LTE ADVANCED

IMT-Advanced . . . .A.1 Evolution to LTE-A . . . .A.2 LTE-Advanced Features . . . .A.3 LTE Frequency Bands . . . .A.4 Carrier Aggregation . . . .A.5 Carrier Aggregation Options . . . .A.6 CA Terminology . . . .A.7 UE Categories . . . .A.8 UE Bandwidth Classes . . . .A.9 CA Operating Bands . . . .A.10 PCells . . . .A.11 SCells . . . .A.12 Scheduling . . . .A.13 Handovers with CA . . . .A.14 MIMO Enhancements . . . .A.15 User Connections . . . .A.16 Relaying for LTE . . . .A.17 R10/R11 Data Handling Improvements . . . .A.18 Co-ordinated Multipoint (CoMP) Transmission/Reception . . . .A.19 SON Enhancements . . . .A.20

At the end of this section you will be able to:

 describe the requirements for 4G networks specified by the ITU IMT-Advanced guidelines

 identify where LTE-Advanced sits within the progression of 3GPP specification Releases

 outline the basic functionalities that were added to LTE in releases 10 and 11 to create LTE-Advanced

 identify some of the more important frequency bands in which LTE use has been specified

 describe the basic functionality of LTE-Advanced Carrier Aggregation

 outline the differences between Inter- and Intra-Band Carrier Aggregation and describe the various types of symmetrical/asymmetrical configuration that are possible

 describe the meaning of CA-related terms such as Carrier Aggregate, Aggregated Channel Bandwidth, Transmission Bandwidth and Aggregate DC Subcarrier

 outline the roles played by configuration descriptors such as the CA Bandwidth Class, UE Categories, CA Operating Bands and Supported Bandwidths

 identify the key functions and main differences between PCells and SCells as employed in Carrier Aggregation

 describe the enhancements made to LTE’s spatial multiplexing or MIMO functionalities in Release 10

 outline the purpose of the LTE Relay and describe the basic elements of this concept

 outline the functionality of some of the other key Release 10 LTE features such as LIPA, SIPTO, MRA and IP Flow Mobility

 describe the basic concept that underpins the Release 11 CoMP (Co-ordinated Multi-Point) feature

 outline some of the enhancements made in Release 10 to the SON (Self Optimising Network) concept

OBJECTIVES

a high degree of commonality of functionality worldwide while retaining the flexibility to support a wide range of services and applications in a cost-efficient manner

compatibility of services within IMT and with fixed networks capability of interworking with other radio access systems high quality mobile services

user equipment suitable for worldwide use

user-friendly applications, services and equipment worldwide roaming capability

enhanced peak data rates to support advanced services and applications (targets of 100 Mbit/s for high mobility and 1 Gbit/s for low mobility) Key features of IMT-Advanced:

International Mobile Telephony

IMT-Advanced

The ongoing design and implementation of cellular systems is pushed forward by equipment vendors, network operators and, in most cases, international specifications bodies such as 3GPP. A degree of central guidance to this process is provided by the ITU, a branch of the United Nations responsible for attempting to harmonize the standards and techniques employed in worldwide telecoms systems.

The ITU set out its vision for 3G cellular systems at the end of the 1990s by devising a framework known as IMT-2000, although the 3G market ended up consisting of several competing technological platforms all of them ultimately adhered to the guidelines espoused by the ITU.

The ITU created a similar framework of expectations for emerging 4G technologies in 2007 with the initial publication of the IMT-Advanced guidance.

Instead of specifying a particular technology or mandating the functionality of a 4G system, the IMT-Advanced guidelines proposed the basic set of capabilities that a system should be able to support for it to be regarded as being a true ‘4G’ system.

In addition to the aspirations outlined in the diagram, the ITU (in ITU-R report M.2134) also provided some more definite technical requirements for 4G systems, including: that an IMT-Advanced system should be able to accommodate radio channels of at least 40MHz in bandwidth; that their peak spectral efficiency should meet or exceed 15bits/Hz in the downlink and 6.75bits/Hz in the uplink; that it should support latencies of less than 100ms for control-plane connections and less than 10ms for the user-plane.

It should be noted that the original (Release 8) version of LTE did not meet the full set of IMT-Advanced requirements, mainly due to its inability to support 1 Gbit/s data connections. To date only Release 10 LTE-Advanced and the updated version of Mobile WiMax (IEEE 802.16m) have been accepted as fully compliant with IMT-Advanced.

Further Reading: www.IMT-2000.org (ITU website), ITU-Report M.2134

GSM900 GSM1800 GSM1900

GPRS EGPRS

UMTS HSDPA

IMS HSUPA HSPA+

EDGE Evolution

LTE/SAE Phase 1 Phase 2 Phase 2+

Rel 96-98

Rel 99 Rel 4 Rel 5 Rel 6 Rel 7 Rel 8 Rel 9

Rel 8 Rel 9

Rel 10 Rel 11 Rel 12 GSM

GPRS GERAN enhancements

UMTS/SAE UTRAN enhancements Rel 10 Rel 11 Rel 12

Rel 10 Rel 11 Rel 12 LTE-A

Evolution to LTE-A

LTE-Advanced constitutes 3GPP's response to IMT-Advanced and was first described in 3GPP Release 10 documents, with additional functionality specified in Releases 11 and 12.

Basic LTE functionality was described in Releases 8 and 9 and most of the techniques developed to support that first version of LTE are still employed in LTE-Advanced.

The main features of LTE-Advanced are Carrier Aggregation, enhanced MIMO features and the use of LTE Relays, all of which are firmly based on Release 8 foundations.

LTE and LTE-Advanced were not the only topics covered by Releases 8, 9, 10 and 11 – both GSM and UMTS continue to be provided with updates and enhancements that enable them to remain relevant and up-to-date in a 4G world.

Further Reading: 3GPP TS36.101:5.5

Cell A

Component Carriers are classified as DL CCs or UL CCs A PCell is always carried by paired DL CC and UL CC An SCell is always carried by a DL CC which may or may not be paired with an UL CC

SCell–

PCell– Primary Serving Cell – there will be one PCell per UE per carrier aggregate. The PCell is bidirectional.

Secondary Serving Cell – a carrier aggregate may consist of between one and four SCells, the number allocated to a UE may vary over time. An SCell may be bidirectional or unidirectional (Downlink only)

The term ‘Component Carrier’ is used to describe either case in this text

Carrier Aggregation

CA (Carrier Aggregation) is the most prominent feature of Release 10 LTE-Advanced. It offers an inverse multiplexing facility that allows a UE to substantially increase the overall data rate it can achieve by allowing an eNB to schedule capacity for it on multiple cells (or 'carriers') simultaneously.

Each carrier (either downlink or uplink) assigned for use by a UE is known as a CC (Component Carrier) and the set of CCs allocated to a UE at any one time forms a Carrier Aggregate. R10 CA permits up to five CCs to be bound into a Carrier Aggregate, potentially providing a suitably-equipped UE with up to 100MHz of bandwidth and an aggregate downlink data rate of over 3Gbit/s.

The lowest level of carrier aggregation allows a UE to connect via just one cell. The radio connectivity of this cell is described as the PCC (Primary Carrier Component) and the cellular service it offers is known as the PCell (Primary Serving Cell). The PCell carries NAS and RRC services for a UE and is also the carrier measured by the UE to support functions like quality feedback and handover measurements.

A Release 8/9 UE (or an R10 UE that didn’t require CA services) would just connect via the PCell and would not be assigned any additional carriers. An R10, CA-capable UE that did require a CA service would be scheduled with capacity on between one and four SCells (Secondary Serving Cells), each of which would be carried by an SCC (Secondary Component Carrier).

The PCC and any SCCs aggregated to provide a CA service for a UE must all be under the control of the same eNB, but the terms ‘primary’ and ‘secondary’ used in relation to CA carriers are determined from the point of view of each UE – different UEs in the same area may have selected different cells to be their PCell and may therefore regard an assigned cell as an SCC which may be employed by another UE as a PCC.

A PCell is always used in a bidirectional manner, as befits the cell that carries NAS and RRC traffic, but an SCell may be used in either a bidirectional or unidirectional manner depending upon local configuration and current requirements. If an SCell is used unidirectionally then it is only able to operate in 'downlink-only' mode, there is no provision for cells to operate in 'uplink-only' mode.

Band A Band B PCells must always be

symmetrical with both

Uplink Downlink Uplink Downlink Inter-Band -

Non-Contiguous

Carrier Aggregation Options

Carrier Aggregation in LTE-Advanced has been designed to operate with as much configurational flexibility as is practical; there is flexibility in the way in which channel aggregates can be spread across frequency bands and there is also flexibility in the symmetry that can be employed by SCCs.

Frequency band options are classified as:

Inter-Band – where the component carriers in an aggregate can belong to two or even three different frequency bands

Intra-Band Contiguous – where the CCs must belong to the same frequency band and must be contiguous (i.e., adjacent to each other) within that band

Intra-Band Non-contiguous – where the CCs must belong to the same frequency band but are not required to be contiguous within that band (i.e., they may be spread out across the band)

The symmetry applied to a channel aggregate can vary in terms of the numbers of uplinks and downlinks and also in terms of the bandwidths of those uplinks and downlinks.

A PCell must always be symmetrical in terms of its uplink and downlink, but the bandwidth allocated to each may vary. UEs that do not support or that do not require CA connections only make use of a PCell and will therefore always receive a service that is symmetrical in terms of CC configuration.

An SCell can be configured with symmetrical or asymmetrical Component Carriers; symmetrical CC configuration means that the SCell employs both an uplink and a downlink, whilst asymmetrical CC configuration would employ just a downlink, it is not possible to configure an SCell to operate in an ‘uplink only’ manner.

Asymmetrical bandwidth allocations are possible for both PCells and SCells and are typically characterized by configuring the cell’s downlink channel to occupy a larger bandwidth than its uplink. An example of this might be a cell with a 20MHz downlink but only a 5MHz uplink. Such configurations are used to reflect the asymmetric nature of typical user demand, in which more data is downloaded than is uploaded.

Further Reading: 3GPP TS36.300:Annex J, 36.807:Annex A

Lower guard

Transmission Bandwidth (25 MHz – guard bands)

Lowest CC Highest CC

Must be a multiple of 300kHz 10 MHz Carrier Bandwidth

5 MHz Carrier

Bandwidth 10 MHz Carrier Bandwidth

DC Subcarrier DC Subcarrier

10 MHz Carrier Transmission Bandwidth

CA Terminology

Carrier Aggregation operates by allowing an eNB to schedule uplink and downlink capacity for a UE across a set of component carriers that have been combined to form an Aggregated Channel.

The total bandwidth occupied by the Aggregated Channel is termed the Aggregated Channel Bandwidth and includes all used and unused subcarriers; unused subcarriers are generally those set aside to act as guard bands at the upper and lower end of each CC. The net usable bandwidth of the Aggregated Channel (which is total bandwidth less all guard subcarriers) is termed the Aggregated Transmission Bandwidth.

Due to the requirements imposed by OFDMA, each CC will still need to have its centre-frequency left unused to act as a DC Subcarrier. To ensure that orthogonality is maintained between subcarriers across an entire aggregated channel, the DC Subcarriers of all CCs within the aggregate must be spaced at multiples of 300kHz from each other. The number of guard subcarriers employed at the top and bottom ends of each CC may be adjusted to accommodate this spacing requirement if necessary.

In a contiguous aggregated channel (i.e., one in which all CCs are adjacent to each other) the DC subcarrier of the central CC will be used as the baseband transmission DC Subcarrier for the entire aggregate. For this reason, it is recommended that aggregate channels are created in a ‘balanced’

manner, as shown in the diagram. The total 25MHz aggregated channel bandwidth in the diagram has been created by aggregating 2x10Mhz and 1x5MHz CCs, but to balance this aggregate the 5MHz CC has been placed in the centre and its DC Subcarrier will be used for the entire aggregated channel.

Un-balanced configurations are also possible – a 25MHz channel aggregate could be created by combining CCs in a 10+10+5 pattern, for example – but in these cases the aggregate DC Subcarrier must be created by using whichever ‘transmission’ subcarrier happens to be at the centre frequency of the aggregate.

In non-contiguous aggregates (like those employed in inter-band configurations), each contiguous section of the aggregate will require its own aggregate DC subcarrier.

Further Reading: 3GPP TS36.807:5.6A & 5.7, 36.104:5.7.1A

UE Category Feature

Peak DL data rate (Mbit/s) Peak UL data rate (Mbit/s) Highest DL modulation scheme

64QAM 64QAM 64QAM 64QAM 64QAM

16QAM 16QAM 16QAM 16QAM 64QAM

1 2 2 2 4

The cost of LTE UEs is partly determined by the sophistication of the set of functions that each can perform. Only a limited subset of UEs will be designed to take advantage of the maximum possible capabilities of an LTE network. It is therefore necessary to allow each UE to signal its capabilities to the network to allow the services offered to be tailored to its abilities.

UE capabilities are signalled in RRC message IEs and are classified into UE Categories.

Release 8/9 UEs have capabilities – those that relate to ‘standard’ LTE access – that place them in UE Categories 1-5, these are signalled in the UE-EUTRA_Capability IE.

Release 10 UEs may have capabilities that relate to LTE-Advanced access which place them in UE Categories 6-8, these are signalled in the UE-EUTRA-Capability-v10 IE.

A Release 8/9 UE with UE Category 5 can, in theory, achieve data rates of up to 300MBit/s in the downlink and 150MBit/s in the uplink using 64QAM modulation in both directions and up to 4 layers of downlink MIMO.

A Release 10 UE with a UE Category of 8 can, in theory, achieve data rates of 3000MBit/s downlink and 1500MBit/s uplink using 64QAM in both directions, up to 8 MIMO layers in the downlink and up to 4 in the uplink. The use of CA with 4 SCells to achieve these data rates is implicitly indicated as they wouldn’t be possible otherwise.

Both UE-EUTRA-Capabilities signal a large number of other parameters in addition to UE Category and other IEs are also employed to carry UE configuration and capability information.

Further Reading: 3GPP TS36.306:4.1 (UE-Category IE), 36.331:6.3.6 (UE-EUTRA-Capability)

Carrier Aggregation

Correct as per TS36.101 v10.2.1 Classes D-F are classed by 3GPP as ‘for further study’ so the values shown here are provisional and may be subject to change

1 x PCell

NRB_agg = Number of Resource Blocks in Aggregated Channel

The level of Carrier Aggregation that is supported by a UE is determined by its Bandwidth Class.

Each Bandwidth Class describes the level of CA capabilities supported by a UE, it includes descriptions of the maximum number of Resource Blocks that a UE can use simultaneously and the maximum number of Component Carriers (with each CC classed as an uplink/downlink pair whether the uplink is actually used or not) the UE can access simultaneously. The largest channel bandwidth available in R10 is 20MHz, so the maximum number of CCs parameter implicitly identifies the maximum operational bandwidth a UE could be assigned.

Bandwidth Class A devices do not support CA, so this classification would be used to describe all Release 8/9 UEs and any Release 10 devices that do not require CA capabilities. Class A devices are able to access up to 100 Resource Blocks on a 20MHz channel in a PCell only and will not be able to access any SCells. Examples of Bandwidth Class A devices might include voice-only LTE terminals and devices designed to support low-bandwidth data applications such as smart utilities meters.

Bandwidth Classes B and upwards support increasing levels of aggregation capability. Class B devices are also limited to using up to 100 RBs but may be assigned one SCell in addition to the PCell. The 100 RB limit means that although a Class B device is able to access two CCs it would not be able to access two 20MHz CCs, as that would entail processing 200 RBs.

Bandwidth Class C devices are able to handle up to 200 RBs and two CCs and would therefore be able to be assigned to, for example, a 20MHz PCell and a 20MHz SCell, although other channel configurations are also possible.

As of v10.2.1 of TS36.101, the 3GPP specification that describes Bandwidth Classes, classes D-F had parameters assigned to them but were described as being FFS (For Further Study), so the parameters

In document LT3600 LTE-SAE Engineering Overview - V3.3 (Page 183-200)

CONTENTS

OBJECTIVES