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What is the default contention-based MAC protocol for LTE?

+2 votes
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What is the default contention-based MAC protocol for LTE?

I came across an article which c-MAC was mentioned and I guess the author was referring to the default MAC for LTE.

Also, in LTE does spectral efficiency and throughput in traditional networks mean the same?

posted Jan 11 by anonymous

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1 Answer

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There are two types of RACH procedures named as "contention-based" and "non-contention based".
I think your questions is related to contention based RACH procedure, in which UE randomly selects one of the sixty four preambles and sends to eNodeB MAC. There are chances two or more UEs may send same premable signature at the same time to eNodeB. In this case eNodeB MAC resolve the contention by sending contention resolution to UE so that UE come to know whether their request is reached to eNodeB MAC or not.
As per my knowledge of LTE, Contention resolution carries the message 3 content and after receiving contention resolution message, UE matches with its own MSG3 sent earlier.
In special case when UE is in RRC-CONNECTED mode and handover is going to be executed for that UE, network (eNodeB) may send dedicated PRACH preamble to use at target eNodeB/cell during RACH procedure at target eNodeB/cell.

answer Jan 12 by Harshita
Similar Questions
+3 votes

Mostly, the MAC control header for contention resolution is of 56-bits(1-byte for DL contention resolution ID+6-bytes for subPdu len of UE-contention resolution id). Please find the below details for your reference.


Source = \Protocol\3GPP\LTE\MAC\Entity Id 17
Destination = \Protocol\3GPP\LTE\PHY\Entity Id 2
Transport Blocks
Transport Block 1 (Codeword 0) Len = 7 =
MAC subheader 1, type: MCE (DL CONTENTION RESOLUTION ID), sub-header length: 1 =
LCID = 28 (DL CONTENTION RESOLUTION ID)
E = 0
R = 0
SubPdu Len = 6
UE Contention Resolution ID = 5E,0E,95,0C,02,C6


Secondly, when does this header if of more than 56-bits as below. 56-bits for contention resolution and 16-bits for padding. Why does the TB1 size is changed?


Source = \Protocol\3GPP\LTE\MAC\Entity Id 17
Destination = \Protocol\3GPP\LTE\PHY\Entity Id 2
Transport Blocks
Transport Block 1 (Codeword 0) Len = 15 =
MAC subheader 1, type: MCE (DL CONTENTION RESOLUTION ID), sub-header length: 1 =
LCID = 28 (DL CONTENTION RESOLUTION ID)
E = 1
R = 0
SubPdu Len = 6
UE Contention Resolution ID = 40,10,00,00,00,16
MAC subheader 2, type: Padding, sub-header length: 1 =
LCID = 31
E = 0
R = 0


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