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LTE
by

## Nidal abdelhafez

on 9 August 2017

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Recursive systematic convolutional (RSC):
rate 1/2
Interleaver

For turbo codes, an interleaver is used between the two component encoders. The Interleaver is used to provide randomness to the input sequences.
the BER Of a turbo code will improve significantly.
Function
Turbo coding is an advanced error correction technique widely used in the communications industry. The basis of turbo coding is to introduce redundancy in the data to be transmitted through a channel. The redundant data helps to recover original data from the received data
turbo encoder
Introduction
Structure of Turbo Decoder

CRC is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data

• The use of systematic cyclic codes, which encode messages by adding a fixed-length check value, for the purpose of error detection in communication networks

•Specification of a CRC code requires definition of a so-called generator polynomial. This polynomial resembles the divisor in a polynomial long division, which takes the message as the dividend and in which the quotient is discarded and the remainder becomes the result,.
•Used polynomials:
- gCRC24(D) = [D24 + D23 + D18 + D17 + D14 + D11 + D10 + D7 + D6 + D5 + D4 + D3 + D + 1] CRC length L= 24

- gCRC16(D) = [D16 + D12 + D5 + 1] for a CRC length L = 16.

- gCRC8(D) = [D8 + D7 + D4 + D3 + D + 1] for a CRC length of L = 8.
CRC
Orthogonal Frequency Division Multiplexing
(OFDM)
OFDM can be viewed as a form of FDM with the special property that each carrier is orthogonal with every other carrier
Orthogonality
Each OFDM subcarrier has a sinc function

ISI occurs due to
1- multipath channel
2- the non linear phase response of the channel

- The OFDM deals with this problen in two ways

2)Cyclic prefix
1) Simple equalization
2)Orthogonality: BW efficiency
3)High data rate
4)Easily implemented
5)Deals with ISI and multipath fading.
LTE layers

-There are lot of interfaces at LTE where in each interface there is a certain protocol to send data with
-These protocols is divided into layers as OSI 7 layers
LTE layers
Orthogonality

FFT/IFFT
•High Data Rates:
LTE data rates reaches
•Very low latency
short setup time and short transfer delay
100ms: IDLE to ACTIVE
50ms : ACTIVE to IDLE

•Capacity
the LTE capacities in the active mode can support 200 users simultaneously at 5MHZ where at BW more than that a cell can support up to 400 simultaneously, while in the IDLE mode it can support more than 400 users at the same time.

•Compatibility and inter-working with earlier 3GPP Releases and Inter-working with other systems,

5 Km with high throughput
30 Km with low throughput
100Km with very low throughput

LTE Features
Modulation Schemes in LTE.
QPSK. 2 bits /symbol
16 QAM. 4 bits/symbol
64 QAM. 6bits /symbol
Why don't we always use 64 QAM ?
Modulation schemes
1) Function:
•Prevents long strings of ones and zeros, as they make the clock regeneration difficult.
•Decrease the DC level depending on the type of line coding used.
•More secure for the data.
•Decrease the interference
2)Theory :
•Circuit:
It consist of:
1) Linear Feedback Shift Register(LFSR)
2) Xor gates
Operation
A scrambler replaces sequences into other sequences without removing undesirable sequences

result is changes in the probability of occurrence of vexatious sequences

The operation according to the polynomials used.
Scrambler/Descrambler
Decoder
LTE physical layer block Diagram

A- priori and A-posteriori Information
•The soft output of every decoder called a posteriori information after certain subtractions it is feeded to the other component decoder and is called a-priori information.

Theory
Turbo encoder consists of two recursive systematic convolutional RSC encoders each with a rate r=1/3

each output has a different resistivity to noise according to the channel. y1 processes the raw input data, while y2 processes an interleaved version of the input data.
The coding operates on the principle that if an input symbol is corrupted in the sequence from y1, then it is unlikely also to be corrupted in the reordered sequence from y2, and vise versa.
input
y1
y2
1G (Analog)
- Voice signal
- Analogue cellular network
- AMPS
First Mobile Phone - Motorola DynaTAC 8000x

2G (GSM Standard)
- Voice and data Signals
- Digital cellular network

Global System for Mobile Communications (GSM)
-TDMA
-CDMA

2.5G (GPRS)
- Part of the GSM System
- Quality of Service
- High data rate

WAP, SMS & MMS Capable
3G ( UMTS)

- Voice , data , video signals
- High speed browsing
- W-CDMA
Generation Of Mobile Networks
Simulation of LTE Physical-Layer

Studying system based on 3GPP Standards , Simulation by MATLAB
Prepared By : Nidal abdelhafez
Supervisor : Dr. Mutamed Khatib
4G - LTE
-All over IP network
- OFDMA
Latency :
Time the terminal takes to transmit small packets to the RAN and Vice versa , the idle mode Terminal unknown for the RAN , Active mode
Terminal is known for the RAN

Coverage
Introduction
scrambled code
Turbo codes
Turbo
coding is an advanced error correction technique widely
used in the communications industry. Turbo encoders and
decoders are key elements in today’s communication
systems to achieve the best possible data reception with the fewest possible errors
it is much more susceptible to noise degradation which means that every little source of noise combines to create one great big noise problem across the system.
OFDM Transmitter
ISI
Problems the OFDM solved
1) Serial to parallel
OFDM
The used FFT size determines the number of subcarriers per symbol