Radio (layer) is the lowest defined layer of the Bluetooth specification.
It defines the requirements of the Bluetooth transceiver device operating
in the 2.4GHz ISM band.
For more details : Download the Radio
Specification from the SIG website, or visit the Documents
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.
In a few countries (i.e France) this frequency band range is (temporarily)
reduced, and a 23-hop system is used. In order to comply with out of band
regulations in each country. In both systems a guard band is used at the
lower and upper band edge
Each device is classified into 3 power 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.
The Bluetooth radio interface is based on a nominal
antenna power of 0dBm. Each device can optionally vary its transmitted
power.Equipment with power control capability optimizes the output power
in a link with LMP commands (see Link Manager Protocol).
It is done by measuring RSSI and report back if the power should be
increased or decreased.
Modulation Characteristics: The Bluetooth radio
module uses GFSK (Gaussian Frequency Shift Keying) where a binary one is
represented by a positive frequency deviation and a binary zero by a
negative frequency deviation. BT is set to 0.5 and the modulation index
must be between 0.28 and 0.35.
Spurious Emissions: The spurious emission,
in-band and out-of-band, is measured with a frequency hopping transmitter
hopping on a single frequency; this means that the synthesizer must change
frequency between receive slot and transmit slot, but always returns to
the same transmit frequency.
Radio Frequency Tolerance: The transmitted initial
center frequency accuracy must be ?5 kHz from Fc. The initial frequency
accuracy is defined as being the frequency accuracy before any information
is transmitted. Note that the frequency drift requirement is not included
in the ?5 kHz.
Sensitivity Level: The receiver must
have a sensitivity level for which the bit error rate (BER) 0.1% is met.
For Bluetooth this means an actual sensitivity level of -70dBm or better.
Interference Performance: The interference
performance on Co-channel and adjacent 1 MHz and 2 MHz are measured with
the wanted signal 10 dB over the reference sensitivity level. On all other
frequencies the wanted signal shall be 3 dB over the reference sensitivity
Out-of-Band blocking: The Out
of band blocking is measured with the wanted signal 3 dB over the
reference sensitivity level. The interfering signal shall be a continuous
wave signal. The BER shall be less than or equal to 0.1%.
Intermodulation Characteristics: The
reference sensitivity performance, BER = 0.1%, shall be met under the
- The wanted signal at frequency f 0 with
a power level 6 dB over the reference
- A static sine wave signal at f 1
with a power level of ?9 dBm
- A Bluetooth modulated signal at f 2
power level of -39 dBm
Such that f 0 =2f
1 -f 2
2 -f 1|
=n*1 MHz, where n can be 3, 4, or 5. The system
must fulfil one of the three alternatives.
Maximum Usable Level: The
maximum usable input level the receiver shall operate at shall be better
than ?0 dBm. The BER shall be less or equal to 0,1% at ?0* dBm input
RSSI: Receiver Signal Strength Indicator (Optional):
A transceiver that wishes to take part in a power-controlled link must be
able to measure its own receiver signal strength and determine if the
transmitter on the other side of the link should increase or decrease its
output power level. A Receiver Signal Strength Indicator (RSSI) makes this
possible. The way the power control is specified is to have a golden
receive power range. This golden receive power
is defined as a range with a lower and higher threshold levelsand a high
limit. The lower threshold level corresponds to a received power between
-56 dBm and 6 dB above the actual sensitivity of the receiver. The upper
threshold level is 20 dB above the lower threshold level to an accuracy of
+/- 6 dB. The instructions to alter the TX power are carried in the LMP
Note , the above text contains excerpts from the Bluetooth SIG's
Specification, as well as various interpretations of the Specs. For
complete details of the various sections, consult the actual Bluetooth