Marketing materials from LPWAN system manufacturers often cite extremely high sensitivity as a major advantage and main argument for long-range operation. All major manufacturers of LPWAN declare first of all the high sensitivity of the receiver: LoRaWAN-137 dBm and Waviot declares the maximum achieved receiver sensitivity up to 148 dBm! Most often this is true, but these values are obtained on the laboratory table, and tests in real conditions make significant adjustments.
In the real radio spectrum, there is often a lot of external interference. In large cities, interference is more noticeable, especially in the unlicensed frequency band. These frequencies are used by car alarm key fobs, barrier opening buttons, baby monitors, modems, and other wireless devices and systems. LPWAN gateway receivers are also strongly influenced by other nearby strong out-of-band radio sources such as cellular operator base stations, radio relay stations and radio modems.
What works perfectly on the table often does not work so well in the field. This is where another critical parameter comes into play: the dynamic range of the gateway receiver.
The easiest way to illustrate this is to use the following simple example. If two transmitters are operating simultaneously in the same channel, the weaker signal can be suppressed by the stronger one.
For example, the LoRaWAN receiver demodulates signals up to 20 dB below the noise floor, but if a transmitter is working in line-of-sight 50 metres away from the gateway, we can receive another transmitter with the same power in the same channel, at a range of no more than 500 metres! Even if these transmitters are LoRaWAN with different spread factors. So, despite the possibility of operating under noise and orthogonality of the LoRa signals with different spread factors, the simultaneous operation of other devices in the channel greatly limits the range of the system as a whole.
The situation is slightly better in the case of UNB systems such as Sigfox, Strizh or Waviot. They declare the possibility of simultaneous decoding of multiple signals in the receiving band, but this possibility is determined by the dynamic range of the UNB receiver by intermodulation. A transmitter with 25 mW power located 50 metres in line of sight of the gateway with are receiving antenna again off 6 dB will provide a level of the signal received at the gateway about -45 dBm. If the value of the dynamic range of the receiver is 70 dB, then the simultaneous reception of weak signals in the channel will be limited to a level of -115 dBm. This is considerably less than the claimed -140…-148 dBm. Increasing the dynamic range of a UNB receiver is a technically difficult task, usually leading to its high cost.
The effects shown in these examples may not be noticeable when testing systems with a small number of devices but will begin to show themselves clearly in high-loaded systems when the range of the system will decrease significantly with the growing number of devices in the system. With 10 devices, everything works fine, but with 200 devices, information skips. Increasing the LoRaWAN bandwidth by reducing the spread factor will have the same effect.
It turns out that the long-range of LPWAN systems in the real world is provided not only by the high sensitivity of the receiver but at the same time, a high dynamic range of the receiving path.
GoodWAN has extensive experience with professional radio systems, including UNB receivers. In our gateway, we use a specially developed receiver with professional features and a relatively low cost. In the basic model, the dynamic range of the receiver exceeds 110 dB. The gateway can receive more than 800 000 messages per day at the maximum range. This exceeds several times the bandwidth of the LoRaWAN gateway at the maximum range at SF=12. The gateway is built according to the "turn on and forget" principle. Once powered up, it configures itself and requires no additional management software, no configuration and no routine maintenance
