Seems the AF5x radios get really grumpy if you don't have a perfect environment with LOS. It has been suggested that OFDM radios will perform better. In NLOS applications I have certainly experienced this going from AF5x at -80 to AF2x at -63 to finally landing on Mikrotik 2.4 that has worked flawlessly for some time now.Mikrotik AC gear seems to choke around 100mbps. Is there something that will perform in similar ways to a Mikrotik in terms of performance through or skimming trees (B5c?) or Cambium PTP.? Something I can swap on existing dishes would be nice. NLOS/NearLOS cause multipath radio signals propagation, that creates for radio receiver self-interference due to changing radio signal amplitude,phase, polarization, etc.This problem partially or fully can be resolved by using OFDM signal with many subcarriers (FFT).
Subcarriers are processed as samples mathematically by receiver and it reduces demodulation errors (BER), stabilizes SNR( RSSI) and others, for example, using OFDM allows to get stable links with moving objects due to processing signal frequency offset (Dopller effect).For example, 802.16 ( wimax) OFDM radio signal has 256-1024 FFT -it was designed to work in NLOS/NearLOS with moving objects. 802.11 OFDM has 64 FFT, it also can work in NLOS ( but only in office/home).Subcarriers quantity defines link distance, where OFDM may be efficient.
![Ofdm 256 Fft Ofdm 256 Fft](/uploads/1/2/5/5/125535721/779921660.png)
# Create OFDM and F-OFDM Transmitter objects ofdmforspectrum = OFDM (K = 256, Kon = 100, CP = 16, qam = 4) ofdmTX = OFDMTransmitter (None, ofdmfor. LTE chooses an FFT length of 2048 and hence theoretically supports 2048 subcarriers. However, to adhere to the channel bandwidth, only 1200 carriers are actually allocated; we will use the LTE. But I would like to know how channel bandwidth is co-related with the FFT size since it is the FFT stage that does actual sub-carrier modulation Use the number of populated subcarriers from the link above, and take the next largest power-of-two N for the FFT size.
802.11 OFDM 64FFT designed for short ( up to 300 meter) link distance with short time delays between mutipath signals to work indoor. Wimax and now Lte) were designed for long distance communications with big multipath signal delays.For this reason any wi-fi based radio devices ( like Ubnt, Mikrotik 802.11n/ac and even ePMP Cambium 802.11n ) work very poor in NLOS/NealLOS, and also over the water (with a lot of multipath reflections from the water). EPMP Cambium works in NearLOS ( also over the water) noticeable better, than Ubnt/Mikrotik/Proxim/etc, because ePMP is real TDMA system, and it's TDMA timing windows works as filter for reflected signals, that are received with big time delays.Single carrier radio AF5X ( it is not confirmed officially) as any microwave system does not have mechanism, that allows to resist to multipath interference. Also this is the reason why for AF5x using dual slant (+- 45 degree polarization is recommended.
Ubnt wants at least to reduce X-Pol multipath interference by dual slant antenna. But it is no efficient. As all already have known, AF5X can not work over the water. And many Ubnt fanboi have to agree, that AF5x requires LOS.There are few BWA 5 GHz system with OFDM 256 FFT ( in every 10 MHz) that are able to work in NLOS/NearLOS:1) Cambium PMP 450i for PtMP and for point to point relatively not expensive PTP450i. Now it supports only 10/15/30 MHz bandwidth channels, In August 2016 - 40 MHz.
It gives 260-280 Mbps UL+DL throughput in 40 MHz in NearLOS.2) But best is PTP650 ( OFDM FFT 1024 ) - 450 Mbps UL+DL in 45 MHz.There are also some other systems(vendor) that have radio OFDM with 256+ subcarriers. Said by:NLOS/NearLOS cause multipath radio signals propagation, that creates for radio receiver self-interference due to changing radio signal amplitude,phase, polarization, etc.This problem partially or fully can be resolved by using OFDM signal with many subcarriers (FFT). Subcarriers are processed as samples mathematically by receiver and it reduces demodulation errors (BER), stabilizes SNR( RSSI) and others, for example, using OFDM allows to get stable links with moving objects due to processing signal frequency offset (Dopller effect).For example, 802.16 ( wimax) OFDM radio signal has 256-1024 FFT -it was designed to work in NLOS/NearLOS with moving objects. 802.11 OFDM has 64 FFT, it also can work in NLOS ( but only in office/home).SYou might consider Double carriage returns in your posts - big blobs of text like this are very hard on the head. At least on mine. This is some extracts of my book ( BWA wimax technology), that was published in 2009 ( second edition) in Russian »One of the key advantages of wimax system, that is provided by using OFDM signal, is opportunity to work in NLOS.
OFDM signal with many subcarriers ( 256FFT) has resilience to multipath radiowave propagation, that occurs due to reflections signal from obstructions between stations.Multipath signal propagation causes 'fadings', when reflected signals, that arrive to receiver with different amplitude, phase and time delay. These signals are added up in receiver and causes decrease of amplitude ( 'bust time fading') of resulted signal.There are some methods to resist to fadings: antenna diversity, using various complex filters, etc. But most efficient method is using OFDM signal with many subcarriers.In OFDM signal receiver amplitude 'bust time fading' are transformed ( mathematically Fourier transform) into 'burst frequency fading'. This frequency fading then can be selected by filters and signal may be recovered.