ECE 4371, Fall, 2015

Introduction to Telecommunication Engineering/Telecommunication Laboratory

Zhu Han

Department of Electrical and Computer Engineering

Class 11

Sep. 28th, 2015

                                                           

                                                           

OutlineOutline Review of Analog and Exam next class

Gray Code

Line Coding Spectrum

Scrambler

Multimedia Transmission

                                                           

Gray CodeGray Code The reflected binary code, also known as Gray code,

Two successive values differ in only one digit.

http://en.wikipedia.org/wiki/Gray_code

If you check the chip, they have the bus number ordered in Gray code.

                                                           

Basic steps for spectrum analysisBasic steps for spectrum analysis Figure

– Basic pulse function and its spectrum P(w) For example, rect. Function (in time) is sinc function

(in freq.)– Input x is the pulse function with different amplitude

Carry different information with sign and amplitude Auto correlation is the spectrum of Sx(w)

– Overall spectrum

01

lim

1 1( ) 2b b

bn k k n

Tk

jnwT jnwTx n n

n nb b

TR a a

T

S w R e R R eT T

2( ) ( ) ( )y yS w P w S w

x

                                                           

Digital Communication SystemDigital Communication System Spectrum of line coding:

– Basic pulse function and its spectrum P(w) For example, rect. function is sinc

– Input x is the pulse function with different amplitude Carry different information with sign and amplitude Auto correlation is the spectrum of Sx(w)

– Overall spectrum

01

lim

1 1( ) 2b b

bn k k n

Tk

jnwT jnwTx n n

n nb b

TR a a

T

S w R e R R eT T

)()()(

2wSwPwS xy

                                                           

NRZNRZ R0=1, Rn=0, n>0

Pulse width Tb/2

P(w)=Tb sinc(wTb/2)

Bandwidth Rb for pulse width Tb

                                                           

RZ scheme

DC Nulling

Split phase 4

4sin 2

T

T

TRtr

                                                           

Polar biphase: Manchester and differential Manchester schemes In Manchester and differential Manchester encoding, the transition at the

middle of the bit is used for synchronization.

The minimum bandwidth of Manchester and differential Manchester is 2 times that of NRZ. 802.3 token bus and 802.4 Ethernet

                                                           

Bipolar schemes: AMI and pseudoternary

R0=1/2, R1=-1/4, Rn=0,n>1,

Reason: the phase changes slower

2

2 2( )( ) 1 cos sin sin

2 4 4 2b b b

y bb

P w T wT wTS w wT c

T

                                                           

EE 541/451 Fall 2006

Multilevel: 2B1Q scheme

NRZ with

amplitude

representing more

bits

                                                           

Pulse ShapingPulse Shaping Sy(w)=|P(w)|^2Sx(w)

– Sx(w) is improved by the different line codes.

– p(t) is assumed to be square

How about improving p(t) and P(w)– Reduce the bandwidth

– Reduce interferences to other bands

– Remove Inter-symbol-interference (ISI)

– In wireless communication, pulse shaping to further save BW

– Talk about the pulse shaping later

                                                           

Small questions in exam 2Small questions in exam 2 Draw the spectrums of three different line codes and describe

why the spectrums have such shapes.

                                                           

ScramblingScrambling

Make the data more random by removing long strings of 1’s or 0’s. Improve timing

The simplest form of scrambling is to add a long pseudo-noise (PN) sequence to the data sequence and subtract it at the receiver (via modulo 2 addition); a PN sequence is produced by a Linear Shift Feedback Register (LSFR).

In receiver, descrambling using the same PN.

Secure: what is the PN and what is the initial

data

scrambleddata

PN sequence length2m – 1 = 26 – 1 = 63

                                                           

ScramblingScrambling Exercise: 100000000000

                                                           

Scrambling ExampleScrambling Example Scrambler

Descrambler

                                                           

Video StandardVideo Standard Two camps

– H261, H263, H264;

– MPEG1 (VCD), MPEG2 (DVD), MPEG4

Spacial Redundancy: JPEG– Intraframe compression

– DCT compression + Huffman coding

Temporal Redundancy – Interframe compression

– Motion estimation

                                                           

Discrete Cosine Transform (DCT)Discrete Cosine Transform (DCT)

120 108 90 75 69 73 82 89

127 115 97 81 75 79 88 95

134 122 105 89 83 87 96 103

137 125 107 92 86 90 99 106

131 119 101 86 80 83 93 100

117 105 87 72 65 69 78 85

100 88 70 55 49 53 62 69

89 77 59 44 38 42 51 58

0 – black255 – white

                                                           

DCT and Huffman CodingDCT and Huffman Coding

0 – black255 – white

700 90 100 0 0 0 0 0

90 0 0 0 0 0 0 0

-89 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

                                                           

Basis vectorsBasis vectors

                                                           

Using DCT in JPEG Using DCT in JPEG

DCT on 8x8 blocks

                                                           

Comparison of DF and DCTComparison of DF and DCT

                                                           

Quantization and CodingQuantization and Coding

Zonal Coding: Coefficients outside the zone mask are zeroed.

•The coefficients outside the zone may contain significant energy

•Local variations are not reconstructed properly

                                                           

30:1 compression and 12:1 Compression30:1 compression and 12:1 Compression

                                                           

Motion CompensationMotion Compensation

I-Frame– Independently

reconstructed

P-Frame– Forward predicted

from the last I-Frame or P-Frame

B-Frame– forward predicted

and backward predicted from the last/next I-frame or P-frame

Transmitted as - I P B B B P B B B

                                                           

Motion PredictionMotion Prediction

                                                           

Motion Compensation Approach(cont.)Motion Compensation Approach(cont.)

Motion Vectors

– static background is a very special case, we should consider the displacement of the block.

– Motion vector is used to inform decoder exactly where in the previous image to get the data.

– Motion vector would be zero for a static background.

                                                           

Motion estimation for different framesMotion estimation for different frames

X Z

Y

Available from earlier frame (X)

Available from later frame (Z)

                                                           

A typical group of pictures in display orderA typical group of pictures in display order

A typical group of pictures in coding order

1 5 2 3 4 9 6 7 8 13 10 11 12

I P B B B P B B B P B B B

I B B B P B B B P B B B P

                                                           

Coding of MacroblockCoding of Macroblock

Y CB CR

Spatial sampling relationship for MPEG-1 -- Luminance sample -- Color difference sample

0 1

2 3

4 5

                                                           

A Simplified MPEG encoderA Simplified MPEG encoder

Framerecorder DCT Quantize

Variable-lengthcoder

Transmitbuffer

Predictionencoder

De-quantize

InverseDCT

Motionpredictor

Referenceframe

Ratecontroller

IN OUT

Scalefactor

Bufferfullness

Prediction

Motion vectors

DC

                                                           

MPEG StandardsMPEG Standards

MPEG stands for the Moving Picture Experts Group. MPEG is an ISO/IEC working group, established in 1988 to develop standards for digital audio and video formats. There are five MPEG standards being used or in development. Each compression standard was designed with a specific application and bit rate in mind, although MPEG compression scales well with increased bit rates. They include:– MPEG1

– MPEG2

– MPEG4

– MPEG7

– MPEG21

– MP3

                                                           

MPEG StandardsMPEG Standards MPEG-1

Designed for up to 1.5 Mbit/secStandard for the compression of moving pictures and audio. This was based on CD-ROM video applications, and is a popular standard for video on the Internet, transmitted as .mpg files. In addition, level 3 of MPEG-1 is the most popular standard for digital compression of audio--known as MP3. MPEG-1 is the standard of compression for VideoCD, the most popular video distribution format thoughout much of Asia.

MPEG-2Designed for between 1.5 and 15 Mbit/secStandard on which Digital Television set top boxes and DVD compression is based. It is based on MPEG-1, but designed for the compression and transmission of digital broadcast television. The most significant enhancement from MPEG-1 is its ability to efficiently compress interlaced video. MPEG-2 scales well to HDTV resolution and bit rates, obviating the need for an MPEG-3.

MPEG-4Standard for multimedia and Web compression. MPEG-4 is based on object-based compression, similar in nature to the Virtual Reality Modeling Language. Individual objects within a scene are tracked separately and compressed together to create an MPEG4 file. This results in very efficient compression that is very scalable, from low bit rates to very high. It also allows developers to control objects independently in a scene, and therefore introduce interactivity.

MPEG-7 - this standard, currently under development, is also called the Multimedia Content Description Interface. When released, the group hopes the standard will provide a framework for multimedia content that will include information on content manipulation, filtering and personalization, as well as the integrity and security of the content. Contrary to the previous MPEG standards, which described actual content, MPEG-7 will represent information about the content.

MPEG-21 - work on this standard, also called the Multimedia Framework, has just begun. MPEG-21 will attempt to describe the elements needed to build an infrastructure for the delivery and consumption of multimedia content, and how they will relate to each other.

                                                           

JPEGJPEG

JPEG stands for Joint Photographic Experts Group. It is also an ISO/IEC working group, but works to build standards for continuous tone image coding. JPEG is a lossy compression technique used for full-color or gray-scale images, by exploiting the fact that the human eye will not notice small color changes.

JPEG 2000 is an initiative that will provide an image coding system using compression techniques based on the use of wavelet technology.

                                                           

DVDV

DV is a high-resolution digital video format used with video cameras and camcorders. The standard uses DCT to compress the pixel data and is a form of lossy compression. The resulting video stream is transferred from the recording device via FireWire (IEEE 1394), a high-speed serial bus capable of transferring data up to 50 MB/sec. – H.261 is an ITU standard designed for two-way communication over

ISDN lines (video conferencing) and supports data rates which are multiples of 64Kbit/s. The algorithm is based on DCT and can be implemented in hardware or software and uses intraframe and interframe compression. H.261 supports CIF and QCIF resolutions.

– H.263 is based on H.261 with enhancements that improve video quality over modems. It supports CIF, QCIF, SQCIF, 4CIF and 16CIF resolutions.

– H.264

                                                           

HDTV 4KTVHDTV 4KTV

4-7 Mbps

25 - 27 Mbps