LTE MAC Layer Interview Que and Ans 6-10

Que 6. What are the timers value of receiving RAR Message?

Ans.

Que 7. What is name of RNTI's in which preamble sent and RAR Received?

Ans. UE continue read PDCCH Channel in which Random Access Preamble are broadcasted by eNb in every sub-frame, So UE generate own preamble against RA-RNTI [Random Access-Radio Network Temporary Identifier], After transmit preamble it’s continue read PDCCH Channel, And RAR is Sent by eNb T-C-RNTI [Temporary-Cell-RNTI].

Que 8. What is contention resolution identity? What UE get information after receiving CRI?

Ans. Contention Resolution Identity [CRI], is also another name RRC Connection Setup, Sent by eNb to UE, after receive RRC Connection request trigger by UE. After receiving this message [CRI], UE change their state from Idle to Connected State, and connect to network.

Que 9. What is the difference between MAC Transport Block and Physical Layer generated Code-word?

Ans. The output comes out from MAC Layer is called Transport Block [TB], and the output comes out from Physical Layer is called Code-Word.

Transport Block carries data which is stored in RLC buffer, the size is varies as per resource available in eNb MAC.

But in Code-Word also carries lots of information like:- (1) information of data received from mac layer, (2) CRC to be added, (3) Codded bits to be added and (4) additional padding added.

Que 10. How to determine Transport Block size?

Ans. UE in E-UTRA RRC_CONNECTED state

[ UE got PDCCH receives DCI format 1 indicating Resource Allocation Type 0, a resource block assignment correspondent to NPRB physical resource blocks and a modulation and coding scheme IMCS]

[ UE decodes the received transport block of size correspondent to the read NPRB and IMCS and forwards it to higher layers ]

Resource Allocation RBG Size vs. Downlink System Bandwidth

System Bandwidth	RBG Size
N^DL_RB	(P)
≤10	1
11 – 26	2
27 – 63	3
64 – 110	4

In resource allocations of type 0, resource block assignment information includes a bitmap indicating the resource block groups (RBGs) that are allocated to the scheduled UE where a RBG is a set of consecutive physical resource blocks (PRBs). Resource block group size (P) is a function of the system bandwidth as shown in Table 7.1.6.1-1. The total number of RBGs (NRBG) for downlink system bandwidth of N^DL_RB PRBs is given by NRBG=[N^DL_RB/P] where [N^DL_RB/P]of the RBGs are of size P and if N^DL_RBMODP>0 then one of the RBGs is of size N^DL_RB-P.[N^DL_RB/P]

MCS Index IMCS	Modulation Order QM	TBS Index ITBS
0	2	0
1	2	1
2	2	2
3	2	3
4	2	4
5	2	5
6	2	6
7	2	7
8	2	8
9	2	9
10	4	9
11	4	10
12	4	11
13	4	12
14	4	13
15	4	14
16	4	15
17	6	15
18	6	16
19	6	17
20	6	18
21	6	19
22	6	20
23	6	21
24	6	22
25	6	23
26	6	24
27	6	25
28	6	26
29	2	reserved
30	4
31	6

ITBS	NPRB
ITBS	1	2	3	4	5	6	7	8	9	10
0	16	32	56	88	120	152	176	208	224	256
1	24	56	88	144	176	208	224	256	328	344
2	32	72	144	176	208	256	296	328	376	424
3	40	104	176	208	256	328	392	440	504	568
4	56	120	208	256	328	408	488	552	632	696
5	72	144	224	328	424	504	600	680	776	872
6	328	176	256	392	504	600	712	808	936	1032
7	104	224	328	472	584	712	840	968	1096	1224
8	120	256	392	536	680	808	968	1096	1256	1384
9	136	296	456	616	776	936	1096	1256	1416	1544
10	144	328	504	680	872	1032	1224	1384	1544	1736
11	176	376	584	776	1000	1192	1384	1608	1800	2024
12	208	440	680	904	1128	1352	1608	1800	2024	2280
13	224	488	744	1000	1256	1544	1800	2024	2280	2536
14	256	552	840	1128	1416	1736	1992	2280	2600	2856
15	280	600	904	1224	1544	1800	2152	2472	2728	3112
16	328	632	968	1288	1608	1928	2280	2600	2984	3240
17	336	696	1064	1416	1800	2152	2536	2856	3240	3624
18	376	776	1160	1544	1992	2344	2792	3112	3624	4008
19	408	840	1288	1736	2152	2600	2984	3496	3880	4264
20	440	904	1384	1864	2344	2792	3240	3752	4136	4584
21	488	1000	1480	1992	2472	2984	3496	4008	4584	4968
22	520	1064	1608	2152	2664	3240	3752	4264	4776	5352
23	552	1128	1736	2280	2856	3496	4008	4584	5160	5736
24	584	1192	1800	2408	2984	3624	4264	4968	5544	5992
25	616	1256	1864	2536	3112	3752	4392	5160	5736	6200
26	712	1480	2216	2984	3752	4392	5160	5992	6712	7480

ITBS	NPRB
ITBS	101	102	103	104	105	106	107	108	109	110
0	2792	2856	2856	2856	2984	2984	2984	2984	2984	3112
1	3752	3752	3752	3752	3880	3880	3880	4008	4008	4008
2	4584	4584	4584	4584	4776	4776	4776	4776	4968	4968
3	5992	5992	5992	5992	6200	6200	6200	6200	6456	6456
4	7224	7224	7480	7480	7480	7480	7736	7736	7736	7992
5	8760	9144	9144	9144	9144	9528	9528	9528	9528	9528
6	10680	10680	10680	10680	11064	11064	11064	11448	11448	11448
7	12216	12576	12576	12576	12960	12960	12960	12960	13536	13536
8	14112	14112	14688	14688	14688	14688	15264	15264	15264	15264
9	15840	16416	16416	16416	16416	16992	16992	16992	16992	17568
10	17568	18336	18336	18336	18336	18336	19080	19080	19080	19080
11	20616	20616	20616	21384	21384	21384	21384	22152	22152	22152
12	22920	23688	23688	23688	23688	24496	24496	24496	24496	25456
13	26416	26416	26416	26416	27376	27376	27376	27376	28336	28336
14	29296	29296	29296	29296	30576	30576	30576	30576	31704	31704
15	30576	31704	31704	31704	31704	32856	32856	32856	34008	34008
16	32856	32856	34008	34008	34008	34008	35160	35160	35160	35160
17	36696	36696	36696	37888	37888	37888	39232	39232	39232	39232
18	40576	40576	40576	40576	42368	42368	42368	42368	43816	43816
19	43816	43816	43816	45352	45352	45352	46888	46888	46888	46888
20	46888	46888	48936	48936	48936	48936	48936	51024	51024	51024
21	51024	51024	51024	52752	52752	52752	52752	55056	55056	55056
22	55056	55056	55056	57336	57336	57336	57336	59256	59256	59256
23	57336	59256	59256	59256	59256	61664	61664	61664	61664	63776
24	61664	61664	63776	63776	63776	63776	66592	66592	66592	66592
25	63776	63776	66592	66592	66592	66592	68808	68808	68808	71112
26	75376	75376	75376	75376	75376	75376	75376	75376	75376	75376