LoRa coverage is constrained by the unique characteristics of the intended area of deployment. For example, indoor deployment with thick walls will drastically reduce the LoRa performance compared to an outdoor free space. On this page we’re going to dive into the elements to consider during a LoRa deployment with VeeaHubs.
LoRa received sensitivity on VeeaHubs
Here are the measurement results of the VeeaHubs LoRa sensitivity.
It is highly recommended that the LoRa antenna is connected with a 2m cable, 2m away from the VeeaHub.
LoRa antenna
LoRa Veeahubs comes with an omnidirectional antenna:
- Indoor VeeaHub - LoRa 800MHz and 900MHz: MPMAB antenna (+0dB) MPAMP Series
- Outdoor VeeaHub - LoRa 800MHz: ET8620NPMR2 antenna (+2dB) ET8620NPMR2_DATASHEET.pdf
- Outdoor VeeaHub - LoRa 900MHz: ET915NPMR antenna (+2dB) ET915NPMR_DATASHEET.pdf
This is the most common antenna. But it might not be the best antenna for any use case.
Here are the different antenna characteristics that will induce performances:
- Directivity
- Gain (for a specific frequency range)
- Impedance
Directional vs. Omnidirectional
Directional antennas have a narrow coverage area, and their radiation pattern is more focused in one direction. These are ideal for long-range applications. They provide a higher gain. Omnidirectional antennas have a wider coverage area, which is more evenly distributed. Their reception pattern is 360 degrees and omnidirectional in vertical and horizontal planes. These are better for shorter-range applications. They have a lower gain than directional antennas.
Usually, antenna that have been mounted on a pole are omnidirectional antennas, while antenna mounted on a wall should be directional antennas.
Antenna gain
Antenna gain indicates how strong a signal an antenna can send or receive in a specified direction. Gain is calculated by comparing the measured power transmitted or received by the antenna in a specific direction to the power transmitted or received by a hypothetical ideal antenna in the same situation. If the comparison is to an ideal (text-book pattern, lossless) antenna radiating or receiving energy equally in all directions, the gain is measured in dBi (decibels-isotropic). If the comparison is to an ideal lossless half-wave dipole antenna, defined as having 2.15 dB gain, the gain is measured in dBd (decibels-dipole). Note that the decibel is a logarithmic unit, meaning a 6dB is almost four times the reference power; 7 dB is five times the reference power, etc.
Direction of the power propagation is a key characteristic of antennas. Gain is often represented in a two-dimensional plot of the radiation pattern where the radius of the plot is on a decibel scale that may be normalized to maximum value for the particular antenna, or to an isotropic radiator. The direction that has the most power is considered the main lobe, exactly opposite the main lobe is the back lobe, and any other unwanted or unintended radiation features are called sidelobes. If no direction is specified, gain refers to peak value in the direction of the antenna’s main lobe.
Impedance
LoRa VeeaHubs are designed with 50 Ohm impedance (also the case for LoRa/LoRaWAN), thus the antenna must also have impedance of 50 Ohm.
Here are a few example of LoRa Antenna: 
Testing and Reviewing LoRa Antennas
LoRa antenna cables
As seen in the performance table, using a 2 meter cable for the LoRa antenna increases the performances.
Use quality connectors and cable (LMR 400 or equivalent, with a loss of less than 1.5 dB per 100 m). To reduce the loss in the connection material, it is also important to keep the length of the connection between the station and antennas as short as possible.
Connectors:
- Directivity Indoor LoRa VeeaHub: SMA male to SMA female
- Outdoor LoRa VeeaHub: type-N male to type-N female
LoRa antenna location
Because of the Fresnel Zone principle, it is usually indicated to install a LoRa antenna as high as possible, on a pole or on a wall (depending the antenna type). The objective is to eliminate as many obstacles as possible from the Fresnel Zone.
The two most common LoRa antenna mounts are pole and wall mounts. Pole-mounted antennas have a vertical orientation, which is ideal for long-range applications. Contrary, wall-mounted antennas are ideal for indoor deployments. They can be mounted horizontally or vertically, depending on your application needs.
Installing a LoRa antenna is not difficult. Before installation, it’s important to check the antenna for tight connections. Also, ensure the mounting structure is secure. After installation, you should check the antenna’s orientation and adjust it to ensure optimal performance.
A VeeaHub, with fixing brackets, could also be fixed to such pole or wall, at the cable distance from the antenna.
Caution: Installation in the vicinity of other radio equipment: Avoid strong interference, for example from surrounding GSM or UMTS stations.
LoRa link-budget and path-loss
Definition:
- A link budget is an accounting of all of the power gains and losses that a communication signal experiences in a telecommunication system; from a transmitter, through a communication medium, to the receiver. It is an equation giving the received power from the transmitter power, after the attenuation of the transmitted signal due to propagation.
- The path loss indicates how much energy is lost in free space over a distance between Tx and Rx. The further the distance between Tx and Rx, the lower the energy.
LoRa Link Budget is calculated using receiver sensitivity of the LoRa Gateway (aka, in our case, the LoRa VeeaHub).
Using a simple model, the link budget can be calculated by adding the device transmitter power (Tx), the gateway receiver sensitivity (Rx) and the gateway antenna gain.
For instance:
- LoRa device Transmit Power: 16dBm
- VeeaHub LoRa Receiver sensitivity: -132dBM (for SF:12, BW:125kHz)
- VeeaHub Antenna Gain: 0dB (default antenna)
- The structural damping factor: 0dB (outdoor free space)
Then: Link budget = - 132dB - 16dB = -148dB
Let’s compare it with the field attenuations: the free space path loss (FSPL, meaning, the distance between the LoRa device and the LoRa gateway) and the potential structural damping factor.
- The Path Loss:
- SPL (dB) = 20log10(d) + 20log10(f) - 147,55 (2)
- for 100m at 902.3MHz (USA): FSPL=71.55 dB
- The damping factor:
- Concrete (20cm): 23 dB
Then: total field attenuation is -93.55dB, which is ok for the previous budget link.
Caution: Before deploying a LoRa solution, it is mandatory to do preliminary measurements on sites. As explained earlier, any obstacles in the Fresnel zone can reduce the LoRa performances.
LoRa network capacity
Each LoRa Channel (up to 8 per VeeaHubs) as a maximum capacity with device communication.
The network capacity can be estimated based on inputs taken from the packet’s time-on-air for the various data rates and the data rate distribution. Firstly the collision rate (or packet loss rate) must be chosen for the network. For asynchronous channel access protocols like LoRaWAN™, the network capacity is only meaningful if it is associated with a given collision rate. A channel load of one (100%) means that this channel duty cycle is 100%. Assuming that all packets have a time-onair of exactly one second, a channel load of 100% corresponds on average to one randomly spread packet per second.
It is highly recommended, during a LoRa deployment preliminary work, to compute the necessary capacity based on:
- the number of devices
- the coverage required (The farer a device is from the gateway, the biggest Spread Factor it should have)
- the device payloads frequency and length
To understand such deployment consideration, please take a look at a real LoRaWAN use case: https://cdn2.hubspot.net/hubfs/2507363/Semtech_Network_Capacity_White_Paper.pdf