Deploy GSM 850 in the existing GSM 900

[trongcongbk]

Dear all friends,
I have a question: one operator had deployed GSM 900 MHz network before. Now they have license to use 850 MHz frequency band.
-1st question: Can they deploy GSM 850 MHz in the existing GSM 900 MHz network?
-2nd question: If possible, can MS be possible to handover/cell reselection between GSM 900 and GSM 850?
Thanks and best regards!!!

[Optimustron]

Is a very dificult situation because depending on the GSM-900 standard, i.e. P, E, R or T, you will have an overlap of 4, 14, 18 for the 3 firsts bands of GSM900 or the entire band of T, the downlink of 850 is defined with that overlaps, the in the best case P-GSM-900 you will need to use filters in the 900 Mhz site mainly because the BCCHs are located in the final part of the 850 Mhz spectrum, you can modify that but I don't know how it works, however if you have the entire spectrum of P-GSM-900 you'll loss at least 5 Mhz to isolate the bands and if you have the entire 850 Mhz too. The HO and cell selection/reselection is very dificult because both bands aren't "partners", they are 850/1900 Mhz and 900/1800 Mhz, the process is something like going from 900 to 1800 then to 1900 and then to 850, from 850 to 900 maybe the oposite way. By the way you need to know the exact ranges of spectrum to see viability, but in advance is very dificult and expensive, best regards,

[trongcongbk]

Thank you very much.
- Firstly, the distance between 850 DL band and 900 UL band is 10 MHz, so the interference between 2 band is not a problem.
- Secondly, why handover/cell reselection from 850 to 900 is the oposite way? Any document (example from 3GPP) about it??
Thanks in advance!

[Optimustron]

Please, don't think in terms of frequency distance, think about filtering, the filters of each band are standard, i.e., the TX Band of 850, has the passband from 869 up to 894 MHz, and the RX passband for P-GSM-900 is from 890 up to 915 MHz, then a BCCH in the range 890-894 MHz will saturate the RX of the P-GSM-900 BTS, in despite of this last band starts up to 904, this is 10 MHz above the 850 MHz, but if you have in the 850 MHz band your upper frequency less than 890 MHz you'll don't have interference, in that case you can use the entire band of P-GSM-900. What case you have?, the case of cell reselection is explained in the 3GPP TS 45.008 V7.15.0 (2009-05).
And excuse me for the first answer in that moment I was biased from an oponion of an expert but in the standard appears the following:

8.4.3 Additional cell reporting requirements for multi band MS
For a multi band MS the number of cells, for each frequency band supported, which shall be included in the
measurement report is indicated by the parameter MULTIBAND_REPORTING, broadcast on BCCH and PBCCH.
An MS attached to GPRS shall use the parameter broadcast on PBCCH if it exists. In all other cases, the MS shall
use the parameter broadcast on BCCH. The parameter may also be sent to the MS on SACCH.
The meaning of different values of the parameter is specified as follows:
Value Meaning
00 Normal reporting of the six strongest cells, with known and allowed NCC part of BSIC,
irrespective of the band used.
01 The MS shall report the strongest cell, with known and allowed NCC part of BSIC, in each of
the frequency bands in the BA list, excluding the frequency band of the serving cell. The
remaining positions in the measurement report shall be used for reporting of cells in the band
of the serving cell. If there are still remaining positions, these shall be used to report the next
strongest identified cells in the other bands irrespective of the band used.
3GPP
45 3GPP T Release 7 S 45.008 V7.15.0 (2009-05)
10 The MS shall report the two strongest cells, with known and allowed NCC part of BSIC, in
each of the frequency bands in the BA list, excluding the frequency band of the serving cell.
The remaining positions in the measurement report shall be used for reporting of cells in the
band of the serving cell. If there are still remaining positions, these shall be used to report the
next strongest identified cells in the other bands irrespective of the band used.
11 The MS shall report the three strongest cells, with known and allowed NCC part of BSIC, in
each of the frequency bands in the BA list, excluding the frequency band of the serving cell.
The remaining positions in the measurement report shall be used for reporting of cells in the
band of the serving cell. If there are still remaining positions, these shall be used to report the
next strongest identified cells in the other bands irrespective of the band used.

And from 3GPP TS 05.08 V8.11.0 (2001-08)
6.6 Measurements for Cell Reselection

Upon completion of cell selection and when starting the cell reselection tasks, the MS shall synchronize to and read the BCCH information for the 6 strongest non‑serving carriers (in the BA) as quickly as possible within the times specified in subclause 6.6.1. For multi band MSs the strongest non‑serving carriers may belong to different frequency bands. If system information message type 2 ter or 2 quater is used in the serving cell, and the MS has decoded all relevant serving cell BCCH data, except system information message 2 ter and/or 2 quater, then the MS shall start cell reselection measurements based on the know part of the BA, until system information message 2 ter and/or 2 quater is decoded and the full BA can be used.

Best regards,