LTE Advanced CA

S a t u r d a y , F e b r u a r y 1 5 , 2 0 1 4

Carrier Aggregation in LTE-A (3gpp Rel-10)Carrier Aggregation in LTE-A (3gpp Rel-10)Carrier Aggregation in LTE-A (3gpp Rel-10)Carrier Aggregation in LTE-A (3gpp Rel-10)

Carrier aggregation (for FDD & TDD) is a technique used in LTE-A (3gpp Rel-10) in order to increase the

bandwidth, and thereby increase the throughput both in DL and UL.

CA combines up to 5 contiguous or non-contiguous Component Carriers (CC) of spectrum into a single

logical channel with resulting maximum transmission bandwidth of up to 100Mhz.

Use of CA with MIMO will achieve max transmission speed of 1Gbps in DL and 500Mbps in

UL.

Aggregation of of up to 5 downlink (DL) CCs and 5 uplink (UL) CCs, irrespective of intra-band

or inter-band CA.

For FDD, N(DL CCs) >= N(UL CCs) ; Asymmetric CA!

For TDD, number of CCs and BW is same in DL & UL!

CCs' can be configured with any bandwidth (1.4, 3, 5, 10, 15, 20 MHz) supported by LTE

Each CC is equivalent to a Rel8/9 carrier for normal operation.

In LTE-A, 3 types of carrier aggregation are specified.

Intra-band Contiguous CA 1.

Intra-band Non-contiguous CA 2.

Inter-band Non-contiguous CA 3.

Carrier Aggregation- Cell Configuration

Pcell : The cell for which R10 UE has established RRCConnection to is called Primary Cell (Pcell) and

the corresponding CC is called (UL/DL) PCC.

Pcell is configured with following charecteristics

PDCCH/PDSCH/PUSCH/PUCCH can be transmitted

Measurement and mobility procedure are based on PCell

Random access procedure is performed over PCell

Can not be deactivated

DL PCell and UL PCell are linked via SIB2

Scell : Additional cell(s) configured after RRCConnectionEstablishment i.e in CONNECTED mode, to

provide additional radio resources is called Scell and the associated CC is called (DL/UL) SCC. Scell is

configured with following charecteristics

PDCCH/PDSCH/PUSCH can be transmitted (not PUCCH)

An Scell never has a PUCCH allocated in it

MAC layer based dynamic activation/deactivation procedure is supported for SCell for UE

battery saving

Can be cross scheduled

For a UE configured for CA there can have only once Pcell and up to four Scells collectively

known as Serving Cells

HO, CCO or RLF is only for Pcell; so, RL monitoring for Scells is not necessary for Scell

UL PCC is used for carrying PUCCH ACK/NAKS, SR & periodic CSI from a UE

UE is not allowed to camp on Scell. No MIB, SIBs are broadcast on it.

Pcell cant be de-activated, but the Scell (CCs) can be activated/de-activated based on traffic

need and UE reported CQI for CC (Scell)

Raghavendra Devareddy

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Blog Archive

LTE-Advanced http://raghudevareddy-lte-a.blogspot.com/2014/02/RaghuDevareddy.html

1 of 10 12/13/2014 1:12 AM

Scells can be one of the three states;

Non-configured: UE performs RRM inter-freq measurements when configured (Similar to R8 UE)1.

Configured but deactivated: UE doesn't receive PDCCH or PDSCH and no CQI measurements2.

Configured and activated: UE receive PDCCH or PDSCH and performs CQI measurements, and

maintains path loss (PL)

3.

Initial access and entering CA mode

The PSS and SSS are transmitted on all CCs for UEs to facilitate cell search.

Once a UE makes a successful cell search, it considers the current cell as the PCell and

performs the random access procedure on the up link CC associated with the PCell.

When CA is c onfigured, First 3 steps are Contention Based RA on Pcell

After Random Aceess Procedure, UE will establish RRCConnection to Pcell as in the case of

R8/9

eNB that owns the Pcell enquires UE whether it supports CA through the RRC

UeCapabilityEnquiry.

UE responds back with UECapabilityInformation containing BandCombinationParameters

field indicating CA (and MIMO) capabilities upported by the UE for configurations with

Intra-band contiguous/non-contiguous or Inter-band CA.

For each band in a band combination, the UE provides, via the Band Parameters UL/DL, the

supported CA bandwidth classes (and the corresponding MIMO capabilities).

UE CapabilityInformation


2 of 10 12/13/2014 1:12 AM

RRCConnectionReconfiguration

The default state for a newly configured SCell is deactivated

PDCCH reception (for DL/UL grants) stopped,

PDSCH/PUSCH, SRS, and CQI transmissions are stopped.


3 of 10 12/13/2014 1:12 AM

DL SCC deactivated implies that linked UL SCC is also deactivated

DL SCC activation/deactivation can be explicit or implicit.

Explicit is via MAC signaling

Ci =1 Activation

Ci =0 Deactivation

Mac PDU sub-header with LCID 27 (8-bit) is used for DL activation/de-activation of Scells.

Implicit deactivation of DL SCC can be triggered via a timer called the sCell-

DeactivationTimer maintained per Scell. But, one common value is configured per UE by

RRC.

L2 Changes for Carrier AggregationWith CA, following changes are needed in protocol stack as shown in the fig. below

RLC Changes

From UE design perspective, a minor aspect of the RLC was changed in comparison to Rel-8

RLC layer has now to provide higher data rates by having a larger buffer size

Three new categories, category 6, 7 and 8 are specified in Release-10 to support this increase

in buffer size.

MAC Changes

With CA, MAC layer plays the role of multiplexing entity for the aggregated component

carriers.

Each MAC entity will provide to his corresponding CC its own Physical Layer (PHY) entity,

providing resource mapping, data modulation, HARQ, and channel coding.

CA capable eNB MAC layer scheduler must have knowledge of all active CCs

eNB MAC scheduler to sequence DL allocations and UL grants optimally, it must consider the

downlink and uplink channel conditions across the entire aggregated bandwidth.


4 of 10 12/13/2014 1:12 AM

In the absence of MIMO, a CA-enabled scheduler allocates, at most, one transport block per

shared channel per TTI

With CA enabled, the HARQ processes delivering the various transport blocks within a TTI

(across SCHs) are independent.

System Information Broadcasting

UE is required to monitor the BCCH on the PCell only for system information (SI) acquisition.

Dedicated signaling (via RRCConnectionReconfiguartion) is used to convey SI of SCells.

Changes in Scell SI is configured by removal and addition of the same Scell using RRC

signaling. Consequently, there is no need for the UE to monitor the BCCH on SCCs.

DL CA Operation

UE configured for CA operation reports CSI feedback for Pcell and Scell

CSI-RS report = CQI + RI + PMI

The eNB, after receiving CSI/CQI report and BSR (data in UEs buffer) from several UEs',

decide which users (UE) data should be transmitted.

Using CSI feedback & BSR, eNB will determine DL transmission parameters for selected UEs'

such as

serving cell(s) to use for DL data transfer

RBs' and data rate

MCS to use

Antenna technique & TM to use.

UE monitors PDCCHs of the Pcell and & any active Scells for PDSCH allocation

Due to PDSCH enhancement in Rel-10 (MIMO 8x8 in DL, DCI 2C. TM9), on a given serving

cells, PDSCH transmission on up to 8 layers is possible.

A single UE specific UL CC (called UL PCC) is configured semi-statically for carrying PUCCH

ACK /NACK, SR, and periodic CSI from a UE

DL PDCCH reception

Information on how the DL data is transmitted is sent on PDCCH.

Two types of PDCCH transmission possible in Rel-10 CA

Separately coded PDCCH per PDSCH on multiple DL component carriers .

2. Cross-Carrier Scheduling (with CIF)


5 of 10 12/13/2014 1:12 AM

Optional feature for the UE introduced in Release-10

Activated using RRC during the UE capability transfer procedure

Reduces interference in Heterogeneous Network (HetNet) scenarios with

carrier aggregation

HetNets = combination of macros, smalls-cells and relays

Cross-carrier scheduling is only used to schedule resources on an Scell

without PDCCH.

PCell cannot be cross scheduled; it is always scheduled through its own

PDCCH

In Rel-8, PDCCH carries DL resource allocation for its own CC and UL grants for associated

UL CC indicated by SIB2

In Rel-10 with cross carrier scheduling configured, PDCCH may carry resource allocation for

one or more CCs with new 3-bit Carrier Indicator Field (CIF)

The CIF is located at the beginning of the DCI and is fixed regardless of DCI format size.

CIF supports cross-carrier scheduling for DCI formats 0, 1, 1A, 1B, 1D, 2, 2A, 2B and 2C in the

UE specific search space

DCI-1 (DL Resource Allocation)

For UE not scheduled with cross carrier scheduling, CIF field will be absent

CIF =0 indicates Pcell; other values (1-4) for Scells configured by RRC signaling

UE may receive multiple DCIs for DL data in the same TTI, one for each serving cells where

UE is receiving data transmission.

PDCCH search space in CA;

One control region per CC in CA

UE decodes a set of PDCCH for control information according to all the monitored

DCI format candidates in every DRX sub frame on one or more activated serving

cells

PCFICH

Independent control region size per CC

On any carrier with a control region, re-use Rel-8 design

Modulation

Coding

RE mapping

PCFICH for cross CC scheduling

In case of cross-carrier scheduling , a standardized solution will be supported to

provide CFI to the UE for the carriers on which PDSCH is assigned.

The PDSCH starting symbol position of the cross-scheduled CC is informed to UE by RRC

signaling.

ACK/NACK for CA (new PUCCH format 3)

In Rel-8 LTE, PUCCH format 1a/1b/2/2a/2b are used by UE to send ACK/NACK

for the reception of transport blocks in DL (PDSCH data transmission)

AC/NACKs can be combined with SR &/or CSI.

For a UE in CA, PUCCH format 3 is introduced with enhancement to 1b

At any given TTI up to 5 ACK/NACKs needs to be transmitted for a UE configured with 5 CCs

(1Pcell + 4Scell)


6 of 10 12/13/2014 1:12 AM

PUCCH format 1b enhanced to carry 4 ACK/NACK bits (rel-8, 2bits) for 2 serving cells

UE with TM9 (DL 8X8 SU-MIMO), using PUCCH format 3, up to 10 ACK/NACK for FDD and

20 ACK/NACK for TTD can be transmitted

Due to the introduction of CA as well as enhanced MIMO transmission of up to 8 spatial

layers there will be a high amount of control information to be fed back to the network.

To avoid the definition of new and additional mechanism to multiplex UL control information

and user data, the decoupling of control information and data transmission has been enabled

in Rel-10

Simultaneous PUCCH & PUSCH transmission

UE can now send PUCCH & PUSCH simultaneously

Power control is done independently for data & control i.e. feedback

In any case max UE transmit power should not exceed 23dbm.

P(PUSCH) + P (PUCCH)

TM1 UE transmits the PUSCH from single antenna

TM2 Closed Loop Spatial Multiplexing with up to 4 layers available for PUSCH

transmission.

Enhanced DCI format 0 with new DCI format 4 are used with TM1 & TM2.

Frequency Hopping : Allocation of RB/REs on different SCs across the RB boundaries

Allowed for Type-0 resource allocation

Not allowed for Type-1.

Mobility in CA Measurement Events

UE can be configured to report measurement events on one or all the CCs

UE can also report measurements on not configured CCs

LTE-A Measurement Events = rel-8 events + event A6

A1/A2 Applicable for both Pcell & Scell.

Triggered when serving cell (== Pcell or Scell) becomes better(A1)/(A2) worse than threshold

(s-measure).

s-measure threshold applies only to Pcell & controls all non serving cells

When Pcell(RSRP) >= s-measure, A1/A2 are disabled (not reported)

A3 A neighbor becomes offset better than Pcell

A5 - Pcell < thr1 & neighbor > thr2

The measurement object for A3/A5 can be any frequency including the Scell

A6 New measurement event introduced for CA.

Intra-frequency neighbor becomes offset better than the Scell on that SCC

Event A6 compares the neighbor cell and the SCell that are on the same carrier frequency.

A stronger neighbor on an SCC may point to the need for handover (HO)

better candidate serving cell is reported by UE via event A6

UL PC in CA (Rel-10)

Similar to rel-8, it will compensate for distance dependent path loss and shadowing, while

reducing the interference generated towards the neighboring cells.

Supports CC specific UL PC for contiguous & noncontiguous CA.

For contiguous CC CA, UL PC is needed to compensate different interference conditions and

requirements of different CCs.

For noncontiguous CA UL PC needed due to quite different propagation conditions on

different CCs

PHR for Rel-10

Power Control in CA


8 of 10 12/13/2014 1:12 AM

Posted by Raghavendra Devareddy at 1:09 AM

In CA multiple PUSCHs and PUCCH are transmitted simultaneously on a single CC and there

are multiple CC transmitted in the UL at the same time, power scaling can be very complicated

in Rel-10

Two types of PHRs are possible in rel-10

PUSCH transmission &

Simultaneous PUSCH & PUCCH transmission

PHR Reporting

UE reports PHR to its serving eNB for scheduling decisions and link adaptation purposes.

PHR = UE maximum transmit power PCMAX - PPUSCH

In LTE-A, the PHR is per-CC based., computed for all CCs and may be sent on any Pcell or

Scell

PHR Types

Tyep1: PCMAX,C PPUSCH (For Scell or Pcell)

Type2: PCMAX,C PPUCCH PPUSCH (Pcell only, with possible simultaneous PUSCH +

PUCCH)

To report PHR for multiple CCs configured, rel-10 introduces new extended PHR format using

extended PHR MAC CE.

The extended PHR MAC CE is identified by a MAC PDU sub header with LCID 17.

MAC CE parameters for PHR description


9 of 10 12/13/2014 1:12 AM

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LTE Advanced CA