Content for  TR 38.844  Word version:  18.0.0

The gNB broadcasts the DL carrier bandwidth and the bandwidth of the initial BWP (BWP#0) in SIB1. For the 7MHz allocation, SIB1 can indicate DL next larger standard channel bandwidth, i.e. 10 MHz, and that the initial DL BWP can be set to 5 MHz: Once the UE established the RRC connection, the gNB can account for the UE capabilities and configure the UE accordingly. At this point the gNB can configure the UE with the larger channel bandwidth (that used by the UE for initial access is not known to the gNB) and with an additional BWP with a bandwidth that differs from the bandwidth of BWP#0. gNB may configure a larger bandwidth part that will cover the whole 7MHz allocation. with the BWP size taken from Table 6.1.1-1. The PRBs within this BWP can be scheduled. the remaining PRBs in the downlink channel bandwidth are blanked. Alternatively, the BWP size is set to 52 PRB with 35 PRBs scheduled. For the UL the UE is configured with a UE channel bandwidth smaller than the irregular block or equal to the UL BWP#0 size such that this is the only possible channel bandwidth and location during initial access. For uplinkChannelBW-PerSCS-List and scs-SpecificCarrierList symmetric operation bands with fixed duplex distance and asymmetric UL/DL channel bandwidth is band specific aspect which is defined in TS 38.101-1 and TS 38.101-2. Bands which utilize the wider channel bandwidth approach for the irregular bandwidths may need to be adopted for this aspect. Another example of interest to some operators is 5 MHz at the bottom of n12 being shared with 6 MHz at the bottom of n85. The details can be found in Annex A.

We begin by listing the prerequisites and assumptions for the method of using a larger channel bandwidth as described in this subclause to verify that these are consistent with existing specifications and features. There is one carrier of carrier bandwidth N_grid ^size,μ for subcarrier spacing configuration μ per serving cell and transmission direction (UL or DL), with N_grid ^size,μ as defined in TS 38.211. The carrier bandwidth N_grid ^size,μ is indicated in SIB1 by the carrierBandwidth for subcarrier spacing configuration μ in the scs-SpecificCarrierList and is thus cell specific. Furthermore

• the carrier bandwidth N_grid ^size,μ is the BS transmission bandwidth configuration for subcarrier spacing configuration μ (not necessarily the same as a BS maximum transmission configuration for a channel bandwidth specified in TS 38.104)
• the gNB configures all UEs in a cell with an initial BWP (denoted BWP#0) and additional BWPs contained within the said carrier bandwidth indicated in SIB1 for the DL and UL
• the fields downlinkChannelBW-PerSCS-List and uplinkChannelBW-PerSCS-List in dedicated signalling are only used for the purpose of configuring the UE with a size and location of a UE regular channel bandwidth in MHz to ensure compliance with regulatory requirements consistent with the clarification of the use of UE dedicated channel bandwidths (MHz) agreed in [5].

The UE channel bandwidth must be located within the BS channel bandwidth as per the existing clause 5.3.1 of TS 38.104,

• The BS channel bandwidth supports a single NR RF carrier in the uplink or downlink at the Base Station. Different UE channel bandwidths may be supported within the same spectrum for transmitting to and receiving from UEs connected to the BS. The placement of the UE channel bandwidth is flexible but can only be completely within the BS channel bandwidth.

and its corresponding maximum bandwidth configuration must fall within the within the BS transmission bandwidth configuration of the BS channel bandwidth as per clause 5.3.4 of TS 38.104

• For each numerology, all UE transmission bandwidth configurations indicated to UEs served by the BS by higher layer parameter carrierBandwidth defined in TS 38.331 shall fall within the BS transmission bandwidth configuration.

For irregular bandwidths implemented with larger bandwidths we assume that similar rules apply:

• the transmission bandwidth configuration (PRB) corresponding to the irregular bandwidth is within the carrier bandwidths N_grid ^size,μ of the DL and UL carriers indicated to the UE by SIB1, that is, the BS transmission bandwidth configuration of the BS DL that also contain blanked PRBs if larger than the irregular block size
• the BS does not configure a UE with any dedicated channel bandwidth (MHz) outside the carrier resource grid indicated in SIB1.
• the BS channel bandwidth supports a single NR RF carrier in the uplink or downlink as specified in TS 38.104.

The UE need not be aware of the actual BS channel bandwidth, the carrier location and bandwidth are indicated to the UE in SIB1:

• From a UE perspective, the UE is configured with one or more BWP / carriers, each with its own UE channel bandwidth. The UE does not need to be aware of the BS channel bandwidth or how the BS allocates bandwidth to different UEs.

The channel raster defines a subset of RF reference frequencies that can be used to identify the RF channel position in the uplink and downlink. The mapping between the channel raster and the corresponding resource element within a resource grid of a carrier within the RF channel is specified in the same way in TS 38.104 and TS 38.101-1:

• The mapping between the RF reference frequency on the channel raster and the corresponding resource element is given in Table 5.4.2.2-1 and can be used to identify the RF channel position. The mapping depends on the total number of RBs that are allocated in the channel and applies to both UL and DL. The mapping must apply to at least one numerology supported by the BS.

k, n_PRB and N_RB are as defined in TS 38.211 We assume that the corresponding notions in 38.211 are N_RB = N_grid ^size,μ and that n_PRB is relative to a BWP starting at the start of the carrier resource grid indicated by the common resource block, N_BWP,i ^start,μ = N_grid ^start,μ, n_PRB is thus the index of the centre PRB within the resource grid of a numerology. For the configuration examples below, we make the assumption that the N_RB can only take values corresponding to the maximum transmission bandwidth configurations corresponding to channel bandwidths in the respective conformance specifications for the BS and the UE. For an operating band with a 100kHz channel raster this implies that any regular BS and UE channel bandwidth are always mapped to the channel raster. For operations in the field this also means that a configured UE-specific bandwidth within a larger BS channel bandwidth must be on the channel raster just like the BS channel bandwidth. The assumption that UE performance can only be ensured for RRC configurations according to the conformance test specification implies restrictions on the location and bandwidth of UE specific CHBW in operating bands with a 100 kHz channel raster. If the carrierBandwith of the carrier resource grid is an odd/even number of PRBs and the maximum transmission bandwidth configuration for the UE CHBW is even/odd for SCS = 15k, then the corresponding UE-specific CHBW cannot be located anywhere within a wider BS carrier resource grid: the said transmission bandwidth configuration cannot both be PRB aligned and separated by a multiple of 100 kHz to the center SC of the resource grid on the channel raster for m*180 + 90 = n*100 has no solution for any integers. If, on the other hand, the carrierBandwidth of the carrier resource grid is an odd/even number and the maximum transmission bandwidth configuration for the UE CHBW is odd/even for SCS = 15k, then the UE-specific CHBW can only be located with 5 PRB granularity, solutions to m*180 = n*100. Notwithstanding the above we assume that symmetric UE-specific channel bandwidths (MHz) can be set at the default duplex spacing: the centre frequencies of the UL and DL channel bandwidths as set by the parameters of the downlinkChannelBW-PerSCS-List and uplinkChannelBW-PerSCS-List should be at default duplex spacing that is, the default TX-RX carrier centre frequency separation as specified in clause 5.4.4 of TS 38.101-1. We also assume that the BWP#0 are configured such that the UE can locate symmetric CHBW at default duplex spacing during initial access. Next, we illustrate the method for a 7 MHz block within an operating band with a 100k channel raster and assuming the restrictions that

• the SIB1 carrierBandwidth and any UE specific channel bandwidth on the 100k channel raster, carrier bandwidths and maximum transmission bandwidth configurations for UL and DL either all odd or all even, otherwise impossible to put a narrower channel inside a wider BS/cell bandwidth
• the BS channel bandwidth supports a single NR RF carrier in the uplink or downlink as specified in TS 38.104. UL/DL carrierBandwidth in SIB1 only to a UE channel bandwidth (Rel-15)

We also note that these restrictions may impact the number of PRB that can be scheduled within the irregular spectrum block (the number of blanked PRB within the carrier resource grid) or the actual irregular spectrum block size that can be supported. Figure 6.1.2.1.2-1 shows the configuration, the next-after-next larger bandwidth is used in this case such that the resource grid size of this and the smaller bandwidth used for the UL are both an odd number of PRBs. The size of the BWP#0 is 25 PRB in both the UL and DL, located at duplex spacing such that a UE only capable at locating its CHBW at the 100k channel raster can attach. UEs supporting the asymmetric channel bandwidth combination 5 MHz and 15 MHz can utilize the irregular block (the cell bandwidth) and legacy UEs not supporting this bandwidth combination can also be supported in the cell. UEs not supporting the 5 MHz channel bandwidth will not attach to the cell thus ensuring that unwanted emissions requirements in the UL are met by all capable UEs.

The SIB1 procedure for initial attach is separate for the UL and DL. In case some UE implementations do not allow different carrier grid for the UL and DL (while still corresponding to UE CHBWs) then the next-after-next larger BW and PRB blanking can be used both in the UL and DL. The downside of this arrangement is that unwanted emissions are not ensure in case the UE uses a bandwidth wider than the BWP#0 (25 PRB) during initial access. The Point A of the UL and DL can be located with 5 kHz granularity. The arrangement in Figure 6.1.2.1.2-1 would not support the case of an irregular block 817-824/862-869 MHz at the lower part of n26. However, the DL carrier grid corresponding to the 15 MHz CHBW can be shifted upwards by n*900 MHz (5 PRB) such that the 15 MHz CHBW is within the band range (above 814 MHz) thus increasing the BS duplex spacing between the UL and DL carriers while maintaining PRB alignment and the default duplex spacing for the 2 x 5 MHz UE-specific bandwidths and the BWP#0. The default duplex spacing is not specified for the BS (cell) bandwidth and the SIB1 procedure for initial attach is separate for the UL and DL. The methods only require one specification change: the UE must support the asymmetric channel bandwidth pair 5/10 MHz or 5/15 MHz for Band n26. Regular CHBW bandwidths are used for UE conformance tests, while the BS must meet the unwanted emissions limits and other regulatory requirements also for the irregular spectrum block.

The method can readily be applied to the TDD case. Most TDD bands have an SCS-based raster rather than a 100k raster for alignment with LTE and therefore not subject to any potential restrictions that UE-specific CHBW cannot be configured with PRB granularity within a carrier resource grid. However, TDD is subject to restrictions on the center frequency of BWPs and the location of the Point A. Asymmetric bandwidths are also supported for TDD in existing specification with restrictions. For the TDD case and bands we make the following additional assumptions:

• the carrier resource grids indicated in SIB1 for the UL and DL, the BWPs configured and UE-specific CHBW are all PRB aligned and use the same center frequency;
• the carrier bandwidths for UL and DL (PRB) advertised in SIB1 are either both even or odd, the same applies for the transmission bandwidth configuration of the UE-specific CHBW are both either even or oddfor PRB alignment;
• the UE dedicated regular channel bandwidths (MHz) with their corresponding maximum transmission bandwidth configurations (including the larger) are located within the DL and UL carrier bandwidths that may also include blanked PRBs.

This would also ensure that the UE-specific CHBW meet the existing conditions for asymmetric bandwidths (Rel-16):

• both center frequency and BWP-ID shall match between DL and UL carriers as defined in TS 38.331;
• in a case a UE is configured with a full width of BWP within both UL/ DL channels, the center frequency of UL/ DL channels shall be same;
• a position of Point A is common between UL and DL carriers as defined in TS 38.331.

Figure 6.1.2.1.3-1 shows an example of a 55 MHz spectrum block with DL and UL carrier grids of different sizes for SCS = 30k, about 145 PRBs used (not blanked) in the DL. The DL carrier resource grid size of mPRB = 189 PRB corresponds to the next-after-next larger DL bandwidth of 70 MHz, while the UL carrier bandwidth indicated in SIB1 is mPRB - 2u = 133 PRB corresponds to the next smaller bandwidth of 50 MHz with 2u the symmetric DL extension (both the UL and DL carrier grids are thus either odd or even sized) also covering blanked PRB. The bandwidth of BWP#0 is equal for the DL and UL and sized 133 PRBs or smaller. Thus legacy UEs only supporting symmetric CHBW can also attach to the cell.

It is recognised that the restrictions above can imply limitations on the transmission bandwidth configuration of an irregular block (PRBs not blanked) or the irregular spectrum block size supported. However, it suffices that UEs support asymmetric bandwidths for the TDD band, a 50/70 MHz combination for the case above. The method above also works for TDD bands with a 100k channel raster. The case of an irregular spectrum block at the band edge is described in clause 6.1.2.4.