Long Term Evolution - Advanced (LTE-Advanced)

Long Term Evolution - Advanced (LTE-Advanced)

OFDMA & SC-OFDMA LTE employs Orthogonal Frequency Division Multiple Access (OFDMA) for downlink data transmission Single Carrier FDMA (SC-FDMA) for uplink transmission

FDM vs. OFDM Improved spectral efficiency The amplitude of each sub-carrier oscillates either side of zero and crosses through zero at regular intervals The peak response of one sub-carrier coincides with zeros of all the others

LTE Uplink (SC-FDMA) SC-FDMA is a new single carrier multiple access technique which has similar structure and performance to OFDMA A salient advantage of SC-FDMA over OFDM is low to Peak to Average Power Ratio (PAPR) and thus increase battery life

OFDM Time Frequency Representation Fourier analysis converts a signal from its original domain (often time or space) to a representation in the frequency domain and vice versa.

Frame Structure Two radio frame structures defined Frame structure type 1 (FS1): FDD Frame structure type 2 (FS2): TDD 1 frame has duration of 10 ms = 10 subframes 1 subframes has duration of 1 ms = 2 slots 1 slot has duration of 0.5 ms 1 subcarrier has bandwidth of 15 khz A resource block (RB) spans 12 subcarriers of 180 khz over a slot duration of 0.5 ms

Frame Structure Type 1 (FDD) 1 frame has duration of 10 ms = 10 subframes 1 subframes has duration of 1 ms = 2 slots 1 slot has duration of 0.5 ms

Frame Structure Type 2 (TDD) 1 frame has duration of 10 ms = 10 subframes 1 subframes has duration of 1 ms = 2 slots 1 slot has duration of 0.5 ms

Resource Grid 0.5ms 180kHz 1 slot has duration of 0.5 ms (each symbol 66.7 us) 1 subcarrier has bandwidth of 15 khz A resource block (RB) spans 12 subcarriers of 180 khz over a slot duration of 0.5 ms

In OFDMA, the BS shares its resources by transmitting to the mobiles at different times and frequencies, so as to meet the requirements of individual applications

Example UE1 receiving a voice over IP stream the data rate, and the num of sub-carriers, is low but constant UE2 receiving a stream of non real time packet data the average data rate is higher the data come in bursts, so the num of sub-carriers can vary

The BS can also respond to frequency dependent fading, by allocating subcarriers on which the mobile is receiving a strong signal UE3 is receiving a VoIP stream, but it is also affected by frequency dependent fading the BS allocates sub-carriers on which the mobile is receiving a strong signal, and changes this allocation as the fading pattern changes

System Architecture

Evolved Packet System (EPS) has three main components User Equipment (UE) Evolved UMTS Terrestrial Radio Access Network (E- UTRAN) Evolved Packet Core (EPC) EPC communicates with Packet Data Networks (PDN) in the outside world such as Internet, private corporate networks or IMS Interfaces between different parts of the system are denoted Uu, S1 and SGi

Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) Handles the radio communications between mobile and EPC Just has one component, evolved Node B (enb)

enb has two main functions enb sends radio transmissions to all its mobiles on the downlink and receives transmissions from them on the uplink, using the analogue and digital signal processing functions of the LTE air interface enb controls the low-level operation of all its mobiles, by sending them signaling messages such as handover commands that relate to those radio transmissions enb combines the earlier functions of Node B and Radio Network Controller (RNC), to reduce the latency that arises when the mobile exchanges information with the network

enb interfaces enb is connected to EPC by S1 interface enb is connected to nearby enb by X2 interface mainly used for signaling and packet forwarding during handover X2 interface is optional - S1 interface can also handle all the functions of X2, though indirectly and more slowly

Home enb (HeNB) a base station to provide femtocell coverage within the home belongs to a Closed Subscriber Group (CSG) and can only be accessed by mobiles with a USIM that also belongs to the CSG HeNB can be connected directly to the EPC in the same way as any other base station, or by way of an intermediate device known as a home enb gateway that collects the information from several HeNBs Only control one cell, and do not support X2 interface until Release 10

Evolved Packet Core Main components of EPC P-GW:Packet Data Network (PDN) Gateway S-GW:Serving Gateway MME:Mobility Management Entity Home Subscriber Server (HSS) a central database that contains information about all the network operator s subscribers the components of LTE carried forward from UMTS and GSM

Main components of the EPC

Packet Data Network (PDN) Gateway (P-GW) EPC s point of contact with outside world through the SGi interface, each P- GW exchanges data with one or more external devices or PDNs, such as network operator s servers, Internet or IMS each packet data network (PDN) is identified by an Access Point Name (APN) a network operator typically uses a handful of different APNs, e.g., one for its own server and one for Internet

Serving Gateway (S- GW) Acts as a router, and forwards data between enb and P-GW each mobile is assigned to a single S-GW but the S-GW can be changed if the mobile moves sufficiently far

Mobility Management Entity (MME) controls the high-level operation of the mobile, by sending it signaling messages about issues such as security and the management of data streams that are unrelated to radio communications each mobile is assigned to a single MME which is known as its serving MME that can be changed if the mobile moves sufficiently far

Comparison with UMTS and GSM P-GW has the same role as the gateway GPRS support node (GGSN) S-GW and MME handle the data routing and signaling functions of the serving GPRS support node (SGSN) Splitting SGSN in two makes it easier for an operator to scale the network in response to an increased load add more S-GWs as the traffic increases add more MMEs to handle an increase in the number of mobiles S1 interface has two components - S1-U interface carries traffic for S- GW - S1-MME interface carries signaling messages for MME

EPC has some other components Cell Broadcast Centre (CBC) previously used by UMTS for Cell Broadcast Service (CBS) in LTE, the equipment is re-used for a service known as Earthquake and Tsunami Warning System (ETWS) Equipment Identity Register (EIR) also inherited from UMTS, and lists the details of lost or stolen mobiles

Roaming Architecture Roaming allows users to move outside their network operators coverage area by using the resources from two different networks Relies on the existence of a roaming agreement, which defines how the operators will share the resulting revenue Architecture of LTE for a roaming mobile

If a user is roaming Home Subscriber Server (HSS) is always in the home network the mobile, E-UTRAN, MME and S-GW are always in the visited network P-GW can be in two places Home routed traffic P-GW lies in the home network, through which all the user s traffic is all routed allows the home network operator to - see all the traffic - charge the user for it directly can be inefficient if the user is traveling overseas, particularly during a voice call with another user nearby Local breakout P-GW is located in the visited network

The interface between S-GW and P-GWs is S5/S8 S5: if two devices are in the same network S8: if two devices are in different networks For mobiles that are not roaming S-GW and P-GWs can be integrated into a single device, so that the S5/S8 interface vanishes altogether

Protocol Model The protocol stack has two planes user plane protocols handle data that are of interest to the users control plane protocols handle signaling messages that are only of interest to the network elements themselves High level protocol architecture of LTE

The protocol stack also has two main layers upper layer manipulates information in a way that is specific to LTE in the E-UTRAN, known as radio network layer lower layer transports information from one point to another in the E-UTRAN, known as transport network layer upper lower High level protocol architecture of LTE

There are then three types of protocol signaling protocols define a language by which two devices can exchange signaling messages with each other user plane protocols manipulate the data in the user plane, most often to help route the data within the network High level protocol architecture of LTE underlying transport protocols transfer data and signaling messages from one point to another

On the air interface, there is an extra level of complexity MME controls the high-level behavior of mobile by sending it signaling messages no direct path between MME and mobile The access stratum and non access stratum on the air interface the air interface is divided into Access Stratum (AS) Non Access Stratum (NAS) High-level signaling messages lie in NAS and are transported using AS protocols of S1 and Uu interfaces

Air Interface Transport Protocols The air interface, Uu, lies between mobile and BS The air interface s transport protocols starting at the bottom physical layer contains the digital and analogue signal processing functions that the mobile and BS use to send and receive information Transport protocols used on the air interface

The next three protocols make up data link layer, the layer 2 of OSI model Packet Data Convergence Protocol (PDCP) carries out higher-level transport functions that are related to header compression and security Radio Link Control (RLC) protocol maintains the data link between the two devices, e.g., by ensuring reliable delivery for data streams that need to arrive correctly Transport protocols used on the air interface Medium Access Control (MAC) protocol carries out low-level control of the physical layer, particularly by scheduling data transmissions between mobile and BS

Fixed Network Transport Protocols Each interface in the fixed network uses standard IETF transport protocols These interfaces use protocols from layers 1 to 4 of the usual OSI model The transport network can use any suitable protocols for layers 1 and 2, such as Ethernet Every network element is then associated with an IP address, and the fixed network uses the Internet Protocol (IP) to route information from one element to another across underlying transport network Transport protocols used by the fixed network

LTE supports both IPv4 and IPv6 for this task in the EPC, support of IPv4 is mandatory and support of IPv6 is recommended in the radio access network, use either or both of the two protocols Transport protocols used by the fixed network

The transport layer protocol across the interface between each individual pair of network elements User Datagram Protocol (UDP) just sends data packets from one network element to another Transmission Control Protocol (TCP) re-transmits packets if they arrive incorrectly Stream Control Transmission Protocol (SCTP) based on TCP, but includes extra features that make it more suitable for the delivery of signaling messages

User plane always uses UDP as its transport protocol, to avoid delaying the data Control plane its choice depends on the overlying signaling protocol

User Plane Protocols LTE user plane contains mechanisms to forward data correctly between mobile and P-GW respond quickly to changes in the mobile s location These mechanisms are implemented by user plane protocols User plane protocols used by LTE

Most of the user plane interfaces use a 3GPP protocol known as GPRS Tunneling Protocol User part (GTP-U) GTPv1-U LTE uses version 1 of the protocol along with the 2G and 3G packet switched domains from Release 99 GTPv0-U earlier 2G networks used version 0 User plane protocols used by LTE

Between S-GW and P-GW, the S5/S8 user plane has an alternative implementation, known as Generic Routing Encapsulation (GRE) GTP-U and GRE forward packets from one network element to another using a technique known as tunneling

Signaling Protocols LTE uses a large number of signaling protocols

Radio Resource Control (RRC) protocol BS controls a mobile s radio communications S1 Application Protocol (S1-AP) MME controls BSs X2 application protocol (X2-AP) communication between two BSs

MME controls a mobile s high-level behavior using EPS Session Management (ESM) controls the data streams through which a mobile communicates with the outside world EPS Mobility Management (EMM) handles internal bookkeeping within EPC The network transports EMM and ESM messages by embedding them into lower-level RRC and S1-AP messages and then using the transport mechanisms of the Uu and S1 interfaces

Inside the EPC, HSS and MME communicate using a protocol based on Diameter Basic Diameter protocol a standard IETF protocol for authentication, authorization and accounting based on an older protocol known as Remote Authentication Dial In User Service (RADIUS) can be enhanced for use in specific applications: the implementation of Diameter on the S6a interface

Most of the other EPC interfaces use a 3GPP protocol known as GPRS Tunneling Protocol Control part (GTP-C) control plane LTE uses version 2 of the protocol, GTPv2-C If the S5/S8 user plane is using GRE, then its control plane uses a signaling protocol known as Proxy Mobile IPv6 (PMIPv6) PMIPv6 is a standard IETF protocol for the management of packet forwarding, in support of mobile devices such as laptops user plane

Operators of legacy 3GPP networks control plane prefer GTP-U and GTP-C, for consistency with their previous systems and with other signaling interfaces in the EPC Operators of non 3GPP networks prefer GRE and PMIP, which are standard IETF protocols, and which are also used for inter-operation between LTE and non 3GPP technologies user plane

Signaling Radio Bearers LTE uses three special radio bearers, known as Signaling Radio Bearers (SRBs), to carry signaling messages between mobile and BS Each of the signaling radio bearers (SRB) is associated with a specific configuration of the air interface protocols, so that the mobile and BS can agree on how the signaling messages should be transmitted and received Signaling radio bearers

SRB0 only used for a few RRC signaling messages, which the mobile and BS use to establish communications in RRC connection establishment procedure its configuration is defined in special RRC messages known as system information messages, which the BS broadcasts across the whole of the cell to tell the mobiles about how the cell is configured

SRB1 configured using signaling messages that are exchanged on SRB0, at the time when a mobile establishes communications with the radio access network used for all subsequent RRC messages, and also transports a few EMM and ESM messages that are exchanged prior to the establishment of SRB2 SRB2 configured using signaling messages that are exchanged on SRB1, at the time when the mobile establishes communications with EPC used to transport all the remaining EMM and ESM messages

Spectrum Allocation The 3GPP specifications allow mobiles and BSs to use a large number of frequency bands The following tables list the bands that support Frequency Division Duplex (FDD) mode and Time Division Duplex (TDD), respectively The tables also show the first release in which each band was introduced Most of the bands are also supported by other systems such as UMTS and GSM

FDD frequency bands (Reproduced by permission of ETSI)

TDD frequency bands (Reproduced by permission of ETSI)

Some of these frequency bands are being released for use by mobile telecommunications in 2008, the US Federal Communications Commission (FCC) auctioned frequencies around 700MHz (FDD bands 12, 13, 14 and 17) that had previously been used for analogue television broadcasting in Europe, similar auctions have been taking place for frequencies around 800 and 2600MHz (FDD bands 7 and 20, and TDD band 38) Network operators can also re-allocate frequencies that they have previously used for other mobile communication systems, as their users migrate to LTE FDD bands 1, 3 and 8 in Europe (originally used by WCDMA, GSM 1800 and GSM 900 respectively) FDD bands 2, 4 and 5 in the USA The result is that LTE is likely to be deployed in a large number of frequency bands, with different bands used by different regions, countries and network operators

4G ( )(2013) 700 MHz 頻段 :(4 個區塊頻譜 ) ( )A1: 上 703~713MHz; 下 758~768MHz( 上下 各 10MHz) ( )A2: 上 713~723MHz; 下 768~778MHz( 上下 各 10MHz) ( 三 )A3: 上 723~733MHz; 下 778~788MHz( 上下 各 10MHz) ( 四 )A4: 上 733~748MHz; 下 788~803MHz( 上下 各 15MHz) 900MHz 頻段 :(3 個區塊頻譜 ) ( )B1: 上 885~895MHz; 下 930~940MHz( 上下 各 10MHz) ( )B2: 上 895~905MHz; 下 940~950MHz( 上下 各 10MHz) ( 三 )B3: 上 905~915MHz; 下 950~960MHz( 上下 各 10MHz) 三 1800 MHz 頻段 :(5 個區塊頻譜 ) ( )C1: 上 1710~1725MHz; 下 1805~1820MHz( 上下 各 15MHz) ( )C2: 上 1725~1735MHz; 下 1820~1830MHz( 上下 各 10MHz) ( 三 )C3: 上 1735~1745MHz; 下 1830~1840MHz( 上下 各 10MHz) ( 四 )C4: 上 1745~1755MHz; 下 1840~1850MHz( 上下 各 10MHz) ( 五 )C5: 上 1755~1770MHz; 下 1850~1865MHz( 上下 各 15MHz)

FDD Band7 TDD Band38 TDD Band41

Enhancements in Release 9 Multimedia Broadcast/Multicast Service (MBMS) Location services Dual layer beamforming Commercial mobile alert system

Multicast/Broadcast over a Single Frequency Network When delivering a broadcast or multicast service the radio access network transmits the same information stream from several nearby cells Multicast/broadcast over a single frequency network LTE exploits this feature to improve the transmission of broadcast and multicast services, using the technique of MBSFN

Using MBSFN nearby BSs - synchronized so that they broadcast the same content at the same time and on the same sub-carriers mobile - receives multiple copies of the information which are identical except for their different arrival times, amplitudes and phases - process the information streams using exactly the same techniques for handling multipath

Because the extra cells are transmitting the same information stream they do not cause any interference to the mobile instead, they contribute to the received signal power - this increases the mobile s SINR and maximum data rate, particularly at the edge of the cell where interference is usually high this allows LTE to reach a target spectral efficiency of 1 b/s/hz for the delivery of MBMS - equivalent to 16 mobile TV channels in a 5MHz bandwidth at a rate of 300 kbps each (= 5MHz / 16)

Architecture of MBMS Broadcast/Multicast Service Center (BM-SC) receives MBMS content from a content provider MBMS GateWay (MBMS-GW) distributes the content to the appropriate BSs Multicell/Multicast Coordination Entity (MCE) schedules the transmissions from all the BSs in a single MBSFN area Delivery of MBMS over LTE architecture

BM-SC (Broadcast/Multicast Service Center) indicates the start of each MBMS session by sending a signaling message across the SGmb interface the message describes the session s QoS and tells the MBMS GW to reserve resources for it the message is propagated across Sm, M3 and M2 interfaces M2 interface also defines - modulation scheme - coding rate - the subframe allocation that the BSs in the MBSFN area should use

BM-SC (Broadcast/Multicast Service Center) BM-SC then broadcasts the data across SGi-mb interface using IP multicast MBMS GW (MBMS GateWay) forwards data to the appropriate BSs across M1 interface, along with a header that indicates each packet s transmission time with an accuracy of 10 ms enb by combining the above info with the scheduling info that it receives from the multicell/multicast coordination entity, the BS can establish the exact transmission time for each packet

Location Services Location services (LCS) or Location Based Services (LBS), allow an application to find out the geographical location of a mobile The biggest motivation is emergency calls in USA, the FCC requires network operators to localize an emergency call to an accuracy between 50 and 300 meters, depending on the type of positioning technology used LCSs are also of increasing importance to the user, for applications such as navigation and interactive games Other applications include lawful interception by the police or security services use of a mobile s location to support network-based functions such as handover

Positioning Techniques LTE can calculate a mobile s position using three different techniques The most accurate and increasingly common technique is the use of a Global Navigation Satellite System (GNSS), a collective term for satellite navigation systems such as the Global Positioning System (GPS)

Global Navigation Satellite System (GNSS) two variants - UE based positioning the mobile has a complete satellite receiver and the mobile calculates its own position the network can send it information to assist this calculation, such as an initial position estimate and a list of visible satellites - UE assisted positioning the mobile has a more basic satellite receiver, so it sends a basic set of measurements to the network the network calculates its position positioning accuracy - typically around 10 meters

The second technique is downlink positioning or Observed Time Difference of Arrival (OTDOA) - the mobile measures the times at which signals arrive from its serving cell and the nearest neighbors reports the time differences to the network - the network calculate the mobile s position by triangulation - the timing measurements are made on a new set of positioning reference signals, which are transmitted on a new antenna port, number 6

- positioning accuracy limited by multipath typically to around 100 meters, has difficulty in meeting the requirements of US FCC - it is often used as a backup to satellite positioning, as a mobile may not be able to receive a satisfactory satellite signal if it is surrounded by tall buildings or is indoors

The last technique is Enhanced cell ID positioning (ECID) the network - estimates the mobile s position from its knowledge of the serving cell identity Round Trip Time (RTT), between the base station and the UE, to estimate the distance to the UE Angle of Arrival (AoA) of signals from the UE to provide directional information positioning accuracy - depends on the cell size - excellent in femtocells (provided that the BS s position is actually known) - very poor in macrocells ECID positioning

The figure shows the main hardware components that LTE uses for LCSs Gateway Mobile Location Center (GMLC) receives location requests from external clients across Le interface retrieves the identity of the mobile s serving MME from HSS forwards the location request to MME MME delegates responsibility for calculating a mobile s position to Evolved Serving Mobile Location Center (E-SMLC) Architecture for location services in LTE

Two other components can be separate devices or can be integrated into GMLC Privacy Profile Register (PPR) - contains the users privacy details, which determine whether a location request from an external client will actually be accepted Pseudonym [ 假名 ] Mediation [ 調節 ] Device (PMD) - retrieves a mobile s IMSI using the identity supplied by the external client

The architecture uses several signaling protocols GMLC communicates with HSS and MME - using Diameter applications MME communicates with E-SMLC - using LCS application protocol (LCS-AP) MME can also send positioning-related information to mobile EMM Diameter OSA - using supplementary service (SS) messages that are embedded into EMM messages on the air interface LCS-AP Diameter E-SMLC communicates with mobile and BS - using LTE positioning protocol (LPP), the messages being transported by embedding them into lower-level LCS-AP and EMM messages GMLC can communicate with external client - using a few different techniques, such as Open Service Architecture (OSA)

Dual Layer Beamforming In dual layer beamforming, the BS transmits two simultaneous data streams using the same set of resource blocks, by processing the data using two parallel sets of antenna weights It can then direct the data either to two different mobiles, or to two antennas on the same mobile

BS configures the mobile into a new transmission mode, mode 8, and schedules it using a new DCI format, 2B DCI Downlink Control Information

It then transmits to the mobile using either or both of two new antenna ports, numbers 7 and 8 Ports 7 and 8 use a new set of UE-specific reference signals, which behave in the same way as the reference signals used for single layer beamforming on port 5

Commercial Mobile Alert System US FCC established the Commercial Mobile Alert System (CMAS) in response to US Warning Alert and Response Network act of 2006 Using this system, participating network operators can transmit three types of emergency message presidential alerts about local, regional or national emergencies imminent [ 緊迫, 眉睫 ] threat alerts about natural disasters such as hurricanes child abduction emergency alerts

In Release 9, LTE supports CMAS by generalizing its earthquake and tsunami warning system to a Public Warning System (PWS) that covers both types of information BS continues to send earthquake and tsunami warnings on SIBs 10 and 11 transmits commercial mobile alerts on a new system information block, SIB 12

Enhancements in Release 10 (LTE-Advanced) Carrier Aggregation Enhancements to multiple antenna transmission on uplink and downlink Enhanced Downlink MIMO Enhanced Uplink MIMO Relays

Carrier Aggregation The ultimate goal of LTE-Advanced is to support a maximum bandwidth of 100 MHz It is most unlikely to be available as a contiguous allocation in the foreseeable future LTE-Advanced allows a mobile to transmit and receive on up to five component carriers (CC), each of which has a max bandwidth of 20 MHz using Carrier Aggregation (CA)

Three scenarios of Carrier Aggregation Inter-band aggregation - CCs are located in different frequency bands - this is the most challenging scenario, because mobile may require different radio components to support each band cell s coverage area in each band may be very different - the component carriers are separated by a multiple of 100 khz, which is the usual LTE carrier spacing

Contiguous intra-band aggregation CCs are in the same band and are adjacent to each other they are separated by a multiple of 300 khz, which is consistent with the orthogonality requirement, so that different sets of subcarriers are orthogonal to each other and do not interfere Non contiguous intra-band aggregation CCs are in the same band

Carrier aggregation only affects physical layer Media Access Control (MAC) protocol on the air interface RRC, S1-AP and X2-AP signaling protocols There is no impact on Radio link control (RLC) Packet Data Convergence Protocols (PDCP) data transport in the fixed network

Scheduling in Release 10, each CC independently scheduled generates an independent set of hybrid ARQ feedback bits (HARQ = FEC + ARQ) the system does, however, support cross carrier scheduling BS can trigger an uplink or downlink transmission on one CC using a scheduling message on another

Release 10 implements cross carrier scheduling by adding a Carrier Indicator Field (CIF) to each DCI format, which indicates the carrier to be used for the subsequent transmission Using cross carrier scheduling DCI Downlink Control Information BS can transmit its scheduling messages on the CC that has the greatest coverage, so as to maximize the reliability of successful reception it can also use technique to balance the loads from traffic and scheduling across different CCs

Data Transmission and Reception CA does not affect data transmission in the downlink, but it does lead to some changes in the uplink Release 8 a mobile uses SC-FDMA, which assumes that the mobile is transmitting on a single contiguous block of sub-carriers Release 10 this assumption is no longer valid the mobile uses a more general technique known as Discrete Fourier Transform Spread Orthogonal Frequency Division Multiple Access (DFT-S-OFDMA) DFT-S-OFDMA is the same as SC-FDMA, except that it supports transmission on a non contiguous allocation of sub-carriers

Enhanced Downlink MIMO Release 8 includes full support for downlink single user MIMO (SU-MIMO) using - max of four antenna ports - four transmission layers includes rudimentary support for downlink multiple user MIMO (MU-MIMO)

Release 9 introduces support for dual layer beamforming BS transmits to two receive antennas that are located on one or two mobiles Release 10 the dual layer beamforming technique is extended as part of release 10, by - providing full support for downlink MU-MIMO - increasing the max no. of BS antenna ports to eight the same technique can also be used to support SU-MIMO, with a max of eight antenna ports and eight transmission layers

The peak downlink data rate in Release 10 is 1200 Mbps this is four times greater than in Release 8 and results from the use of two CCs each CC carries eight transmission layers rather than four Eventually, LTE should support a peak downlink data rate of 3000 Mbps, through the use of five CCs

Enhanced Uplink MIMO The only multiple antenna scheme supported by Release 8 uplink is MU- MIMO This increases the cell capacity while only requiring the mobile to have a single transmit power amplifier and was far easier to implement than on the downlink In LTE-Advanced (Release 10), the uplink is enhanced to support SU- MIMO, using up to four transmit antennas and four transmission layers

Release 10 only supports SU-MIMO in TDD band 40 FDD bands 1, 3 and 7 The peak uplink data rate in Release 10 is 600 Mbps this is eight times greater than in Release 8, and results from the use of four transmission layers and two CCs Eventually, LTE should support a peak uplink data rate of 1500 Mbps, through the use of five CCs

Relays Repeaters and relays are devices that extend the coverage area of a cell They are useful in sparsely populated areas, in which the performance of a network is limited by coverage rather than capacity They can also increase the data rate at the edge of a cell, by improving the SINR there

Repeater a repeater receives a radio signal from the transmitter, and amplifies and rebroadcasts it, so appears to the receiver as an extra source of multipath unfortunately the repeater amplifies the incoming noise and interference as well as the received signal, which ultimately limits its performance FDD repeaters - fully specified in Release 8 - with sole specification referring to radio performance requirements TDD repeaters - harder to implement, because of the increased risk of interference between uplink and downlink - have not yet been specified

Relay decode the received radio signal, before reencoding and rebroadcasting it it removes the noise and interference from the retransmitted signal, so can achieve a higher performance than a repeater relays are first specified in Release 10, for both FDD and TDD modes

Relaying architecture the relaying functions are implemented in Relay Node (RN) this appears to mobile as a perfectly normal BS it has one or more physical cell IDs of its own broadcasts its own synchronization signals and system information responsible for scheduling all the uplink and downlink transmissions on the Uu interface

RN is controlled by a Donor enb (DeNB), which is otherwise a normal BS that can control mobiles of its own Un interface the air interface between RN and DeNB typically implemented as a point-to-point microwave link across this interface - DeNB acts like any other BS - RN acts like a mobile

Un and Uu interfaces can use either the same carrier frequency, or different ones If the carrier frequencies are different Un interface can be implemented in exactly the same way as a normal air interface e.g. - RN acts like a BS on the Uu interface towards mobile - RN independently acts like a mobile on the Un interface towards DeNB If the carrier frequencies are the same Un interface requires some extra functions to share the resources of the air interface with Uu

There is a variant of X2 interface between DeNB and RN supports handovers between RN and any other BS implemented in the same way as a normal X2 interface but transports data and signaling messages using the functions of the Un interface instead of IP A similar variant of S1 interface allows RN to communicate directly with MME and S-GW A new instance of S11 interface allows MME to configure the S1 tunneling functions inside the donor enb, by treating it in the same way as a S-GW

Restrictions on the use of relaying in Release 10 RNs are assumed to be stationary - a RN cannot be handed over from one DeNB to another multi-hop relaying is not supported - one RN cannot control another RN - no impact on the mobile, which is completely unaware that it is being controlled by a relay - this implies that Release 8 mobiles support relaying in just the same way as Release 10 mobiles

Enhancements in Release 11 Coordinated Multipoint Transmission and Reception Enhanced Carrier Aggregation

Coordinated Multipoint Transmission and Reception (CoMP) CoMP is a wide-ranging term, which refers to any type of coordination between the radio communications that are taking place in nearby cells its aim is to increase the data rate at the cell edge and the overall throughput of the cell

Two main varieties from the viewpoint of downlink (similar issues apply on the uplink) Coordinated Scheduling and Beamforming (CS/CB) - a mobile receives data from one cell at a time, its serving cell - however, the serving cell can coordinate its scheduling and beamforming processes with those of cells nearby, so as to minimize the inter-cell interference - e.g., a cell can configure its beamforming pattern on the subcarriers that a mobile in a neighboring cell is using

Joint Processing (JP) - a mobile receives data from multiple cells - these cells can be controlled by one BS, which is not too hard to implement - alternatively, the cells can be controlled by multiple BSs, which offers better performance but makes issues such as backhaul and synchronization far harder

The cells used for joint processing can transmit the same data stream as each other, in which case they are operating as diversity transmitters (the same technique is used for soft handover in UMTS) Alternatively, they can transmit different data streams, in an implementation of spatial multiplexing that is known as cooperative MIMO (shown in the figure) this has some similarities with MU-MIMO, but instead of separating the mobile antennas onto two different devices, we separate the network s antennas onto two different cells

Enhanced Carrier Aggregation CA will also be enhanced in forthcoming releases of LTE Three main aspects aggregation using more CCs and resource blocks, so as to increase the mobile s peak data rate aggregation in more FDD and TDD bands allow mobile to use multiple values of the uplink timing advance, one for each CC - this is helpful when CA is used in conjunction with relaying, as it allows the mobile to send one uplink CC to a DeNB another with a different timing advance to a RN