Is it possible to have freq. hopping BCCH ?

[coursekec]

Is it possible to have freq. hopping BCCH ? In most cases i've seen is that hopping is only deployed in TCH ? what are the complications associated with a hopping BCCH ?

[danikd]

Is it possible to have freq. hopping BCCH ? In most cases i've seen is that hopping is only deployed in TCH ? what are the complications associated with a hopping BCCH ?

You should be pretty clear with you question. Many terms that you are using misleading.

Just to clarify:
1. BCCH - is a common name for timeslot 0 on the first frequency carrier in GSM cell. BCCH timeslot contains multiplex of few different logical channels for DL (FCH, SCH, BCH, PCH, AGCH, sometimes SDCCH/4 or SDCCH/3+CBCH) and RACH on UL.
2. BCCH - is a common name for frequency carrier on which BCCH timeslot is transmitted.
3. BCCH TRX is TRX, which transmits BCCH timeslot
4. TCH - is a timeslot for handling TCH (traffic channel)
5. TCH - a common name for frequency carrier which does not contain BCCH timeslot.
6. TCH TRX is a TRX which does not contain BCCH timeslot

Now close to your question:
The following restrictions applied for frequency hopping in GSM
1. BCCH timeslot should be transmitted on the fixed frequency for specific cell.
2. BCCH frequency should transmit a constant full power 100% even when some timeslots have no traffic to serve.
3. Based on 1. and 2. from above BCCH TRX/Frequency/Timeslot can not hopp i.e. change frequency!!!

There are two major hopping schemes for hopping implementation in GSM base station:
Synthesizer (RF) and BaseBand.
Just to remind you - the mobile station has no idea what hopping type is used at base station since, hopping is a change of TX/RX frequency according to predefined sequence every frame.

Synthesizer hopping implemented in the TRX part by changing TX/RX frequency every frame, while all connections (SDCCH/TCH/PDCH) are remaining on their TRXs and timeslots within the TRXs.
As you may see from SY hopping definition, the frequency change affecting all timeslots on specific TRX. This fact restricts utilization of SY hopping to TCH TRXs only.

Baseband hopping (BB) implemented on baseband processor level before RF part of the base station. The baseband processor implements switching every frame between specific connection (SDCCH/TCH/PDCH) and specific TRX, while each TRX frequency remains the same all the time.
BB hopping allows to involve into the hopping timeslots from 1 to 7 on BCCH TRX.

Hope this helps....if you need more, just ask more specific questions.

Enjoy

[Optim]

Thanks danikd, I have add thanks and reputation:)
Means we can have hopping in BCCH Trx but not in BCCH time slot (TS=0)?
Best Regards.

[danikd]

Thanks danikd, I have add thanks and reputation:)
Means we can have hopping in BCCH Trx but not in BCCH time slot (TS=0)?
Best Regards.

Yes, you are right. Use Baseband hopping for such implementation.

There are few things that you should pay attention while dealing with GSM hopping:

Cavity tunable combiners can not be used for SY (Synthesizer) Hopping.
SY hopping can be used only with hybrid combiners.

The hopping gain has its maximum at 8 frequencies (so - hopping list (MAL) longer than 8 frequencies is useless) this due to GSM interleaver which works over 8 frames.

The typical value for hopping with best possible reuse when you'll use 3-5 frequencies in the MAL.
Once you have more than 3 TRXs per sector, then Baseband hopping become preferable over SY hopping.
For 2 TRXs sector BB is also preferable over SY due to possibility to put almost all voice traffic in hopping even over 2 frequencies (it is still better than no hopping on BCCH TRX).

Not all vendors are supporting BB hopping in case of GPRS.
More than that once EDGE implemented, then BB hopping required that all TRXs within the cell will be EDGE capable.

[Optim]

Thanks:) Kindly can you explain in which cases I have to use SFH or BBH?
In my knowledge we use BBH when we have less frequencies and less traffic! because in case of high cell configuration there is no enough of frequencies so we prefer to use SFH...plz correct me if I'm wrong:)

[dacoder]

thanks danikd for the explanation... but I didn't understand the RF and BB hopping part. I got lost especially in this part "... while all connections (SDCCH/TCH/PDCH) are remaining on their TRXs and timeslots within the TRXs." Could you please explain it in more detail?

[danikd]

thanks danikd for the explanation... but I didn't understand the RF and BB hopping part. I got lost especially in this part "... while all connections (SDCCH/TCH/PDCH) are remaining on their TRXs and timeslots within the TRXs." Could you please explain it in more detail?

It is pretty easy:

SY Hopping

Each connection (speech for example) assigned to specific TRX on specific timeslots (just for clarification TS on TRX called also Physical channel). Now the Frequency hopping performed by RF Synthesized in TRX by changing transmit/receive frequency every TDMA frame. In other words Physical channel always the same during the conversation. As result from MS point of view - every frame reception/transmission performed on different frequency.

BB Hopping:

TRX always transmitting the same frequency (it is a stable part), while every TDMA frame BTS processor switching connection from one TRX to another...in cyclic order (typically) i.e. Frame1 - TS2 on TRX1, Frame2 - TS2 on TRX2, Frame3 - TS2 on TRX3.....FrameX - TS2 on TRX1.....and etc.
In other words, TRX frequency always the same, but no permanent allocation of Physical channel per conversation.
As result from MS point of view - every frame reception/transmission performed on different frequency.

Just like this.

[Optim]

Thanks dankid, just other question: if I have network with most of cells with configuration 2trx by cell and intersite distance is 500m and total frequencies is 22 frequencies..is better to use SFH or BBH? Thanks

[danikd]

Thanks dankid, just other question: if I have network with most of cells with configuration 2trx by cell and intersite distance is 500m and total frequencies is 22 frequencies..is better to use SFH or BBH? Thanks

My personal experience telling me:

If you have good automatic frequency optimization tool, which is based on mobile measurements reports data, then optimize your frequency allocation and go for baseband hopping.

Do not forget, that 22 ARFCNs is a pretty small amount, hope your Cell Plan (Antenna pattern, Tilt) adjusted with respect to the frequency band available.