Random Access For Mac Layer


The Random access protocols are further subdivided as: (a) ALOHA – It was designed for wireless LAN but is also applicable for shared medium. In this, multiple stations can transmit data at the same time and can hence lead to collision and data being garbled. This module discusses the need for medium access control (MAC), and introduces representative random access and scheduling MAC protocols - including the carrier-sense multiple access with collision detection CSMA-CS protocol which forms the basis for the Ethernet LAN standard. In 802.11, the Distributed Coordination Function hoc networks is the medium access control (MAC) layer. (DCF) represents the basic access method that mobile nodes Current random access MAC protocols for ad hoc networks utilize to share the wireless channel.

  1. Random Access For Mac Layers
  2. Random Access For Mac Layer Protocols

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.

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.

Refer to 36.321 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 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 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.





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


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


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

Item 0

N1PUCCH-AN-CS-r10: 4 items

Item 0

N1PUCCH-AN-CS-r10 item: 361

Random Access For Mac Layer

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

Random Access For Mac Layer

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




sCellToAddModList-r10: 1 item

Random Access For Mac Layers

Item 0


sCellIndex-r10: 2



physCellId-r10: 1

dl-CarrierFreq-r10: 3100



dl-Bandwidth-r10: n50 (3)


antennaPortsCount: an1 (0)


phich-Duration: normal (0)

phich-Resource: one (2)


referenceSignalPower: 18dBm

p-b: 0





transmissionMode-r10: tm1 (0)

ue-TransmitAntennaSelection: release (0)

release: NULL


p-a: dB0 (4)



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

Random Access For Mac Layer Protocols

cqi-ReportPeriodicSCell-r10: release (0)

release: NULL

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 Extended Power Headroom MAC Control Element >

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

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

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

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

uplink >

< 36.321 Rel 13 - Figure Extended PHR MAC Control Element supporting 32 serving cells with configured Parallels desktop 9 for mac activation key.

uplink and PUCCH on SCell >

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 Timing Advance Command MAC control element >

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