Hirayr M. Kudyan PhD
Bvs Senior RF Designer
Bvs E M 3 Sales Manager
How Does One Find Them?
PUS DECT 6.0 Iifil+rat1
Use of DECT 6.0 phones in Europe by U.S. expatriates has been noticed to cause significant interference in the up-link bands of the European UMTS licensed services. This paper discusses the problem
and proposes a detection-based strategy for preventing such use of
DECT 6.0 phones. The proposed approach consists of monitoring and
locating such phones, thereby helping network operators minimize
incremental operating costs due to interference. The technologies for
realizing this are relatively simple and in existence today. Monitoring
records of Base Transceiver Stations (BTS) already compile lists of
such sources within each cell that can be traced to neighborhoods or
city blocks. The technology for the actual location of DECT 6.0 phones
(as well as cell phones) is also in existence. A family of such devices
is produced by Berkeley Varitronics Systems in Metuchen, New Jersey, consisting of, among others, a scanning narrow-band receiver
equipped with a multi-band high-gain directional antenna capable
of guiding the user to within an arm's reach of the culprit phone(s).
Discussion of the Problem
The Digital Enhanced Cordless Telecommunicationsstandard, better
known as DECT, was developed by ETSl in Europe. It is used for creating cordless phone systems primarily for homes and small offices.
DECT phones have been developed and marketed in Europe, Australia, South America and North America. The introduction of the DECT
standard to North America was delayed because U.S. FCC regulations required a slightly different frequency allocation. This resulted
in the development of the DECT 6.0 standard for North America which
assigned the 1920-1930 MHz band to cordless phone voice channels
only. As a result, DECT 6.0 phones are highly immune to interference
from other wireless applications (e.g., baby monitors, wireless networks, etc.). The frequency allocations for DECT, DECT 6.0 and UMTS
up link bands in the E.U. and North America are listed in Table 1:
Table 1. DECT, DECT 6.0 and UMTS Up-link Frequency Allocations for
Europe and North America
The careful frequency allocation of DECT and DECT 6.0 phones in
the E.U. and North America assures that these phones will neither
cause nor be susceptible to Electromagnetic Interference (EMI)
with respect to other licensed wireless services, as long as the
phones are deployed in their respective geographic region(@ for
which they were designed for. However, when DECT 6.0 phone systems are deployed in the E.U., their RF signals can interfere with
some of the up-link channels of European UMTS services because
the two bands overlap (see Table 1). DECT 6.0 systems are particularly potent EM1 sources for several reasons:
1. The system uses the same frequency band (1920-1930MHz) for
both of its uplink and downlink channels.
2. All handsets and base unit will contribute to the cumulative level
of EM1 simultaneously.
3. Except for the few "green" versions, most DECT systems keep
the RF signal always on.
4. Unlike cell phones, the RF output level from cordless phones and
base is fixed.
According to some European network operators, a signal level of
only -97 dBm or higher in the UMTS uplink band is considered as
interference. If the UMTS phone(s) are located within the confines
of the same city block, transmission(s) from a DECT 6.0 phone can
very easily exceed this threshold. This may be demonstrated by
considering the estimated free-space path loss for electromagnetic
waves, as a function of distance d
6.0 phones purchased cheaply on-line. According to some wireless
operators in the U.K., sites where this kind of interference is occurring right now is readily identified from BTS records for each cell.
where do and dl represent the transmit and receive antenna positions
respectively in the same units of length. Thus, signals originating
from a DECT phone located 1 meter from a point of reference to a
point 1 Kilometer from the same point of reference would attenuate
by 60dB. If the RF power level near the antenna was -10dBm (this is
a conservative output level for a typical cordless phone) the DECT 6.0
uplink signal level has the potential to exceed the -97dBm threshold
over an area equivalent to a small city block or over an apartment
complex with hundreds of residents only after allowing for propagation loss as well as attenuation caused by typical obstacles (walls,
doors, trees, etc) between the DECT phone and the point of observation. Other wireless devices do not present the same type of challenge as a result of their inherent operating schemes (see Table 2).
Table 2. Relative Likelihood of Interference from Different Devices
WiFi Access Point
The risk of interference from cell phones t
UMTS services is insignificant. The cell phon
flrmware must first passively detect the local
cell BTS and recognize it as a "valid" host.
Then it will attempt to register over a channel
assigned by the BTS. Cell phone RF power output levels are purposefully kept to a bare minimum by l e BTS in order to maximize freque
re-use over ea~4.cell.
~ a ~ t connectsd
o ~ s to local WiFi hot spots in the
E.U. or elsewhere pose no risk of interference
because the up-link frequencies for them are
defined and c&lled
by the local hot spot(s).
Network operators in the U.K. routinely identify lists of sites where
DECT 6.0 and other cordless phones have been causing interference to licensed UMTS services over the 900MHz up-link (880915MHz) and 1900MHz uplink (1920-1980MHz) frequency bands.
There is a clear need for routinely locating these sources of interference after they have been identified from the BTS monitoring
records down to the last few hundred feet. The technology for locating undesirable DECT or cell phones is already in existence. One
such family of devices has been developed by Berkeley Varitronics
Systems of Metuchen, New Jersey. The --- --- undTM-P-- product is a hand-held lightweight instrument consisting of a scanning
narrow-band receiver equipped with a high-gain directional broadband antenna capable of guiding the user to the culprit sources; be
they cellphones or cordless phones (including DECT and DECT 6.0).
- V product
is a wall-mounted networked version
equipped with a multi-band omni-directional antenna which can be
networked over a wired LAN to upload chronological data in realtime for round-the-clock monitoring of same.
Wolfhound-PROcell 0h0ne detector with DF Direction Findina antenna
Cordless Phones DECT 6.0 and other cordless phones brought
(DECT 6.0 & other) from the U.& for personal use in Europe pose
a serious risk of interference in GSMlUMTS services on the 900' and 1900 MHz up link bands.
Aggravatlng faem: same frequency band used
for up and down link channels, RF signal level
fbred, handset(s) and base contribute to EM1simultaneously.
The interference problem discussed here has amply been observed
and documented in the U.K.. The problem could proliferate if in addition to U.S. expatriates, growing numbers of locals start to use DECT
Contad our European soles office for more information:
BVS EMEA Sales Manager
Phone: +41 71 278 1311
Mobile: +41 79 600 4546
WatchHound cell phone monitor is networked via LAN & wall-mountable
Prondir;p u,~reiesssolui~onsbr ovsr 37years
1 Some non-OECT 6.0 cordless phones made for the U.S. use channels in the 900 MHz band which are also allocated to European GSMIUMTS services' up-link channels (880-915 MHz).
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