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558074 D01 DTS Meas Guidance v03r02
Page 1
Federal Communications Commission
Office of Engineering and Technology
Laboratory Division
June 5, 2014
Guidance for Performing Compliance Measurements on
Digital Transmission Systems (DTS) Operating Under §15.247
1.0 General
The measurement procedures provided herein are applicable only to digital transmission system (DTS)
devices operating in the 902 MHz to 928 MHz, 2400 MHz to 2483.5 MHz, and/or 5725 MHz to 5850
MHz bands under §15.247 of the FCC rules
1
.
This procedure is not applicable to frequency-hopping
spread spectrum systems (FHSS) that are not hybrid systems, authorized under the same rule part. For
measurements of non-hybrid FHSS devices, see DA 00-705, released on March 30
th
, 2000. It should be
noted that whenever a device utilizes combined technologies (e.g., DTS and U-NII), each component
must be shown to be in compliance with the applicable rule requirements.
2.0 Power limits, definitions and device configuration
The maximum output power limit for DTS devices is specified as 1 watt and is expressed in terms of
either maximum peak conducted output power or maximum conducted output power.
2
The maximum peak conducted output power is defined as the maximum power level measured with a
peak detector using a filter with width and shape of which is sufficient to accept the signal bandwidth.
However, when a filter with adequate width is not available, an integrated method utilizing a peak
detector is acceptable.
The maximum conducted output power is defined as the total transmit power delivered to all antennas and
antenna elements averaged across all symbols in the signaling alphabet when the transmitter is operating
at its maximum power control level.
The minimum 6 dB bandwidth of a DTS transmission shall be at least 500 kHz.
3
Within this document,
this bandwidth is referred to as the DTS bandwidth. The procedures provided herein for measuring the
maximum peak conducted output power assume the use of the DTS bandwidth.
The procedures provided herein for measuring the maximum conducted (average) output power assume
the use of the occupied bandwidth (OBW) as the reference for power integration. See ANSI C63.10
4
for
guidance pertaining to measuring the OBW.
1
Starting June 2, 2015, devices operating in the 5725-5850 MHz band will no longer be certified under the §15.247
rules and will instead be subject to the §15.407 rules and requirements. For further information on permissive
changes and marketing restrictions see KDB Publications 789033 and 926956.
2
See 47 CFR 15.247(b)(3)
3
§15.247(a)(2)
558074 D01 DTS Meas Guidance v03r02
Page 2
3.0 Acceptable measurement configurations
The measurement procedures described herein are based on the use of an antenna-port conducted test
configuration. However, if antenna-port conducted tests cannot be performed on an EUT (e.g., portable or
handheld devices with integral antenna), then radiated tests are acceptable for demonstrating compliance
to the conducted emission requirements. The guidance provided herein is applicable to either antenna-port
conducted or radiated compliance measurements.
If a radiated test configuration is used, then the measured power or field strength levels shall be converted
to equivalent conducted power levels for comparison to the applicable output power limit. This may be
accomplished by first measuring the radiated field strength or power levels using a methodology for
maximum peak conducted power or maximum conducted (average) power as applicable and peak or
average power spectral density as applicable. The radiated field strength or power level can then be
converted to EIRP (see ANSI C63.10 for guidance). The equivalent conducted output power or power
spectral density is then determined by subtracting the EUT transmit antenna gain (guidance applicable to
devices utilizing multiple antenna technologies is provided in KDB 662911) from the EIRP (assuming
logarithmic representation). All calculations and parameter assumptions shall be provided in the test
report.
Antenna-port conducted measurements shall be performed using test equipment that matches the nominal
impedance of the antenna assembly to be used with the EUT. Additional attenuation may be required in
the conducted RF path to prevent overloading of the measurement instrument. The measured power levels
shall be adjusted to account for all losses or gains introduced into the conducted RF path, including cable
loss, external attenuation or amplification. These adjustments shall be recorded in the test report.
Radiated measurements shall utilize the procedures specified in ANSI C63.10, as applicable.
Averaging over the symbol alphabet is permitted when measuring the maximum conducted (average)
output power; however, time intervals when the transmitter is off or transmitting at reduced power levels
are not to be considered. Thus, whenever possible the EUT shall be configured to transmit continuously
(i.e., with a duty cycle of greater than or equal to 98 %) at the maximum power control level over a
random symbol set. Alternatively, sweep triggering/signal gating may be employed within the
measurement instrumentation so that all measurements are performed while the EUT is transmitting at its
maximum power control level.
The DTS emission limits apply to the total of the emissions from all outputs of the transmitter. Thus,
emissions from the transmitter outputs must be summed before comparing the measured emissions to the
emission limit. See KDB 662911 for additional guidance.
4.0 Test suite considerations
Depending on the operational frequency range utilized by a particular DTS EUT, compliance
measurements can be required on multiple frequencies or channels. §15.31(m) specifies the number of
frequencies/channels that shall be tested as a function of the frequency range over which the EUT
operates.
Many DTS EUTs utilize wireless protocols that provide for operation in multiple transmission modes,
where the data rate, bandwidth, modulation, coding rate, and number of data streams are often variable.
4
ANSI C63.10, American National Standard for Testing Unlicensed Wireless Devices, Institute for Electrical and
Electronic Engineers (IEEE).
558074 D01 DTS Meas Guidance v03r02
Page 3
When such multiple modes of operation are possible, then compliance to the applicable technical
requirements shall be confirmed for any and all realizable operational modes.
In some cases, it might be possible to identify one or more specific operational modes that produce the
“worst-case” test results with respect to all of the required technical limits (e.g., output power, power
spectral density, unwanted emission power at the band edge and in all spurious emissions, and for each
possible output data stream), and then reduce the testing to just these modes on each of the
frequencies/channels required per §15.31(m). Whenever this type of test reduction is utilized, a complete
and detailed technical justification shall be provided in the test report, to include measurement data where
applicable.
5.0 Reference level/attenuation/headroom
5.1 General considerations
For measurements where the bandwidth of the emission is greater than the resolution bandwidth of the
measuring instrument care must be taken to ensure that the input mixer of the instrument is operating in
its linear region, and is not saturating or clipping the signal.
For measurements where the bandwidth of the emission is less than or equal to the resolution bandwidth
of the measuring instrument it is generally sufficient that the peak of the displayed signal be less than the
reference level, as long as the instrument attenuation is set to AUTO.
5.2 Setting the proper reference level and input attenuation
Set attenuation to auto. If finer control of attenuation is required to achieve a sufficiently low noise floor
for out-of-band measurements, manual setting of attenuation is permitted provided that the power level
corresponding to the reference level setting specified below falls within the mixer level range
recommended by the instrument manufacturer.
Set the reference level based on power measurements of the signal or by ensuring that the "head room"
between the maximum spectrum level and the reference level is at least 10 log (99% occupied
bandwidth/RBW). The nominal channel bandwidth or the Emission Bandwidth may be substituted for
99% occupied bandwidth in this formula if a measurement of occupied bandwidth is not available.
Additional headroom (i.e., higher reference level) equal to 10 log(1/duty cycle) will be needed if the
headroom calculation is based on power or spectrum measurements that are averaged across the on/off
cycle of the transmission. For example, the reference level should be set 3 dB higher if the settings are
based on power or spectrum measurements that are averaged across the on/off cycles of a 50 percent duty
cycle transmission.
For in-band measurements the reference level is based on in-band power or maximum in-band spectrum
level.
The same reference level is also used for out-of-band measurements unless a preselector attenuates the in-
band signal sufficiently to justify a lower reference level.
558074 D01 DTS Meas Guidance v03r02
Page 4
6.0 Duty cycle, transmission duration and maximum power control level
Preferably, all measurements of maximum conducted (average) output power will be performed with the
EUT transmitting continuously (i.e., with a duty cycle of greater than or equal to 98%). When continuous
operation cannot be realized, then the use of sweep triggering/signal gating techniques can be utilized to
ensure that measurements are made only during transmissions at the maximum power control level. Such
sweep triggering/signal gating techniques will require knowledge of the minimum transmission duration
(T) over which the transmitter is on and is transmitting at its maximum power control level for the tested
mode of operation. Sweep triggering/signal gating techniques can then be used if the measurement/sweep
time of the analyzer can be set such that it does not exceed T at any time that data is being acquired (i.e.,
no transmitter off-time is to be considered).
When continuous transmission cannot be achieved and sweep triggering/signal gating cannot be
implemented, alternate procedures are provided that can be used to measure the average power; however,
they will require an additional measurement of the transmitter duty cycle. Within this guidance
document, the duty cycle refers to the fraction of time over which the transmitter is on and is transmitting
at its maximum power control level. The duty cycle is considered to be constant if variations are less than
± 2 percent, otherwise the duty cycle is considered to be non-constant.
The term “maximum power control level” is intended to distinguish between operating power levels of
the EUT and differences in power levels of individual symbols that occur with some modulation types
such as quadrature amplitude modulation (QAM). During testing, the EUT is not required to transmit
continuously at its highest possible symbol power level. Rather, it should transmit all of the symbols and
should do so at the highest power control level (i.e., highest operating power level) of the EUT.
Measurements of duty cycle and transmission duration shall be performed using one of the following
techniques:
a) A diode detector and an oscilloscope that together have sufficiently short response time to permit
accurate measurements of the on and off times of the transmitted signal.
b) The zero-span mode on a spectrum analyzer or EMI receiver if the response time and spacing
between bins on the sweep are sufficient to permit accurate measurements of the on and off times
of the transmitted signal. Set the center frequency of the instrument to the center frequency of the
transmission. Set RBW ≥ OBW if possible; otherwise, set RBW to the largest available value. Set
VBW ≥ RBW. Set detector = peak or average. The zero-span measurement method shall not be
used unless both RBW and VBW are > 50/T and the number of sweep points across duration T
exceeds 100. (For example, if VBW and/or RBW are limited to 3 MHz, then the zero-span
method of measuring duty cycle shall not be used if T ≤ 16.7 microseconds.)
7.0 Transmit antenna performance considerations
The conducted output power limits for DTS EUTs are based on the use of transmit antennas with
directional gains that do not exceed 6 dBi. If transmit antennas with an effective directional gain greater
than 6 dBi are used, then the conducted output power from the EUT shall be reduced, as specified in the
applicable requirements for DTS.
5
5
See 47 CFR 15.247(b) and 15.247(c).
558074 D01 DTS Meas Guidance v03r02
Page 5
For those cases where the rule specifies that the conducted output power be reduced by the amount in dB
that the directional gain of the transmitting antenna exceeds 6 dBi, the applicable output power limit shall
be calculated as follows:
(
)
6
G
PP
TxLimit
Out
−−
=
(1)
where:
P
Out
is the maximum conducted output power in dBm,
P
Limit
is the output power limit in dBm,
G
Tx
is the maximum transmitting antenna directional gain in dBi.
For those cases where the rule specifies that the conducted output power be reduced by 1 dB for every 3
dB that the directional gain of the transmitting antenna exceeds 6 dBi, the applicable output power limit
shall be calculated as follows:
( )
[ ]
36GFloorPP
TxLimitOut
−−=
(2)
where:
P
Out
is the maximum conducted output power in dBm,
P
Limit
is the output power limit in dBm,
Floor[x] is the largest integer not greater than x (i.e., drop all fractional portions of the real number
retaining only the least integer value of the operation),
G
Tx
is the maximum transmitting antenna directional gain in dBi.
Additional guidance for determining the effective antenna gain of EUTs that utilize multiple transmit
antennas simultaneously or sequentially is provided in KDB 662911.
8.0 DTS bandwidth
One of the following procedures may be used to determine the modulated DTS bandwidth.
8.1 Option 1:
a) Set RBW = 100 kHz.
b) Set the video bandwidth (VBW) ≥ 3 × RBW.
c) Detector = Peak.
d) Trace mode = max hold.
e) Sweep = auto couple.
f) Allow the trace to stabilize.
g) Measure the maximum width of the emission that is constrained by the frequencies associated with
the two outermost amplitude points (upper and lower frequencies) that are attenuated by 6 dB
relative to the maximum level measured in the fundamental emission.
8.2 Option 2:
The automatic bandwidth measurement capability of an instrument may be employed using the X dB
bandwidth mode with X set to 6 dB, if the functionality described above (i.e., RBW = 100 kHz, VBW ≥
3 × RBW, peak detector with maximum hold) is implemented by the instrumentation function. When
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