LTE-Training-With Basic Parameters and tecgnology

For internal use only
1 © Nokia Siemens Networks
Long Term Evolution (LTE)
Helsinki
12th May, 2009
Harri Holma, Antti Toskala
Nokia Siemens Networks

Outline
• Background of LTE
• 3GPP Status & LTE Schedule
• LTE Physical Layer
• LTE Layer 2/3
• LTE Architecture
• LTE UE Connection management
• LTE Network Algorithms
• LTE Network Performance
• LTE Frequency variants
• LTE Benchmarking with HSPA+
• LTE Advanced
Reference material:

Background of LTE
• End 2004 3GPP workshop on UTRAN Long Term Evolution
• March 2005 Study item started
• December 2005 Multiple access selected
• March 2006 Functionality split between radio and core agreed
• September 2006 Study item closed & approval of the work items
• December 2007 1st version of all radio specs approved for Release 8
• March 2009 Backwards compatibility (ASN.1) started
2005 2006 2007 2008
Feasibility
study
started
Multiple
access
selected
Feasibility
study closed
Work item
started
Work plan
approved
Stage 2
approved
Stage 3
approved
ASN.1
frozen!
2009

LTE Status in 3GPP
• LTE functional freeze has been reached, so no new
functionality to be introduced anymore in Release 8
• RRC (Radio Resource Control) specification is the biggest
open issue in LTE specifications
• NSN/Nokia and Vodafone introduced an action plan in
3GPP in September to ensure things are completed.
Different companies took responsibility of different areas
• For December 2008 version most of the open issues also in
LTE RRC were solved, target freezing date for ASN.1 for
March 2009 was reached.
– Any commercial devices thus needs to be build on top of the March
2009 RRC specification (Freeze also for X2/S1 specs)
– First feedback from 1st round of meetings did not reveal major
problems (that could not be solved with backwards compatible CRs)

LTE Timing in 3GPP
• LTE started backwards compatibility March 2009
• Historically, it has taken 1.25-1.5 years from the backwards compatibility
until commercial launch with HSDPA and HSUPA
– Note that then the basis was existing and stable Release 99
• LTE commercial launch expected 2H/2010
2003 2004 2005 2006 2007
1 2
1 2
1.5 years
1.25 years
1 = Backward compatibility
2 = 1st commercial launch
HSDPA
HSUPA
2008 2009 2010
1 2
1.5 years
LTE

General Requirements for UTRAN Evolution
Feasibility study started in 3GPP for UTRAN Long Term Evolution with the
following requirements
• Packet switched domain optimized
• One way (radio) delay below 5 ms
• Peak rates uplink/downlink 50/100 Mbps
• Ensure good level of mobility and security
• Improve terminal power efficiency
• Frequency allocation flexibility with 1.25/2.5, 5, 10, 15 and 20 MHz
allocations, possibility to deploy adjacent to WCDMA*
• WCDMA evolution work on-going to continue with full speed
Operators are also requiring higher radio capacity
• Depending on the case 3-4 times higher capacity expected than
with Release 6 HSDPA/HSUPA reference case
* For small bandwidths 1.4 and 3.0 MHz adopted instead

Multiple Access Selection
Due to the large bandwidth, up to 20 MHz, and up to 100 Mbps data rates ->
something more than just a new modulation or larger chip rate was needed
3GPP decided in the feasibility study to use as multiple access OFDMA
(Downlink) and SC-FDMA (Uplink)
3GPP considered several alternatives
• OFDMA
• SC-FDMA
• And use of Multi-carrier WCDMA
• For the downlink the choice was clear, while for the uplink a bit more
debate too place between OFDMA and SC-FDMA as especially
companies with WiMAX background preferred similarity with WiMAX.
– SC-FDMA was also our preference (see later slides on PAR issues)
– The chosen multiple access methods will be driven with reuse 1 like in WCDMA

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RAN1#54bis
RAN1#54
RAN1#53bis
RAN1#53
RAN1#52b
RAN1#52
RAN1#51bis
Nokia/NSN Most Active in 3GPP LTE Work
• Nokia/NSN most active contributor in 3GPP RAN1 for LTE
Nokia/NSN
most active

OFDMA in LTE Downlink

OFDM benefits
Superior performance in frequency selective fading channels
Complexity of base-band receiver is much lower
Good spectral properties and handling of multiple bandwidths
Link adaptation and frequency domain scheduling
offer high potential for throughput etc gain
Other cell interference can be effectively reduced by
Interference Rejection Combining (IRC).

FFT – a fundamental element in OFDM
FFT = Fast Fourier Transform, IFFT = Inverse FFT
FFT/IFFT allows to move between time and frequency domain representation and is
a defacto block in an OFDMA system where system parameters enable that
As an example a sinusoidal wave input and “block wave” input for an FFT block
Time Domain
FFT
Frequency Domain
FFT
f
f
This corresponds to the frequency
Of the input sinusoidal wave
t
Fundamental frequency

Bandwidth Scalability
1.4 MHz
3.0 MHz
5 MHz
10 MHz
20 MHz
FFT size
128
256
512
1024
2048
Bandwidth
Scalable bandwidth 1.4 – 20 MHz using different number of sub-carriers and
different FFT size
Large bandwidth provides high data rates
Small bandwidth allows simpler spectrum re-farming, e.g. 450 MHz and 900 MHz
Narrow spectrum refarming
High data rates

DL air interface technology
OFDM-based DL air interface
Frequency bandwidth options are 1.4
MHz, 3.0 MHz, 5 MHz, 10 MHz, 15 MHz
and 20 MHz
Each BW has fundamentally similar
features
• Symbols are parameterized equally
• 15 kHz subcarrier spacing
• Clock is 2N (8x) multiple of 3.84 MHz
• FFT scales as a power of two
3GPP is discussion also alternative
parameters for the broadcast use
(Mobile TV case
Up to 20 MHz

OFDM Transmitter/Receiver Chain
OFDM is used in various
systems, like:
• DVB-T
• DVB-H
• WLAN (IEEE family)
– Including WiMax
• Key component is the
inverse discrete Fourier
transform
• IDFT/IFFT
• Moving between time and
frequency domain
representation
frequency
Transmitter
totalradio BW (
eg. 20 MHz)
Modulator
Cyclic
Extension
Remove
Cyclic
Extension
Equaliser
Bits
frequency
Receiver totalradio BW (
eg. 20 MHz)
Modulator
Bits
IFFT
IFFT
Serial to
Parallel
…
IFFT
Serial to
Parallel
FFT
…
Demodulator

OFDM symbol fundamentals
At 20 MHz BW, FFT=2048
OFDM symbol length 66.68 μs
• Robust for mobile radio channel with
the use of guard internal/cyclic
prefix (see next slide)
• Overheads of guard interval and
channel spacing are not excessive
6 OFDM data symbols per one 0.5 ms
slot
• Additionally one symbol for pilot
sequence (& TS), Shared Control
signaling and occasionally for
system info
copy of Np last samples
cyclic
prefix
OFDM symbol, Tsym
FFT length NFFT
Guard
Interval
symbol window
OFDM symbol before
CP insertion
delay
spread
cyclic
prefix
symbol window
cyclic
prefix
OFDM symbol before
CP insertion
OFDM symbol, T sym
FFT length N FFT
Guard
Interval
OFDM symbol at the transmitter
OFDM symbol at the receiver

Cyclic Prefix – Preventing Inter-symbol
Interference (ISI)
Having the cyclic prefix longer than the channel multi-path delay
spread prevents ISI
The part of the signal waveform itself is copied to be used and
cyclic prefix (instead of a break in transmission)

Maintaining sub-carriers orthogonal
The OFDMA refers indeed to the Orthogonal FDMA as the
parameters for the sub-carrier are chosen to that neighboring
sub-carriers have zero value the desired sampling point for any
sub-carrier
Sampling point for
a single sub-carrier
Zero value for
other sub-carriers
15 kHz
Total transmission bandwidth

OFDMA Transmitter
Windowing is needed for pulse shaping for meeting the spectrum masks
• This is even more needed if some clipping is applied (typical) in the
transmitter as that makes the spectrum wider compared to the ideal OFDM
spectrum
• Compare to pulse shaping filters with WCDMA
The length of the filters will “eat” part of the time from cyclic prefix
Serial
to
Parallel
X0
XN-1
x0
xN-1
IFFT
Parallel
to
Serial
Add
CP
Windowing
DAC
RF Section
Input
Symbols

Downlink Multiple Access – OFDMA
User multiplexing in sub-carrier domain
Smallest allocation is 12 sub-carrier i.e. the bandwidth of 180 kHz.
• Largest 20 MHz, supported by all devices (if specified for the given
frequency band)
Single Resource
Block
…
180 kHz
Total
System
Bandwidth
1 ms Allocation Period
…
Sub-carriers for the
First Symbol in a
Single Resource
Block
Resource Blocks for User 1

OFDMA Channel Estimation
Reference Signals
Symbols / Time Domain
Sub-carriers /
Frequency domain
•Channel estimation
based on reference
symbols.
•Interpolation in time
and frequency domain
• In WCDMA common
pilot channel (CPICH)
was used for this
(together with
reference symbols on
DCH)

OFDM challenges
Peak-to-average ratio of the transmitted signal (crest factor,
also referred in 3GPP discussions as Cubic Metric, CM)
Sensitivity to frequency error
• This addressed by having sufficiently large sub-carrier
spacing
• In case of too large frequency error, the sub-carriers start to
interfere each others

Why not to use OFDM in the uplink?
The transmitted OFDM signal should be seen as a sum of sinusoid
This is not suited for a highly linear, power efficient terminal amplifier
The envelope needs to be with as low Peak-to-Average Ratio (PAR) as
possible.
Power Amplifier sees this!
IFFT
…
Frequency domain
QAM modulated inputs
Time domain signal
(sum of sinusoids)
FFT
…
Frequency domain
QAM modulated outputs

SC-FDMA in LTE Uplink

SC-FDMA with CP
Sending only one symbol at the time results to low PAR envelope
• In 3GPP Cubic Metric being considered as it represents better the
device amplifier impact than PAR
This allows to benefit from the modulation PAR/CM properties in devices
This is important for small size devices aiming for up to 23 dBm TX
power.
frequency
Transmitter
Receiver
total radio BW (eg. 20 MHz)
Modulator Cyclic
Extension
Remove
Cyclic
Extension
FFT
MMSE
Equaliser
IFFT Demodulator Bits
Bits
frequency
Transmitter
Receiver
total radio BW (eg. 20 MHz)
Modulator Cyclic
Extension
Remove
Cyclic
Extension
FFT
MMSE
Equaliser
Bits
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
CM vs rolloff with different modulations
rolloff
CM
[dB]
SC pi/2-BPSK
SC QPSK
SC 16-QAM
OFDM pi/2-BPSK
OFDM QPSK
OFDM 16-QAM

SC-FDMA Transmitter Chain
The receiver is expected to
use e.g. frequency domain
equalizer
• This is simpler as ISI does
not need to be considered
due to the cyclic prefix
• Other possibilities exists
such as Turbo equalizer
This example uses the
frequency domain generation
of the SC-FDMA signal, in
theory could be generated
without FFT as well in the
transmitter. Use of FFT
however ensures good
spectral properties
Remove
Cyclic
Extension
FFT
MMSE
Equaliser
Remove
Cyclic
Extension
FFT
MMSE
Equaliser
Modulator
Bits
Modulator
Cyclic
Extension
IFFT
…
Sub-
carrier
mapping
frequency
Total radio BW (E.g. 20 MHz)
Transmitter
Receiver
DFT
IDFT

Uplink Multiple Access – SC-FDMA
User multiplexing in frequency domain
Smallest uplink bandwidth 180 kHz.
• Largest 20 MHz (terminal are required to able to receive & transmit up to
20 MHz, depending on the frequency band though.)
IFFT
Terminal 1 Transmitter
Terminal 2
Transmitter
frequency
frequency
IFFT
FFT
FFT
frequency BTS Receiver

SC-FDMA Change of data rate
…
Double
data rate
… Bandwidth
Symbol duration
•When data rate changes, more symbols per slot is being
transmitted. As the bandwidth increases the symbol duration
decreases.
•For double data rate the amount of FFT inputs in transmitter
doubles (as well as total BW) and symbol duration is halved

Physical Layer Structures

Introduction
• LTE physical layer based on OFDMA
downlink and SC-FDMA in the uplink
direction
• This is the same for both FDD and
TDD mode of operation
• There is no macro-diversity in use
• System is reuse 1, single frequency
network operation is feasible
– Interference control done by the BTS
scheduler, supported by the inter-BTS
information exchange (over X2 interface)
X2
X2

LTE Physical Layer Structure – Frame Structure
(FDD)
The slot structure (allocation with 1 ms sub-frame resolution) has been
designed to facilitate short round trip time
With TDD there were originally two different frame structures but agreement
was reached on a single TDD frame structure that is otherwise as with FDD
but some specific fields to enable also TD/SCDMA co-existence (China)
10 ms frame
0 1 19
18
…
0.5 ms slot
1 ms sub-frame

LTE Physical Layer Structure – Frame Structure
(cont)
Data Symbols
Control Symbols
D
L
Sub-carriers
0.5 ms Slot
1 ms Sub-frame
10 ms Radio Frame
…
0 1 2 3 19
18
17
1-3 symbols for control
(2-4 for 1.4 MHz)
Data symbols only in every 2nd symbol

LTE Physical Layer Structure – Downlink
The following downlink physical channels are defined
• Physical Downlink Shared Channel, PDSCH
– This is intended for the user data (compare with HS-PDSCH in
WCDMA)
• Physical Downlink Control Channel, PDCCH
• Physical Broadcast Channel, PBCH
• Physical Control Format Indicator Channel, PCFICH
• Physical Multicast Channel, PMCH (Not in Release 8)
• Physical Hybrid ARQ Indicator Channel, PHICH
Configuration
Normal cycli
c prefix kHz
15
=
Δf 7
kHz
15
=
Δf 6
Extended cyclic prefix
kHz
5
.
7
=
Δf 3
OFDMA Symbols
PMCH only

LTE Physical Layer Structure – Downlink
Reference Signal
1
1
1
Not used for
transmission on
this antenna port
Reference
signals on this
antenna port
Resource element
R0
R0
R0
R0
R0
R0
R0
R0
reference signal: R1
reference signal:
R1 R1
R1
R1
R1
R1
R1
R1
subframe x
subframe x
1RB
Needed for receiver channel estimation (like CPICH in WCDMA)
Sufficient distribution in time and frequency domain needed.

Downlink channels for data & control
(PDCCH/PDSCH)
Downlink control information in the few first symbols to indicate which
resources (resource blocks) are allocated for a given user (UL&DL!)
Respectively the uplink resources to be used are informed by eNode B
• PDCCH allocation is dynamic (see next slide for PCFICH)
• QPSK modulation for PDCCH.
Data Symbols
Control Symbols
D
L
U
L
Uplink Allocations
User 1 Data & Control
User 2 Data & Control
Frequency
Sub-carriers
0.5 ms slot

Other downlink channels
• Physical Broadcast Channel, PBCH
– This carriers the BCH (system information like RACH parameters)
• Physical Control Format Indicator Channel, PCFICH
– Indicates how many OFDM symbols (1 to 3) are used for PDCCH(s)
Physical Multicast Channel, PMCH
– MBMS (multicast) data
• Physical Hybrid ARQ Indicator Channel, PHICH
– HARQ feedback for uplink packets

Sub-frame structure
Short cyclic prefix
Long cyclic prefix
Copy
= Cyclic prefix
= Data
5.21 μs
16.67 μs
Sub-frame length is 1 ms for all bandwidths
• 0.5 ms is the slot length
• Originally it was planned to use 0.5 ms sub-frame but
signaling overhead was too excessive
Slot carries 7 symbols with short cyclic prefix or 6 symbols
with long cyclic prefix

Resource Blocks
Resource allocation can be done with Resource blocks
Resource block has bandwidth of 180 kHz, equal to 12
subcarriers
10 MHz = 50 resource blocks = 600 subcarriers
Resource block
180 kHz = 12
subcarriers
Subcarrier 15 kHz

Synchronization Signal in Downlink
Synchronization Signal is allocated in the 1.08-MHz block in the
middle of downlink bandwidth to faciliate UE cell search
ƒ Cell search procedure (see later slides) not dependent on system BW
Info is located in the end of slots 0 and 10 (In FDD)
ƒ Synchronisation Signal can indicate 504 (168 x 3) different values and
from those one can determine the location of cell specific reference
symbols
#0
Frame Tf = 10 ms
#19
1.08 MHz (= 6 resource blocks)
Slot 0.5 ms

Subcarrier Modulation
QPSK
2 bits/symbol
16QAM
4 bits/symbol
64QAM
6 bits/symbol
In both directions QPSK, 16QAM or 64QAM are used, depending on the
channel (Control channels to be using mainly QPSK, RACH sequences are
phase modulated sequences but not pure QPSK)

Downlink Physical Layer Parameters
3.0 MHz 5 MHz 10 MHz 15 MHz 20 MHz
Subframe (TTI) 1 ms
Subcarrier 15 kHz
FFT 128 256 512 1024 1536 2048
Subcarriers1 72+1 180+1 300+1 600+1 900+1 1200+1
1DC subcarrier included
Symbols per frame 7 with Short CP and 6 with Long CP
Cyclic prefix 5.21 μs with Short CP and 16.67 μs with Long CP
1.4 MHz

Channel Coding
•The user data (including
paging messages and
multicast data) are turbo
encoded, (encoder from
WCDMA)
•The control information with
convolutional encoding
– Note however open issues in
the specs currently
– Tail biting convolutional codes
to be used
• Turbo codes would be
difficult to beat with big
margin thus no point
adapting something
different
CRC Attachment
Code Block
Segmentation and
CRC Attachment
Channel Coding
Rate Matching
Channel Coding
Code Block
Concatenation
Data and Control
Multiplexing
Channel
Interleaver
Control
Data

LTE Physical Layer Structure – Uplink
The following uplink physical channels are defined
• Physical Uplink Shared Channel, PUSCH
– This is intended for the user data (compare with HSUPA in WCDMA,
but this is now fully dynamic allocation not just rate control like in
WCDMA)
• Physical Uplink Control Channel, PUCCH
• Physical Random Access Channel, PRACH

Uplink Subframe Structure (PUSCH)
In the uplink direction the QAM modulation is sending only one
symbol at the time.
Momentary data rate (controlled by the eNode B scheduler)
depends on the allocated transmission bandwidth (and CP
length)
Reference Symbol
Normal CP slot
0 1 2 3 4 5 6
Extended CP slot
0 1 2 3 4 5

Uplink resource mapping
Subcarriers
Reference Symbols
Resource Block
Resource Elements
Modulation
Symbols for
Data
Time domain
Signal Generation
0.5 ms slot
Reference Symbols
Control Information Elements
(Only part of the resource elements)
Modulation
Symbols for
Control
Control Information Elements

Random Access Channel (RACH)
The RACH operation uses around 1.08 MHz MHz bandwidth
This is equal to 6 resource blocks of 180 kHz
Similar ramping as with WCDMA (due inaccuracy of absolute
power level setting in devices, +/- 9 dB in WCDMA, similar
values also in LTE though uplink power setting dynamic range a
bit smaller than in WCDMA)
307200×Ts
TPRE TGT
TCP
Preamble
CP
0.1 ms 0.1 ms
0.8 ms

Physical Layer Compared to HSPA
LTE builds on the learning of several WCDMA/HSPA Releases
and covers from the start HARQ, BTS scheduling and adaptive
coding and modulation (+ multiple antenna TX/RX with MIMO)
Feature
Multiple Access
Fast power control
Adaptive modulation
BTS based scheduling
LTE
OFDMA
SC-FDMA
No
Yes
Time/Freq
HSUPA
WCDMA
Yes
Yes
Time/Code
Fast L1 HARQ Yes Yes
HSDPA
WCDMA
No
(associated DCH only)
Yes
Time/Code
Yes
Largest BW 20 MHz 5 MHz 5 MHz
Soft handover No Yes No
(associated DCH only)

Physical Layer Procedures

LTE Uplink Power Control
LTE uplink is using also closed loop power control, rate slower
than with WCDMA
• This needed due reuse 1 and to limit uplink receiver
dynamic range
Power control commands connection with scheduling grants
Control over power spectral density, not absolute power
-> Thus power is changing based on the BW used (as
allocated by the BTS)
frequency
frequency
Power per Hz unchanged
TTI 1
TTI 2

LTE Uplink Power Control (cont)
Cell wide overload indicator (OI) exchanged over X2 between nodes on a
slow basis,
• Expected average delay is in the order or 20 ms, number of bits is still for
discussion in 3GPP
• This can be used for Inter-Cell Interference Coordination (ICIC) as well
UE
eNode B
Serving eNode B
Overload
indicator
Scheduling and TPC
Uplink data
X2
A neighboring
eNode B
Interference
To AGW

LTE Timing Advance
When UE has previously established time alignment:
• TA update rate: on a per-need basis, 2 Hz is fast enough also for high speed UEs
• Granularity of TA signalling: 0.52us
•What to base the TA command on:
– When the UE has data to transmit, implementation issue in Node B (e.g. based on
sounding RS, CQI)
– If the UE has no data to transmit, e.g. periodic signals such as sounding RS may be
ordered
• How to transmit TA in the downlink: Part of MAC layer signalling
When no TA is established or UE is out of sync
• TA command is based on RACH preamble
• Initial TA will have to cover the full cell range, part of RACH procedure
UE
eNode B
Timing Advance
Uplink data or RACH

LTE Channel Quality Information (CQI)
• To enable frequency domain scheduling, one needs channel
CQI not only on the time domain (like in HSDPA) of the
expected link quality but also in the frequency domain.
• Different combinations exists in specs, and also event and
period reporting options (-> a lot for testing) :
– Wideband feedback (this is also always together with following
options)
ƒ UE to report one wideband value
– Higher Layer-configured sub-band feedback or UE selected sub-bands
ƒ Delta to configured sub-bands is signaled or in the UE selected case UE
report M best sub-bands
UE
eNode B
Data with modulation &
Position in frequency domain
Based on the CQI received
CQI

Cell Search Procedure
• Upon power on, UE will search for the primary synchronization
signals (3 different possibilities)
• In Step 2 UE will determine out of each 168 values the which
of the 168 possible secondary synchronization signal is used
– Thus total of 504 different values possible for the physical cell ID
• The synchronization signal information is also used to
determine what kind of cell specific reference symbols are in
use in the cell to facilitate demodulation of BCH after obtaining
frequency and timing synchronization from synchronization
signals
• After a successful BCH decoding UE may access the system
from the radio perspective (see later RACH procedure)

Physical Layer Retransmission (HARQ) procedure
• 8 processes are used for continuous operation both uplink and
downlink (no process number configuration like in HSDPA)
•HARQ principle used is stop-and-wait-ARQ
PUSCH/PDSCH 1 2 3 4 5 6 1 2
…
CRC Check Result Fail Pass
NACK
ACK
RLC layer
1st TX 1st TX
2nd TX
1st TX (new packet)
…
From scheduler buffer
7 8

LTE Measurements
• measurements from LTE on LTE (intra-LTE):
– UE measurements:
ƒ RSRP (reference signal received power ),
ƒ E-UTRA carrier RSSI (received signal strength indicator)*,
ƒ RSRQ (reference signal received quality)
– eNode B measurement:
ƒ DL reference signal transmit power
• measurements from LTE on other systems:
– UTRA FDD: CPICH RSCP, carrier RSSI, CPICH Ec/No
– GSM : GSM Carrier RSSI
– UTRA TDD: P-CCPCH RSCP ,carrier RSSI
* Not reported as part of the RSRQ definition

LTE Measurements – Carrier RSSI & RSRQ
E-UTRA Carrier Received Signal Strength Indicator, comprises the total
received wideband power observed by the UE from all sources, including
co-channel serving and non-serving cells, adjacent channel interference,
thermal noise etc.
Reference Signal Received Quality (RSRQ) is defined as the ratio
N×RSRP/(E-UTRA carrier RSSI), where N is the number of RB’s of the
E-UTRA carrier RSSI measurement bandwidth. The measurements in the
numerator and denominator shall be made over the same set of resource
blocks.

LTE Measurements – RSRP & DL Reference Signal
Transmitted Power
Downlink reference signal transmit power is determined for a considered
cell as the linear average over the power contributions (in [W]) of the
resource elements that carry cell-specific reference signals which are
transmitted by the eNode B within its operating system bandwidth.
Reference signal received power (RSRP) is determined for a considered
cell as the linear average over the power contributions (in [W]) of the
resource elements that carry cell-specific reference signals within the
considered measurement frequency bandwidth.
If receiver diversity is in use by the UE, the reported value shall be
equivalent to the linear average of the power values of all diversity
branches.

RACH Procedure
• RACH procedure = preamble + random access response
• Any user data or signaling data is carried on the shared data
channel. RACH does not carry data (different from WCDMA
Release 99)
• RACH occupies 6 resource blocks in a sub-frame
– The eNode B may also schedule data in the resource blocks reserved
for random access channel preamble transmission.
• Power ramping between preambles
Downlink / eNode B
PUSCH
PRACH
response
Uplink / UE
Preamble
Not detected
UE specific data
Preamble
Next
PRACH
resource
On the resources
indicated by
PRACH response

LTE TDD Aspects

TDD Multiple Access
• In LTE TDD mode same
multiple access as in FDD
• This is a big difference
compared to WCDMA
where TDD was totally
different
– Some harmonization was
done e.g. chip rates and
channel coding solutions
• From market
perspective China
Mobile pushing this
– As evolution step for the
on-going TD-SCDMA
deployment
UE with TDD support
TDD eNode B
OFDMA
SC-FDMA
f1
f1
Downlink TX
allocation
Time
Uplink TX
allocation
Time

LTE TDD Frame Structure
TDD may change between uplink and downlink either with 5 or 10 ms period
The specific fields (DwPTS, GP, UpPTS) are inherited from TD-SCDMA
• GP = Guard Period, DwPTS/UpPTS = DL/UL pilots
• 1 ms sub-frame otherwise same as FDD UL or DL sub-frame
10 ms frame
0.5 ms slot
1 ms sub-
frame
One half-fame (5 ms)
UpPTS
DwPTS
GP
Change between DL and UL

TD-SCDMA co-existence with LTE TDD
• With the common frame structure (& slot) duration it is still
possible to parameterize the LTE TDD mode to operation so
that the site can have compatible uplink and downlink split
– This would need to be rather static parameter
0.5 ms slot
1 ms LTE TDD sub-frame
UpPTS
DwPTS
GP
Change between DL and UL
…
…
TD-SCDMA slot
Adjusted relative timing to avoid UL/DL overlap

Differences in procedures for TDD
The reason for differences procedures is the needed change
between uplink and downlink
• This impacts especially the control signaling
• Cell search symbols (PSS and SSS) have different location
• ACKs/NACks in one go more than in FDD (with varying
timing, see next slide)
DL UL UL DL DL UL UL DL
S S
SSS
PSS
S-RACH/SRS
RACH
P-BCH D-BCH
SSS
PSS
S-RACH/SRS
RACH
SF#0 SF#2 SF#3 SF#4 SF#5 SF#7 SF#8 SF#9
1 ms
SF#1 SF#6

Differences in procedures for TDD - HARQ
The HARQ timing is not constant like in FDD
• This has made some combinations not feasible (like semi-
persistent scheduling + TTI bundling) in TDD.
Data DATA
3ms
1ms
Data ACK DATA ?? ACK
3ms 3ms 3ms
5ms
1ms
ACK ACK
3ms
1ms
3ms
3ms DATA
(a) Conceptual example of FDD HARQ Timing (propagation delay and timing advance is ignored)
(b) Conceptual example of TDD HARQ Timing (special subframe is treated as ordinary DL subframe)

TDD performance – For coverage FDD had
advantage
UL Coverage for TDD and FDD, UE target bitrate 2 Mbps
3
8
13
18
23
28
33
38
43
48
0.00 0.10 0.20 0.30 0.40 0.50
Distance [km]
#
of
PRB
0.00
0.50
1.00
1.50
2.00
2.50
Bitrate
[Mbps]
UE BW FDD
UE BW TDD
Bitrate FDD
Bitrate TDD
Data rates
Resources
When coming closer to cell edge, TDD needs to earlier to try to
increase bandwidth as TX time is reduced

LTE Layer 2/3

LTE Protocol Layers
RRC:
• Broadcast of system information
• Radio connection & Radio bearers
• Paging, handovers, QoS
management, radio measurement
control
RLC:
• Retransmission control (ARQ)
• Segmentation
• Flow control towards aGW
MAC:
• Mapping & mux of logical channels to
transport channels
• Traffic volume measurement reporting
• Hybrid-ARQ
• Priority handling
PHY:
• FEC encoding/decoding
• Error detection
• Support of HARQ
• Modulation/demodulation
• Frequency and time synchronization
• Power control, antenna diversity,
MIMO
RRC
RLC
MAC
Physical Layer
PDCP
Transport Channels
Logical Channels
Radio Bearers
Control-plane User-plane
L1
L2
L3
PDCP:
• Ciphering
• Header Compression

LTE layer 2
The Layer 2 protocols (MAC & RLC), terminate in the BTS
(known in 3GPP as eNode B)
Also PDCP (Packet Data Convergence Protocol) terminates
in the eNode B
User Plane LTE protocol stacks
PDCP
UE
RLC
MAC
Physical Layer
PDCP
eNode B
RLC
MAC
Physical Layer

LTE layer 2 Structure Header
Compressions
Ciphering

Layer 2 (MAC)
The Medium Access Control (MAC) signaling is also terminated in eNode
B, similar to MAC-hs with HSDPA (or MAC-e with HSUPA)
The transport channels from the MAC layer are mapped to the physical
channels, and respectively the MAC layer provides the logical channels to
RLC layer.
The following transport channels are defined in the downlink:
ƒ Broadcast Channel (BCH)
ƒ Downlink shared Channel (DL-SCH)
ƒ Paging Channel (PCH)
ƒ Multicast Channel (MCH)
In the uplink
ƒ Uplink Shared Channel (UL-SCH)
ƒ Random Access Channel (RACH)
• No DCH like in WCDMA!

MAC PDU Structure
MAC header MAC Control Elements MAC SDU MAC SDU
… Padding
Payload with type indicated in the header
DL-SCH: Types of payload
elements
• Logical channel identity
• CCCH
• UE contention resolution
identity
• Timing Advance
• DRX command
• Field lengths
UL-SCH: Types of payload elements
• Logical channel identity
• CCCH
• Power Headroom Report
• C-RNTI
•Short Buffer Status Report
• Long Buffer Status Report

LTE layer 2 – RLC AM
AM-SAP
DCCH/
DTCH
Transmission buffer
Data Field
Receiving buffer
Reassembly
DCCH/
DTCH
Transmitting side Receiving side
AMD Header
STATUS
Data Field
AMD Header
Segmentation/
concatenation
Retransmission
buffer
Control
Biggest difference to WCDMA: Lack of ciphering, data
comes ciphered from PDCP layer
Header has sequence number and info of the last received
packet

LTE layer 2 – RLC UM
UM-SAP
DCCH/ DTCH
Transmission buffer
Data Field
Receiving buffer
& HARQ Reordering
Reassembly
AMD Header Data Field
AMD Header
Segmentation/
concatenation
DCCH/ DTCH
Also un-acknowledged mode supported (in figure) and
transparent mode (not shown)
Transparent mode RLC only to common channels (BCCH,
CCCH and PCCH) which do not have HARQ

LTE layer 2 – PDCP
NAS
RLC
Sequence
numbering
RLC
Header
compression
Integrity
protection
User Plane
Control Plane
Ciphering
Data Field
PDCP Header Data Field
PDCP Header
Deciphering
Re-ordering
Integrity
protection
User Plane
Control Plane
Header
decompression
In WCDMA PDCP was only for user plane, now also for
control plane due ciphering

Layer 3 (RRC)
• The Radio Resource Control (RRC) signaling is also terminated in eNodeB
(compared to RNC in WCDMA)
• One of the enablers for the flat model is the lack of macro-diversity
• No need for RNC like functional element -> everything radio related can
be terminated in eNodeB
• RRC to handle: Broadcast, Paging, RRC connection management,
Mobility managements and UE measurements …
– Only two states in LTE RRC (see later slides)
Control Plane LTE protocol stacks
RRC
UE
RLC
MAC
Physical Layer
RRC
eNodeB
RLC
MAC
Physical Layer
PDCP PDCP

Mapping of the Logical/Transport Channels to L1
In the uplink direction both control and user data all mapped to PUSCH
RACH UL-SCH
PUSCH
PRACH
Physical Channels
Logical Channels CCCH DCCH DTCH
In the downlink direction unicast user data on PDSCH, multicast
data can be also on PMCH. RRC Control information all on DL-SCH
BCH DL-SCH
PDSCH
PBCH
CCCH DCCH DTCH MCCH MTCH
PDCCH
PCH
PCCH BCCH
MCH
PMCH
Transport Channels
Physical Channels
Logical Channels
Transport Channels

LTE Architecture

LTE Architecture Evolution
GGSN
Node B
HSPA R6
SGSN
LTE R8
RAN
eNode B
SAE
Gateway
Only user plane elements shown!
RNC
The LTE architecture is
flat, only two nodes for
the user data
• See later slides for
details
This is similar that is
enabled in I-HSPA when
deployed together with
the one tunnel solution
Also the ciphering is in
eNodeB
One key facilitator is lack
of macro-diversity (soft
handover)

LTE Architecture – Control Plane
The interface between
RAN & Core network is
called S1 interface
Interface between
eNodeBs is named X2
Note: for ciphered RRC messages
also PDCP used
S1_MME
between MME&
eNodeB
X2
RRC
UE
RLC
MAC
Physical Layer
RRC
eNode B
RLC
MAC
Physical Layer
RRC
eNode B
RLC
MAC
Physical Layer MME
S1_MME
S1_MME
NAS NAS
MME = Mobility Management Entity

LTE Architecture – X2 interface
The X2 interface has the following
functionalities:
• In inter- eNode B handover to
facilitate handover and provide data
forwarding
• In RRM to provide e.g. load
information to neighboring eNode Bs
to facilitate interference
management
•X2 is a logical interface i.e. it can
routed via core network as well,
does not need direct site-to-site
connection
– User data only in case of handover
event (data forwarding unit rerouted
from WG)
X2
PDCP
eNode B
RLC
MAC
Physical Layer
RRC
PDCP
eNode B
RLC
MAC
Physical Layer
RRC

X2 Interface – Interference Management
Downlink TX
eNode B
…
One PRB = 180
kHz
… …
Measurement Granularity in Frequency
In the downlink direction measurement is: Maximum Tx Power per PRB normalized
Threshold level
X2-interface
eNode B
PRBs Exceeding
Threshold level

X2 Interface – Interference Management (2)
Uplink RX
eNode B
One PRB = 180 kHz
…
Uplink RX bandwidth
In the uplink direction measurement is: Maximum Tx Power per PRB normalized
Threshold levels
for Interference
X2-interface
eNode B
Interference
Level of PRBs
Measured
Interference

LTE Architecture – S1 interface
The S1 interface has the following
functionalities:
• It connects the eNode B to the evolved
packet core. Divided to control plane
(S1_MME) and user plane (S1_U) parts
• S1_U carries the user data to SAE
gateways
• S1_MME connects to the mobility
management entity
• Carriers the NAS (non access stratum)
signaling (authentication etc. protocols
between core and UE)
• Separate ciphering for S1 interface (as
PDCP in eNode B)
RRC
eNode B
RLC
MAC
Physical Layer
MME
S1_MME
S1_U
SAE Gateways
PDCP

LTE/SAE Architecture (Radio and Core)
PCRF
MME
HSS
IP
Networks
Data
Control
S1_MME
Serving SAE
Gateway
eNode B
S1_U
PDN SAE
Gateway
S11
SGI
Operator Services
(IMS etc…)
Radio
eNode B
X2

LTE Peak Bit Rates

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