� IRAT mobility: real time delay < 300ms, non-real time
delay < 500ms
This speed is real!!
LTE Goals
All-IP:
� better integration with other open standard such as GSM,
UMTS, CDMA, Wi-Fi
� scalable bandwith: 1.4, 3.5, 10, 15, 20 MHz
Lower Deployment Cost:
� no RNC
� uses existing tower structure
UE
eNodeB MME
P-GW
PCRF
HSS
Gx
S1-
MME
S1-
MMEUu
X2
Uu
S1-U
S1-U
S11
S5
S8
S6a
SGI
E-UTRAN EPCE-UTRA
Long Term Evolution (LTE) Architecture
PDN
eNodeB
S-GWP-GW
SGI
EPC consists of the following network elements:
The Mobility Management Entity (MME), which, as the name indicates, is
primarily responsible for managing the UE‟s mobility-related context. The
MME is also responsible for selection of the PDN Gateway, triggering and
enabling authentication, and saving the subscriber profile downloaded from
the HSS.
The Serving Gateway is responsible for anchoring the user plane for inter-
eNB handover and inter-3GPP mobility.
The PDN Gateway is responsible for IP-address allocation to the UE. The
PDN GW is also the policy enforcement point to enforce Quality of Service
(QoS)-specific rules on traffic packets.
The HSS is a user database that contains subscription-related information
and performs authentication and authorization of the user.
LTE uses Orthogonal
Frequency Division Multiple
Access (OFDMA) technology
for downlink transmission,
and Single Carrier Frequency
Division Multiple Access (SC-
FDMA) technology for uplink
transmission. LTE supports
both TDD (Time Division
Duplex) and FDD (Frequency
Division Duplex) modes of
operation.
The 3GPP standards call LTE‟s
radio access network the Evolved
Universal Terrestrial Radio Access
Network (E-UTRAN). In order to
reduce the latency experienced
by packets, LTE reduces the
UTRAN network to a single node
type called an evolved NodeB
(eNB). The eNB combines the
functions of the Radio Network
Controller (RNC) and the Node B,
reducing the number of nodes in
the network.
LTE: eNodeB
•Radio Bearer management – this includes Radio Bearer setup & release procedures and also involves RRM functionalities for initial
admission control and bearer allocation. This set of functions is controlled by the MME through the S1 interface during session setup, release
and modification phases.
•Radio interface transmission and reception – this includes radio channel modulation/demodulation as well as channel coding/decoding.
•Uplink and Downlink Dynamic RRM and data packet scheduling – this is probably the most critical function which requires the eNodeB to
cope with many different constraints (like radio-link quality, user priority and requested Quality of Service) so as to be able to multiplex
different data flows over the radio interface and make use of available resources in the most efficient way.
•Mobility management – this function relates to terminal mobility handling while the terminal is in an active state. This function implies radio
measurement configuration and processing as well as the handover algorithms for mobility decision and target cell determination. Radio
Mobility has to be distinguished from Mobility Management in Idle, which is a feature handled by the Packet Core.
•User data IP header compression and encryption – this item is the key to radio interface data transmission. It answers to the requirements
to maintain privacy over the radio interface and transmit IP packets in the most efficient way.
•Network signaling security – because of the sensitivity of signaling messages exchanged between the eNodeB itself and the terminal, or
between the MME and the terminal, all this set of information is protected against eavesdropping and alteration.
Rel 8, 9
Rel 10
UE Categories
REF 3GPP TS 36.306
•The existing UE categories 1-5 for
Release 8 and Release 9.
•In order to accommodate LTE-
Advanced capabilities, three new UE
categories 6-8 have been defined.
Mobility Management Entity (MME)
MME is the entity in the network responsible for authenticating and allocating resources to the UE when it first connects to the network. To
provide additional security to the UE, MME assigns each UE a temporary identity called the “Globally Unique Temporary Identity (GUTI)”,
which eliminates the need to send IMSI of the UE over radio channels. The GUTI may be periodically refreshed and changed to prevent
unauthorized tracking of the UE.
The MME tracks all UEs present in its service area. The MME will keep tracking the UE‟s location either on an eNB level in case the UE is
connected, or at a Tracking Area (TA) level in case the UE is in idle mode.
The MME is also responsible for setting up of resources for the UE. MME does this by retrieving the user profile from HSS and determine what
Packet Data Network connections should be allocated to the UE at initial „attach‟ point. MME automatically sets up the default bearer,
thereby giving UE the basic IP connectivity including CP signaling with the eNB and the S-GW. MME is also involved in setting up the dedicated
bearers for the users.
The MME also participates in control signaling for handover of an active mode UE between eNBs, S-GW‟s or MME‟s. MME is involved in
every eNB change, since there is no separate RNC to hide most of these events. In principle the MME may be connected to any other MME in
the system. Connectivity to a number of HSSs will also need to be supported. The MME may serve a number of UEs at the same time.
Serving Gateway (S-GW)
The S-GW is involved mainly in the User Plane (UP) tunnel management, switching and other operations. It is not involved in the Control Plane
(CP) operations. S-GW can only handle 12
its own resources and it allocates them based on requests from MME, P-GW or PCRF. An illustration describing S-GW logical interfaces and
primary functions is shown in figure 2.4.
S-GW can use either GTP tunnels or PMIP tunnels for data flow depending on the data bearer setup. S-GW acts as a local mobility anchor
during handovers between eNBs. It can monitor data inside the tunnels for Lawful Interception and Charging purposes.
All S-GW connections are “one-to-many”. One S-GW may be serving only a particular geographical area with a limited set of eNBs, and there
may be a limited set of MMEs that control that area.
Figure 2.4: S-GW main logical connections and functions [12]
The S-GW should be able to connect to any P-GW in the whole network as the P-GW will not change during mobility, while the S-GW may be
relocated. For connections related to one UE, the S-GW will always signal with only one MME and the UP points to one eNB at a 13
time. If one UE is allowed to connect to multiple PDN‟s through different P-GW‟s, then the S-GW needs to connect to those separately.
PDN Gateway (P-GW)
PDN-GW (also often abbreviated as P-GW) is the edge router between the EPS and external packet data networks. It acts as the highest level
mobility anchor in the EPS and as the IP point of attachment for the UE. It performs traffic gating and filtering functions as required by the
service in question. Typically, P-GW assigns an IP address to the UE which it uses for communication with external network. The P-GW
performs the required Dynamic Host Configuration Protocol (DHCP) functionality.
P-GW is the highest level mobility anchor in the system. When a UE moves from one S-GW to another, the bearers have to be switched in the
P-GW. The P-GW will receive an indication to switch the flows from the new S-GW.
Each P-GW may be connected to one or more PCRF, S-GW and external network. For a given UE that is associated with the P-GW, there is
only one S-GW, but connections to many external networks and respectively to many PCRFs may need to be supported, if connectivity to
multiple PDNs is supported through one P-GW.
Policy Charging and Resource Function
PCRF is the network element that is responsible for Policy and Charging Control (PCC). It makes decisions on how to handle the
services in terms of QoS, and provides information to the PCEF located in the P-GW, and if applicable also to the BBERF located in
the S-GW, so that appropriate bearers and policing can be set up. The EPC bearers are then set up based on those. The
connections between the PCRF and the other nodes are shown in Figure 2.6. Each PCRF may be associated with one or more AF,
P-GW and S-GW. There is only one PCRF associated with each PDN connection that a single UE has.
Home Subscription Server (HSS)
Home Subscription Server (HSS) is the subscription data repository for all permanent user data. The HSS stores the master copy of
the subscriber profile, which contains information about the services that are applicable to the user. It also records the location of
the user in the level of visited network control node, such as MME.
For supporting mobility between non-3GPP ANs, the HSS also stores the Identities of those P-GWs that are in use. The permanent
key, which is used to calculate the authentication vectors that are sent to a visited network for user authentication and deriving
subsequent keys for encryption and integrity protection, is stored in the Authentication Center (AuC), which is typically part of the
HSS. In all signaling related to these functions, the HSS interacts with the MME and the HSS will need to be able to connect with
every MME in the whole network.
LTE Interworking
Two interfaces in the LTE network are provided for interworking. The S3 is the reference point, based on the legacy Gn interface. It
lies between the SGSN and the MME where it enables user and bearer information exchanges for inter-3GPP access system
mobility. The S4 is the reference point, based on the older GTP-based Gn interface in UMTS, between the SGSN in the GPRS core
network and the S-GW.
The preferred way to interwork UMTS with LTE is though a Serving GPRS Support Node (SGSN) upgraded to Release 8. This
enhancement deploys the S3 and S4 interfaces that somewhat mimics the strict separation of user data flows from the control plane
messages so evident in LTE.
Though the protocol stacks are incompatible with each other, LTE supports interworking with the legacy 3GPP and non-3GPP
accesses. The intention is to provide LTE service continuity that is transparent to the access technology. Access independence is one
of the requirements of the NGN visions. The idea assumes a generic approach, which decouples the NGN core network and its
procedures as much as possible from the access technologies.
LTE Key Parameters
Example how to calculate number of RB:
•Lets say 10 MHz BW = 10000kHz
•1 RB = 12 subcarriers, 1 subcarrier = 15kHz
so 1 RB = 180kHz
•1MHz for guard band (500kHz each)
•(10000-1000)/180 = 50RB
LTE Qos Clasess
REF 3GPP TS 23.203
QoS in LTE Networks
Since LTE and UMTS employ different QoS mechanisms, we need to be able to map between LTE's QCI parameters for EPS bearers and
the four QoS categories and associated parameters of Pre-Release 8 PDP Contexts. The 3GPP recommendations provide rules for
mapping QoS definitions between the systems.
The QoS parameter sets supported within the EPC concern themselves with how packets are handled as they enter, traverse and leave a
network. Adding more bandwidth at the edge of a network may resolve some capacity or congestion problems, but it does not resolve
jitter, nor can it fix traffic prioritization problems.
QoS in an all-IP Environment
QoS is the management of the data traffic in a network. Be it a LAN, WAN or wireless, packets are subjected to scrutiny and control. QoS
is primarily a layer 3 Internet Protocol (IP) concept. It uses tools that have existed since the early days of IP plus some newer tools and
protocols that are designed to aid in the provisioning of precisely defined and predictable data transfers in accordance with certain
characteristics.
LTE and QoS
Each bearer (user data) path in LTE is assigned a set of QoS criteria. In the case a user may have services requiring different QoS criteria,
additional bearer paths may be added. LTE identifies a set of QoS criteria with QoS Class Identities (QCIs). These are listed in Figure 2.
The critical QoS parameter for any EPS bearer is its QCI, which represents the QoS features an EPS bearer should be able to offer for a
Service Data Flow (SDF). Each SDF is associated with exactly one QCI. Network operators may pre-configure all QCI characteristics in an
eNB, for example, based on their actual characteristics. The parameters they choose to define these determine the allocation of bearer
resources in the E-UTRAN.
EPS Bearer Service – User Plane
The term "EPS Radio Bearer Service" describes the overall connection between the UE and the Core Network
edge node, PDN-GW. The EPS Bearer carries the end-to-end service and is associated with QoS (Quality of
Service) attributes as decided by the operator. For user data, it maps down to a Radio Bearer from the UE to the
eNB, and an S1 transport bearer between the eNB and the S-GW in the CN. Between the S-GW and the PDN-
GW, a S5/S8 bearer is used to convey the transport between these nodes. The E-RAB is carried by a Radio
Bearer between the UE and the RBS, and a user plane S1 Bearer.
Control Plane
All services require a Signaling Connection to carry Radio Resource Control (RRC) signaling between the
UE and eNB and ‘Non Access Stratum’ (NAS) signaling between the UE and MME.
The NAS messages are carried between the UE and the eNB using the Radio Resource Control (RRC)
protocol on a Signaling Radio Bearer (SRB). They are transmitted between the eNB and the MME using
the S1 Application Protocol. The SRBs carrying RRC messages are carried by Logical Channels that are
mapped onto a transport channel and scheduled together with the user data onto the physical
resources (Radio Link) by the MAC layer,
eNodeB
UE
LTE Air Interface
• Downlink (DL) transmission: uses Orthogonal Frequency Division Multiple
Access (OFDMA)
• Uplink (UL) transmission: uses Single Carrier Frequency Division Multiple Access
(SC-FDMA)
• Supports both TDD (Time Division Duplex) and FDD (Frequency Division Duplex)
modes of operation.
FDM: Each user transmits their data on a different
subcarrier. To avoid interference, guard bands are
assigned between subcarriers. Since guard bands do
not transmit any information, they introduce spectrum
inefficiency.
Multicarrier FDM: the user data is converted from
serial to parallel. Then, the parallel data substreams are
sent over multiple subcarriers. At the receiver, the
parallel data is combined back into a serial data stream.
A higher data rate can be achieved by using multicarrier
multiplexing.
OFDM: adds the orthogonal feature into multicarrier
FDM. Orthogonal means “do not cause interference
with each other.” In OFDM, the subcarriers are
FDM, MC-FDM, OFDM and OFDMA
with each other.” In OFDM, the subcarriers are
designed to be orthogonal. This allows subcarriers to
overlap and saves bandwidth. Therefore, OFDM obtains
both higher data rates and good spectrum efficiency.
OFDMA: allows multiple users to access subcarriers
simultaneously. In this example, three users share four
subcarriers. At each symbol time, all users can have
access. The assignment of subcarriers for a user can be
changed at every symbol time.
OFDMA provides more flexibility for system design.
Different combinations of the number of carriers and
symbol times can be allocated.
The motivation for adding the cyclic
extension is to avoid inter-symbol
interference (ISI). When the transmitter
adds a cyclic extension longer than the
channel impulse response, the effect of the
previous symbol can be avoided by
removing the cyclic extension at the
receiver.
The cyclic prefix is added by copying part of
the symbol at the end and attaching it to
the beginning of the symbol, used to
Cyclic Prefix
the beginning of the symbol, used to
"signal" a break in the transmission or as
guard interval and the OFDM symbol seems
to be periodic. This guard interval is
designed as such that it exceeds the delay
spread in the environment caused by multi-
path effect. Therefore the aim is to
preserve sub-carrier orthogonality by
ensuring the time dispersion is shorter than
the cyclic prefix length.
LTE Frame Structure
• The basic type 1 (FDD) LTE frame has an overall length of 10 ms.• This is then divided into a total of 20 individual slots.• This is then divided into a total of 20 individual slots.
• LTE Sub-frames then consist of two slots - in other words there are ten LTE sub-frames within a frame.
Physical Resource Block (PRB)
How To Calculate Peak Data Rate in LTE?
1. Calculate the number of resource elements (RE) in a subframe with 20 MHz channel bandwidth: 12
subcarriers x 7 OFDMA symbols x 100 resource blocks x 2 slots= 16800 REs per subframe. Each RE
can carry a modulation symbol.
2. Assume 64 QAM modulation and no coding, one modulation symbol will carry 6 bits. The total bits
in a subframe (1ms) over 20 MHz channel is 16800 modulation symbols x 6 bits / modulation symbol
= 100800 bits. So the data rate is 100800 bits / 1 ms = 100.8 Mbps.
3. With 4x4 MIMO, the peak data rate goes up to 100.8 Mbps x 4 = 403 Mbps.
4. Estimate about 25% overhead such as PDCCH, reference signal, sync signals, PBCH, and some
coding. We get 403 Mbps x 0.75 = 302 Mbps.
Ok, it is done through estimation. Is there a way to calculate it more
accurately? If this is what you look for, you need to check the 3GPP accurately? If this is what you look for, you need to check the 3GPP
specs 36.213, table 7.1.7.1-1 and table 7.1.7.2.1-1. Table 7.1.7.1-1
shows the mapping between MCS (Modulation and Coding Scheme)
index and TBS (Transport Block Size) index. Let's pick the highest MCS
index 28 (64 QAM with the least coding), which is mapping to TBS
index of 26. Table 7.1.7.2.1-1 shows the transport block size. It
indicates the number of bits that can be transmitted in a subframe/TTI
(Transmit Time Interval). For example, with 100 RBs and TBS index of
26, the TBS is 75376. Assume 4x4 MIMO, the peak data rate will be
75376 x 4 = 301.5 Mbps.
Logical Channels in LTE
Transport Channels in LTE
LTE Physical Channels differ somewhat from their UMTS
counterparts, since the majority of LTE Physical Channels are
shared resources, carrying information for multiple users.
Consequently, Physical Channels generally answer the
question, “WHERE is the information to be found?”.
LTE Physical Channels include:
•Physical Broadcast Channel (PBCH)
•Physical Downlink Shared Channel (PDSCH)
•Physical Downlink Control Channel (PDCCH)
Physical Channels in LTE
•Physical Downlink Control Channel (PDCCH)
•Physical Control Format Indicator Channel (PCFICH)
•Physical Hybrid ARQ Indicator Channel (PHICH)
•Physical Random Access Channel (PRACH)
•Physical Uplink Shared Channel (PUSCH)
•Physical Uplink Control Channel (PUCCH)
Multiple Antenna Techniques
Diversity
Receive Diversity Transmit Diversity
MIMO/Spatial Multiplexing
SU-MIMO (Single User MIMO)
MU-MIMO (Multi User MIMO)
Beam Forming
SDMA (Spatial Division Multiple Access)
Special Case of SU-MIMO
Multiple path between
Multiple path between
transmitter and receiver
created by using multiple
receive antennas
Multiple Antenna Techniques
Multiple path between
transmitter and receiver
created by using multiple
transmit antennas
Single User MIMO (SU-MIMO)
SU-MIMO (also known as Spatial Multiplexing) sends
different sets of data over the transmit antennas, using the
same subcarriers. The UE receives both streams at the same
time, and performs channel estimation to separate the
streams, using the unique reference signals sent from each
antenna to determine how the transmitted signals have been
affected by the RF environment. Although this technique is
very complex and requires a good downlink SINR (Signal to
Interference and Noise Ratio), it allows the UE to potentially
receive twice as much data (in 2x2 MIMO) or four times as
much data (in 4x4 MIMO) as it would get with a single
transmit antenna. The primary benefit of SU-MIMO is
increased throughput; it has little effect on coverage or
capacity.
Multi-User MIMO (MU-MIMO)
MU-MIMO is a form of Space Division Multiple Access (SDMA),
which uses beamforming techniques to focus the energy of the
transmitted signal at the receiver. Beamforming adjusts the
relative phases of the transmitted signals so that they arrive at
the receiver in phase, resulting in a stronger signal; the beams
may be dynamic (able to respond to the location and
movement of the UEs) or fixed (also known as switched beams,
similar to very narrow directional antennas). Each UE
communicates with the eNodeB over a single beam; this
approach allows the same subcarriers to be used
simultaneously by multiple UEs with little or no interference,
due to the physical separation between the users. The primary
benefit of MU-MIMO is increased capacity.
Antenna Multibeam
http://www.youtube.com/watch?v=uzfUqhbohWc
AT&T's multi-beam wireless technology delivers five times
more data capacity, and can be used at large sporting events
and concerts. This innovative wireless technology provides
users with more reliable, faster mobile coverage.
Many different bands are currently available for
LTE operation. The table shows frequency bands
for uplink operation defined in 3GPP TS 36.101.
(For the mobile terminal, the uplink band is the
band of interest, since this is the transmit
frequency.)
While many bands are available, and both FDD
and TDD options are shown, the main bands of
interest for North America are bands 13 and 14
(700-MHz bands) and band 4 (1710 to 1755
MHz). In Europe, band 7 is expected to be widely
used, with operation from 2500 to 2570 MHz. In
Japan, it is likely that band 1 (1920 to 1980 MHz)
Japan
US
US
US
Europe
LTE Frequency Bands
Japan, it is likely that band 1 (1920 to 1980 MHz)
will be deployed first for LTE.
REF 3GPP TS 36.101
Physical Cell Identity (PCI)
Read System Info & RS
◦ timing
◦ sequence
◦ frequency shift
•PSS signal
3 different sequences called Physical-Layer Identities (0-2)
PCI: Primary and Secondary Synchronization
• SSS signal
168 different sequences called Physical-Layer Cell-Identity groups (0-
167)
• 168 Physical-Layer Cell-Identity groups with 3 Physical-Layer Identities per
group
168 x 3 = 504 Physical-Layer Cell Identities
In cellular networks, when a mobile moves from cell to cell and performs cell selection/reselection and handover, it has to
measure the signal strength/quality of the neighbor cells. In LTE network, a UE measures two parameters on reference signal:
RSRP: Reference Signal Received Power
RSRQ: Reference Signal Received Quality
RS Reference Signal
RSRP
RSRQ
3GPP TS 36.214
LTE Measurement
measure the signal strength/quality of the neighbor cells. In LTE network, a UE measures two parameters on reference signal:
RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality).
RSRP is a RSSI type of measurement. It measures the average received power over the resource elements that carry cell-
specific reference signals within certain frequency bandwidth. RSRP is applicable in both RRC_idle and RRC_connected
modes, while RSRQ is only applicable in RRC_connected mode. In the procedure of cell selection and cell reselection in idle
mode, RSRP is used.
RSRQ is a C/I type of measurement and it indicates the quality of the received reference signal. It is defined as (N*RSRP)/(E-
UTRA Carrier RSSI), where N makes sure the nominator and denominator are measured over the same frequency bandwidth;
The carrier RSSI (Receive Strength Signal Indicator) measures the average total received power observed only in OFDM
symbols containing reference symbols for antenna port 0 (i.e., OFDM symbol 0 & 4 in a slot) in the measurement bandwidth
over N resource blocks. The total received power of the carrier RSSI includes the power from co-channel serving & non-
serving cells, adjacent channel interference, thermal noise, etc.
The RSRQ measurement provides additional information when RSRP is not sufficient to make a reliable handover or cell
reselection decision. In the procedure of handover, the LTE specification provides the flexibility of using RSRP, RSRQ, or both.
LTE System Information Message
System Information have existed since the days of GSM (and probably before) and inform
mobile devices about all important parameters of how to access the network and how to find
neighboring cells. Here's an overview of those that have been defined for LTE so far. For details
see 3GPP TS 36.331 Chapter 6.3.
Compared to GSM and UMTS, the amount of parameters inside seems quite a bit less bloated:
•Master Information Block (MIB): Most essential parameters
•SIB 1: Cell access related parameters and scheduling
•SIB 2: Common and shared channel configuration
•SIB 3: Parameters required for intra-frequency cell reselections
•SIB 4: Information on intra-frequency neighboring cells •SIB 4: Information on intra-frequency neighboring cells
•SIB 5: Information inter-frequency neighboring cells
•SIB 6: Information for reselection to UMTS (UTRAN) cells if no suitable LTE cell is available
•SIB 7: Information for reselection to GSM (GERAN) cells if no suitable LTE or UMTS cell is
available
•SIB 8: Information for reselection to CDMA2000 systems (mostly for North America)
•SIB 9: Home eNodeB name – for future LTE femtocell applications
•SIB 10 + 11: ETWS (Earthquake and Tsunami Warning System) information
•SIB 12: Commercial Mobile Alerting System (CMAS) information. Never heard about this
before!?
UMTS
SIB19: Information for reselection to LTE cells
The random access procedure in LTE is performed at any of the following five
events:
1) initial access of an idle mobile
2) reestablishment after radio link failure
3) handover to a different cell
4) downlink data transmission to a mobile, which is out of time-synchronization
5) uplink data transmission from an out-of-synch mobile.
Random Access (RA) Procedure
Random Access Procedure:
1) Contention Based Random Access
2) Non-Contention Based Random Access
1. Random access preamble: sent on a special set of
physical layer resources, which are a group of
subcarriers allocated for this purpose
• Uses Zadoff-Chu sequence, a CDMA-like coding, to allow
simultaneous transmissions to be decoded
•6-bit random ID
2. Random access response
• Sent on Physical Downlink Control Channel (PDCCH)
• Sent within a time window of a few TTI
• For initial access, conveys at least RA-preamble identifier,
timing alignment information, initial UL grant, and
RA: Contention Based Random Access
timing alignment information, initial UL grant, and
assignment of temporary C-RNTI
One or more UEs may be addressed in one response
3. Scheduled transmission
• Uses HARQ and RLC transparent mode on UL-SCH
• Conveys UE identifier
4. Contention resolution: The eNodeB uses this optional
step to end the RACH procedure
In the non-contention based random access procedure, there is no
chance of a preamble collision because the code is pre-assigned by
the eNodeB.
1. Random access preamble assignment: the eNodeB assigns the
6 bit preamble code
2. Random access preamble: the UE transmits the assigned
preamble
3. Random access response
• Same as for contention based RA
• Sent on PDCCH (Physical Downlink Control Channel)
• Sent within a time window of a few TTI
RA: Non-Contention Based Random Access
• Sent within a time window of a few TTI
• Conveys at least the timing alignment information and
initial Ul grant for handover, and the timing alignment
information for DL data arrival. In addition, RA-preamble
identifier if addressed to RA-RNTI on L1/L2 control channel.
• One or more UEs may be addressed in one response
CQI reports can be
•Wideband or per sub-band
•Semi static, Higher Layer Configured or
UE selected single or multiple sub-bands
•CQI only, or CQI plus Pre-coding Matrix
Indicator (PMI) / Rank Indicator (RI)
•Transmitted on PUCCH for sub-frames
with no PUSCH allocation or PUSCH with
or without scheduling grant or if no UL-
CQI Mapping
or without scheduling grant or if no UL-
SCH
•Depends on spatial multiplexing
•Reports can be periodic or aperiodic
(when signaled by DCI format 0 with CQI
request field set to 1)
3GPP TS 36.213
UE States in LTE
In the RRC_CONNECTED state, the UE is registered with the network and has an RRC connection with the eNB.
In RRC_CONNECTED state, the network knows the cell to which the UE belongs and can transmit/ receive data
from the UE.
The RRC_IDLE state is a power-conservation state for the UE, where typically the UE is not transmitting or
receiving packets. In RRC_IDLE state, no context about the UE is stored in the eNB. In this state, the location of
the UE is only known at the MME and only at the granularity of a tracking area (TA) that consists of multiple
eNBs. The MME knows the TA in which the UE last registered and paging is necessary to locate the UE to a
cell.
� Handover: UE moves between eNodeB and on dedicated mode
� There are two types in Intra LTE Handover
1. X2 based handover
• Using interface between the source and target eNodeB
2. S1 based handover
• When x2 based handover can not be used
Intra LTE Handover
• When x2 based handover can not be used
Intra LTE Handover: X2 Based
Intra LTE Handover: S1 Based
Interim Option for Voice Over LTE
• LTE Phase 2 CS Fallback to WCDMA (or GSM) is to
enable voice services when on LTE. LTE Phase 3 will
support LTE IMS VoIP.
• LTE device will reselect to WCDMA (or GSM) when
either Paged or a Voice call requested when on LTE
network (either Idle/Connected)
• This is a temporary solution until we have IMS VoIP
capabilities supported on the LTE network. However
UE that does not support IMS will continue to
perform CSFB after the network support IMS VoIP.
• CS Fallback will be the only option for single radio
UEs to provide CS services (until VoIP). Some CDMA
carriers use Dual Radio technology for CS call that
Circuit Switch Fallback (CSFB)
carriers use Dual Radio technology for CS call that
disconnect its RRC connection from the LTE network
to answer or initiate a CS call on 1xRTT.
• CSFB adds a small delay to the overall call setup; this delay is the time the UE takes to move from the 4G network to the CS
network (typically 1-2 seconds).
• To support CSFB all the 3G and 2G MSCs, GMSCs and HLR will need CSFB enhancement (new SW) in order to be able to
provide adequately circuit switched voice services to the LTE subscribers with LTE voice capable smart phones.
• The LTE UE will perform EPS/IMSI combined attach meaning it will be attached to the MSC by the MME once the attach to the
LTE network is successful. The MSC that the MME attaches the UE to becomes the serving MSC for that UE.
• Incoming call to the LTE subscriber will arrive to the home MSC which will query the HLR to determine and route the call to
the serving MSC. The serving MSC will initiate a paging request toward the MME. When the UE responds to the page, the 4G
network will request the mobile to relocate to the CS mobile network to receive the call.
• As part of CSFB, Mobile Terminating Roaming Retry functionality gets added to the MSC. The MSC which acts as the gateway
MSC will be able to reroute the incoming call to the new serving MSC if the UE ends up on a different serving MSC as part of
the CSFB IRAT procedure.
� Key Drivers
� Reduction CAPEX and OPEX
� Complexity of networks
� Components of SON
� Self Configuration
Snapshot
Action
Feedback
Monitor and
Trigger
Smart Algorithm
Validation
Self Organizing Network (SON)
� Self Configurationplug and play functionality where network elements are configured
(identity allocation, software upgrade, communication link establishment,
etc) automatically.
� Self Optimizationmore or less continuous adaptation of parameters to meet specified
requirements, typically specified at a high level.
� Self Healingalgorithms to handle disruptive events and to minimize negative
consequences on services.
Centralized SON
In Centralized SON, optimization algorithms are stored and executed from the OAM
System. In such solutions SON functionality resides in a small number of locations, at a
high level in the architecture. Figure on the right shows an example of Centralized SON.
In Centralized SON, all SON functions are located in OAM systems, so it is easy to deploy
them. But since different vendors have their own OAM systems, there is low support for
optimization cases among different vendors. And it also does not support those simple
and quick optimization cases. To implement Centralized SON, existing Itf-N interface
needs to be extended.
Distributed SON
In Distributed SON, optimization algorithms are executed in eNB. In such solutions
SON functionality resides in many locations at a relatively low level in the architecture.
SON Architecture
SON functionality resides in many locations at a relatively low level in the architecture.
Figure on the right shows an example of Distributed SON. In Distributed SON, all SON
functions are located in 56
eNB, so it causes a lot of deployment work. And it is also difficult to support complex
optimization schemes, which require the coordination of lots of eNBs. But in
Distributed SON it is easy to support those cases, which only concern one or two eNBs
and require quick optimization responses. For Distributed SON, X2 interface needs to
be extended.
Hybrid SON
In Hybrid SON, part of the optimization algorithms are executed in the OAM system,
while others are executed in eNB. Figure on the right shows an example of Hybrid
SON. In Hybrid SON, simple and quick optimization schemes are implemented in
eNB and complex optimization schemes are implemented in OAM. So it is very
flexible to support different kinds of optimization cases. And it also supports the
optimization between different vendors through X2 interface. But on the other
hand, it costs lots of deployment effort and interface extension work.
Automatic Neighbor Relation (ANR)
Automatic PCI Configuration
Automatic IRAT Configuration
New Site Self Establishment
Self Configuration ad Self Healing eNodeB
ANR for Hetnet
3GPP TS32.501
SON: Self Configuration
Self-configuration mechanism is desirable during the pre-
operational phases of network elements such as network
planning and deployment, which will help reduce the
CAPEX. Some Self-Configuration use cases are defined in the
following table.
Coverage and Capacity Optimization (CCO)
Interference Reduction
Mobility Robustness Optimization (MRO)
Mobility Load Balancing Optimization (MLBO)
RACH Optimization
Inter Cell Interference Coordination (ICIC)
Self Optimization due to Troubleshooting
Continues Optimization due to Dynamic Changes in the Network
Optimization QoS Related Parameters
SON: Self Optimization
Optimization QoS Related Parameters
HetNet Coverage Optimization
Self-optimization mechanism is desirable during the
operational stage so that network operators get benefits of
the dynamic optimization, e.g., mobility load balancing to
make network more robust against environmental changes
as well as the minimization of manual optimization steps to
reduce operational costs.
System Initializations (at different levels)
Reload of a Backup of Software,
Activation of a Fallback Software Load
Download of a Software Unit
Reconfiguration
3GPP TS 32.541
The purpose of the Self-healing functionality of SON is to solve or mitigate the faults which could be solved automatically
by triggering appropriate recovery actions.
SON: Self Healing
by triggering appropriate recovery actions.
For the fault management functionality, appropriate alarms shall be generated by the faulty network entity for each of the
detected faults, regardless of whether it is an automatically detected/automatically cleared or an automatically
detected/manually cleared fault.
As described above, alarms can be used to trigger Self-healing mechanisms. The Self-healing function continuously
monitors these alarms, and when it is able to resolve which alarm/s could be solved automatically, it gathers necessary
information, makes a deep analysis of the issue and then according to the derived results, the mechanism will trigger
appropriate recovery actions to solve the fault automatically, if necessary.
For some Self-healing functions which are located in NEs and require more rapid response, the trigger of Self-healing can
be the detection of a fault. Hence, when a fault is detected, an appropriate Self-healing Process will be triggered to try to
heal the fault automatically.
The Self-healing functionality also monitors the execution of the recovery action/s and decides the next step accordingly.
After a Self-healing procedure has ended, the Self-healing functionality shall generate and forward appropriate
notifications to inform the IRP Manager about the Self-healing result and all the information of the performed recovery
actions may be logged.
Retainability
AccessibilityAvailability
•ERAB retainability
•ERAB drop causes: drop MME, HO, UE lost, transport
•RRC
•ERAB
•S1
•CS Fallback to GSM/WCDMA
•Paging
•Cell downtime
LTE Key Performance Indicator (KPI)
MobilityIntegrity•Intra LTE handover
•Inter LTE handover
•UL/DL throughput
•Latency
3GPP TS 32.450: Key Performance Indicator for E-UTRAN Definitions
3GPP TS 32.451: Key Performance Indicator for E-UTRAN Requirements
System Utilization
Vendor Specific
� The probability that a service, once obtained, continues to be provided under given conditions for
a given time duration.
� Number of ERABs with data in a buffer that was abnormally released, normalized with number of
success.
= 1-(ERAB drops / ERAB Success)
� Drop call reasons:
� drop due to cell downtime (eNodeB)
� drop due to handover execution failures (eNodeB)
� drop due to handover preparation (eNodeB)
KPI: Retainability
� drop due to handover preparation (eNodeB)
� drop due to radio connection with the UE lost (eNodeB)
� drop due to S1 interface down (transport)
� drop due to initiated by MME (MME)
� Probability for an end-user to be provided with an E-RAB at request.
� Probability success rate for E-RABs establishment. Successful attempts compared with total
number
of attempts for the different parts of the E-RAB establishment.
= RRC Success Rate x S1 Success Rate x ERAB Success Rate
