NR SA FDD Asymetric Channel Bandwidth
The purpose of this tutorial is to show you how to set different channel bandwidth for downlink and uplink in NR SA. It is assumed that you don't have any previous experience with Amari callbox.
Asymetric Channel Bandwidth in this tutorial indicates the case where Bandwidth for DL and UL are different. In most cases, it is assumed that the bandwidth of DL and UL is same in most of the default configuration. I think we can think of two ways to configure DL bandwidth and UL bandwidth differently as listed below.
- Setting the number of RBs differently for DL and UL within initial BWP
- Setting a BWP (non-initial BWP) with different bandwidth for DL and UL and switch to the BWP
The first method is used in this tutorial.
Table of Contents
- NR SA FDD Asymetric Channel Bandwidth
Test Setup
Test setup for this tutorial is as shown below.
Key Configuration Parameters
Followings are important configuration parameters for this tutorial. You may click on the items for the descriptions from Amarisoft documents.
Configuration
An important thing in using UE sim is to do proper matching between UE sim configuration and Call box configuration In this tutorial, I used the ue.default.cfg and and enb.default.cfg without any change
If you use other Network (e.g, other network simulator or real network), you have to make it sure to configure UE sim according to the settings on network side
I used ue-sa-fdd-asym.cfg which is copied from ue-nr-sa.cfg.
I used gnb-sa-fdd-asym.cfg which is copied from gnb-sa.cfg.
The configuration in gnb-sa-fdd-asym.cfg (Callbox) is set as follows. The keypoint is that the nuber of RB for n_rb_dl and n_rb_ul are set to be different. NR_TDD is set to 0 since this is for FDD test. The important point in this configuration is that n_rb_dl and n_rb_ul are set differently. n_rb_dl (Downlink bandwidth) is set to the channel bandwidth of 20 Mhz and n_rb_ul (Uplink bandwidth) is set to the channel bandwidth of 10 Mhz
The configuration in ue-sa-fdd-asym.cfg (Callbox) is set as follows. In this configuration, you would notice that only n_rb_dl is configured. UL bandwidth will be detected from SIB1 decoding. NR_TDD is set to 0 since this is for FDD test. In this configuration, bandwidth parameter is commented out since the different bandwidth will be used for DL and UL. Only dl bandwidth is configured with n_rb_dl for UEsim to detect the cell and decode SIBs. UL bandwidth will be informed to UE by SIB1.
Perform the Test
Check out cell configuration with cell phy command and see if the cell is configured as intended. NOTE that there is no information showing the different BW for DL and UL.
If the cell is properly configured. Check if the cell can be detected by UEsim. You can check the cell detection status with cells command. Once cell is properly detected, power on UE.
Now check if UE gets connected to the cell properly. You can do this with t command. If UE properly completes the attach, check if the IP data can go through both uplink and downlink. The simplest way to do this is to ping the UE. If you get the ping reply, it indicates both DL and UL connection is properly established with asymatric bandwidth configured in this test.
Log Analysis
You can confirm on DL and UL bandwidth in SIB1 message.
Confirm DL Bandwidth in locationBandwidth in initialDownlinkBWP. The start RB and bandwidth is configured as RIV in RRC. If you want to convert this RIV to start RB and NRB, use this calculator.
Confirm DL Bandwidth in locationBandwidth in initialUplinkBWP. The start RB and bandwidth is configured as RIV in RRC. If you want to convert this RIV to start RB and NRB, use this calculator.
check if your UE (DUT) support the bandwidth that you configured. You can check it out via featureSetDownlinkPerCC and featureSetUplinkPerCC in UE Capability Information message from the UE.
The same information can be confirmed by Amarisoft Internal log NR band combination.
You would notice that the max PRB does not go over 51st RB for PDSCH (Downlink transmission)
You would notice that the max PRB does not go over 24th RB for PUSCH (Uplink transmission)
RRC / NAS Signaling
SIB1 (SA)
: This is the SIB1 message sent by gNB to configure NR SA. (
{
message c1: systemInformationBlockType1: {
...
servingCellConfigCommon {
downlinkConfigCommon {
frequencyInfoDL {
frequencyBandList {
{
freqBandIndicatorNR 78
}
},
...
},
initialDownlinkBWP {
genericParameters {
locationAndBandwidth 13750,
subcarrierSpacing kHz30
},
offsetToPointA 36,
scs-SpecificCarrierList {
{
offsetToCarrier 0,
subcarrierSpacing kHz30,
carrierBandwidth 51
}
}
},
uplinkConfigCommon {
frequencyInfoUL {
scs-SpecificCarrierList {
{
offsetToCarrier 0,
subcarrierSpacing kHz30,
carrierBandwidth 24
}
},
p-Max 10
},
initialUplinkBWP {
genericParameters {
locationAndBandwidth 6325,
subcarrierSpacing kHz30
},
}