Sec.  15.323   Specific requirements for devices operating in the 1920–1930 MHz
sub-band.

   (a) Operation shall be contained within the 1920–1930 MHz band. The emission
   bandwidth shall be less then 2.5 MHz. The power level shall be as specified
   in  Sec. 15.319(c), but in no event shall the emission bandwidth be less than 50
   kHz.

   (b) [Reserved]

   (c)  Devices  must incorporate a mechanism for monitoring the time and
   spectrum windows that its transmission is intended to occupy. The following
   criteria must be met:

   (1) Immediately prior to initiating transmission, devices must monitor the
   combined time and spectrum windows in which they intend to transmit for a
   period  of  at  least 10 milliseconds for systems designed to use a 10
   milliseconds or shorter frame period or at least 20 milliseconds for systems
   designed to use a 20 milliseconds frame period.

   (2) The monitoring threshold must not be more than 30 dB above the thermal
   noise power for a bandwidth equivalent to the emission bandwidth used by the
   device.

   (3) If no signal above the threshold level is detected, transmission may
   commence and continue with the same emission bandwidth in the monitored time
   and spectrum windows without further monitoring. However, occupation of the
   same combined time and spectrum windows by a device or group of cooperating
   devices  continuously over a period of time longer than 8 hours is not
   permitted without repeating the access criteria.

   (4) Once access to specific combined time and spectrum windows is obtained
   an  acknowledgment  from  a system participant must be received by the
   initiating  transmitter  within one second or transmission must cease.
   Periodic acknowledgments must be received at least every 30 seconds or
   transmission must cease. Channels used exclusively for control and signaling
   information may transmit continuously for 30 seconds without receiving an
   acknowledgment, at which time the access criteria must be repeated.

   (5) If access to spectrum is not available as determined by the above, and a
   minimum of 40 duplex system access channels are defined for the system, the
   time and spectrum windows with the lowest power level below a monitoring
   threshold of 50 dB above the thermal noise power determined for the emission
   bandwidth  may  be accessed. A device utilizing the provisions of this
   paragraph must have monitored all access channels defined for its system
   within the last 10 seconds and must verify, within the 20 milliseconds (40
   milliseconds for devices designed to use a 20 milliseconds frame period)
   immediately preceding actual channel access that the detected power of the
   selected time and spectrum windows is no higher than the previously detected
   value. The power measurement resolution for this comparison must be accurate
   to within 6 dB. No device or group of co-operating devices located within 1
   meter of each other shall during any frame period occupy more than 6 MHz of
   aggregate bandwidth, or alternatively, more than one third of the time and
   spectrum windows defined by the system.

   (6) If the selected combined time and spectrum windows are unavailable, the
   device may either monitor and select different windows or seek to use the
   same windows after waiting an amount of time, randomly chosen from a uniform
   random distribution between 10 and 150 milliseconds, commencing when the
   channel becomes available.

   (7) The monitoring system bandwidth must be equal to or greater than the
   emission bandwidth of the intended transmission and have a maximum reaction
   time less than 50xSQRT (1.25/emission bandwidth in MHz) microseconds for
   signals at the applicable threshold level but shall not be required to be
   less than 50 microseconds. If a signal is detected that is 6 dB or more
   above the applicable threshold level, the maximum reaction time shall be
   35xSQRT (1.25/emission bandwidth in MHz) microseconds but shall not be
   required to be less than 35 microseconds.

   (8) The monitoring system shall use the same antenna used for transmission,
   or an antenna that yields equivalent reception at that location.

   (9) Devices that have a power output lower than the maximum permitted under
   this  subpart may increase their monitoring detection threshold by one
   decibel for each one decibel that the transmitter power is below the maximum
   permitted.

   (10) An initiating device may attempt to establish a duplex connection by
   monitoring both its intended transmit and receive time and spectrum windows.
   If both the intended transmit and receive time and spectrum windows meet the
   access criteria, then the initiating device can initiate a transmission in
   the intended transmit time and spectrum window. If the power detected by the
   responding device can be decoded as a duplex connection signal from the
   initiating  device,  then  the responding device may immediately begin
   transmitting  on the receive time and spectrum window monitored by the
   initiating device.

   (11) An initiating device that is prevented from monitoring during its
   intended  transmit  window  due to monitoring system blocking from the
   transmissions of a co-located (within one meter) transmitter of the same
   system, may monitor the portions of the time and spectrum windows in which
   they  intend to receive over a period of at least 10 milliseconds. The
   monitored time and spectrum window must total at least 50 percent of the 10
   millisecond frame interval and the monitored spectrum must be within 1.25
   MHz of the center frequency of channel(s) already occupied by that device or
   co-located co-operating devices. If the access criteria is met for the
   intended receive time and spectrum window under the above conditions, then
   transmission in the intended transmit window by the initiating device may
   commence.

   (12) The provisions of (c)(10) or (c)(11) of this section shall not be used
   to extend the range of spectrum occupied over space or time for the purpose
   of denying fair access to spectrum to other devices.

   (d) Emissions outside the sub-band shall be attenuated below a reference
   power of 112 milliwatts as follows: 30 dB between the sub-band and 1.25 MHz
   above or below the sub-band; 50 dB between 1.25 and 2.5 MHz above or below
   the sub-band; and 60 dB at 2.5 MHz or greater above or below the sub-band.
   Emissions inside the sub-band must comply with the following emission mask:
   In the bands between 1B and 2B measured from the center of the emission
   bandwidth the total power emitted by the device shall be at least 30 dB
   below the transmit power permitted for that device; in the bands between 2B
   and 3B measured from the center of the emission bandwidth the total power
   emitted  by  an intentional radiator shall be at least 50 dB below the
   transmit power permitted for that radiator; in the bands between 3B and the
   sub-band edge the total power emitted by an intentional radiator in the
   measurement bandwidth shall be at least 60 dB below the transmit power
   permitted for that radiator. “B” is defined as the emission bandwidth of the
   device in hertz. Compliance with the emission limits is based on the use of
   measurement  instrumentation  employing peak detector function with an
   instrument resolution bandwidth approximately equal to 1.0 percent of the
   emission bandwidth of the device under measurement.

   (e) The frame period (a set of consecutive time slots in which the position
   of each time slot can be identified by reference to a synchronizing source)
   of  an  intentional  radiator operating in these sub-bands shall be 20
   milliseconds or 10 milliseconds/X where X is a positive whole number. Each
   device that implements time division for the purposes of maintaining a
   duplex  connection on a given frequency carrier shall maintain a frame
   repetition rate with a frequency stability of at least 50 parts per million
   (ppm). Each device which further divides access in time in order to support
   multiple communication links on a given frequency carrier shall maintain a
   frame repetition rate with a frequency stability of at least 10 ppm. The
   jitter (time-related, abrupt, spurious variations in the duration of the
   frame interval) introduced at the two ends of such a communication link
   shall not exceed 25 microseconds for any two consecutive transmissions.
   Transmissions shall be continuous in every time and spectrum window during
   the frame period defined for the device.

   (f) The frequency stability of the carrier frequency of the intentional
   radiator shall be maintained within  �10 ppm over 1 hour or the interval
   between channel access monitoring, whichever is shorter. The frequency
   stability shall be maintained over a temperature variation of −20 ° to +50  °C
   at normal supply voltage, and over a variation in the primary supply voltage
   of 85 percent to 115 percent of the rated supply voltage at a temperature of
   20  °C. For equipment that is capable only of operating from a battery, the
   frequency stability tests shall be performed using a new battery without any
   further requirement to vary supply voltage.

   [ 58 FR 59180 , Nov. 8, 1993;  59 FR 15269 , Mar. 31, 1994. Redesignated at  59 FR 32852 , June 24, 1994, as amended at  59 FR 32853 , June 24, 1994;  59 FR 40835 , Aug. 10, 1994;  59 FR 55373 , Nov. 7, 1994;  60 FR 3303 , Jan. 13, 1995;
    69 FR 62621 , Oct. 27, 2004]

Subpart E—Unlicensed National Information Infrastructure Devices