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4G/LTE - LTE Advanced

MAC

If you are not familiar with details of MAC operation, first refer to Release 8 MAC. In this page, I will post only those features that is new to Release 10.

There is not so much differeces in overal MAC architecture. Even in Carrier Aggregation, still single MAC is used to control/schedule all the carrier components. However, there are a couple of small components newly added to handle the details of new features of LTE Advanced.

Followings are the topics to be described in this page.

LCID

There is one LCID newly added for Downlink and another one for Uplink. In Rel 10 (The first release with Carrier aggregation) the new LCID for downlink is for 'Activation/Deactivation' and the new LCID for uplink is for 'Extended Power Headroom Report'. As LTE Advanced evolves into higher release, we see more and more new items getting added as shown below. Following tables are based on 36.321-6.2.1.

Now let's look into those MAC CEs newly added to LTE Advanced.

First refer to LTE MAC pages for release 8 MAC CE to understand general MAC CE. Here I only post the MAC CE that is added only LTE Advanced.

MAC CE - Activation/Deactivation MAC Control Element

Refer to 36.321 6.1.3.8 Activation/Deactivation MAC Control Element if you want to have formal description. The field structure is as shown below.

< 36.321 Rel 10,11,12 - Figure 6.1.3.8-1: Activation/Deactivation MAC control element >

From Rel 13, UE Category 17 is added. Based Category 17, we can achieve 32 CC Carrier Aggregation and 25 Gbps. To support 32 CC (31 SCC), a new Activation/Deactivation MAC CE is added as shown below.

< 36.321 Rel 13 - Figure 6.1.3.8-2: Activation/Deactivation MAC control element of four octets >

Now the question is to figure out what does C1, C2, C3 etc mean ? Does it automatically mean C1 = SCC1, C2 = SCC2 etc ?

No.. the mapping between C1, C2,..,C7 and SCC1,SCC2,...,SCC7 is defined in RRC Connection Reconfig message. One example is as follows : (In example, sCellIndex-r10 for SCC1 (the first SCC) is set to be 2. It means C2 field in MAC CE is mapped to SCC1. Therefore, in this case 00000100 means that the first SCC shall be activated. This mean that absolution bit position in MAC CE does not specify whether it is for SCC1 or SCC2 etc. The meaning of each bit in MAC is indicated by RRC message. It means what is important is the matching between sCellIndex-r10 and MAC CE bit position. I hope following illustration would sound clearer to you.

Following is an example of RRC Connection Reconfiguration message to add SCC1.

rrcConnectionReconfiguration-r8

radioResourceConfigDedicated

physicalConfigDedicated

pucch-ConfigDedicated-v1020

pucch-Format-r10: channelSelection-r10 (1)

channelSelection-r10

n1PUCCH-AN-CS-r10: setup (1)

setup

n1PUCCH-AN-CS-List-r10: 2 items

Item 0

N1PUCCH-AN-CS-r10: 4 items

Item 0

N1PUCCH-AN-CS-r10 item: 361

Item 1

N1PUCCH-AN-CS-r10 item: 362

Item 2

N1PUCCH-AN-CS-r10 item: 363

Item 3

N1PUCCH-AN-CS-r10 item: 364

Item 1

N1PUCCH-AN-CS-r10: 4 items

Item 0

N1PUCCH-AN-CS-r10 item: 365

Item 1

N1PUCCH-AN-CS-r10 item: 366

Item 2

N1PUCCH-AN-CS-r10 item: 367

Item 3

N1PUCCH-AN-CS-r10 item: 368

nonCriticalExtension

sCellToAddModList-r10: 1 item

Item 0

SCellToAddMod-r10

sCellIndex-r10: 2

cellIdentification-r10

physCellId-r10: 1

dl-CarrierFreq-r10: 3100

radioResourceConfigCommonSCell-r10

nonUL-Configuration-r10

dl-Bandwidth-r10: n50 (3)

antennaInfoCommon-r10

antennaPortsCount: an1 (0)

phich-Config-r10

phich-Duration: normal (0)

phich-Resource: one (2)

pdsch-ConfigCommon-r10

referenceSignalPower: 18dBm

p-b: 0

radioResourceConfigDedicatedSCell-r10

physicalConfigDedicatedSCell-r10

nonUL-Configuration-r10

antennaInfo-r10

transmissionMode-r10: tm1 (0)

ue-TransmitAntennaSelection: release (0)

release: NULL

pdsch-ConfigDedicated-r10

p-a: dB0 (4)

ul-Configuration-r10

cqi-ReportConfigSCell-r10

nomPDSCH-RS-EPRE-Offset-r10: 0dB (0)

cqi-ReportPeriodicSCell-r10: release (0)

release: NULL

MAC CE - Extended Power Headroom

The functionality of Extended Power Headroom is same as Power Headroom MAC CE. The main difference is that Extended Power Headroom can report multiple power headroom value simultaneously. Each of these multiple value is mapped to each component carrier. You will see this part evolves as LTE Advanced release evolves.

< 36.321 Rel 10,11,12 - Figure 6.1.3.6a-2: Extended Power Headroom MAC Control Element >

< 36.321 Rel 10,11,12 - Table 6.1.3.6a-1: Nominal UE transmit power level for Extended PHR >

< 36.321 Rel 13 - Figure 6.1.3.6a1-3: Extended PHR MAC Control Element supporting PUCCH on SCell >

< 36.321 Rel 13 - Figure 6.1.3.6a2-4: Extended PHR MAC Control Element supporting 32 serving cells with configured

uplink >

< 36.321 Rel 13 - Figure 6.1.3.6a3-5: Extended PHR MAC Control Element supporting 32 serving cells with configured

uplink and PUCCH on SCell >

MAC CE - Timing Advance

As you see in the following figures, for Rel 8,9,10 there is no special tag for each component carrier, meaning that even in Carrier Aggregation single Timing Advanced value apply to all the component carriers. But in Rel 11, the first 2 bits are allocated to indicate whether the value is for PCC or SCC. If TAG id is 0, it means it is for PCC.

< 36.321 Rel 8,9,10 - Figure 6.1.3.5-1: Timing Advance Command MAC control element >

< 36.321 Rel 11 - Figure 6.1.3.5-1: Timing Advance Command MAC control element >

MAC CE - Differential KOffset

< 36.321 Rel 17 - Figure 6.1.3.21-1: Differential Koffset MAC CE >

MAC CE - Timing Advance Report

< 36.321 Rel 17 - Figure 6.1.3.20-1: Timing Advance MAC CE >