Presentation of the paper: Multiple Description Coding: Compression Meets the Network by Vivek K...

Presentation of the paper:

Multiple Description Coding: Multiple Description Coding: Compression Meets the NetworkCompression Meets the Network

by Vivek K Goyal

Angelos Chatzipapas

Alper Kivrak

Maria Michalopoulou

• Problem: – The web browser repeatedly gets stuck with partially

loaded web pages• Solution:

– More antennas on laptops => higher throughput and better reliability

– More cellular base stations imply smaller cells => fewer conflicts with other users

– Wireless service provider could provide higher capacities in the wired connections to its based stations => fewer packets lost due to buffer overflows

Introduction (1)

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Seminar in Communications EngineeringSeminar in Communications Engineering

Focus of this article: Compressed representations of the picturesThe representation does not affect how many bits get from the web server to your laptop, but it determines the usefulness of the bits that arrive.

Introduction (2)

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Current systems typically generate

content with a progressive coder and

deliver it with TCP

In a progressive transmission the quality improves steadily as the number of consecutive packets received, starting from the first, increases

The order of the packets is critical

Progressive transmission works well

when the packets are sent and

received in order without loss

Where does a conventional system go wrong?

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Background:– MD coding was invented at Bell Laboratories in

connection with communicating speech over the telephone network

Telephone system = reliability but outages of transmission links are inevitable

– 1970: the primary mechanism for providing uninterrupted service despite link outages was to divert calls to standby transmission links

=> increases cost and not all the installed links are used in normal operation

MD Model - History (1)

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– To improve reliability without standby links

=> split the information from a single call and send on two separate links or paths

in normal operation both halves of the transmitted data would be combined for the usual voice quality an outage of one link would allow for communication at reduced quality


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In telephony, speech signal is bandlimited to 3.2 kHz and sampled at 8 kHz

Jayant: sampling at 12 kHz so that subsampling by a factor of two results in only slight aliasing. The odd- and even-numbered samples are compressed separately with differential pulse code modulation and sent on two separate channels. Decoding from both channels requires a DPCM decoder for each channel and the interleaving of the samples, resulting in a signal with 12 kHz sampling and some amount of DPCM quantization noise. To decode from a single channel, adaptive linear interpolation is used.


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•During “Channel Splitting”, following question comes to mind,

•“If an information source is described with diferrent descriptions, what are the limitations on qualities of these descriptions taken separately and jointly?”

• This is known as MD problem

MD Problem (1)

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•MD situation with two descriptions;

•Scenario for 2 channels and 3 receivers•General case has M channels and 2^(M-1) receivers

MD Problem (2)

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•MD coding is difficult because of conflicting requirement;

• If we have good description at rate R1 and R2,no need to spend R1+R2 total bits•Just use better one•Also, good compressed R1+R2 is difficult to split into two

• Making descriptions individually good is the fundamental trade of MD coding

MD Problem (3)

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•So, MD Model leads to several problems in rate distortion theory and practical compression

Problem to determine corresponding values (R1,R2,D0,D1,D2)

•Aim is to code with no more total bits than would be necessary to communicate the source in one description•This is the original motivation of channel splitting

MD Problem (4)

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•Successive Refinement Coding•Special case of MD coding

•Decoder 2 is removed•Information on Channel 2 is not useful without Channel1

SR Coding (1)

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•Important data should be sent on Channel1•Additional data on channel1 improve reconstruction quality•For example: for images, low pass version can be sent on channel1 and additional details can be sent on channel2•This situation occurs in packet communication when multicasting to users with different available bandwidths

SR Coding (2)

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• MD coding is unlikely to be useful under absence of following conditions– One or more users sometimes fail to receive one or

more descriptions.– Various distortions are acceptable and

distinguishable. Distortion measure must reflect utility. Central distortions lower than side distortions should create some value.

MD Coding Conditions

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Where to Use MDs (1)

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• Distributed Storage SystemsDistributed Storage Systems

Distributed Storage systems are rapidly evolving

- Internet is best example; we access every day Web pages whose display requires data from dozens of machines around the world.

The concept of Distributed Storage matches the MD framework

incredibly well.

Example Scenario: Downloading images from an Internet image library.

-Case 1: identical data is stored at the servers.

Potential Congestion very high delays or even total failure

-Case 2: low resolution versions of the image at multiple sites

Potential Congestion users have to satisfy themselves with a lower resolution version of the image reconstructed using the sites that become available within a reasonable delay.


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• In Packet NetworksIn Packet Networks

When and Why?

Retransmission mechanisms are not always

possible

- in wireless environments the links are not always bidirectional

- in real time communications the added delay is not acceptable (e.g. video streaming, voice transmission etc)

FEC performance is not sufficient if the number of packets is not

large enough

The implementation of MD in packet transmission is quite The implementation of MD in packet transmission is quite

straightforward and thus, this possibility is mentioned in many recently straightforward and thus, this possibility is mentioned in many recently

published works related to MD techniquespublished works related to MD techniques


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unit interval

1 … 2 3 4

…

TIME L

• Frequency Hopping Wireless SystemsFrequency Hopping Wireless Systems

Frequency hopping provides protection against a long-term interference

or long-term fading at the location of the receiver.

•Error characteristics are constant within unit interval

•The L carrier frequencies can be considered separate channels for and MD source code.

FREQ

channel


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• Hybrid Digital BroadcastHybrid Digital Broadcast

At the edge of a radio station’s range the interference from a station

with neighboring frequency may be significant.

200MHz

interference interference

Adding digital information to radio broadcasts for eliminating the

interference at the edges of the band

But, some users have interference at the upper edge and others have it

at the lower edge.

Thus, these edges make for good MD channels; some users will get only

one or the other channel and other users will get both.

For what types of Data?

• The data must be useful at various quality levelsThe data must be useful at various quality levels

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- Generally, it can be applied to

most data that are lossily

compressed

• audio

• images

• video

etc

- It would not be useful for:

• text

• numerical data

etc

Summarizing…

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• MD Coding in a few words:MD Coding in a few words:

- fragments a single media stream into n independent sub streams

- in order to decode the media stream, any description can be used, however, the quality improves with the number of descriptions received in parallel

• When and Why to use MD

- in many cases, it is better to have lower quality data than no data !

- So, when the transport mechanism is not perfect, compensate this with appropriate coding !

That’s all!That’s all!

Thank you for your attention!

Date post:	18-Dec-2015
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Presentation of the paper: Multiple Description Coding: Compression Meets the Network by Vivek K...

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