Skip to main content

Data logger with Bluetooth scatternet

Short answer

Capture with antenna, 2.4 GHz BPF, LNA, mixer driven by hop synthesiser, FM demod, and data slicer, then baseband controller and logger. Each piconet has a master that polls its slaves in TDD; bridge nodes connect piconets in a scatternet. With three piconets of one master and three slaves, bridges link adjacent piconets.

A data logger receives signals from a Bluetooth scatternet. The scatternet consists of three piconets and within each piconet there are four bluetooth devices. The piconets communicate within themselves and amongst each other using the master/slave protocol. (a) Describe an analog transmission mechanism to capture the blue tooth signals by the data logger. Draw a complete system block diagram. (b) Describe the master/slave protocol that is present in blue tooth piconets and scatternets. (c) Draw the scatternet topology depicting the scenario maintained in the question. Make sure you adhere to the rules of the masters/slave protocol.

(a) Capturing the Bluetooth signals by the data logger

Bluetooth transmits an analog radio signal in the 2.4 GHz band using GFSK (Gaussian frequency shift keying) with 1600 hops/s. The data logger uses an RF receiver (analog front end) followed by digital processing.

 Antenna -> BPF 2.4 GHz -> LNA -> Mixer -> IF filter -> FM demod
                                    ^                       |
                      Hop synthesiser (follows hop sequence)|
                                                            v
   Data slicer -> Baseband / link controller -> uP -> Memory (logging)
                                                  \-> Display, USB/PC

Steps: the antenna and band-pass filter select the 2.4 GHz band; the LNA amplifies; the mixer, driven by a frequency synthesiser tuned according to the hop sequence, converts to an intermediate frequency; the FM discriminator recovers the baseband GFSK signal; a data slicer converts it to bits; the baseband controller recovers packets (access code, header, payload), and the microprocessor time-stamps and stores the data in the logger memory.

(b) Master/slave protocol

  • Each piconet has one master and up to seven active slaves. The master's clock and address define the hopping sequence and timing.
  • Time division duplex with 625 us slots: the master transmits only in even slots and a slave replies in the next odd slot only if it was addressed (polled) by the master.
  • Slaves communicate only with their master, never directly with each other.
  • In a scatternet, a bridge device belongs to two piconets (slave in both, or master in one and slave in the other) and divides its time between them. A device cannot be the master of two piconets.

(c) Scatternet topology (3 piconets, 4 devices in each)

Each piconet = 1 master + 3 slaves. Piconets are joined through two bridge slaves: B12 (in piconet 1 and 2) and B23 (in piconets 2 and 3). Count: P1 = M1, S11, S12, B12; P2 = M2, B12, S21, B23; P3 = M3, B23, S31, S32.

   S11   S12         S21           S31   S32
     \   /             \             \   /
      M1 ---- B12 ---- M2 ---- B23 ---- M3
   [piconet 1]      [piconet 2]     [piconet 3]

All links are master-slave links (every line joins a master to a slave). The data logger sniffs all three piconets: it follows the hop sequence of each master in turn (or uses three receivers) and stores the packets.

✓ Answer checked by Claude Sonnet 5.5

Related questions

All Instrumentation II chapter 5 questions →