InfiLINK 2x2 / InfiMAN 2x2: Initial Link Configuration and Installation

Wireless link statistic

To assess the wireless link state in the web interface, go to the "Device status" section - "Link statistics for the rf5.0 interface. Targeted parameters:

• Retries Rx/Tx: maximum 5 %.
• EVM Rx/Tx: not less than 21 dB in absolute value.
• SNR Rx/Tx: not less than 27 dB.

If these conditions are met and the maximum bitrate is reached, the wireless connection quality is good.

Performance tests

The throughput test can be performed with the "Performance Tests" tool built into the web interface, in the section "Device status" → "Link statistics for the rf5.0 interface". This tool generates test traffic between the devices and it allows to obtain data about the real link throughput both in one direction and in a two-way manner. The throughput evaluation is performed using traffic with the specified priority without taking into account the service traffic required to maintain the link operational. To exclude the influence of the data traffic on the test's result, it is recommended to set the highest priority for the test traffic (at least 15).

In case of software with Polling technology support testing is performed on each modulation available. In case of TDMA software or "use MINT" checkbox is on, performance tests are always performed on the highest modulation. 

Optimization of the link

Polling

In case that the MINT software version is installed on the devices, make sure that "Polling" mode is enabled. This mode improves the efficiency of the radio medium usage and avoids collisions. In addition, to improve the wireless system's efficiency, we recommend updating to the software version having support for the TDMA technology. A detailed description and the benefits of each software version can be found in the "TDMA and Polling: Application features" article.

Greenfield

The "Greenfield" mode allows to reduce the frame preamble during the transmission over a wireless connection, increasing the link performance by 10-15%.

Autobitrate and ATPC

To keep a balance between the wireless link's performance and the retries number, we recommend to always set the "Bitrate" parameter to "Auto" mode. Also enable the automatic transmit power control (ATPC) in order to increase the operational life of the devices.

Frame size

If the device has a software version with TDMA technology support, make sure that the selected frame size ensures the best performance for your wireless system. A short frame will transmit less payload than a long one, however it ensures a smaller delay. A detailed description of the frame sizes in the TDMA technology is available in the "TDMA and Polling: Application features" article.

Packet retries management

The "Turbo" and "SCS" modes are available in the TDMA software version, which allow to increase the wireless link throughput in case that the degradation is caused by a large number of errors in the radio.

Detailed information about the radio parameter configuration via the web interface is available in the "Link Settings" article or via CLI in the articles: "mint command (TDMA version)"/"mint command (MINT version)" and "rfconfig command (TDMA version)"/"rfconfig command (MINT version)".

Dynamic Frequency Selection (DFS)

Dynamic Frequency Selection is an interference mitigation technique that aims to:

• Protect the radar systems by avoiding co-channel operation with the broadband wireless systems
• Ensure a uniform distribution of the applications across the spectrum (according to the EN 301 893 standard, a uniform spreading is required across 5150 MHz to 5350 MHz and 5470 MHz to 5725 MHz)

The standards specify the performance requirements for the wireless systems in order to avoid the interference with the radars but do not define how to implement DFS practically. Vendors have the responsibility to implement DFS using their specific means to comply with the requirements of the standard. Detection requirements:

• Channel Availability Check - when initially powered on, or in case that radar is detected on the operating channel, a frequency scan must be performed to determine the available channels
• In-service monitoring - the operating channel is constantly monitored for the presence of radar signals (the detection thresholds are the same as in case of CAC)
• In-service monitoring is performed in between each data transmission, and its duration is of µs order
• Off-channel Channel Availability Check - in addition to CAC, DFS can also decide to select a better channel (less interfered) if the SNR of the operational channel falls below a certain threshold; this operation requires link interruption as the radio module can either transmit/receive data or perform the medium scan

DFS technology implementation in the InfiLINK 2x2, InfiMAN 2x2 families devices has following options:

• In "DFS only" mode, the DFS system monitors interferences but does not perform radar detection.
• In "DFS with Radar Detection" mode, the DFS system monitors interferences and performs radar detection.
• For the base stations with two radio modules, the "Instant DFS" option is available (one of the two radios is used for DFS scanning, Radar detection and Spectrum analyzing).

Automatic frequency selection configuration

At the Slave device:

• Go to the Basic Settings section, then to Link settings, set the Frequency to "Auto".
• In the Custom Frequency Grid, change the range of the available channels for the selected bandwidth so that only 10 frequencies are available (choose the least interfered part of the range) and apply the configuration.

At the Master device:

• Go to the Basic Settings section, then to Link settings and:
  • Select "DFS with Radar Detection" or "DFS only" for the DFS parameter and "Auto" for Frequency.
  • In the Custom Frequency Grid, change the range of the available channels for the working bandwidth as well as only 10 frequencies to be available (chose the less interfered part of the range) and apply the configuration.

The initial Channel Availability Check takes 3 seconds per each frequency; thus for the 10 available frequencies, the initial CAC must take 30 seconds, so the link is established in between 30 and 40 seconds because the Slave unit scans too each frequency in 1 second to find the Master unit

Instant DFS

In case of Instant DFS, Off-channel CAC is performed by an additional radio card that scans all the channels (besides the operational channel which is monitored during initial CAC) defined in the frequency grid.

Advantages of Instant DFS compared to regular DFS:

• No link interruption if radar is detected, by using the frequency database maintained during the Off-channel CAC
• In case of link quality deterioration, the Master can decide to switch the channel to a better one without link interruption
• The Spectrum Analyzer built-in tool can be ran without interrupting the link

At the Slave device:

• Go to the Basic Settings section, then to Link settings, set the Frequency to "Auto".

At the Master device:

• Go to the Basic Settings section, then to Link settings and:
  • Select "DFS with Radar Detection" or "DFS only" for the DFS parameter and "Auto" for Frequency.

A device with a second radio module scans the grid constantly, even if a fixed frequency is selected. When setting the "Frequency" parameter to the "Auto" position, the Master device will automatically switch to the least noisy frequency channel, moving the connected Slave devices.