4. LTE VS UMTS NETWORK ARCHITECTURE
GGSN
Evolved Packet Core
MME MME
S-GW or P-GW S-GW or P-GW
SGSN
RNC RNC
e-NodeB e-NodeB
NodeB NodeB NodeB NodeB e-NodeB e-NodeB
GGSN : Gateway GPRS Support Node MME : Mobility Management Entity
SGSN : Serving GPRS Support Node P-GW : PDN (Packet Data Network) Gateway
RNC : Radio Network Controller S-GW : Serving Gateway
NodeB : Base Stations eNodeB : envolved NodeB
5. E-UTRA ARCHITECTURE
► According to 3GPP TR 25.912, E-
UTRAN is described as follows.
► “The evolved UTRAN consists of
eNB, providing the evolved UTRAN U-
plane and C-plane protocol
terminations towards the UE. The
eNBs are interconnected with each
other by means of the X2 interfaces.
It is assumed that there always exist
an X2 interface between the eNBs
that need to communicate with each
other, e.g., for support of handover
of UEs in LTE_ACTIVE. The eNBs are
also connected by means of the S1
interface to the EPC (Evolved Packet
Core). The S1 interface supports a
many-to-many relation between
aGWs and eNBs.”
6. SYSTEM ARCHITECTURE EVOLUTION (SAE)
► System Architecture Evolution (SAE) is the network architecture and designed to simplify the network to other IP
based communications network. SAE uses an eNB and Access Gateway (aGW) and removes the RNC and SGSN from
the equivalent 3G network architecture, to make a simpler mobile network. This allows the network to be built as an
“All-IP” based network architecture. SAE also includes entities to allow full inter-working with other related wireless
technology (WCDMA, WiMAX, WLAN, etc.). These entities can specifically manage and permit the non-3GPP
technologies to interface directly into the network and be managed from within the same network.
9. LTE PROTOCOL STACK
► C-plane Protocol Stack on Uu (UE/eNB) and S1-C (eNB/MME) ► U-plane Protocol Stack on Uu (UE/eNB) and S1-U (eNB/MME)
► C-plane Protocol Stack on X2-C (eNB/eNB) ► U-plane Protocol Stack between eNB/eNB
10. SUMMARY OF THE 3GPP ORIGINAL LTE
REQUIREMENTS
► Increased peak data rates : 100Mbps downlink and 50Mbps uplink
► Reduction of RAN latency to 10ms
► Improved spectrum efficiency ( 2 until 4 times compared with HSPA Release 6)
► Cost effective migration from Release 6 Universal Terrestrial Radio Access
(UTRA) radio interface and architecture
► Improved broadcasting
► IP-optimized (focus on services in the packet switched domain)
► Scalable bandwidth of 20 MHz, 15 MHz, 10 MHz, 5 MHz, 3 MHz and 1.4 MHz
► Support for both paired and unpaired spectrum
► Support for inter-working with existing 3G systems and non-3GPPP specified
systems
11.
12. LTE CHARACTERISTIC
► LTE introduced in Rel 8
► Minor improvements in Rel 9 and Rel 10
► Significantly increased data throughput
► Downlink target 3-4 times greater than HSDPA Release 6
► Uplink target 2- 3 times greater than HSUPA Release 6
► Increased cell edge bit rates
► Downlink: 70% of the values at 5% of the Cumulative Distribution Function (CDF)
► Uplink: same values at 5% of the Cumulative Distribution Function (CDF)
► Significantly reduced latency
► High mobility
► Cell ranges up to 5 km; with best throughput, spectrum efficiency and
mobility. Cell ranges up to 30 km ; Mobility with some degradation in
throughput and spectrum efficiency permitted. Cell ranges up to 100 km;
Supported; degradations accepted
13. LTE KEY PARAMETERS
Frequency Range UMTS FDD bands and UMTS TDD bands
Channel bandwidth 1 1.4 MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz
Resource Block = 180
kHz
6 Resource 15 Resource 25 Resource 50 Resource 75 Resource 100 Resource
Blocks Blocks Blocks Blocks Blocks Blocks
Modulation Scheme Downlink : QPSK, 16QAM, 64QAM
Uplink : QPSK, 16QAM, 64QAM
Multiple Access Downlink : OFDMA
Uplink : SC-FDMA
MIMO Technology Downlink : Wide Choice of MIMO configuration options of transmit diversity, spatial multiplexing, and cyclic delay
diversity (max 4 antennas at base stations and handset)
Uplink : Multi user collaborative at MIMO
Peak Data Rates Downlink : 150 Mbps (UE category 4, 2x2 MIMO, 20MHz)
Uplink : 75 Mbps (20MHz)
19. LTE RADIO INTERFACE
► Physical Layer
► OFDMA
► SC-FDMA
► MIMO
► Physical Channel
► Layer 2
► Transport Channel
► Layer 2 Structure
► Logical Channel
► RRC Protocol
► Convolutional Code
► Convolutional Decoder
► Interleaver and Deinterleaver
► Signal Mapping
20. PHYSICAL LAYER
► Enables exchange of data and control info between eNodeB and UE and transport of data to and from
higher layer
► Consist of Physical Signal for
► system synchronization,
► cell identification,
► channel estimation
► Physical Channel, for
► Transporting control
► Scheduling
► User payload from higher layer
► OFDMA in Downlink, SC-FDMA in Uplink
► Function performed : Error detection, FEC, MIMO, antenna processing, synchronization
► LTE Support FDD and TDD modes operation
21. DOWNLINK TRANSMISSION SCHEME OFDMA
► For transmission scheme in FDD and TDD mode E-UTRA : OFDMA
► Available spectrum is devided into multiple carriers, called sub-carriers, which are orthogonal to each other
and each sub-carriers independently modulated by a low rate data stream.
22. UPLINK TRANSMISSION SCHEME SC-FDMA
► SC-FDMA is the LTE uplink transmission scheme for TDD and FDD mode, with cyclic prefix
► Have a better PAPR (peak to average power ratio) properties compared to an OFDM signal for cost effective
design of UE powers amplifier
► Compare OFDMA vs SC-FDMA
OFDMA :
► Parallel transmission
► Multi carrier structure
► Increase M high PAPR
SC-FDMA
► Serial transmission
► Each symbol represented by a wide
signal – DFT spreads
► Increase M not affected PAPR
23. LTE FRAME STRUCTURE
Applicable for FDD and Half Duplex FDD
Each Radio frame is Tf=307200 x Ts = 10 ms long and consist of 20 slots of length Tslot = 15360 x Ts = 0.5 ms numbered from 0 to 19 (Ts = 1/(15000x2048) s
One radio frame, Tframe = 10 ms
One subframe, Tsubframe = 1 ms One slot, Tslot 15360 x Ts = 0.5 ms
UL f UL
FDD DL f DL
Subframe #0 #1 #2 #3 #4 #5 #6 #7 #8 #9
Applicable only For TDD
Each Radio frame consist of two half frame length Tf=153600 x Ts = 5 ms long each half frame consist of 8 slot of length Tslot = 15360Ts = 0.5 ms
Three special field DwPTS, GP, UpPTS in subframe #1 and #6 (special subframe)
The subframe 0 and 5 and DwPTS are always reserved for downlink transmission
The lengths of DwPTS and UpPTS is given below subject to the total length of DwPTS, GP and UpPTS being equal to 30720 Ts = 1ms
Supported configurations of uplink-downlink subframe allocation are specified
Special subframe =30720 Ts = 1ms Special subframe
UL
TDD f UL/DL
DL
D wP TS GP UpPTS
24. UPLINK DOWNLINK CONFIGURATION
► To meet different
requirements on
uplink/downlink traffic
asymmetries, LTE
support seven different
uplink/downlink
configuration
27. LTE PHYSICAL CHANNEL
DL Channels Full Name Purpose
PBCH Physical Broadcast Channel Carries cell specific information
PDSCH Physical Downlink Shared Channel Payload
PMCH Physical Multicast Channel Carries the MCH transport channel
PCFICH Physical Control Format Indicator Channel Defines number of PDCCH OFDMA symbols per
sub-frame (1,2 or 3)
PDCCH Physical Downlink Control Channel Scheduling ACK/NACK
PHICH Physical Hybrid ARQ Indicator Channel Carries HARQ ACK/NACK
UL Channels Full Name Purpose
PRACH Physical random access channel Call setup
PUCCH Physical uplink control channel Scheduling ACK/NACK
PUSCH Physical uplink shared channel Payload
28. PBCH
►
The coded BCH transport block is mapped to four
subframes (subframe #0) within a 40 ms interval
40 ms timing is blindly detected , i.e. there is no explicit
signaling indicating 40 ms timing
Coded BCH mapped to 4 OFDM symbols within a
subframe
Each subframe is assumed to be self-decodable , i.e the
BCH can be decoded from a single reception, assuming
sufficiently good channel conditions.
29. PDSCH
► Detailed on TS36.213, Resource allocation of PDSCH
► No compact assignment on Downlink only
► Bitmap approach 1 (group wise bitmap)
► Bitmap approach 2 (bitmap within subset)
► Compact assignment for Downlink and Uplink
► Resource indication value (RIV) corresponding to a starting resource block and a length in terms of contiguously
allocated resource blocks
30. PMCH
► Only transmitted in sub-frames allocated for MBSFN transmissions
► Only TDM on sub-frame basis of data transmission
► Multiplexing of MBSFN and Non-MBSFN data
► No transmit diversity for MBSFN and the transmission shall use antenna port 4
► Not to transmitted in subframe 0 and 5 on a carrier supporting a mix of PDSCH and PMCH)
31. PCFICH
► PCFICH carries CCFI
► CCFI (Control format indication) : information about the number of OFDM symbols (1,2 or 3) used for transmission
of PDCCH in a subframe.
► The number of bit : 32 bits
► Cell-specific scrambling prior to modulation
► Modulation: QPSK
► Mapping to resource elements: four groups of fo ur contiguous REs not used for RS in the first OFDM symbol
► Spread over the whole system bandwidth
► Same mapping for 1, 2 and 4 antennas
32. PDCCH
► The physical downlink control channel carries scheduling assignments
► A physical control channel is transmitted on an aggregation of one or several control channel elements, where a
control channel element (CCE) corresponds to a set of resource elements
► 1PDCCH = 1, 2, 4, 8 CCEs
► 1 CCE = 9 REGs
► Multiple PDCCHs can be transmitted in a sub-frame
► The PDCCH supports multiple formats
► Maximum number of blind decoding for LTE_ACTIVE users is 44 in total
33. PDCCH cont’
Aggregation of CCE
Tree-based aggregation with 1, 2, 4, 8 CCE
► 1-CCE start on any CCE position (i=0,1,2,3,4,...)
► 2-CCE every second location (i=0,2,4,6,...)
► 4-CCE on every fourth (i=0, 4, 8, ...)
► 8-CCE on every eight position (i=0, 8, ...)
The number of available CCEs in a cell depends on
► Semi-static: bandwidth, #antenna ports, PHICH conf, ...
► Dynamic: PCFICH value
34. ► Common search space PDCCH cont’
► Common search space corresponds to CCEs 0-15 (four decoding candidates on level-4, CCEs 0-3, 4-7, 8-11, 12-
15 and two decoding candidates on level-8, CCEs 0-7, 8-15
► Monitored by all UEs in the cell
► Can be used for any PDCCH signalling (not restricted to ’common’ PDCCH, can be used to resolve ’blocking’)
• Format 1C
• Format 0/1A/3A
► May overlap with UE-specific search space
► Aggregation levels
• 4-CCE and 8-CCE
► Number of blind decodes spent on common search space = 12
► UE-specific search space
► 32 blind decoding attempts
► Aggregation levels 1, 2, 4, 8
► Decoding attempts per payload size (assuming 2 payload sizes per aggregation level)
• 6 decoding attempts of 1-CCE aggregation
• 6 decoding attempts of 2-CCE aggregation
• 2 decoding attempts of 4-CCE aggregation
• 2 decoding attempts of 8-CCE aggregation
• FFS if the above can be changed with RRC signalling (max 2 configurations in total)
► DCI formats, semi-static configuration of one of the alternatives
• 0/1A, 1 (”non-spatial-multiplexing”)
• 0/1A, 2 (”spatial multiplexing”)
• 0/1A, 1B(“rank-1 precoding”)
35. PHICH
PHICH carries the downlink hybrid-ARQ ACK/NACK
• PHICH group
– 1 PHICH group = 8 PHICHs (Normal CP)
– 1 PHICH group = 4 PHICHs (Extended CP)
• Repetition factor is 3
PHICH mapping
– Time and frequency location of PHICH
36. Orthogonal sequence
PHICH con’t
0 [+1 +1 +1 +1] [+1 +1]
1 [+1 -1 +1 -1] [+1 -1]
Orthogonal sequence of SF = 4 for normal CP and SF =2 for extended CP 2 [+1 +1 -1 -1] [+j +j]
case 3 [+1 -1 -1 +1] [+j -j]
Example of extended CP case (SF = 2) and TX=4 case
4 [+j +j +j +j] -
► d0 and d1 represent the SF=2 spread ACK/NAK symbol, red and green are
two different PHICH groups 5 [+j -j +j -j] -
6 [+j +j -j -j] -
7 [+j -j -j +j] -
37. LTE LOGICAL CHANNEL
Logical Channel are offered by the MAC layer
Control Channel for control Plane information
► Broadcast Control Channel (BCCH)
► Paging Control Channel (PCCH)
► Common Control Channel (CCCH)
► Multicast Control Channel (MCCH)
► Dedicated Control Channel (DCCH)
Traffic Channel for user plane information
► Dedicated Traffic Channel (DTCH)
► Multicast Traffic Channel (MTCH)
38. LAYER 2 - LTE TRANSPORT CHANNEL
Physical layer transport channel offers information transfer to medium access control (MAC) and carrying originating
from higher layers
UPLINK
► Uplink Shared Channel (UL-SCH) characterized by:
► possibility to use beamforming (likely no impact on specifications)
► support for dynamic link adaptation by varying the transmit power and potentially modulation and coding
► support for HARQ
► support for both dynamic and semi-static resource allocation.
► Random Access Channel(s) (RACH) characterized by:
► limited control information
► collision risk
DOWNLINK
► Broadcast Channel (BCH) characterized by:
► fixed, pre-defined transport format
► requirement to be broadcast in the entire coverage area of the cell.
► Multicast Channel (MCH) (from Release 9) characterized by:
► requirement to be broadcast in the entire coverage area of the cell
► support for MBSFN combining of MBMS transmission on multiple cells
► support for semi-static resource allocation e.g., with a time frame of a long cyclic prefix.
39. LAYER 2 - LTE TRANSPORT CHANNEL CONT’
► Downlink Shared Channel (DL-SCH) characterized by:
► support for HARQ
► support for dynamic link adaptation by varying the modulation, coding and
transmit power
► possibility to be broadcast in the entire cell
► possibility to use beamforming
► support for both dynamic and semi-static resource allocation
► support for UE discontinuous reception (DRX) to enable UE power saving.
► Paging Channel (PCH) characterized by:
► support for UE discontinuous reception (DRX) to enable UE power saving (DRX
cycle is indicated by the network to the UE)
► requirement to be broadcast in the entire coverage area of the cell
► mapped to physical resources which can be used dynamically also for
traffic/other control channels.
42. LTE PHYSICAL SIGNAL
DL Signal Full Name Purpose
P-SCH Primary Synchronization Signal Used for cell search and identification by the UE.
Carries part of the cell ID (one of three
orthogonal sequences)
S-SCH Secondary Synchronization Signal Used for cell search and identification by the UE.
Carries the remainder of the cell ID (one of 168
binary sequences)
RS Reference signal (pilot) Used for DL channel estimation.
Exact sequence derived from cell ID (one of 3 x
168 = 504 pseudo random sequence)
UL Channels Full Name Purpose
RS Reference signal (Demodulation and Sounding) Used for synchronization to the UE and UL
channel estimation
43. P-SCH & S-SCH
► Synchronization signals needed during cell search
► The synchronization acquisition and the cell group identifier are obtained from different SCH signals
► Transmitted on the 72 center sub-carriers (around DC sub-carrier) within the same predefined slots (twice per 10
ms) on different resource element.
REFERENCE SIGNAL (RS)
► Three types of downlink reference signals are defined:
► Cell-specific reference signals, associated with non-MBSFN transmission (unicast RS)
► MBSFN reference signals, associated with MBSFN transmission
► UE-specific reference signals (Dedicated RS)
► There is one reference signal transmitted per downlink antenna port.
► REs used for RS transmission on any of the antenna ports in a slot shall not be used
44. SYNCHRONIZATION SIGNAL
FDD
TDD
► DwPTS and Location of PSS and SSS
► P-SCH is always transmitted in the 3rd OFDM
symbols of DwPTS (subframe 1 and 6)
► PDDCH in DwPTS (subrfame 1 and 6) may span 1
and 2 OFDM symbols
► PSS ► Data is transmitted after the control region as in
Using not coherent detection estimate 5 ms timing and physical layer identity other DL subframes
Channel estimation information for SSS ► Same cell specific RS patterns as in other DL
► SSS subframe, RS in GP are muted
Physical layer identity (Cell ID) obtained ► UpPTS
Mapped to one of 168 cell ID groups (168 cell groups for 504 cell IDs) ► SRS transmission on UpPTS
Radio frame timing (10ms) identification ► Agreement on 1 SRS symbol in UpPTS
Max # of hypotheses; 336 hypotheses (2x168 : 2 for half frame, 168 for ID group ► Discuss further whether 2 SRS symbols in UpPTS
Can be detect RS structure information from SSS and PSS
46. LTE INITIAL ACCESS
System
Cell Search and
Power On Information Random Access User Data Tx/Rx
Selection
Receive
Initial access procedure
Three step initial access on LTE
► Cell Search (PSC, RRC, RS)
► System Information Receive (PBCH, PCFICH, PDCCH)
► Random Access
48. DOWNLINK PHYSICAL CHANNEL PROCESS
Scrambling
Modulation Mapping Mapping onto one or more
transmission layer
Generation of signals each
Layer Mapping antenna port
MIMO Related Processing
Precoding
Resource Element Mapping
OFDM signal IDFT operation
generator
49. LTE MIMO CONCEPT –
► MIMO is one of spatial diversity technique to transmit different streams of data simultaneously on the
same downlink resource blocks and increase data rate and capacity
► Increase data rate data stream belong to one single user
► Increase capacity different user
51. E-NODEB
► According to overview of 3GPP Release 8, the eNB hosts the following functions:
► Radio Resource Management
► Radio Admission Control
► Radio Bearer Control
► Dynamic allocation of resources to UEs in both uplink and downlink (scheduling)
► Connection Mobility Control
► IP header compression and encryption of user data stream
► Scheduling and transmission of paging messages (originated from the MME)
► Selection of an MME at UE attachment when no routing to an MME can be
determined from the information provided by the UE
► Routing of User Plane data towards Serving Gateway
► Scheduling and transmission of broadcast information (originated from the MME or
O&M)
► Measurement and measurement reporting configuration for mobility and scheduling