DC Carrier in NR_2

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In this article, we will learn the interview QUS and ANS of DC Carrier for NR and LTE and why it is needed.



Why in LTE, Data is not transmitted on DC subcarrier?

DC subcarrier is typically excluded in LTE because it can suffer interference from local oscillator leakage. Local oscillator leakage can impact the performance of the DC subcarrier.

Why in NR, Data is transmitted on DC subcarrier?

New Radio (NR) allows the DC subcarrier to be used based upon the assumption that modern transceivers are able to manage the impact of local oscillator leakage.

For Different BWP, is it possible to configure DC subcarrier location?

Yes, the network can configure different DC locations for different BWP.

In Which message The device can find DC subcarrier location in the case of ENDC (NSA)?

In RRC reconfigure msg for SCG addition (which is also known as CG-config)

In Which message The device can find DC subcarrier location in the case of SA?

From SIB1


How does the device locate the DC subcarrier location in NSA or SA case?

DCsubcarrier location is located by device based on the higher layer parameter “txDirectCurrentLocation” in the SCS-SpecificCarrier IE.


Where does devices can find DC location for downlink BWP and what is the range?

For the downlink, the higher layer (RRC) parameter “txDirectCurrentLocation” (we can say it is optional if the operator does not configure this IE it will take some default value, we ll learn in upcoming QUS ) in the ‘SCS-SpecificCarrier’ IEs indicates the location of the transmitter DC subcarrier in the DL for each of the numerologies (15/30/60/120/240 KHz) configured in the downlink. The UE receiver can benefit from knowing the position of the DC subcarrier, i.e. knowing which subcarrier may have degraded performance.
Values in the range 0 – 3299 (Maximum RB 275*15) represent the number of the DC subcarrier.


Is it necessary to configure txDirectCurrentLocation in SCS-SpecificCarrier IE for Downlink BWP? Or

What if txDirectCurrentLocation does not configure for Downlink BWP?


It is the optional IE, if this IE is not configured then, as per spec device will take the value 3300 indicates that the DC subcarrier is located outside the resource grid.
txDirectCurrentLocation indicates the DL Tx Direct Current location for the carrier. A value in the range 0 to 3299 indicates the subcarrier index within the carrier. The values in the value range from 3301 to 4095 are reserved and ignored by the UE.
If this field is absent (operator does not configure) for downlink within Serving CellConfigCommon and Serving CellConfigCommonSIB, the devices assumes the default value of 3300 i.e. "Outside the carrier". The network does not configure this field via Serving CellConfig or for uplink carriers.

Where does devices can find DC location for uplink BWP and what is the range?

For the UL, the higher-layer (RRC) parameter txDirectCurrentLocation in the Uplink TxDirectCurrent BWP IE indicates the location of the transmitter DC subcarrier in the UL (Uplink) for each of the configured BWP (bandwidth parts). Including whether the Direct Curren subcarrier location is offset by 7.5 kHz relative to the center of the indicated subcarrier or not.
Values in the range 0 to 3299 represent the number of the DC subcarrier.

Is it necessary to configure txDirectCurrentLocation in SCS-SpecificCarrier IE for uplink BWP? Or

What if txDirectCurrentLocation does not configure for uplink BWP?

It is the optional IE, if these IE is not configure then, As per spec device will take, the value 3300 indicates that the DC subcarrier is located outside the resource grid, and the value 3301subcarrier indicates that the position of the DC subcarrier in the UL is undetermined. 
txDirectCurrentLocation The uplink Tx Direct Current location for the carrier. Only values in the value range of this field between 0 subcarrier to 3299 subcarrier, which indicates the subcarrier index within the carrier corresponding to the numerology of the corresponding uplink BWP and value 3300 subcarrier, which indicates "Outside the carrier" and value 3301 subcarrier, which indicates "Undetermined position within the carrier" is used in this version of the specification. 

What does the txDirectCurrentLocation value specifies?

The value specifies the subcarrier index which can range from 0 to 3299, i.e. 275 x 12 = 3300 values.  A special value of 3300 indicates that the DC subcarrier is outside the channel bandwidth (BWP).



Stay tune for more Update…………………

Pinal Dobariya…  







References:
TS 38.211, clause 4.4.2
TS 38.331

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