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

    (a) Operation shall be contained within one of eight 1.25 MHz 
channels starting with 1920-1921.25 MHz and ending with 1928.75-1930 
MHz. Further sub-division of a 1.25 MHz channel is permitted with a 
reduced power level, as specified in Sec. 15.319(c), but in no event 
shall the emission bandwidth be less than 50 kHz.
    (b) Intentional radiators with an intended emission bandwidth less 
than 625 kHz shall start searching for an available time and spectrum 
window within 3 MHz of the sub-band edge at 1920 MHz and search upward 
from that point. Devices with an intended emission bandwidth greater 
than 625 kHz shall start searching for an available time and spectrum 
window within 3 MHz of the sub-band edge at 1930 MHz and search downward 
from that point.
    (c) Isochronous 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

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this comparsion must be accurate to within 6 dB. No device or group of 
cooperating devices located within 1 meter of each other shall occupy 
more than three 1.25 MHz channels during any frame period. Devices in an 
operational state that are utilizing the provisions of this section are 
not required to use the search provisions of paragraph (b) of this 
section.
    (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 the 1.25 MHz frequency 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 shall be attenuated below a reference power of 112 
milliwatts as follows: 30 dB between the channel edges and 1.25 MHz 
above or below the channel; 50 dB between 1.25 and 2.5 MHz above or 
below the channel; and 60 dB at 2.5 MHz or greater above or below the 
channel. Systems that further sub-divide a 1.25 MHz channel into X sub-
channels 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 1.25 MHz channel edge the total power emitted by an intentional 
radiator in the measurement bandwidth shall be at least 60

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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 a 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 &177;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 deg. to +50  deg.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  deg.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]

    Subpart E--Unlicensed National Information Infrastructure Devices

    Source:  62 FR 4656 , Jan. 31, 1997, unless otherwise noted.