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