Download - LTE Course
3GPP(LTE)courseClick to edit Master subtitle style
Presented B Eng.karim Banawa Eng.Yasser Youssr
5/4/12
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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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
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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
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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
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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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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: