1. Purpose

This Engineering Study evaluates alternative arrangements for the timing and transmission of successive Traffic Control Frames (TCF) within packet-based personal signalling networks. The objective is to identify an arrangement that minimises receiver complexity, while providing deterministic network behaviour and acceptable power consumption.

2. Background

Receivers are dependent on the transmitter to establish overall network timing and cadence, and to indicate when reception is required. Once synchronised, a receiver maintains a shared notion of network time, allowing it to wake only for the Traffic Control Frame (TCF) and traffic slots of interest. This substantially reduces average power consumption compared with continuously monitoring the channel.

A receiver that powers on without an established notion of network time must first acquire synchronisation before deterministic sleep scheduling can begin. The frequency and arrangement of TCF transmissions therefore directly influence receiver acquisition latency.

Transmitters must also balance power consumption, maintaining network timing, minimising acquisition latency, while adhering to regulatory duty cycle requirements.

The timing arrangements discussed in this study assume that network timing parameters remain constant during normal operation. Although a network could vary these parameters dynamically, such behaviour is outside the scope of this study and was not considered further due to the additional complexity imposed on receivers.

3. Candidate Timing Models

3.1 Fixed-duration cycles with inter-cycle gaps

Inter-cycle gaps between TCFs allow the successive TCFs to be spaced independently of the overall traffic cycle duration.

Figure 3-1: Traffic cycle with inter-cycle gap

  | TCF | TS0 | TS1 | ... | TS19 | <inter-cycle gap> | TCF | TS0 | ... |

Once all traffic slots have been transmitted, there is a fixed duration of radio silence before the following TCF. This allows for operation in regulatory environments with low duty cycle requirements. The following example illustrates the resulting transmitter duty cycle.

Figure 3-2: Representative Network Configuration

  TCF                1 s
  Traffic Slots     20 s
  Idle              39 s

  Total Cycle       60 s

  Effective TX Duty Cycle:
  35%

3.2 Continuous Traffic Control Frames

Continuous TCFs, where the final traffic slot is immediately followed by the next TCF, provide a continuous network cadence with no intentional inter-cycle gap. Once synchronised, receivers can predict the timing of future traffic cycles without accounting for variable idle periods between successive TCFs.

Figure 3-3: Continuous traffic cycle

  | TCF | TS0 | TS1 | ... | TS19 | TCF | TS0 | ... |

Longer traffic cycles may increase receiver acquisition latency. This may be mitigated through the use of optional Periodic Acquisition Beacons.

3.3 Periodic Acquisition Beacons

Longer traffic cycles increase the maximum time required for a receiver to acquire network synchronisation. Periodic Acquisition Beacons (ABs) provide additional synchronisation opportunities between Traffic Control Frames, reducing receiver acquisition latency while preserving the benefits of longer traffic cycles.

Acquisition Beacons are optional synchronisation frames transmitted within a traffic cycle. They provide sufficient information for receivers to acquire and synchronise with the network but do not begin a new traffic cycle. An AB does not modify or replace the authoritative schedule established by the preceding TCF, and does not carry transient scheduling information such as Active Traffic Slot or Forced Wake Slot bitmaps.

An AB occupies a scheduled transmission opportunity that is not advertised as an Active Traffic Slot by the preceding TCF. Receivers already synchronised to the network are therefore not expected to wake for its reception.

Deployments using extended traffic-cycle durations may transmit ABs at a periodic interval (for example, every 15 seconds) to reduce receiver acquisition time.

Figure 3-4: Long traffic-cycle network without Acquisition Beacons

  | TCF | TS0 | TS1 | ... | TS14 | TS15 | TS16 | ... | TS29 | TCF |

Figure 3-5: Long traffic-cycle network with periodic Acquisition Beacons

  | TCF | TS0 | TS1 | ... | TS14 |  AB  | TS16 | ... | TS29 | TCF |

4. Assessment

Continuous timing provides the simplest receiver model and the most deterministic network behaviour. While longer traffic cycles increase receiver acquisition latency, this may be addressed independently through optional Periodic Acquisition Beacons. On balance, continuous timing offers the most straightforward implementation for both transmitters and receivers.

5. Recommendation

KPSAG recommends that personal signalling networks using extended traffic-cycle durations employ continuous Traffic Control Frames with optional Periodic Acquisition Beacons.