| luetooth devices will normally operate at 2.4 GHZ | | | | use next. |
| in the license free, globally available ISM radio band. | | | | The connected devices however, must agree |
| The advantage to this band includes worldwide | | | | upon the frequency they will use next. The |
| availability and compatibility. A disadvantage to this | | | | specification in Bluetooth ensures this in two ways. |
| however, is that the devices must share this | | | | First, it defines a master and slave type |
| band with other RF emitters. This includes | | | | relationship between bluetooth devices. Next, it |
| automobile security systems, other wireless | | | | specifies an algorithm that uses device specific |
| devices, and other noise sources, such as | | | | information when calculating the frequency hop |
| microwaves. | | | | sequences. |
| To overcome this challenge, Bluetooth employs a | | | | A Bluetooth device that operates in master mode |
| fast frequency hopping scheme and therefore | | | | can communicate with up to seven devices that |
| uses shorter packets than other standards within | | | | are set in slave mode. To each of the slaves, the |
| the ISM band. This scheme helps to make | | | | master Bluetooth device will send its own unique |
| Bluetooth communication more robust and more | | | | address and the value of its own internal clock. |
| secure. | | | | The information sent is then used to calculate the |
| Frequency hopping Frequency hopping is basically | | | | frequency hop sequences. |
| jumping from frequency to frequency within the | | | | Because the master device and each of the slave |
| ISM radio band. After a bluetooth device sends or | | | | devices use the same algorithm with the same |
| receives a packet, it and the device (or devices) | | | | initial input, the connected devices will always |
| it's communicating with hop to another frequency | | | | arrive together at the next frequency that they |
| before the next packet is sent. This scheme | | | | have agreed upon. |
| offers three advantages: 1. Allows Bluetooth | | | | As a replacement for cable technology, it's no |
| devices to use the entirety of the available ISM | | | | wonder that Bluetooth devices are usually battery |
| band, while never transmitting from a fixed | | | | powered, such as wireless mice and battery |
| frequency for more than a short period of time. | | | | powered cell phones. To conserve the power, |
| This helps insure that Bluetooth conforms to the | | | | most devices operate in low power. This helps to |
| ISM restrictions on the transmission quantity per | | | | give Bluetooth devices a range of around 5 - 10 |
| frequency. 2. Ensures that any interference won't | | | | meters. |
| last long. Any packet that doesn't arrive safely to | | | | This range is far enough for wireless |
| its destination can be resent to the next | | | | communication but close enough to avoid drawing |
| frequency. 3. Provides a base level of security as | | | | too much power from the power source of the |
| it's very hard for an eavesdropping device to | | | | device. |
| predict which frequency the Bluetooth devices will | | | | |