Mimosa SRS protocol practical migration guide

Following such a dynamic development of Mimosa products, we were looking forward to the latest firmware for Mimosa A5, A5c and C5x products.

It comes with many improvements, the most noteworthy of which is the implementation of the proprietary Mimosa SRS (TDMA) protocol and the possibility of using the 5GHz band from 4900MHz to 6200MHz.

And before you start to update, it is worthwhile to familiarize yourself with the procedure for updating the new firmware version and the new features it brings.

And this is what we will focus on in this article... I will try to explain in a few points what benefits the implementation of the Mimosa SRS protocol brings.

You need to understand the differences in the functioning of the protocols, read the recommendations for implementation and know what the requirements for channel reuse are.

Idea is as follows:

1. Protocol comparison (WiFi Interop/SRS)

There are some important differences that you should know when migrating to the Mimosa SRS protocol, because otherwise you can disconnect client antennas.

• First of all, the SRS mode no longer supports devices that use a different protocol, and the sensitivity threshold of the device (AGC) must be tuned to optimal performance.
• Unlike WiFi Interop, the SRS only supports one SSID at 5GHz, i.e. before turning on SRS on the Mimosa A5-360 all clients should be switched to the first SSID at 5GHz. After switching on SRS mode, Mimosa A5-360 will retain only the first SSID at 5GHz.
• SRS is configured on Mimosa A5-360, while client devices Mimosa C5x have the default "Auto" mode and automatically detect the protocol.
• It is also important that Mimosa C5x can reboot itself if it does not detect the configured SSID for 4 minutes. After rebooting Mimosa C5x will start scanning (in the background) the entire channel range to look for its SSID to which it should connect.

An overview of the differences between protocols is best illustrated by the following table:

It is also worth noting that Mimosa plans to increase the number of connected clients, improve the TDMA protocol for 75/25 traffic and introduce Radius-based authentication options in the following software versions.

2. Latency in SRS

Latency tests are performed using the "ping" tool (ICMP) run from the command line or directly from the built-in interface (Diagnostic>Ping).

"Ping" returns the value of RTT (Round-trip time), i.e. the minimum time required to send the signal in both directions - from sender to receiver and back.

You have to remember that the average delay is limited by the size of the TDMA window, and Mimosa uses fixed SRS to maximize efficiency.

As a result Average time RTT is 20ms.

Let's now get to the most important topic - the very procedure of migration to Mimosa SRS, which will be presented in several steps:

1. If we have several SSIDs configured on Mimosa A5-360, we have to switch all client devices C5x to the first SSID at the very beginning, because as I mentioned earlier, Mimosa SRS only supports one SSID n 5GHz.
2. Next, save all frequency exclusions that will be reused in SRS mode.
3. We update the software to version 2.2 in the following order:
1. First step - update all C5 to version 2.2
2. Step two - update A5 to version 2.2
4. Please wait until all devices have updated and reconnected. Both A5-360 and C5 will start in Interop WiFi mode.
5. Select SRS mode on Mimosa A5:
1. A5 will automatically send a signal to all connected C5 to change the protocol to SRS
2. All C5 and A5 will automatically reboot
6. After a successful reboot, the following settings should be configured on Mimosa A5:
1. Turn off "Automatic channel selection"
2. Recheck that the channel width is 20/40/80MHz (default 80MHz)
3. Set the appropriate center frequency. The SRS protocol allows you to select a channel in increments of 5MHz.
4. Set the appropriate power (TX Power)
5. Re-enable frequency exclusions
7. At the very end, check that all C5 are connected and tune the TX Power and channel if necessary.

4. Agjustment of AGC mechanism (device sensitivity threshold)

In order to avoid too much interference and maximize the network capacity, it is also recommended to set AGC precisely.

Default AGC for A5-360 is set to -62 dBm and for A5c -72 dBm.

With an appropriate AGC setting, we achieve high immunity to interference from nearby home Wi-Fi devices and potential interference between antennas.

The above values have been set based on the assumption that Mimosa A5-360 will be implemented in MicroPOP style, where the lengths of individual links will not be longer than 1km, while Mimosa A5c will be implemented in GigaPOP style, where the length of the link no longer than 4km.

To fine-tune the AGC settings correctly, follow these steps:

1. First check that all C5 client devices connect in Mimosa SRS mode.
1. Monitor the client list to verify that all devices have connected correctly.
2. If any customer has not connected, it means that the AGC value is too high.
3. The AGC value should then be reduced in 1dB steps until all devices connect correctly. (e.g. from -62dB -> -63dB)

4. The new value of AGC should be set 2dB less than the worst signal of the connected client.
2. If all C5 clients have correctly connected at the default value of AGC, it means that we can increase the value of AGC even more so that Mimosa A5 is even more resistant to interference.
1. You should increase the AGC value in steps of 1dB in relation to the default value. For example, in Mimosa A5-360 we change the value of AGC from -62dBm to -61dBm and check if all clients are still connected.
2. Furthermore we increase the value of the AGC until the customers disconnect.
3. At the very end as in point 1 we set the value of AGC by 2dB less than the worst signal of the connected client.

5. Re-use of band in A5c and A5-14 (GigaPOPs/MicroPOPs)

Reuse of channels (SRS) can significantly reduce the number of channels needed to cover the geographical area.

While inappropriate reuse of channels (resulting from the user's ignorance) can greatly impair network performance due to unintended interference with client radio C5.

What's most important!?

If you want to use the channel reuse properly, you have to follow the recommendations.

In the case of Mimosa A5-360 and Mimosa C5 devices, which are excellent in urban areas (MicroPOPs) with high population density, it should be noted that C5 requires a minimum 25dBm of signal separation between individual access points operating on the same channel.

Because, for example, if the signal difference is only 10dBm between the Mimosa A5 (A) and Mimosa A5 (B), then C5 will not be able to correctly recognize its "own transmitter" signal and bases A and B they must work on different channels.

Analogical assumption applies to devices Mimosa A5c, used for out-of-town solutions (GigaPOPs).

Again, it is very important that the signals of sector antennas connected to the Mimosa A5c, are separated from each other by a value of -25dB, and the devices themselves should preferably face away from each other...

Then, both the client antennas C5 and the whole network segment will be able to work very efficiently - using only one channel!

... and yet we have a lot more channels at our disposal, and by adding to this the knowledge and sense we can design really interesting units.

In summary, ... if we follow this approach, we can innovatively build mega efficient access points for our customers, with very high data transfer capacity.

What's probably most important nowadays... everything that has been mentioned can be achieved and implemented in a network - not cluttering the ether unnecessarily!!

Author:

Leszek Błaszczyk

[email protected]