localized through the use of resynchronization markers. With this syntax, the motion information is separated from the texture information, which facilitates the recovery of the more important motion vector information in the case of bit errors, as will be discussed in the next section. In the Bitstream Decoder, the detection, localization, containment and concealment of errors is one of the most crucial components of PacketVideo technology for wireless video.
PacketVideo algorithms also address compression artifacts with practical solutions for the complex postprocessing problem, which is critical to the subjective quality of the decoded video, especially at lower bit rates. With this syntax, when motion vectors are correctly reconstructed but errors are detected in the texture component, it is possible to use only the motion vector information to recreate the decoded image.
3G – Third Generation Mobile Communications
When errors are detected in the motion data, PacketVideo algorithms recover lost motion vector information via smart bitstream decoding 28 , which is then used for concealment. This clearly shows the benefit of PacketVideo error resilient decoding techniques. In addition to error resilience, wireless multimedia delivery faces several other challenges, especially in dealing with bandwidth variations Wireless channel bandwidth can vary significantly, depending on the signal strength and interference level that a user receives.
As a result, as a user travels through different parts of the cell, different bandwidths may be dynamically assigned to the user. In addition, depending on the quality of service QoS capability of the wireless network, multiuser sharing of the wireless channel with heterogeneous data types can also lead to significant user channel bandwidth variation. This bandwidth variation can further lead to network buffer overflow and hence packet loss.
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This unpredictability of available wireless channel bandwidth introduces high delay jitter for the multimedia streaming data. QoS guarantee in a wireless network is often costly, if not impossible, since the capacity of a wireless network is related to the uncontrollable RF condition. To deal with such issues, technologies such as dynamic rate control DRC based on estimated network bandwidth 25 , 29 , selective retransmission 30 and streaming in advance 31 need to be employed.
During streaming, PVPlayer monitors many different aspects of the PacketVideo stream to detect packet loss and fluctuations in bandwidth and communicates these through RTCP reports to the streaming module. The streaming module then uses a unique set of algorithms, specifically designed for wireless networks, to make a rate decision and regulate the frame rate.
The result is uninterrupted video streaming at decent quality. It has been demonstrated that PacketVideo DRC streaming server effectively tracks the variation of bandwidth for scalable video streaming and significantly reduces player rebuffering Another way to deal with channel bandwidth variation is, albeit at the cost of storage overhead, to do dynamic bitstream switching among multiple bitstreams with different bit rates PacketVideo has developed fast intelligent switching algorithms to reduce the drifting artifacts caused by bitstream switching.
With such intelligent switching, a more complex solution such as the SP frame solution 32 may not be necessary. To facilitate efficient network and service planning, it is important to have a good understanding of the feasibility and impact of delivering streaming video over a 3G network. Packetvideo has performed various field trials and lab trials on streaming video over various 2.
It has been found that the average throughput for scalable video streaming is much better than that for nonscalable video streaming under a pure video traffic condition.
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Moreover, the packet loss rate for scalable video streaming is much lower than that for nonscalable video streaming, which demonstrates that scalability is a critical element for a successful deployment of wireless video streaming service. It was also found that with a mixed scalable video and web traffic, the CDMA 1x system is able to achieve higher spectrum efficiency than that for web traffic only. Other approaches to deal with channel bandwidth variation and packet loss include selective retransmission 30 and streaming in advance Thus time slots in a physical channel are divided into transmission and reception part.
A pair of frequency bands with specified separation is assigned for a connection. Since different regions have different frequency allocation schemes, the capability to operate in either FDD or TDD mode allows for efficient utilization of the available spectrum.
Support of high data rate transmission: Kbps with wide area coverage, 2 Mbps with local coverage. High service flexibility: support of multiple parallel variable rate services on each connection. Built in support for future capacity and coverage enhancing technologies like adaptive antennas, advanced receiver structures and transmitter diversity. Support of inter frequency hand over and hand over to other systems, including hand over to GSM. Providing good in-building coverage plays an important role in attracting and retaining mobile subscribers.
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Ordinarily, coverage from the macro network extends into buildings but should be complemented by dedicated in-building systems. Greater data capacity and the ability of third-generation networks to provide high-speed data services increase the demands put on the cellular network. Published in: Technology , Business. Full Name Comment goes here. Are you sure you want to Yes No. Md Sahab Uddin. Ahmed Elaraby , Communication engineer at Communication engineer. Mona Dadhich , completed mba in ib now searching for job.
Introduction to 3G Mobile Communications, Second Edition
Show More. No Downloads. Views Total views. Actions Shares. Embeds 0 No embeds. No notes for slide. Introduction to 3G 1. By June , the millionth 3G subscriber had been connected.