Can My design include signal propagation through steel grate floors to the lower level?

     The $5 million question.....

     Throughout the development of 802.11 wireless advancements, signal propagation has been questioned, tested, and requestioned in numerous scenarios. Fact is that in the earlier developed technologies refractions and reflections produced noise and interference against the original transmission, but now with MIMO and its abilities, reflections are used to the advantage of the transmission.

     The reflected signal ultimately is out of phase and has fallen behind in time of arrival when compared to the original transmission, but now the two or more signals (main and out of phase reflections) become combined and used as multiple paths to transmit data packets on. When the reflected signal shows up at the target device say... 10 micro-seconds after the primary signal, then the primary signal is slowed down to be synchronized with the reflected signal. MIMO uses reflected paths to its advantage to transmit more data faster.

     As far as the grated floors, the reflected signals work out the same way, but you do end up with a smaller RF footprint (coverage area) below due to the many unusable reflections.  You should use your survey software on the lower level and measure the RSSI against the noise floor and packet losses and you will find the dependable area of coverage in a clean SNR with little to no packet loss. By no means is this area as big as the area covered on the upper floor, but it is absolutely dependable for VoIP grade coverage and can and should be incorporated into your overall design for access point placement. If you don't use this area, then you will end up with a very non-standard overlap in your cell coverage and VoIP will most likely suffer because of it.

     VoIP works great at or around 20% overlap and this overlap needs to remain consistent across your design. 20% on one the 5% on another and 35% on the next will cause roaming issues for VoIP clients so any bleed through from floor to floor should be factored into the design to avoid issues.


Brett Hill, CWNE #147