LTE MAC Layer Interview Que and Ans 11-20

Que11: Define Mac Protocol Design?

Ans11: MAC is layer 2 protocol deals with Many Logical channels and control elements shown in below mentioned diagram.

FIG : MAC PROTOCOL DIAGRAM

Que12:- If Mac Pulling Data from 4 Logical Channel and make a Transport   Block [TB], then How many Sub-Header we have?

Ans12:- If padding space is available than there are 6 sub header present shown below otherwise 5 sub headers present.

Que13:- Why Timing Advance not dealing by Physical layer in Transmission?

Ans13:-Timing advance is not dealing with physical layer because physical layer only deals with transmission of transport block not to make TB but MAC layer is the one who deals with making of transport block that’s why Timing advance is work under MAC-C.

Que14:- What is delta Value? Why delta value use in Mac Layer?

Ans14:-This is one of the values used for generating and mapping PUCCH and DMRS PUCCH, the max value is calculated by the system BW, Cyclic prefix, N_RB(2), N_CS(1) and delta shift.

Que15:- What is Truncated BSR?

Ans15:-when UE transmit a Mac Pdu and the numbers of padding bits is > the size of a short bsr + it's sub-header but smaller than a size of a long BSR + it's sub-header and the UE has available data for transmission from more than 1 LCG in the TTI where the bsr is transmitted then ue report a truncated BSR of the LCG with highest priority logical channel with data available for transmission.

Ques16:- UE in connected state, Now UE Required Uplink Resource to transmit data after a long time [Long DRX], So UE will do?

Ans16:-If UE have a data to send than UE again redo Random access procedure for getting uplink resources.

Que17:- In Connected State does UE send MSG3 [RRC Connection Request? if yes Which RNTI's against?

Ans17:-Yes UE will send MSG3(RRC CONNECTION REQ) reservation against C-RNTI.

Que18:- What is DRX and DRX active period? What channels does it monitor in active period?

Ans18:-DRX is Discontinuous Reception used for UE to not continuously read the PDCCH channel. Here Active DRX mode meant to continuously listening to PDDCH channel to know weather the resource allocated to it or not.

Que19:- What is MAC-ContentionResolutionTimer – What is the start and end activity?

Ans19:-Its a Timer which tells that to UE that how much time to wait for a CRI, If its a not back in a time limit than UE consider that its MSG3 transmission is failed so UE again send the msg3. Its start at the time of sending MSG3 and End at the time of UE get CRI from eNB.

Ques20:- In Logical Channel Prioritization, what is PBR, GBR and BSD?

Ans20:-GBR-Its a Guaranteed bit delivery which means to promising for delivery IP packets guaranteed. Its unit is in kbps.

BSD: Its a Bucket size duration, nothing but a duration of size and its unit is in ms.

PBR: Its a Prioritized bit rate, nothing but a bit size and its unit is in kb.

Formula    GBR=(PBR*1000)

                                                                           BSD