LTE Layer 2 Understanding: Transport Channel

LTE Layer 2 Understanding: Transport Channel: Transport channel define the characterstics of the trasmission. Uplink transport channel as follows - 1) RACH - used during random acce...

Transport Channel

Transport channel define the characterstics of the trasmission.

Uplink transport channel as follows -

1) RACH - used during random access procedure.

2) UL-SCH - Uplink shared channel used for higher layer data (user & control information)

Downlink transport channel as follows -

1) BCH - Used for system information broadcast (Ex- MIB)

2) DL-SCH - downlink shared channel used for higher layer data (user and control information) and system information.

3) PCH - used to page a UE.

MAC FAQ

1) What is BSR and how it work ?
2) What is PHR & how it works ?
3) Scheduling Request procedure.
4) RACH procedure.
5) Logical channel prioritization.
6) MAC SDU multiplexing.
7) HARQ procedure.
8) Resource allocation by MAC.
9) Use of MAC-CRNTI CE.
10) Contention resolution identity MAC CE and its use.
11) Impact on MAC in Carrier Aggregation (CA).
12) How HARQ procedure work in MIMO.
13) Timing adavnce procedure.
14) Uplink synchronization (Time alignment timer).
15) Logical channel ID & Logical channel group ID.

HARQ

HARQ is stop and wait mechanism. It is basically a layer 1 retransmission and controlled by MAC & PHY layer.
Each HARQ entity has some associated HARQ process ID. By considering the RTT of each HARQ transmission, maximum 8 HARQ process has been defined under the 3GPP standard.

1) Uplink HARQ procedure is synchronous and adpative/no adaptive.
2) Downlink HARQ procedure is non-synchronous and adaptive.