4G/LTE - LTE NB

Multi Carrier Operation

NB-IoT can operate in multi carrier mode. In this case, a specific carrier is configured for initial connection setup + data transfer and other carriers are configured only for data communication. The carrier for the initial connection setup is called Anchor carrier and the other carriers are called Non-Anchor carrier.

When NB-IoT is operating in 'inband with the same PCI' mode, only a specific PRB within the legacy LTE System Band can be configured as Anchor carrier. The PRB index within LTE System BW are as follows.

 LTE System BW LTE PRB indices for NB-IoT synchronization 3 Mhz 2, 12 5 Mhz 2, 7, 17, 22 10 Mhz 4, 9, 14, 19, 30, 35, 40, 45 15 Mhz 2, 7, 12, 17, 22, 27, 32, 42, 47, 52, 57, 62, 67, 72 20 Mhz 4, 9, 14, 19, 24, 29, 34, 39, 44, 55, 60, 65, 70, 75, 80, 85, 90, 95

The above table is derived from following equation and table described in 36.213-16.8. The values in above table is nPRB in the following equation. is the max number of RB for a specific channel bandwidth. eutra-CRS-SequenceInfo is the parameter in NPBCH (NR MIB).

For example, if eutra-CRS-SequenceInfo = 7 and LTE channel Bandwidth is 5 Mhz. The nPRB can be calculated as follows.

n'PRB = 5 (for 5Mhz, = 25 which is odd number)

5 = nPRB - floor(25/2) = nPRB - 12

Therefore, nPRB = 17

< 36.213 - Table 16.8-1: Definition of eutra-CRS-SequenceInfo >

In terms of physical channel composition, there are some differences between Anchor and Non-Anchor carrier.

• Anchor Carrier : As shown in Figure 1, Anchor Carrier carries NRS, NPSS, NSS, NPBCH, NPDSCH, NPDCCH
• NonAnchor Carrier : As shown in Figure 2, NonAnchor Carrier carries only NRS, NPDCCH, NPDSCH

NOTE : I created Figue 1 and 2 using Matlab LTE Toolbox based on Matlab 2018b

< Figure 1 :  Physical Channel Composition - Anchor Carrier >

< Figure 2 :  Physical Channel Composition - NonAnchor Carrier >

Reference :

[1] Narrowband Internet of Things (R&S Whitepaper)