Telecommunications – Transmitter and receiver at separate stations – Optimum frequency selection
Reexamination Certificate
1999-04-06
2004-03-09
Kincaid, Lester G. (Department: 2685)
Telecommunications
Transmitter and receiver at separate stations
Optimum frequency selection
C455S450000
Reexamination Certificate
active
06704546
ABSTRACT:
The present invention relates to a method and apparatus for allocation of a frequency band within a given frequency spectrum of a telecommunications system, as well as the telecommunications network itself The present invention may also relate to a control element for transceiver such as a base station, a base station controller or a mobile station in a radio telecommunications system capable of carrying out the method in accordance with the present invention. The invention is particularly suited to a telecommunications system which includes at least one radio system, particularly a mobile radio system using spread spectrum techniques or a combination of spread and non-spread techniques.
TECHNICAL BACKGROUND
FIG. 1
is a schematic representation of a telecommunications system
100
which A includes a network
104
which may be a wireline telephone and/or data network. Network
104
may be connected via service node
103
to further networks
101
and
102
which may be synchronous (STM) or asynchronous (ATM), wireline or wireless networks. The network
104
may be connected to radio telecommunications transceivers
106
-
1
,
106
-
2
,
106
-
3
,
106
-
4
via access nodes
105
-
1
,
105
-
2
,
105
-
3
. The transceivers
106
may be part of the telecommunications network
104
or may be part of separate cellular mobile telephone or public radio system or systems. Further, the network
104
may be connected via a transceiver
109
to a satellite system including at least one satellite
110
. The foot-print of the beam from the satellite
110
may overlap with the radio coverage of the transceivers
106
. The network
104
may also be connected to a telecommunications system in building
111
which may form a micro- or picocellular radio telecommunications system within a macrocellular telecommunications system served by one or more of the transceivers
106
and/or satellite
110
. Alternatively, building
111
may contain a cordless telephone system connected to network
104
by a wireline. Mobile stations
108
may be able to receive and transmit messages via any of the transceivers
106
and
109
and satellite
110
including communication via the cordless or wireless network within building
111
. In addition the building
107
which may be a private house may be connected to network
104
by a so-called wireless local loop (fixed wireless access), i.e. a part of the connection to building
111
is via a radio link.
In addition to the above telecommunications systems there may also be other sources of radio noise, e.g. point-to-point microwave communication systems, CB radio, military communications systems. The result is a considerable amount of radio activity within a certain, normally allocated or regulated frequency spectrum. Conventional approaches to preventing interference between the types of radio system mentioned above require the allocation of fixed frequency bands as exemplified by the conventional systems described in U.S. Pat. Nos. 5,452,471, 5,428,819 or EP 0 719 062 for instance.
When all the telecommunications systems mentioned above are operating, there are a plurality of existing transmissions as indicated schematically in
FIG. 2
a.
Within a frequency spectrum S between the lower and higher frequency limits f
o
and f
e
various radio telecommunications transmissions occupy part of the spectrum, e.g. wideband communications W, narrow band communications N, a point-to-point microwave communications transmission O. At any arbitrary location within the geographical coverage area served by all the systems at which a transmission is to be initiated these signals, each one of which is a function of power and frequency, combine as shown schematically in
FIG. 2
b.
The resulting cumulative power/frequency diagram will be called a “power spectrum” in accordance with the present invention whereas “frequency spectrum” will be used to refer to the range of frequencies which can be used for communications within a telecommunications system.
Parts of the generalised communications systems of
FIG. 1
may have fixed and protected frequency bands, e.g. the microwave system O, or emergency, hospital or police communications transmissions which may be wideband, broadband or narrowband. Narrowband in accordance with the present invention means a communication which requires relatively little bandwidth because the amount of information to be transmitted is small. Wideband in accordance with the present invention means a communication which has a significantly wider bandwidth than required for the information to be carried. Broadband in accordance with the present invention means a communication which requires a broad bandwidth due to the amount of information to be transmitted. In accordance with conventional methods, any new telecommunications system is allocated a fixed bandwidth in a remaining part of the frequency spectrum S in such a way as to avoid interference between the systems, i.e. usually by providing a frequency guard gap between the new system and any existing system. One disadvantage of such conventional allocation methods is that frequency spectrum may be left unused or may be inefficiently used, i.e. the spectral efficiency is low unless every system is used heavily.
So-called etiquette regulations are known for unlicensed bands of radio frequency for use by mobile radio, e.g. telephone or data services as described for instance in the article “Coexistence and Access Etiquette in the United States Unlicensed PCS Band”, by Steer, IEEE Personal Communications Magazine, fourth quarter 1994. The main etiquette rules described in this article are:
1) the co-ordination rule—every communication between a fixed station (sometimes called a port) and a mobile station must start from a fixed station. A mobile station “listens” for a marker or beacon signal from a fixed station and requests access thereto before a communication may be initiated from a mobile station.
2) The listen before transmit (LBT) rule—before the fixed station transmits a marker or beacon signal it first measures the interference in the time/frequency window in which it intends to transmit.
3) The 30-second rule—a marker or beacon signal may only be transmitted for 30 seconds maximum without acknowledgement from another station wishing to transmit to it and periodic acknowledgements must be received every 30 seconds.
4) The packing rule—the LBT must be carried out so that frequencies are either scanned in increasing or decreasing order and the first acceptable frequency must be taken. Transmissions having a bandwidth below a first limit, e.g. below 625 kHz, scan from the lower frequency limit upwards and transmissions having a second bandwidth, e.g. above 625 kHz, scan from the upper frequency limit downwards. This rule packs the wider bandwidth communications in the upper part of the frequency spectrum and the narrower bandwidth communications in the lower part of the frequency spectrum.
5) The power level rule, the power level of a communication is limited by its bandwidth.
One application of such rules is described in the article “On channel definitions and rules for continuous dynamic channel selection in coexistence etiquettes for radio systems”, by D. Akerberg, 44th IEEE Technology conference Stockholm, June 1994, pp. 809-13. In this scheme a system access channel is described as free, i.e. available for transmission, if the power at a particular frequency as determined during LBT is less than the thermal noise floor plus 24 dB. If no free channel is available then a least interfered channel (LIC) is selected if the result of the LBT is a frequency having a power level of less than the thermal noise floor plus 60 dB. It is stated that such an etiquette regulation is not suitable for use with frequency hopping code division multiple access (FH-CDMA) or Direct sequence code division multiple access schemes (DS-CDMA). One reason for this is that DS-CDMA suffers from the “near-far problem” and this is normally solved by power control particularly on handover. The power rules mentioned above
Lucidarme Thierry
Vincent Paul
Barnes & Thornburg
Kincaid Lester G.
Mehrpour Naghmeh
Nortel Matra Cellular
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