Factors affecting the LoRaWAN range

Factors affecting the LoRaWAN range
Factors affecting the LoRaWAN range

This blog post describes the range of physical properties of wireless networks – especially LoRaWAN range. The information presented supports the planning process and the assessment of use cases of LoRaWAN.

We’ll also explain the factors affecting radio range and their relationships,and evaluate examples of independent measurements from the real world.

There are basically three characteristics that can be used to describe a network in a radio technology:
•Range
•Data transfer speed
•Energy consumption

It’s hard to place equal importance on all three criteria because the laws of physics have clear limits on this: for example, LoRaWAN can transmit data over long distances with relatively little energy, but at very low data rates.

WiFi and Bluetooth can achieve high data rates, but the power consumption is relatively high and the range is small. All smartphone users are only too familiar with this hunger for energy. The base stations of the big telecom operators provide high data rates and relatively long distances, but must provide a lot of energy to do so. Therefore, power supply is important factor in such installations.

range

The power transmission balance

The power transmission balance indicates the quality of the radio transmission channel. By adding transmitting power (transmitter power, Tx), receiver sensitivity (receiver power, Rx), antenna gain, and free space path loss (FSPL),it can be calculated.

LoRaWAN calculates the power transmission balance.
Path loss will represents the amount of energy lost in free space over a distance between Tx and Rx. The farther away Tx is from Rx, the lower the energy is. Path loss is usually expressed as :FSPL = (4πd / λ) 2 = (4πdf/c) 2(1) where:

FSPL = (4πd / λ) 2 = (4πdf / c) 2 (1)

Where means:

FSPL = Free Space Path Loss
d = distance between Tx and Rx in meters
f = frequency in Hertz

There is also a widely used logarithmic formula for free-space attenuation :FSPL (dB) = 20log10 (d) + 20log10 (f) -147.55 (2)

Twice the distance (d) means a loss of 6dB.

At the receiving end (Rx), the sensitivity of the receiving end is the size that affects the power tansimission balance. The Rx sensitivity describes the minimum possible received power and thermal noise tolerance:
Rx sensitivity = -174 + 10log10 (BW) + NF + SNR (3)

Where means:
BW = bandwidth in Hz,
NF = noise factor in dB,
SNR = signal to noise ratio. It tells how far the signal is about
must lie with the noise.

LoRaWAN’s Rx is more sensitive and therefore better than WLAN. The extreme case of path loss without considering antenna gain and other types of free-space attenuation: power transmission balance= Max has been represented in the quation (4).
Rx sensitivity (dB) – Max. Tx power (dB) (4)

An example of calculating a LoRaWAN power transmission balance:

Tx power = 14 dBm
BW = 125KHz = 10log10 (125000) = 51
NF = 6 dB (the gateways in LoRaWAN networks have lower NF values)
SNR = -20 (for SF = 12)

These numbers entered in formula (3) result in an Rx sensitivity of -137 dBm

Rx sensitivity = – 174 + 51 + 6 – 20 = -137 dBm

The power transmission balance can then be calculated as follows using formula (4):

power transmission balance = -137dB – 14dB = -151dB

With the specified values, the LoRaWAN range power transmission balance is 151 dB, so it can overcome distances of up to 800 km under optimal conditions (pure free-space attenuation). The LoRaWAN range is 702 km at the world record.

Of course, these ideal values are not achieved under real conditions. Several factors is essential on this.

Factors

Free space attenuation factor

By doubling the distance, LoRaWAN’s free-space attenuation increases by 6dB, so radio propagation attenuation follows a logarithmic function (see Formula below).

Besides from the energy loss caused by LoRaWAN range, reflection and refraction of radio waves on objects can also cause radio waves to overlap.

Structural damping factor

Structural attenuation coefficient Structural attenuation, that is, the attenuation of radio signals as they pass through different obstacles, affects the reception of transmitted signals and ensures that the signal range is greatly reduced. For example, the glass attenuation is only 2dB. This affects far less than a concrete wall 30 centimeters thick. The table below shows the various materials and their typical attenuation.

lorawan range

Fresnel zone factor

It is essential to establish as much straight line of sight between transmitter and receiver as possible if you want to cover long distances effectively and get a good power transmission balance. Certain areas of space between the lines of sight of the radio transmission are Fresnel regions. The propagation of the waves will be negatively affected If there are objects in these areas, despite the usual visual contact between the transmitting and receiving antennas. For each object in the Fresnel belt, the signal level drops and the LoRaWAN range shrinks (see figure).

Fresnel zone factor

Omnidirectional antennas is a common technology to be used in LoRaWAN range networks. Thus, radiated energy diffuses into the horizontal plane and the network nodes and gateways are located there. In Europe, ISM band transmission power is limited to 14 dBm at 868mhz. 2.15 dBi is the maximum antenna gain.

Factor spreading factor

In LoRaWAN networks, the specific setting of the data transfer rate uses spread Factors (SF). The LoRaWAN network uses SF7 to SF12. Due to its chirped spread spectrum modulation and the different phase shift frequencies used in the chirp, the LoRaWAN network is insensitive to interference, multipath propagation and fading. In LoRaWAN range networks, the Tx side uses chirp to encode data, while the Rx side uses inverse chirp to decode signals. How many chirps are used per second, the definition of the bit rate and the amount of energy radiated by each symbol and the LoRaWAN range that can be achieved have been represented above. For example, the bit rate of SF9 is four times slower than SF7,which can be achieved by the scalability of LoRaWAN. The slower the bitrate, the higher the energy and greater the range of each data set.

Factor spreading factor

Conclusion

Transport equalization refers to the maximum transmission range of the LoRaWAN network.
Free space attenuation range of influence. By doubling the distance, the free-space attenuation increases by 6dB.
The reflection and refraction of radio waves on obstacles and the ground affect the level and range of the signal. In LoRaWAN networks, one end of a radio link is usually close to the ground.
The signal level on the Rx side will be affected in the first Fresnel and the distance will be shorten.
The SF value and transmitter range depend on propagation conditions. LoRaWAN range allows automatic network management, using ADR to adjust the range of transmitters. Signal-to-noise ratio (SNR), noise factor (NF) and bandwidth (BW) will affect the Rx sensitivity.

LoRaWAN range optimization strategy

In order to improve the network reach of LoRaWAN technology, the following points must be noted:
Gateway location: Establishes visibility between Tx and Rx antennas. Increase the height of antennas to improve visibility between antennas. Antennas is suitable for being used in outdoors rather than indoors.

Antenna choice: Classic rod-shaped antennas concentrate energy on a horizontal plane. Avoid obstacles near the antenna. Also, these should always be attached to a column, not the side of the building. The range should be increased if the antenna is carefully selected and optimized for antenna polarization and maximum defined antenna gain.

Choose connecting materials: use quality plugs (N-plugs) and cables (LMR 400 or equivalent, loss less than 1.5 per 100 dB). In order to reduce the loss of connection material, it is also important to keep the connections between stations and antenna lengths as short as possible.

In general, as outlined in this article, LoRaWAN range gateways should be installed to ensure adequate overvoltage and lightning protection.

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