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# <center><i class="fa fa-edit"></i> LTE MAC </center>
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[TOC]
### Introduction
Medium access control protocols are mechanisms that allow several users or transmitters to access a common medium or channel. They play an important role in the development of both wired and wireless networks. The distributed protocols facilitate network deployment and allow networks to accommodate more users/transmitters without any change.
### MAC Structure Overview


- All the logical channes ([PCCH](https://www.mpirical.com/glossary/pcch-paging-control-channel), [BCCH](https://en.wikipedia.org/wiki/Broadcast_control_channel), [CCCH](https://www.mpirical.com/glossary/ccch-common-control-channel-umts), [DCCH](https://www.mpirical.com/glossary/dcch-dedicated-control-channel-gsm), [DTCH](https://www.mpirical.com/glossary/dtch-dedicated-traffic-channel)) goes through MAC layer.
- It seems that PCCH does not get manipulated by MAC in any special way. It just looks as if it is by passing MAC process. It does not use [HARQ](https://www.mpirical.com/glossary/harq-hybrid-automatic-repeat-request) procedure meaning 'no retransmission' mechanism being used.
- CCCH, DCCH, DTCH all go through the same procedure (Prioritization, [Mux/DeMux](https://www.mpirical.com/glossary/mux), HARQ).
- Some BCCH goes through HARQ, but some BCCH does not go through HARQ. Do you know which BCCH go through HARQ and which does not ? BCCH for [MIB](https://www.mpirical.com/glossary/mib-master-information-block) does not go through HARQ, but BCCH for [SIB](https://www.mpirical.com/glossary/sib-service-independent-building-block) go through HARQ. (But this HARQ is a little different from normal HARQ that we know of.. It does not expecting any ACK/NACK response from the reciever.. but perform 'retransmission' based on a predefined rule).
- Random Access process orignated within MAC layer, it does not have the correspoding logical channel. (This may apply to Msg1, Msg2 of RACH procedure.. Msg3,4,5 involves [RRC](https://www.mpirical.com/glossary/rrc-radio-resource-control) layer intervention as well).

### Overview of MAC Procedure

| Procedure Name | Description|
| -------- | -------- |
| [Random Access Procedure](http://www.sharetechnote.com/html/RACH_LTE.html) | Get the initial uplink grant and perform synchronization to network |
| [DL-SCH data transfer (NW)](http://www.sharetechnote.com/html/BasicProcedure_LTE_DataTransmission_DL.html) | Do everything needed to perform DL Data Transfer (DCI-Scheduling, HARQ etc) |
| UL-SCH data scheduling (NW) | Schedule UL data transmission by sending DCI 0 (UL Grant) |
| UL-SCH data transfer (UE) | Do everything needed to perform UL Data Transfer (DCI 0 decoding, HARQ, multiplexing and assembly) |
| [SR-Scheduling Request](http://www.sharetechnote.com/html/Handbook_LTE_SR.html) | Send the request to Network to get a UL Grant |
| [BSR - Buffer Status Report](http://www.sharetechnote.com/html/Handbook_LTE_BSR.html) | Provide NW with information about how much data in its buffer waiting to be transmitted. |
| [PHR - Power Headroom Report](http://www.sharetechnote.com/html/Handbook_LTE_PHR.html) | Provide eNB with the information about the difference between the nominal max UE Tx power and the estimated power for UL-SCH transmission |
| [DRX - Discontinous Reception](http://www.sharetechnote.com/html/Handbook_LTE_DRX.html) | Control UE's PDCCH monitoring activity in special pattern mainly to save energy consumption |
| SPS - Semi Persisent Scheduling | Scheduling DL/UL transmission in special pattern to reduce scheduling overhead |
| [PCH Reception](http://www.sharetechnote.com/html/Paging_LTE.html) | Monitoring Paging message in special period |
| BCH Reception | Get basic information on cell (MIB and SFN) |