Specifications

ETSI
Final draft ETSI EN 300 328 V1.8.1 (2012
-
04)
18
4.3.1.6 Adaptivity (Adaptive Frequency Hopping)
This requirement does not apply to non-adaptive equipment or adaptive equipment operating in a non-adaptive mode
providing the equipment complies with the requirements and/or restrictions applicable to non-adaptive equipment.
In addition, this requirement does not apply for equipment with a maximum declared RF Output power level of less
than 10 dBm e.i.r.p. or for equipment when operating in a mode where the RF Output power is less than 10 dBm e.i.r.p.
Adaptive Frequency Hopping equipment is allowed to operate in a non-adaptive mode providing it complies with the
requirements applicable to non-adaptive frequency hopping equipment.
Adaptive Frequency Hopping equipment is allowed to have Short Control Signalling Transmissions (e.g. ACK/NACK
signals, etc.) without sensing the frequency for the presence of other signals. See clause 4.3.1.6.3.
Adaptive Frequency Hopping (AFH) equipment uses a Detect And Avoid (DAA) mechanism which allows an
equipment to adapt to its environment by identifying frequencies that are being used by other equipment.
Adaptive Frequency Hopping systems shall implement either of the DAA mechanisms provided in clauses 4.3.1.6.1 or
4.3.1.6.2.
NOTE: Adaptive systems are allowed to switch dynamically between different adaptive modes.
4.3.1.6.1 Adaptive Frequency Hopping using LBT based DAA
4.3.1.6.1.1 Definition
Adaptive Frequency Hopping using LBT based DAA is a mechanism by which a given hopping frequency is made
'unavailable' because signal was detected before any transmission on that frequency.
4.3.1.6.1.2 Requirements & Limits
Adaptive Frequency Hopping equipment using LBT based DAA shall comply with the following minimum set of
requirements:
1) At the start of every dwell time, before transmission on a hopping frequency, the equipment shall perform a Clear
Channel Assessment (CCA) check using energy detect. The CCA observation time shall be not less than 0,2 % of
the Channel Occupancy Time (see step 3) with a minimum of 20 µs. If the equipment finds the hopping frequency
to be clear, it may transmit immediately (see step 3).
2) If it is determined that a signal is present with a level above the detection threshold defined in step 5. the hopping
frequency shall be marked as 'unavailable'. Then the equipment may jump to the next frequency in the hopping
scheme even before the end of the dwell time, but in that case the 'unavailable' channel can not be considered as
being 'occupied' and shall be disregarded with respect to the requirement to maintain a minimum of 15 hopping
frequencies. Alternatively, the equipment can remain on the frequency during the remainder of the dwell time.
However, if the equipment remains on the frequency with the intention to transmit, it shall perform an extended
CCA check in which the (unavailable) channel is observed for a random duration between the value defined for
the CCA observation time in step 1 and 5 % of the Channel Occupancy Time defined in step 3. If the extended
CCA check has determined the frequency to be no longer occupied, the hopping frequency becomes available
again.
The CCA observation time used by the equipment shall be declared by the supplier.
3) The total time during which an equipment has transmissions on a given hopping frequency without re-evaluating
the availability of that frequency is defined as the Channel Occupancy Time.
The Channel Occupancy Time for a given hopping frequency, which starts immediately after a successful CCA,
shall be less than 60 ms followed by an Idle Period of minimum 5 % of the Channel Occupancy Time with a
minimum of 100 µs. After this, the procedure as in step 1 shall be repeated before having new transmissions on
this hopping frequency during the same dwell time.
EXAMPLE: A system with a dwell time of 400 ms can have 6 transmission sequences of 60 ms each, separated
with an Idle Period of 3 ms. Each transmission sequence was preceded with a successful CCA
check of 120 µs.