Content for  TR 38.844  Word version:  18.0.0

• Studied spectrum blocks covered by "main RF carrier" and "additional RF carrier"
• The "main RF carrier" is Rel-15 compatible and contains the SSB as well as all necessary broadcast information, legacy UEs and UEs which do not support this solution are able to camp on it and be connected without being aware of the "additional RF carrier"
• The "additional RF carrier" , which is partially overlapping with the "main RF carrier", is aligned to the "main RF carrier" PRB grid and utilizes further PRBs that fit in relevant spectrum block. UEs which support this solution would be reconfigured (once UE capabilities are known) in RRC_CONNECTED to use wider CBW and BWP than used for initial access.
• The "main RF carrier" and the "additional RF carrier" are treated as single cell (one carrier from baseband perspective) to allow for a single BWP to cover studied spectrum block in RRC_CONNECTED
• Both the "main RF carrier" and the "additional RF carrier" would clearly define the size and position of the guard band which allows for an unambiguous placement of the overlapping channel filters and thus prevents problems with OBUE, ACS or in-band blocking
• From UE perspective, supported in downlink only

In this section we provide further signaling details on how to support irregular channels given the 7MHz allocation as an example. The gNB broadcasts the DL carrier bandwidth and the bandwidth of the initial BWP (BWP#0) in SIB1. For the 7MHz allocation, SIB1 would indicate DL standard channel bandwidth (i.e. 5 MHz), the initial DL BWP would be set to 5 MHz to accommodate legacy and new UEs: Once the UE established the RRC connection, the gNB can account for the UE capabilities and re-configure the UE accordingly. At this point the gNB may override the carrier bandwidth value that the UE obtained from SIB1 and configure a dedicated 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. It should be noted that 36 PRBs do not correspond to any channel bandwidth currently defined in TS 38.101-1. It is possible from signalling point of view to override the SIB1 channel bandwidth by the dedicated channel bandwidth signalling in RRC_CONNECTED if the UE is capable of the dedicated channel bandwidth, and if the network ensures the SIB1 channel bandwidth and dedicated channel bandwidth use the same PRB grid. New capability might be needed to support such configuration [3].

With respect to the UE architecture, the following assumptions are made (according to SID objectives):

• New (dedicated) channel filters (e.g. non-integer-multiples of 5 MHz) are not considered
• UEs not supporting this solution (both legacy and new UEs) should be able to use the next lower supported channel bandwidth in the UL and DL without implications

Two different UE architecture scenarios are explained (legacy UEs using next smaller bandwidth in clause 6.6.2 and UEs supporting two receive chains for reception described below): This option is for new UEs that contain transceiver architectures and configurations that have flexibility in local oscillator and receive chain assignments. The flexibility in the configuration allows the UEs to configure their receive paths (Antenna to FFT) similarly to non-contiguous carrier aggregation, allowing the two LO and receive chains to down-convert the spectrum of the irregular bandwidth as if it consisted of two separate carriers on the UE side. Based on the channel center of the main RF carrier and the configured irregular bandwidth, the UE would know where to place the center frequency of the additional RF carrier that follows the PRB grid (which overlaps with the main RF carrier and includes the remaining agreed PRBs for the irregular BW). The UE down-converts two different sets of PRBs, with an overlapping segment and may use for irregular bandwidth below 15MHz the next smaller bandwidth channel filtering on both of the receive chains as shown in Figure 6.2.2.3-1 ("DigRF" serves as an example only and corresponds to the interface between RF and baseband chipset). This allows the UE to benefit from channel filtering designed for the specific bandwidth. Using the next smaller bandwidth channel filtering on both of the two carrier parts, the baseband signal processing following the FFTs must be modified such that the signals from these two carrier parts are combined and processed as a single codeword instead of being process separately. Since the LOs on the UE will operate at different frequencies, there will be a phase difference of the two signals contained in the two receive chains for the separate carriers. In order to prevent problems in the channel estimation if there is an averaging or interpolation across reference signals at different subcarriers, the phases of the symbols in the frequency domain from both RF receive chains caused by the UE's use of separate LOs should be aligned. This can be achieved by a new function comparing the overlapping symbols from both FFT outputs and phase shifting one FFT output accordingly before the FFT outputs are merged.

Depending on the receiver architecture and the distribution of the channel filtering between the analogue and the digital domain, it is also possible to A/D convert a frequency range that accommodates the entire irregular BW and to split the signal afterwards by means of NCOs (instead of LOs) into the 2 RF carriers with their individual channel filter positions as shown in Figure 6.2.2.3-2.