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Shariq Yasin Senior RF Consultant
Long Term Evolution (LTE) is the latest step in moving forward from the cellular 3G services ( e.g. GSM to UMTS to HSPA to LTE or CDMA to LTE). LTE is based on standards developed by the 3rd Generation Partnership Project (3GPP).
LTE may also be referred more formally as Evolved UMTS Terrestrial Radio Access (E-UTRA) and Evolved UMTS Terrestrial Radio Access Network (E-UTRAN
The following are the main objectives for LTE. ◦ Increased downlink and uplink peak data rates. ◦ Scalable bandwidth ◦ Improved spectral efficiency ◦ All IP network ◦ A standard’s based interface that can support a multitude of user
types. ◦ LTE networks are intended to bridge the functional data exchange
gap between very high data rate fixed wireless Local Area Networks (LAN) and very high mobility cellular networks.
ITU (International Telecommunication Union) Specialized agency of UN. Standardization of Telecommunication and allocation of
Spectrum The Telecommunication Standardization Sector, ITU-T The Radiocommunication Sector, ITU-R The Telecommunication Development Sector, ITU-D IMT-2000 (International Mobile Telecommunications) ◦ Defined by ITU for the Global Standard for 3rdGeneration wireless
communications in 1999 ◦ Includes six radio interfaces as a part of the ITU-R M.1457
Recommendation: 1. WCDMA (UTRA-FDD) 2. CDMA2000 3. TD-CDMA and TD-SCDMA 4. EDGE 5. DECT 6. IP-OFDMA TDD WMAN (in 2007)
3GPP (3rd Generation Partnership Project) Created in Dec 1998, for the collaboration between
telecommunication associations to develop globally acceptable 3G mobile phone system under the scope of IMT-2000
Technical Specifications and Technical Reports for a 3G Mobile System based on evolved GSM core networks and the radio access technologies that they support (i.e., Universal Terrestrial Radio Access (UTRA) both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes).
Global Standard for cost effectiveness New Services (Video Telephony) Spectral Efficiency to accommodate more
subscribers More Throughput (more UL and DL requirements) Global Roaming Achieving Customer Expectations Roadmap to Future Evolution Vendor Support ◦ EOM: (End of marketing) End of new order (1~2 Yr) ◦ EOFS: (End of Full support) End of bug fixing (3 Yr) ◦ EOS: (End of Service) End of Service Supporting (4 Yr)
The Third Generation Partnership Project (3GPP) has approved the functional freeze of LTE (Long Term Evolution) as part of 3GPP Release 8 -11thDecember 2008
Orthogonal Frequency Division Multiplexing (OFDM) has been selected for the Downlink and Single Carrier-Frequency Division Multiple Access (SC-FDMA) for the Uplink. The Downlink will support data modulation schemes QPSK, 16QAM, and 64QAM and the Uplink will support BPSK, QPSK, 8PSK and 16QAM.
Supports MIMO and SMART Antenna technology Increased downlink and uplink peak data rates. Scalable bandwidth Improved spectral efficiency All IP network A standard’s based interface that can support a multitude of user
types. LTE networks are intended to bridge the functional data
exchange gap between very high data rate fixed wireless Local Area Networks (LAN) and very high mobility cellular networks.
Increased peak data rate:100Mbps for DL with 20MHz (2 Rx Antenna at UE), 50Mbps for UL with 20MHz
Improved spectral efficiency: 5bps/Hz for DL and 2.5bps/Hz for UL
Improved cell edge performance (in terms of bit rate)
Reduced latency
The key driving factors for LTE are: ◦ Efficient spectrum utilization ◦ Flexible spectrum allocation ◦ Reduced cost for the operator ◦ Improved system capacity and coverage ◦ Higher data rate with reduced latency ◦ The E-UTRAN uses a simplified single node architecture
consisting of the eNBs (E-UTRAN Node B). ◦ The eNB communicates with the Evolved Packet Core
(EPC) using the S1 interface; specifically with the MME (Mobility ManagementEntity) and the UPE (User Plane Entity) identified as S-GW (Serving Gateway) using S1-C and S1-U for control plane and user plane respectively. The MME and the UPE are preferably implemented as separate network nodes so as to facilitate independent scaling of the control and user plane. Also the eNB communicates with other eNB using the X2 interface (X2-C and X2-U for control and user plane respectively).
32 Commercial Networks
ITU has introduced a term IMT-Advanced for mobile systems beyond IMT-2000 scope.
In June 2008, 3GPP held two workshops on “Requirements for Further Advancements for E-UTRA”
IMT-Advanced 3GPP RAN working on LTE-Advanced
Evolved NodeB (eNB) Evolved Radio Access Network (eRAN) Serving Gateway (SGW) Mobility Management Entity (MME) Packet Data Network Gateway (PDN GW)
e-Node hosts the following functions: Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility
Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of user data stream;
Selection of an MME at UE attachment;
Routing of User Plane data towards Serving Gateway;
Scheduling and transmission of paging and broadcast messages (originated from the MME);
Measurement and measurement reporting configuration for mobility and scheduling;
MME (Mobility Management Entity) hosts the following functions: NAS signaling and security;
AS Security control;
Idle state mobility handling;
EPS (Evolved Packet System) bearer control;
Support paging, handover, roaming and authentication.
P-GW (PDN Gateway) hosts the following functions: Per-user based packet filtering; UE IP address allocation; UL and DL service level charging, gating and rate
enforcement;
S-GW (Serving Gateway) hosts the following functions: Packet routing and forwarding; Local mobility anchor point for handover; Lawful interception; UL and DL charging per
UE, PDN, and QCI; Accounting on user and QCI granularity for inter-operator charging.
OFDMA
Modulation
Adaptive Modulation and Coding (AMC) Adaptive Modulation and Coding refers to the ability of the network to determine the modulation type and the coding rate dynamically based on the current RF channel conditions reported by the UE in Measurement Reports. The RF digital modulation used to transport the information is QPSK, 16-QAM, and 64-QAM. The pictures below show the ideal constellations for each modulation where each dot represents a possible symbol. In the QPSK case, there are four possible symbol states and each symbol carries two bits of information. In 16-QAM, there are 16 symbol states. Each 16-QAM symbol carries
4 bits. In 64-QAM, there are 64 symbol states. Each 64-QAM symbol carries 6 bits. Higher-order modulation is
more sensitive to poor channel conditions than the lower-order modulation because the detector in the receiver must resolve
smaller differences as the constellations become more dense. Coding refers to an error-correction methodology that adds extra bits to the data
stream that allow error correction. Specified as fractions, Code Rates specify the number of data bits in the
numerator and the total number of bits in the denominator. Thus if the Code Rate is 1/3, protection bits are added so one bit of
data is sent as three bits.
LTE takes advantage of OFDMA, a multi-carrier scheme that allocates radio resources to multiple users. OFDMA uses
Orthogonal Frequency Division Multiplexing (OFDM). For LTE, OFDM splits the carrier frequency bandwidth into many
small subcarriers spaced at 15 kHz, and then modulates each individual subcarrier using the QPSK, 16-QAM, or 64-
QAM digital modulation formats. OFDMA assigns each user the bandwidth needed for their transmission. Unassigned
subcarriers are off, thus reducing power consumption and interference.
OFDMA uses OFDM; however, it is the scheduling and assignment of resources that makes OFDMA distinctive. The
OFDM diagram in Figure 2 below shows that the entire bandwidth belongs to a single user for a period. In the OFDMA
diagram, multiple users are sharing the bandwidth at each point in time.
SISO (Single Input Single Output)Traditional radio
MISO (Multiple Input Single Output)Transmit diversity Space Frequency Block Coding (SFBC) or Cyclic Delay
Diversity (CDD)
SIMO (Single Input Multiple Output)Receive diversity Maximal Ratio Combining (MRC)
MIMO (Multiple Input Multiple Output)Spatial
Multiplexing (SM) to transmit multiple layers (streams) simultaneously; can be used in conjunction with Cyclic Delay Diversity (CDD); works best in high SINR environments and channels de-correlated by multipath
TX and RX diversity, used independently or together;
used to enhance throughput in the presence of adverse channel conditions.
All the following functions are assigned to eNodeB(s) in the E-UTRAN
Radio bearer control Radio admission control Connection mobility management Dynamic resource allocation Inter cell interference coordination Load balancing Inter RAT RRM functions
internet
eNB
RB Control
Connection Mobility Cont.
eNB MeasurementConfiguration & Provision
Dynamic Resource Allocation (Scheduler)
PDCP
PHY
MME
S-GW
S1MAC
Inter Cell RRM
Radio Admission Control
RLC
E-UTRAN EPC
RRC
Mobility Anchoring
EPS Bearer Control
Idle State Mobility Handling
NAS Security
P-GW
UE IP address allocation
Packet Filtering
Control Channel ◦ Broadcast Control Channel (BCCH) ◦ Paging Control Channel (PCCH) ◦ Common Control Channel (CCCH) ◦ Multicast Control Channel (MCCH) ◦ Dedicated Control Channel (DCCH)
Traffic Channel ◦ Dedicated Traffic Channel (DTCH) ◦ Multicast Traffic Channel (MTCH)
Downlink Channels ◦ Broadcast Channel (BCH) ◦ Downlink Shared Channel (DL-SCH) ◦ Paging Channel (PCH) ◦ Multicast Channel (MCH)
Uplink Channels ◦ Uplink Shared Channel (UL-SCH) ◦ Random Access Channel (RACH)
Downlink Channels： Physical Broadcast Channel (PBCH): Carries system
information for cell search, such as cell ID.
Physical Downlink Control Channel (PDCCH) : Carries the resource allocation of PCH and DL-SCH, and Hybrid ARQ information.
Physical Downlink Shared Channel (PDSCH) : Carries the downlink user data.
Physical Control Format Indicator Channel (PCFICH) : Carriers information of the OFDM symbols number used for the PDCCH.
Physical Hybrid ARQ Indicator Channel (PHICH) : Carries Hybrid ARQ ACK/NACK in response to uplink transmissions.
Physical Multicast Channel (PMCH) : Carries the multicast information.
Uplink Channels： Physical Random Access Channel (PRACH) : Carries the
random access preamble.
Physical Uplink Shared Channel (PUSCH) : Carries the uplink user data.
Physical Uplink Control Channel (PUCCH) : Carries the HARQ ACK/NACK, Scheduling Request (SR) and Channel Quality Indicator (CQI), etc.
BCH PCH DL-SCHMCH
DownlinkPhysical channels
DownlinkTransport channels
PBCH PDSCHPMCH PDCCH
Mapping between downlink transport channels and downlink physical
channels
Physical Layer MAC Layer
UplinkPhysical channels
UplinkTransport channels
UL-SCH
PUSCH
RACH
PUCCHPRACH
Mapping between uplink transport channels and downlink physical
channels
Physical Layer
MAC Layer
The downlink transmission uses the OFDM with cyclic prefix . Some of the reasons for using OFDM are given below:
Multiple carrier modulation (MCM) helps in countering the frequency selective fading as the channel appears to have nearly flat frequency response for the narrow band subcarrier.
The frequency range of the resource block and the number of resource blocks can be changed (or adapted to the channel condition) allowing flexible spectrum allocation.
Higher peak data rates can be achieved by using multiple resource blocks and not by reducing the symbol duration or using still higher order modulation thereby reducing the receiver complexity.
The multiple orthogonal subcarriers inherently provides higher spectral efficiency. The cyclic prefix (CP) is the partial repetition of the bit/symbol sequence from the end to the
beginning. This makes the time domain input sequence to appear periodic over a duration so that the DFT representation is possible for any frequency domain processing. Also the duration if chosen larger than the channel delay spread, will help in reducing the inter-symbol interference.
The following pilot signals are defined for the downlink physical layer:
Reference signal: The reference signal consists of known symbols transmitted at a well defined
OFDM symbol position in the slot. This assists the receiver at the user terminal in estimating the channel impulse response so that channel distortion in the received signal can be compensated for. There is one reference signal transmitted per downlink antenna port and an exclusive symbol position is assigned for an antenna port (when one antenna port transmits a reference signal other ports are silent).
Synchronization signal: Primary and secondary synchronization signals are transmitted at a fixed subframes (first and sixth) position in a frame and assists in the cell search and synchronization process at the user terminal. Each cell is assigned unique Primary sync signal.
The uplink transmission uses the SC-FDMA (Single Carrrier FDMA) scheme. The SC-FDMA scheme is realized as a two stage process where the first stage transforms the input signal to frequency domain (represented by DFT coefficients) and the second stage converts these DFT coefficients to an OFDM signal using the OFDM scheme. Because of this association with OFDM, the SC-FDMA is also called as DFT-Spread OFDM. The reasons (in addition to those applicable for OFDM for downlink) for this choice are given below:
The two stage process allows selection of appropriate frequency range for the subcarriers while mapping the set of DFT coefficients to the Resource Blocks. Unique frequency can be allocated to different users at any given time so that there is no co-channel interference between users in the same cell. Also channels with significant co-channel interference can be avoided.
The transformation is equivalent to shift in the center frequency of the single carrier input signal. The subcarriers do not combine in random phases to cause large variation in the instantaneous power of the modulated signal. This means lower PAPR (Peak to Average Power Ratio).
The PAPR (Peak to Average Power Ratio) of SC-FDMA is lesser than that of the conventional OFDMA, so the RF power amplifier (PA) can be operated at a point nearer to recommended operating point. This increases the efficiency of a PA thereby reducing the power consumption at the user terminal.
The following pilot signals are defined for the uplink physical layer: Demodulation Reference signal: This signal send by the user terminal along with the uplink
transmission, assists the network in estimating the channel impulse response for the uplink bursts so as to effectively demodulate the uplink channel.
Sounding Reference Signal: This signal is sent by the user terminal assists the network in estimating the overall channel conditions and to allocate appropriate frequency resources for uplink transmission.
Downlink Modulation Schemes
Uplink Modulation Schemes
Phy Ch Modulation
Scheme Phy Ch
Modulation Scheme
PBCH QPSK PCFICH QPSK
PDCCH QPSK PHICH BPSK
PDSCH QPSK, 16QAM, 64QAM PMCH QPSK, 16QAM, 64QAM
Phy Ch Modulation Scheme
PUCCH BPSK, QPSK
PUSCH QPSK, 16QAM, 64QAM
PRACH Zadoff-Chu
Local cell identity = 1 Cell name = DXBL32331 Sector No. = 1 Csg indicator = False Uplink cyclic prefix length = Normal Downlink cyclic prefix length = Normal Frequency band = 3 Uplink earfcn indication = Not configure Uplink earfcn = NULL Downlink earfcn = 1850 Uplink bandwidth(MHz) = 20M Downlink bandwidth(MHz) = 20M Cell identity = 1 Physical cell identity = 66 Additional spectrum emission = 1 Cell active state = Active Cell admin state = Unblock Cell middle block timer(min) = NULL
Cell FDD TDD indication = FDD Subframe assignment = NULL Special subframe patterns = NULL Cell specific offset(dB) = 0dB Intra frequency offset(dB) = 0dB Root sequence index = 728 High speed flag = Low speed cell flag Preamble format = 0 Cell radius(m) = 10000 Customization bandwidth configure indicator = Not
configure Customization real uplink bandwith(0.1MHz) = NULL Customization real downlink bandwidth(0.1MHz) = NULL
Page 36
Separate antenna/feeder for LTE
LTE 2G/3G
Disadvantage: Require more tower
installation space;
Require higher tower load.
Advantage: Individual network planning
for LTE: No additional feeder and
connector loss for LTE; No negative impact to
2G/3G network. Convenience and accuracy
network optimization for LTE: Individual antenna
adjustment
Conclusion: Select the Co-antenna/feeder solution
based on the real situation Need to evaluate and balance the
benefits and risks of the solution
LTE LTE LTE
4 ports antenna Co-feeder
Risks: Additional loss by co-feeder will: Reduce 11~14% cell radius Increase 26~35% site quantity (2.6GHz, 30m 7/8’’ feeder)
2 ports antenna Co-feeder
4 ports antenna RRU inst. near antenna
In LTE there are only Two States: ◦ Idle Mode ◦ Connected Mode
As for UMTS, there were five UE States: ◦ Idle ◦ Cell_FACH ◦ Cell_DCH ◦ Cell_PCH ◦ URA_PCH
Basic Principle of Cell Search: Cell search is the procedure of UE synchronizes with E-UTRAN in time-freq domain, and acquires the serving cell ID.
Two steps in cell search:
Step 1: Symbol synchronization and acquirement of ID within Cell Group by demodulating the Primary Synchronization Signal;
Step 2: Frame synchronization, acquirement of CP length and Cell Group ID by demodulating the Secondary Synchronization Signal.
Initial Cell Search: The initial cell search is carried on after the UE power on. Usually, UE doesn’t know the network bandwidth and carrier
frequency at the first time switch on.
UE repeats the basic cell search, tries all the carrier frequency in the spectrum to demodulate the synchronization signals. This procedure takes time, but the time requirement are typically relatively relaxed. Some methods can reduce time, such as recording the former available network information as the prior search target.
Once finish the cell search, which achieve synchronization of time-freq domain and acquirement of Cell ID, UE demodulates the PBCH and acquires for system information, such as bandwidth and Tx antenna number.
After the procedure above, UE demodulates the PDCCH for its paging period that allocated by system. UE wakes up from the IDLE state in the specified paging period, demodulates PDCCH for monitoring paging. If paging is detected, PDSCH resources will be demodulated to receive paging message.
Basic Principle of Random Access :
Random access is the procedure of uplink synchronization between UE and E-UTRAN.
Prior to random access, physical layer shall receive the following information from the higher layers:
Random access channel parameters: PRACH configuration, frequency position and preamble format, etc.
Parameters for determining the preamble root sequences and their cyclic shifts in the sequence set for the cell, in order to demodulate the random access preamble.
Two steps in physical layer random access: UE transmission of random access preamble
Random access response from E-UTRAN
Basic Principle of Power Control:
Downlink power control determines the EPRE (Energy per Resource Element);
Uplink power control determines the energy per DFT-SOFDM (also called SC-FDMA) symbol.
Downlink Power Control: The transmission power of downlink RS is usually constant. The transmission power of PDSCH is
proportional with RS transmission power.
Downlink transmission power will be adjusted by the comparison of UE report CQI and target CQI during the power control.
Uplink Power Control: Uplink power control consists of opened loop power and closed loop power control.
A cell wide overload indicator (OI) is exchanged over X2 interface for integrated inter-cell power control, possible to enhance the system performance through power control.
PUSCH, PUCCH, PRACH and Sounding RS can be controlled respectively by uplink power control. Take PUSCH power control for example:
PUSCH power control is the slow power control, to compensate the path loss and shadow fading and control inter-cell interference. The control principle is shown in above equation. The following factors impact PUSCH transmission power PPUSCH: UE maximum transmission power PMAX, UE allocated resource MPUSCH, initial transmission power PO_PUSCH, estimated path loss PL, modulation coding factor △TF and system adjustment factor f (not working during opened loop PC)
UE report CQI
DL Tx Power
X2
UL Tx Power
System adjust parameters
The uplink uses three physical channels: • Physical uplink shared channel (PUSCH): This carries the uplink shared channel. It can also carry the uplink control information, if a mobile needs to transmit data and control information at the same time. • Physical uplink control channel (PUCCH): This carries the uplink control information, if the mobile does not need to transmit data at the same time. • Physical random access channel (PRACH): This carries the random access channel. The downlink uses six: • Physical downlink shared channel (PDSCH): This carries the downlink shared channel and the paging channel. • Physical multicast channel (PMCH): This carries the multicast channel. • Physical broadcast channel (PBCH): This carries the broadcast channel. • Physical control format indicator channel (PCFICH): This carries the control format indicators. • Physical downlink control channel (PDCCH): This carries the downlink control information. • Physical hybrid ARQ indicator channel (PHICH): This carries the hybrid ARQ indicators.
64QAM only used by Category 5 UE Assumption: Ideal channel conditions with
optimum coding rate (approximately .98)
LTE UE testing includes a large number of test
configurations. Configurations should include support for: 5, 10, 15 and 20 MHz bands ◦ UE categories 1-4 ◦ Up to 2x2 MIMO ◦ Periodic, aperiodic and closed loop CQI, PMI, RI ◦ Variety of handover scenarios ◦ UL sequence and frequency hopping ◦ All the required DCI formats ◦ DL distributed VRB (virtual RB) ◦ MU-MIMO ◦ Scheduling ◦ TTI bundling ◦ HARQ
The above are just examples. Total number of features and configurations is extremely large due to the considerable complexity of the LTE standards.
Reference signal received power (RSRP) identifies the signal level of the Reference Signal. It is defined ◦ as the linear average over the power contributions
of the resource elements that carry cell-specific reference signals within the considered measurement frequency bandwidth.
Reference Signal Received Quality (RSRQ) identifies the quality of the Reference Signal. It is defined as ◦ the ratio N×RSRP/(E-UTRA carrier RSSI), where N is the
number of RB"s of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator shall be made over the same set of resource blocks.
◦ E-UTRA Carrier Received Signal Strength Indicator (RSSI), comprises the linear average of the total received power observed only in OFDM symbols containing reference symbols for antenna port 0, in the measurement bandwidth, over N number of resource blocks by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc
Every EPS bearer ◦ QoS class identifier (QCI) ◦ Allocation and retention priority (ARP)
Every GBR bearer ◦ Guaranteed bit rate (GBR) ◦ Maximum bit rate (MBR) ◦ Non-GBR bearers, collectively ◦ Per APN aggregate maximum bit rate (APN-AMBR) ◦ Per UE aggregate maximum bit rate (UE-AMBR)
Every EPS bearer is associated with a number called the QoS class identifier (QCI).
Network nodes use the QCI as a reference, so as to look up the parameters that control the
way in which packets from that data stream are forwarded. Example parameters include
scheduling weights and queue management thresholds. Some QCI values have been standardised, and are
associated with quality-of-service parameters that are listed in the table above. The
parameters are as follows: • QCI: Standardised QoS class identifier. Other values can
be defined by the network operator. • Bearer: Whether or not the bearer has a guaranteed bit
rate. • Priority: This affects the scheduling at the network
nodes. 1 is the highest priority. • Delay: Upper bound (with 98% confidence) for the delay
that a packet can experience between the UE and the P-GW. • Packet error loss rate (PELR): Upper bound for the
proportion of packets that are lost. (Non-GBR services can experience additional packet
loss due to congestion.)
Test Items PCI (Planned) PCI (Test) MIMO (2X2) Sector Swap (LTE) Sector Swap (3G) if Antenna is replaced
Coverage (RSRP > -90dbm) Quality (RSRQ > -10db)
S1-MME Reference point for the control plane protocol between EUTRAN and MME. The protocol over this reference point is eRANAP and it uses Stream Control Transmission Protocol (SCTP) as the transport protocol
S1-U Reference point between EUTRAN and SGW for the per-bearer user plane tunneling and inter-eNB path switching during handover. The transport protocol over this interface is GPRS Tunneling Protocol-User plane (GTP-U)
S2a It provides the user plane with related control and mobility support between trusted non-3GPP IP access and the Gateway. S2a is based on Proxy Mobile IP. To enable access via trusted non-3GPP IP accesses that do not support PMIP, S2a also supports Client Mobile IPv4 FA mode
S2b It provides the user plane with related control and mobility support between evolved Packet Data Gateway (ePDG) and the PDN GW. It is based on Proxy Mobile IP
S2c It provides the user plane with related control and mobility support between UE and the PDN GW. This reference point is implemented over trusted and/or untrusted non-3GPP Access and/or 3GPP access. This protocol is based on Client Mobile IP co-located mode
S3 It is the interface between SGSN and MME and it enables user and bearer information exchange for inter 3GPP access network mobility in idle and/or active state. It is based on Gn reference point as defined between SGSNs
S4 It provides the user plane with related control and mobility support between SGSN and the SGW and is based on Gn reference point as defined between SGSN and GGSN
S5 It provides user plane tunneling and tunnel management between SGW and PDN GW. It is used for SGW relocation due to UE mobility and if the SGW needs to connect to a non-collocated PDN GW for the required PDN connectivity. Two variants of this interface are being standardized depending on the protocol used, namely, GTP and the IETF based Proxy Mobile IP solution
S6a It enables transfer of subscription and authentication data for authenticating/ authorizing user access to the evolved system (AAA interface) between MME and HSS
S7 It provides transfer of (QoS) policy and charging rules from Policy and Charging Rules Function (PCRF) to Policy and Charging Enforcement Function (PCEF) in the PDN GW. This interface is based on the Gx interface
S10 Reference point between MMEs for MME relocation and MME to MME information transfer
S11 Reference point between MME and SGW SGi It is the reference point between the PDN GW and the packet data network. Packet
data network may be an operator-external public or private packet data network or an intra-operator packet data network, e.g. for provision of IMS services. This reference point corresponds to Gi for 2G/3G accesses
Rx+ The Rx reference point resides between the Application Function and the PCRF in the 3GPP TS 23.203
Wn* This is the reference point between the Untrusted Non-3GPP IP Access and the ePDG. Traffic on this interface for a UE initiated tunnel has to be forced towards ePDG.
3GPP TS 36.201: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; General description".
3GPP TS 36.211-Evolved Universal Terrestrial Radio Access E-UTRA Physical Channels and Modulation
3GPP TS 36.133 (EUTRA Requirements and Radio Resource Management)
http://en.wikipedia.org/wiki/3GPP_Long_Term_Evolution
UMTS –Global Standard for 3G Wireless Communication (NUST Lecture by Shariq Yasin)
http://sites.google.com/site/lteencyclopedia/home
