Course Objectives:
·Understand the
development of mobile communications, and Long Term Evolution (LTE) position
and network architecture.
·Understand the protocol
architecture and basic technologies of E-UTRAN.
·Understand
key LTE technologies.
1 Overview
& Knowledge points
1.1 Background
1.1.1 Mobile Communications Evolution
The development history from 2G and 3G to
3.9 G is the development history from low-speed voice services to high-speed
multimedia services of mobile communications.
3GPP has been progressively perfecting LTE
R8 standard:
1. LTE R8 RAN1 was frozen in December 2008.
2. LTE R8
RAN2, RAN3, and RAN4 were frozen in December 2008..
3. LTE R8
standard was complete by March 2009, implementing basic LTE functions at the
first commercial use of LTE systems.
Figure 1.1‑1 shows
the development and evolution of wireless communication technologies.
1.1.2 Comparison
Among WCDMA, TD-SCDMA, and CDMA2000
Table 1.1‑1 Comparison among WCDMA,
TD-SCDMA, and CDMA2000
Standard
|
WCDMA
|
CDMA2000
|
TD-SCDMA
|
Inheritance
basis
|
GSM
|
Narrowband
CDMA
|
GSM
|
Synchronous
mode
|
Asynchronous
|
Synchronous
|
Synchronous
|
Chip
rate
|
3.84
Mcps
|
1.2288
Mcps
|
1.28
Mcps
|
System
bandwidth
|
5 MHz
|
1.25
MHz
|
1.6
MHz
|
Core
network
|
GSM
MAP
|
ANSI-41
|
GSM
MAP
|
Voice
coding mode
|
AMR
|
QCELP,
EVRC, and VMR-WB
|
AMR
|
1.1.3 WCDMA
Evolution
Figure 1.1‑2 shows
the WCDMA technology roadmap.
1.1.4 TD-SCDMA Evolution
ZTE wireless network equipment supports
smooth evolution of recent TD evolution software.
TD evolution can be divided into two
stages: standard stage of CDMA technologies and that of OFDMA technologies.
The standard stage of CDMA technologies can
smoothly evolve to HSPA+ with spectrum efficiency close to that of LTE.
1.1.5 CDMA200 Evolution
CDMA One is a collection of all
IS-95-based CDMA products. More specifically, IS-95 is used as a standard for key
technologies of all CDMA One-based products.
When CDMA2000 1x employs 1.25 MHz bandwidth, the highest
rate of single-carriers reaches 307.2 kbit/s, the peak rate of 1xEV-DO Rev.0 reaches
2.4 Mbit/s in the downlink, and the peak rate of Rev.A reaches 3.1 Mbit/s in the
downlink.
1.2 LTE Overview and Standards Development
3GPP working groups started LTE
standardization in December 2004. LTE focuses on the enhancement of UTRAN and
UTRA.
The establishment of 3GPP standards can be
divided into four stages including requirements proposal, architecture
establishment, detailed specifications, and testing and verification.
3GPP works in workgroup mode and RAN1/2/3/4/5
workgroups are directly related to LTE.
2 LTE Indexes
and Requirements
2.1 Overview
& Knowledge points
Spectrum division
LTE system requirements
Others
Physical channels and mapping
relationship
Figure 2.1‑1 shows
the LTE indexes and requirements prescribed by 3GPP.
2.2 Frequency Band Division
E‑UTRA Operating Band
|
Uplink (UL) operating band BS receive UE
transmit
|
Downlink (DL) operating band BS transmit UE
receive
|
Duplex Mode
|
|||||||||
FUL_low – FUL_high
|
FDL_low – FDL_high
|
|||||||||||
1
|
1920 MHz
|
–
|
1980 MHz
|
2110 MHz
|
–
|
2170 MHz
|
FDD
|
|||||
2
|
1850 MHz
|
–
|
1910 MHz
|
1930 MHz
|
–
|
1990 MHz
|
FDD
|
|||||
3
|
1710 MHz
|
–
|
1785 MHz
|
1805 MHz
|
–
|
1880 MHz
|
FDD
|
|||||
4
|
1710 MHz
|
–
|
1755 MHz
|
2110 MHz
|
–
|
2155 MHz
|
FDD
|
|||||
5
|
824 MHz
|
–
|
849 MHz
|
869 MHz
|
–
|
894MHz
|
FDD
|
|||||
6
|
830 MHz
|
–
|
840 MHz
|
875 MHz
|
–
|
885 MHz
|
FDD
|
|||||
7
|
2500 MHz
|
–
|
2570 MHz
|
2620 MHz
|
–
|
2690 MHz
|
FDD
|
|||||
8
|
880 MHz
|
–
|
915 MHz
|
925 MHz
|
–
|
960 MHz
|
FDD
|
|||||
9
|
1749.9 MHz
|
–
|
1784.9 MHz
|
1844.9 MHz
|
–
|
1879.9 MHz
|
FDD
|
|||||
10
|
1710 MHz
|
–
|
1770 MHz
|
2110 MHz
|
–
|
2170 MHz
|
FDD
|
|||||
11
|
1427.9 MHz
|
–
|
1452.9 MHz
|
1475.9 MHz
|
–
|
1500.9 MHz
|
FDD
|
|||||
12
|
698 MHz
|
–
|
716 MHz
|
728 MHz
|
–
|
746 MHz
|
FDD
|
|||||
13
|
777 MHz
|
–
|
787 MHz
|
746 MHz
|
–
|
756 MHz
|
FDD
|
|||||
14
|
788 MHz
|
–
|
798 MHz
|
758 MHz
|
–
|
768 MHz
|
FDD
|
|||||
…
|
||||||||||||
17
|
704 MHz
|
–
|
716 MHz
|
734 MHz
|
–
|
746 MHz
|
FDD
|
|||||
...
|
||||||||||||
33
|
1900 MHz
|
–
|
1920 MHz
|
1900 MHz
|
–
|
1920 MHz
|
TDD
|
|||||
34
|
2010 MHz
|
–
|
2025 MHz
|
2010 MHz
|
–
|
2025 MHz
|
TDD
|
|||||
35
|
1850 MHz
|
–
|
1910 MHz
|
1850 MHz
|
–
|
1910 MHz
|
TDD
|
|||||
36
|
1930 MHz
|
–
|
1990 MHz
|
1930 MHz
|
–
|
1990 MHz
|
TDD
|
|||||
37
|
1910 MHz
|
–
|
1930 MHz
|
1910 MHz
|
–
|
1930 MHz
|
TDD
|
|||||
38
|
2570 MHz
|
–
|
2620 MHz
|
2570 MHz
|
–
|
2620 MHz
|
TDD
|
|||||
39
|
1880 MHz
|
–
|
1920 MHz
|
1880 MHz
|
–
|
1920 MHz
|
TDD
|
|||||
40
|
2300 MHz
|
–
|
2400 MHz
|
2300 MHz
|
–
|
2400 MHz
|
TDD
|
|||||
2.3 Peak Data
Rate
The instantaneous downlink peak rate
reaches 100 Mbit/s (5 bit/s/Hz) at 20 MHz downlink spectrum band (two transmit
antennas on the network side and two receive antennas on the UE side).
The instantaneous uplink peak rate reaches 50
Mbit/s (2.5 bit/s/Hz) at 20 MHz uplink spectrum band (one receive antenna on
the UE side).
2.4 Control Plane Delay
Additionally, if the
control plane operates at 5 MHz spectrum band, each cell is expected to support
200 activated users. In the case of higher spectrum bands, each cell is
expected to support 400 activated users.
2.5 User Plane
Delay
User plane delay is the unidirectional
transmission time that a packet is transmitted from the IP layer of a UE/RAN
edge node to the IP layer of a RAN edge node/UE. The RAN edge node indicates
the interface nodes of the RAN and core network.
In the case of "zero loads"
(a single user and a single data flow) and "small IP packets" (only
one IP header and no effective load), the user plane delay is expected to be no
longer than 5 ms.
2.6 User Throughput
Downlink:
1. The
user throughput per MHz at the 5% Cumulative Distribution Function (CDF) must
reach two to three times the throughput of R6 HSDPA.
2. The
average user throughput per MHz must reach three to four times the throughput of
R6 HSDPA.
R6 HSDPA uses one transmitter one receiver (1T1R) while
LTE uses two transmitter/two receiver (2T2R).
Uplink:
1. The
user throughput per MHz at the 5% CDF must reach two to three times the
throughput of R6 HSUPA.
2. The
user throughput per MHz must reach two to three times the throughput of R6
HSUPA.
2.7 Spectrum Efficiency
Downlink: On a network with effective load,
the target LTE spectrum efficiency (measured by the bit quantity per site, per Hz,
and per second) is three to four times more efficient than R6 HSUPA. R6 HSDPA
uses 1T1R while LTE uses 2T2R.
Uplink: On a network with
effective load, the target LTE spectrum efficiency (measured by the bit
quantity per site, per Hz, and per second) is two to three times more efficient
than R6 HSUPA. R6 HSUPA uses 1T2R, and so does LTE.
2.8 Mobility
E-UTRAN can provide optimum
network performance for mobile users at the speed of 0–15 km/h, high performance services at the
speed of 15–120
km/h, and cell network services at the speed of 120–350 km/h (the speed even reaches 500 km/h at
specified bands).
Voice services and other realtime services provided
in the R6 CS domain are supported by PS domain on the E-UTRAN and all these
services can reach or exceed the quality of UTRAN services. The interrupt time
caused by handovers within the E-UTRA system must be shorter than or equal to
the handover time of the GERAN CS domain.
In a special case where the
moving speed exceeds 250 km/h (in a high-speed train), the physical layer
parameters of E-UTRAN must be set to be capable of protecting the connections between
users and networks at the highest speed of 350 km/h (the speed even reaches 500
km/h at specified bands).
2.9 Coverage
The E-UTRA system must flexibly support all
coverage scenarios on the basis of reusing the current UTRAN sites and
frequencies to meet the preceding performance indexes such as the user
throughput, spectrum efficiency, and mobility.
The performance requirements of the E-UTRA
system within different coverage scope are listed as follows:
1. Coverage
radius within 5 km: The preceding performance indexes such as the user
throughput, spectrum efficiency, and mobility must be fully satisfied.
2. Coverage
radius within 30 km: The throughput and spectrum efficiency are allowed to
slightly drop but within an acceptable range, and the mobility index must be
fully satisfied.
2.10 Spectrum Flexibility
On the one hand, the spectrum flexibility allows
deployment of E-UTRA at varied bands including 1.4 MHz, 3 MHz, 5 MHz, 10 MHz,
15 MHz, and 20 MHz. The E-UTRA supports paired and unpaired spectrums.
2.11 Coexistence and Interoperability with Existing 3GPP Systems
Interoperability
requirements of the E-UTRA and 3GPP systems include but
not limited to:
1. E-UTRAN
and UTRAN/GERAN multi-mode terminals support UTRAN/GERAN measurement and handover
between E-UTRAN systems and UTRAN/GERAN systems.
2. The
E-UTRAN system supports inter-system measurement.
3. The handover
interrupt time between R-UTRAN and UTRAN must be shorter than 300 ms for
realtime services.
4. The handover
interrupt time between E-UTRAN and UTRAN must be shorter than 500 ms for
non-realtime services.
5. The handover
interrupt time between E-UTRAN and GERAN must be shorter than 300 ms for
realtime services.
6. The handover
interrupt time between E-UTRAN and GERAN must be shorter than 500 ms for
non-realtime services.
7. Paging information of only one of the GERAN, UTRA, or E-UTRA
systems needs to be monitored for multi-mode terminals in non-active state
(similar to R6 Idle mode or Cell_PCH state).
2.12 Reducing CAPEX and OPEX
The flattening of the system architecture
and the decrease in intermediate nodes dramatically reduces the equipment costs
and maintenance costs.
3 LTE
Architecture
& Knowledge points
Radio protocol structure
S1 interface
X2 interface
3.1 System
Architecture
LTE adopts an OFDM-based air interface
technology which is different from those of 2G and 3G. LTE adopts a flat
network architecture within which E-UTRAN contains only eNodeBs instead of RNC,
so as to optimize the traditional 3G network architecture. LTE supports functions
of PDCP/RLC/MAC/physical layer protocols on the E-UTRA user plane and functions
of the RRC protocol on the control plane. Figure 3.1‑1 shows
the E-UTRAN system architecture.
eNodeBs are connected over an x2 interface
and every eNodeB is connected to the Evolved Packet Core (EPC) network over an S1
interface. The user plane of S1 interfaces terminates on the Serving-Gateway
(S-GW) and the control plane of S1 interfaces terminates on the Mobile
Management Entity (MME). The other end of the control plane and user plane terminates
on the eNodeB. Functions of all NEs in the preceding figure are listed as
follows:
· eNodeB
Besides
the original eNodeB functions, eNodeB of LTE undertakes most of original RNC
functions such as physical layer, MAC (including HARQ), RLC layer (including
ARQ functions), PDCP, RRC, scheduling, radio access control, access mobility
management, and radio resource management among different cells.
LTE eNodeBs
have the following functions:
Manage
radio resources: Radio bearer control, radio access control, connection
mobility control, and dynamic resource assignment of uplink and downlink (scheduling).
Compress
IP headers and encrypt user data streams.
Choose
the UE-attached MME when the MME routing information cannot be known from the
information provided for the UE.
Transmit
routing data of user planes to the S-GW.
Schedule
and transmit the paging information initiated by the MME.
Schedule
and transmit the broadcast information initiated by the MME or O&M.
Schedule
and transmit the Earthquake and Tsunami Warning System (ETWS) information initiated
by the MME.
· MME
As the
control core of the SAE, MME implements such functions as user access control,
service bearer control, paging, and handover control.
The
function of the MME is separated from that of the gateway. The control
plane/user plane separated structure facilitates network deployment, single
technology evolution, and flexible capacity expansion.
NAS
signaling
NAS
signaling security
AS
security control
Mobile
signaling among 3GPP radio networks
The
reachability of an UE in the idle state (including the control and
implementation of paging signal re-transmission)
P-GW
or S-GW selection
MME selection
at the time of handover
SGSN
selection at handover to 2G or 3GPP network
Roaming
Authentication
Bearer
management, including dedicated bearer establishment
ETWS
signal transmission
· S-GW
Local
mobile anchor points at eNodeB handover
Mobile
anchor points among 3GPP systems.
Downlink
packet buffering and initialization of network-triggered service request
procedure in the E-UTRAN idle mode
Lawful
interception
Packet
routing and forwarding
Transport-layer
packet marking (uplink/downlink)
Accounting
on user and QCI granularity for inter-operator charging.
Uplink/downlink
charging per UE, PDN, or QCI
· PDN gateway (P-GW)
Per-user
packet filtering (for example, utilize deep packet inspection)
Lawful
interception
IP
address assignment of the UE
Transport-layer
packet marking (downlink)
Aggregate
Maximum Bit Rate (AMBR)-based downlink rate control
As shown in the preceding figure, the
original lu interface, lub interface, and lur interface are replaced with the
S1 interface and X2 interface in the new LTE architecture.
Figure 3.1‑2 shows
the functional split between E-UTRAN and EPC. Yellow boxes depict the logical
nodes, white boxes the functional entities of the control plane, and blue boxes
the radio protocol layers.
3.2 Radio
Protocol Architecture
3.2.1 Control Plane Protocol Architecture
Figure 3.2‑1 shows
the control plane protocol architecture.
The PDCP terminates at eNodeB and implements
functions such as control plane encryption and integrity protection.
The RLC and MAC terminate at eNodeB on the
network side and implement identical functions of the user plane and control
plane.
The RRC terminates at eNodeB and implements
such functions as broadcast, paging, RRC connection management, RB control,
mobility, and UE measurement reporting and control.
The NAS terminates at MME
and implements such functions as EPS bearer management, authentication, idle-mode
EPS Connection Management (ECM), idle-mode ECM paging, and security control.
3.2.2 User Plane Protocol Architecture
Figure 3.2‑2 shows
the user plane protocol architecture.
The user plane PDCP, RLC,
and MAC terminate at eNodeB and implements such functions as header
compression, encryption, scheduling, ARQ, and HARQ.
3.3 S1 Interface and X2 Interface
Different from those in 2G
and 3G systems, S1 interface and X2 interface are newly added in the LTE system.
3.3.1 S1 Interface
The S1 interface is defined as the
interface between the E-UTRAN and EPC. The S1 interface contains two parts: the
control plane S1-MME interface and user plane S1-U interface. The S1-MME
interface is defined as the interface between the eNodeB and MME; the S1-UE
interface is defined as the interface between the eNodeB and S-GW. Figure 3.3‑1 and Figure 3.3‑2 respectively
show the protocol stack architecture of the S1-MME interface and S1-U
interface.
The S1 interface has the following
acknowledged functions:
· E-RAB service management
Establishment,
modification, and release
· UE mobility in the
ECM-CONNECTED state
Handover
within the LTE system
Handover
between the LTE system and the 3GPP system
· S1 paging
· NAS signaling transmission
· S1 interface management
Reset
· Network sharing
· Roaming and area restriction
· NAS node selection
· Initial context establishment
· UE context modification
· MME load balance
· Location report
· ETWS message transmission
· Overload
· RAN information management
· The S1 interface has the
following acknowledged signaling procedures:
· E-RAB signaling procedure
E-RAB establishment
E-RAB
modification
MME-initiated
E-RAB release
eNodeB-initiated
E-RAB release
· Handover signaling procedure
Handover
preparation
Resource
assignment
Handover termination
Handover cancellation
· Paging
· NAS transmission procedure
Direct uplink transmission (initial UE
message)
Direct uplink transmission (uplink NAS
transmission)
Direct downlink transmission (downlink
NAS transmission)
· Error indication procedure
eNodeB-initiated
error indication
MME-initiated
error indication
· Reset
eNodeB-initiated
reset
MME-initiated
reset
· Initial context establishment
· UE context modification
· S1
establishment
· eNodeB configuration update
· MME configuration update
· Location report
Location
report control
Location
report
Location
report failure indication
· Overload startup
· Overload stop
· Directly transmitted
information transfer
Figure 3.3‑3 shows
the S1 interface signaling procedure.
The similarities between S1
interface and X2 interface lie in the fact that S1-U and X2-U adopt the same
user plane protocol to reduce protocol processing at eNodeB data forward.
3.3.2 X2 Interface
The X2 interface is defined as the
interface between eNodeBs. The X2 interface contains two parts: the X2-CP and
X2-U, where the X2-CP is the control plane interface between eNodeBs and the
X2-U is the user plane interface between eNodeBs. Figure 3.3‑4 and Figure 3.3‑5 respectively
show the protocol stack architecture of the X2-CP interface and X2-U interface.
The X2-CP has the following functions:
· UE mobility in the
ECM-CONNECTED state within the LTE system
Context
transfer from the source eNodeB to the target eNodeB
User
plane channel control between the source eNodeB and the target eNodeB
Handover
cancellation
· Uplink load management
· General X2 interface
management and error processing
Error
indication
The X2-CP interface has the following
acknowledged signaling procedures:
· Handover preparation
· Handover cancellation
· UE context release
· Error indication
· Load management
The management of load among cells is
implemented over the X2 interface.
Figure 3.3‑6 shows
that the LOAD INDICATOR message is used for load state communication among eNodeBs.
4 Physical
Layer
4.1 Frame Structure
The LTE system supports the following two
radio frame structures:
· Structure 1: Applicable to
the FDD mode.
· Structure 2: Applicable to
the TDD mode.
Figure 4.1‑1 shows
the frame structure 1. Every 10 ms radio frame is divided into ten sub-frames of
fixed length. Each sub-frame contains two time slots each of which is 0.5 ms
long.
For FDD, at every 10 ms,
ten sub-frames can be used for downlink transmission and another ten sub-frames
can be used for uplink transmission. The uplink transmission and downlink
transmission are separated on the frequency domain.
4.2 Physical Resources
The minimum resource unit for
uplink/downlink transmission in the LTE system is called the Resource Element
(RE).
At the time of data transmission, the LTE
system consolidates uplink and downlink time-frequency domain physical
resources into Resource Blocks (RBs) for scheduling and allocation.
Several REs constitute an RB. There are 12 consecutive
sub-carriers on the frequency domain and seven consecutive OFDM symbols (six
marks with the Extended CP). That is, the frequency domain width is 180 kHz and
the time length is 0.5 ms.
Figure 4.2‑1 and Figure 4.2‑2 respectively
show the physical resource structures of downlink and uplink slots.
4.3 Physical Channels
The downlink physical channels contain the
following channels:
1. Physical
Broadcast Channel (PBCH)
The
coded BCH transmission block maps to four sub-frames within an 40 ms interval.
With
excellent-enough channels, every sub-frame that the PBCH located can separately
decode signals.
2. Physical
Control Format Indicator Channel (PCFICH)
Notify
the number of PDCCH-occupied OFDM mark to the UE.
Transmit
the information in every sub-frame.
3. Physical
Downlink Control Channel (PDCCH)
Notify
the resource assignment information of the PCH and DL-SCH and DL-SCH-related
HARQ information to the UE.
Carry
the uplink scheduling information.
Carry
the HARQ ACK/NACKs for uplink data transfer.
5. Physical
Downlink Sharing Channel (PDSCH)
Carry
the DL-SCH and PCH information.
6. Physical
Multicast Channel (PMCH)
Carry
the MCH information.
The uplink physical channels contain the
following channels:
1. Physical
Uplink Control Channel (PUCCH)
Carry
HARQ ACK/NACKs for downlink data transfer.
Carry
the scheduling request information.
Carry
the CQI report information.
2. Physical
Uplink Sharing Channel (PUSCH)
Carry
the UL-SCH information.
3. Physical
Random Access Channel (PRACH)
4.4 Transport Channels
The downlink transport channels contain the
following channels:
1. Broadcast
Channel (BCH)
Fixed
predefined transport format
Broadcast
in the entire coverage area of the cell
2. Downlink
Sharing Channel (DL-SCH)
Support
HARQ.
Implement
dynamic link adaptation by varying the demodulation, coding mode, and transmit
power.
Support
broadcast in the entire cell.
Support
beamforming.
Support
dynamic or semi-static resource allocation.
Support
the UE Discontinuous Reception (DRX) to enable UE power saving.
Support
the MBMS transmission.
3. Paging
Channel (PCH)
Support
the UE DRX to save power. (The network notifies the DRX period to the UE.)
Broadcast
in the entire coverage area of the cell
Map
to physical resources which can be used dynamically also for traffic or other
control channels.
4. Multicast
Channel (MCH)
Broadcast
in the entire coverage area of the cell
Support
Multicast/Broadcast over Single Frequency Network (MBSFN) combing of MBMS
transmission on multiple cells.
Support
semi-static resource allocation.
The uplink transport channels contain the
following channels:
1. Uplink
Sharing Channel (UL-SCH)
Support
beamforming.
Implement
dynamic link adaptation by varying the transmit power, potential demodulation,
and coding mode.
Support
HARQ.
Support
dynamic or semi-static resource allocation.
2. Random
Access Channel (RACH)
Carry
limited control information.
Have
collision risks.
4.5 Mapping
Between Transport Channels and Physical Channels
Figure 4.5‑1 and Figure 4.5‑2 respectively
show the mapping relationships between downlink/uplink transport channels and downlink/uplink
physical channels.
4.6 Physical Signals
Physical signals correspond to several
physical layer REs, but do not carry any information that comes from higher layers.
The downlink physical signals include the
reference signal and the synchronization signal.
· Reference signal
The
downlink reference signals include the following three types of reference
signals:
Cell-specific
reference signals, associated with non-MBSFN transmission
MBSFN
reference signals, associated with MBSFN transmission
UE-specific
reference signals
· Synchronization signals
The
synchronization signals include the following two types of signals:
Primary
synchronization signal
Secondary
synchronization signal
For
FDD, the primary synchronization signal maps to the last OFDM symbol of the
time slot 0 and time slot 10. The secondary synchronization signal maps to the
second last OFDM symbol of the time slot 0 and time slot 10.
The
uplink physical signals include the reference signals.
· Reference signals
The
uplink reference signals include the following two types of signals:
Demodulation
reference signals, associated with PUSCH or PUCCH transmission
Sounding
reference signals, not associated with PUSCH or PUCCH transmission
The demodulation reference signals and the sounding reference
signals use the same base sequence set.
4.7 Physical Layer Model
The following figures show the physical
layer models of various types of channels. Node Bs in all of the following
figures are called eNodeBs or eNodeB in LTE.
4.8 Physical
Layer Procedures
4.8.1 Synchronization Procedures
· Cell search
· Timing synchronization
Timing synchronization procedures include radio link
monitoring, inter-cell synchronization, and transmission timing adjustments.
4.8.2 Power Control
Power control determines the energy per
resource element (EPRE). EPRE denotes the energy prior to CP insertion. EPRE
also denotes the average energy taken over all constellation points for the
modulation scheme applied. Uplink power control determines the average power of
one DFT-SOFDM symbol on a physical channel.
· Uplink power control
Uplink
power control procedure controls the transmit power of different uplink
physical channels.
· Downlink power allocation
4.8.3 Random Access Procedures
Prior to initiation of the non-synchronized
physical random access procedure, physical layer shall receive the following
information from the higher layers:
1. Random
access channel parameters (PRACH configuration, frequency position, and
preamble format).
2. Parameters
for determining the root sequences and their cyclic shifts in the preamble
sequence set for the cell (index to root sequence table, cyclic shift (Ncs),
and set type (normal or high-speed set)).
From the physical layer perspective, the
physical random access procedure encompasses the transmission of random access
preamble and random access response. The remaining messages are scheduled for
transmission by the higher layer on the shared data channel and are not
considered part of the L1 random access procedure.
The following steps are required for the
physical random access procedure:
1. Physical
layer procedure is triggered upon request of a preamble transmission by higher
layers.
2. A
preamble index, preamble transmission power (PREAMBLE_TRANSMISSION_POWER),
associated RA-RNTI, and PRACH resource are indicated by higher layers as part
of the request.
3. Determine
preamble transmit power: PPRACH = min{Pmax, PREAMBLE_RECEIVED_TARGET_POWER
+ PL}; where, Pmax indicates the maximum allowed power configured at
higher layers, and PL indicates UE-calculated downlink path loss.
4. A
preamble sequence is then selected from the preamble sequence set using the
preamble index.
5. A
single preamble transmission then occurs using the selected preamble sequence
with transmission power PREAMBLE_TRANSMISSION_POWER on the indicated PRACH
resource.
6. The associated PDCCH with RA-RNTI is detected in the random
access response window controlled by higher layers. If an associated PDCCH with
RA-RNTI is detected then the corresponding PDSCH transport block is passed to
the higher layers. Higher layers resolve the transport block and indicate the
20-bit UL-SCH grant to the physical layer.
5 Layer 2
Layer 2 consists of three sublayers PDCP,
RLC, and MAC.
Figure 28 and Figure 29 respectively show Layer 2 downlink and uplink
structures.
The connection points among sublayers are
known as the Service Access Points (SAP). The service provided by PDCP is
referred to as the radio bearer. The PDCP provides the Robust Header Compression
(ROHC) and security protection. The SAP between physical layer and MAC layer
provides transport channels and that between MAC layer and RLC layer provides
logical channels.
The MAC layer provides multiplexing and
mapping of logical channels (radio bearer) to transport channels (transport
block).
Only one transport block is
generated at each TTI (1 ms) in the uplink or downlink in the case of non-MIMO.
5.1 MAC
Sublayer
5.1.1 MAC Functions
The MAC sublayer provides the following
functions:
· Mapping between logical
channels and transport channels.
· MAC Service Data Unit (SDU)
multiplexing/demultiplexing.
· Scheduling information
report.
· Error correction through
HARQ
· Logical channel
prioritization of the same UE.
· UE prioritization through
dynamic scheduling.
· Selection of transmission
formats.
5.1.2 Logical Channels
MAC provides different types of data
transmission services. The type of each logical channel is defined based on the
type of transmitted data.
Logical channels are categorized into:
· Control channels: used to
transfer data on the control plane.
· Traffic channels: used to
transfer data on the user plane.
Control channels include:
· Broadcast Control Channel
(BCCH).
The
BCCH is a downlink channel used to broadcast system control messages.
· Paging Control Channel
(PCCH).
The
PCCH is a downlink channel used to transfer paging messages and system
information change notifications. The PCCH is used to page a UE when the UE
cell location is unknown to the network.
· Common Control Channel
(CCCH).
The
CCCH is used to transfer control messages between UEs and network when there is
no RRC connection between them.
· Multicast Control Channel
(MCCH).
A
point-to-multipoint downlink channel used for transmitting MBMS control
information from the network to the UE, for one or several MTCHs. This channel
is only used to UEs that receive MBMS.
· Dedicated Control Channel
(DCCH).
A
point-to-point bi-directional channel that transmits dedicated control
information between a UE and the network. This channel is
used by UEs having an RRC connection.
Traffic channels include:
· Dedicated Traffic Channel
(DTCH).
The
DTCH is a point-to-point channel, dedicated to one UE, for the transfer of user
information.
· Multicast Traffic Channel
(MTCH).
A point-to-multipoint downlink channel for transmitting
traffic data from the network to the UE. This channel is only used to UEs that
receive MBMS.
5.1.3 Mapping Between Logical Channels and Transport Channels
Figure 5.1‑1 and Figure 5.1‑2
respectively show the mapping between downlink and uplink logical channels and
transport channels.
5.2 RLC
Sublayer
5.2.1 RLC Functions
The RLC sublayer provides the following
functions:
· Transfer of upper layer
PDUs.
· Error Correction through ARQ
(only for AM data transfer).
· Concatenation, segmentation
and reassembly of RLC SDUs (only for UM and AM data transfer).
· Re-segmentation of RLC data
PDUs (only for AM data transfer).
· In sequence delivery of
upper layer PDUs (only for UM and AM data transfer).
· Duplicate detection (only
for UM and AM data transfer).
· Protocol error detection and
recovery.
· RLC SDU discard (only for UM
and AM data transfer).
· RLC re-establishment.
5.2.2 PDU
Structure
Figure 5.2‑1 shows
the RLC PDU structure.
· The PDU sequence number
carried by the RLC header is independent of the SDU sequence number (that is,
the PDCP sequence number).
· The red dotted lines in
Figure 32 indicate segmentation positions.
5.3 PDCP
Sublayer
5.3.1 PDCP Functions
The main services and functions of the PDCP
sublayer for the user plane include:
· Header compression and decompression:
ROHC only.
· Transfer of user data.
· In-sequence delivery of
upper layer PDUs at PDCP re-establishment procedure for RLC AM.
· Duplicate detection of lower
layer SDUs at PDCP re-establishment procedure for RLC AM.
· Retransmission of PDCP SDUs
at handover for RLC AM.
· Ciphering and deciphering.
· Timer-based SDU discard in
uplink.
· The main services and
functions of the PDCP sublayer for the control plane include:
· Ciphering and Integrity
Protection.
· Transfer of control plane
data.
5.3.2 PDU Structure
Figure 5.3‑1 shows
the PDCP PDU structure.
· PDCP PDU and PDCP header are
octet-aligned.
· PDCP header can be either 1
or 2 bytes long.
6 RRC
6.1 RRC
Functions
Main Functions of RRC include:
· Broadcast of system
information related to the NASs
· Broadcast of system
information related to the ASs
· Paging
· Establishment, retention,
and release of RRC connection between UEs and E-UTRANs, including:
Allocation
of temporary identifiers between UEs and E-UTRANs
Configuration
of the Signaling Radio Bearers (SRBs) for RRC connection
Low
priority and high priority SRBs
· Security management
including key management
· Establishment,
configuration, retention, and release point-to-point RBs
· Mobility management,
including:
Measurement
report and reporting control of the mobile UEs between cells and between RATs.
Handover
UE
cell selection and reselection; cell selection and reselection control
Context
forwarding during handover
· MBMS notification
· Establishment,
configuration, retention, and release of RBs for the MBMS
· QoS management
· UE measurement report and
reporting control
· NAS direct transfer
6.2 RRC State
RRC state includes RRC_IDLE and
RRC_CONNECTED
· RRC idle state (RRC_IDLE)
PLMN
selection
DRX
configured by NAS
System
information broadcast
Paging
Cell
reselection mobility
A
unique identifier allocated to a UE within a Tracking Area (TA)
No
RRC contexts stored in eNodeBs
· Connection state
(RRC_CONNECTED)
The
UE has an E-UTRAN-RRC connection.
The
UE has a context in E-UTRAN.
The
E-UTRAN knows the cell which the UE belongs to.
The
network can transmit and receive data to/from the UEs.
Network
controlled mobility (handover).
Neighbor
cell measurements.
The
PDCP/RLC/MAC features of the RRC_CONNECTED
The
UE can transmit and receive data to/from the networks.
The
UE intercepts controlled signaling channels related to the shared data channels
to view that whether the UE is allocated any data on the shared data channel.
The
UE also reports channel quality information and feeds back information to
eNodeB.
The
DRX cycle can be conformed according to the UE mobility level to save UE power
and enhance resource efficiency. This function is controlled by eNodeB.
6.3 NAS State
and the Relationship With the RRC state
The NAS state model can be described by the
two-dimensional state model of the EPS Mobility Management state (EMM) and the
EPS Connection Management state.
· EMM state:
EMM-DEREGISTERED
state
EMM-REGISTERED
state
· ECM state:
ECM-IDLE
state
ECM-CONNECTED
state
Note: The EMM state and the ECM state are
mutually independent.
The relationship between the NAS state and
the RRC state is as follows:
· EMM-DEREGISTERED state +
ECM-IDLE state Þ RRC_IDLE state
Mobility
feature: PLMN selection
UE location:
Unknown to the network.
· EMM-REGISTERED state +
ECM-IDLE state Þ RRC_IDLE state
Mobility
feature: Cell selection
UE location:
Known to the network at TA level.
· EMM-REGISTERED state +
ECM-CONNECTED state + RB Established Þ
RRC_CONNECTED state
Mobility
feature: Handover
6.4 RRC Procedure
RRC procedure includes the
System Information, Connection Control, mobility procedure, measurements, and direct
transfer.
6.4.1 System Information
System information includes the Master
Information Block (MIB) and a series of System Information Blocks (SIBs).
· Master Information Block:
defines the most important physical information of the cells and is used to
receive a further system information.
· System Information Block
Type 1: assesses the related information of whether the UE is allowed to access
to a cell and defines the dispatch of other system information blocks.
· System Information Block
Type 2: includes common and shared channel information.
· System Information Block
Type 3: includes cell reselection information; mainly related to the service
cells.
· System Information Block
Type 4: includes cell reselection related service frequency points and
intra-frequency neighboring cell information.
· System Information Block
Type 5: includes cell reselection related other E-UTRA frequency points and
inter-frequency neighboring cell information.
· System Information Block
Type 6: includes cell reselection related UTRA frequency points and UTRA
neighboring cell information.
· System Information Block
Type 7: includes cell reselection related GERAN frequency points information.
· System Information Block
Type 8: includes cell reselection related CDMA2000 frequency points and
CDMA2000 neighboring cell information.
· System Information Block
Type 9: includes home eNodeB identifiers (HNBID).
· System Information Block
Type 10: includes ETWS primary notification.
· System Information Block Type
11: includes ETWS secondary notification.
· The MIB maps to the BCCH and
BCH. The SI maps to the BCCH and DL-SCH, and is identifies through the System Information RNTI (SI-RNTI). The MIB uses a
fixed dispatch cycle of 40 ms. The System Information Block Type 1 uses a fixed
dispatch cycle of 80 ms. The other SI dispatch cycle is not fixed and indicated
by the System Information Block Type 1.
6.4.2 Connection Control
RRC connection control includes:
· Paging
· RRC connection establishment
· Initial security activation
· RRC connection
reconfiguration
· Counter check
· RRC connection
re-establishment
· RRC connection release
· Radio resource configuration
SRB
addition/ modification
DRB
release
SRB
addition/ modification
MAC
main reconfiguration
Semi-persistent
scheduling reconfiguration
Physical
channel reconfiguration
· Radio link failure related
actions
7 Core LTE Technologies
7.1 Duplex Mode
In addition to FDD and TDD duplex modes,
the LTE system is expected to further support the half-duplex FDD.
7.2 Multi-access Mode
OFDMA is employed as the multiplexing
scheme in the LTE downlink systems.
DFT-S-OFDM (also called SC-FDMA) is employed
as the multiplexing scheme in the LTE uplink systems.
7.3 Multi-antenna Technologies
Downlink multi-antenna transmission:
Multi-antenna transmission supports two or
four antennas. The maximum number of code words is 2 and irrelevant of the
number of antennas, but there is a fixed mapping relationship between core
words and layers. Figure 35 shows the general relationship among code words,
layers, and antenna ports.
Multi-antenna technologies include the SDM
and transmit diversity. The SDM supports SU-MIMO and MU-MIMO. When a MIMO
channel is solely assigned to a single UE, this is called SU-MIMO. When MIMO
data streams are spatially assigned to different UEs, this is called MU-MIMO.
Uplink multi-antenna transmission:
The baseline antenna
configuration for uplink MIMO is either SIMO 1X2 antenna configuration or
MU-MIMO. To allow for MU-MIMO reception at the Node B, allocation of the same
time and frequency resource to several UEs, each of which transmitting on a
single antenna, is supported.
Closed loop type adaptive antenna selection
transmit diversity shall be supported for FDD (optional in UE).
7.4 Link Adaptation
Downlink adaptation:
Refer to the adaptive modulation and coding
(AMC) that is applied with three modulation schemes (QPSK, 16QAM, and 64QAM)
and variable code rates.
Uplink adaptation:
Include three link
adaptation techniques: 1) adaptive transmit bandwidth, 2) transmit power
control, and 3) adaptive modulation and channel code rate.
7.5 HARQ and ARQ
7.5.1 HARQ
The HARQ within the MAC sublayer has the
following characteristics:
· N-process Stop-And-Wait HARQ
is used.
· The HARQ transmits and
retransmits TBs.
In the downlink:
· Asynchronous adaptive HARQ
· PUSCH or PUCCH used for
ACK/NACKS for DL (re-)transmissions
· PDCCH used to signal the
HARQ process number and if re-transmission or transmission
· Adaptive re-transmissions
scheduled through PDCCH
In the uplink:
· Synchronous HARQ
· Maximum number of
re-transmissions configured per UE (instead of per radio bearer)
· PHICH used to transmit
ACK/NACKs for non-adaptive UL (re-)transmissions
· HARQ operation in uplink is
governed by the following principles:
Regardless
of the content of the HARQ feedback (ACK or NACK), when a PDCCH for the UE is
correctly received, the UE follows what the PDCCH asks the UE to do i.e.
perform a transmission or a retransmission (referred to as adaptive
retransmission).
When
no PDCCH addressed to the C-RNTI of the UE is detected, the HARQ feedback
dictates how the UE performs retransmissions.
NACK:
The UE performs a non-adaptive retransmission.
ACK:
The UE does not perform any UL (re)transmission and keeps the data in the HARQ
buffer.
· Measurement gaps are of a
higher priority than HARQ retransmissions: Whenever an H-ARQ retransmission
collides with a measurement gap, the H-ARQ retransmission does not take place.
7.5.2 ARQ
The ARQ within the RLC sublayer has the
following characteristics:
· The ARQ retransmits RLC SDUs
or RLC PDUs (segments).
ARQ
retransmissions are based on either RLC status reports or HARQ/ARQ
interactions.
· Status reports can be
triggered by upper layers.
7.5.3 HARQ/ARQ Interactions
Appendix A Abbreviations
Abbreviation
|
Full Name
|
3GPP
|
3rd Generation Partnership Project
|
BPSK
|
Binary Phase Shift Keying
|
CAPEX
|
Capital Expenditure
|
DFT
|
Discrete Fourier Transform
|
DRX
|
Discontinuous Reception
|
E-MBMS
|
Evolved Multimedia Broadcast and Multicast
Service
|
eNodeB
|
Evolution Node B
|
E
|
evolved
|
EPC
|
Evolved Packet Core
|
E-UTRA
|
Evolved Universal Terrestrial Radio Access
|
HCR
|
High Chip Rate
|
HeNB
|
Home eNodeB
|
IASA
|
Inter Access System
Anchor
|
IFFT
|
Inverse Discrete Fourier transform
|
LCR
|
Low Chip Rate
|
LDPC
|
low-density parity-check
|
LTE
|
Long Term Evolution
|
MIMO
|
Multiple Input Multiple Output
|
MME
|
Mobile Management Entity
|
OFDM
|
Orthogonal Frequency
Division Multiplex
|
OPEX
|
Operating Expenditure
|
PAPR
|
Peak to Average Power Ratio
|
QAM
|
QUADRATURE AMPLITUDE
MODULATION
|
QoS
|
Quality of Service
|
QPSK
|
QUADRATURE PHASE SHIFT
KEYING
|
RRC
|
Radio Resource Control
|
SAE
|
System Architecture Evolution
|
SC-FDMA
|
Single Carrier – Frequency Division Multiple Access
|
SDM
|
Spatial Division Multiple
|
S-GW
|
Serving Gateway
|
TTI
|
Transmission Time Interval
|
Appendix B References
SN
|
Name
|
1
|
25.912 Feasibility study for evolved Universal
Terrestrial Radio Access (UTRA) and Universal Terrestrial Radio Access
Network (UTRAN)
|
2
|
25.913 Requirements for Evolved UTRA (E-UTRA)
and Evolved UTRAN (E-UTRAN)
|
3
|
36.300 Evolved Universal Terrestrial Radio
Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network
(E-UTRAN), Overall description
|
4
|
25.814 Physical layer aspects for evolved Universal
Terrestrial Radio Access (UTRA)
|
5
|
36.211 Physical Channels and Modulation
|
6
|
36.212 Multiplexing and channel coding
|
7
|
36.213 Physical layer procedures
|
8
|
36.214 Physical layer – Measurements
|
9
|
36.302 Services provided by the physical layer
|
10
|
36.331 Radio Resource Control (RRC)
|
11
|
36.104 Base Station (BS) radio transmission and
reception
|
12
|
36.321 Medium Access Control (MAC) protocol
specification
|
13
|
23.401 General Packet Radio Service (GPRS)
enhancements for Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access
|
14
|
23.203 Policy and charging control architecture
|
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