5G/NR - SUL                                                     Home : www.sharetechnote.com

 

 

 

 

 

SUL stands for Supplimentary Uplink. Basic idea (or Use Case) on SUL is described/illustrated as shown below in 38.300.

 

 

< 38.300-Figure B.1-1: Example of Supplementary Uplink >

 

The basic idea behind this is as follows.

    i) Usually cell coverage in UL direction is lower than DL direction because UE Tx Power(UL Power) is not as strong as gNB Tx Power(DL Power).

    ii) The performance degradation on UL direction due to this difference gets very serious as the UE approaches to cell edge.

    iii) As a possible solution, an idea to use very low frequency than the original UL frequency is proposed. As you know, cell coverage gets larger as frequency gets lower.

    iv) this (to use a secondary UL at much lower frequency) is the idea behind SUL. When the channel condition is good, Network tell UE to use the original UL frequency and when channel condition gets poor than a certain criteria, Network directs UE to use the secondary(supplementary) UL frequency.

There are several NR bands dedicated for SUL which are n80, n81, n82, n83, n84, n86. As you see in this table, these are all under 2Ghz which is lower than commonly used NR frequency(e.g, over 3Ghz). However, one possible drawback of this approach is that these SUL bands are colliding with existing LTE bands. So it would cause NR-LTE Co Existance issues. You would need some researches on SUL and NR/LTE Coexistance issue before you make decision to deploy any SUL. See TR 37.872 and TR 37.716 for the details on SUL and NR/LTE CoExistance.

 

 

Would SUL be useful in real practice and widely deployed ? See this blog by Martin.

 

 

 

Operation Highlights

 

What I mentioned above is based on my intuitive understanding on SUL operation. In this section, I will quote some formal description from 3GPP specification for your (my) reference.

 

38.300 - 5.4.2 state as follows :

    In conjunction with a UL/DL carrier pair (FDD band) or a bidirectional carrier (TDD band), a UE may be configured with additional, Supplementary Uplink (SUL). SUL differs from the aggregated uplink in that the UE may be scheduled to transmit either on the supplementary uplink or on the uplink of the carrier being supplemented, but not on both at the same time.

38.300 - 6.9 state as follows :

    In case of Supplementary Uplink, the UE is configured with 2 ULs for one DL of the same cell, and uplink transmissions on those two ULs are controlled by the network to avoid overlapping PUSCH/PUCCH transmissions in time. Overlapping transmissions on PUSCH are avoided through scheduling while overlapping transmissions on PUCCH are avoided through configuration (PUCCH can only be configured for only one of the 2 ULs of the cell).

38.300 - 9.2.6 state as follows :

    For initial access in a cell configured with SUL, the UE selects the SUL carrier if and only if the measured quality of the DL is lower than a broadcast threshold. Once started, all uplink transmissions of the random access procedure remain on the selected carrier.

38.300 - 10.3 state as follows :

    When CA is configured, at most one configured uplink grant can be signalled per serving cell. When BA(Bandwidth Adaptation) is configured,at most one configured uplink grant can be signalled per BWP. On each serving cell, there can be only one configured uplink grant active at a time. A configured uplink grant for one serving cell can either be of Type 1 or Type 2. For Type 2, activation and deactivation of configured uplink grants are independent among the serving cells. When SUL is configured, a configured uplink grant can only be signalled for one of the 2 ULs of the cell.

 

 

 

Band Combinations for SUL

 

Followings are the table that I consolidated multiple tables from TR 37.872

 

SUL Band combination

NR Band

Uplink (UL) band

Downlink (DL) band

Duplex

mode

BS receive / UE transmit

BS transmit / UE receive

FUL_low FUL_high

FDL_low FDL_high

SUL_n78-n80

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n80

1710 MHz

1785 MHz

SUL

SUL_n79-n80

n79

4400 MHz

5000 MHz

4400 MHz

5000 MHz

TDD

n80

 1710 MHz

1785 MHz

SUL

SUL_n78-n84

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n84

 1920 MHz

1980 MHz

N/A

SUL

SUL_n78-n82

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n82

 832 MHz

862 MHz

N/A

SUL

SUL_n78-n81

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n81

 880 MHz

915 MHz

N/A

SUL

SUL_n78-n83

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n83

 703 MHz

748 MHz

N/A

SUL

SUL_n78-n86

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n86

 1710 MHz

1780 MHz

N/A

SUL

SUL_n79-n81

n79

4400 MHz

5000 MHz

4400 MHz

5000 MHz

TDD

n81

 880 MHz

915 MHz

N/A

SUL

 

 

Following is the table for SUL with ENDC. You would notice that all LTE is FDD and all NR is TDD, and NR SUL is in same frequency range in LTE UL range implying that NR UL and LTE UL would share the frequency range.

 

E-UTRA and NR DC Band

E-UTRA and NR Band

Uplink (UL) band

Downlink (DL) band

Duplex

mode

BS receive / UE transmit

BS transmit / UE receive

FUL_low FUL_high

FDL_low FDL_high

DC_3-SUL_n79-n80

3

1710 MHz 

1785 MHz

1805 MHz 

1880 MHz

FDD

n79

4400 MHz

5000 MHz

4400 MHz

5000 MHz

TDD

n80

1710 MHz

1785 MHz

NA

SUL

DC_1-SUL_n78-n84

1

1920 MHz 

1980 MHz

2110 MHz 

2170 MHz

FDD

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n84

1920 MHz

1980 MHz

NA

SUL

DC_20-SUL_n78-n82

20

832 MHz 

862 MHz

791MHz 

821 MHz

FDD

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n82

832 MHz

862 MHz

NA

SUL

DC_8-SUL_n78-n81

8

 880 MHz

915 MHz

 925 MHz

960 MHz

FDD

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n81

 880 MHz

915 MHz

N/A

SUL

DC_28-SUL_n78-n83

28

 703 MHz

748 MHz

758 MHz 

803 MHz

FDD

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n83

 703 MHz

748 MHz

N/A

SUL

DC_66-SUL_n78-n86

66

1710 MHz 

1780 MHz

2110 MHz 

2200 MHz

FDD

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n86

 1710 MHz

1780 MHz

N/A

SUL

DC_8-SUL_n79-n81

8

880 MHz 

915 MHz

925 MHz 

960 MHz

FDD

n79

4400 MHz

5000 MHz

4400 MHz

5000 MHz

TDD

n81

880 MHz

915 MHz

N/A

SUL

DC_3-SUL_n78-n82

3

1710 MHz 

1785 MHz

1805 MHz 

1880 MHz

FDD

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n82

832 MHz

862 MHz

N/A

SUL

DC_20-SUL_n78-n83

20

832 MHz 

862 MHz

791 MHz 

821 MHz

FDD

n78

3300 MHz

3800 MHz

3300 MHz

3800 MHz

TDD

n83

703 MHz

748 MHz

N/A

SUL

 

 

 

 

Reference

 

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