Transcript 3 December 2013, Mainz

CG-GSM-R(13)035
Protection of GSM-R from Public Mobile Radio
Current GSM-R - Protection against neighbouring UMTS
Block in Germany
According to ETSI EN 301 908-3 the maximum UMTS spurious emissions in the
adjacent channel (first GSM channel) are to be considered with -12.5 dBm/30 kHz.
With a bandwidth-converted UMTS usage signal power of 43 dBm this results to an
ACLR (GSM-R) of 47.8 dB.
FUMTS max  FGSM -R usage min - C/IGSM -R  ACLRGSM -R
= 38,5 dBµV/m – 12 dB + 47,8 dB
= 74,3 dBµV/m
Currently, a UMTS application in the GSM adjacent frequency block
is rejected if it generates more than 74.3 dB dBµV/m 4 m above the railway line.
(For comparison with the neighbouring countries, e.g. 59 dB dBµV/m at the borderline have
been agreed.)
Reducing of the Restrictions against the
neighbouring UMTS Channel after measurements
Measurements of the monitoring station Itzehoe (in the North of Germany) showed
that the transmitters used by the UMTS operator using the block 925-930 MHz
generate spurious emissions which are falling into the GSM-R channel with the
centre frequency 924.8 MHz are 17.5 dB lower than allowed according to the
standards. Since on one hand the operator using the block 930-935 MHz possibly
uses the same mast and on the other hand, the variances of the field strength
prediction must be taken into account, instead of 17.5 dB improvement will be taken
3 dB lower, i.e. 14.5 dB for allocation. Thus, the allowable usage field strength for
UMTS in the GSM-R neighbouring on the affected railway lines block increases on:
FUMTS max  74,3dBµV/m  14,5dB  88,8dBµV/m
Due to this restriction reduction, the mean interference range between the base stations
(within 925-930 MHz) and the concerned railway lines will be reduced to about 20% (by 80%)
of the previous distances.
Prerequisite is of course that the operator does not change the equipment. If a product of
another manufacturer is used, new spurious emission measurements should be carried out.
Restrictions on the next UMTS Channel
Further measurements in the investigated base stations showed
that the spurious emissions are 8 dB lower in the next frequency
block (930-935 MHz) than in the adjacent frequency block (925930 MHz). If these conditions are applied to the block 930-935
MHz then the following equation has to be considered:
FUMTS max  88,8dBµV/m  8 dB  96,8 dBµV/m
Further Possible Reduction of Restrictions by
Considering of actual GSM-R Usage Field Strengths
In both slides before, only the minimum field strength of 38.5 dB dBµV/m is assumed
along the entire railway lines. However, if the values for the actual (real) GSM-R usage
field strengths on the railway lines are available, higher UMTS field strengths can be
tolerated, depending on them. Since the GSM-R receivers are not particularly
intermodulation tight the threshold increase must be mitigated by a usage field strength
depending variable. The monitoring station examined the IM3 strength of various
railway receivers. The worst results occurred for the cab radios. This results in the
following equation for the IM3 protection:
FUMTS max(IM3)  0,33 FGSM -R usage  80 dB
At the same time the protection against UMTS spurious emissions is still with:
FUMTS max(spur.emiss.)  FGSM -R usage  50,3 dB
FUMTS max 
the smaller value, either
FUMTS max(IM3)
or
FUMTS max(spur.emiss.)
By this measure, the restriction area again can be reduced by more than 70%.
Restrictions compared to a GSM Mobile Network
by IM3 Products
In case if GSM were operated in the blocks 925-930 MHz or 930-935 MHz
respectively instead of UMTS, the IM3 interference situation would be worse,
according to measurements by 6 dB, so that in this case:
FGSM max(IM3)  0,33 FGSM -R-usage  74 dB
is to be limited.
The spurious emissions of GSM plays a minor role.
Thanks you for your attention