LTE (4G)

By

Waseem Ahmed Siddiqi

Assistant Professor

Electronic Department

Sir Syed University of Engineering & Technology

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LTE

LTE stands for Long Term Evolution

LTE an initialism of Long Term Evolution, marketed as 4G LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals.

It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements.

The standard is developed by the 3GPP (3rd Generation Partnership Project) and is specified in its Release 8 document series, with minor enhancements described in Release 9.

The LTE format was first proposed by NTT DoCoMo of Japan and has been adopted as the international standard.

Although marketed as a 4G wireless service, LTE as specified in the 3GPP Release 8 and 9 document series does not satisfy the technical requirements.

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CONTINUE LTE

Due to marketing pressures and the significant advancements that WIMAX, HSPA+ the LTE Advanced standard formally satisfies the ITU-R requirements to be considered IMT-Advanced.

LTE Advanced is a mobile communication standard, formally submitted as a candidate 4G system to ITU-T in late 2009, was approved into ITU, International Telecommunications Union, IMT-Advanced and was finalized by 3GPP in March 2011.

The first commercial services were launched in Sweden and Norway in December 2009[4] followed by the United States and Japan in 2010.

More LTE networks were deployed globally during 2010 as a natural evolution of several 2G and 3G systems, including Global system for mobile communications(GSM) and Universal Mobile Telecommunications System (UMTS) (3GPP as well as 3GPP2).

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FOURIER TRANSFORM

Decomposes into its constituent frequencies.

• Types of FT

DFT

Transform the discrete time domain signal in to discrete frequency domain signal

FFT

Same but faster

IDFT

Transform the discrete frequency domain signal in to discrete time domain signal

IFFT

Same but faster

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DIFFERENCE BETWEEN SINGLE

AND MULTI CARRIER

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Single carrier Multi carrier

[http://www.nt.tuwien.ac.at/fileadmin/users/wkarner/OFDMA_SCFDMA.pdf]

MULTIPLE ACCESSES TECHNIQUES

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OFDM/OFDMA

Uses multiple carriers

Each data symbol carried by individual sub

carrier

Guard band is removed

Orthogonally division

Required less bandwidth

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OFDM/OFDMA

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Frequency

Orthogonally Division

[Google images]

FDM/FDMA

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Guard

Band

OFDM TRANSMITTER

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OFDM RECIEVER

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PAPR

Peak to Average Power Ratio • Problem in OFDM/OFDMA

• Because each data symbol is carried by individual sub carrier

• The PAPR is define as

• PAPR = Peak value of the signal

Root mean square value (Average value)

• Consider single tone

Peak value is +1

RMS value is ½

PAPR is 2

• PAPR depends on RMS value

• Linear Amplifier (Solution)

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PAPR

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[http://www.dsplog.com/2008/02/24/peak-to-average-power-ratio-for-ofdm/]

OFDMA AT DOWNLINK

Why use OFDMA at downlink?

• Because of PAPR (peak to average power ratio)

• At downlink linear amplifier equipment is easily

available

• Use low power battery in mobile

• So at the uplink use SCFDMA

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CYCLIC PREFIX

Provide guard interval

Avoid ISI (inter symbol interference)

Caused by

Multipath

Band limited Channel

• For LTE the standard length of CP 4.69µsec

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CYCLIC PREFIX

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[http://www.dsplog.com/2008/02/17/cylcic-prefix-in-orthogonal-

frequency-division-multiplexing/]

LTE CHANNEL BANDWIDTH

The channel B.W for LTE is

1.4 MHz

3 MHz

5 MHz

10 MHz

15 MHz

20 MHz

• Sub carrier are spaced 15khz apart

• Symbol rate is 1/15k = 66.7µsec

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