NR 1 Band 2 sdr
The purpose of this tutorial is to show you how to use multiple sdr cards combined (called Stereo Mode) to implement wide bandwidth that is wider than the maximum bandwidth of single sdr card. As of now, Amarisoft products are based on one of the following two types sdr cards as follows. The main difference between them are maximum bandwidth it can cover.
- SDR50 : It can conver up to 50Mhz bandwidth. Callbox mini and Callbox Classics are using this type of sdr cards. (For further details of this type, check out this document)
- SDR100 : It can cover up to 100Mhz bandwidth. Callbox Pro, Callbox Ultimate are using this type of sdr cards. (For further details of this type, check out this document)
There is no issues (no major differences) for LTE regardless of whether you use SDR50 or SDR100 since the max bandwidth of LTE is only 20 Mhz, but there would be some cases where you come across issues for NR if you are using SDR50 since there are various kinds of configuration that uses the bandwidth wider than 50Mhz. Then how do we test NR with Bandwidth greater than 50Mhz with sdr50 ? This tutorial would provide you with the solution for the case. The idea is to combine two sdr50 cards that enables to handle max 100 Mhz bandwidth.
Table of Contents
- NR 1 Band 2 sdr
Test Setup
Test setup for this tutorial is as shown below.
- SIM Card used in this tutorial is the one delivered with the system as it is.
- If you want to change the configuration, The tutorial Configuration Guide would help
Key Configuration Parameters
Followings are important configuration parameters for this tutorial. You may click on the items for the descriptions from Amarisoft documents.
- rf_driver
- rf_ports
- sample_rate
- n_subband
- guard_band
- band
- bandwidth
Test 1 : NR SA 100 Mhz BW with 2 x sdr50
In this test, I will show you how to configure a SA cell of 100Mhz BW using two sdr50. The max bandwidth that can be supported by a sdr50 is 50Mhz. So with sdr50 card, it would have not been able to simulate a cell with bandwidth greater than 50Mhz. To overcome this limitation, we implemented the feature to combine two sdr50 cards to simulate a cell with the bandwidth greater than 50 Mhz. So in this test, we need to use two SDR 50 cards even though the number of cell is only one.
Configuration
I used the configuration file gnb-sa-2sdr-0-1.cfg which is copied from gnb-sa.cfg and modified.
Configured in gnb-sa-2sdr-0-1.cfg is as shown below. I set NR_BANDWIDTH to 100 Mhz. args:"dev0=/dev/sdr0,dev1=/dev/sdr1" mean that two sdr card sdr0 and sdr1 will be enabled for this test. Another important parameter to configure one cell with multiple sdr card is n_subband parameter in rf_ports. The sample_rate and guard_band are configured to fine tune the two combined sdr cards.
Perform the Test
Run LTE service and check cell configuration in (enb) screen as shown below. Confirm that the Bandwidth are configured as you intended.
Check tx_gain and rx_gain and see if there is any changes comparing to 1 sdr cases. (NOTE : the default / max gain are same as 1 sdr case). In this case, TX0 and TX1 is from sdr0. TX2 and TX3 is from sdr1. RX0 is for sdr0 and RX1 is for sdr1.
Check how RF of each sdr cards are configured. With rf_info command, you can figure out the center frequencies that each sdr cards are tuned to.
Enable bcch log capturing in (enb) as shown below
Check ss-PBCH-BlockPower as shown below. This value would vary depending on channel Bandwidth and Frequency.
Power on UE and let it complete the attach
Test 2 : NR NSA 100 Mhz BW with 2 x sdr50
In this test, I will show you how to configure a NSA cell of 100Mhz BW using three sdr50. The max bandwidth that can be supported by a sdr50 is 50Mhz. So with sdr50 card, it would have not been able to simulate a cell with bandwidth greater than 50Mhz. To overcome this limitation, we implemented the feature to combine two sdr50 cards to simulate a cell with the bandwidth greater than 50 Mhz. So in this test, we need to use three SDR 50 cards in total even though the number of cell is only two. One LTE cell uses one sdr50 card and one NR cell uses tw0 sdr50 cards in this test.
Configuration
I used the configuration file gnb-nsa-2sdr-1-2.cfg which is copied from gnb-nsa.cfg and modified.
Configured in gnb-sa-2sdr-1-2.cfg is as shown below. I set NR_BANDWIDTH to 100 Mhz. If TRX_MAX_BANDWIDTH is narrower than NR_BANDWIDTH, multi sdr card is automatically selected.
args:"dev0=/dev/sdr0,dev1=/dev/sdr1,dev2=/dev/sdr2" mean that two sdr card sdr0,sdr1 and sdr2 will be enabled for this test. The configuration in gnb-nsa.cfg in 2021-11-19 release is automatically handling dev with combined sdr card as follows. This is just for your reference. You don't need to change anything in this part.
Another important parameter to configure one cell with multiple sdr card is n_subband parameter in rf_ports. The sample_rate and guard_band are configured to fine tune the two combined sdr cards. The configuration in gnb-nsa.cfg in 2021-11-19 release is automatically handling rf_ports with combined sdr card as follows. This is just for your reference. You don't need to change anything in this part.
Perform the Test
Run LTE service and check cell configuration in (enb) screen as shown below. Confirm that the Bandwidth are configured as you intended.
Check tx_gain and rx_gain and see if there is any changes comparing to 1 sdr cases. (NOTE : the default / max gain are same as 1 sdr case)
Check how RF of each sdr cards are configured.
Power on UE and let it complete the attach
Check out ue configuration. You would notice that one core network id is assigned and two different cell ID (RAN ID) and RAN_UE_ID are assigned for the same UE in case of NSA cell. One of the cell ID is for LTE cell and the other is for NR cell.
Tips
Using other combinations of sdr card
If you want to combine other two sdr cards (i.e, other than sdr 0 and sdr 1), you can do it by simply changing sdr card number as shown below.
args: "dev0=/dev/sdr
args: "dev0=/dev/sdr