PTP 670/700 Spectrum Expert

Summary:

PTP 670 Spectrum Expert tab explanation

The Spectrum Expert explanation and to verify link drop and fluctuation from this tab.

Cause:                                                                                          

How to confirm the interference issue for the link?

What are the features of the Spectrum Expert?

How the Spectrum Expert works in the PTP 650/670/700?

Solution:

Interference level of the link can be checked from the Spectrum Expert tab.

The Spectrum Expert feature of the PTP 670 Series monitors the wireless spectrum and provides a real-time spectrum analyzer display to indicate the levels of interference in the available channels. This interference analysis supports a manual or automatic selection of the best operating channel.

The PTP 670 Series supports two methods for spectrum management control:

  • Fixed frequency
  • Dynamic Spectrum Optimization (DSO)

Master and Slave ODUs in a PTP link, or in an HCMP sector, must be configured with the same setting for spectrum management control.

Fixed frequency

Transmit and receive frequencies can be fixed in a PTP 670 wireless link. Once fixed frequency mode is configured, the spectrum management software will not attempt to move the wireless link to a channel with lower co-channel and adjacent-channel interference. Therefore, this mode of operation is only recommended for deployments where the installer has a good understanding of the prevailing interference environment.

Fixed frequency mode is not available in regions where radar detection is required by the regulations.

Dynamic spectrum optimization

Dynamic Spectrum Optimization (DSO) is an interference mitigation technique where the operating channel is selected based on background spectrum measurements at each of the ODUs. This is a dynamic process allowing the PTP 670 to move to a channel with a minimum level of co-channel and adjacent channel interference.

PTP topology

Two modes of DSO operation are available:

  • Symmetric: The two link directions use the same frequency, determined by the Master ODU based on worst-case measurements at Master and Slave ODUs.
  • Asymmetric: The frequency of operation is determined independently for each direction. The Asymmetric mode is not permitted in radar regions. The default configuration of symmetric operation constrains the link to operate symmetrically, using the same transmit and receive channels. When in symmetric mode the slave unit will always follow the master. If the master moves to a new channel the slave will hop to the same channel. When the Point-to-Point link is configured as an asymmetric link both the master and slave are free to select the best channel from their own set of local interference metrics.

HCMP topology

In the HCMP topology, only the Symmetric mode of DSO is supported. The Master ODU selects the optimum channel considering co-channel and adjacent channel interference measured in the uplink direction, together with co-channel and adjacent channel

Spectrum Expert Settings

All spectrum management configuration changes are applied at the master ODU only. These changes are then sent from the master to the slave, so that both master and slave keep identical copies of spectrum management configuration. It is, therefore, possible to swap master and slave roles on an active PTP 670 link without modifying spectrum management configuration.

The Spectrum Expert algorithm evaluates the metrics every “Hopping Period” seconds (180 seconds by default) looking for a channel with lower levels of interference. If a better channel is located, Spectrum Expert performs an automated channel hop.

If the interference level of the target channel is lower than that of the active channel by at least the Hopping Margin, the link will hop to the target channel. The default setting is 3 dB in non-radar regions or 10 dB in radar regions.

Spectrum Expert uses the interference threshold to perform instantaneous channel hops. If the measured interference on a channel exceeds the specified threshold, then DSO will instruct the wireless to immediately move to a better channel. If a better channel cannot be found the PTP 670 Series will continue to use the current active channel. (Default –85 dBm).

To check the interference of the link we have to check the spectrum expert management tab (System >>> Spectrum Expert) of the link. This page is used to view and configure spectrum usage.

The Spectrum Expert page displays the following plots:

  • The Local Receive Spectrum (local radio), and The Peer Receive Spectrum (remote radio).

  spectrum -1.png Spectrum -2.png

Graphical explanation of the spectrum management page:

spectrum-3.png

The X-axis shows a stylized view of the selectable wireless channels. Note that the distance between adjacent channels may be smaller than the channel bandwidth. If this is the case, adjacent channels overlap. Channels are displayed separately for clarity. The axis is labeled using the channel center frequencies in MHz. The Y-axis shows the interference power levels from –100 to –40 dBm.

The active channel is always marked using hatched green and white lines on the Spectrum Management page or solid green on the Spectrum Expert page. The width of the hatching is directly proportional to the channel bandwidth or spectral occupancy of the channel.

The individual channel metrics are displayed using a colored bar and an “I” bar. The colored bar represents the channel state. The “I” bar indicates the maximum and the minimum level of interference for that channel/frequency. When considering the interference level for the Link planner, the “I” bar should be considered.

Performance review of the link with interference:

  • If the link has an interferer, then there will be link flcuatution.
  • Verify the vector error and receive level graph on the diagnostic plotter.
  • If the vector error is fluctuating and receive level is constant or steady, then it will be due to interference.
  • We have to add the interference level of the link into the LINKPlanner project file.
  • LP will automatically update the link availability when the interference is added.

If there are multiple PTP 670 device, then we have to use the PTP sync device to reduce the self-interference. You can try with different bands available as per your local regulatory requirements and check for improvements in the interference level.

The complete bandwidth ( Channel BW configured) should be interference-free to have a stable link.

The centre frequency ( green color/ active channel)  and the wireless spectrum occupied by the active channel should be interference-free.

3 Likes

Jerry, Nice article.  Very helpful!