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Air Interface Evolution in Mobile NetworksAir Interface Evolution in Mobile NetworksCapacity & Performance Enhancing TechniquesCapacity & Performance Enhancing Techniques
The Way to LTE & 4The Way to LTE & 4thth Generation NetworksGeneration Networks
Prepared By: Ziad Z. Zorkot
Motorola Lebanon
Date: 14 April 2010
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Wireless EvolutionMobile Networks Evolution Starting from 2G
GSM
HSCSD
GPRS
EDGE
Enhanced EDGE
WCDMA
HSUPA
HSPA+
LTE
|
| HSPA
|
HSDPA
|
|
|
| UTRAN
|
|
|
|
|
|
| GERAN
|
|
|Based on TDMA
Based on CDMA
Based on OFDMA
20091990 1999
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GSM Evolution
CEPT GSM decision
to use TDMA
technology
Phase 1
Phase 2
Phase 2+ (R96)
Service provider display
EFR codec
Multiband operation & roaming
3V SIM SMS Cell Broadcast discontinuous operation
R97
14.4 kb/s data
Data compression
High Speed Circuit Switched Data (HSCSD)
PRM functions (group call, broadcast call, )
Multi-level precedence and pre-emption
Fast moving mobile
SIM application toolkit
Enhanced Advanced Speech Call
Calling Name presentation, CCBS, services
Improved fault management
SIM security
Private Numbering Plan
GPRS (1)
R98
1987
GSM
standardizationtransferred to ETSI
1990 1992 1995 1996 1997 1998
3GPP created
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3G Evolution
2009
R99
1999 2000
Rel-4
Rel-5
New codecs, codec management
Low chip rate TDD UMTS variant Location based services enhancement
UMTS Tx site diversity selection
LCS enhancements
IP multimedia subsystem (IMS)
Adaptive multirate codec
E-to-e QoS concepts
2001 2002 2003 2004 2005 2006 2007 2008
Rel-6
Rel-7
UTRAN Long Term Evolution study
System Architecture study
MIMO studies
UTRAN/GERAN/GAN handover
Rel-8
IMS (2) inc interworking with other IP networks
Packet-switched streaming services
Enhanced network security
Electrically tilting antennas
PS conversational codec characterization GERAN flexible layer 1
Generic access to GERAN services
HSPA+ study
UMTS radio technology (WCDMA)
Charging & billing enhancements
GPRS p-p service
1.5V SIM
Virtual Home Environment
OSA
>>>>>>> Work transferred from ETSI to 3GPP >>>>>>>
Evolved UTRAN [ie LTE]
E-UTRAN interworking with GERAN
eCall data transfer
Services alignment (for FMC) Reduced signalling latency
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Peak Data Rates
2G, 2.5G, 2.75G, 3G, 3.5G, 3.75G & 3.9G
HSPA+
42 Mbps
HSDPA
14.4 Mbps
GSM
9.6 kbps
GPRS in 2000
GSM First callmade in 1991
HSDPA in 2005
3G in 2001
EDGE in 2003
HSPA+ in 2008
LTE
320 Mbps
EDGE
473 kbpsWCDMA384 kbps
GPRS
114 kbps
3G3G
HSPA: 120 million cnt
WCDMA: 238 million cnt
2G2G GSM: 3.8 billion cnt
1990
2000
2003
2004
2006
2009
2010
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The Way to LTE
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Contents
Capacity & Performance Constraints
Enhancing Techniques
OFDM OFDMA
SC-FDMA
LTE Overview
LTE Interfaces
LTE Physical Layer
LTE Channels
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Contents
Capacity & Performance Constraints
Enhancing Techniques
OFDM OFDMA
SC-FDMA
LTE Overview
LTE Interfaces
LTE Physical Layer
LTE Channels
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High Data Rates
Fundamental Constraints
Shannon Theorem: The Capacity of a Channel is determined by the Bandwidth
and the signal to noise ratio
C: Capacity, BW: Bandwidth, S: Received Signal power, N: White Noise power
For a given C There is no limit to how small the BW can be provided that the S/N is sufficiently large
There is no limit to how small the S/N can be provided that the BW is large enough
For a given BW
There is no limit to the capacity C provided that the S/N is large enough
There is no limit to how small the S/N can be provided that the capacity C will reduceaccordingly
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Capacity vs. Bandwidth
With Respect to S/N
Rearranging The capacity equation:
When S/N = -30C/B = 0.0014
When S/N = -25C/B = 0.0046
When S/N = -20C/B = 0.014
When S/N = -15C/B = 0.045
When S/N = -10C/B = 0.138
When S/N = -5C/B = 0.396
When S/N is 0C/B = 1
When S/N is largeC/B = 0.322 * S/N
0 5 10 15 20 25 30-30
1
2
4
6
8
10
12
C/B
S/N
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Capacity Limitations
Required Eb/N0as a Function of BW utilization
Re-writing the equation as a function of:
Eb: Energy/bit, R: Information Rate, No: Constant noise power spectral density
= Eb/No (BW Utilization)
High : Any increase in
the data rate requires a
much larger relative
increase in the received
signal power
Low : Any increase of
the data rate requires
approximately the same
relative increase in the
received signal power
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Improving S/N
Increasing Data Rate
Assuming a constant transmit power, the received signal power can always be
increased by reducing the distance between the transmitter and the receiver
In a mobile communication system this would correspond to a reduced cell size andthus the need for more cell sites to cover the same overall area
High data rates are only available for mobile terminals in the center of the cell, i.e. not
over the entire cell area
Another means to increase the overall received signal power for a given transmitpower is the use of additional antennas at the receiver side, also known as
receive-antenna diversity
The signal-to-noise ratio after the antenna combining can be increased in proportion to
the number of receive antennas
Multiple antennas can also be applied at the transmitter side
The use of beam-forming by means of multiple transmit antennas will focus the transmit
power in the direction of the target receiver
Combination of multiple antennas at the transmitter and receiver side can be used to
increase the data rate (MIMO)
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Other Constraints
Nyquists Theorem
Nyquists Theorem: a channel of BW B can carry a maximum capacity of 2Bsymbols per second
C = 2B symbols / second
Example:
C = 9600 bit/s, B = 2000 Hz, Calculate S/N? bits/symbols?
C/B = log2(1 + S/N)
S/N = 14.3 dB
C = 2B symbols / second = 4000 symbols / second (baud)
in order to the required C, each symbol must contain x number of bits
9600 bit/s = x bit * 4000 symbols/s x = 9600/4000 = 2.4
So at least 3 bit/s should be available
use 8PSK modulation
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Higher Order Modulation
High Data Rate Within a Limited BW
The use of higher-order modulation provides the possibility for higher bandwidth
utilization, that is the possibility to provide higher data rates within a given
bandwidth. The higher bandwidth utilization comes at the cost of reduced robustness to noise and
interference
Higher-order modulation schemes, such as 16QAM or 64QAM, require a higher Eb/N0
at the receiver for a given bit-error probability, compared to QPSK
2 bits / symbol 4 bits / symbol 6 bits / symbol
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Spectral Efficiency
Spectral efficiency, spectrum efficiencyor bandwidth efficiencyrefers to the
information rate that can be transmitted over a given bandwidth in a specific
communication system.
It is a measure of how efficiently a limited frequency spectrum is utilized by the physical
layer protocol, and sometimes by the media access control (the channel access
protocol)
The link spectral efficiencyof a digital communication system is measured in bit/s/Hz
or simply (bit/s)/Hz
The spectral efficiency can be improved by radio resource management
techniques such as efficient fixed or dynamic channel allocation, power control,
link adaptation and diversity schemes
frequency reuse, spectrum spreading and forward error correction reduce the spectralefficiency in (bit/s)/Hz but substantially lower the required SNR ratio in comparison to
non-spread spectrum techniques
In Wireless networks, spectral efficiency is better expressed in bit/s/Hz per unit area
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Spectral Efficiency Figures
Comparison Between Different Mobile Technologies
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Contents
Capacity & Performance Constraints
Enhancing Techniques
OFDM OFDMA
SC-FDMA
LTE Overview
LTE Interfaces
LTE Physical Layer
LTE Channels
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Radio Channel Conditions
Instantaneous Variations
Mobile Radio communications are characterized by rapid and significant
variations in the instantaneous channel conditions
Frequency-selective fadingwill result in rapid and random variations in the channel
attenuation related to multipath propagation component having different propagations delays & attenuations;
when summing up in the receiver results in received signal where different frequencies of the
modulated waveform are experiencing different attenuations & phase changes
Shadow fading and distance-dependentpath loss will affect the average received
signal strength significantly (related to mobility of the receiver) The interference at the receiver due to transmissions in other cells and by other MS
Deep Fades
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Link Adaptation
Power Control
Dynamic power control dynamically adjusts the radio-link transmit power to
compensate for variations and differences in the instantaneous channel
conditions
The aim of these adjustments is to maintain a (near) constant Eb/N0at the receiver to
successfully transmit data without a too high error probability
Efficient for circuit switched voice services
transmit-power control
increases the power atthe transmitter when the
radio link experiences
poor radio conditions
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Link Adaptation
Rate Control
Data rate is dynamically adjusted to compensate for the varying channelconditions
Rate control does not aim at keeping the instantaneous radio-link data rate constant
Efficient for packet-switched data traffic Rate control implies that the power amplifier is always transmitting at full power
Radio-link data rate is controlled by adjusting the modulation scheme and/or thechannel coding rate
Rate control maintains the Eb/N0~ P/R at the desired level by changing the rate (not TX PWR)
Changing from 16
QAM 4/3 coding
rate to QPSK, coding rate
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Channel-Dependent Scheduling
Downlink Scheduling
With channel-dependent scheduling, the scheduler takes the instantaneous
radio-link conditions into account.
Scheduling the user with the instantaneously best radio link conditions is often referred
to as max-C/I (or maximum rate) scheduling
Measurements reports & signaling are needed to implement dynamic resource allocation
The channel used for transmission will typically have a high quality and, with rate
control, a correspondingly high data rate can be used
This translates into a high system capacity resulted from Multi-User Diversity
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Different Scheduling Behaviors
Max C/I, RR & PF
Max C/I Scheduling
Beneficial from system
capacity point of view but not
fair in all situation. A mobilewith bad C/I all the time will
never be scheduled
Round Robin Scheduling
the users will take turns in
using the shared resources,
without taking the instant C/Iinto account. Not fair in the
sense of providing same QoS
Proportional-fair Scheduler
it utilizes fast variations in
channel conditions as much
as possible while stillsatisfying some degree of
fairness between users
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Uplink Scheduling
Unlike the downlink, where pure TDMA often can be used, uplink scheduling
typically has to rely on sharing in the frequency and/or code domain in addition to
the time domain
Channel-dependent scheduling is also beneficial in the uplink case
In case of a non-orthogonal multiple-access scheme such as CDMA, power
control is typically essential for proper operation
Power control also serves the purpose of controlling the amount of interferenceaffecting other users
In case of orthogonal multiple-access scheme, intra-cell power control is
fundamentally not necessary and the benefits with channel-dependent
scheduling become more similar to the downlink case A terminal can transmit at full power and the scheduler assigns a suitable part of the
orthogonal resources (suitable part of the overall BW)
In Practice, a certain degree of power control maybe necessary
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Advanced Retransmission Schemes
Hybrid ARQ with Soft Combining
Hybrid ARQ is a combination of:
Forward error-correcting FEC coding
It uses forward error correcting codes to correct a subset of all errors and rely on error detection
to detect uncorrectable errors
Automatic repeat request ARQ
Erroneously received packets are discarded and the receiver requests retransmissions of
corrupted packets
Hybrid ARQ schemes are built around a CRC code for error detection and
convolutional or Turbo codes for error correction
Retransmission in any hybrid ARQ scheme must, by definition, represent the same set
of information bits as the original transmission
The set of coded bits transmitted in each retransmission may be selected differently
Hybrid ARQ with soft combining is categorized into Chase combining and
Incremental Redundancy
The received signal still contains information despite that the packet was not decoded
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Chase Combining
The retransmissions consist of
the same set of coded bits as the
original transmission.
The receiver uses MRC to
combine each received channel bit
with any previous transmissions of
the same bit and the combined
signal is fed to the decoder
Chase combining does not
give any additional coding
gain but only increases the
accumulated received Eb/N0
for each retransmission a lowaverage channel quality. (No
new redundancy is added)
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Multiple Antennas
Multiple antennas at the transmitter and/or the receiver can be used to provide
additional diversity against fading on the radio channel This is called Spatial
Diversity or Transmit / Receive Diversity
Multiple antennas at the transmitter and/or the receiver can be used to shape
the overall antenna beam (transmit beam and receive beam, respectively) in a
certain way This is called Beam Forming or Smart Antenna
For example, to maximize the overall antenna gain in the direction of the targetreceiver/transmitter or to suppress specific dominant interfering signals
The simultaneous availability of multiple antennas at the transmitter and the
receiver can be used to create what can be seen as multiple parallel
communication channels over the radio interface This is called SpatialMultiplexing or MIMO (Multiple Input Multiple Output)
This provides the possibility for very high BW utilization without a corresponding
reduction in power efficiency i.e. the possibility for very high data rates within a limited
bandwidth without an un-proportionally large degradation in terms of coverage
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Receive Diversity
Multiple antennas at the
receiver side. This is often
referred to as receive
diversity or RX diversity.the aim of the multiple
receive antennas is to
achieve additional diversity
against radio channel fading
Phase rotate the signals received
at the different antennas to
compensate for the corresponding
channel phases and ensure that
the signals are phase alignedwhen added together
Weight the signals in proportion totheir corresponding channel gains,
that is apply higher weights for
stronger received signals
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Diversity Benefits
MRC Operation
SNR enhanced
for all users after
MRC
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Spatial Multiplexing
Multiple TX/RX Antennas
Single Antenna Multiple AntennasNL: min {NT, NR)
NT: # of Tx Antennas
# of Rx Antennas
spatial multiplexing: allow for more efficient utilization of high signal-to-noise
/interference ratios and significantly higher data rates over the radio interface
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MIMO Configurations
Single Codeword Transmission
Increases the users Performance
(SNR) by sending the same data
over several channels (multiple TxAntennas for same data)
Multi-Codeword Transmission
Increases the users Throughput
and cell capacity by sending thedifferent data over several
channels (multiple Tx Antennas for
different data)
Space Time Coding
Spatial Multiplexing
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MIMO Benefits
Spatial Multiplexing
SU-MIMOIncreases the users
capacity by allowing a
single user to benefit from
multiple data streams
MU MIMO
Increases sector capacity by
selecting users having goodRF channel conditions and
sharing their data streams
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Adaptive MIMO
High SNRLow SNR
Efficiency
STBC Space Time Block Coding SM Spatial Multiplexing
Adaptive Mode
Selection
CoverageEnhancement
Capacity
Enhancement
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Smart Antennas
Beam Forming
Sectorized Configuration Simple Beamforming Full Adaptive Antenna
System
Distribution of radio energy and number of users per radio resource in sector
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Multi-Carriers Transmission
Frequency Selectivity Impact
Multi-carrier transmission is used to increase the overall transmission BW,
without suffering from signal corruption due to radio-channel frequency selectivity
Multi-carrier transmission implies the transmission of multiple narrowband signals
instead of more wideband signal (often referred to as sub-carriers)
Frequency selectivity fading
has more impact on large BW
transmission. All data within
the whole BW will be impacted
and requires retransmission
With Multi-carriers
transmission, the impact of
frequency selective fading
will be on few limited small
BW carriers only
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Concept of Multi-Carriers
Drawbacks: spectrum of each sub-
carrier does not allow for very tight
sub-carrier packing. (negative
impact on overall BW spectrumefficiency) Resulting in limited
number of sub-carriers
The parallel transmission of multiple
carriers will lead to larger variations
in the instantaneous transmit
power. (negative impact on the
transmitter power amplifier -increased power consumption and
power amplifier cost)
Single Carrier Transmission
Multi-carriers
Transmission
Extension to
wider BW
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Dual Carriers Operation
Special Case of Multi-Carriers Transmission
To increase the data rate, it is possible to assign to a mobile station two carriers
in the downlink or uplink
Better resource utilization and spectrum efficiency by means of joint resource allocation
and load balancing across the carriers
Normal Operation in
HSDPA System. 5
MHz CH BW
allocated per user
Dual Carrier Operation
Two carriers can be
allocated to serve one
user, two users or
more
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Contents
Capacity & Performance Constraints
Enhancing TechniquesOFDM OFDMA
SC-FDMA
LTE Overview
LTE Interfaces
LTE Physical Layer
LTE Channels
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OFDM Concept
Orthogonal Frequency Division Multiplexing (OFDM) is a spread spectrum
technology that distributes the data over a large number of carriers that are
spaced apart at precise frequencies
The carriers for each channel are made orthogonal to one another, allowing them
to be spaced very close together
The number of OFDM subcarriers can range from less than one hundred to
several thousand, with the subcarrier spacing ranging from several hundred kHzdown to a few kHz
This results in the signal having a high tolerance to multipath delay spread, as the delay
spread must be very long to cause significant intersymbol interference
What subcarrier spacing to use depends on what types of environments the
system is to operate in, including the maximum expected radio channel
frequency selectivity and the maximum expected rate of channel variations
For 3GPP LTE the basic subcarrier spacing equals 15 kHz
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OFDM Transmission
Special Case of Multi-Carriers & FDM
Benefits: Use of relatively
large number of sub-carriers.
WCDMA multi-carrier
evolution to a 20MHz
overall transmission
bandwidth could consist of
four (5 MHz BW sub-
carriers). In comparison,
OFDM transmission caninclude several hundred
sub-carriers transmitted
over the same radio link to
the same receiver
Tight frequencydomain packing of
the subcarriers with
a subcarrier spacing
f =1/Tu, where Tu is
the per-subcarrier
modulation-symbol
time
Orthogonal Frequency Division
Multiplexing
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OFDM Processing Steps
Example using BPSK
O
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OFDM Modulation
OFDM transmission is block
based, implying that, during
each OFDM symbol interval,
Nc modulation symbols are
transmitted in parallel.The modulation symbols can
be from any modulation
alphabet, such as QPSK,
16QAM, or 64QAM.
The physical resource in
case of OFDM
transmission is often
illustrated as a time
frequency grid. According
to the Figure, eachcolumn corresponds to
one OFDM symboland
each row corresponds to
one OFDM subcarrier
OFDM S b l & S b i
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OFDM Symbols & Sub-carriers
OFDM D d l ti
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OFDM Demodulation
OFDM demodulator consists
of bank of correlators, one for
each sub-carrier
IFFT & FFT
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IFFT & FFT
OFDM Modulation & Demodulation
IFFT OFDM Modulator
FFT OFDM Demodulator
Important Parameters (Values
related to BW size)
Nc: Number of sub-carriers
N: FFT Size
f: Carrier Spacing
fs: sampling Rate = f x N
ODFM Transmission
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ODFM Transmission
Example
OFDM Operation
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OFDM Operation
Example
IFFT Modulator
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IFFT ModulatorExample
FFT Demodulator
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FFT DemodulatorExample
OFDM
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OFDMOrthogonal Frequencies (Harmonics)
Time Dispersion
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Time Dispersion
In case of a time dispersive
channel, the orthogonality
between the subcarriers will,
at least partly, be lost.
the demodulator
correlation interval for
one path will overlap with
the symbol boundary of adifferent path
This will result in inter-symbol interference
within a subcarrier and
interference between
subcarriers
Cyclic Prefix Insertion CP
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Cyclic Prefix Insertion CP Minimizing the Impact of Time Dispersion
CP: the last part of the
OFDM symbol is copied
and inserted at the
beginning of the OFDM
symbol
subcarrier orthogonality will be preserved in
case of a time-dispersive channel, as long as
the span of the time dispersion is shorter than
the cyclic-prefix length
CP Insertion Example
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CP Insertion Example
OFDM Example
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OFDM ExampleUsing 4 Subcarriers
Channel Estimation
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Channel EstimationOFDM Transmission / Reception
Using a known reference signal
Reference Pilot, the receiver can
estimate the frequency domain
channel and recover properly the
transmitted symbol
Basic OFDM Parameters
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Basic OFDM Parameters
The subcarrier spacing f
The number of subcarriers Nc Together with the subcarrier
spacing, determines the overall
transmission bandwidth of the
OFDM signal
The cyclic-prefix length TCP.
Together with the subcarrier
spacing f =1/TU, the cyclic-prefix
length determines the overall OFDM
symbol time T =TCP+TUor,equivalently, the OFDM symbol rate
Nc
Frequency Diversity
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eque cy e s tyIn coordination with Channel Coding
Each information bit will
experience frequency
diversity in case of
transmission over a radio
channel that is frequency
selective over the
transmission bandwidth.
This is called alsofrequency interleaving
OFDM Multiplexing / Multiple Access
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p g pDownlink / Uplink (Localized)
In the downlink direction, OFDM as a
user multiplexing scheme implies that, in
each OFDM symbol interval, different
subsets of the overall set of available
subcarriers are used for transmission to
different mobile terminals
Similarly, in the uplink direction, OFDM as a
user-multiplexing or multiple-access scheme
implies that, in each OFDM symbol interval,
different subsets of the overall set of subcarriers
are used for data transmission from different
mobile terminals This is often called OFDMA
Distributed Multiplexing
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p gAdditional Frequency Diversity
Distributing the subcarriers to/from a mobile terminal in
the frequency domain is also possible. The benefit of such
distributed user multiplexing or distributed multiple access
is possibility for additional frequency diversity as each
transmission is spread over a wider bandwidth
OFDM vs. OFDMA
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OFDM / OFDMA
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The Choice for 4th Generation Mobile Networks
Contents
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Capacity & Performance Constraints
Enhancing Techniques
OFDM OFDMA
SC-FDMA
LTE Overview
LTE Interfaces
LTE Physical Layer
LTE Channels
SC-FDMA
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Single Carrier Frequency Division Multiple Access
OFDM modulation has a drawback like any kind ,multi-carrier transmission, is the
large variations in the instantaneous power of the transmitted signal
Such power variations imply a reduced power-amplifier efficiency and higher power-
amplifier cost.
This is especially critical for the uplink, due to the high importance of low mobile-
terminal power consumption and cost
SC-FDMA (single carrier frequency division multi access) was chosen because it
combines: The low PAPR techniques of single-carrier transmission systems, such as GSM and
CDMA
With the multi-path resistance and flexible frequency allocation of OFDMA
SC-FDMA is a new multiple access technique that utilizes Single carrier modulation, DFT-spread orthogonal frequency multiplexing, and
frequency domain equalization
DFT Spread OFDM (DFTS-OFDM)F D i G ti
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Frequency Domain Generation
SC-FDMA can be generated in the time domain or in the frequency domain
Frequency-domain-generated SCFDMA is simply a pre-coded OFDMA scheme where
pre-coding is carried out by the DFT matrix
a block of M modulation
symbols from some modulation
alphabet, e.g. QPSK or16QAM, is first applied to a
size-M DFT different mobile
terminals
The output of the DFT is then
applied to consecutive inputs of a
size-N inverse DFT where N >M
and where the unused inputs of
the IDFT are set to zero
Single Carrier
(Time Domain)
Sequential transmission of
the symbols over a single
frequency carrier
FDMA -User multiplexing
in the frequency domain
SC-FDMA Generation
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Despite its name, Single Carrier Frequency Division Multiple Access (SC-FDMA)
also transmits data over the air interface in many sub-carriers but adds an
additional processing step (DFT)
Data symbols in the time domain are converted to the frequency domain using adiscrete Fourier transform (DFT)
Then in the frequency domain they are mapped to the desired location in the overall
channel bandwidth
And after that, converted back to the time domain using an inverse FFT (IFFT)
SC-FDMA ExampleU i 4 S b i
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Using 4 Subcarriers
DFT Converts M symbols in the time domain into M subcarriers in the frequency domain
DFT Length and sampling rate are chosen so that each signal is represented by M bins spaced
15KHz apart
Each Bin will have its own fixed amplitude & phase
OFDMA vs. SC-FDMA
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OFDMA transmits the four
QPSK data symbols in
parallel, one per subcarrier
SC-FDMA transmits the four QPSK
data symbols in series at four times
the rate, with each data symbol
occupying M x 15 kHz bandwidth
Each symbol
represented by awide signal
DFT spreads
symbols over all
subcarriers
Peak To Average Power RatioOFDM vs DFTS OFDM
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OFDM vs. DFTS-OFDM
16 QAM
QPSK
the PAR is significantly lower for DFTS-
OFDM, compared to OFDM. In case of
16QAM modulation, the PAR of DFTS-
OFDM increases somewhat as
expected
For OFDM, the
PAR distribution is
more or less
independent of the
modulationscheme
SC-FDMA Receiver
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The operations are basically the reverse
of those for the DFTS-OFDM signal
generation i.e. size-N DFT (FFT)
processing, removal of the frequency
samples not corresponding to the signal
to be received, and size-M inverse DFT
processing
SC-FDMA & OFDMACommon Elements
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Common Elements
Constellation mapper: Converts incoming bit stream to single carrier symbols (BPSK, QPSK, or 16QAM depending on channel
conditions) Serial/parallel converter: Formats time domain SC symbols into blocks for input to FFT engine
M-point DFT: Converts time domain SC symbol block into M discrete tones
Subcarrier mapping: Maps DFT output tones to specified subcarriers for transmission. SC-FDMA systems either use contiguoustones (localized) or uniformly spaced tones (distributed). LTE uses localized subcarrier mapping
N-point IDFT: Converts mapped subcarriers back into time domain for transmission
SC-FDMA Only Common to OFDMA & SC-FDMA
Uplink Users Multiplexing
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By dynamically adjusting the transmitter DFT size
and, consequently, also the size of the block of
modulation symbols a0, the nominal bandwidth of
the DFTS-OFDM signal can be dynamically
adjusted DFTS-OFDM
By shifting the IDFT inputs to which the DFT outputs
are mapped, the exact frequency-domain position
of the signal to be transmitted can be adjusted. By
these means, DFTS-OFDM allows for uplink FDMA
with flexible bandwidth
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SC-FDMA Distributed
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The PAPR performance
of Distributed SC-FDMA is better
than that of Localized SC-FDMA
PAR Difference (Example)Nc = 256 system subcarriers, M = 64 subcarriers per user
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Nc 256 system subcarriers, M 64 subcarriers per user
Distributed
SC_FDMA
Localized
SC_FDMA
OFDMA
QPSK 16 QAM
In the case of no pulse shaping, thePAPR of Distributed SC-FDMA is 10.5
dB lower than the PAPR of OFDMA
for QPSK modulation. The PAPR of
Localized FDMA is lower than the
PAPR of OFDMA by 3 dB for QPSK
The PAPR of Distributed SC-FDMA is7 dB lower than the PAPR of OFDMA
for 16 QAM modulation. The PAPR of
Localized SC-FDMA is lower than the
PAPR of OFDMA by 2 dB for 16 QAM
Contents
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Capacity & Performance Constraints
Enhancing Techniques
OFDM OFDMA
SC-FDMA
LTE Overview
LTE InterfacesLTE Physical Layer
LTE Channels
GERAN NetworkGSM, GPRS, EDGE (Releases .., 96, 97, 98 & 99)
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, , ( , , , )
UMTS Release 99 & 4
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UMTS Release 5HSDPA & IP Interfaces
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UMTS Release 6HSUPA
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UMTS Release 7HSPA+ (MIMO)
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UMTS Release 8LTE Introduction
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LTE Overview
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Evolved Packet CoreEvolved Universal Terrestrial
Radio Access Network
LTE Network ElementsEPS (EPC + E-UTRAN + UE)
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LTE Air InterfaceE-UTRA Specifications
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LTE CharacteristicsAdaptive Modulation
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Adaptively select the modulation type and coding ratedepending on the received SINR
LTE Scalable Bandwidth (1.4MHz to 20 MHz)DL Performance Figures
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LTE Soft Frequency Reuse
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SFR
Inner zones of the cell use all sub-bands
with less power
Outer zones uses reserved sub-bands
with high power
LTE CharacteristicsChannel Dependent Scheduling
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Downlink channel-
dependent scheduling
in time and frequency
domains.
in addition to assigning the time
frequency resources to the mobile
terminal, the eNodeB scheduler is also
responsible for controlling the transport
format (payload size, modulation
scheme) the mobile terminal shall use
LTE CharacteristicsHRQ with Soft Combining
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CRC insertion, rate-1/3 Turbo
coding Puncturing to
generate different
redundancy versions match the number of
coded bits to the channel
LTE CharacteristicsHRQ with Soft Combining DL Operation
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LTE CharacteristicsHRQ with Soft Combining UL Operation
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LTE System PerformanceDL/UL FDD & TDD (20 MHz BW)
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E-UTRANEvolved Universal Terrestrial Radio Access Network
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EPCEvolved Packet Core
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UESpectrum, Power & Category
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24
eNodeB Functions
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MME Functions
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PDN GW Functions
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LTE InterfacesEPS Reference Points
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E-UTRAN Protocol StackControl Plane
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Radio Resource Management
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E-UTRAN Protocol StackUser Plane (S1-U)
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E-UTRAN Protocol StackUser Plane (S5-U)
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E-UTRAN Protocol StackControl Plane (S5-C)
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E-UTRAN Protocol StackUser Plane
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E-UTRAN Protocol StackControl Plane (S10)
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E-UTRAN Protocol StackControl Plane (S11)
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E-UTRAN Protocol StackControl Plane (S6a)
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E-UTRAN Protocol StackControl Plane (X2-CP)
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E-UTRAN Protocol StackUser Plane (X2-UP)
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X2 Interface MobilityHandover Initiation
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X2 Interface MobilityHandover Completion
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Contents
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Air Interface Evolution in Mobile Networks
Capacity & Performance Constraints
Enhancing Techniques
OFDM OFDMA
SC-FDMA
LTE Overview
LTE Interfaces
LTE Physical Layer
LTE Channels
E-UTRA Physical Layer
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Subcarriers TypesData, Reference, Guard & DC
Subcarrier associatedUsed to estimate the RF
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Subcarrier associated
with the channel center
frequency
conditions
Used to carry traffic and
signalingUsed to eliminate inter-
channel interference
OFDM Symbol
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One subcarrier
OFDM Data SubcarriersExample: FFT Size 512
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OFDM Symbol Mapping
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LTE Generic Frame Structure
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LTE Frame Length & Subcarriers
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LTE Time Domain Structure
different time intervals within theLTE radio access specification can
be expressed as multiples of a
basic time unit Ts =1/30720000
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basic time unit Ts 1/30720000
Tframe =307200 *Ts
Tsubframe =30720*Ts.
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Resources per SlotOFDMA Symbols & PRB Within Slot (0.5 msec)
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Resources per Slot3D View(OFDMA Symbols & PRB Within 0.5 msec)
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Downlink resource blockassuming normal cyclic
prefix, i.e. seven OFDM
symbols per slot
Resources AllocationsSub-frame, Slot, PRB, Element
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One slot consist of 7 OFDMsymbols in case of normal CP
and 6 symbols in case of
extended CP
Symbols / SlotCP & eCP Parameters
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2048 Samples160 Samples
144 Samples
Symbols / SlotCP & eCP Parameters (Timing Derivation)
Tu =1/f 66.7s (2048 * Ts).
TCP =160 Ts = 5 2s (first OFDM symbol)
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TCP=160Ts = 5.2s (first OFDM symbol),
TCP =144Ts = 4.7s (remaining OFDM
symbols)
TCP-e = 512Ts = 16.7s
Used for extended
cell range
LTE CP Parameters
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The reduced subcarrier spacing specifically targets MBSFN-
based multicast/broadcast transmissions.
More specifically the possibility to make synchronous multi-
cell multicast/broadcast transmissions appear as a singletransmission over a multi-path channel
Available Resource Blocks
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OFDMA Subcarrier MappingExample: QPSK Symbol Mapping
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SC-FDMA Subcarrier MappingExample: QPSK Symbol Mapping
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OFDM BW Allocation
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OFDMA BW Allocation
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OFDMA Modulation Mapping
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PS Call
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Contents
Capacity & Performance Constraints
Enhancing Techniques
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Enhancing Techniques
OFDM OFDMASC-FDMA
LTE Overview
LTE Interfaces
LTE Physical Layer
LTE Channels
LTE Channel Architecture
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Logical Channels
Common Control Channel (CCCH)
Carries RRC signaling when no RRC
connection currently exists for the UE
Dedicated Control Channel (DCCH)
A bidirectional control channel used
to carry signaling information when an
RRC connection exists for the UE
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Dedicated Traffic Channel (DTCH) A
point-to-point channel dedicated to one
UE for transmission of user data. The
DTCH may be uplink, downlink, or both.
Broadcast Control Channel
Paging Control Channel
Multicast Channel
Transport ChannelsLogical to Transport Channel Mapping
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Downlink Shared Channel
(DL-SCH) Carries DL data
and some control traffic.
Uplink Shared Channel (UL-
SCH) Carries UL data and
some control traffic.
Physical ChannelsTransport to Physical Channel Mapping
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Carries Hybrid ARQ (HARQ) ACKs or
NACKs for the UL transmissions on the
PUSCH. The PHICH uses BPSK encoding.
Transmitted every subframe to inform the UE about
the number of OFDM symbols used for the PDCCH
channel. The PCFICH uses QPSK encoding
Channels MappingLogical to Transport to Physical
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Other Physical Signals
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LTE Specific Signals
Downlink Physical Signals
DL Demodulation Reference Signals (RS)
Synchronization Signals
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Uplink Physical Signals
UL Demodulation Reference Signals
Sounding Reference Signals
Random Access Preamble
Signals and Synchronization Signals.
The eNodeB and UE use Demodulation Reference Signals (DRS) to estimate RF
channel quality (measure SNR)
The eNodeB transmits periodic Synchronization Signals (SS) to synchronize each UE
with the recurring physical slots and frames. The eNodeB uses Sounding Reference Signals (SRS) to control frequency-
dependant scheduling for a UE.
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DL Reference Signal2 Ports & 4 Ports Antennas
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LTE Synchronization ChannelsPrimary & Secondary
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Used for cell search and
identification by the UE.
Carries part of the cell ID
Used for cell search and
identification by the UE.
Carries the remainder of
the cell ID
Uplink DRS & SRSDemodulation and Sounding Reference Signals
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DRS: Used for channel estimation to help
the demodulation of the control and datainformation in the eNB. Located on the 4th
symbol of the SC-FDMA sub-frame and
uses the same BW allocated of the UE in
the UL (0ccupies all Subcarriers)
SRS: provides the eNB uplink
channel quality information to be
used for scheduling when no ULdata transmission is available. The
SRS is transmitted in the last
symbol of the sub-frame
DL LTE FDD Sub-Frame Structure
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FDD LTE DL Frame Structure
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FDD LTE UL Frame StructureShowing PUSCH
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FDD LTE UL Frame StructureMapping of PUCCH in
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