U
SER
M
ANUAL
WRAP
P
RODUCT
S
ERIES
The Bluetooth frequency band is divided into distinct channels with 1 MHz channel spacing. In order to
comply with out-of-band regulations in each country, a guard band is used at the lower and upper band edge.
For the USA, Europe, and most other countries the frequency range is 2.400 – 2483.5 MHz and the
corresponding channels are f = 2402 + k MHz; k = 0 ¼ 78. In France, the frequency range is 2.4465 – 2.4835
GHz and the corresponding channels are f = 2454 + k MHz; k = 0 ¼ 22. Transmission utilises channel
hopping over the specified range at 1600 kHz hop frequency. When operating in countries that permit only a
subset of the overall spectrum, transmission utilises only the approved portions of the spectrum. The
Bluetooth system utilises Gaussian frequency shift keying (GFSK). The signalling rate is 1 Mbit/s.
5.2 P
OWER
C
ONSIDERATIONS
The Bluetooth system transceivers are classified into three power classes to support different link ranges.
•
Power Class 1. Output power is 1 – 100 mW (0 – 20 dBm) with mandatory power control ranging
from 4 to 20 dBm.
•
Power Class 2. Output power is 0.25 – 2.5 mW (-6 – +4 dBm) with optional power control.
•
Power Class 3. Output power is less than 1 mW (0 dBm) with optional power control.
BlueGiga’s WRAP products support 10 m link range with Option 1 (Power Class 1).
5.3 R
ADIO
F
REQUENCY
P
ROPAGATION
The radio frequency signal propagates in free space as a spherical wave, from a point source to all directions
equally. In reality, the signal source always differs from a theoretic isotropic signal source. The power
distribution of wireless telecommunication equipment in space is determined by the antenna radiation
pattern. In free space the signal propagates with the speed of light and attenuates with 1/r2 relation. In reality,
the environment always differs from free space. The propagation environment of wireless telecommunication
equipment is restricted by all obstacles.
The basic mechanism of radio propagation is attributed to reflection, diffraction, and scattering depending on
existing obstacles. Since the radio frequency signal propagates in all directions the transmitted signal arrives
at the receiver following multiple paths deformed by the aforementioned propagation mechanisms. The
received signal is the superposition of attenuated and delayed replicas of the transmitted signal leading to
fading of the transmitted signal and broadening of the duration of the transmitted pulse. The transmitted
pulse delay spread leads to inter-symbol interference (ISI) because the subsequent symbols interfere with
each other. The ISI leads to a bit error probability (BIT) floor that is independent of the signal to noise ratio
(SNR). Depending on the time delay spread of the transmitted pulse or the amount of widening that the
transmitted pulse experiences across the radio channel, the multipath interference differs. When the time
delay spread of the transmitted signal is very small with respect to the signalling time the multipath
interference essentially leads to the signal fading phenomena of the received signal. When the time delay
spread of the transmitted signal is high with respect to the signalling time the multipath interference leads to
the symbol interference phenomena of the received signal as well.
A major difference between indoor and outdoor environments is that the former is considerably more
sensitive to changes in the geometry of the environment than the latter. This is because of the differences in
distance between obstacles. For example, a door being shut rather than open may have a major impact on an
indoor environment whereas a comparable event in an outdoor environment may have a minor impact.
The Bluetooth standard has been designed to operate in noisy radio frequency environments. Transmission
utilises fast frequency hopping and short packages to make the link efficient and robust. Fast hopping and
short packages limit the impact of interfering devices on the same frequency band.
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