Electrical Engineering and Computer Science Department

Analysis of Coding Techniques in

LTE-Advanced / 4G

Advisor: Dr. TorkamaniInstructor: M. Naslcheraghi

Jan, 2015

Retransmission of data

Information

Reliable Information

number of symbols in the

source encodedmessage is increased

Error

Detection

Correction

Amount Depends on SNR

coding techniques in LTE-Advancea broadly used term mostly referring to the

forward error correction code

Transmission channel

can often be avoided, at the cost of higherbandwidth requirements on average

Performance Evaluation of physical layer of 4G

•Reed-Solomon Coding

•convolution codingFor Coding Schemes

•Cyclic Prefix

•Interleaving

For Modulation

Schemes

Physical Layer Infrastructure Setup

Random Data Generation

IFFT Cyclic Prefix insertion

Chanel Encoding Mapping

Cyclic Prefix Removal

FFT

De-mappingChanel DecodingOutput Data

IEEE 802.162004

Step 1• Randomization

Step 2• Forward Error Correction (FEC)

Step 3• Interleaving

Step 2.1 • Reed-Solomon (RS)

Step 2.2• Convolutional Code

Channel Encoding Setup

Full Channel Coding/Decoding Setup

Data Randomization

Reed-Solomon Encoding

Convolutional Encoding

Interleaving

De-Interleaving

Convolutional Encoding

Reed-Solomon Encoding

De- Randomization

Encoding Setup

Decoding Setup

Randomization necessityOn each burst of each allocation, a long sequence of continuous ones and zeros will be generated.

Solution is Randomization with ScramblerImplementation with a Pseudo Random Binary Sequence (PRBS) Generator which uses 15 stage shift register with a generator polynomial of 1+x14+x15with XOR gates in feedback configuration.

Reed-Solomon coding setup

Block Format Randomized

Data

Before Coding

single 0X00 tail byte is appended to the end of each burst

RS Encoder

Implementation of RS (Specially in LTE Systems)

Encoder

• Systematic RS with these Parameters:

(N=255, K=239, T=8) With GF= 2

Code Generator and Field Generator Derived from

8

Main Characteristic of LTE-RS Encoder

• support shortened and punctured code to facilitate variable block sizes and variable error correction capability.

k´ bytes Shortened Block ?

adding 239k´zero

bytes

Data Block

RS- EncodingEncoded Data Block

Will be Discarded after decoding

Convolutional Coding Setup

• Fed for encoder ?

convolutional encoder

RS-Encoded Data Block

Final Encoded Data Block

Implementation of Convolutional Encoder (Specially in LTE)

native rate of ½constraint length of 7

Size of the block is depended on the numbers of bit encoded per sub channel.In one OFDM symbol. Defined in IEEE 802.16

Final Encoded Data Block B

lock

In

terl

eave

r

Interleaved Data

RSCC

IFFT

• The grey mapped data are then sent to IFFT for time domain mapping. Mapping to time domain needs the application of Inverse Fast Fourier Transform (IFFT). In our case we have incorporated the MATLAB ´IFFT´ function to do so. This block delivers a vector of 256 elements, where each complex number clement represents one sample of the OFDM symbol.

Cyclic Prefix Insertion

• A cyclic prefix is added to the time domain samples.

• to combat the effect of multipath

References

1. International Journal of Computer Applications (0975 –8887), Analysis of Coding Techniques in LTE.

2. Google!

Direct Downloadwww.Teleinfra.net/download/coding.pdf