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The Bluetooth 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
Page.
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
Power Classes: 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 ±75 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 ±75 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 level.
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 following
conditions.
- The wanted signal at frequency f 0 with a power level 6 dB over the
reference sensitivity level.
- A static sine wave signal at f 1 with a power level of –39 dBm
- A Bluetooth modulated signal at f 2 with a power level of -39 dBm
Such that f 0 =2f 1 -f 2 and |f 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 –20 dBm. The
BER shall be less or equal to 0,1% at –20* dBm input power.
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 link
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 Specification. |
