Wireless Communication Protocols
Common protocols for wireless communication are Wi-Fi and Bluetooth. With Wi-Fi it is possible to connect several units/users to the same access point, but not control the latency. With Bluetooth it is possible to connect several units/ users to each other, but it is not possible to control the latency, and the connection range is usually low. The Kvaser Air Bridge has developed its own proprietary protocol. The Kvaser Air Bridge splits one system into two parts, with very low latency and powerful range. The developed protocol of the Kvaser Air Bridge is based on 2.4GHz Gaussian Frequency-Shift Keying (GFSK) with Frequency Hopping Spread Spectrum (FHSS) modulation. This gives it the advantage that the latency can be controlled, it is approximately 4.8 ms. And when compared to Bluetooth, the Kvaser Air Bridge has better connection range, it can work up to 70 m. It transmits at close to maximum power (18 dBm) with internal antennas. The units are delivered in pairs, several pairs can co-exist in the same vicinity without interfering with each other. Error Frames and Arbitration information are not transmitted by the Air Bridge units across the wireless link.Wireless Connection Range
Determining the range of a wireless connection is not an exact science. Regardless if it is Wi-Fi, Bluetooth, Kvaser Air Bridge or some other wireless connection, there are many factors that might affect the connection. The Kvaser Air Bridge utilizes the same frequency as Wi-Fi and Bluetooth, 2.4 GHz. The number of other wireless users using the same frequency within the vicinity of the Air Bridge’s operating environment will affect performance. The less units in the vicinity that have a wireless connection at that frequency, the better the Air Bridge will work. In order to determine what the wireless connection range is for Your application, it is best to test it in the actual environment. The Kvaser Air Bridge Light HS consists of two units and is a wireless supplement to a cable connection. As long as the two units are connected to their respective power supplies, they will automatically pair to each other. The Air Bridge functions optimally as long as the two paired units have line of sight and are within 70 meters of each other. The wireless signal that travels between the two Air Bridge units can be absorbed, or attenuated, by different materials and environments. Some examples of materials that will absorb the signals are: • Walls, trees, dirt, water, metals, i.e. car door and concrete • Atmospheric conditions affect the way which wireless signals travel through the air • Lower humidity is better for the connection range • The amount of wireless users in the vicinity The more that obstructs the line of the sight of the Air Bridge, the lower the connection range will be. Determining the connection range of any wireless connection is not an exact science, since the environment is dynamic and the climate may affect it as well. Higher humidity attenuates the signal more than a lower one. If the wireless signal between the two Air Bridge units is absorbed, or attenuated, the connection might not work or it might reduce the connection range. The Air Bridge units are weatherproof and work better if the antenna part of the units are not encapsulated when they are installed. The Air Bridge units are not meant to be submerged or used for wireless communication underwater.Connection Example
Beneath the steering wheel in cars is an OBD-II port that connects to the CAN network. If you connect one of the Air Bridge units to that connector (using a DB9 to OBD-II adapter cable), the Air Bridge will function correctly when the other unit is within the same car. If you take the other device outside the car, the wireless signal will be absorbed by the metal in the car body and the wireless connection will not work.Path Loss
As a wireless signal moves further away from its source, the signal strength is reduced. A doubling of the distance traveled means that one quarter of the signal strength is left.When the signal strength is reduced, the wireless connection range is reduced.Multipath Propagation
The transmitted signal itself may cause interference. It may bounce off of, for example, walls and buildings in the environment and reach the receiving antenna from a different angle and at a different time then the direct signal. This means that the receiver receives the same signal through different paths and the scenario is illustrated in the figure below.
Multipath propagation may either be constructive or destructive for the wireless connection. If the performance of the wireless connection is sometimes reduced, multipath propagation might be one reason.
Wireless CAN Bridge
• Wireless connection range up to 70 m • Supports both CAN 2.0A and CAN 2.0B • Automatic baud rate (125k, 250k, 500k, 1M) • And as with any other wireless connection, you do not want to obstruct the line of sight between the antennas as this will affect the connection range • Note: Error Frames and Arbitration information are not communicated through the Air Bridge’s wireless linkEXAMPLE 1: Bridging a Single CAN Network
The Air Bridge units allow a single CAN network to be split into two CAN networks and bridged together.
Figure 1: A simple CANbus.
Figure 2: Splitting that CANbus in two using the Kvaser Air Bridge.
EXAMPLE 2: Bridging Two Different CAN Networks
The Air Bridge units allow two CAN networks, even operating at different baud rates, to be bridged and to communicate.
Figure 3: Two different CANbus networks.
Figure 4: Those two CANbus networks linked by the Kvaser Air Bridge, even though they operate at different baud rates.
Note: In both Example 1 and Example 2, Error Frames and Arbitration information are not communicated across the wireless link by the Air Bridge units.