Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2001-02-14
2004-01-06
Maung, Nay (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S067150, C455S069000
Reexamination Certificate
active
06675020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radio telecommunications systems, particularly to a method and system for protecting co-existent wireless application services interfering with cellular telecommunications systems.
2. Description of the Related Art
Cellular and wireless services are known for a number of years, and become more and more popular. In wireless telephony, frequency spectrum is allocated for supporting radio communications between a network and Mobile Stations (MSs). In every national jurisdiction, a public organism, such as for example the Federal Communications Commission (FCC) in the United States of America has authority to manage the allocation of the frequency spectrum to various wireless applications, such as for example for television broadcasting, cellular telecommunications, public safety radio services (police, fire-fighters, or paramedics radio communications), military transmission applications, and others. Since most frequency spectrum holders try to maximize their investment by using high spectral density transmissions in their allocated bandwidth, the interference generated into neighboring frequency spectrums become important and non-negligible. Frequency guard bands, which are non-assigned bands of frequency spectrum, is one known partial remedy for copping with existing frequency interference generated by one system into a second system's allocated frequency spectrum.
For better understanding the concept of Out Of Band radio Emissions (OOBEs), reference is now made to
FIG. 1.
a,
wherein there is shown a schematical representation of a frequency spectrum assigned to a radio frequency operator. The allocated frequency spectrum shown in
FIG. 1.
a
has a nominal bandwidth the operator is allowed to use for its radio application, such as for example for operating a cellular telecommunications network. A maximal nominal power level is also set and allowed for the radio transmissions within the nominal bandwidth. However, due to the imperfect nature of transceivers, OOBEs are most always generated outside the nominal bandwidth, as shown. The generated OOBEs may interfere with other radio applications that are allocated the frequency spectrum neighboring the allocated nominal bandwidth.
Reference now being made to
FIG. 1.
b,
wherein there is shown another schematical representation of an allocated frequency spectrum assigned to a radio frequency operator. In
FIG. 1.
b,
the Guard Bands GB A and GB B are used around the assigned nominal bandwidth for coping with OOBE. In such manner, if there are OOBEs, they are generated within the guard bands, which are not used by any other wireless application.
FIG. 2
illustrates an example of a frequency spectrum assigned in the United States of America, where the FCC has decided to re-allocate frequency spectrum formerly used for Ultra-High Frequency (UHF) television channels 60 through 69, both for new wireless services (cellular network operators) and for public safety radio services (operated by police, paramedics, etc). This frequency spectrum ranges from 746 MHz to 806 MHz. A first license of 5 MHz, and a second license of 10 MHz have been assigned in both downlink and uplink cellular applications, as shown. Adjacent to the cellular applications, but separated by 1 and 2 MHz guard bands, were allocated two 12 MHz frequency spectrums for public safety services, one for the downlink radio transmissions (base station to terminals) and one for public safety uplink radio transmissions (terminals to base station). It was noted in many instances that, for example, cellular downlink transmissions effectuated in the frequency band just before the 762 MHz high-end limit, negatively interfere with the public safety downlink transmissions in the frequency band just above the 764 MHz low-end limit. Furthermore, it was also observed that the uplink cellular transmissions effectuated on radio channels just above the frequency of 777 MHz also create OOBE affecting the public safety downlink radio transmissions on channels just below the 776 MHz limit. These problems may further be accentuated in situations wherein there are no guard bands between the cellular network's spectrum and the coexistent network's spectrum, and when the two systems' sub-bands are used for transmission in the same direction (downlink or uplink).
The interference problems described in relation to
FIG. 2
can be better understood with reference to
FIG. 3
, wherein there is shown a schematical representation of a typical near-far type interference problem involving a cellular network
10
which geographical radio coverage overlaps a coexistent public safety radio network
12
radio coverage. As known in the art, the cellular telecommunications network
10
comprises a plurality of cells
16
i,
each such cell being served by a Base Station (BS)
14
i.
The BSs provide radio service to all MSs within their corresponding cell. For example, in
FIG. 3
, BS
14
3
provides cellular service to MS
18
which is within the cell
16
3
. The coexistent radio network
12
, such as for example a public safety radio network, has itself a central radio station
20
providing radio coverage to its radio terminals, such as to radio terminal
22
, over an area typically much bigger than a cell
16
i.
For example, the central radio station
20
may service a police station and thus provide radio service for police radio terminals over an entire city.
Instances arise when a public safety radio terminal such as terminal
22
, served by central radio station
20
, arrive in positions physically close to a BS of a cellular system, such as BS
16
3
of system
10
. In such conditions, the radio terminal
22
receives not only a radio frequency signal
21
(attenuated because of the distant location of the terminal
22
with respect its central radio station
20
) from its own central station
20
, but also a strong interfering radio signal
23
from a close emitter, i.e. from BS
14
3
, the radio frequency signal
23
being intended not for the terminal
22
, but for MSs served by BS
14
3
, like the MS
18
. When the frequencies of signals
21
and
23
are too close, and when like in the example of
FIG. 3
the public safety radio terminal is far from its central radio station but physically close to the interfering emitter, the downlink communications between the central station and the terminal are substantially disturbed by the so-called near-far interference, oftentimes to such an extent that the terminal
22
is no longer able to receive communication from the station
20
.
Reference is now made to
FIG. 4
, wherein there is shown an exemplary detailed representation of the near-far interference engendered by a first system, such as a cellular system, into a second system, such as a public safety radio system. In
FIG. 4
, it is assumed that the cellular telecommunications system
10
shown in
FIG. 3
uses the frequency spectrum X, which is divided, like in Time Division Multiple Access (TDMA) based cellular telecommunications networks in a plurality of frequency channels (all cellular systems use radio channel, but they may vary in bandwidth). For the purpose of the present example, it is assumed that the last three frequency channels at the high end of the frequency spectrum X are frequency channels A, B, and C. A Guard Band GB is allocated to separate in frequency the spectrum X used by the cellular telecommunications system
10
from another frequency spectrum Y assigned and used by the radio network
12
of a public safety organization. The frequency spectrum Y is also divided into a plurality of frequency channels, such as for example frequency channels
1
,
2
and
3
, and so on.
FIG. 4
shows that cellular frequency channels A, B, and C are received at a given location within the cell
14
3
with a given power level, L
1
. At the same given location, because of the transmission attenuation due to the distance, the public safety radio channels
1
,
2
, and
3
are received with
Alex Nicolaescu, Ericsson Canada Inc.
Maung Nay
Telefonaktiebolaget LM Ericsson (publ)
Trinh Tan
LandOfFree
Self-sacrificing cellular system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Self-sacrificing cellular system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self-sacrificing cellular system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3265760