Seperate carriers sharing GSM infrastructure?

On Tue, 03 Feb 2004 07:56:31 -0600, Jer wrote:

> Donald Newcomb wrote:
>
>> I want to ask about the options for multiple carriers to share GSM
>> infrastructure. The two extremes seem to be 1) no sharing of any
>> infrastructure 2) a virtual network running on the back of a host network.
>> What's available in-between the extremes? Clearly, carriers can easily share
>> towers, back-haul, emergency generators, etc. But how closely can they
>> actually be intertwined and remain separate? Can carriers share the entire
>> BSC/BTA system (antennas, cables, tower, transmitters) and still transmit
>> separate signals? Are there any examples where competing carriers have
>> developed a modis vivendi for this type of infrastructure sharing, without
>> trying to cut each other's throats on the deal?
>>
>> Donald Newcomb
>> DRNewcomb (at) attglobal (dot) net
>
>
> Your #1 would be the winning answer. There is no such thing as a
> virtual network.

Here in the UK we have two virtual networks. Virgin Mobile which is
carried on the T-mobile GSM network, and Tesco Mobile carried on the O2
GSM network. Neither Virgin or Tesco have their own infrastructure.

http://www.virginmobile.com/mobile/
http://www.tesco.com/mobile/


--
Michael Turner

"Jer" <gdunn@airmail.ten> wrote in message
news:bvo99n$lr1@library1.airnews.net...
> Your #1 would be the winning answer. There is no such thing as a
> virtual network.

Don't know about in your country, but here in the UK there are several
Mobile Virtual Network Operators or "MVNO". Virgin is perhaps the biggest
MVNO in the UK, and Virgin use T-Mobile infrastructure (i.e. Airways, BTS,
BSC and MSC).

> Firstly, nobody shares infrastructure (radios). Nobody. Ever. The
> antennas you see are exclusively owned and operated by a carrier, and an
> antenna is connected to a radio - owned by the same carrier. Those
> radios are connected to only one switching system, also owned and
> operated by the same carrier. Cellular radios operate on only one
> frequency - whichever frequency the owner has designated for that site.
> Cellular carriers don't share any BSC. Ever.

Again there are Network Operators sharing antennas in the UK due to planning
restrictions and congested areas. There was a programme on the TV (the BBC
IIRC) which discussed the clever technology involved in combining the
signals from different BTS's for transmissions via a single antenna.
Unfortunately I didn't watch the whole programme, so didn't see how the
Received signals were split to the various BTS's. It was a very interesting
programme for me because they featured a cell site not very far from where I
work and commute past every day.

Gordon Brown wrote:

> "Jer" <gdunn@airmail.ten> wrote in message
> news:bvo99n$lr1@library1.airnews.net...
>
>>Your #1 would be the winning answer. There is no such thing as a
>>virtual network.
>
>
> Don't know about in your country, but here in the UK there are several
> Mobile Virtual Network Operators or "MVNO". Virgin is perhaps the biggest
> MVNO in the UK, and Virgin use T-Mobile infrastructure (i.e. Airways, BTS,
> BSC and MSC).
>
>
>>Firstly, nobody shares infrastructure (radios). Nobody. Ever. The
>>antennas you see are exclusively owned and operated by a carrier, and an
>>antenna is connected to a radio - owned by the same carrier. Those
>>radios are connected to only one switching system, also owned and
>>operated by the same carrier. Cellular radios operate on only one
>>frequency - whichever frequency the owner has designated for that site.
>> Cellular carriers don't share any BSC. Ever.
>
>
> Again there are Network Operators sharing antennas in the UK due to planning
> restrictions and congested areas. There was a programme on the TV (the BBC
> IIRC) which discussed the clever technology involved in combining the
> signals from different BTS's for transmissions via a single antenna.
> Unfortunately I didn't watch the whole programme, so didn't see how the
> Received signals were split to the various BTS's. It was a very interesting
> programme for me because they featured a cell site not very far from where I
> work and commute past every day.
>
>

Okay, yes, my post was predicated on U.S. carriers, and this is the
first I've heard of combiners and splitters being used for cellular in
any network. Frankly, I don't even want to think about the insertion
losses and noise inherent in such a design. But, I suppose some
compromises are available for desperate designers.

Like you, the whole premise of this is intereting and I'll start poking
around to see what's up. Thanks to you and Michael for the feedback.


--
jer email reply - I am not a 'ten' ICQ = 35253273
"All that we do is touched with ocean, yet we remain on the shore of
what we know." -- Richard Wilbur

Jer <gdunn@airmail.ten> wrote in news:bvpkcl$5b9@library1.airnews.net:

> Okay, yes, my post was predicated on U.S. carriers, and this is the
> first I've heard of combiners and splitters being used for cellular in
> any network. Frankly, I don't even want to think about the insertion
> losses and noise inherent in such a design. But, I suppose some
> compromises are available for desperate designers.

There are at least two more examples of aerial sharing networks in the
world I've heard about, aimed at providing indoor coverage : in the Paris
Subway (France) and in the Chigago subway in the US, the latter still
being under construction IIRC.

I know the Paris network very well. It's based on specific underground
network shared by the three French GSM operators. Each operator is
responsible for its own BTS, but the RF distribution network (including
optical links and repeaters) is operated by the transportation authority,
responsible for the whole RF design and antenna implementation. Aerials
are made of either omni or panel Kathrein dualband indoor products for
stations, corridors and short tunnels coverage, and Jaybeam dualband
yagis in longer tunnels. No radiating cables are used (due to supposed
money saving issues), the 900/1800 feed being carried through the same
coaxial cables (antennas have internal diplexers).

Two of the three operators, Orange and SFR, operate a dual band network
(900 & 1800 MHz, dual BCCH) on this infrastructure. The third one
(Bouygues) only operates at 1800 MHz for the time being.

The global RF design is, as you can guess, very poor. Insertion losses
are of course an issue, but mainly for Bouygues, whose RF outpout power
is strictly limited as all three network use a 1800 MHz component. The
two others cope better on their 900 MHz layer in term of RXlevel and cell
overlapping.

These issue are not as critical as the high level of intermodulation
products during heavily loaded hours (when mostry all TRX are "on air"),
probably the worst problem they have to cope with.

Moreover, some antenna location choices have been made against the basic
rules of RF design and planning. It's hard being a transportation company
but still thinking one can easely turn into a RF specialist ;-)...


--
A+,

Olivier

Olivier Boudot wrote:
> Jer <gdunn@airmail.ten> wrote in news:bvpkcl$5b9@library1.airnews.net:
>
>
>>Okay, yes, my post was predicated on U.S. carriers, and this is the
>>first I've heard of combiners and splitters being used for cellular in
>>any network. Frankly, I don't even want to think about the insertion
>>losses and noise inherent in such a design. But, I suppose some
>>compromises are available for desperate designers.
>
>
> There are at least two more examples of aerial sharing networks in the
> world I've heard about, aimed at providing indoor coverage : in the Paris
> Subway (France) and in the Chigago subway in the US, the latter still
> being under construction IIRC.
>
> I know the Paris network very well. It's based on specific underground
> network shared by the three French GSM operators. Each operator is
> responsible for its own BTS, but the RF distribution network (including
> optical links and repeaters) is operated by the transportation authority,
> responsible for the whole RF design and antenna implementation. Aerials
> are made of either omni or panel Kathrein dualband indoor products for
> stations, corridors and short tunnels coverage, and Jaybeam dualband
> yagis in longer tunnels. No radiating cables are used (due to supposed
> money saving issues), the 900/1800 feed being carried through the same
> coaxial cables (antennas have internal diplexers).
>
> Two of the three operators, Orange and SFR, operate a dual band network
> (900 & 1800 MHz, dual BCCH) on this infrastructure. The third one
> (Bouygues) only operates at 1800 MHz for the time being.
>
> The global RF design is, as you can guess, very poor. Insertion losses
> are of course an issue, but mainly for Bouygues, whose RF outpout power
> is strictly limited as all three network use a 1800 MHz component. The
> two others cope better on their 900 MHz layer in term of RXlevel and cell
> overlapping.
>
> These issue are not as critical as the high level of intermodulation
> products during heavily loaded hours (when mostry all TRX are "on air"),
> probably the worst problem they have to cope with.
>
> Moreover, some antenna location choices have been made against the basic
> rules of RF design and planning. It's hard being a transportation company
> but still thinking one can easely turn into a RF specialist ;-)...
>
>


Holy Cow! What a mess!! )) I do find all this interesting, even a
little amuzing. Terrain issues will always offer challenges to the RF
system engineer and the above is clearly an indication of where
technology can lead the pack. And your comment on the intermod is well
noted. And I can't even imagine what that must look like on a spectrum
analyzer, but it'd be a giggle to take a peek.

--
jer email reply - I am not a 'ten' ICQ = 35253273
"All that we do is touched with ocean, yet we remain on the shore of
what we know." -- Richard Wilbur

>> Firstly, nobody shares infrastructure (radios). Nobody. Ever.

You might want to re-think your statement. We here all know that Cingular and
T-Mobile share their infastucture in California/Nevada and the New York
markets.

Same antenna, tower, radio, coax, switch etc.....

Keep in mind that switches can be partitioned so that billing is split but that
is about all that isn't shared!

--
John S.
e-mail responses to - john at kiana dot net

Jer <gdunn@airmail.ten> wrote in news:bvte8h$c1o@library1.airnews.net:

> Holy Cow! What a mess!! ))

Simply imagine all the people trying to get on with their calls on moving
trains with a HO failure rate of nearly 50% during rush hours, and
regularly moaning on their cell phones ;-)...

> I do find all this interesting, even a little amuzing.

I'd better give you a practical exemple : Chatelet les Halles commuter
train station, platform level (7 tracks, 3 lines, 2 million
passengers/day). Two dualband indoor panels at the West end of the
station, two others at the East end. Platform length : 250 meters (

Orange : 48% market share (BSS = Motorola M-6 Cell, EFR only). Two
dedicated cells targeted at tracks coverage.
900 MHz cell : 8 TRX
1800 MHz cell : 7 TRX (might be eight now, haven't checked for a while).
Both use East and West end aerials.

SFR : 35 % market share (BSS = Nokia Ultrasite, EFR/HR, AMR expected
during forthcoming spring). Two dedicated cells targeted at tracks
coverage.
900 MHz cell : 5 TRX
1800 MHz cell : 5 TRX
Both use East and West end aerials.

Bouygues Telecom : 17% market share (BSS = Nortel S8000, EFR only), 1800
MHz only, split in two cells (still talking about the platform level
only). 7 TRX (East end aerials cell), and 5 TRX (West end aerials cell).

These TRX (one per cell support a BCCH, of course) are connected to FOUR
(two as far as Bouygues is concerned) Kathrein 738 573 indoor dualband
panels.
Aerial gain : 4.85 dBd, max. overall imput power per panel : 25 W. LOL.

No information about VSWR nor intermod rating in dBc on the
manufacturer's catalog, of course... LOL once again.

Apart from that, all three network are regularly congested in this
station between 4 and 7 PM. You're not even sure to get a SDCCH in order
to send or recieve a SMS. But how could the operators even think about
installing extension cabinets as the antenna systems already seem close
to overload ?

The operators are clearly loosing money (but not the transportation
company of course, as the annual fee it receives from the three networks
is known to be quite high, even though no precise figure has ever been
publicly disclosed).

> And I can't even imagine what that must look like on a
> spectrum analyzer, but it'd be a giggle to take a peek.

:-))))... AFAIK, the only obligation of the transportation company is to
provide > - 90 dBm signals in each band everywhere, including in moving
trains. I regularly measure RXlevel in the whole underground system, and
- 105 dBm figures are quite frequent. Thus, SFR has recently moved is
RXlev access min from - 101 to - 106 dBm on its 900 MHz underground layer
;-)...

If they want to do a serious job, they'll have to overlay their existing
system with a radiating cable based network IMO. Allgon, for instance,
has developped very good engineering solutions. And they're not the only
ones. Of course the best way to deal with all the above mentionned
problems would be to let each operator build its own network, but this
can't reasonnably be achieved, as the network company already refused
such a scheme.

They could keep their existing network on a 1800 MHz only basis in order
to cope with traffic issues especially in main station platforms, subway
entrances and lobbies, and use a 900 MHz only system based on radiating
cables in tunnels and long corridors. This is the only way to achieve
good handoff figures in moving trains (up to 60 MPH) as cell overlapping
is then easyer to implement in a cost-effective way with a reasonable QOS
(the existing system is based on optical repeaters feeding multiple
antenna systems in long tunnels, so I doubt it is globally cheaper).
Each system being independant from the other, the max number of TRX could
be higher for a given QOS, load sharing between bands being achieved by
fine tuning the C2 criteria, as it already works on existing dualband
networks.

Fortunately, Orange, SFR and Bouygues all operate in the underground
network on a single LAC, so signalling issues should take place where the
old and the new network would still operate simultaneously.


--
Olivier

John S. wrote:

>>>Firstly, nobody shares infrastructure (radios). Nobody. Ever.
>
>
> You might want to re-think your statement. We here all know that Cingular and
> T-Mobile share their infastucture in California/Nevada and the New York
> markets.
>
> Same antenna, tower, radio, coax, switch etc.....


Let me clarify...

Sharing antennas/coax is apparently done in a rare few systems - none in
the U.S. that I'm aware of (yet). Sharing radios does not happen
because it cannot happen. A radio can only be connected and controlled
from one switch. For a BSC radio to be connected to more than one
switch, the control channel would have to have a data splitter and it
would have to lock out any other control channel that wasn't active. If
a control channel goes inactive, the BSC goes offline and the switch
generates an alarm for that BSC. Restoring a control channel in most
systems requires a moment or two for each data link (there are always
two), first one, then the other. The idea of the control channel going
in and out of service due to multiple switches attempting to control the
same radio is simply ludicrous. A flapping BSC will not be allowed to
return to service due to hold-over timing, thus preventing voice radios
from being opened to traffic just in time for another flap to occur,
removing the BSC from service again, and clearing all voice channels
again. Did I get that right Lee? I'm sorry, I didn't introduce Lee...
Lee is a long time RF systems engineer for Cingular visiting me tonight.
Lee's a good egg, and I'll (he'll) repeat, BSc radios are never shared
- they are always connected to only one switch, and that one switch
always controls all calls on that BSC radio. All radios in a BSC are
located in the same cabinet and there's only one pair of control
channels for that cabinet. No exceptions.

Yes, multiple radios can be connected to a single RF radiator (antenna)
using combiners, circulators and splitters. Virtually all panel
antennas at the top of Cingular's AMPS/TDMA/CDMA/GSM sites are actually
multiple radiators hiding under a single plastic cover, and each
radiator is connected to it's radio cabinet with a separate pair of coax
cables - a pair being one transmit and one receive. A single radio
cabinet can contain radios for multiple codecs used in the same
frequency band, which is commonly done in 'overlay' systems. 800Mhz
systems and 1900Mhz systems will have separate cabinets for each, and
each cabinet will be connected to it's own antennas via it's own coax.
This can cause a tower to appear to be a co-locate due to more than one
set of panel antennas, but if both sets of antennas are conected to the
same carrier, it's not a co-locate - it is simply two separate service
bands offered by the same carrier at that cell site.

Now, to the sharing of infrastructure... the term "co-locate" means a
tower is shared with multiple carriers, but each carrier still has their
own antennas on that tower, and each antenna set is connected via coax
to indivisdual cell sites (BSCs), and each BSC is housed in a separate
enclosure at the tower base. This is often considered 'sharing
infrastucture' since each carrier's radios/antennas are sharing the same
tower - but each carrier's radios are still housed in a separate
enclosures, and equipment in each enclosure (BSC) is only connected to
that carrier's switch. So apparently, 'sharing infrastructure' in most
cases means only the tower is shared, but each carrier still has all
it's own equipment securely enclosed and not shared with any other carrier.

>
> Keep in mind that switches can be partitioned so that billing is split but that
> is about all that isn't shared!


If a BSC radio is connected to a switch, than that switch is the only
control point for that radio, hence it is not shared. Earlier in this
thread, it was noted that some systems (radios) are sharing antennas -
i.e. one antenna connected to more than one radio, but each radio is
still connected to only one switch, hence only one control point for
that radio.

Switches are not partioned, but billing records have been split ever
since the first roamer made the first call. A single BSC, connected to
it's switch, can easily handle calls for home users as well as roamers -
each getting their bills separately - but it's still only one BSC, one
switch, and one carrier maintaining the whole enchilada.


I know this is verbose, but...

--
jer email reply - I am not a 'ten' ICQ = 35253273
"All that we do is touched with ocean, yet we remain on the shore of
what we know." -- Richard Wilbur