The primary application for OBSAI RF is to check for interference on the RFM-to-BBM uplink. When monitoring traffic over the OBSAI link, the Anritsu test instrument will extract the IQ data and process the signal into data points to be plotted on the instrument screen.

The OBSAI parameters described in this section are needed for the OBSAI Analyzer to process and display the data correctly. Note that configurations may be different for the uplink and downlink. The uplink signal represents mobile phone LTE data. The downlink signal is the display of BBM LTE signals to RFM.

All OBSAI IQ data is at baseband frequency. To allow the OBSAI signal to move off center (pan), turn the Center Frequency Reference setting on and adjust the center frequency to a different value. Depending on the value entered, this may automatically adjust the frequency span, as there cannot be panning without zooming. Refer to Freq Menu.

Link Rate is the speed, or bit rate, of the OBSAI link. The instrument automatically sets the link rate when it detects valid OBSAI carriers. On dual-SFP models, the link rate applies to both SFP data streams. Table: OBSAI Link Rates lists the supported link rates and associated rate indices.

When the rate index is 8x (6144.0 Mbps), the instrument will automatically detect and display the scrambling seed associated with each SFP link.

OBSAI Reference Point 3 (RP3) defines the digital interface between the Radio Frequency and Base Band Modules of a base station. Your Anritsu instrument automatically scans for active RP3 addresses in the IQ stream when a new OBSAI link is detected. The RP3 list will then refresh with new addresses found on the SFP link, if any, and the link rate will be set based on the newly plugged in fiber.

You can also initiate a scan by pressing Start OBSAI under the Measurements menu. Refer to Measure Menu. On instrument models with dual SFP ports, Start OBSAI will scan both SFPs.

If Start OBSAI detects valid RP3 addresses, it will reset the display to a single Spectrum graph with Carrier Trace 1 displaying the first RP3 address in the available address list. If no OBSAI carriers are found, a message indicating the RP3 address list is empty will display when you attempt to configure a carrier trace with the RP3 Address key.

The RP3 list is empty following an instrument power cycle. You must then either establish a new SFP link or run a scan with Start OBSAI to obtain valid address entries.

Upon fiber plug-out or when a Loss of Signal (LOS) is detected at an SFP port, RP3 addresses associated with that OBSAI link are dropped from the list. Active addresses associated with the other port (on dual-SFP models) remain available for carrier trace configuration.

Table: RP3 Link Capacity lists the maximum number of antenna-carriers that will fit in an RP3 link, depending on channel bandwidth and link rate.

This is the bandwidth of the LTE carrier that is transmitted via OBSAI. Supported LTE carrier bandwidths are 5 MHz, 10 MHz, 15 MHz, and 20 MHz. The maximum span is approximately 50% greater than the carrier bandwidth. For example, if the LTE bandwidth is 10 MHz, the maximum span will be 15 MHz.

The LTE bandwidth is set independently for each of Display 1 and 2 in dual display mode. In spectrum view, the LTE bandwidth of the currently active display is shown on the left side of the sweep window.

When selecting the RP3 address of a carrier trace, the display bandwidth may need to be changed to match the RP3 bandwidth. If prompted, press OK in the message box or press Enter to change the display’s LTE bandwidth.