So far the Uplink power control loop did not filter the Uplink RSSI
measurements (reported by the BTS) at all. The lack of filtering
makes our implementation too quick on the trigger, so in the real
deployments there will be unneeded Tx power oscillations.
In order to reduce this effect, let's implement a very simple EWMA
(also known as Single Pole IIR) filtering that is defined as follows:
Avg[n] = a * Pwr[n] + (1 - a) * Avg[n - 1]
where parameter 'a' determines how much weight of the latest UL RSSI
measurement result 'Pwr[n]' carries vs the weight of the average
'Avg[n - 1]'. The value of 'a' is usually a float in range 0 .. 1, so:
- value 0.5 gives equal weight to both 'Pwr[n]' and 'Avg[n - 1]';
- value 1.0 means no filtering at all (pass through);
- value 0.0 makes no sense.
This formula was further optimized with the use of '+=' operator.
The floating point math was also eliminated by scaling everything
up (by 100). For more details, see:
https://en.wikipedia.org/wiki/Moving_averagehttps://en.wikipedia.org/wiki/Low-pass_filter#Simple_infinite_impulse_response_filterhttps://tomroelandts.com/articles/low-pass-single-pole-iir-filter
The EWMA filtering is now *enabled by default*, but can be disabled
or (re-)configured over the VTY at any time:
! Completely disable filtering
no uplink-power-filtering
! Enable EWMA smoothing with the given parameters
uplink-power-filtering algo ewma beta <1-99>
Note that the VTY command expects 'beta' instead of 'alpha':
alpha = (100 - beta)
and the value must be in %. This is done for simplicity:
1% means lowest smoothing,
99% means highest smoothing.
Let's say we have EWMA filtering enabled with alpha = 0.4, and get
-98 dBm on the input, while the last output value was -60 dBm.
The new output would be:
Avg[n] = 0.4 * Pwr[n] + 0.6 * Avg[n - 1]
Avg[n] = (0.4 * -98) + (0.6 * -60)
Avg[n] = -75.2 => around -75
Of course, this is not a silver bullet, but better than nothing.
Change-Id: Ib6dcadbf14ef59696c6a546bd323bda92d399f17
Related: SYS#4916
It's not a good idea to request big changes in MS Power based on
sporadic bad signal received, let's instead change announced MS power
levels more smoothly to avoid possible big signal strength fluctations,
similar to what is already done in osmo-bts-trx specific loop (loops.c).
Related: OS#1851
Change-Id: Iecc4ec7e21471ec853ad2d5659af4052aba5444c
Several improvements have been made lately to MS Power Control loop from
osmo-bts-trx in loops.c. Let's port these to the common algorithm.
Related: OS#1851
Change-Id: I579967cc8bb69dc76a315c6c9d3a351f5961d92f
Thies field is used to store and retrieve whether MS power needs to be
calculated and updated by osmo-bts software or autonomously by lower
layers. Previous name was not clear
and may have been understood as indicating whether MS Power Control loop
is done or not in general, and the responsible for that is located under
lchan's ms_power_ctrl.fixed.
Related: OS#1851
Change-Id: Ic690ab69866a7377f1597e24aa7b0214831c1cbe
gsm_bts_role_bts was introduced at a time when we still shared
gsm_data_shared.[ch] between BSC and BTS, and where we then subsequently
needed a BTS-private structure. Since that sharing was abandoned quite
some time ago, we can merge gsm_bts_role_bts into gsm_bts and do away
with the bts/btsb dualism in a lot of the code.
Change-Id: I4fdd601ea873d9697f89a748cc77bcf7c978fa3e
Power control loop test outputs next to nothing which is not very
helpful. Make it more verbose. While at it, also move duplicated code
into static function to make test cases less cluttered.
Change-Id: I0a5e65e23e62442ef8758ecbcf8e7820b4f15d7b
Related: OS#2223
There's nothing sysmobts specific in this test so let's move it into
separate directory and run unconditionally. The test itself is unaltered
except for intro text.
Change-Id: I0d1957cd9cf5497826be095c7a42b7bb4fa10397
Related: OS#2223
