FAQ BLUETOOTH

Q1. What is the significance of "PIN CODE" in Bluetooth ?

Ans. The PIN code is a secret code provided for security applications. This number has to be manually entered by the user or stored by his application. Once the device knows the PIN of the device it wants to connect to, it can start the security procedures relevant to authentication and encryption.In some devices like access points or headsets, which do not have an interface good enough to allow the users to enter a PIN, the PIN is prefed and used by other devices to connect to it.
Q2. What forms the host and what is the host controller in a Bluetooth device?

Ans. The host is the device which wants to use Bluetooth for its communication requirements. It could be a laptop, a headphone, a PDA or any other device. The host controller is a special module on the Bluetooth hhardware which formats the data packets being communicated from the host to the Bluetooth module into a format suitable for the link between the host and the module. For example, if the host is a laptop and the Bluetooth module a USB card, the the host controller will format the packets from host's USB format to the Bluetooth LMP format.
Q3. Explain the modulation index used in the radio layer in Bluetooth.

Ans. The modulation index is between 0.28 to 0.35. This gives a frequency deviation of 140kHz to 175 kHz on the 1MHz carrier, with binary FSK.
Q4. How is the situaion handed if two devices launch an inquiry simultaneously?

Ans. When two devices start an inquiry simultaneously, then they cannot discover ech other in that inquiry sequence. (They do not cause collissions for other devices as the inquiry hop sequence is different for the two devices. ) To prevent the devices never being able to discover each other, the specification requires that the interval between two inquiries be random. This ensures that the two devices which collided once will not collide again in the next inquiry.
Q5. How does the device schedule itself (figure out which piconet to service/listen)?

.For example ,there may be slots in which the device has obligations on BOTH piconets.Ans. The Bluetooth specification says that different piconets accessed are multiplexed in time. The exact details of how the device wans to do it depend on the implementation as the specification does not give any fixed priority or scheduling structure. Depending on whether a slave is active/parked etc. if would spend different amounts of time with different masters.
Q6. For a computer having all its peripherals connected through Bluetooth, who will be master and whowill be slave?

Ans. The Bluetooth specification does not require any particular device to be the master. However as all communications would probably be through the unit attached to the CPU, it seems most efficient for that unitto become the master.
Q7. Are there any specifications for the timing recovery in the radio layer?

Ans. The specifications do not provide any fixed procedures. The receiver designer may use any of the well known methods for the purpose.

Q8.Where does a bluetooth device store the list of other bluetooth devices in the area?

Ans. This is implementation specific. The Profiles specifications specify that the Bluetooth controller module should store addresses of all devices in proximity and the addresses of devices with which links are open.

Q9. What is the Bluetooth data capacity and throughput?

Ans. The raw data rate is 1Mbps. But the available data rate is 723 kbps.Bluetooth can support:
an asynchronous data channel,
up to three simultaneous synchronous voice channels, or
a channel which simultaneously supports asynchronous data and synchronous voice.
Each voice channel supports 64 kb/s synchronous (voice) link in each direction. The asynchronous channel can support an asymmetric link of maximally 723.2 kb/s in either direction while permitting 57.6 kb/s in the return direction, or a 433.9 kb/s symmetric link.The actual data rates depend on the kind of error correction capability introduced into the data which determines the type of packet used. See the table below.
Packet Type
Max Symmetric rate (two way)
Max Forward (Assymetric) rate
Max Reverse (Assymetric) rate
DM1
108.8
108.8
108.8
DH1
172.8
172.8
172.8
DM3
258.1
387.2
54.4
DH3
390.4
585.6
86.4
DM5
286.7
477.8
36.3
DH5
433.9
723.2
57.6
AUX1
185.6
185.6
185.6
Note: The packet types containing an 'H' in their type field (eg. DH1) refer to packet types with low error correction overhead and high data rates. 'M' refers to medium datarate .
Q10. If a master unit leaves a piconet, what happens?

Ans. If the master leaves, the link managers of all the slaves eventually time out the connections to the master and the piconet is lost. A new piconet must then be established.