In radio technology, basically three characteristics can be used to characterize a radio network:
● Range/distance
● Data transfer speed
● Power consumption.
The criteria for these three indicators are certainly not the same, since the laws of physics set clear limits in this case. For example: LoRa can transmit data over long distances and requires relatively little energy, but the data rate is low.
For example, WiFi and Bluetooth achieve very high data rates, but consume relatively high energy and have a small range. All smartphone users are well aware of this energy need. The base stations of large telecom providers offer high data rates and relatively high range, but for this they must provide large amounts of energy. Therefore, power supply is always a very important planning factor for this type of installation.
Typically, up to 2 of the above criteria can be optimized.Therefore, it is necessary to decide which factors affecting lora transfer rate should be prioritized
link budget
Link budget represents the quality of the wireless transmission channel.
Using a simple model, the link budget can be calculated by adding transmit power (transmitter power Tx), receiver sensitivity (receiver power Rx), antenna gain, and free space path loss (FSPL).
In a further process, the link budget of LoRaWAN will be calculated.
radio signal path loss
The path loss represents how much energy is lost in free space over the distance between Tx and Rx. The further the distance between Tx and Rx, the lower the energy level. Path loss is usually expressed as follows:
FSPL =(44πd/λ)2 =(44πdf/ c)2(1)
These factors illustrate:
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 path loss:
FSPL(dB)= 20log10(d) 20log10(f)– 147.55(2)
Doubling the distance (d) means a path loss of 6dB (in free space).
On the receiver side (Rx), the receiver’s sensitivity is the value that affects the link budget. The so-called Rx sensitivity describes the minimum possible received power and thermal noise margin and is calculated as follows:
Rx sensitivity = -174 10log10(BW) NF SNR(3)
Means of doing this:
BW = Bandwidth in Hz,
NF = Noise factor in dB,
SNR = Signal-to-noise ratio indicates how much stronger the signal is compared to the noise
LoRaWAN’s Rx sensitivity is higher than Wifi, so it’s better.
Equation (4) shows the extreme case of path loss, which does not include antenna gain and other types of free space attenuation:
Link budget = Maximum Rx sensitivity (dB) – Maximum transmit power (dB) (4)
Calculation example of LoRaWAN link budget:
Tx power = 14 dBm
BW = 125KHz = 10log10(125000)= 51
NF = 6 dB (gateways in LoRaWAN networks have lower NF values)
SNR = -20 (for SF = 12)
Entering these numbers into equation (3) gives an Rx sensitivity of -137 dBm
Rx sensitivity = – 174 51 6 – 20 = -137 dBm
Then, it can be calculated using expression (4) as follows
Link budget: Link budget = -137dB – 14dB = -151dB
The given values result in a LoRaWAN Link budget of 151 dB.
With LoRaWAN’s dedicated 150 dB link budget, a distance of 800 kilometers can be covered under optimal conditions (pure space loss). The current LoRaWAN world record is 702 kilometers.
Under real conditions these ideal values cannot be achieved. So what are the factors that affect lora transmission distance? It depends on several influencing factors.
Factor 1: Free Space Path Loss
By doubling the distance, LoRaWAN’s free-space path loss increases by 6 dB, so the pass-through loss of the radio signal is affected by a logarithmic function (see equation (1)).
In addition to energy loss as a function of distance, factors such as reflection and refraction of radio waves on objects can cause radio waves to overlap, which can also have a negative impact on range. (Note: Thomas Telkamp has a good explanation of these connections in the video “LoRa Crash Process” starting at location 15:41).
Factor 2: Path loss due to structural elements
Passage losses caused by structures, ie the absorption of radio signals when penetrating different obstacles such as buildings, can affect the reception of the transmitted signal and can significantly reduce the transmission distance. For example, glass only reduces the signal by 2dB. This affects a much smaller area than a 30cm thick concrete wall. The table below lists various materials and their typical effects on radio signals.
| Material | Path loss (dB) |
| Glass(6mm) | 0,8 |
| Glass (13mm) | 2 |
| Wood (76mm) | 2,8 |
| Brick (89mm) | 3,5 |
| Brick (178mm) | 5 |
| Brick (267mm) | 7 |
| Concrete (102mm) | 12 |
| Stone wall (203mm) | 12 |
| Brick Concrete (192mm) | 14 |
| Stone wall (406mm) | 17 |
| Concrete (203mm) | twenty three |
| Reinforced concrete (89mm) | 27 |
| Stone wall (610mm) | 28 |
| Concrete (305mm) | 35 |
Factor 3: Fresnel Zone
In order to effectively cover long distances and obtain a good link budget, it is also important to establish direct line of sight between the sender and receiver as often as possible. In radio transmission, the specific area of space between lines of sight is called the Fresnel zone. If objects are present in these areas, they may have a negative impact on wave propagation, although they usually provide visual contact between the transmitting and receiving antennas. For each object located in the Fresnel zone, the signal level decreases and the range decreases (see image below).
Omnidirectional antennas are commonly used in LoRaWAN networks. This causes the emitted energy to propagate in the horizontal plane where the network nodes and gateways are located. In Europe, the power limit for the ISM band is defined as 14 dBm for the frequency 868 MHz. Additionally, the maximum antenna gain is limited to 2.15 dBi.
Factor 4: Expansion factor
LoRaWAN networks use spreading factors (SF) to specifically set data transfer rates relative to range. In LoRaWAN networks, SF7 to SF12 are used. Due to its chirp spread spectrum modulation (CCS) and the various phase shift frequencies used for the chirp, it is insensitive to interference, multipath propagation and fading. The chirp encodes data in the LoRaWAN network on the Tx side, while the reverse chirp is used on the Rx side for signal decoding. The SF above indicates how many chirps are used per second and defines the bit rate, radiated power per symbol and achievable range.
For example, SF9 is 4 times slower than SF7 in terms of bitrate. SF can achieve the scalability of LoRaWAN. The slower the bitrate, the higher the energy and the larger the range of each data set. LoRaWAN supports automatic adjustment of the SF factor Based on network configuration, the so-called Adaptive Data Rate (ADR).
Summarize
The factors that affect lora transmission rate and distance are:
1. The link budget specifies the maximum range of the LoRaWAN network.
2. Free space path loss will affect the range. Doubling the distance will increase the path loss by 6 dB.
3. The reflection and refraction of radio waves on obstacles and the ground will affect the signal level and range. In a LoRaWAN network, one side of the radio link is usually located near the ground.
4. Obstacles in the first Fresnel zone will affect the signal level on the Rx side and shorten the range.
5. The SF value, and therefore the transmitter range, depends on the launch conditions. LoRaWAN allows automatic network management via ADR, regulating the range of the transmitter.
6. Rx sensitivity depends on signal-to-noise ratio (SNR), noise factor (NF) and bandwidth (BW).
Strategies for optimizing LoRaWAN range
In order to increase the range of networks using LoRaWAN technology, the following aspects should be considered:
lora gateway location: Provides visible light between Tx and Rx antennas. Increase the height of the antennas to achieve optical visibility between them. Always better than using an outdoor antenna outdoors.
Antenna Selection: Classic rod antennas concentrate energy in a horizontal plane. Avoid obstacles near the antenna. Additionally, they should always be mounted on columns and never on the sides of buildings. If the antenna is chosen carefully and the antenna polarization and maximum defined antenna gain are optimally adjusted to each other, the range should improve.
Use high quality connectors (N connectors) and cables (LMR 400 or equivalent, less than 1.5 dB loss per 100 m). In order to reduce the loss of connection material, the connection length between the station and the antenna must also be kept as short as possible.
Co-location: When installing near other radio systems, try to avoid strong interference, such as from surrounding GSM or UMTS stations. Please refer to the manufacturer’s instructions for use.
In general, it should be briefly mentioned that the installation of the LoRaWAN gateway should ensure adequate surge and lightning protection.