Inside Wireless: Path Loss

Every wireless network designer has to count with path loss. What is path loss and how does it work? Which spectrum is the best for WISP networks? Check out this #InsideWireless episode to find out!

Path loss is attenuation of the signal caused by expansion of an EM wave as it travels away from a transmitter. It is a measure of dilution of the waves’ energy as it expands in the space. While the signal strength is decreasing with distance, path loss is growing and corresponds to the inverse of the signal strength.

Path loss (PL) is part of the link budget equation and it increases with not only with distance, but also frequency. Moreover, it grows exponentially, due to the second power.
WISPs often use 2.4 GHz spectrum, because it is license free and the RF wave travels further than higher frequency signals. The 5 GHz spectrum which is unlicensed as well has somewhat higher path loss which can result in more hardware needed to cover the same area as with 2.4 GHz gear. The 60 GHz spectrum shows a great promise for future networks with gigabit speeds, but has a much higher path loss, which considering the state of the art of todays’ hardware, enables around 2 km link distance at best.

The path loss should definitely be considered while deciding which part of the spectrum to use. But, the decision goes beyond the simple physics of achievable coverage distance.

At 2.4 GHz, the waves travel far, but the huge amount of other devices operating in the same bandwidth generates enough interference to clutter the spectrum making the network highly unstable and unreliable and the throughput speeds achievable in the limited bandwidth are increasingly insufficient for todays’ growing demand.

At 5 GHz, the path loss is about 7 dB higher, so the RF waves do not travel as far, which can be an advantage acting as a natural protection against interference. But despite the shorter achievable distances, the 5 GHz spectrum is quickly headed towards the same interference saturated state.

At 60 GHz, the path loss is about 28 dB, or, about 700 times higher than at 2.4 GHz. Combined with the wide bandwidth available, the possibilities for future multigigabit networks are vast, but, only in densely populated areas due to the short distances achievable which also makes for a naturally high security network.

So which spectrum is the best for WISP networks? There is no perfect solution that fits every situation, every choice comes with a tradeoff, due to the principles and limitations we just described. So eventually, what is a strength in one place, can be a weakness elsewhere and vice versa. But the awareness of path loss can be a good starting point when designing your next link.

0:00 Intro
0:39 Spectra example
1:11 Path loss - a decision factor?
2:21 Which frequency is the best for WISPs?

#RFelements #InsideWireless #PathLoss #Antennas #AntennaTheory #WISP #SaveSpectrum #RejectNoise #growsmart #UbiquitiNetworks #CambiumNetworks #MimosaNetworks #Mikrotik

[Rfelements]

Which frequency spectrum do you use for WISP links?

[burdmate]

I've watched all 23 videos of this series. They are absolutely magnificent! You guys should be awarded.

In this particular instance I gotta point out though that the path loss does not grow exponentially, but with a square function (which is a power function).

A power function (variable base, constant exponent) grows way slower than an exponential function (constant base, variable exponent).

Cheers!

[hammasahmed]

In 3 minutes you explained what my teacher failed to in 30 minutes .

[Supermath]

I've seen 24 Ghz on Ubiquiti's website, is that not common enough for WISPs?

[antoniobragancamartins]

I work with long distance link over the sea and higher frequencies can't be used because rain attenuation!

[riccardotruant]

why does path loss increase with frequency? Is there a physical region?

[bstanis]

Excellent and great episodes. Please I need to understand what's EVM and the standard EVM threshold for 2.4 GHz WiFi at 54 Mbps and the same issue about SNR. And all these in 5 GHz and 60 GHz too make into account OFDM technique.
Please I need the understand them these days by episodes.
All the best.
Many thanks for theses great work.

[TheGmr]

a dB equation be nice FSPL_dB = 20 * log10 ( (4*pi*d) / wavelength)

[chrisv]

You can choose for one of the above gifts