chapman@alc.com (Brent Chapman) (01/02/91)
On a drive from the San Francisco Bay Area to Northern Arizona and
back over the holidays, I was amazed by the extent of cellular service
coverage. My phone was claiming there was at least intermittent
service almost the whole time I was in California. The only place in
California where service got spotty was in the desert East and West of
Barstow, along California Highway 58 (between Bakersfield/Mojave
coverage and Barstow coverage) and Interstate 40 (between Barstow
coverage and Needles coverage); even there, though, I would estimate
that the phone showed coverage at least 75% of the time, and "No
Service" only 25% of the time. I don't have a signal strength display
on my phone, so I'm not certain how good most of the coverage was, but
I successfully placed a few calls from these rather desolate areas,
and the quality didn't seem much worse than what I usually get in the
Bay Area.
What are the propagation characteristics of cellular service? I was
under the impression that it was tuned to be strictly a short-range
(i.e., less than ten miles) system, and that in fact this short-range
characteristic is fundamental to making the system work (because
shorter range allows smaller cells, and thus more total callers by
reusing the same frequencies in more non-adjacent cells). How, then,
was I receiving service when I'm sure I was at least 60 miles from the
nearest cell?
On a related topic, I've been told that cell size is not uniform, and
that it is a common practice in densely populated areas (like downtown
San Francisco, for instance) to reduce the power of each cell in order
to reduce the cell size to the absolute minimum and thereby increase
the total capacity of the system. Is this true?
Thanks!
Brent Chapman Ascent Logic Corporation
Computer Operations Manager 180 Rose Orchard Way, Suite 200
chapman@alc.com San Jose, CA 95134
Phone: 408/943-0630john@bovine.ati.com (John Higdon) (01/02/91)
Brent Chapman <chapman@alc.com> writes: > What are the propagation characteristics of cellular service? I was > under the impression that it was tuned to be strictly a short-range > (i.e., less than ten miles) system, and that in fact this short-range > characteristic is fundamental to making the system work (because > shorter range allows smaller cells, and thus more total callers by > reusing the same frequencies in more non-adjacent cells). How, then, > was I receiving service when I'm sure I was at least 60 miles from the > nearest cell? And what makes you think you were sixty miles from the nearest cell? I have watched, over the past several years, as the PacTel Cellular has been adding site after site to service the high desert area. There are a couple of sites near Barstow, as well as a couple near Victorville. Lately, the coverage has been improved on the Mojave to Barstow route via 58 by the addition of more sites. The main thrust has been the coverage of I15. It is now possible (unlike in the past) to carry on a continuous conversation from Newport Beach to some miles past Barstow on the way to Las Vegas. But take my word for it, there are cell sites involved. It isn't magic propagation. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !
dfpedro@uunet.uu.net (Donn Pedro) (01/03/91)
In article <15746@accuvax.nwu.edu>, chapman@alc.com (Brent Chapman) writes:
: On a drive from the San Francisco Bay Area to Northern Arizona and
: back over the holidays, I was amazed by the extent of cellular service
: coverage. My phone was claiming there was at least intermittent
: service almost the whole time I was in California.
With the advent, and installation of Cellular RSA (Rural Service
Areas), I would not be surprised.
: coverage and Needles coverage); even there, though, I would estimate
: that the phone showed coverage at least 75% of the time, and "No
: Service" only 25% of the time.
Remember that the coverage could have been for carriers other than
your own if your mobile was set to scan both systems.
: I don't have a signal strength display
: on my phone, so I'm not certain how good most of the coverage was, but
: I successfully placed a few calls from these rather desolate areas,
: and the quality didn't seem much worse than what I usually get in the
: Bay Area.
You were most likely working off of one of the new RSAs.
: What are the propagation characteristics of cellular service?
Depends on the site. A cell can be tuned to serve almost any area.
This can exceed ten miles, especially if it is a repeater site.
Transmit power can be as high as 500 watts in some instances. The
pattern of service can also be shaped to meet the needs of terrain and
traffic considerations.
: I was under the impression that it was tuned to be strictly a
: short-range (i.e., less than ten miles) system, and that in fact this
: short-range characteristic is fundamental to making the system work
: (because shorter range allows smaller cells, and thus more total
: callers by reusing the same frequencies in more non-adjacent cells).
This is especially true in a densly packed metropolitan area. In a
rural area, where it is not ecnomical to have a site every few miles,
power is stepped up to conpensate.
:How, then, was I receiving service when I'm sure I was at least 60
:miles from the nearest cell?
Sounds far away, but could have been if you were working off of a high
power repeater site.
: On a related topic, I've been told that cell size is not uniform, and
: that it is a common practice in densely populated areas (like downtown
: San Francisco, for instance) to reduce the power of each cell in order
: to reduce the cell size to the absolute minimum and thereby increase
: the total capacity of the system. Is this true?
It is. Cells can also be "tiered". That is: a single cell can
actually act like two cells. An inner cell and an outer cell. Cells
can also have "sides". These can be tuned seperatly to deal with
traffic and terrain found in highly congested cities.
May I suggest a book.
Mobile Cellular Telecommunications
Author: William C. Y. Lee
Publisher: McGraw Hill
ISBN: 0-07-037030-3
It is pretty deep in places but should tell you almost anything you
would want to know about cellular, as of 1989.
Jenner dfpedro@uswnvg.UUCP
*Disclaimer? You bet! I speak for myself only.*rees@pisa.ifs.umich.edu (Jim Rees) (01/03/91)
In article <15746@accuvax.nwu.edu>, chapman@alc.com (Brent Chapman) writes: >... What are the propagation characteristics of cellular service? I >was under the impression that it was tuned to be strictly a >short-range (i.e., less than ten miles) system... At cellular frequencies (800 MHz) it's pretty much line-of-sight. If you are on one mountain top and the cell antenna is on another, you could have a range of over a hundred miles even running very low power. I always get a kick out of the business droids on the subway in Hong Kong, impatiently punching their cellphone buttons while the no-service light is on in the tunnels. They've been talking of putting slotline (leaky coax) in the tunnels to extend the coverage. Two questions: If I buy a cellphone in HK or Singapore, will it work in North America? And if I have no "home" cell service provider, or my provider is in HK, can I get roaming service here in the US?
lemson@ux1.cso.uiuc.edu (David Lemson) (01/03/91)
chapman@alc.com (Brent Chapman) writes: >On a related topic, I've been told that cell size is not uniform, and >that it is a common practice in densely populated areas (like downtown >San Francisco, for instance) to reduce the power of each cell in order >to reduce the cell size to the absolute minimum and thereby increase >the total capacity of the system. Is this true? That is exactly right. Cellular phones are directed to increase or decrease power according to their distance (and thus, signal strength) from the cell tower. This allows more cell sites in a certain area, and thus, more potential users in that same area. This is the principle behind the "Microcells" that will soon adorn the halls of airports and office buildings. A cell every few hundred yards. David Lemson U of Illinois Computing Services Student Consultant Internet : lemson@ux1.cso.uiuc.edu University of Illinois, Urbana
Tad.Cook@cs.washington.edu (01/04/91)
In article <15746@accuvax.nwu.edu>, chapman@alc.com (Brent Chapman) writes: > On a drive from the San Francisco Bay Area to Northern Arizona and > back over the holidays, I was amazed by the extent of cellular service > coverage. (stuff deleted) > What are the propagation characteristics of cellular service? I was > under the impression that it was tuned to be strictly a short-range > (i.e., less than ten miles) system, and that in fact this short-range > characteristic is fundamental to making the system work (because > shorter range allows smaller cells, and thus more total callers by > reusing the same frequencies in more non-adjacent cells). How, then, > was I receiving service when I'm sure I was at least 60 miles from the > nearest cell? The size of the cell depends on the elevation of the cell site. In urban areas it makes sense to have a lot of little cells to handle a large number of callers. Out in the desert you could be served by just a few cells at high elevation, or directional cells that cover a whole lot of highway. You also can't be too sure (if you are an average user without special knowledge of the system) just how far you were from the nearest cells. Over the route you travelled, there is probably plenty of incentive for the cellular providers to have coverage at least along the main highways. > On a related topic, I've been told that cell size is not uniform, and > that it is a common practice in densely populated areas (like downtown > San Francisco, for instance) to reduce the power of each cell in order > to reduce the cell size to the absolute minimum and thereby increase > the total capacity of the system. Is this true? Yes. Tad Cook Seattle, WA Packet: KT7H @ N7HFZ.WA.USA.NA Phone: 206/527-4089 MCI Mail: 3288544 Telex: 6503288544 MCI UW USENET:...uw-beaver!sumax!amc-gw!ssc!tad or, tad@ssc.UUCP
Paul.Schleck@iugate.unomaha.edu (Paul Schleck) (01/05/91)
Cellular phone operates at about 900-950 Mhz. This may be properly termed microwave. Propogation of waves at this frequency are essentially line of sight. They are so energetic that they (usually) cannot be bent by the atmosphere, so hence no significant multi-hop, over the horizon propogation. Under conditions of tropospheric inversion, i.e. higher layers of the atmosphere warmer than lower ones, a phenomenon known as "ducting" may occurr, under which the waves are made to conform to the curve of the earth. Propogation under ducting conditions may be up to several hundred miles. It is true that usually microwave RF does not travel very far for a number of reasons. For one, it does not follow the curve of the earth under normal circumstances. For another, its short wavelenth means that it is rapidly attenuated by foliage, walls, humid air, etc. What is the height difference between where you were and the cell sites back in CA? If there was enough of a height difference to cause an obstruction-free straight line path, that may be another explanation. One of the reasons that cellular technology works is "capture effect." What that means is that only the strongest signal being received is actually demodulated in an FM signal. The reasons are beyond the scope of this discussion group. Also, cellular systems use a voting system to insure that only the cell with the strongest signal is used for the phone conversation. In short, it is the combined reasons of line-of-sight paths, capture effect, and cell voting that cellular systems work. For another propogation anecdote, a friend of mine accessed the Washington DC cell system from the middle of New Jersy under conditions of tropospheric ducting, so it certainly can be done. I wonder what the phone company or the FCC thinks of these "long distance" calls? Paul W. Schleck, KD3FU --- Ybbat (DRBBS) 8.9 v. 3.12 r.5 [1:285/27@fidonet] Neb. Inns of Court 402/593-1192 (1:285/27.0)
sichermn@beach.csulb.edu (Jeff Sicherman) (01/06/91)
In article <15768@accuvax.nwu.edu> lemson@ux1.cso.uiuc.edu (David Lemson) writes: >That is exactly right. Cellular phones are directed to increase or >decrease power according to their distance (and thus, signal strength) >from the cell tower. This allows more cell sites in a certain area, >and thus, more potential users in that same area. This is the >principle behind the "Microcells" that will soon adorn the halls of >airports and office buildings. A cell every few hundred yards. When we all carry personal phones around, will their be enough bandwidth capacity in the cellular system to handle all the phone traffic. How will the assumptions that underly capacity estimates hold up when more/most calls are made from/to callers static in a cell instead of moving from cell to cell ? Jeff Sicherman
russ@unmvax.cs.unm.edu (Russ Kepler) (01/08/91)
In article <15767@accuvax.nwu.edu> uswnvg!dfpedro@uunet.uu.net (Donn Pedro) writes: >In article <15746@accuvax.nwu.edu>, chapman@alc.com (Brent Chapman) writes: >:How, then, was I receiving service when I'm sure I was at least 60 >:miles from the nearest cell? OK - shall we have a "largest cell" contest? I wouldn't propose it unless I thought I had a good chance at winning. In Albuquerque we have a cellular service and a mountain. Said mountain is about 5000' above the city, a in view of a lot of the surrounding area. I can hit the Albuquerque cell from as far west as Grants (90 mi), north to Los Alamos (70 mi), south to almost Socorro (about 80 mi), and east for Santa Rosa (70 mi, but not good coverage). This is with good signal quality. I'm waiting to see what happens when the new service in Santa Fe goes in this year - will my system decide to roam or will it stay in a home cell? I'll check it out when the new system is up. Russ Kepler - Basis Int'l SNAIL: 5901 Jefferson NE, Albuquerque, NM 87109 UUCP: bbx.basis.com!russ PHONE: 505-345-5232
johnl@iecc.cambridge.ma.us (John R. Levine) (01/11/91)
In article <15874@accuvax.nwu.edu> you write: >OK - shall we have a "largest cell" contest? Why not? My entry is the cell on Tortola in the British Virgin Islands. Apparently boats 100 miles away can use it due to the excellent ground provided by salt water that the fact that Tortola has a fairly high hill on which the antenna is placed. Perhaps some cell with an antenna on a higher hill on another island is even bigger. Regards, John Levine, johnl@iecc.cambridge.ma.us, {spdcc|ima|world}!iecc!johnl [Moderator's Note: When I was visiting in Independence, KS this past summer I had my Radio Shack CT-301 with me. In most areas of town there was no cellular service, yet when I went to the second floor of the home where I was visiting, the phone went out of NO SVC mode into ROAM mode. Curious, I tried the 0 operator, and ask who she was: Tulsa, OK -- sixty plus miles to the south! Returning home on I-55, Ameritech only guarentees service when you get 'close to' Morris, IL, the southwestern-most point for Chicago area service. When HOME kicked in on my unit, a nearby highway sign said we were 70 miles from Morris. All that on a .6 watt handheld ... see why I don't concern myself with the exact specifics of the antenna I use? Admittedly, I had the 'standard' antenna for a handheld, not the little 1/8 wave loaded stub I installed a month or so ago. PAT]
amanda@visix.com (Amanda Walker) (01/12/91)
The last time I did a road trip back to DC from Ohio, I was amused to find that I could hit one of DC/Balt Cell One's cells from I-70 as it crossed a ridge near Hancock, MD. Thinking quickly, I pulled over onto the shoulder and called in to my answering machine. I couldn't hit a DC cell again for almost another 45 minutes worth of driving time ... you can also see DC cells from Skyline Drive in Shenandoah National Park, as long as you are on the east side of the ridge :) Amanda Walker anda@visix.com Visix Software Inc. ...!uunet!visix!amanda
dave@westmark.westmark.com (Dave Levenson) (01/13/91)
In article <15965@accuvax.nwu.edu>, johnl@iecc.cambridge.ma.us (John R. Levine) writes: > >OK - shall we have a "largest cell" contest? > [Moderator's Note: ... > the southwestern-most point for Chicago area service. When HOME kicked > in on my unit, a nearby highway sign said we were 70 miles from > Morris. All that on a .6 watt handheld ... see why I don't concern > myself with the exact specifics of the antenna I use? Admittedly, I > had the 'standard' antenna for a handheld, not the little 1/8 wave > loaded stub I installed a month or so ago. PAT] It has been my experience that the HOME or ROAM indication (i.e. something other than NO SERVICE) means only that the mobile or portable cellular telephone is receiving the setup channel from a cell. It doesn't necessarily mean that the cell would receive your signal if you tried to SEND. At 70 miles range, you may well be able to receive the setup channel which is transmitting at a hundred watts or more. Moreover, if you are receiving it 'most of the time' with a lot of fading, you'll still probably display an in-service indication. But try to initiate a call with your 0.6-watt hand-held with its 1/8th-wave antenna when the cell's access channel receiver is 70 miles away! The cell may not hear you. You may also have a signal too weak or intermittent for conversation. Dave Levenson Internet: dave@westmark.com Westmark, Inc. UUCP: {uunet | rutgers | att}!westmark!dave Warren, NJ, USA AT&T Mail: !westmark!dave Voice: 908 647 0900 Fax: 908 647 6857 [Moderator's Note: My question is why would there be such an extreme difference in output from the cell versus my output? What point is there in having the cell talking to a unit which can't get back to it? Wouldn't it make better sense to tone down the cell just a little so a more realistic range *in both directions* could be observed? I've done the same thing with my cordless phones in the past: Mounted the base antenna on the roof and peaked up the base output a little so I could hear it on the remote unit two or three city blocks away ... but to what avail if I can't make the trip back? PAT]
gmp@rayssd.ssd.ray.com (Gregory M. Paris) (01/14/91)
> [Moderator's Note: My question is why would there be such an extreme > difference in output from the cell versus my output? What point is > there in having the cell talking to a unit which can't get back to it? > Wouldn't it make better sense to tone down the cell just a little so a > more realistic range *in both directions* could be observed? I've The point is to keep customers' phones from roaming. As long as a cell phone is receiving the setup signal from its home system, it won't roam (at least, not automatically). A cynical person would say that cellular providers do this to make more money, since it makes customers have to wait until they get in range of their home system to make calls. Being less cynical, perhaps there's good to this too. Probably many people don't want to pay roaming charges to another provider just because they happen to be a bit out of range or in a dead spot. Considering how outrageous such charges can be, one might say that the home system is providing a valuable protection service by preventing its customers from accidentally roaming. Greg Paris <gmp@quahog.ssd.ray.com>
ghg@en.ecn.purdue.edu (George Goble) (01/14/91)
>[Moderator's Note: When I was visiting in Independence, KS this past >summer I had my Radio Shack CT-301 with me. In most areas of town . . . >Tulsa, OK -- sixty plus miles to the south! Returning home on I-55, >Ameritech only guarentees service when you get 'close to' Morris, IL, >the southwestern-most point for Chicago area service. When HOME kicked >in on my unit, a nearby highway sign said we were 70 miles from >Morris. All that on a .6 watt handheld ... Ameritech/Chicago is notorious for cranking up the xmitter power on their "paging" (control) channels. (Mouth is bigger than their ears). Running my Motorola in "maint" mode, to display received signal strength, I approached Chicago from Lafayette, IN, coming up I-65 from the south. I received "usable" (i.e. phone goes "in service") signal strengths 50 or 60 miles out from known cell sites. However, one could not initiate any calls until approx 25-30 miles away. These cells are not "balanced". The intense competition, where xmitter power is "jacked up", to make your phone jump over to the B carrier (even though not usable for service), just to keep your phone from locking onto the A-carrier (for those whom leave "A or B" selected). The second reason, is that Ameritech (Chicago) uses AT&T built RF equipment which sucks (in receive) compared to Motorola RF equipment. Motorola receivers do at least 10db better than AT&T I have noticed. This is more of a difference than the .8W or 3W between portables or transportables. When returning to Lafayette, IN, one starts to receive GTE Mobilnet about thirty miles out, and within one mile, the system is usable to initiate calls also. Roger Reeves (Mobilnet Engineering) says Mobilnet is very careful about balancing the cellsites and pointed out many other carriers conduct "power wars" with their control channels to "steal away" phones, and this results in large areas of "no service", even though the phone is indicating "in service". ghg [Moderator's Note: I did not try actually making a call when I was that far south of Morris, but in the case with Tulsa, I did speak with the operator, provided I stayed on the second floor by the window. PAT]
john@icjapan.info.com (John Higdon) (01/15/91)
In article <72173@bu.edu.bu.edu> dave@westmark.westmark.com (Dave Levenson) writes: >At 70 miles range, you may well be able >to receive the setup channel which is transmitting at a hundred watts >or more. >[Moderator's Note: My question is why would there be such an extreme >difference in output from the cell versus my output? What point is >there in having the cell talking to a unit which can't get back to it? None, and there isn't. While cell sites generally run more power than a mobile, the whole point of cellular is the non-interference of alternate or distant cells and running megapower from a site would defeat that just as much a high power from a mobile. Dave is correct when he points out that there are many times when you may have indication of service when indeed you can't make a call, but there are many reasons for that. The most common is that the mobile has a much less efficient transmitter/antenna combination than the site, or that it is a 0.6 watt handheld with no ground plane vs a well set up vehicle installation. Personal experience has been that my handheld frequently shows service available but refuses to connect to a site, where my truck phone almost always can make a call if service appears available, even in the most out-of-the-way desert rural areas.