UK WP8F
WP(02)030
Orange PCS Ltd Comments to ITU-R Document 8F/183(Rev.1)-E
Version 1.0
31 January 2002
The general methodology used for calculating the effect of BS to BS interference between
systems is thought to be satisfactory however Orange believe that using the standard, non
co-siting, values for ACS and ACLR is an assumption that results in unrealistically high intersite distances.
When UMTS FDD is widely deployed operators will be faced with the problem of trying to
ensure co-existence of UMTS TDD and FDD systems with typical intersite distances in the
order of 50 – 100m in urban areas.
To solve this co-existence problem it will be necessary to deploy filtering in the TDD system
that more or less meet the TDD co-siting requirements specified in the standards.
For the FDD system it will be necessary to at least meet the emissions standard for “BS in
geographical coverage area as TDD” (25.104, section 6.6.3.7.1.1) and possibly the co-siting
requirements (25.104, 6.6.3.7.2.1).
In the existing standards there appears to be no consideration for the blocking requirements
for a FDD BS in close proximity to TDD BS. However it is likely that many operators will have
deployed additional filtering to protect their FDD uplink from being blocked by either their own
TDD carriers to facilitate co-siting or may consider that such filtering is prudent to ensure long
term resilience against such interference.
Given then, that these issues must be solved for co-existence of the current UMTS FDD/TDD
frequency allocations, it is logical to introduce similar assumptions into the study for future
frequency allocations.
Orange therefore suggest that the report should be re-written including an analysis that
considers the following assumptions ;
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Intersite distances as specified in table 17 of the current draft
TDD BS emissions meet co-siting standard (-80 dBm)
FDD emissions meet “TDD co-geographical” limits of 25.104 (-52 dBm) and/or “co-siting”
limits (-86 dBm)
FDD blocking spec is that required for “co-geographical” or “co-siting” with TDD (values to
be agreed)
Site engineering based solutions are non ideal since the interference environment is
constantly changing and site visits to retrofit filters is an expensive exercise.
With respect to TDD BS specifications, Orange would prefer to see mandatory emissions and
blocking levels that permit random co-geographical deployment scenarios with other systems
(TDD/FDD/GSM), with typical intersite distances TBD but of the order 50 – 100 m. Only cositing should require additional filtering, although some vendors may decide to include this as
standard.
With respect to FDD BS specifications Orange believe that the existing standards are
satisfactory and it should be left to Operators to choose whether they need to fit filters that
provide the additional blocking required for protection against TDD. This is mainly because of
the increasing difficulty in providing such protection as the frequency difference between TDD
& FDD reduces and a single generic integrated solution is not really appropriate. Also there
would be unnecessary cost penalties for Operators in geographical areas where TDD is not
present.
One further area of concern is that reducing the TDD BS’s emissions levels to that of the cogeographical or co-siting levels, whilst facilitating simpler BS deployment, has the effect of
reducing its protection against desensitisation from close UE’s operating on adjacent (or near)
channel TDD frequencies. Should UE manufacturers then improve ACS without a
corresponding improvement in ACLR the UE gains the potential to cause significant
desensitisation of the BS without the BS having the protection mechanism of its
ACLR/emissions in the UE’s frequency band. This is the same issue raised previously by
Orange in the RA/3G operators group meetings with respect to the standard for FDD UE’s
(TS 25.101). The solution is to change the standard so that there is a fixed minimum
relationship between UE ACLR & ACS and that unilateral improvements to ACS are not
permitted (although unilateral improvements changes to ACLR are OK).
This could be controlled by the following relationship :
ACLR – ACS = 0 dB + x/ - 0
Where x > 0