NR FDD bands with variable duplex and corresponding framework

NR FDD bands with variable duplex and corresponding framework

  November 07, 2020    Mr. Standards

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Supplementary downlink (SDL) frequency bands are defined within NR specifications in accordance with regulated licensed bands such as in the 1400-1500MHz range in Europe, and Uplink Sharing is defined as a means to operate NR uplink on the uplink resources of other bands, e.g. sharing the uplink carrier with that of an LTE carrier. Such a configuration may be particularly useful when there is not a desire to allocate downlink NR resources in a 2nd downlink carrier, e.g. for an EN-DC configuration with the SDL band as part of the secondary cell group (SCG).

This work item allows the uplink and downlink of the introduced bands to be from 2 different licensed spectrum blocks, and new paired bands are defined in the RF specifications as n91, n92, n93 and n94.

System parameters

System parameters for the new variable duplex FDD bands are defined in all the related RAN4 specifications including, operating bands, channel bandwidth, rasters, Tx-Rx separation, etc.

Operating bands and NR-ARFCN

Newly introduced variable duplex bands have the same UL frequency parts as in SUL bands either n81 or n82, while they also have the same DL frequency parts as in SDL bands n75 or n76.

n91	832 MHz – 862 MHz	1427 MHz – 1432 MHz	FDD9
n92	832 MHz – 862 MHz	1432 MHz – 1517 MHz	FDD9
n93	880 MHz – 915 MHz	1427 MHz – 1432 MHz	FDD9
n94	880 MHz – 915 MHz	1432 MHz – 1517 MHz	FDD9

A note 9 is specified in the table that says ‘Variable duplex operation does not enable dynamic variable duplex configuration by the network, and is used such that DL and UL frequency ranges are supported independently in any valid frequency range for the band’. This comes from the concern that the operator may want to dynamically configure the duplex distance used in the network.

Channel bandwidth

Since the frequency parts of the variable duplex FDD bands are acquired independently, asymmetric bandwidths must be introduced to accommodate most of the desired deployments.

NR Band	Channel bandwidths for UL (MHz)	Channel bandwidths for DL (MHz)
n911	10	5
n921	5	10, 15, 20
	10	15, 20
n931	10	5
n941	5	10, 15, 20
	10	15, 20
NOTE 1:   The assignment of the paired UL and DL channels are subject to a TX-RX separation as specified in clause 5.4.4.

Hence other bandwidth configurations of the variable duplex FDD bands follow what was defined for the corresponding UL or DL bands that are consisted of.

Tx-Rx separation

It is worth noting that Tx-Rx separation is defined in a different way for the variable duplex bands since the default separation no longer applies with them.

NR Operating Band	TX – RX carrier centre frequency separation
n91	570 MHz – 595 MHz (NOTE 2)
n92	575 MHz – 680 MHz (μ = 0) 580 MHz – 675 MHz (μ = 1) (NOTE 2)
n93	517 MHz – 547 MHz (NOTE 2)
n94	522 MHz – 632 MHz (μ = 0) 527 MHz – 627 MHz (μ = 1) (NOTE 2)

Note 2 says that the range of Tx-Rx frequency separation given paired UL and DL channel bandwidths BW_UL and BW_DL is given by the respective lower and upper limit F_{DL_low} – F_{UL_high} + 0.5(BW_DL + BW_UL) and F_{DL_high} – F_{UL_low} – 0.5(BW_DL + BW_UL). The UL and DL channel bandwidth combinations specified in Table 5.3.5-1 and 5.3.6-1 depend on the subcarrier spacing configuration μ.

UE requirements

UE requirements considering the characteristics when operating in the variable duplex bands and band combinations are defined including REFSENS and related configurations.

REFSENS and UL configurations

REFSENS requirements follow the ones defined for n75 and n76 correspondingly for the variable duplex bands but UL configurations are not necessarily the same with those defined for n8 and n20. For n20, additional restrictions on the UL RBs are specified so that the same REFSENS value can be achieved with such a narrow duplex distance. Since the variable duplex bands have much larger expected Tx-Rx separation, additional restrictions on the UL RB allocations are not specified.

BS requirements

BS requirements span among a series of specifications such as 38.104, 38.141-1, 37.104, 37.105, 37.141, 37.145-1, 37.145-2, 36.104, 36.141, etc. Mainly coexistence requirements are defined in these specs.

Additional spurious emission requirements

Respective requirements which correspond to BS spurious limits for co-existence with systems operating in the new variable duplex FDD bands are introduced in the mentioned spec, with maximum measured spurious levels and bandwidth configurations.

Out of band blocking requirements

Another set of Tx requirements is also defined with the similar manner as the above one. The requirements apply when co-location with other BS-s operating in the variable duplex FDD bands is observed.

Receiver response under co-location requirements

Receiver response requirements are defined in the mentioned specifications that the BS operating in the introduced bands should have the ability to block unwanted interband interferences from any other collocated BS.

For all the above mentioned BS requirements, both conducted and radiated requirements are defined.