|Numéro de publication||WO1992004796 A1|
|Type de publication||Demande|
|Numéro de demande||PCT/US1991/004957|
|Date de publication||19 mars 1992|
|Date de dépôt||15 juil. 1991|
|Date de priorité||4 sept. 1990|
|Numéro de publication||PCT/1991/4957, PCT/US/1991/004957, PCT/US/1991/04957, PCT/US/91/004957, PCT/US/91/04957, PCT/US1991/004957, PCT/US1991/04957, PCT/US1991004957, PCT/US199104957, PCT/US91/004957, PCT/US91/04957, PCT/US91004957, PCT/US9104957, WO 1992/004796 A1, WO 1992004796 A1, WO 1992004796A1, WO 9204796 A1, WO 9204796A1, WO-A1-1992004796, WO-A1-9204796, WO1992/004796A1, WO1992004796 A1, WO1992004796A1, WO9204796 A1, WO9204796A1|
|Inventeurs||Robert Louis Breeden|
|Exporter la citation||BiBTeX, EndNote, RefMan|
|Citations de brevets (6), Citations hors brevets (2), Référencé par (45), Classifications (12), Événements juridiques (3)|
|Liens externes: Patentscope, Espacenet|
CORDLESS TELEPHONE SYSTEM FOR RESIDENTIAL, BUSINESS AND PUBLIC TELEPOINT OPERATION
Field of the Invention
This invention relates in general to radio frequency telephone communication systems, and in particular to cordless telephone system operation in residential, business and public environments.
Background of the Invention
The increase in cellular telephone networks has led to an increase in the popularity of cellular telephones and highly portable telecommunications. Yet the large coverage area of cellular networks necessitates high powered operation of cellular telephones (cellular handsets must produce approximately 600 milliwatts output) . High power consumption requires a costly handset and costly service to the consumer. High power consumption also limits the size to which a cellular telephone can be reduced. To combat these limitations of cellular telephones, a second generation of cordless telephones (CT-2) utilizing digital telephone technology operating in conjunction with telepoint stations has been developed.
Because of the relatively small size of the telepoint coverage areas, cordless telephones operate at much lower power levels than cellular telephones (approximately 10 milliwatts) . Cordless telephones can be built smaller, lighter and cheaper than cellular phones. The cordless telephone technology is older than cellular technology and therefore leads to lower development and manufacturing costs. A cordless telephone can be used with private base stations in controlled environments, such as residential or office settings. In the public arena, a service provider can provide telepoint base stations for CT-2 communications. A cordless handset can be used within all telepoint coverage areas within a given service area, and thus would approximate the convenience of a cellular telephone with much less cost to the consumer. In addition, though the cost of infrastructure construction can be a substantial investment, using lower-powered telepoint stations which operate relatively independent of each other, results in significantly less cost to the service provider than construction of a cellular network.
Referring to FIG. 1, conventional residential CT-2 operation allows for two way calling between a cordless telephone or CT-2 handset 10 and all telephones 12 hardwired to the public switched telephone network (PSTN) 14 via a residential base station 16. Similarly, conventional business CT-2 systems allow for two-way calling between other handsets 11 on premise and the PSTN 14 via an office base station 18. Away from the home or office base station 16, 18, the user initiates a telephone call by establishing an RF link between another handset 19 or 19' and a telepoint base station 20 or 20' coupled to the PSTN 14. The telepoint stations 20 and 20' provide cordless communication from the handsets 19 and 19', respectively, within islands of coverage 22 and 22 ' , respectively, each having approximately 150 meter radius of the telepoint station depending upon terrain and man-made objects which could interfere with the signalling. For example, cordless telephone operation within a mall or airport would require location of a telepoint station or stations such that the island(s) of coverage would include the mall or airport building.
Public CT-2 systems utilize approximately forty radio frequency (RF) channels for communication between handsets and the telepoint base station. Conventionally, to originate a call, the cordless telephone would scan the forty channels to find an available channel and then attempt to access the telepoint station. The telepoint station, likewise, would be scanning the forty available channels for incoming calls from the CT-2 handsets. When the telepoint station detects a call request from a handset, interconnection with the PSTN is provided. To facilitate development of cordless telephone networks, the Great Britain Department of Trade and Industry has developed and published a Common Air Interface (CAI) Specification which has been adopted by most countries of the world working on cordless telephone development. The CAI spells out all aspects of the communications interface standards to be used for the interworking between second generation cordless telephone apparatus, including public access services. The CAI specifies cordless telephone operation on 40 to 100 kHz wide frequency channels within the frequency band bounded by 864 MHz at the low end and 868 MHz at the high end. In the United States, though, the CAI standard frequency band falls within the Public Safety Trunking frequency band allocated under the Federal Communications Commission (FCC) Part 15 Rules.
The rules and regulations of the FCC requires that radio frequency operation within an allocated frequency band be licensed by the FCC. In the United States, virtually no frequencies below 3 GHz in the RF spectrum are unallocated. Currently no frequency band is allocated for CT-2 cordless telephone usage. To obtain reallocation of a frequency band for cordless telephone communications from the FCC could take several years and require a substantial investment of time and funds for political lobbying and other bureaucratic requirements. The first generation of cordless telephones—analog cordless telephones—are crowded into only ten analog channels in the United States, therefore reuse of the analog cordless telephone channels would be impractical. Certain frequency bands under FCC Part 15 Regulations are allocated for unlicensed operation. Unlicensed operation within a frequency band, though, must tolerate interference from other unlicensed users in the frequency band and must not interfere with any licensed users in the radio frequency (RF) spectrum. Conventional frequency hopping spread spectrum techniques are permitted in certain frequency bands under FCC Part 15
Regulations for unlicensed operation, and would provide a high degree of immunity from causing or receiving interference to or from other single-frequency radio services which may be operating nearby, yet a service provider who provides a CT-2 system utilizing unlicensed RF operation cannot predict the future use of the RF channels adopted. Many communication service providers are reluctant to invest much money in public telepoint stations which would operate in an unlicensed spectrum because of the risk that the spectrum could become overcrowded, chaotic, and ultimately unusable for public telepoint service.
Some cellular providers believe that it would be possible to share their currently allocated cellular frequencies for both cellular use and CT-2 public telepoint use without diminishing cellular capacity. They believe that due to the low power and short distance characteristics of cordless telephone service, a cellular provider who desires also to provide public telepoint stations could reuse selected cellular frequencies which could not be reused locally by the higher power cellular system. Unfortunately, this shared cellular frequencies approach would not work for business or residential cordless telephone systems, due to the inability of the cellular provider to control and coordinate the frequencies of such systems to prevent interference.
Thus, what is needed is a single cordless telephone system which can provide service in all three environments—residential, public telepoint, and business- -without requiring the user to have multiple handsets.
Summary of the Invention There is provided in one form a method for transparent frequency reuse which uses a first frequency for high power RF communications in a first area and a second frequency for the high power RF communication in a second area. The first frequency is reused in the second area for low power RF communications.
In another form there is provided a method for radio frequency communications on a plurality of frequencies by broadcasting information identifying those frequencies on another frequency.
In yet another form there is provided a method for cordless telephone operation comprising the steps of determining whether user selectable controls indicate operating in a first mode of operation or a second mode of operation. In the first mode of operation, cordless telephone operation provides communications on at least one frequency within a first frequency band. In the second mode of operation, cordless telephone operation provides communications on at least one frequency within a second frequency band.
Brief Description of the Drawings
FIG. 1 depicts conventional cordless telephone operation in residential, business and public environments.
FIG. 2 depicts reuse of cellular frequencies for cordless telephone operation according to the preferred embodiment of the present invention.
FIG. 3 is a block diagram of a cordless telephone for operation in residential, business and public environments according to the preferred embodiment of the present invention. FIGs. 4A and 4B are a flowchart of the operation of the microprocessor of the cordless telephone according to the preferred embodiment of the present invention.
Detailed Description of the Invention
Referring to FIG. 1, a second generation cordless telephone (CT-2) system according to the present invention comprises one or more private base stations 16, 18 for residential or business use which operate on a common non-cellular frequency band. Preferably, the private base stations 16, 18 communicate with the handsets 10 on RF frequencies within the 902-928 MHz frequency band allocated for Industrial, Scientific and Medical usage (the ISM band) , which lies just slightly above the 869-894 MHz frequency band used for cellular base station transmission.
A spread spectrum approach utilizing conventional frequency hopping techniques is permitted in the ISM band under FCC Part 15 Regulations. FCC Part 15 spread spectrum operation in the ISM band would be advantageous for the business system 18 without much likelihood of interference from other systems (licensed or unlicensed) , due both to the attenuation of the building walls and to the building manager's ability to effect a measure of control of the types of radio systems used within the building. FCC Part 15 spread spectrum operation in the ISM band would work well also for the residential system 16, due to the relatively low density of residential users and would offer an order of magnitude improvement over present analog cordless telephone systems which are crowded into only ten allocated analog channels in the United States.
Accordingly, the private base stations (residential 16 and business 18) utilize conventional frequency hopping schemes for improved unlicensed operation on frequencies in the ISM allocated frequency band. In accordance with a second aspect of the present invention, approximately forty RF channels comprising licensed cellular frequencies are utilized by each telepoint base station 20 of the present invention for CT-2 communications. The public telepoint base stations 20 of the preferred embodiment of the present invention share cellular frequencies and utilize conventional spread spectrum frequency hopping schemes for reliable unlicensed RF communications in a public environment. Use of the spread spectrum approach in public telepoint operation allows economy of handset design because the same spread spectrum circuits could be used in private operation on unlicensed frequencies and public telepoint operation. Each public telepoint base station 20 is designed to be programmable by the service provider to hop only among selected cellular frequencies usable for a given location. Further, each public base station 20 would have a call set-up protocol which would inform the handset 10 of the correct set of hopping frequencies to use. The use of the spread spectrum frequency hopping schemes reduces the chance of interference to or from the cellular system users.
Referring to FIG. 2, the scheme of the present invention for transparent cellular frequency reuse is described. To ensure cellular telephone communication coverage of an area, conventionally, a plurality of cellular zones 30a, 30b and 30c are established, each zone operating on different frequencies. All of the zones are typically interconnected through a central cellular network controller, each zone having a control frequency associated therewith for control by the controller. Cellular zones 30a (Zl) , 30b (Z2), and 30c (Z3) are adjoining zones which have, respectively, control frequencies Al, A2, and A3. Each of the three cellular zones communicate on communication frequencies Bl, B2 and B3, respectively. When setting up zones for cellular communications, the channels for each cellular zone 30a are allocated such that adjoining zones 30b and 30c do not have the same frequencies for communication or control. Telepoint stations 20a, 20b, and 20c for CT-2 communications operate at less power than cellular transmitters and, accordingly, the island of coverage of each telepoint station 22a, 22b and 22c, is smaller than cellular zones 30a, 30b and 30c. According to the present invention, a system provider of a cellular system wishing to construct a CT-2 system with telepoint operation can designate the approximately forty frequencies for telepoint communications by determining the communication and control frequencies of the adjoining cellular zones and assigning them to the telepoint base station such that the telepoint base station has one control frequency for operation and forty communication channels, none of which are utilized by the cellular zone in which the telepoint station is located or a cellular zone near enough to create interference. In the preferred embodiment of the present invention, each public telepoint base station will continually transmit a predetermined CT-2 identifier, identifying the signal as one transmitted by a CT-2 telepoint base station, followed by frequency information indicating the frequencies to be used for communication therewith and the spread spectrum technique to be used, if any, over the one control frequency assigned thereto. The handsets will use the information broadcast on the control channel to determine the frequencies on which to communicate.
The FCC has allocated a plurality of frequencies for cellular communications. The set of cellular frequencies which would provide the highest degree of interference control is the set used for cellular base station transmission because the base transmitters remain stationary. Therefore, the preferred frequencies for assigning to CT-2 reuse would be the cellular base station frequencies. Four hundred and sixteen frequencies with a 30 KHZ spacing located between the frequencies bounded by 880 MHZ to 890 MHZ and 891.5 MHZ to 894 MHZ are reserved for cellular base station transmissions on systems provided by the Regional Bell Operating Companies (RBOCs) . The RBOCs also have reserved the frequencies bounded by 879.4 MHZ at the low end and 880 MHZ at the high end for cellular base station control channels, wherein the transmitters can communicate with the central network controller.
Likewise, non-RBOC cellular service providers have reserved 416 cellular base station transmitting frequencies with a 30 KHZ spacing within the frequencies of 869 to 880 MHZ and 890 to 891.5 MHZ, with control frequencies reserved in the band of 834.4 MHZ to 835 MHZ. Telepoint base station 20b could be assigned control frequency A2 and forty of the communication frequencies B2 allowing telepoint base station operation in the cellular zone 30a and proximate to the cellular zone 30c. Likewise, telepoint base station 20a would be assigned control frequency A3 and communication frequencies from the frequency channels B3.
As a further example of the operation of the preferred embodiment of the present invention, telepoint base station 20c could be assigned control frequency Al or A2 and communication frequencies from the frequencies Bl and B2. In a true cellular network, there are a plurality of zones and the particular method for reassigning cellular frequencies for CT-2 public telepoint station operation could be expanded to a multiple of telepoint stations within one cellular zone or even a telepoint base station located within two or more cellular zones.
Since the cellular frequencies have been reserved by the FCC for use by the service provider within a predetermined geographic region, the same service provider can provide CT-2 telepoint communications without the time and expense of requesting new FCC frequency allocation and without fear of future interference from an FCC licensed user. Furthermore, the use of conventional spread spectrum frequercy hopping techniques according to the preferred embodiment of the present invention provides decreased probability of interference from or with cellular communications while allowing economy of handset design. The same spread spectrum circuits could be used in the handset to provide for unlicensed operation in the 902-928 MHz ISM band during residential and/or business operation and public operation on cellular frequencies in the 869-894 MHz cellular base station transmission band, which lies just below the ISM band. Referring next to FIG. 3, a CT-2 handset according to the present invention comprises an antenna 100 coupled to a transmitter circuit 102 and a receiver circuit 104. The microprocessor controller 108 receives a signal from the receiver circuit 104 indicating the received signal strength (the RSSI signal) . A time division duplexer 106 controls the signal provided to the transmitter 102 and received from the receiver 104 to facilitate two-way communications by alternately transmitting and receiving on the same channel at a high rate. The operation of the timed division duplexer 106 is controlled by a signal from the microprocessor controller 108.
The microprocessor controller 108 provides a signal to a frequency synthesizer 110 for controlling the operation thereof. The frequency synthesizer 110 supplies the operating channel information to the transmitter 102 and the receiver 104 for modulation and demodulation of the communication signal. In the preferred embodiment of the present invention, the microprocessor controller 108 signals the frequency synthesizer in a manner to provide spread spectrum communications, i.e., instructs the frequency synthesizer 110 to hop between a plurality of frequencies in a predetermined manner.
A public/private switch 112 allows the handset user to indicate the environment of use. During operation, the only action required of the handset user in order to select operation on either a public telepoint system or a private system would be the selection of either the "PUBLIC" or the "PRIVATE" setting of the switch 112. In a business or residential use, the switch 112 is placed in the private mode. The microprocessor controller 108 signals the frequency synthesizer to frequency hop among a predetermined set of frequencies assigned to the residential base station 16 or the office base station 18 (FIG. 1) in a predetermined manner. In the preferred embodiment of the present invention, the frequencies assigned to the residential base station 16 and the office base station 18 and synthesized by the frequency synthesizer 110 are predetermined frequencies in the ISM frequency band (902 to 928 MHZ) which is just above the cellular base transmitting bands. When the switch 112 is in the public mode, the microprocessor controller 108 instructs the frequency synthesizer 110 to synthesize frequencies identified by a signal received on a control channel in the manner discussed below. Conventional CT-2 handsets comprise user selectable public and private controls performing the same function as switch 112 to accommodate the slightly different call set-up procedures on public and private systems and to prevent inadvertent use of a nearby public telepoint system by a user intending to place a call via his residential or business base unit.
The signal received by the receiver 104 or transmitted by the transmitter circuit 102 is a digitally encoded signal which passes through an adaptive differential pulse code modulated codec 114 for digital- to-analog or analog-to-digital conversion. The signal received via the receiver circuit 104 and converted by the codec 114 is supplied as an analog signal to audio circuitry 116 and thence to a speaker 118. Likewise, an analog signal received from a microphone 120 passes through the audio circuitry 116 and is converted to a digital signal by the adaptive differential pulse code modulated codec 114 before being provided to the transmitter circuit 102.
For other operations, such as dialling up a telephone number, user controls 113 provide appropriate signals to the microprocessor controller 108. In addition, the microprocessor controller 108 supplies a signal to a display driver 122 for generation of a visual message for presentation to the user on a display 124.
Referring next to FIGs. 4A and 4B, the operation of the microprocessor controller 108 (FIG. 3) begins 150 upon energization of the CT-2 handset. If an input interrupt is received 152 from the public/private switch 112 (FIG. 3) processing determines whether the switch 112 is in the public or private position 154. If the switch 112 is in the public position 154, a public mode flag within the microprocessor controller 108 (FIG. 3) is set 156. Alternatively, if the switch 112 is in the private position 154, the public mode flag is cleared 158. Processing then returns to await the next operation. If an input interrupt is not received 152 from the switch 112, processing determines whether a call has been initiated by the user 160 as indicated by activation of one of the user controls 113 in a conventional manner. If a call has not been initiated 160 and the switch 112 has not provided an input interrupt 152, and the headset is operating in the public mode 162, i.e., the public mode flag is set within the microprocessor 108, processing returns to remain in an idle loop awaiting an input interrupt 152 from the switch 112 or a call initiation signal 160 from the user controls 113. When operating in the private mode 162, i.e., operating in conjunction with a residential or business base station, the user can also receive calls. Therefore, when the public mode flag is not set 162 indicating that operation is in the private mode, the signal on the predetermined private channel, is sampled 164. To facilitate operation on more than one private base station, the microprocessor controller 108 could store the predetermined frequencies of operation with the various base stations (either predetermined by the manufacturer, programmed by the service provider, or entered via the user controls 113) and the user could indicate which base station he is presently communicating by the user controls 113 (FIG. 3) . If sampling the signal 164 does not indicate that a call is received 166 by the handset, processing returns to remain in an idle loop awaiting an input interrupt 152 from the switch 112, a call initiated by the user 160, or a call received for the user 166.
If a call is received for the user as indicated by the signal sample 164, a radio frequency link is established with the private base station 168 in a conventional manner. In accordance with the present invention, the private base station will be assigned a plurality of frequencies within the ISM frequency band and a predetermined frequency hopping scheme. Therefore, the step of establishing an RF link 168 with the private base station involves not only loading the proper frequency to the frequency synthesizer, but also loading the frequency synthesizer with the subsequent frequencies at the times indicated by the particular frequency hopping scheme assigned to the private base station.
Once the link is established 168, operation awaits for the call to be completed 170. When the call is completed, operation returns to the idle loop to await the next input interrupt 152, call initiation 160, or call received 166.
If a call is initiated 160, the public mode flag is examined 172 to determine whether the microprocessor 108 is operating in the public mode or the private mode. If private mode operation is indicated 172, an RF link with the private base station is established 174 as described above and completion of the call is awaited 176. Upon completion of the call 176, operation returns to await the input interrupt 152 from the switch 112, a subsequent call initiation 160, or a call received 166.
If examination of the public mode flag 172 indicates public mode operation, a scan timer is set to its maximum value 178. The scan timer sets a maximum time for the
CT-2 handset to determine whether it is within range of a public telepoint base station in order to establish an RF link therewith. According to the preferred embodiment of the present invention, the maximum value of the scan timer may be user programmable via the user controls 113. After loading the maximum value of the scan timer 178, the microprocessor controller 108 then loads a first public control channel to the frequency synthesizer 110 and samples the signal thereon 180. If the receive signal strength indicator (the RSSI signal) is not greater than a predetermined threshold 182, the microprocessor 108 loads the next public control channel 184 to the frequency synthesizer 110 and samples the signal on that channel 180. If a sample signal has a receive signal strength indicator greater than a predetermined threshold 182, indicating that the handset is within communication range of a transmitter transmitting that signal, processing determines whether a predetermined CT-2 identifier has been detected 186 in the sample signal. The CT-2 identifier establishes that the transmitter transmitting the signal is a CT-2 telepoint base station. According to the present invention, each public telepoint base station will continually transmit a predetermined CT-2 identifier followed by frequency information indicating the frequencies to be used for communication therewith and the spread spectrum technique to be used, if any. If the predetermined CT-2 identifier is not detected 186 and the scan timer does not equal zero (i.e., has not timed out) 188, the microprocessor 108 loads the next public control channel 184 to the frequency synthesizer 110 and the signal on that channel is sampled 180.
If the scanned timer times out 188, the microprocessor controller 108 provides appropriate signals to the display driver 122 to generate a message for display on the display 124 indicating to the user that a telephone base station was not located 190. In this manner, when a signal from a telepoint base station is not found on a control channel within the maximum value of the scan timer, the user will be notified 190 and may then go to a location where he has a better chance of initiating a call.
Once the predetermined CT-2 identifier is detected 186, the frequency information transmitted on the CT-2 telepoint control channel is decoded 192. The frequency information, as explained above, indicates the communication frequencies of the telepoint base station and the spread spectrum technique to be used to establish an RF link therewith. After decoding the frequency information 192, the microprocessor controller 108 loads those frequencies to the frequency synthesizer 110 in the identified frequency hopping manner to establish a spread spectrum RF link with the public telepoint base station on the designated frequencies 194. The caller then dials the telephone number via the user controls 113 (FIG. 3) and makes the telephone call. Processing then awaits completion of the call in a conventional manner 196, after which processing will return to await the next input interrupt 152 from the switch 112 or a subsequent call initiation 160.
By now it should be appreciated that there has been provided a cordless telephone communications system which offers service providers the protection of licensed spectrum for their public telepoint service investment on cellular communications allocated frequencies without diminishing the subscriber capacity of the shared cellular system. In addition, private base stations in the business and residential environments would be able to share spectrum unobtrusively with other users via spread spectrum techniques without the need for licensing, thereby requiring no new frequency bands allocated for use by the cordless telephone communications system. What is claimed is :
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|Classification internationale||H04W16/12, H04W16/02, H04W16/32, H04W16/14|
|Classification coopérative||H04W16/16, H04W16/12, H04W16/02, H04W16/32, H04B1/713|
|Classification européenne||H04W16/02, H04W16/12, H04B1/713|
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