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Alexander Chemeris alexander.chemeris at gmail.comOn Wed, Jan 1, 2014 at 10:46 PM, Harald Welte <laforge at gnumonks.org> wrote: > On Tue, Dec 31, 2013 at 08:13:15PM +0100, Sylvain Munaut wrote: >> I also think multi-TRX could be fun (possibly using fairwaves HW), but >> we can run out of ARFCN easily. > > I was thinking of ARFCN re-use. If the transmit power is low and we > have ultra-low-radius cells, then we should be able to have a frequency > re-use pattern. Of course not among immediate neighbors, but with one > in between. Also, I don't think that 8 ARFCN is all we could get from > the regulatory authority. I remember the DECT guard band being slightly > wider than that. We could also try to use adjacent ARFCNs for non-adjacent cells to increase frequency re-use. Compared to re-using the same ARFCNs, it requires less distance between interfering cells. Back side of the medal is that this setup requires very good Rx selectivity from the BTS equipment, as it could be easily jammed by close MS's, working with another BTS. So this will require very detailed frequency planning and probably some experimentation on the ground. >> It would be nice if we could sync the L1 of the BTS and use "shared >> ARFCN" where for eg one TS is used by one BTS and another for another >> BTS (dynamically of course so the capacity self-adapts). > > I think that's unrealistic and requires a lot of effort on all layers, > including the BSC who currently has no view at all about that. That's almost a shared OFDMA :) But I don't see how this could increase capacity, as number of available TSs will stay the same. AFAICT, it would even decrease capacity. Lets say we re-use TSs on ARFCN A. If we used it for a single cell, it would have interference radius of this cell. But if we try to share it with an adjacent cell, we'll have interference radius of these two cells, while number of available TSs stays the same. This may make sense only for better load balancing between cells on secondary ARFCNs. But this is possible only for multi-ARFCN BTSs, like our UmTRX based ones. Also a degree of such balancing can be done for multi-ARFCN BTSs on a more rough per-ARFCN basis instead of per-TS basis. I.e. one BTS can claim a whole ARFCN. This will also require changes to the BSC, but they seem smaller to me. OTOH, similar balancing can be achieved with the frequency hopping. This will lead to gradual decease of quality as the system becomes more and more loaded, though. Good thing is that the frequency hopping can be enabled even for single-ARFCN BTSs. -- Regards, Alexander Chemeris. CEO, Fairwaves LLC / ООО УмРадио http://fairwaves.ru