abstract wireless video in cdma

7/29/2019 Abstract Wireless Video in Cdma

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Abstract of Wireless Video Service in CDMA Systems

Video services are becoming an integral part of future communication systems.

Especially for the upcoming 3G-CDMA system wireless networks such as UMTS,

video may very well turn out to be the key value addition that achieves the required

return of investment. While previous generations of wireless communication systemswere primarily designed and used for voice services, next generation systems have to

support a broad range of applications in a wide variety of settings. The early market

stages were characterized by the needs of early adopters, mostly for professional use.

As the market matures from the early adopters to normal users, new services will be

demanded. These demands will likely converge toward the demands that exist for

wired telecommunications services.

Market research finds that mobile commerce for 3G wireless systems and beyond will

be dominated by basic human communication such as messaging, voice, and video

communication [1]. Because of its typically large bandwidth requirements, videocommunication (as opposed to the lower rate voice and the elastic e-mail) is expected

to emerge as the dominant type of service in 3G/4G wireless systems. Video services

obth real-time services and streaming services are gaining a lot of importance and

applications in CDMA systems.

There are three ways to spread the bandwidth of the signal:

Frequency hopping. The signal is rapidly switched between different frequencies

within the hopping bandwidth pseudo-randomly, and the receiver knows beforehand

where to find the signal at any given time.

Time hopping. The signal is transmitted in short bursts pseudo -randomly, and the

receiver knows beforehand when to expect the burst.

Direct sequence. The digital data is directly coded at a much higher frequency. The

code is generated pseudo-randomly, the receiver knows how to generate the same

code, and correlates the received signal with that code to extract the data.

These direct sequence spread spectrum signals can be digitized voice, ISDN channels,

modem data, etc.

Why real-time video Traffic is difficult to handle

Video Requires Extremely Large Bitrate

Large Bandwidth Requirement for Video Sources vs. Limited Resources of Wireless

Networks.

High Compression Ratio Bitstreams Extremely Sensitive to Channel Errors and


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Network Impairments.

Stringent Latency Requirements.

Compressed Video Requires Error Protection

Most Existing Video Compression Standards Originally Not Designed for LossyChannels.

Appropriate Error Protection Schemes: an Important Research Topic.

Video Streaming over CDMA-Based Wireless Networks

In video streaming services, the playout begins when the queue length of the receiver

buffer is above a threshold. This threshold must be large to reduce the buffer

underflow probability and absorb the bit rate variations caused by the wireless

channel. On the other hand, it is important to reduce this threshold in order to reduce

the initial playout delay and also the size of the receiver buffer. Here a videostreaming service is considered, where the last link is a wireless CDMA-based link

and it has been shown how a truncated power control allows to reduce the pre-roll

delay without increasing the average transmission power and without degrading the

video quality. It presents the proposed truncated power control and an analytical

model to evaluate the achievable pre-roll delay reduction.


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System ModelThe system model consists of a source, a server and a client. As shown in Figure 2,

the video streaming passes through a wired network without losses and a lossy

wireless link with CDMA-based transmission. The source can be a live program or a

prestored program; in the first case the source passes a video frame to the server everyt seconds, while in the second case the source passes all of the video frames to the

server at the beginning of the session. The server is responsible of delivering video

frames from the source to the client through a heterogeneous wired/wireless network;

in this paper we refer to a UDP-based transport platform. The UDP protocol does not

permit to recover from data losses and this functionality is left to the link.

The server encapsulates each video frame within a UDP packet and each packet is

enqueued into the UDP transmission buffer. Both at the server side and at the client

side a link layer ARQ buffer and a playout/UDP buffer are needed. At the client side,

the playout begins when the queue length n of the playout buffer is above a specifiedthreshold Npr. Such a phase is called pre-roll process and it is needed in order to

reduce the buffer underflow probability at the expenses of an initial delay (pre-roll

delay). At the client side, underflow occurs when n = 0; after the buffer underflow

occurrence the receiver temporarily suspends the playout of the video and a new pre-

roll process starts. Both the pre-roll delay and the buffer underflow probability

depends on the pre-roll threshold Npr and on the channel reliability. Large Npr results

in a small underflow probability but increase the pre-roll delay.It is common for

streaming media clients to have a 5 to 15 seconds of buffering delay before playback

starts.

Video Conferencing

Videoconferencing is a medium where two or more people at different locations can

meet face-to-face in real time .Offers new possibilities to connect with guest speakers

and experts.Can make relevant learning opportunities more accessible and exciting.

Videoconferencing is the conduct of a videoconference (also known as a video

conference or video teleconference) by a set of telecommunication technologies which

allow two or more locations to communicate by simultaneous two-way video and

audio transmissions. It has also been called 'visual collaboration' and is a type ofgroupware .

Videoconferencing uses audio and video telecommunications to bring people at

different sites together. This can be as simple as a conversation between people in

private offices (point-to-point) or involve several (multipoint) sites in large rooms at

multiple locations. Besides the audio and visual transmission of meeting activities,


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allied videoconferencing technologies can be used to share documents and display

information on whiteboards.

abstract wireless video in cdma

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