Calibrating TX – RX Turnaround Time Delay for MIMO Application Framework 1.1

Publish Date: Oct 17, 2017 | 0 Ratings | 0.00 out of 5 | Print | Submit your review

Table of Contents

  1. Introduction
  2. Calibration Process

1. Introduction

During the development of LabVIEW Communications MIMO Application Framework 1.1, the antennas in either the base station (BS) or the mobile station (MS) were connected directly to the USRP RIO device without using extra cables. Therefore, the calibration parameters were derived based on this setup.  However, you may use antenna arrays in your setup. Both sides of the communication link use extra cables. As a result, the calibration parameters should be modified. The following sections summarize those parameters. For more information about the receive-transmit timing calibration, refer to Section 6.3.3 in the MIMO Application Framework 1.1 Manual.

Locating Single Antenna Mobile Station Parameters

1. Open Single Antenna Mobile Station Host.
2. Open MIMO Initialize SISO Mobile Station.
3. Find MIMO Configure UE Trigger Delays as shown in the following figure.

MIMO Configure UE Trigger Delays

Figure 1: MIMO Configure UE Trigger Delays

Inside the above block, MIMO Configure UE Trigger Delays uses a switch case with two cases based on the USRP RIO model (40 MHz bandwidth (BW) or 120 MHz BW). The following figures present the calibration parameters of both models.

Figure 2: Single Antenna MS Calibration Parameters for USRP RIO 40 MHz BW (120 MS/s)

Figure 3: Single Antenna MS Calibration Parameters for USRP RIO 120 MHz BW (200 MS/s)

Locating Base Station and Multi-Antenna Mobile Station Parameters

The calibration parameters of BS and multi-antenna MS are in the same node. Complete the following steps to locate this node.

For BS:

1. Open Base Station Host.
2. Open MIMO Initialize System.
3. Open MIMO Initialize RRH Transceivers.
4. Open MIMO Configure Trigger Delays.

For multi-antenna MS:

5. Open Multi Antenna Mobile Station Host.
6. Open MIMO Initialize System.
7. Open MIMO Initialize RRH Transceivers.
8. Open MIMO Configure Trigger Delays.

A switch case is used with two cases based on the USRP RIO model. Figures 4 and 5 present the calibration parameters of both models.

Figure 4: BS and Multi-antenna MS Calibration Parameters for USRP RIO 40 MHz BW (120 MS/s)

Figure 5: BS and Multi-antenna MS Calibration Parameters for USRP RIO 120 MHz BW (200 MS/s)

Back to Top

2. Calibration Process

Selecting the Test Benches

To calibrate the above parameters, some test benches were created and placed in a ZIP file. Complete the following steps to select the test benches.

The hardware setup must be similar to that of the BS or multi-antenna MS in the MIMO Prototyping System Getting Started Guide. However, you must only use the master USRP device with another USRP device in the BS rack.

1. Launch LabVIEW Communications System Design Suite 2.0 by selecting LabVIEW Communications 2.0 from the Start menu.
2. Select Application Frameworks from the Project Templates on the launched Project tab.
3. Select MIMO Development to launch the project.
4. Save the created project in an appropriate folder.
5. Copy the calibration file into this folder so that the test benches are available for use.
6. Click on Refresh Icon presented in the toolbar. The calibration folder should appear.
7. Right-click on the calibration folder and then include it to the project.
8. Click on the given 5 test benches and select Controller for PXI for all of them.

UE Bit Processing Calibration

Tip: To calibrate the TX radio frame baseband delay, use the calibration test bench UE Bit Processing Delay Calibration. It is very useful for future modifications.

Figure 6: Front panel of the UE Bit Processing Delay Calibration Test Bench

TX – RX Turnaround Time of MS and RRH Calibration

You must calibrate the time delay of the MS's TX chain from radio frame start trigger to the first sample falling into the first-in-first-out memory buffer (FIFO) of the MS RX chain. The test bench Tx Rx Turnaround Time Calibration UE was created for this issue. This test bench measures the rx start trigger delay shown in Figures 2 and 3.

Similarly, the Tx Rx Turnaround Time Calibration RRH test bench was created for the remote radio head (RRH) USRP RIO device. It measures the rx start trigger delay shown in Figures 4 and 5 based on the USRP RIO model. As an example, Figure 7 shows the delay of RRH. A Boolean control is used to select the USRP RIO model. The estimated value for the rx start trigger delay is 282, which is similar to that shown in Figure 4.

Figure 7: Rx start trigger delay of RRH

TX – RX Turnaround Time Calibration

The calibration test bench Tx Rx Turnaround Time Calibration 2x2 was created to calibrate the TX radio frame trigger delay. The required parameters are shown in Figure 8 and are as follows:

• The RRH RIO address and the MS RIO address. The RRH RIO should be the master USRP RIO that provides the reference trigger in the BS rack.
• The number of TX radio frames
• The USRP RIO model
• The TX trigger selection: external trigger or synchronization

Figure 8: Test Bench Parameters

Many indicators are available in the front panel of the Tx Rx Turnaround Time Calibration 2x2 test bench.  The most important parameter is the UE TX delay [Clock cycles].

In the following experiment, the USRP-2943 Software Defined Radio Reconfigurable Device (40 MHz BW) is used during the test. The experiment is repeated two times based on the synchronization mode. The default parameters presented above were left without any change as shown in Figure 9. In both modes of synchronization, the calibration mode uses the default parameters of external trigger.

Figure 9: Default Parameters in MIMO Application Framework 1.1

In this experiment, the antennas connect directly to RRH USRP RIO and MS USRP RIO without any cables. The resulting UE TX delays [Clock cycles] for both cases of synchronization (using external trigger and over the air) are shown in the following figures, respectively.

Figure 10: Using External Trigger

Figure 11: Using Over the Air Synchronization

In case of using external trigger, the UE TX delay [Clock cycles] is approximately 0 shown in Figure 10. While in case of using over the air synchronization, it is approximately 394 clock cycles shown in Figure 11. The tx radio frame trigger delay should be updated by subtracting the resulting value from the default value of tx radio frame trigger delay (1,199,965) that is shown in Figure 9. Hence, the tx radio frame trigger delay of over the air synchronization mode, should be adjusted as follows: 1,199,965 – 394 = 1,199,571. Figures 2 and 3 show the default values of MS trigger delays for the USRP RIO 40 MHz BW and USRP RIO 120 MHz BW, respectively.

Figure 14 shows the required connections if cables are used.

Figure 14: Cable Connections for TX – RX Turnaround Time Delay Calibration


Locating the Time Division Duplex (TDD) Switching Delay

Complete the following steps to locate the TDD switching delay.

Single antenna MS:

1. Open Single Antenna Mobile Station Host.
2. Open MIMO Initialize SISO Mobile Station.
3. Find MIMO Configure TDD Switching.

BS:

1. Open Base Station Host.
2. Open MIMO Initialize System.
3. Open MIMO Initialize RRH Transceivers.
4. Find MIMO Configure TDD Switching.

Multi-antenna MS host:

1. Open Multi Antenna Mobile Station Host.
2. Open MIMO Initialize System.
3. Open MIMO Initialize RRH Transceivers.
4. Find MIMO Configure TDD Switching.

The TDD switching delay is shown in Figure 15 for both USRP models.

Figure 15: TDD Switching Delay

To re-calibrate the TDD switching delay, the TDD Switching Calibration test bench was created using two USRP RIO devices. The TDD switching delay (clock cycles) indicator shows the TDD switch delay in clock cycles as shown in Figure 16 for USRP RIO 120 MHz. Figure 17a shows the antenna connections based on the default setup in the MIMO Application Framework 1.1. You can select two USRP RIO devices from the rack of MIMO Prototyping System, where the transmitter USRP device should be the Master USRP in the BS rack. Figure 17b shows the required connections if you use cables. Add two attenuators if you have a direct connection.

Note: If the valley shown in Figure 17 is not detected, you can change the value of Amplitude Difference (dB) control to identify the valley.

Figure 16: TDD Switching Delay

(a) Using Antennas

(b) Using Cables with Attenuators

Figure 17: Required Setup to Measure the TDD Switching Delay

 

 

 

 

 

 

 

 

Back to Top

Bookmark & Share


Downloads


Ratings

Rate this document

Answered Your Question?
Yes No

Submit