SWRA791 February   2024 CC2340R5 , CC2340R5-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Basics of Bluetooth Channel Sounding
  6. 3Bluetooth Channel Sounding Procedure
  7. 4Bluetooth Channel Sounding Flow for Phase-Based Ranging
  8. 5Channel Sounding Security
  9. 6Summary
  10. 7References
  11.   Appendix A: Basics of Phase Based Ranging and Multi-Carrier Phase Ranging

3 Bluetooth Channel Sounding Procedure

A channel sounding procedure can be divided into one or more CS events. CS events can be comprised of one or more CS subevents. Subevents are a set of predefined time and frequency slots in which the two Bluetooth devices agree to communicate and exchange a combination of RF signals. These exchanges are bidirectional, as both devices take turns sending and receiving RF signals. Within a CS subevent, one or more CS steps are used perform the actual exchanges of ranging tones and security packets (see Section 5 for further details regarding Bluetooth CS security). Bluetooth CS specification defines four CS step types: mode 0 through mode 3. Each mode is used for a specific purpose.

Table 3-1 CS Step Types: Mode 0 to Mode 3
ModeDescription
Mode 0Used to exchange synchronization information to align on timing and calibrate frequency of one side w.r.t. the other
Mode 1Used to exchange a Round Trip Timing (RTT) packets
Mode 2Used to exchange phase-based ranging (PBR) CS tones, to measure phase and amplitude of the communication channel
Mode 3Used to exchange both RTT and PBR CS tones

Figure 3-1 shows the relationship between CS procedures, CS events, CS subevents, and CS steps.

GUID-20231002-SS0I-PB3M-VNRC-LP3XCSFDV5ZM-low.svgFigure 3-1 CS Procedure, Event, Subevent, Step Hierarchy
Note: T_FCS refers to frequency change spacing time period between transmitting two CS steps

To allow for flexible scheduling of CS procedure amidst other ongoing Bluetooth LE connections, multiple CS subevents can be scheduled to be offset from a single LE connection event. A CS subevent offset is used to separate the multiple CS subevents in time. The number of CS subevents allowed in between LE connection events is selectable.

The general structure of Channel Sounding events and subevents started at an offset from the timing of LE ACL (asynchronous connection logical transport) connection event anchor points is as shown in Figure 3-2.

GUID-20231002-SS0I-ZTST-ML4Q-DPNZZF8JP0FK-low.svgFigure 3-2 Channel Sounding Events and Subevent Scheduling