bluetooth -- radio layer

7/27/2019 Bluetooth -- Radio Layer

1/16

Bluetooth

Radio Layer


2/16


3/16

Bluetooth Radio Layer

The Bluetooth Radio (layer) is the lowestdefined layer of the Bluetooth specification.

The radio layer moves the bits from master to

slave, or vice versa(similar to physical layer inOSI model).

It is a low-power system with a range of 10

meters operating in the same 2.4-GHz ISM It defines the requirements of the Bluetooth

transceiver device.


4/16

Main Contents concerned to Radio

Layer

Frequency Bands and Channel Arrangement

(includes spread spectrum technology, FHSS)

Transmitter Characteristics

Receiver Characteristics


5/16

Frequency Hopping Spread Spectrum

BT System uses Frequency Hopping Spread

Spectrum for transmission.

The Bluetooth radio accomplishes spectrum

spreading by frequency hopping in 79 hops

displaced by 1 MHz, starting at 2.402GHz and

finishing at 2.480GHz.

It has a fast hopping rate of 1600 hops/sec

which makes the slot time as 625 sec.


6/16

How actually it happens.

For frequency hopping spread spectrum

(FHSS)systems, the total available bandwidth

is split into many channels of smaller

bandwidth.

Transmitter and receiver stay on one of these

channels for a certain time and then hop to

another channel.

This system implements FDM & TDM.


7/16

What is Hopping Sequence?The pattern of channel usage is called thehopping sequence.

What is dwell time?The time spent on a channel with a certainfrequency is called the dwell/slot time.-- Since in BT, transmitter performs 1600 hopsbetween channels in 1 sec, its dwell time is1/1600 sec.


8/16

FHSS cont.(Fast and Slow Hopping)


9/16

In slow hopping, the transmitter uses one

frequency for several bit periods.

Slow hopping systems are typically cheaper.

They are not as immune to narrowband

interference as fast hopping systems.


10/16

In fast hopping, the transmitter uses severalfrequencies for one bit period.

Fast hopping systems are expensive because

the transmitter and receiver have to staysynchronized(at lower tolerance) to performhopping at more or less the same points intime.

They handle narrowband interference moreefficiently.


11/16

FHSS Transmitter Workflow


12/16

Steps in transmitting

Modulation of user data according to one ofthe digital-to-analog modulation schemes(e.g., FSK). This results in a narrowband signal.

Perform frequency hopping in 2nd modulation,based on a hopping sequence(which is fed tofrequency synthesizer to generate carrierfrequencies).

Transmit the spread transmit signal receivedafter 2nd modulation.


13/16

FHSS Receiver Workflow

NB. The receiver of an FHSS system has to

know the hopping sequence and must stay

synchronized.

It performs the inverse operations of the

modulation to reconstruct user data.


14/16

FHSS Receiver Workflow(cont)


15/16

Transceiver Chrateristics

Power Classes: Each device is classified into 3power classes, Power Class 1, 2 & 3.

Power Class 1: is designed for long range (~100m)devices, with a max output power of 20 dBm,

Power Class 2: for ordinary range devices (~10m)

devices, with a max output power of 4 dBm, Power Class 3: for short range devices (~10cm)

devices, with a max output power of 0

dBm(1mW).


16/16

Transmitter Chrateristics(cont)

Modulation Characteristics: The Bluetoothradio module uses FSK (Frequency ShiftKeying) where a binary one is represented by

a positive frequency deviation and a binaryzero by a negative frequency deviation.

Sensitivity Level: The receiver must have asensitivity level for which the bit error rate(BER) 0.1% is met. For Bluetooth this meansan actual sensitivity level of -70dBm or better.

bluetooth -- radio layer

Documents