Almost every other person we see on the street has some form of Bluetooth device. Whether it is a cell phone, headset, or some other device, Bluetooth has been taking over the world of wireless communications by storm. But, you ask, how does Bluetooth actually work? Well, Bluetooth devices generally operate in the 2.4 GHZ ISM radio band, which is available and compatible everywhere in the world. One distinct disadvantage, however, is that Bluetooth devices must share this band with other RF (Radio Frequency) emitters like automobile security systems, other wireless devices, and other noise sources like microwaves. In order to beat this challenge, Bluetooth employs a fast frequency hopping scheme that uses shorter packets compared to other standards within the ISM band. This thereby helps to make Bluetooth communication more robust and a lot more secure.
This brings us to another question: What is frequency hopping? Well, frequency hopping is basically jumping from frequency to frequency within the ISM radio band. After a bluetooth device sends or receives a packet, both that device and the other device(s) that it is communicating with hop to another frequency before the next packet is sent. This set up offers three key advantages:
1. It allows Bluetooth devices to use the entire ISM band while never transmitting from a fixed frequency for more than a short period of time. This helps to ensure that Bluetooth conforms to the ISM restrictions on the transmission quantity per frequency.
2. It ensures that any interference will be temporary. Any packet that does not arrive safely to its destination can be resent to the next frequency.
3. It provides a base level of security as it is very hard for an eavesdropping device to predict which frequency the Bluetooth devices will use next.
The connected devices, however, must agree upon the frequency they will use next. Bluetooth specifications ensure this in two ways:
A. It defines a master and slave type relationship between Bluetooth devices.
B. Next, it specifies an algorithm that uses device-specific information when calculating the frequency hop sequences.
A Bluetooth device that operates in master mode can communicate with up to seven devices that are set in slave mode. To each of the slaves, the master Bluetooth device will send its own unique address and the value of its own internal clock. The information sent is then used to calculate the frequency hop sequences. Because the master device and each of the slave devices use the same algorithm with the same initial input, the connected devices will always arrive at the same time at the next frequency that they have agreed upon.
As a replacement for cable technology, it is no wonder that Bluetooth devices, like wireless mice and cell phones, are usually battery powered. To conserve power, most Bluetooth devices operate in low power, allowing them to have a range of around 5 – 10 meters. This range is far enough for wireless communication and close enough to avoid drawing too much power from the power source of the device.
Tomorrow we will continue with Part 2 as we look at the benefits of Bluetooth.
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