[OpenWrt-Devel] Fix TX power handling

[Eric Luehrsen]

On 4/29/19 8:24 PM, Matthias Schiffer wrote:
> This is just the factor of 1/2/3/4 (approximated) in dB:
> 
> 10^0.0 = 1
> 10^0.3 ≈ 2
> 10^0.5 ≈ 3
> 10^0.6 ≈ 4
> 
> I've seen these numbers being used in WLAN drivers to account for the
> antenna array gain, so at least this part of the TX power computation might
> already be working as expected.
> 
> Kind Regards,
> Matthias
> 
> 
> On 4/30/19 12:39 AM, Vincent Wiemann wrote:
>> Hi Matthias,
>>
>> thank you for the hint. That's funny, because someone from the German Federal Network Agency
>> said that when radios have multiple antennas, the aggregated EIRP of the antenna array must not exceed the
>> EIRP limits of a single antenna, but I've assumed this is done in hardware and not in software.
>>
>> Can you hint me to the source for this lookup table?
>>
>> Regards,
>>
>> Vincent Wiemann
>>
>>
>> On 29.04.2019 08:50, Matthias May wrote:
>>> On 25/04/2019 17:54, Vincent Wiemann wrote:
>>>> First EIRP is by definition ERP + antenna gain - cable loss.
>>>
>>> Hi
>>> Small detail: Don't forget the antenna array gain.
>>>
>>> So EIRP as:
>>> Antenna Port Power
>>> + Antenna Gain
>>> + Antenna Array Gain
>>> - Cable Loss
>>>
>>> The Array Gain as a simple lookup table:
>>> 1 Antenna: 0
>>> 2 Antennas: 3
>>> 3 Antennas: 5
>>> 4 Antennas: 6
>>>
>>> BR
>>> Matthias

A concern could be a simple count of antennas may over estimate EIRP and 
reduce enabled power below what is allowed. A cheap example of simple 
diversity, only one antenna is used for TX based on which of the other 
antennas RX the best connection to a client (gain=0). Even with beam 
forming, a few antennas may be included in TX phased array and others RX 
monitors.
- Eric


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