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LTE: Overview and Deployment Considerations
80-W2691-1 Rev A
Spring 2010
LTE: Overview and Deployment Considerations 80-W2691-1 Rev A
QUALCOMM Incorporated 5775 Morehouse Drive San Diego, CA 92121-1714
U.S.A.
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Outline
Introduction
Overview of LTE
Architecture Downlink Uplink
LTE Deployment Considerations Spectrum and Overlay
Emissions and Load Balancing
Coverage
Link Budget
Voice
3GPP Releases & Features
DL: 384 kpps peak UL: 384 kbps peak
Broadband uploads Reduced end to end delay Real-time services (VoIP, packet VT, PTT)
Multicast (MBMS)
Enhanced capacity for real- time service (i.e., VoIP…) MIMO
Backward compatibility New Radio Interface (UTRA)
FDD and TDD at 3.84 Mcps Concurrent CS and PS Services Multimedia Messaging
GSM/GPRS Internetworking Basic UMTS Security
Rel-99
WCDMA
All-IP Services Broadband downloads
DL: 1.8-14.4 Mbps peak1 UL: 384 kbps peak
DL: 1.8-14.4 Mbps peak1 UL: 5.72 Mbps peak Rel-5 (HSDPA) Rel-6 (HSUPA)
HSPA
DL: 14-42 Mbps peak2 UL: 11.5 Mbps peak
Rel-7 Rel-8
HSPA Evolved (HSPA +)
LTE
CDMA CDMA/TDM OFDMA
OFDMA in DL SC-FDMA in UL
Flexible carrier bandwidths up to 20 MHz
Common FDD & TDD modes 1 – 14.4 Mbps supported in standard; incremental product release expected
2 – Upper range for DL peak rates includes 64-QAM and 2x2 MIMO (Rel 8)
UMTS Mobile Broadband Evolution Path
ESG Experience In LTE
Development &
Delivery of LTE Training Material
Execution of LTE IOTs With All Major
Infrastructure Vendors
Consulting Services For LTE Technology Trial & Execution of
LTE Trial
Representing Qualcomm In LTE Standards & LSTI
Forum ESG is Well
Positioned To Offer
LTE Services
LTE Overview
Basic EPS entities & interfaces
Overall EPS Architecture
SG i S1-C or S6a
S1-MME
PCRF Gx S10 Other
MMEs
Rx
UE
HSS/
AuC
LTE-Uu
S11
S5 S1-U
X2
E-
UTRAN
EPC
Gx c
eNode B
MME
S-GW P-GW
Operator's IP Services
(e.g., Internet, Intranet, IMS, PSS)
Signaling (Optional) Data Other
eNBs
EPS entities:
• eNB: Evolved Node B
• MME: Mobility Management Entitiy
• S-GW: Serving Gateway
• P-GW: PDN Gateway
Other entities:
• HSS: Home Subscriber Server
• PCRF: Policy and Charging Resource Function
• IMS: IP Multimedia Subsystem
• PSS: PS Streaming Service
SPR
Sp
E-UTRA Design Performance Targets
Scalable transmission bandwidth (up to 20 MHz)
Improved Spectrum Efficiency
Downlink (DL) spectrum efficiency should be 2-4 times Release 6 HSDPA.
– Downlink target assumes 2x2 MIMO for E-UTRA and single Tx antenna with Type 1 receiver HSDPA.
Uplink (UL) spectrum efficiency should be 2-3 times Release 6 HSUPA.
– Uplink target assumes 1 Tx antenna and 2 Rx antennas for both E-UTRA and Release 6 HSUPA.
Coverage
Good performance up to 5 km
Slight degradation from 5 km to 30 km (up to 100 km not precluded)
Mobility
Optimized for low mobile speed (< 15 km/h)
Maintained mobility support up to 350 km/h (possibly up to 500 km/h)
Advanced transmission schemes, multiple-antenna technologies
E-UTRA Air Interface Capabilities
Bandwidth support
Flexible from 1.4 MHz to 20 MHz
Waveform
OFDM in Downlink SC-FDM in Uplink
Duplexing mode
FDD: full-duplex (FD) and half-duplex (HD) TDD
Modulation orders for data channels
Downlink: QPSK, 16-QAM, 64-QAM Uplink: QPSK, 16-QAM, 64-QAM
MIMO support
Downlink: SU-MIMO and MU-MIMO (SDMA)
Uplink: SDMA
UE-eNB Communication Link
Single and same link of communication for DL & UL
• DL serving cell = UL serving cell
• No UL or DL macro-diversity
– UL softer HO reception is an implementation choice – UE’s Active Set size = 1
• Hard-HO based mobility
– UE assisted (based on measurement reports) and network controlled (handover decision at specific time) by default
– During a handover, UE uses a RACH based mobility procedure to access the target cell
– Handover is UE initiated if it detects a RL failure condition
•
E-UTRA Air Interface Peak Data Rates
Downlink
~300 Mbps in 20 MHz Assumptions:
4 stream MIMO
14.29% Pilot overhead (4 Tx antennas)
10% common channel overhead
– Note: This overhead level is adequate to serve 1
UE/subframe.
6.66% waveform overhead (CP + window)
10% guard band
64-QAM code rate ~1
Uplink
• ~75 Mbps in 20 MHz
• Assumptions:
– 1 Tx antenna
– 14.3% Pilot overhead – 0.625% random access
overhead
– 6.66% waveform overhead (CP + window)
– 10% guard band
– 64-QAM code rate ~1
Cyclic Prefix (CP)
In OFDM, multipath causes loss of orthogonality
Delayed paths cause overlap between symbols
Cyclic Prefix (CP) insertion helps maintain orthogonality
Reduces efficiency (or Usable Symbol time, T )
Direct Path Reflected Path Reflected Path
T
u+T
CPT
u1ms Radio Frame Tf = 10 ms
Subframe (2 slots)
Slot Tslot=0.5 ms
0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6
OFDM Symbol CP
Time Domain Organization
CP length (config. by higher layer)
Number of OFDM Symbols/Slot
4.69µs (Normal CP) 16.66μs (Extended CP) 33.3µs (MBSFN only)
7 OFDM/LFDM symbols 6 OFDM/LFDM symbols 3 OFDM symbols
UL Symb DL
Symb
N
N or
Radio Frame has 2 structures:
• Type 1 (FS1) for FDD DL/UL
• Type 2 (FS2) for TDD
FS1 is considered in this presentation
LTE Time Domain is organized as:
• Frame (10 ms)
• Subframe (1 ms)
• Slot (0.5 ms)
• Symbol (duration depending on
configuration)
Frequency Domain Organization
Frequency Channel Bandwidth
f = 15 KHz Resource Block 1
180 KHz
DC Subcarrier
... ...
RB
N SC
ULRB DL
RB
N
N or
Guard Band
LTE DL/UL air interface waveforms use several orthogonal subcarriers to send user traffic data, Reference Signals (Pilots), and Control Information.
• ∆ f: Subcarrier spacing
• DC Subcarrier: Direct Current subcarrier at center of frequency band
Frequency Domain Configurations
Channel Bandwidth [MHz] 1.4 3 5 10 15 20
N. of Occupied Subcarriers
including DC (N SC ) 73 181 301 601 901 1201
FFT Size (N) 128 256 512 1024 1536 2048
Sampling Rate [MHz] 1.92
½ 3.84 3.84 7.68 2x3.84
15.36 4x3.84
23.04 6x3.84
30.72 8x3.84 N. of Resource Blocks
(N RB ) 6 15 25 50 75 100
Assuming 15 KHz Carrier Spacing
• Various channel bandwidths that may be considered for LTE deployment are shown in the table.
• One of the typical LTE deployment options (10 MHz) is highlighted.
:
Resource Block Group
Resource Element (RE)
One element in the time/frequency resource grid.
One subcarrier in one OFDM/LFDM symbol for DL/UL. Often used for Control channel resource assignment.
Resource Block (RB)
Minimum scheduling size for DL/UL data channels
Physical Resource Block (PRB) [180 kHz x 0.5 ms]
Virtual Resource Block (VRB) [180 kHz x 0.5 ms in virtual frequency domain]
–
Localized VRB
–
Distributed VRB
DL
N
symb OFDM symbols:
T
slot One downlinkslot
UL/DL Resource Grid Definitions
:
DL RBNXRB SCN subcarriers Resource element (k, l) k = 0… - 1 l = 0… - 1
RB SCN subcarriers
DL
NRBXNRBSC
DL
Nsymb
:
DL
NsymbX RB
NSC Resource elements Resource block (180 KHz x 0.5 ms) Example: Frame Structure Type 1 (FS1)
12 subcarriers (15 KHz spacing) 7 OFDM symbols
Resource block =
DL
N
symb OFDM symbolsl = 0
:
:
DL RBNXRB SCN subcarriers
DL
l = N -1
symbT
slot One downlinkslot
RB SCN subcarriers
Resource Element Group
UL/DL Resource Grid Definitions
Resource Element Group (REG)
Groups of Resource Elements to carry control information.
4 or 6 REs per REG depending on number of reference signals per symbol, cyclic prefix configuration.
REs used for DL Reference Signals (RS) are not considered for the REG.
–
Only 4 usable REs per REG.
Control Channel Element (CCE)
Group of 9 REGs form a single CCE.
–
1 CCE = 36 REs usable for control information.
Both REG and CCE are used to specify resources for LTE DL control channels.
Antenna Port
One designated reference signal per antenna port.
Set of antenna ports supported depends on reference signal configuration within cell.
RS DL
N
symb OFDM symbolsl = 0
:
:
DL RBNXRB SCN subcarriers
DL
l = N -1
symbT
slot One downlinkslot
RB SCN subcarriers
Resource Element Group
RS RS
RS RS
Control Channel Element
RS RS
Downlink Channelization Hierarchy
Dedicated Data/Control
BCCH
PCCH
CCCHDCCH DTCH MCCH MTCH
BCH
PCH DL-SCH MCH
Downlink
Logical channels
Downlink
Transport channels
Downlink
Physical Channels
PDSCH PDCCH
PBCH PHICH
PCFICH SCH
DL-RS PMCH
Paging
System MBSFN
Common Control
Downlink
Synchronization Signals (PSS & SSS)
• PSS and SSS Functions
– Frequency and Time synchronization
Carrier frequency determination
OFDM symbol/subframe/frame timing determination
– Physical Layer Cell ID determination
Determine 1 out of 504 possibilities
• PSS and SSS resource allocation
– Time: subframe 0 and 5 of every Frame
– Frequency: middle of bandwidth (6 RBs = 1.08 MHz)
• Primary Synchronization Signals (PSS)
– Assists subframe timing determination
– Provides a unique Cell ID index (0, 1, or 2) within a Cell ID group
• Secondary Synchronization Signals (SSS)
– Assists frame timing determination
M-sequences with scrambling and different concatenation methods for SF0 and SF5)
– Provides a unique Cell ID group number among 168 possible Cell ID groups
PDSCH
Reference Signal Embedded OFDM
Symbols
PHICH PDCCH
6-100 RBs
1 ms
6 RBs = 72 Subcarriers 6x180KHz=1.08MHz
(PSS & SSS effectively use only 62 Subcarriers)
5 ms
10 ms
subframe
0 1 2 3 4 5 6 7 8 9
PDSCHPDSCH
PCFICH PHICH PDCCH SSS PSS PBCH
Physical Broadcast Channel (PBCH)
PDSCH
PDCCH
6-100 RBs 6 RBs 6x180KHz=1.08MHz
5 ms
10 ms
subframe
0 1 2 3 4 5 6 7 8 9
PDSCH
PCFICH PHICH PDCCH S-SCH P-SCH PBCH
• PBCH Function
– Carries the primary Broadcast Transport Channel
– Carries the Master Information Block (MIB), which includes:
Overall DL transmission bandwidth
PHICH configuration in the cell
System Frame Number
Number of transmit antennas (implicit)
• Transmitted in
– Time: subframe 0 in every frame
– 4 OFDM symbols in the second slot of corresponding subframe
– Frequency: middle 1.08 MHz (6 RBs)
• TTI = 40 ms
– Transmitted in 4 bursts at a very low data rate
– Same information is repeated in 4 subframes
Physical Control Format Indicator Channel (PCFICH)
PDSCH
Reference Signal Embedded OFDM
Symbols
PDCCH
6-100 RBs 6 RBs 6x180KHz=1.08MHz
5 ms
10 ms
subframe
0 1 2 3 4 5 6 7 8 9
PDSCHPDSCH
PCFICH PHICH PDCCH PBCH
• Carries the Control Format Indicator (CFI)
• Signals the number of OFDM symbols of PDCCH:
– 1, 2, or 3 OFDM symbols for system bandwidth > 10 RBs – 2, 3, or 4 OFDM symbols for system bandwidth > 6-10 RBs – Control and data do not occur in same OFDM symbol
• Transmitted in:
– Time: 1 st OFDM symbol of all subframes
– Frequency: spanning the entire system band
4 REGs -> 16 REs
Mapping depends on Cell ID
• PCFICH in Multiple Antenna configuration
– 1 Tx: PCFICH is transmitted as is
– 2Tx, 4Tx: PCFICH transmission uses Alamouti Code
Physical Downlink Control Channel (PDCCH)
PDSCH
PDCCH
6-100 RBs 6 RBs 6x180KHz=1.08MHz
5 ms
10 ms
subframe
0 1 2 3 4 5 6 7 8 9
PDSCH
PCFICH PHICH PDCCH PBCH
CCH
• Used for:
– DL/UL resource assignments
– Multi-user Transmit Power Control (TPC) commands
– Paging indicators
• CCEs are the building blocks for transmitting PDCCH
– 1 CCE = 9 REGs (36 REs) = 72 bits
– The control region consists of a set of CCEs, numbered from 0 to N_CCE for each subframe
– The control region is confined to 3 or 4 (maximum) OFDM symbols per subframe (depending on system bandwidth)
• A PDCCH is an aggregation of contiguous CCEs
(1,2,4,8)
Physical Downlink Shared Channel (PDSCH)
Transmits DL packet data
One Transport Block transmission per UE’s code word per subframe
A common MCS per code word per UE across all allocated RBs
– Independent MCS for two code words per UE 7 PDSCH Tx modes
Mapping to Resource Blocks (RBs)
Mapping for a particular transmit antenna port shall be in increasing order of:
– First the frequency index,
– Then the time index, starting with the first slot in a subframe.
PDSCH
Reference Signal Embedded OFDM
Symbols
PDCCH
6-100 RBs 6 RBs 6x180KHz=1.08MHz
5 ms
10 ms
subframe
0 1 2 3 4 5 6 7 8 9
PDSCHPDSCH
PHICH PCFICH PDCCH PDCCH PDSCH
PDSCHPDSCHPDSCH
Physical HARQ Indicator Channel (PHICH)
Used for ACK/NAK of UL-SCH transmissions Transmitted in:
Time
– Normal duration: 1 st OFDM symbol
– Extended duration: Over 2 or 3 OFDM symbols
Frequency
– Spanning all system bandwidth – Mapping depending on Cell ID
FDM multiplexed with other DL control channels
Support of CDM multiplexing of multiple PHICHs
PDSCH
PDCCH
6-100 RBs 6 RBs 6x180KHz=1.08MHz
5 ms
10 ms
subframe
0 1 2 3 4 5 6 7 8 9
PDSCH
PHICH PCFICH PDCCH DCCH
DL Reference Signals: 1 Tx Antenna
DL Reference Signals transmitted on 2 OFDM symbols every slot 6 subcarrier spacing
R0
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 7 8 9 10 11 R0
R0
R0
R0
R0
R0
R0
subcarrier
subframe slot RB
0 1 2 3 4 5 6 7 8 9
10 ms Normal CP
OFDM symbol
slot 0 slot 1
subframe R0
0 1 2 3 4 5 0 1 2 3 4 5
R0
R0
R0
R0
R0
R0
R0
OFDM symbol
0 1 2 3 4 5 6 7 8 9 10 11
subcarrier RB
Extended CP
slot 0 slot 1
subframe
DL Reference Signals: 2 Tx Antenna
R0
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 7 8 9 10 11 R0
R0
R0
R1
R1
R1
R1
R0
R0
R1
R1
R1
R1
R0
R0
subcarrier
subframe slot RB
0 1 2 3 4 5 6 7 8 9 10 ms
Normal CP
OFDM symbol
slot 0 slot 1
subframe R0
0 1 2 3 4 5 0 1 2 3 4 5
R0
R0
R0
R1
R1
R1
R1
R0
R0
R1
R1
R1
R1
R0
R0
OFDM symbol
0 1 2 3 4 5 6 7 8 9 10 11
subcarrier RB
Extended CP
slot 0 slot 1
subframe
DL Reference Signals: 4 Tx Antenna
R0 R2
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 7 8 9 10 11 R0
R0
R0
R1
R1
R1
R1
R0
R0
R1
R1
R1
R1
R0
R0
R2
R2
R2
R3
R3
R3
R3
subcarrier
subframe slot RB
0 1 2 3 4 5 6 7 8 9 10 ms
Normal CP
OFDM symbol
slot 0 slot 1
subframe R0 R2
0 1 2 3 4 5 0 1 2 3 4 5
R0
R0
R0
R1
R1
R1
R1
R0
R0
R1
R1
R1
R1
R0
R0
R2
R2
R2
R3
R3
R3
R3
OFDM symbol
0 1 2 3 4 5 6 7 8 9 10 11
subcarrier RB
Extended CP
slot 0 slot 1
subframe
Overheads Normal CP Extended CP
1 Tx antenna 4.76% 5.56%
2 Tx antennas 9.52% 11.11%
4 Tx antennas 14.29% 15.87%
Downlink Transmission – An Example
Example of Frame Structure Type 1 (extended CP) transmission
0
PCFICH PHICH PDCCH RS
PDSCH
Physical Resource Block (PRB)
2
1 3
Frequency
T im e
Slot
Sub
Frame
DL Operation: Similarities to HSPA
Shared Channel Operation
Channel Dependent Scheduling (CDS)
Requires Channel Quality Information (CQI) sent on the UL Requires Pre-coding and Rank information sent on the UL for MIMO
Adaptive Modulation and Coding (AMC)
Requires informing the UE about allocated resources
Requires informing the UE about Modulation and Coding Schemes (MCS)
Hybrid ARQ (HARQ)
Uses Asynchronous adaptive retransmissions Uses Synchronous ACK/NAKs
Requires ACK/NAK sent on the UL
DL Modulation: QPSK, 16-QAM, 64-QAM
• Multiple Access Dimensions:
• DL Scheduler:
– Assigns Time/Frequency resources rather than Time/Code resources.
– May coordinate with neighbor Base Stations for interference management.
• DL Reference Signals (Pilots):
– Have fixed time duration and frequency sub-band allocations.
• ARQ runs at eNode B
– ARQ architecture is conceptually similar to HSPA.
Supports TM, UM, and AM modes
Retransmissions are based on status reports
– Optional HARQ assisted ARQ operation is possible in LTE.
DL Operation: Differences from HSPA
LTE HSPA (R7)
Time (TDMA) Time (TDMA)
Frequency (OFDMA) Code (CDMA)
Space (SU-MIMO, SDMA/MU-MIMO) Space (SU-MIMO)
Initial Acquisition Procedure
UE searches for a strong cell in the DL band
(Monitors central part of the spectrum regardless of bandwidth capability)
UE performed a rough frequency synchronization
(UE has found a good carrier candidate with strong 72 (6x12) subcarriers which might carry the Sync signals and PBCH)
UE is switched on
UE determined:
- Exact carrier frequency
- Cell ID index within a Cell ID group (1 out of 3).
- Subframe timing (UE knows the timing of subframes 0 and 5) - Cyclic Prefix Length (by trial and error method)
UE looks for the (PSS)
Attempts to match one out of three possible primary Sync signals (Cell ID index within a Cell ID Group)
UE attempts to detect (SSS)
Tries to match 1 out of 168 possible secondary Sync signals (Cell ID Groups)
UE knows:
- Frame timing
(Generation method of S-SCH sync sequences is slightly different for subframes SF0 and SF5)
- Cell ID group (1 out 168)
(Since the specific Cell ID within this group was identified in previous step, physical layer Cell ID (1 out of the 504) is known now
UE acquired most essential system information.
UE can read PDCCH/PDSCH and register in the system.
PBCH is time aligned with the Sync channels
UE can read PBCH channel now
E-NodeB
E-NodeB MME
X1
DL Scheduled Operation Overview
IP Network
X2
1. UE reports CQI (Channel Quality Indicator), PMI (Precoding Matrix Index), and RI (Rank Indicator) in PUCCH (or PUSCH if there is UL traffic).
2. Scheduler at eNode B dynamically allocates resources to UE:
– UE reads PCFICH every subframe to discover the number of OFDM
symbols occupied by PDCCH.
– UE reads PDCCH to discover Tx Mode and assigned resources (PRB and MCS).
3. eNode B sends user data in PDSCH.
4. UE attempts to decode the received packet
Dynamic Scheduling: E-UTRAN dynamically allocates resources
(PRBs and MCS) to UEs at each TTI via the C-RNTI on PDCCH(s).
UE monitors the PDCCH(s) to find possible allocation when its Downlink reception is enabled (activity governed by DRX when configured).
Semi-persistent Scheduling : Initially PDCCH indicates if the DL grant can be implicitly reused in the following TTIs according to the
periodicity defined by RRC.
RRC defines the periodicity of the semi-persistent DL grant.
Characterized by a start frame number, periodicity, and packet format (one or more may be defined).
Retransmissions are explicitly signalled via the PDCCH(s).
E-UTRA DL Scheduling Principles
DL ARQ/HARQ Principles
HARQ Principles (within MAC Layer)
N-process Stop-And-Wait, Asynchronous adaptive HARQ.
Uplink ACK/NAKs are sent on PUCCH or PUSCH.
PDCCH signals the HARQ process number and whether it is a transmission or retransmission.
Retransmissions are always scheduled through PDCCH.
ARQ Principles (within RLC Layer)
ARQ retransmits RLC PDUs or RLC PDU segments.
ARQ retransmissions are based on RLC status reports and, optionally, ARQ/HARQ interactions.
Polling for RLC status report is used when needed by RLC.
ARQ/HARQ Interaction
Optional HARQ assisted ARQ operation.
CQI/PMI/RI and ACK/NACKs multiplexing on PUCCH is possible:
Format 2:
CQI/PMI/RI not multiplexed with ACK/NAK
Format 2a/2b
CQI/PMI/RI multiplexed with ACK/NAK (normal CP)
Format 2:
CQI/PMI or RI multiplexed with ACK/NAK (extended CP)
ACK/NACK for PDSCH Transmissions
The UE shall, upon detection of a PDSCH transmission in subframe n-4 intended for the UE and for which an ACK/NAK shall be provided,
transmit the ACK/NAK response in sub-frame n.
ACK/NAKs alone can be delivered PUCCH format 1a and 1b.
CQI/PMI/RI Reporting Overview
eNode B
Reporting on PUSCH
– Aperiodic and periodic reports
– Wideband CQI (multiple-PMI per sub-band)
– UE-selected sub-band CQI (No-PMI, Multiple-PMI)
– Higher layer configured sub-band CQI (No-PMI, Single-PMI)
– Frequency selective/non-selective scheduling
Reporting on PUCCH
– Periodic reports
– Wideband CQI
Uplink Channelization Hierarchy
No dedicated transport channels: Focus on “shared” transport channels.
Dedicated Control/Traffic Common
Control
UCI
Physical Control
PUSCH PRACH
Uplink
Physical channels
PUCCH
CCCH DCCH DTCH
UL-SCH RACH
Uplink
Logical channels
Uplink
Transport channels
DM-RS SRS
Uplink
Reference
Signals
E-UTRA UL Channels and Signals
Signals
• Demodulation Reference Signal (DM-RS)
• Sounding Reference Signal (SRS) Control
• ACK, CQI, Rank Indicator (RI), Precoding support (PMI)
• Scheduling Request (SR)
• Single “control” channel
- Physical Uplink Control Channel (PUCCH) Data
• Unicast data and data + control
• Single “data” channel
- Physical Uplink Shared Channel (PUSCH)
Random Access
E-UTRA Uplink Reference Signals
Two types of E-UTRA/LTE Uplink Reference Signals:
Demodulation reference signal
Associated with transmission of PUSCH or PUCCH Purpose: Channel estimation for Uplink coherent
demodulation/detection of the Uplink control and data channels Transmitted in time/frequency depending on the channel type (PUSCH/PUCCH), format, and cyclic prefix type
Sounding reference signal
Not associated with transmission of PUSCH or PUCCH
Purpose: Uplink channel quality estimation feedback to the Uplink scheduler (for Channel Dependent Scheduling) at the eNode B
Transmitted in time/frequency depending on the SRS bandwidth and
the SRS bandwidth configuration (some rules apply if there is overlap
with PUSCH and PUCCH)
OFDMA versus SC-FDMA
Physical Uplink Shared Channel (PUSCH)
PUSCH
Normal Cyclic Prefix
Extended Cyclic Prefix
Demodulation-RS Embedded SC- FDMA Symbols
6-100 RBs
1 Subframe = 1 ms PUSCH
PUSCH 5 ms
1 Radio Frame = 10 ms Subframe
0 1 2 3 4 5 6 7 8 9
1 Time Slot
Frequency Hopping
No Frequency
Hopping
Frequency diversity through
hopping
Demodulation Reference Signal (DM-RS)
l = 0 l = 7
l = 0 l = 6
PUSCH may carry:
• UL Data
• ACK/NAK for DL data
• CQI/PMI/RI
Physical Uplink Control Channel (PUCCH)
6-100 RBs
PUCCH 5 ms
1 Radio Frame = 10 ms Subframe
0 1 2 3 4 5 6 7 8 9
PUCCH
PUCCH PUCCH
PUCCH
PUCCH
Frequency Hop at Time Slot Boundary
Format 2, 2a, 2b 1 Time Slot
PUCCH
l = 0
Normal Cyclic Prefix
Extended Cyclic Prefix
PUCCH
Normal Cyclic Prefix
Extended Cyclic Prefix 1 Time Slot
Format 1, 1a, 1b
l = 7 l = 0 l = 7
PUCCH may carry:
• ACK/NAK for DL data
• Scheduling Request
• CQI/PMI/RI
Sounding Reference Signals (SRS)
Demodulation-RS Embedded SC- FDMA Symbols
6-110 RBs
1 ms PUSCH
PUSCH
SRS Sounding-RS Embedded SC- FDMA Symbols
SRS shall be transmitted on the last symbol of the subframe.
PUSCH:
• The mapping to resource elements only considers those not used for transmission of reference signals.
PUCCH Format 1 (SR) / 1a / 1b (HARQ-ACK):
• When ACK/NAK and SRS are to be transmitted in SRS cell-specific subframes:
– If higher-layer parameter Simultaneous-AN-and-SRS is TRUE => Use shortened PUCCH format.
– Else UE shall not transmit SRS.
PUCCH Format 2 / 2a / 2b (CQI):
• UE shall not transmit SRS whenever SRS and PUCCH 2 / 2a / 2b coincide.
SRS multiplexing:
• Done with CDM when there is one SRS bandwidth, and
FDM/CDM when there are multiple SRS bandwidths.
6-110 RBs
R A C H 6 R B s
RA offset
n
PRBPRACH
Sequence CP
T
CPT
SEQ• The preamble format determines the length of the Cyclic Prefix and Sequence.
• FDD has 4 preamble formats (for different cell sizes).
• 16 PRACH configurations are possible.
• Each configuration defines slot positions within a frame (for different bandwidths).
• Each random access preamble occupies a
E-UTRA Uplink Operation Highlights
Link Adaptation (CDS – Channel Dependent Scheduling)
Adaptive transmission Bandwidth
Adaptive Modulation and Channel Coding Rate (AMC) Meets QoS requirements
UL Power Control
Intra-cell power control: the power spectral density of the Uplink transmissions can be influenced by the eNB.
UL Timing Control
Objective is to compensate for propagation delay and thus time-align the transmissions from different UEs with the receiver window of the eNB.
The timing advance is derived from the UL received timing, and sent by the eNB to the UE. UE uses this information to advance/delay its timings of transmissions to the eNB.
Random Access procedure
UL Data transfer and HARQ
UL HARQ Principles
N-process Stop-And-Wait
N configured by higher layers
8 processes for Normal HARQ Operation 4 processes for subframe Bundling Operation
– A bundle of PUSCH transmissions consists of 4 consecutive Uplink subframes.
Synchronous HARQ
Normal HARQ Operation: PDCCH and/or PHICH will be evaluated for adjusting PUSCH transmissions four subframes later.
subframe Bundling Operation: PDCCH in subframe n and/or PHICH in subframe n-5, will be evaluated for adjusting PUSCH transmissions in subframe n+4.
PDCCH (DCI Format 0) carries information about UL-SCH assignments (UL grant) as well as a 1-bit New Data indicator (NDI), which determines if HARQ retransmission is needed.
HARQ retransmission is needed if the NDI does not toggle, and/or the
HARQ NAK is received on PHICH.
• UE sends SR (Scheduling Request – part of Uplink Control Information), BSR (Buffer Status Report) and PHR (Power Headroom Report) on PUCCH (or starts random access if no PUCCH is configured).
• Scheduler at eNode B dynamically allocates UL resources to UE:
– Grant is assigned to UE on PDCCH.
– Assigned resources (PRB and MCS) are communicated to the UE.
• UE sends user data on PUSCH.
• If eNode B decodes the Uplink data successfully, it changes the New Data Indicator (NDI) on PDCCH, and/or sends ACK/NAKs on PHICH.
PUCCH Physical Uplink Control Channel PDCCH Physical Downlink Control Channel PUSCH Physical Uplink Shared Channel
eNode B
eNode B MME
X1
IP Network
X2
E-UTRA UL Scheduled Operation
(Link Adaptation)
• UE transmits PUCCH or PUSCH.
• Serving eNode B monitors link quality and takes into account the overload indicators (over X2) from neighbor cells.
• Serving eNode B sends Transmit Power Control commands (TPC) as part of Downlink Control Information (DCI) on PDCCH.
• UE adjusts transmit power levels of PUCCH or PUSCH.
• Go back to 1.
eNode B
eNode B MME
X1
IP Network
X2
Overload Indicator
Single Serving Cell
E-UTRA UL Closed Loop Power
Control
Timing Advance / Alignment (TA)
units
s time
T A T
N
N T A
Timing Advance / Alignment compensates for the over-the-air radio transmission round trip time, and allows all Uplink received signals to be in sync in the time domain.
eNode B
Downlink Radio Frame #i
Uplink Radio Frame #i
N T A
Time
Rx in Sync
1. Either network indicates specific PRACH resource or UE selects from common PRACH
resources.
2. UE sends random access
preambles at increasing power.
3. UE receives random access response on the PDCCH which includes assigned resources for PUSCH transmission.
• Physical Resource Blocks (PRB) and Modulation and Coding Scheme (MCS) eNode B
eNode B MME
S1
E-UTRA Random Access
IP Network
X2
Deployment Considerations
Doppler and Delay Spread Tradeoffs
Doppler, delay spread, and spectral efficiency are competing entities
LTE specification needed to balance:
Delay Spread – larger CP size improves tolerance
Spectral Efficiency – larger CP increases overhead
Doppler Shift – larger Δf increases tolerance
Larger Δf – implies sample time (Ts) is smaller
Smaller Ts – implies less tolerance for delay
spread
Doppler Shift
Doppler Shift – Changes in the received carrier frequency due to the relative motion of the mobile to the Base Station
Doppler Frequency = f d = (v/λ) cos(θ) (Doppler Shift in Hz) Where
» Cos (θ) = 1 is worst case direct reflection
» v = velocity in m/s
» λ = wavelength in m
Sub Carrier (1/symbol time) width affects Doppler Tolerance (Coherence Bandwidth) 3GPP Specifies Low (5 Hz), Medium (70 Hz), and High (300 Hz) Doppler
Lower frequencies
imply lower Doppler
shift
RMS Delay
Total Delay Spread h
0h
1h
2h
30 1 2 3
Effective Channel
h
0h
1h
2h
30 1 2 3
Outside CP window - Is not estimated
Estimated Channel = CP
Excess Delay Spread
The Need for Cyclic Prefix
CP mitigates the effects of multipath
• EDS – Excess Delay Spread
– Total time delay between first and last multipath received signal
• r.m.s. delay – root mean square delay
– Specified tolerance in 3GPP
• CP contains all multipath, implies:
– No inter-symbol interference (ISI)
– No inter-carrier interference (ICI)
Also called “FFT Leakage”
• Too small CP
Implies EDS outside CP window
H(t) H(t)
Bottom Line
LTE is Optimized for lower mobility
With CP normal , LTE supports Typical Urban Multipath at Vehicle Speeds
With CP extended, LTE supports Larger Cell Radii and Heavy Urban Multipath
With fast sampling and lower frequency bands, LTE supports Higher Speed Doppler Shifts, e.g.,
High Speed Train at 300 km/hr (some delay/frequency planning required)
3GPP Covers Doppler and Delay Spread Planning in 36.101
Category Channel Model Acronym r.m.s Delay Spread (ns)
Low Delay Spread Extended Pedestrian A EPA 43
Medium Delay Spread Extended Vehicular A EVA 357
High Delay Spread Extended Typical Urban ETU 991
• For 4G systems, or OFDMA base systems, coverage is limited by the maximum
allowable pathloss for a given tone.
• Achievable peak data rate is limited by the bandwidth
available and interference.
• Achievable capacity is limited by the available bandwidth and interference.
• Both interference management and frequency planning should be done.
Interference management:
Increase the geometry available.
Dimensioning Nominal Design
Site Survey
Design for Capacity Design for
Coverage
Project Setup Network Requirements
Network Planning Overview – 4G
LTE Coverage Planning
Select the frequency to deploy LTE
Consider the impact of coexistence
Consider the impact of Frequency on coverage
Define the inputs for Network Planning
Estimate the coverage of LTE
Define the settings
required for LTE network planning
Estimate the performance of LTE in case of overlay with exiting technology
Dimensioning Nominal Design
Site Survey
Design for Capacity Design for
Coverage
Network Deployment
Initial Optimization
Project Setup
Network Requirements
LTE Interference
LTE coverage can be defined in terms of interference (quality)
• Demodulation of a target radio bearer (i.e., data rate) at the target BLock Error Rate (BLER)
– Channel model,
receiver architecture, modulation, and
mobility need to be taken into account – Target data date, or
Transport Block Size (TBS) need to be defined in relation to the available
bandwidth
Es/Iot also
represents the s tem
I ot (N oc )
Frequency Deployment Scenarios
Two LTE Frequency Reuse Schemes N=1
Same Frequency all cells (sectors) More cell edge / overlap design
FFR – Fractional Frequency Reuse
Emulates N=1 near cell
Resource Block Planning at Cell Edge
N=1
Pros
Higher spectral efficiency Higher overall bits/Hz
Resource utilization of 100%
No frequency planning
Handoff transition more critical
Preferred choice once ICIC (Inter-Cell Interference Coordination) available
Cons
As usage increases, interference increases
Creates low SNR (poor CQI) at the sector and cell boundaries
Interference mitigation via downtilting
F1
F1 F1
Future Feature: Fractional Frequency Reuse
Pros
N=1 reuse in cell interior
Specific RB (Resource Block) clusters reused
(reserved/scheduled) at higher power for:
Cell Edge (Reuse=3)
Improves cell overlap SNR / CQI Improves cell edge SNR / CQI 50 to 60% cell edge throughput improvement
Cons
Scheduling load higher in mobility More RF planning
Capacity Reduction
Less bits/Hz than N=1 RB Group 2 Cell Edge N=1 Interior All RBs
RB Group 3 Cell Edge
RB Group 1 Cell Edge
LTE Interference Mitigation
3GPP LTE Implementations
Radio Resource Management (RRM) Processes
Radio Bearer Control (RBC)
Radio Admission Control (RAC)
Connection Mobility Control (CMC)
Dynamic Resource Allocation (DRA) or Packet Scheduling (PS)
Inter-Cell Interference Coordination (ICIC) Load Balancing (LB)
Self Optimizing Network (SON)
Interference Mitigation Techniques Mobile
Connection
Management
Interference – Transmitter Emission Model
Fundamental emission:
Fundamental emission is defined on the basis of a modulation envelope model with respect to the bandwidth of transmission covering 250% of the necessary bandwidth.
Out of band emission (OOBE):
OOBE is an unwanted emission immediately outside the channel bandwidth resulting from the modulation process and non-linearity in the transmitter, but excluding spurious emissions.
OOBE requirement is specified in terms of a spectrum emission mask and adjacent channel leakage power ratio for the transmitter.
Spurious emission:
Spurious emissions are caused by unwanted transmitter effects such as harmonics emission, parasitic emission, intermodulation products and frequency conversion products, but exclude out of band emissions.
E-UTRAACLR1 UTRA ACLR2 UTRAACLR1
RB
E-UTRA channel Channel ΔfOOB
