Bluetooth (IEEE 802.15.1)

Bluetooth (IEEE 802.15.1)
An Introduction

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Background

Purpose:
- Short-range, low-power, low-cost wireless communications
About the Name:
- Named after King Harald Blatand of Denmark (who united the warring factions in what is now Norway, Sweden and Denmark)

Devices

Power-Saving Modes

Hold:
- The device does not actively exchange data
Sniff:
- The device periodically listens for messages
Park:
- The device listens for messages and resynchronizes its clock but does not actively communicate

The Physical Layer

Frequency:
- 2.4GHz band
Spread Spectrum:
- 79 1MHz channels
- Frequency hopping spread spectrum (FHSS) in which each transmission lasts 625 microseconds
Modulation:
- v1 uses Gaussian Frequency Shift Keying (GFSK) for a throughput of about 1 Mbit/s
- v2 also uses Phase Shift Keying (PSK) for a throughput of about 3 Mbit/s

Networks

Terminology:
- Piconet - A group of (synchronized) communicating devices
- A device that is involved in more than one piconet at the same time is said to be part of a scatternet
Roles:
- 1 boss (the first device that initiates communication)
- Up to 7 minions
Piconet Topology:
- Star - for purposes of clock and hopping sequence synchronization (i.e., the boss's clock is used)
- Completely Connected - for other purposes

Procedures

Inquiry (a.k.a. Discovering):
- An inquiring device is attemping to find other nearby devices
- A discoverable device is available to be found and responds to inquiries
- Uses a special physical channel
Paging (a.k.a. Connecting):
- A paging (a.k.a. connecting) device initiates
- A page scanning (a.k.a. connectable) device listens for pages
- Uses a special physical channel

Types of Links

Synchronous Connection Oriented (SCO):
- Reserved time slots are set aside (between the boss and a particular minion)
Asynchronous Connectionless (ACL):
- Can use any time slot (not being used for SCO links)

Frames in Bluetooth

Access Code (68 or 72 bits):
- A Channel Access Code (CAC) is used to identify a particular piconet
- A Device Access Code (DAC) is used in signaling (e.g., paging)
- An Inquiry Access Code (IAC) is used primarily to discover other Bluetooth devices
Header (54 bits):
- 3-bit active member address (AM_ADDR)
- PM_ADDR (used for park mode)
- 4-bit type (ID, Null, Poll, FHS, DM1)
- 1-bit flow control (i.e., stop or not)
- 1-bit acknowledgment (ARQN)
- 1-bit "sequence number" (SEQN) -- alternates between 0 and 1
- 8-bit header error check (HEC)
- Other stuff...
Payload (0-2745 bits)

Bluetooth Profiles