3GPP(LTE)courseClick to edit Master subtitle style

Presented B Eng.karim Banawa Eng.Yasser Youssr

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Mobile Communication style Click to edit Master subtitle part (4) : 4G mobilesEng. Karim Banawan Faculty of Engineering Electronics and communication department5/4/12

OFDM and OFDMA technologies

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OUTLINE

NEED FOR MULTI-CARRIER ENTERS INTO THE PICTURE TIME INSERTION ESTIMATION5/4/12 RESULTS

OFDM FFT GUARD

/ IFFT

OFDM DRAWBACKS BLOCK DIAGRAM

CHANNEL OFDM

SIMULATION

NEED FOR MULTICARRIERTime Domain Analysis

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NEED FOR MULTICARRIER cont.

Pulse completely distorted. ISI is significant in this case.

Pulse extended but the extension are much smaller than T the output behaves like the transmitted rectangular pulse.5/4/12

NEED FOR MULTICARRIERcont.Frequency Domain Analysis

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NEED FOR MULTICARRIER cont.

Conclusion

Wide pulses is needed for simple equalization, But Narrow pulses is needed for high data rateSolution

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NEED FOR MULTICARRIERcont.

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NEED FOR MULTICARRIER cont.Problem

Solution Orthogonality5/4/12

NEED FOR MULTICARRIERcont.

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NEED FOR MULTICARRIERcont.

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OFDM ENTERS INTO THE PICTUREInterference Orthogonality B.W efficiency Min Separation

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OFDM ENTERS INTO THE PICTURE cont.Min

Separation

Problem

Difficult Implementation with traditional oscillators DFT But DFT needs high processing5/4/12

Solution

Solution

FFT / IFFT

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FFT/IFFT

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GUARD TIME INSERTIONChannel Filtering

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GUARD TIME INSERTION cont.Problem

.ISI occurs5/4/12

GUARD TIME INSERTION cont.Solution Cyclic Prefix

. No ISI Circular Convolution achieved.5/4/12

Cyclic prefix

The CP allows the receiver to absorb much more efficiently the delay spread due to the multipath and to maintain frequency Orthogonality. CP that occupies a duration called the Guard Time (GT), often denoted TG, is a temporal redundancy that must be taken into account in data rate computations.

The

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OFDM DRAWBACKScont.Peak to Average Power Ratio (PAPR)

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OFDM DRAWBACKScont.

Sensitivity to frequency offset

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CHANNEL ESTIMATION Estimation Pilot Based ChannelReceived Signal after FFT Estimated Channel Response

Known

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CHANNEL ESTIMATIONcont. Pilot Arrangement TypesBlock Pilot PatternsFrequency( sub carriers)

Comb Pilot PatternsFrequency( sub carriers)

Pilot symbols Data symbols

Time (OFDM High channel Symbols)

Time (OFDM 5/4/12 rapid changing Symbols)

OFDMAOFDMA is

a multiple access method based

on OFDM signaling that allows simultaneous transmissions to and from several users along with the other advantages of OFDM.

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OFDM versus OFDMA

IEEE802.16d IEEE802.16e

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Diversity and mimo principles

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What is diversity?Is a technique that combats the fading by ensuring that there will be many copies of the transmitted signal effected with different fading over time, frequency or space.

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1-Time diversity:We averaging the fading of the channel over time by using : 1-The channel coding and interleaving. 2-Or sending the data at different times. to explain this we will see an example:5/4/12

1-time diversity:| H(t)|

t

No interleaving x1 x2 x3 x4 y1 y2 y3 y4 z1 z2 z3 z4 h1

h2 h3 h4 interleaving y4 z4 h4 x1 y1 z1 h1 x2 y2 z2 h2 x3 y3 z3 h3 x45/4/12

2- frequency diversity:This type of diversity used for the frequency selective channels as we will averaging the fading over the frequency by using: 1-Multi-carrier technique like OFDM. 2-FHSS (frequency hope spread spectrum). 3-DSSS (direct sequence spread 5/4/12 spectrum).

2- frequency diversity:

We can see that each sub-band will effecting with different fading over 5/4/12 the frequency.

3-spatial diversity:we will have many copies of the transmitted signal effects with different fading over the space . we use multi-antenna systems at the transmitter or the receiver or at both of them.

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Receive diversity:

1-The receiver will has many antennas . 2-Each one has signal effecting with different fading. 3-number of different paths =Mr.

Diversity order=Mr5/4/12

MIMO:

In this type we use multi antennas at both the transmitter and receiver as Diversity shown. order=Mt x Mr5/4/12

Notes:The higher diversity order we have the better we combat the fading

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Notes:1-The diversity reduces the BER of the communication system. 2-Diversity order BER .5/4/12

Notes:

The distance between the antennas must be larger than the coherent distance to ensure that data streams are not correlated . 5/4/12

Question?How the receiver get the signal from the many copies reached ?

Answer

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Diversity combining technique1-Combines the independent fading paths signals to obtain a signal that passed through a standard demodulator. 2-The techniques can be applied to any type of diversity. 3-combining techniques are linear as the output of is a weighted sum of the different fading signals of branches. 5/4/12

Diversity combining techniqueThe signal output from the combiner is the transmitted signal s(t) multiplied by a random complex amplitude term Diversity order

Fading of the path

Type of techniqu e

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Random SNR from the

Diversity combining technique

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selection combining technique1-the combiner outputs the signal on the branch with the highest SNR . 2-no need here for the cophasing.

0

0

1

0

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Threshold combining technique

so that its performance less than the SC technique.

As in SC since only one branch output is used at a time and outputting the first signal with SNR above a given threshold so that Does not take co-phasing is not required. the largest SNR

Special case at diversity order =2 5/4/12 (SSC)

Maximal ratio combiningIn maximal ratio combining (MRC) the output is a weighted sum of all branches due to its SNR

h1 *

h2 *

h3 *

hi*

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Equal gain combining technique

A simpler technique is equal-gain combining, which co-phases the signals on each branch and then combines them with equal weighting

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MIMO Traditional

diversity is based on multiple receiver antennas Multiple-In Multiple-Out (MIMO) is based on both transmit and receive diversity known as Space Time Coding (STC) Mt transmission antennas and Mr receiver antennas we have Mt Mr branches and Rx processing is performed over space (antennas) and time (successive symbols)

Also With Tx

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47 47

MIMO or STC In

Mobile communication systems it may be difficult to put many antennas in the mobile unit in the downlink (from base station to mobile station) can be achieved by Multiple-In Single-Out (MISO) (i.e., Mr=1) the uplink (from mobile station to base station) diversity is achieved my conventional diversity (SIMO) all diversity cost is moved to the base station

Diversity

In

Hence, All

3G and 4G mobile communication system 48 5/4/12 employ MIMO in their standard 48

Type of MIMOTwo

major types of space time codingSpace time block coding (STBC) Space time trellis coding (STTC)

STBC STBC

is simpler by STTC can provide better performance is used in mobile communications. STTC is not used in any systems yet5/4/12

49 49

Space Time Block CodesThere

are few major types

Transmit diversity: main goal is diversity gain Spatial multiplexing: main goal is increase data rate Eigen steering: main goal is both. Requires knowledge of the channel at the transmitter side Mix of the above: Lots of research

Transmit

diversity, spatial 5/4/12

50 50

Transmit DiversityTake Two

Mt=2 and Mr=1

symbols so and s1 are transmitted over two transmission periods change in data rate (denoted as rate 1 STBC) is known at receiver only

No

Channel

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Transmit Diversity TransmissionA nt o Ant1 matrix:6 4 7 48 s o s1 Timeo S = * s1 s o* Time1

Transmission

matrix columns are orthogonal to guarantee simple linear processing at the receiver ro s o s1 are no Other transmission matrices g o defined in R = = * + n * literature r1 s1 s o g 1 1 Received

signal is:

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Transmit Diversity

Take Mt=2 and Mr=2 is the same as MRC with M=4 if Tx Power is the same, then transmit diversity (2x2) is 3 dB worse than (1x4)

Performance However,

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Performance MRRC=Maximal Note

Ratio Receiver Combining

3 dB difference in favor of Rx MRC diversity

Reference: S. Alamouti, a simple transmit diversity technique for wireless communications, IEEE JSAC, October 98No diversity Order 2

Orde r4

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Spatial Multiplexingro = s o g o + s 1 g 1 r1 = s o g 2 + s1 g 3 Purpose The

is to increase data rate (2x2 gives twice data rate) 4 gains must be known at receiver way zero forcing algorithm: r 1 s o H H o s = G G G r 1 15/4/12 55 55

Simplest

ro g o g 1 s o r = g g 3 s1 1 2 2 43 14G

Spatial Multiplexingro = s o g o + s 1 g 1 r1 = s o g 2 + s1 g 3

Optimum method: Maximum Likelihood

Try all combinations of s1 and s2 Find the combination that minimizes the squared 2 2 2 +error: ro so g o s1 g1 + r1 so g 2 s1 g3 e1 =5/4/12 56 56

eo2

Performance

Equal rate comparison Reference: David Gesbert, Mansoor Shafi, Da-shan Shiu, Peter J. Smith, and Ayman Naguib, From theory to practice: an overview of MIMO space time coded wireless systems, IEEE JSAC, April 2003 5/4/12

Zero forcing ML Alamo uti

57 57

Eigenvalue Steering

Assume a MIMO system

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Eigenvalue Steering Example

with Mt = 2 and Mr=4

y 1 h11 y h 2 = 21 y 3 h31 y 4 1 42 h41

H

h12 h 22 h32 h 42 43

n1 x 1 n 2 x + n 2 3 n 4

[ y ] = H [ x ] +[ n]

H H can V H represented Any matrix = U be using Singular Value Decomposition asU5/4/12 is Mr by Mr and V is Mt by Mt 59 59

Eigenvalue Steering

Using transmit pre-coding and receiver shaping

% y =U H ( H x + n ) = U H ( U VH

% = U H ( U V H V x + n ) % = U H U V H V x +U H n % % = x +n5/4/12 60 60

x +n)

Eigenvalue Steering This The

way we created r paths between the Tx and specific Rx without any cross interference channel (i.e., Channel State Information) must be known to both transmitter and receiver Mr) value of r = rank of matrix H, r min(Mt, all r paths have good SNR rate can increase by factor r

The Not

Data See See

Appendix C for Singular Value Decomposition Matlab function [U,S,V] = svd(X)5/4/12 61 61

Example

Reference: Sanjiv Nanda, Rod Walton, John Ketchum, Mark Wallace, and Steven Howard, A high-performance MIMO OFDM wireless LAN, IEEE Communication Magazine, February 2005

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62 62

Introduction to LTE and Its Unique technologies.

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What is LTE??

The 3GPP LTE is acronym for long term evolution of UMTS . order to ensure the competitiveness of UMTS for the next 10 years and beyond, concepts for UMTS Long Term Evolution (LTE) have been introduced in 3GPP release 8. LTE is also referred to as EUTRA (Evolved UMTS5/4/12 Terrestrial Radio

In

What is LTE(cont.)?The

architecture that will result from this work is called EPS (Evolved Packet System) and comprehends E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved Packet Core) on the core side. be considered the real 3.9G & invited to join the 4G family. considered a competitive 5/4/12

Can

Also

What is LTE (cont.)?

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LTE design targets

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(a) capabilities:

Scalable BW: 1.25, 2.5, 5.0, 10.0 and

20.0 MHz.Peak

data rate:

Downlink (2 Ch MIMO) peak rate of 100 Mbps in 20 MHz channel Uplink (single Ch Tx) peak rate of 50 Mbps in 20 MHz channel

Supported antenna configurations:Downlink: 4x4,4x2, 2x2, 1x2, 1x1 Uplink: 1x2, 1x1

Duplexing

modes: FDD and TDD Number of active 5/4/12 mobile terminals:

Spectrum efficiencyDownlink: 3 to 4 x HSDPA Rel. 6 5bits/s/Hz Uplink: 2 to 3 x HSUPA Rel. 62.5bits/s/hz

Latency

C-plane: