ECE 6332, Fall, 2014

Wireless Communication

Zhu Han

Department of Electrical and Computer Engineering

Class 21

Apr. 7th, 2014

                                                           

                                                           

OutlineOutline MIMO/Space time coding

Trellis code modulation

BICM

Video transmission (optional)

Unequal error protection and joint source channel coding

Homework 4– Will announced by email.

                                                           

MIMOMIMO Model

TNTMMNTN WXHY

T: Time index

W: Noise

                                                           

Alamouti Space-Time Code Alamouti Space-Time Code • Transmitted signals are orthogonal =>

Simplified receiver

• Redundance in time and space => Diversity

• Equivalent diversity gain as maximum ratio combining => Smaller terminals Antenna

1Antenna 2

Time n d0 d1

Time n + T

- d1* d0

*

                                                           

Space Time Code PerformanceSpace Time Code Performance

STBC

Block of K symbols

Block of T symbols

nt transmit antennas

Constellation mapper

Data in

• K input symbols, T output symbols T K• R=K/T is the code rate code rate • If R=1 the STBC has full rate full rate • If T= If T= nt the code has minimum delayminimum delay• Detector is Detector is linearlinear !!! !!!

                                                           

BLASTBLAST Bell Labs Layered Space Time Architecture V-BLAST implemented -98 by Bell Labs (40 bps/Hz) Steps for V-BLAST detection

1. Ordering: choosing the best channel

2. Nulling: using ZF or MMSE

3. Slicing: making a symbol decision

4. Canceling: subtracting the detected symbol

5. Iteration: going to the first step to

detect the next symbol

Time

s0

s0

s0

s0

s0

s0

s1

s1

s1

s1

s1

s2

s2

s2

s2

V-BLAST

D-BLAST

Ante

nna

s1 s1 s1 s1 s1 s1

s2 s2 s2 s2 s2 s2

s3 s3 s3 s3 s3 s3

                                                           

Trellis Coded ModulationTrellis Coded Modulation

1. Combine both encoding and modulation. (using Euclidean distance only)

2. Allow parallel transition in the trellis.

3. Has significant coding gain (3~4dB) without bandwidth compromise.

4. Has the same complexity (same amount of computation, same decoding time and same amount of memory needed).

5. Has great potential for fading channel.

6. Widely used in Modem

                                                           

Set PartitioningSet Partitioning

1. Branches diverging from the same state must have the largest distance.

2. Branches merging into the same state must have the largest distance.

3. Codes should be designed to maximize the length of the shortest error event path for fading channel (equivalent to maximizing diversity).

4. By satisfying the above two criterion, coding gain can be increased.

                                                           

Coding GainCoding Gain About 3dB

                                                           

Bit-Interleaved Coded ModulationBit-Interleaved Coded Modulation Coded bits are interleaved prior to modulation.

Performance of this scheme is quite desirable

Relatively simple (from a complexity standpoint) to implement.

BinaryEncoder

BitwiseInterleaver

M-aryModulator

SoftDecoder

BitwiseDeinterleaver

Soft Demodulator

Channel

                                                           

BICM PerformanceBICM PerformanceM

inim

um E

b/N

o (i

n dB

)

Code Rate R

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

2

4

6

8

10

12

CMBICM

M = 2

M = 64

M = 16

M = 4

AWGN Channel,Noncoherent Detection

M: Modulation Alphabet Size

                                                           

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

                                                           

HDTVHDTV

4-7 Mbps

25 - 27 Mbps

                                                           

Unequal Error ProtectionUnequal Error Protection

Multiple Description Coding

Video– Base layer vs. enhancement layer

                                                           

Unequal Error ProtectionUnequal Error Protection

For different packets with different importance, different channel coding is used.

                                                           

Joint Source Channel CodingJoint Source Channel Coding

Limited bandwidth

If source data is more, less channel protection data.

What is the best tradeoff