Page 232 - GuideFWA

most of the DECT deployments) the sites are sectorized (typically 6 sectors, with antennas of
maximum 60º). This last real value will decrease (at least in 1/6) the number of FWA
transmitter which can cause interference to an UPCS system, and therefore the calculations
made in [16] are wrong.
• The methodology used in [16] does not contemplate the fact that re-use of co-channel
interferers within the DECT FWA system is not random (uniform distribution of interferers),
since the same frequency/time-slot will not be used if it is already used, for example, in any
adjacent sector due to the own interference avoidance mechanisms (DCS) of the DECT FWA
system. Therefore, the assumption of uniform distribution of FWA interference transmitters
(co-channel) is not well used in [16].
• In addition, it is only considered the LOS free-space propagation condition (since the Fresnel
breakpoint is too far from UPCS systems due to antenna heights assumptions -which are
different than those agreed by the Experts Group-), and this is not a typical situation specially
in high traffic urban areas as described in [16].

In the other hand it is important to remark that making reference to ETSI ETR 310 report, as
made in [16], it should be mentioned that in this ETSI report is clearly indicated that coexistence
between any DECT system and North American Personal Wireless Telecommunication (PWT)
systems in a common spectrum is completely feasible, giving an argument against the own
conclusions of [16], since PWT is an Isochronous UPCS device.

As a conclusion, the document [16] contains an enough number of errors to consider it as an
invalid document to analyse the interference between FWA TDD and UPCS systems. In addition,
it does not contemplate all the cases of FWA TDD and UPCS systems and therefore it is not only
incorrect but also incomplete.

Nevertheless, it should be noted that even with all the wrong and pessimistic assumptions made
in [16] the results ARE CLEARLY BELOW THE LIMITS OF THE ALLOWED
INTERFERENCE, and therefore the conclusion is also wrong.

Note: Related to the multiple interference analysis made in [16] and appointed as an “open issue”
by PCS proponents, it is important to say that since this matter will be treated later in Section 6,
is not included here, in order to avoid repetitions.

As already indicated in report PCC.III/935/97 [1], the DECT/PHS proponents’ viewpoint
regarding to the coexistence between FWA TDD and UPCS systems in the 1910-1930 MHz is
reflected in document PCC.III/922/97 [18]. It is not intended to repeat here what was already
indicated in document [18], but just to comment some important remarks and conclusions.

This document [18] shows that private office and residential systems could be allowed on
secondary bases in the band 1920 - 1930 MHz, if a regulator so wishes. Additional
considerations were discussed in the Interference Expert Group in both Brasilia and Mexico
meetings, and could have made the report [1] very conclusive, if the political will had been
present.

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