§ 101.141   Microwave modulation.

   (a) Microwave transmitters employing digital modulation techniques and
   operating below 25.25 GHz (except for MVDDS stations in the 12,200-12,700
   MHz  band) must, with appropriate multiplex equipment, comply with the
   following additional requirements:

   (1) The bit rate, in bits per second, must be equal to or greater than the
   bandwidth  specified  by the emission designator in Hertz (e.g., to be
   acceptable, equipment transmitting at a 20 Mb/s rate must not require a
   bandwidth of greater than 20 MHz), except the bandwidth used to calculate
   the minimum rate may not include any authorized guard band.

   (i) Stations authorized prior to December 1, 1988 may install equipment
   after  that  date  with  no minimum bit rate. Equipment applied for or
   authorized prior to April 1, 2005 in the 21.2-23.6 GHz band may be installed
   with no minimum bit rate.

   (ii) However, any digital equipment applied for after April 1, 2005 and
   equipment replacing existing equipment in the 21.2-23.6 GHz band must meet
   the bit rate standard.

   (2)  Equipment  to  be  used for voice transmission placed in service,
   authorized, or applied for on or before June 1, 1997 in the 2110 to 2130 and
   2160 to 2180 MHz bands must be capable of satisfactory operation within the
   authorized bandwidth to encode at least 96 voice channels. Equipment placed
   in service, authorized, or applied for on or before June 1, 1997 in the
   3700-4200, 5925-6425 (30 MHz bandwidth), and 10,700-11,700 MHz (30 and 40
   MHz bandwidths) bands must be capable of satisfactory operation within the
   authorized bandwidth to encode at least 1152 voice channels. These required
   loading  levels  may  be  reduced  by  a factor of 1/N provided that N
   transmitters may be operated satisfactorily, over the same radio path,
   within  an  authorized  bandwidth  less than, or equal to, the maximum
   authorizable bandwidth (e.g., the 1152 channel requirement may be reduced to
   576 if two transmitters can be satisfactorily operated over the same path
   within the maximum bandwidth). Where certificated equipment is designed to
   operate on the same frequency in a cross polarized configuration to meet the
   above  capacity requirements, the Commission will require, at the time
   additional  transmitters  are authorized, that both polarizations of a
   frequency be used before a new frequency assignment is made, unless a single
   transmitter installation was found to be justified by the Commission at the
   time it authorized the first transmitter.

   (3)(i) Except as noted in paragraph (a)(7) of this section, the payload
   capacity of equipment shall meet the following minimum efficiency standards:
   Frequency Emission bandwidth ≤5 MHz Emission bandwidth >5 MHz and ≤20 MHz
   Emission bandwidth >20 MHz
   3,700-10,550  MHz  2.4  bits/second/Hertz  4.4  bits/second/Hertz  4.4
   bits/second/Hertz.
   10,550-13,250  MHz  2.4  bits/second/Hertz  4.4  bits/second/Hertz 3.0
   bits/second/Hertz.

   (ii) Traffic loading payload shall exceed 50 percent of payload capacity
   within 30 months of licensing. During anomalous signal fading, licensees
   subject to the capacity and loading requirements may adjust to a modulation
   specified in their authorization if such modulation is necessary to allow
   licensees to maintain communications, even if the modulation will not comply
   with the capacity and loading requirements specified in this paragraph.
   Links that must comply with the capacity and loading requirements that use
   equipment capable of adjusting modulation must be designed using generally
   accepted multipath fading and rain fading models to meet the specified
   capacity  and loading requirements at least 99.95% of the time, in the
   aggregate of both directions in a two-way link.

   (4) If a transmitter is authorized to operate in a bandwidth that is not
   listed in paragraph (a)(3) of this section, it must meet the minimum payload
   capacity  and traffic loading requirements of the next largest channel
   bandwidth listed in the table; e.g., if the authorized bandwidth is 3.5 MHz,
   the minimum payload capacity must be 12.3 Mbits/s.

   (5) Transmitters carrying digital motion video motion material are exempt
   from the requirements specified in paragraphs (a)(2) and (a)(3) of this
   section, provided that at least 50 percent of the payload is digital video
   motion material and the minimum bit rate specified in paragraph (a)(1) of
   this  section is met. In the 6, 10, and 11 GHz bands, concatenation of
   multiple contiguous channels is permitted for channels of equal bandwidth on
   center frequencies, provided no other channels are available and the minimum
   payload capacity requirements are met.

   (6) Digital systems using bandwidths of 10 MHz or larger will be considered
   50 percent loaded when at least 50 percent of their total capacity is being
   used. For purposes of this subsection, a Fixed Service channel is being used
   if it is attached to a communications system that is capable of providing
   data to it at a rate that is sufficient to occupy at least 50 percent of the
   payload capacity of the Fixed Service channel, after header compression is
   applied.

   (7) Equipment placed in service after June 1, 1997 and prior to October 5,
   2012 may comply with the provisions of § 101.141(a)(3) in effect as of the
   date the equipment was placed in service.

   (b) For purposes of compliance with the emission limitation requirements of
   § 101.111(a)(2)  and the requirements of paragraph (a) of this section,
   digital modulation techniques are considered as being employed when digital
   modulation occupies 50 percent or more to the total peak frequency deviation
   of a transmitted radio frequency carrier. The total peak frequency deviation
   will  be  determined  by  adding the deviation produced by the digital
   modulation signal and the deviation produced by any frequency division
   multiplex (FDM) modulation used. The deviation (D) produced by the FDM
   signal must be determined in accordance with § 2.202(f) of this chapter.

   (c) Analog Modulation. Except for video transmission, an application for an
   initial working channel for a given route will not be accepted for filing
   where the anticipated loading (within five years for voice, or other period
   subject to reasonable projection) is less than the minimum specified for the
   following frequency bands. Absent extraordinary circumstances, applications
   proposing additional frequencies over existing routes will not be granted
   unless it is shown that the traffic load will shortly exhaust the capacity
   of the existing equipment. Where no construction of radio facilities is
   requested, licensees must submit this evidence with their filing of any
   necessary authority required pursuant to section 214 of the Communications
   Act and part 63 of this chapter.
   Frequency band (MHz) Minimum number of voice channels (4 KHz or equivalent)
   3700 to 4200 (20 MHz bandwidth) 900
   5925 to 6425 (10 MHz bandwidth) 300
   5925 to 6425 (20 MHz bandwidth) 600
   5925 to 6425 (30 MHz bandwidth) 900
   6525 to 6875 (10 MHz bandwidth) 300
   10,700 to 11,700 (10 MHz bandwidth) 300
   10,700 to 11,700 (20 MHz bandwidth) 600
   10,700 to 11,700 (30 MHz bandwidth) 900
   10,700 to 11,700 (40 MHz bandwidth) 900

   [ 61 FR 26677 , May 28, 1996, as amended at  62 FR 24583 , May 6, 1997;  63 FR 36611 , July 7, 1998;  65 FR 59358 , Oct. 5, 2000;  67 FR 43039 , June 26, 2002;
    68 FR 4958 , Jan. 31, 2003;  76 FR 59572 , Sept. 27, 2011;  77 FR 54433 , Sept.
   5, 2012]

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