1. Technology training (Part 1)
Long Term Evolution
Technology training
(Part 1)

2. Outline LTE and SAE overview LTE radio interface architecture
LTE radio access architecture
LTE multiple antenna techniques

3. Part 1
LTE/SAE overview

4. Mobile broadband (3GPP)
Release
Standardized
Commercial
Major features
3GPP R99
1999
2000
Bearer services
64 kbit/s CS
384 kbit/s PS
Location services
Call services: compatible with GSM
3GPP R5
2002
2006
IP Multimedia Subsystem (IMS)
IPv6, IP transport in UTRAN
Improvements in GERAN
HSDPA
3GPP R6
2004
2007
Multimedia broadcast and multicast
Improvements in IMS
HSUPA
Fractional DPCH
3GPP R7
2008
Enhanced L2
64 QAM , MIMO
VoIP over HSPA
CPC - continuous packet connectivity
FRLC - Flexible RLC
3GPP R8
2010
DC-HSPA+ (Dual Cell HSPA+)
HSUPA 16QAM
3GPP R8 (LTE)
New air interface (OFDM/SC-FDMA)
New core network
3G continues to evolve
Standardized through 3GPP
3G gracefully evolves into 4G – starting from R7 and R8
Date rates
R99: 0.4Mbps UL, 0.4Mbps DL
R5: 0.4Mbps UL, 14Mbps DL
R6: 5.7Mbps UL, 14Mbps DL
R7: 11Mbps UL, 28Mbps DL
R8: 50Mbps UL on LTE, 160 Mbps DL on LTE, 42Mbps DL on HSPA
Two branches of the standards
HSPA : Gradual performance improvements at lower incremental costs
LTE: revolutionary changes with significant performance improvements (higher cost, first step towards IMT advanced)

5. LTE Releases LTE – has an “evolution path” of its own
Standardized
Commercial
Major features
3GPP R8 (LTE)
2008
2010
Multi antenna support
Channel dependent scheduling
Bandwidth flexibility
ICIC (Intercell Interference Coordination)
Hybrid ARQ
FDD + TDD support
3GPP R9 (LTE)
2009
Dual layer beam forming
Network based UE positioning
MBSFN (Multicast/Broadcast Single Frequency Network)
3GPP R10 (LTE)
LTE Advanced
Multi antenna extension
Relaying
Carrier aggregation
Heterogeneous networks (HetNet’s)
LTE – has an “evolution path” of its own
Evolution is towards IMT-Advanced (LTE advanced)
LTE advanced – spectral efficiency 30bps/Hz (DL), 15bps/Hz (UL)
Note: This presentation focuses on R8 features

6. DL target relative to base line UL target relative to baseline
LTE requirements
Outlined in 3GPP TR
Seven different areas
Capabilities
System performance
Deployment related aspects
Architecture and migration
Radio resource management
Complexity, and
General aspects
DL data rate > 100 Mbps in 20 MHz
UL data rate > 50 Mbps in 20MHz
Rate scales linearly with spectrum
Latency user plane: 5ms (transmission of small packet from UE to edge of RAN)
Latency control plane: transmission time from camped state – 100ms, transmission time from dormant state 50 ms
Support for 200 mobiles in 5MHz, 400 mobiles in more than 5MHz
System performance
Baseline is HSPA Rel. 6
Throughput specified at 5% and 50%
Maximum performance for low mobility users (0-15km/h)
High performance up to 120 km/h
Maximum supported speed 500km/h
Cell range up to 100km
Spectral efficiency for broadcast 1 b/s/Hz
Throughput requirements relative to baseline
Performance measure
DL target relative to base line
UL target relative to baseline
Average throughput per MHz
3-4 times
2-3 times
Cell edge user throughput per MHz
Spectrum efficiency (bit/sec/Hz)

7. Non-real time services (ms) Real time services (ms)
LTE requirements (2)
Deployment related aspects
LTE may be deployed as standalone or together with WCDMA/HSPA and/or GSM/GPRS
Full mobility between different RANs
Handover interruption time targets specified
Spectrum flexibility
Both paired and unpaired bands
IMT 2000 bands (co-existence with WCDMA and GSM)
Channel bandwidth from MHz
Handover interruption time
Non-real time services (ms)
Real time services (ms)
LTE to WCDMA
500
300
LTE to GSM
LTE duplexing options

8. LTE requirements (3) Architecture and migration
Single RAN architecture
RAN is fully packet based with support for real time conversational class
RAN architecture should minimize “single points” of failure
RAN should simplify and reduce number of interfaces
Radio Network Layer and Transport Network Layer interaction should not be precluded in interest of performance
QoS support should be provided for various types of traffic
Radio resource management
Support for enhanced end to end QoS
Support for load sharing between different radio access technologies (RATs)
Complexity
LTE should be less complex than WCDMA/HSPA

9. SAE design targets SAE – Service Architecture Evolution
SAE = core network
Requirements placed into seven categories
High level and operational aspects
Basic capabilities
Multi-access and seamless mobility
Man-machine interface aspects
Performance requirements for Evolved 3GPP system
Security and privacy
Charging aspects
SAE requirements mainly non access related (highlighted ones have impact on RAN)

10. Basic principles – Air interface
Downlink OFDM
OFDM = Orthogonal Frequency Division Multiplexing
OFDM = Parallel transmission on multiple carriers
Advantages of OFDM
Avoid intra-cell interference
Robust with respect to multi-path propagation and channel dispersion
Disadvantage of OFDM
High PAPR and lower power amplifier efficiency
Uplink DFTS-OFDM (SC-FDMA)
DFTS = DFT spread OFDM
SC-FDMA = Single carrier FDMA
Advantages (all critical for UL)
Signal has single carrier properties
Low PAPR
Similar hardware as OFDM
Reduced PA cost
Efficient power consumption
Disadvantage
Equalizer needed (not critical from UL)
UL modulation
DL modulation

11. Basic principles – Air interface
Shared channel transmission
Only PS support
No CS services
Fast channel dependent scheduling
Adaptation in time
Adaptation in frequency
Adaptation in code
Hybrid ARQ with soft combining
Chain combining
Incremental redundancy
One shared channel simplifies the overall signaling
Scheduler takes the advantage of time-frequency variations of the channel
ARQ reduces required Eb/No

12. Basic principles – air interface
MIMO support
MIMO = Multiple Input Multiple Output
Use of multiple TX / RX antennas
Three ways of utilizing MIMO
RX diversity/TX diversity
Beam forming
Spatial multiplexing (MIMO with space time coding)
MIMO transmission in Rayleigh fading environment increases theoretical capacity by a factor equal to number of independent TX RX paths
As a minimum LTE mobiles have two antennas (possibly four)
Outline of spatial multiplexing idea
Note: Rayleigh fading de-correlates the paths and provides multiple uncorrelated channels

13. Basic principles – air interface
ICIC – Inter-cell interference coordination
LTE affected by inter-cell interference (more than HSDPA)
In LTE interference avoidance becomes scheduling problem
By managing resources across multiple cells inter-cell interference may be reduced
Standard supports exchange of interference indicators between the cells
One possible implementation of ICIC. Cell edge implements N=3. Cell interior implements N=1.

14. SAE-Architecture LTE Network layout
SAE – flat architecture
Core network,
RAN
RAN consist of single elements: eNode B
Single element simplifies RAN
No single point of failure
Core network provides two planes
User plane (through SGSN)
Control plane (through MME)
Interfaces
S1-UP (eNode B to SGSN)
S1-CP (eNode B to MME)
X2 between two eNode Bs (required for handover)
Uu (UE to eNode B)
LTE Network layout
UE – user equipment (i.e. mobile)
eNode B – base station
SGSN – Support GPRS Serving Node
GGSN – Gateway GPRS Serving Node
MME – Mobility Management Entity
PCRF - Policy and Charging Rules function
SAE = System Architecture Evaluation

15. LTE protocol-control plane
NAS – Non Access Stratum
RRC – Radio Resource Control
PDCP – Packet Data Convergence Protocol
RLC – Radio Link Control
MAC – Medium Access Control
S1-AP – S1 Application
SCTP – Stream Control Transmission Prot.
IP – Internet Protocol
Note: LTE control plane is almost the same as WCDMA (PDCP did not exist in WCDMA control plane)

16. LTE protocol- user plane
PDCP – Packet Data Convergence Protocol
RLC – Radio Link Control
MAC – Medium Access Control
GTP-U - GPRS Tunneling Protocol
Note: LTE user plane is identical to UMTS PS side. There is no CS in LTE – user plane is simplified.

17. LTE protocol – X2
Connects all eNodeB’s that are supporting end user active mobility (handover)
Supports both user plane and control plane
Control plane – signaling required for handover execution
User plane – packet forwarding during handover
Control plane
GTP-U: GPRS tunneling protocol
STCP: Stream Transmission Control Protocol
User plane

18. Channel structure Channels – defined on Uu Logical channels
Formed by RLC
Characterized by type of information
Transport channels
Formed by MAC
Characterized by how the data are organized
Physical channels
Formed by PHY
Consist of a group of assignable radio resource elements
Uu interface
Note: LTE defines same types of channels as WCDMA/HSPA

19. LTE - channel mapping

20. Logical channels BCCH – Broadcast Control CH PCCH – Paging Control CH
System information sent to all UEs
PCCH – Paging Control CH
Paging information when addressing UE
CCCH – Common Control CH
Access information during call establishment
DCCH – Dedicated Control CH
User specific signaling and control
DTCH – Dedicated Traffic CH
User data
MCCH – Multicast Control CH
Signaling for multi-cast
MTCH – Multicast Traffic CH
Multicast data
Red – common, green – shared, blue - dedicated
LTE Channels

21. Transport channels BCH – Broadcast CH PCH – Paging CH
Transport for BCCH
PCH – Paging CH
Transport for PCH
DL-SCH – Downlink Shared CH
Transport of user data and signaling. Used by many logical channels
MCH – Multicast channel
Used for multicast transmission
UL-SCH – Uplink Shared CH
Transport for user data and signaling
RACH – Random Access CH
Used for UE’s accessing the network
Red – common, green – shared
LTE Channels

22. PHY Channels LTE Channels Red – common, green – shared
PDSCH – Physical DL Shared CH
Uni-cast transmission and paging
PBCH – Physical Broadcast CH
Broadcast information necessary for accessing the network
PMCH – Physical Multicast Channel
Data and signaling for multicast
PDCCH – Physical Downlink Control CH
Carries mainly scheduling information
PHICH – Physical Hybrid ARQ Indicator
Reports status of Hybrid ARQ
PCIFIC – Physical Control Format Indicator
Information required by UE so that PDSCH can be demodulated (format of PDSCH)
PUSCH – Physical Uplink Shared Channel
Uplink user data and signaling
PUCCH – Physical Uplink Control Channel
Reports Hybrid ARQ acknowledgements
PRACH – Physical Random Access Channel
Used for random access
LTE Channels
Red – common, green – shared

23. Time domain structure Radio frame : Type 1 Radio frame : Type 2
Two time domain structures
Type 1: used for FDD transmission (may be full duplex or half duplex)
Type 2: used for TDD transmission
Both Type 1 and Type 2 are based on 10ms radio frame
Radio frame : Type 1
Radio frame : Type 2

24. TDD frame configurations
Different configurations allow balancing between DL and UL capacity
Allocation is semi-static
Adjacent cells have same allocation
Transition DL->UL happens in the second subframe of each half-frame
Note: TDD frame structure allows co-existence between LTE TDD and TD-SCDMA

25. Allocatable resources
LTE – radio resource = “time-frequency chunk”
Resource Block (RB) = 12 carriers in one TS (12*15KHz x 0.5ms)
Time domain
1 frame = 10 sub-frames
1 subframe = 2 slots
1 slot = 7 (or 6) OFDM symbols
Frequency domain
1 OFDM carrier = 15KHz
Note: In LTE resource management is along three dimensions: Time, Frequency, Code

26. Bandwidth flexibility
LTE supports deployment from 6RBs to 110 RBs in 1 RB increments
6RBs = 6 x 12 x 15KHz = 1080KHz -> 1.4MHz (with guard band)
110RBs = 110 X 12 X 15KHz = 19800KHz -> 20MHz (with guard band)
Typical deployment channel bandwidths: 1.4, 3, 5, 10, 15, 20 MHz
Straight forward to support other channel bandwidths (due to OFDM)
UE needs to support up to the largest bandwidth (i.e. 20MHz)

27. UE States
UE may be in three states
Detached: not connected to the network
Idle: attached to the network but not active
Connected: attached and active
UE tracking
Detached state: UE position unknown
Idle state: UE position know with the Tracking Area (TA) resolution
Connected: UE location known to the eNodeB resolution
Note: Both the UE states and UE tracking are simpler than in UMTS

28. 3GPP Specifications
All 3GPP specs are available at
RAN xx series PHY layer
RAN2 36.3xx series Layers 2 and 3
RAN3 36.4xx series S1 and X2 interfaces
RAN4 36.1xx series Core performance requirements
RAN xx series Terminal conformance testing
Example specs organization

29. Section review What are 3GPP broadband cellular technologies?
What releases of 3GPP standard contains LTE?
What were target DL and UL throughputs for LTE?
What does SAE stand for?
What are components of the CS part of the LTE core network?
What is the access scheme used on the DL?
What is the role of fast scheduler on LTE DL?
What is the smallest allocateable resource in LTE DL?
What is Radio Block (RB)?
What are spectrum bandwidth deployment options for LTE?
How many radio blocks are in 20MHz deployment?
Does LTE support TDD deployment?
What are three UE States supported by LTE?

30. Part 2
LTE Radio Access

31. Overview Overview of OFDM/OFDMA LTE Downlink transmission
Overview of DFTS-OFDM
LTE Uplink transmission
Multi-antenna transmission

32. Single carrier transmission
Data are used to modulate amplitude/phase (frequency) of a single carrier
Higher data rate results in wider bandwidth
Over larger bandwidths ( > 20KHz), wireless channel is frequency selective
As a result of frequency selectivity the received signal is severely distorted
Channel equalization needed
Complexity of equalizer increases rapidly with the signal bandwidth requirements
Transmission of single carrier in mobile terrestrial environment
Note: over small portion of the signal spectrum, fading may be seen as flat

33. Multi-carrier transmission
Channel fading over smaller frequency bands – flat (no need for equalizer)
Divide high rate input data stream into many low rate parallel streams
At the receiver – aggregate low data rate streams
Signal for each stream experiences flat fading

34. FDM versus OFDM
OFDMA minimizes separation between carriers
Carriers are selected so that they are orthogonal over symbol interval
Carrier orthogonality leads to frequency domain spacing Df=1/T, where T is the symbol time
In LTE carrier spacing is 15KHz and useful part of the symbol is 66.7 microsec
Note: orthogonality between carriers in time domain allows closer spacing in frequency domain.
FDM versus OFDM

35. OFDM transmitter/receiver
Practically OFDM TX/RX is implemented using IFFT/FFT
Use of the IFFT/FFT at the baseband means that there is no need for separate oscillators for each of the OFDM carriers
FFT (IFFT) hardware is readily available – TX/RX implementation is simple

36. Guard time OFDM symbols with guard time
Duration of the OFDM symbol is chosen to be much longer than the multi-path delay spread
Long symbols imply low rate on individual OFDM carriers
In multipath environment long symbol minimizes the effect of channel delay spread
To make sure that there is no ISI between OFDM symbols – guard time is inserted
OFDM symbols without guard time
OFDM symbols with guard time

37. Cyclic prefix Guard time eliminates ISI between OFDM symbols
Multipath propagation degrades orthogonality between carriers within an OFDMS symbol
To regain the orthogonality between subcarriers – cyclic prefix is used
Cyclic prefix fills in the guard time between the OFDM symbols

38. Block diagram of full OFDM TX/RX
LTE supports numerous AMC schemes
AMC adds additional level of adaptation to the RF channel
Size of CP depends on the amount of dispersion in the channel
Two CP are used: normal (4.7 us) and extended (16.7 us)

39. OFDMA time-frequency scheduling
Minimum allocateable resource in LTE is Resource Block pair
Resource block pair is 12 carriers wide in frequency domain and lasts for two time slots (1ms)
Depending on the length of cyclic prefix RB pair may have 14 or 12 OFDM symbols
PHY channels consist of certain number of allocated RB pairs
Overhead channels are typically in a predetermined location in time frequency domain
Within a RB different AMC scheme may be used
Allocation of the radio block is done by scheduler at eNode B

40. LTE Downlink Transmission
Part 3
LTE Downlink Transmission

41. LTE OFDM Basic timing unit: Ts = 1/(2048 x 15000) ~ 23.552 ns
Parameter
Value
Bandwidth (MHz)
1.4 3 5 10 15 20
Frame /subframe duration
10/1 ms
Subcarrier spacing
15KHz
Useful symbol part
66.7us
FFT size
128
256
512
1024
1536
2048
Resource blocks 6 25 50 75
100
Number of used subcarriers 72
180
300
600
900
1200
Cyclic prefix length
Normal: 5.1us for first symbol in a slot and 4.7us for other symbols , Extended: 16.7us
OFDM symbols /slot
7 (normal CP), 6 (extended CP)
Error coding
1/3 convolutional (signaling); 1/3 turbo (data)
Basic timing unit: Ts = 1/(2048 x 15000) ~ ns

42. Detailed time domain structure
Need for two different CP:
To accommodate environments with large channel dispersion
To accommodate MBSFN (Multi-Cast Broadcast Single Frequency Network) transmission
In case of MBSFN it may be beneficial to have mixture of sub-frames with normal CP and extended CP. Extended CP is used for MBSFN sub-frames
TCP: 160Ts (5.1us) for first symbol, 144Ts (4.7us) for other six symbols
TCP-e: 512 Ts (16.7 us) for all symbols

43. Exercise – OFDM data rate capability at the PHY
Case 1. Normal CP (no MIMO)
Resource block: 12 carriers x 14 OFDM symbols = 168 resource elements
Each resource element carries one modulation symbol
For 64 QAM: 1 symbol = 6 bits
Number of bits per subframe = 168 x 6 = 1008 bits/subframe
Raw PHY data rate = 1008/1ms = 1,008,000 bits/sec/resource block (180KHz)
For 20MHz, Raw PHY data rate = 100 RB x 1,008,000 bits/sec/RB = 100.8Mbps
Case 2. Extended CP (no MIMO)
Resource block: 12 carriers x 12 OFDM symbols = 144 resource elements
Number of bits per subframe = 144 x 6 = 864 bits/subframe
Raw PHY data rate = 864/1ms = 864,000 bits/sec/resource block (180KHz)
For 20MHz, Raw PHY data rate = 100 RB x 864,000 bits/sec/RB = 86.4Mbps
Note: with the use of MIMO the rates are increased

44. Downlink reference signals
For coherent demodulation – terminal needs channel estimate for each subcarrier
Reference signals – used for channel estimation
There are three type of reference signals
Cell specific DL reference signals
Every DL subframe
Across entire DL bandwidth
UE specific DL reference signals
Sent only on DL-SCH
Intended for individual UE’s
MBSFN reference signals
Support multicast/broadcast
Note: Reference signals are staggered in time and frequency. This allows UE to perform 2-D complex interpolation of channel time-frequency response

45. Cell specific reference signals
Two port TX
DL transmission may use up to four antennas
Each antenna port has its own pattern of reference signals
Reference signals are transmitted at higher power in multi-antenna case
Reference signals introduce overhead
4.8% for 1 antenna port
9.5% for 2 antenna ports
14.3 % for 4 antenna ports
Reference symbols vary from position to position and from cell to cell – cell specific 2 dimensional sequence
Period of the sequence is one frame
Four port TX
One port TX

46. Cell specific reference signals (2)
There are 504 different Reference Sequences (RS)
They are linked to PHY-layer cell identities
The sequence may be shifted in frequency domain – 6 possible shifts
Each shift is associated with 84 different cell identities (6 x 84 = 504)
Shifts are introduced to avoid collision between RS of adjacent cells
In case of multiple antenna ports – only three shifts are useful
For a given PHY Cell ID - sequence is the same regardless of the bandwidth used – UE can demodulate middle RBs in the same way for all channel bandwidths
Shifts for single port transmission

47. UE Specific RS UE specific RS – used for beam forming
Provided in addition to cell specific RS
Sent over resource block allocated for DL-SCH (applicable only for data transmission)
Note: additional reference signals increase overhead. One of the most beneficial use of beam forming is at the cell edge – improves SNR

48. PHY channels supporting DL TX
SCH – allows mobile to synchronize to the DL TX during acquisition
PBCH – used to broadcast static portion of the BCCH
PDSCH – carries user information and signaling from upper layers of protocol stack
PDCCH – channel used by MAC scheduler to configure L1/L2 and assign resources (DL scheduling and UL grants)
PCFICH – explains to the UE the format of the DL transmission
PHICH – support for HARQ on the uplink
PUCCH – support for HARQ on the downlink
Channels required for DL transmission

49. Summary of PHY DL channels
L1/L2 signaling
L1/L2 Control
Coding scheme
PHY Channel
Modulation
CFI (Channel format Indicator)
Block code R=1/16
PCFICH
QPSK
HI (HARQ information)
Repetition 1/3
PHICH
BPSK
DCI (Downlink control Information)
Convolutional 1/3 with rate matching
PDCCH
Services to upper layers
Transport channel
Coding scheme
PHY Channel
Modulation
DL-SCH
Turbo 1/3
PDSCH
QPSK, 16-QAM, 64-QAM
BCH
Convolutional 1/3
PBCH
QPSK
PCH
MCH
PMCH

50. Downlink L1/L2 signaling
Signaling that supports DL transmission
Originates at L1/L2 (no higher layer data or messaging)
Consists of
Scheduling assignments and associated information required for demodulation and decoding of DL-SCH
Uplink scheduling grants for UL-SCH
HARQ acknowledgements
Power control commands
L1/L2 signaling is transmitting in first 1-3 symbols of a subframe – control region
Size of control region may vary dynamically – always whole number of OFDM symbols (1,2,3)
Signaling – beginning of the subframe
Reduces delay for scheduled mobiles
Improves power consumption for non-scheduled mobiles
Three different PHY channel types
PCFIC (PHY Control Format Indicator Channel)
PHICH (PHY – Hybrid ARQ Channel)
PDCCH (PHY Downlink Control Channel)

51. PCFICH PCFICH – PHY Channel Format Indicator Channel
Indicates to UE the size of the control region (1,2 or 3 OFDM symbols)
PCFICH value may be 1, 2 or 3 (0 is reserved for future use)
Decoding of PCFICH is essential for UE operation
Encoded with 1/16 repetition code
Uses QPSK modulation
Mapped to the first symbol of each subframe
16 resource elements in 4 groups of 4 (RE Groups)
Location of the resource elements depends on cell identity
Processing of PCFICH
Note: REGs of the PCFICH are spread in frequency domain to achieve frequency diversity

52. PHICH Processing of PHICH PHICH = PHY Hybrid-ARQ Indicator Channel
HARQ acknowledgements for UL-SCH transmission
As many PHICH channels as the number of UEs in the cell
A set of PHICH channels is multiplexed on the same resource elements (8 normal CP, 4 extended CP)
Transmitted in the first OFDM symbol of the subframe
Occupies 3 resource element groups (REGs) = 12 resource elements (RE)
PHICH response comes 4 sub-frames after PU-SCH
Processing of PHICH

53. PDCCH PDCCH = Physical Downlink Control Channel Used for
DL scheduling assignments
UL scheduling grants
Power control commands
PDCCH message occupies 1,2,4 or 8 Control Channel Elements (CCEs)
CCE = 9 Resource Element groups (REGs) = 36 Resource Elements (REs)
One PDCCH carrier one message with a specific Downlink Control Information (DCI)
Multiple UE-s scheduled simultaneously -> Multiple PDCCH transmissions in a subframe

54. PDCCH DCIs DCI formats of PDCCH
PDCCH carrier Downlink Control Information (DCI)
Multiple DCI formats are defined based on type of information
DCI formats of PDCCH
Format
Purpose
Content
# of bits (FDD)
UL PUSCH grant
RB assignment, MCS, hopping flag, NDI, cyclic shift of DM-RS, CQI, … 44 1
DL PDSCH grant for single code word
Resource allocation header, RB allocation, MCS, HARQ, HARQ PID, … 55 1A
Compact DL PDSCH grant of single code word
Similar to format 1, but with smaller flexibility
RACH initiated by PDCCH order
Localized/distributed VRB assignment flag, preamble index, PRACH message mask index 1B
Compact DL PDSCH grant with pre-coding information
Similar to 1, but with distributed VRB flag, reduced RB allocation flexibility, transmit PMI and pre-coding 49 1C
Very compact DL PDSCH grant
Reduced payload for improved coverage, always uses QPSK on associated PDSCH, restricted RB assignment, No HARQ, … 31 1D
Compact DL PDSCH grant with pre-coding information and power offset
Same as 1, but with reduced RB allocation flexibility and addition of distributed VRB transmission flag. Transmit PMI information for pre-coding, DL power offset 2
MIMO DL grant
Same as 1, but for MIMO transmission 76 2A
Compact MIMO DL grant
Same as 1A, but for MIMO transmission 68 3
2-bit UL power control
TPC for 14 UEs plus 16 bit CRC 3A
1-bit UL power control
TPC for 28 UEs plus 16 bit CRC

55. PDSCH DL-SCH = DL Shared channel
Used for user data coming from upper layers (both signaling and payload)
Optimized for low latency and high data rate
Individual steps in the processing chain operate on data blocks – enables parallel processing
Many different adaptation modes
Modulation
Coding
Transport block size
Antenna mapping (TX diversity, beam forming, spatial multiplexing)

56. Time/Frequency location of PBCH and SS - FDD
PBCH = Physical Broadcast Channel
Used for BCH transport channel
SS = Synchronization Signal
P-SS = Primary Synchronization Signal
S-SS = Secondary Synchronization Signal
SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity
Note: PBCH and SS use innermost part of the spectrum. This way the system acquisition is the same regardless of deployed bandwidth

57. Time/Frequency location of PBCH and SS - TDD
PBCH = Physical Broadcast Channel
Used for BCH transport channel
SS = Synchronization Signal
P-SS = Primary Synchronization Signal
S-SS = Secondary Synchronization Signal
SS are used only on Layer 1 – for system acquisition and Layer 1 cell identity
Note: The position of the P-SS is different in TDD and FDD. By acquiring P-SS, the UE already knows if the system is FDD or TDD.

58. Synchronization Channel (SCH)
SCH – first channel acquired by UE
Based on SCH, UE determines eNode B PHY cell identity
504 possible PHY layer cell IDs
168 groups with 3 identities per group
SCH consist of 2 signals
PSS (Primary Synchronization Signal)
SSS (Secondary Synchronization Signal)
3 possible PSS sequences: NID(2) = 0,1, 2
168 possible SSS sequences: NID(1) = 0,1, …, 167
Cell ID: NIDcell = 3* NID(1) + NID(2)
For FDD (frame type 1)
PSS is transmitted on OFDM symbol 7 in the first time slot of subframe 0 and 5
SSS is transmitted on OFDM symbol 6 in the first time slot of subframe 0 and 5
For TDD (frame type 2)
PSS is transmitted on OFDM symbol 3 in the first time slot of subframe 1 and 6

59. Mapping of the BCCH information
PBCH
PBCH = PHY Broadcast Channel
PBCH provides PHY channel for static part of Broadcast Control Channel (BCCH)
BCCH carriers RRC System Information (SI) messages
SI messages carry System Information Blocks (SIBs)
SI-M is a special SI that carrier Master Information Block (MIB)
In LTE BCCH is split into two parts
Primary broadcast: Carriers MIB and provides UE with fast access to vital system broadcast information. Primary broadcast is mapped to PBCH
Dynamic broadcast: Carries all SIBs that contain quasi-static information on system operating parameters. Dynamic broadcast is mapped to PDSCH
Mapping of the BCCH information

60. PCH PCH = Paging Channel
Transmitted over PDSCH (messages), PDCCH (paging indicator)
LTE support DRX (UE sleeps between paging occasions)
LTE defines DRX cycle
UE is assigned to P-RNTI (Paging – Radio Network Temporary Identifier)
P-RNTI is set on PDCCH
UE that finds set P-RNTI reads PCH on PDSCH to determine if it is being paged
DRX cycle compromise
Long cycle: good battery life, higher paging delay
Short cycle: faster paging response, shorter UE battery life
DRX and paging
Mapping of PCCH

61. Section review Explain the main idea behind OFDM?
How is OFDMA different from FDMA?
What is the role of cyclic prefix (CP) in OFDM?
What are DL reference signals?
How are cell specific reference signals linked to cell’s physical identity?
What is the role of PCFICH?
What is the role of PHICH?
What is the channel used for user data and higher layer signaling?
What is SCH?
What portion of the time-frequency resources is occupied by SCH?
What is the duration of LTE frame?
How many subframe are in LTE frame?
What is the time duration of one LTE time slot?

62. DFTS-OFDM Note: In DFTS-OFDM, M < N Outline of the DFTS-OFDM
DFTS-OFDM = DFT Spread OFDM
Also known as s Single Carrier FDMA (SC-FDMA)
Used on RL of LTE
Advantages:
Lower PAPR than OFDM (4dB for QPSK and 2dB for 16-QAM)
Orthogonality between the users in the same cell
Low complexity TX/RX due to DFT/FFT
Disadvantage:
Needs an equalizer at the Node B RX
Need for some synchronization in time domain
Note: In DFTS-OFDM, M < N
Outline of the DFTS-OFDM

63. DFTS-OFDM TX/RX chain
Note: the TX/RX of DFTS-OFDM is almost the same as OFDM. The DFT pre-coding / decoding and equalization are done in software

64. Uplink user multiplexing
Two ways of mapping the output of the DFT
Consecutive carriers: Localized DTFS-OFDM
Distributed carriers: Distributed DTFS-OFDM
Distributed OFDM has benefit of frequency diversity
Note 1: Mapping between output of the OFDM and carriers is performed by MAC scheduler
Note 2: Spectrum bandwidth may be allocated in dynamic fashion
Distributed DFTS-OFDM
Localized DFTS-OFDM

65. Uplink frame format Need for two different CP:
To accommodate environments with large channel dispersion
To accommodate MBSFN (Multi-Cast Broadcast Single Frequency Network) transmission
Note: UL and DL frame formats are identical
TCP: 160Ts (5.1us) for first symbol, 144Ts (4.7us) for other six symbols
TCP-e: 512 Ts (16.7 us) for all symbols

66. PHY channels supporting UL TX
PRACH – initial random access and UL timing alignment
PUSCH – channel used for transmission of user data and upper layer signaling
PUCCH – uplink control channel used for scheduling requests for synchronized UEs
PDCCH – uplink scheduling grants
PHICH – HARQ feedback channel supporting UL transmission

67. Uplink reference signals (1)
Used for uplink channel estimation
Two types of sequences
Data demodulation Reference Signal (DM-RS)
Sounding Reference Signal (SRS)
DM-RS
Sent on each slot transmission to help demodulate data
Occupies center part of the slot transmission (symbols 4) in both transmission slots
Use same bandwidth as the UL data (multiples of 12 carrier RBs)
Properties of DM-RS sequences
Small power variations in frequency domain
Small power variations in time domain

68. Uplink reference signals (2)
SRS
Allow network to estimate channel quality across entire band
Used by MAC scheduler to perform frequency dependent scheduling
Optional implementation
UE can be configured to send SRS sequence at time intervals from 2ms to 160ms
Two modes of operation
Wideband SRS – UE send the sequence across the entire spectrum
Hopping SRS – UE sends narrowband sequence that hops across different parts of the spectrum

69. PUSCH Example: 2 UE’s, 10MHz (50 RB)
PUSCH = PHY Shared channel
PUSCH carries UL-SCH (user data/higher layer signaling)
During data transmission L1/L2 signaling also mapped o PUSCH – preserve single carrier TX
Resources allocated to the UE on per subframe basis
Allocation is done in PRB (12 carriers by 1 ms)
Modulation used may be QPSK, 16-QAM or 64-QAM (optional)
Allocated PRBs may be hopped from subframe to subframe
Two modes of hopping
Intra subframe and inter subframe
Only inter subframe
Hopping may be on the basis of explicit grants from Node B or following predefined cell-specific mirroring patterns
Example: 2 UE’s, 10MHz (50 RB)
Note: Frequency hopping provides frequency diversity and interference averaging for the UL transmission

70. PUCCH
PUCCH = PHY Uplink Control Channel
Used for L1/L2 signaling
Scheduling request
ACK/NACK/DTX for DL-SCH transmission
Feedback on DL channel quality (CQI/PMI/RI)
Used only when there is no scheduled PUSCH transmission (single carrier TX)
Uses PRBs at the very end of the allocated channel bandwidth
Increases frequency diversity
Allows scheduling of larger resource “chunks” for uplink transmission
Number of PRBs is configured by the network in a semi-static manner
Bandwidth of a single resource block in a subframe is shared by several UE’s
Economical use of allocated resources
Reduces signaling overhead
Note: PUCCH performs frequency hopping between two slots of a subframe

71. PUCCH formats
PUCCH format
Modulation
Purpose
Bits/subframe 1
On/off keying
Scheduling requests
N/A 1a
BPSK
ACK/NACK for SIMO 1b
QPSK
ACK/NACK for MIMO 2
CQI/PMI/RI 20 2a
QPSK+BPSK
CQI/PMI/RI+ACK/NACK for SIMO 21 2b
QPSK+QPSK
CQI/PMI/RI+ACK/NACK for MIMO 22
Note 1: There are 2 formats: Format 1 (1, 1a and 1b) and Format 2 (2, 2a and 2b)
Note 2: PUCCH power offset depends on the PUCCH format

72. PUCCH – Format 1
Small in size (1 or 2 bits)
Used for
DL HARQ ACK/NACK for MIMO/SIMO
Scheduling request
By using different cyclic shifts and different covers sequences, multiple users may be multiplexed on the same PUCCH resource
Typically there are 6 shifts and 3 cover sequences – 18 UE’s per PUCHH resource
Note: Format 1 is repeated in two corresponding slots in the subframe

73. Processing of CQI report
PUCCH – Format 2
Larger in size (20, 21 or 22 bits)
10 bits for CQI report
2 bits for ACK/NACK
Used for
DL HARQ ACK/NACK for MIMO/SIMO
Scheduling request
CQI/PMI and RI information
By using different cyclic shifts of the CAZAC sequence multiple UE’s may be multiplexed on one PUCCH resource
Format 1 and 2 share the same basic format
Note: for Format 2, both CQI report and ACK/NACK information are sent
Processing of CQI report

74. UL time frequency resources for PRACH
PRACH = PHY Random Access Channel
Physical channel used in support of random access
In LTE initial access is handled only on PHY, all the signaling is sent through UL-SCH (PUSCH)
PRACH carries one of 64 preambles
Available preambles are signaled in SIB-2
UE selects a preamble based on the amount of data it needs to send on UL-SCH (this way Node B knows how to reserve resources)
PRACH preamble is sent over PRACH time frequency resource
Occupies middle 1.08MHz of spectrum
Same spectrum regardless of total LTE bandwidth
PRACH access subframe may occur every 1, 2, 5, 10 or 20 ms (20 ms – optional, only in synchronized networks)
Subframe allowed for access – signaled on SIB-2, paremeter PRACH_Configuration index
UL time frequency resources for PRACH

75. Section review Why is OFDM not suitable for UL transmission?
What is PAPR?
What is DFTS-OFDM?
What are two types of UL reference signals?
Why is there need for sounding reference signals?
How often can a mobile configured to send SRS signals?
What is PUSCH?
What is PUCCH?
What are PUCCH formats?
What information is carried on PUCCH?
What is PRACH?
How does UE learn what preamble sequences are available for PRACH?

76. Multiple antenna techniques
Part 3
Multiple antenna techniques

77. Multi antenna configuration
LTE uses of multiple antennas at both communication ends
LTE standard requires support for
4 antennas at the eNodeB
2 antennas at the UE
Multiple antennas may be used in three principle ways
Reception/transmission diversity
Beam forming
Spatial multiplexing (MIMO antenna processing)
Downlink MIMO
TX diversity
Beam forming or SDMA
Spatial multiplexing
Uplink MIMO
Multi user MIMO (SDMA)
Downlink MIMO
Uplink MIMO
Note: UL MU MIMO avoids use of multiple PAs at the UE

78. DL transmit diversity Two implementations CDD STTD CDD TX diversity
Cyclic Delay Diversity (CDD)
Space-Time Transmit Diversity (STTD)
CDD
Multiple antenna elements are used to introduce additional versions of the signal that are cyclically delayed
UE perceives these signals as additional multi-paths
Assuming low correlations between TX antennas –created “multi-paths” fade independently – source of diversity
STTD
Uses Space-Frequency Block Codes
Special encoding (SFBC) makes the channel matrix unitary (full rank)
Reference symbols are used to estimate and invert channel matrix
CDD TX diversity
SFBC TX diversity

79. TX Diversity - CDD
OFDM is robust with respect to multi-path propagation (within CP interval)
CDD simulates multi-path propagation
No modification in RX signal processing – UE ‘sees’ single antenna transmission in dispersive environment
Note: Extension of CDD to more than 2 antennas is straightforward. Each antenna has its own cyclic delay.
Processing in case of 2 antenna CDD TX diversity

80. TX Diversity – 2 TX SFBC
Data sent to different antenna are encoded using SFBC
2 symbols at the time for 2 antennas TX diversity
Open loop
SFBC in case of 2 TX diversity
Note 1: UE needs to have good estimate of the channel – estimate obtained using PHY reference sequences

81. TX Diversity – 4 TX SFBC
Data sent to different antenna are encoded using SFBC
4 symbols at the time for 4 antennas TX diversity
TX diversity operates on a resource element group (REG)
Open loop
SFBC in case of 4 TX diversity
Note 1: 4 TX SFBC diversity may be seen as two 2 TX SFBC diversity transmissions multiplexed in time

82. Spatial multiplexing
Basic idea: fading channel provides uncorrelated parallel paths for data transmission
Capacity benefit of SM MIMO
NT - number of TX antennas
NR - number of RX antennas
Example: 2 by 2

83. Spatial multiplexing in LTE
Two types
Open loop (used high speed scenarios)
Large delay Cyclic Delay Diversity (CDD)
Closed loop (used in low speed scenarios)
Mobile provides channel feedback to eNode B
Feedback
Closed loop spatial multiplexing
Open loop spatial multiplexing
PMI (Pre-coded matrix indicator)
PMI feedback from UE based on instantaneous channel state
No feedback from UE. Fixed pre-coding at eNode B implementing cyclic delay diversity (CDD)
CQI (Channel quality indicator)
Separate CQI for each code word
Aggregate CQI (one value)
RI (Rank indicator)
Based on the rank of estimated channel matrix
(indicates number of spatial channels)
Based on the rank of estimated channel matrix when SFBCs are used
Closed loop spatial multiplexing

84. Code word – layer mapping
LTE uses either 1 or 2 code words
Code words are mapped onto layers
1 layer for 1 codeword
2, 3 or 4 layers for 2 code words
Number of modulation symbols in each layer is the same
Accomplished through numerous transport-block formats and sizes
Through a pre-coding matrix the layers are mapped onto the antennas
There is a set of pre-defined pre-coded matrices
Through PMI, UE recommends to eNodeB which pre-coded matrix to use
eNodeB may not follow UE’s recommendation – informs UE about pre-coding matrix through explicit signaling
Mapping between code-words and layers
Note: layers are mapped to antennas one symbol at the time

85. Antenna configurations
Transmission modes
Description
Comments 1
Single antenna (Port 0)
Used for SISO and SIMO transmission 2
Transmit diversity
Used in low SNR and high mobility 3
Open loop spatial multiplexing
(large delay CDD)
Beneficial in high SNR and rich multipath environment 4
Closed loop spatial multiplexing
(Rank 2, 3 or4) 5
Multi-user MIMO
Beneficial in high SNR environment for interference reduction 6
Closed loop Rank = 1
Beneficial in low SNR environments 7
Single antenna port (Port 5)
Used for beam forming of antenna arrays

86. SIMO/MIMO mode selection
Note: Detection of the environment type and best use of MIMO/SIMO is one of the tasks for scheduler – major differentiating factor between different equipment vendors

87. Section review What is MIMO? What is receive diversity?
What is transmit diversity?
What is beam forming?
What is SDMA?
What is spatial multiplexing?
How much is capacity of link increased using spatial multiplexing?
What is CQI?
What is RI?
How is RI used by the scheduler?
What is the main idea behind SFBC?
What is CDD?
Explain the main idea behind CDD?