Amendment of Section 95.193(a) and 95.631(d) ) RM - 10070.
To Authorize manufacture, Sale and Use of GPS Transmission Enhanced Family
Radio Service Units.
Amendment of Section
95.193(a), 95.193(b) ) and 95.631(d) of the Commission's Rules ) Governing
Permissible Communications in the ) Family Radio Service
The Nothern California GMRS User Group
filed comments this week on the Garmin company's FCC petition to allow GPS data
bursts on FRS channels. Popular Wireless Magazines joined with NorCal in
support of this petition.
Garmin is prepared to release a
twenty-two channel GMRS radio with GPS mapping fuctionality built in when the
FCC acts. NorCal's Chairman and Popular Wireless GMRS Techncal Editor, Greg
Forest authored the following comments. Greg's words reflect the editorial
opinion of this magazine.
You may obtain a PDF version of these
comments tha includes all footnotes below:
COMMENTS ON NOTICE OF PROPOSED
RULEMAKING
Comment Date: February 10,
2002
COMMENTS OF Northern California GMRS
Users Group (NCGUG) Gregory J. Forrest, P.E. (KAF1291) - Author; Doug Smith,
Editor of Popular Wireless Magazines (KAF9830); Paul Shinn, P.B.E. (KAF8333);
Anne and Edward Borden (KAF4328); Karen and Ricco Lorenzi (KAF4428); Mike Moran
(KAF4349); Jane and Tom Forrest (KAF4364); Brett Sharenow (WPQY281)
INTRODUCTION
I represent a group of GMRS licensees
who cooperatively own and operate several suburban repeater systems 30 miles
east of San Francisco, California. This "ad-hoc" group forms the
Northern California GMRS Users Group (NCGUG).
The NCGUG and Popular Wireless Magazine
(www.popularwireless.com) have been the lead organizations involved in
identifying the sources of interference to GMRS systems (including interference
from FRS) for over three years. The Magazine and its associated GMRS forums
have been instrumental in expanding various interference identification and
awareness programs nationwide.
The NCGUG, as well as the Magazine
promote the legal and cooperative use of GMRS and FRS.
Doug Smith, Editor of the Popular
Wireless Magazines, as well as Paul Shinn, a Professional Broadcast Engineer,
have been instrumental in developing close working relationships with FCC
management and field operations staff in Northern California in the areas of
interference identification, mitigation and management.
I am a Registered Professional Engineer
(Electrical) in the State of California and Arizona. I am one of several
Technical Editors for Popular Wireless Magazine, and am involved in the
planning, design and implementation of public safety communications systems on
a full-time basis for a national communications engineering firm.
COMMENTS
1. Although we believe that
location information transmission over FRS channels would be a benefit to the
public, we have significant concerns with the Commission's proposed rule
changes.
2. We believe that data
transmissions as proposed will create additional GMRS interference similar to
that experienced today from FRS voice and "call tone" transmissions,
but on a recurring and repetitive basis. We have proposed limiting data
transmission to particular FRS channels, and recommended a slightly reduced
data bandwidth, to mitigate interference problems. We also note that the NPRM
appears to be incomplete since §95.633(c)(Emission Bandwidth) and
§95.635 (Unwanted Radiation) must also be modified to permit Garmin's
proposed F2D emission.
3. We also believe that FRS
users could experience interference under certain conditions, and we have
proposed a practical mitigation method.
4. Finally, the Commission's
proposed language is too general and will also permit unintended operation that
could increase the level and frequency of both FRS and GMRS
interference.
FURTHER INTERFERENCE TO GMRS
OPERATIONS
5. Our GMRS users, as well as
many others throughout the United States have been receiving significant
destructive interference from adjacent channel FRS transmissions for several
years now. Our research has found that FRS interference is caused in three
different ways. These are (1) directly from nearby FRS transmitters operating
on 462 MHz FRS channels 1-7 (into mobile and base station receivers); (2) from
distant FRS transmitters into our mountain-top repeater receivers from FRS
transmitters operating on 467 MHz FRS channels 8-14); and (3) from other GMRS
repeaters being activated by adjacent-channel FRS transmissions by (2) above.
This interference has been effecting both our mobile and base stations as well
as our three GMRS repeater systems.
6. Interference directly from
FRS transmitters (on FRS channels 1-7) is unusually severe for mobile and base
stations in metropolitan areas and near city parks in the outlying suburbs. It
is most sever during the spring and summer when FRS activity is the greatest.
This interference is frequently strong enough to completely cover weaker
"direct" GMRS transmissions on the primary GMRS channels,1 and even
signals from our repeater systems when operating in reduced signal areas. I
live near three city parks, and this interference has made my GMRS base
station/control station unusable during these months.
7. Of significant concern is the
ongoing misuse of FRS call tones, which are primarily used to attract
attention, derive entertainment or to deliver intentional interference to other
FRS users. GMRS licensees now suffer from the almost continuous use of such
call tones. Some FRS radios even play music. Call tone interference is
especially troublesome since it creates more adjacent channel interference than
FRS voice.
8. Interference measurements
made on two of our GMRS repeater receivers2 indicates an average of a 3-6 dB
degradation to the 12 dB SINAD receiver sensitivity from adjacent channel FRS
activity (FRS channels 8-14). The 3 dB figure is typical of voice interference;
6 dB was found to be typical of FRS "call tones" that contain
higherfrequency audio components. This causes weaker GMRS signals into our
repeaters to be disrupted by local FRS transmissions.
9. In a more disturbing trend,
at least two of the seven GMRS primary channels here in the San Francisco Bay
Area are often unusable due to the indirect effect of FRS interference on
repeater receivers. Often, FRS transmissions will actually activate mountaintop
repeater systems. These systems then rebroadcast distorted3 FRS call tones and
voice transmissions, covering other co-channel GMRS transmissions. Due to the
elevation of these repeaters, these particular channels become practically
unusable over large portions of the Bay Area. Although these repeaters are
equipped with coded squelch, FRS radios routinely transmit signals with coded
squelch, defeating the repeaters coded squelch systems.
10. We understand that repeater
owners have attempted to shut down the repeaters when this occurs, but the
interference has been so frequent and random that it has become impractical to
disable the repeater numerous times a day. In these cases, the owners have had
to disable the stations or remove them from service.
11. It may be too late to solve
the FRS interference problem. FRS interference to GMRS repeaters has been
reported to the Commission. We believe, as does the Commission when it relates
to the Amateur Service, that a repeater suffering from FRS interference is a
repeater operating without a control operator. It is a malfunctioning repeater.
FRS interference to repeaters is a problem that the NCGUG and the Magazine deal
with in user forums every month.
12. In order to ensure reliable
data transmissions, and to maximize data throughput, it is likely that the
proposed data transmissions will use the maximum permissible bandwidth. As
such, we expect the interference from these signals to cause significant
adjacent-channel interference to licensed GMRS users.
13. Although Garmin's proposal
restricts data bursts to one second every ten seconds, it would not be unusual
for a high-elevation GMRS repeater to have line-of-sight to five or ten
data-capable FRS units, resulting near continuous adjacent-channel interference
over an extended period of time.
14. To eliminate interference to
GMRS repeater receivers, we suggest limiting FRS F2D data transmissions to FRS
channels 1-7 only. We suggest the following modification to the next to last
sentence in §95.193(b):
"…The FRS unit may
transmit digital data containing location information only on FRS channels 1
through 7. "
15. After considering various
solutions to adjacent channel interference to GMRS base and mobile receivers,
it became obvious that the only effective way to mitigate such interference is
to reduce the amount of energy present on adjacent primary GMRS channels. We
know that typical commercial repeater receivers need approximately 6 dB of
additional protection from FRS call tones, for a Delivered Audio Quality (DAQ)
of 3.0,4 and even more isolation is needed for mobile and base station
operations since this interference has been more severe. We estimate that at
least 10 dB (minimum) of additional isolation is necessary.
16. To achieve the 10 dB
(minimum) goal for base and mobile receiver protection, we suggest that the
following be appended to §95.633(c)(Emission Bandwidth):
…(c) The authorized bandwidth
for emission type F3E transmitted by a FRS unit is 12.5 kHz. The authorized
bandwidth for emission type F2D transmitted by an FRS unit is 8 kHz.
Please note that 8 kHz is an estimate.
Our goal is a minimum of 10 dB additional isolation.
17. We further note that
§95.633 is mute on the subject of authorized bandwidth for emission type
F2D. In any event, a bandwidth must be specified.
18. Also, §95.635 (Unwanted
Radiation) will require modification to allow for the F2D emission. No mention
of a proposed modification appears in the NPRM.
INTERFERENCE TO FRS VOICE
COMMUNICATIONS
19. We support Garmin's proposed
use of FRS to facilitate location determination. However, we disagree with the
Commission's assertion that such the proposed use will not cause interference
to other FRS users. The Commission must also realize that this NPRM also
directly effects GMRS since FRS channels 1-7 are shared with the GMRS.
20. In a low-power and direct
unit-to-unit service such as the FRS, it will be unlikely that short-duration
transmissions will cause a significant interference problem to other FRS voice
transmissions in rural and suburban environments. However, it is well known
that FRS becomes extremely congested on a local basis in and around large theme
parks, metropolitan environments, and ski areas, etc. In these cases, we
believe that data transmissions could interfere with voice-based emergency
communications from FRS and/or GMRS interstitial5 users since the rule changes
have not proposed any form of "pre-transmission monitoring".
21. In Paragraph 9, the
Commission correctly notes that "It appears that these restrictions will
result in digital data emission being a secondary use of FRS and that voice
communications will remain the primary use of FRS." Garmin has not
proposed any method to mitigate interference to FRS or GMRS interstitial voice
communications. Since children use FRS units with a limited understanding of
pre-transmission monitoring, such protection should be automatic and designed
into the all FRS products capable of F2D operation. The single and most
cost-effective way to accomplish this would be to restrict data communications
based on simple channel activity, using the squelch circuit that is already
present in every FRS radio. If the FRS unit detects channel activity, whether
voice or data, it would refrain from data transmission (referred to as
"data-lockout"). Furthermore, once the channel is open, it has been
industry practice to have the queued data transmission delayed for a random
time period before transmitting. This avoids numerous FRS data units from
transmitting at the same time and covering each other immediately following a
co-channel signal. This will result in the data signal being more reliable for
the public.
22. Also, it appears that no
restriction is placed on outboard or after-market location determination
equipment that could be attached to the FRS unit. Any rulemaking should
consider such use and "data-lockout" methods as well.
23. With regard to interference
to GMRS interstitial use, it would appear that Garmin's proposed use would
frustrate §95.143 (Managing a GMRS System in an Emergency), which
specifies that "The stations in a GMRS system must cease transmitting when
the station operator of any station on the same channel is communicating an
emergency message…". Although this rule does not directly apply to
FRS stations, secondary FRS data transmissions could cover GMRS emergency
transmissions if in close proximity.
24. We suggest that the
Commission append the following to the proposed wording of 95.193(a):
"….Digital data
communications are secondary to voice communications, and must protect voice
communications though automatic methods. FRS transmitters must incorporate a
transmitter lockout system to prevent data transmission when other co-channel
signals are present. Timing of a data transmission following a lockout shall
occur at a random time period after the channel is clear consistent with good
engineering practice."
UNINTENDED LOOPHOLE
25. A secondary concern is with
the type of operation that could result given text of the proposed rule change
on §95.193.
26. In paragraph 9, the
Commission notes that "limiting digital data transmission to one second
out of a ten second period and requiring that the digital data transmission be
initiated manually by the FRS user appears to be, in combination, a reasonable
method of minimizing interference between data communications and voice
communications on FRS channels."
27. We note that §95.193(b)
as proposed does not explicitly require that EVERY data transmission is
manually initiated, only that "…data transmissions…must be
initiated by a manual key press...". Therefore, a SERIES of transmissions
could be initiated by pressing a button only once, or could mean pressing the
"power button", resulting in hours, if not an endless number of data
signals being transmitted. For example, this ambiguity could result in FRS
units being used on large transit fleets or other industries requiring location
determination capability (i.e., shipping container locations, inventory
systems, etc.) where the installer could activate the FRS unit ONCE and
configure it to transmit one second bursts continually. This could result in
dozens, of not hundreds off transmissions per hour.
28. In addition, §95.193(a)
as proposed may not incorporate enough protection. The method of activating
data transmission is not explicitly restricted to the FRS unit intending to
send the data - it could be initiated from another FRS unit sending an
activation command to another ("send your location to me" message).
Although the proposed rule change restricts data to "one-way"
location messages, the activation command could be encapsulated with location
information to meet the rule requirement as written. For example, one or more
FRS units could then be setup to activate (or poll) many others, directing the
other units to transmit location data, resulting in twice the number of
transmissions (per sets of radios) and increasing the frequency of message
collisions and interference with voice and other data transmissions.
29. To mitigate this risk, we
suggest the following modification to the last sentence in
§95.193(b):
"…Each digital data
transmission shall not exceed one second and must be initiated by a manual key
press on the FRS unit transmitting the location data, and shall be limited to
no more than one digital transmission within a ten second
period."
Respectfully Submitted,
Gregory Forrest, PE
Chairman, Northern California GMRS
Users Group (NCGUG)
END
