Specifications
ETSI
Final draft ETSI EN 300 328 V1.8.1 (2012
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04)
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2) If the equipment finds the channel occupied, it shall not transmit on this channel during the next Fixed Frame
Period.
NOTE 1: The equipment is allowed to switch to a non-adaptive mode and to continue transmissions on this
channel providing it complies with the requirements applicable to non-adaptive systems.
See clause 4.3.2.5. Alternatively, the equipment is also allowed to continue transmissions on this
channel providing it complies with the requirements 4.3.2.5.3.
3) The total time during which an equipment has transmissions on a given channel without re-evaluating the
availability of that channel, is defined as the Channel Occupancy Time.
The Channel Occupancy Time shall be in the range 1 ms to 10 ms followed by an Idle Period of at least 5 % of the
Channel Occupancy Time used in the equipment for the current Fixed Frame Period.
4) An equipment, upon correct reception of a packet which was intended for this equipment can skip CCA and
immediately (see note 2) proceed with the transmission of management and control frames (e.g. ACK and Block
ACK frames are allowed but data frames are not allowed). A consecutive sequence of such transmissions by the
equipment without a new CCA shall not exceed the maximum Channel Occupancy Time.
NOTE 2: For the purpose of multi-cast, the ACK transmissions (associated with the same data packet) of the
individual devices are allowed to take place in a sequence.
5) The energy detection threshold for the CCA shall be proportional to the transmit power of the transmitter: for a
20 dBm e.i.r.p. transmitter the CCA threshold level (TL) shall be equal or lower than -70 dBm/MHz at the input to
the receiver (assuming a 0 dBi receive antenna). For power levels below 20 dBm e.i.r.p. the CCA threshold level
may be relaxed to TL = -70 dBm/MHz + 20 - Pout e.i.r.p. (Pout in dBm).
4.3.2.5.2.2.2 Load Based Equipment
Load Based Equipment may implement an LBT based spectrum sharing mechanism based on the Clear Channel
Assessment (CCA) mode using energy detect, as described in IEEE Std. 802.11™-2007 [i.4] clauses 9, 15, 18 or 19, in
IEEE Std. 802.11n™-2009 [i.4], clauses 9, 11 and 20 or in IEEE Std. 802.15.4™-2011 [i.5], clauses 4 and 5 providing
they comply with the conformance requirements referred to in clause 4.3.2.5.2.3.
Load Based Equipment not using any of the mechanisms referenced above shall comply with the following minimum
set of requirements:
1) Before a transmission or a burst of transmissions, the equipment shall perform a Clear Channel Assessment
(CCA) check using energy detect. The equipment shall observe the operating channel for the duration of the CCA
observation time which shall be not less than 20 µs. The channel shall be considered occupied if the energy level
in the channel exceeds the threshold given in step 5) below. If the equipment finds the channel to be clear, it may
transmit immediately. The CCA time used by the equipment shall be declared by the supplier.
2) If the equipment finds the channel occupied, it shall not transmit on this channel (see note 1). The equipment shall
perform an Extended CCA check in which the channel is observed for the duration of a random factor R
multiplied by the CCA observation time. R defines the number of clear idle slots resulting in a total Idle Period
that needs to be observed before initiation of the transmission. The value of R shall be randomly selected in the
range 1..q every time an Extended CCA is required and the value stored in a counter. The value of q is selected by
the manufacturer in the range 4..32. This selected value shall be declared by the manufacturer (see clause 5.3.1 d).
The counter is decremented every time a CCA slot is considered to be 'unoccupied'. When the counter reaches
zero, the equipment may transmit.
NOTE 1: The equipment is allowed to switch to a non-adaptive mode and to continue transmissions on this
channel providing it complies with the requirements applicable to non-adaptive systems. See
clause 5.3.2.5. Alternatively, the equipment is also allowed to continue transmissions on this channel
providing it complies with the requirements 4.3.2.5.3.
3) The total time that an equipment makes use of a RF channel is defined as the Channel Occupancy Time. This
Channel Occupancy Time shall be less than (13/32) × q ms, with q as defined in 2) above, after which the device
shall perform the Extended CCA described in 1) above.