United States Patent (19)
`Wichman
`
`54 RADIO FREQUENCY COMMUNICATION
`SYSTEM WITH A REPEATER THAT
`OPERATES WITH A TIME DIVISION
`MULTIPLE ACCESS PROTOCOL
`
`75 Inventor: Johan Wichman, Bjarred, Sweden
`73 Assignee: Telia AB, Farsta, Sweden
`21 Appl. No.:
`08/750,148
`22 PCT Filed:
`May 30, 1995
`86 PCT No.:
`PCT/SE95/00610
`S371 Date:
`Jan. 29, 1997
`S 102(e) Date: Jan. 29, 1997
`87 PCT Pub. No.: WO95/35603
`PCT Pub. Date: Dec. 28, 1995
`Foreign Application Priority Data
`30
`SEl Sweden .................................. 9402028
`Jun. 10, 1994
`(51) Int. Cl." ....................................................... H04B 7/14
`52 U.S. Cl. ........................... 370/315; 370/328; 370/336
`58 Field of Search ..................................... 370/315, 328,
`370/336,337,345, 347, 437, 442,280;
`455/11.1
`
`56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,713,809 12/1987 Mizota .................................... 370/315
`10
`
`
`
`USOO5930240A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,930,240
`Jul. 27, 1999
`
`5,113,394 5/1992 Kotzin ..................................... 370/315
`5,365,590 11/1994 Brame.
`5,371,734 12/1994 Fischer .................................... 370/311
`
`FOREIGN PATENT DOCUMENTS
`
`O 605 182 A2
`O 637 144 A1
`WO 92/09148
`
`7/1994 European Pat. Off..
`2/1995 European Pat. Off..
`5/1992 WIPO.
`
`Primary Examiner Jeffery A. Hofsass
`ASSistant Examiner Mitchell Slavitt
`Attorney, Agent, or Firm-Oblon, Spivak, McClelland,
`Maier & Neustadt, P.C.
`57
`ABSTRACT
`
`In a mobile radio System, which comprises densely posi
`tioned base Stations working with a short range between the
`affected base Stations and mobile units, repeating functions
`are carried out by means of a simplified variant of a base
`Station. This simplified variant of a base Station is positioned
`between the ordinary base station and the mobile unit, which
`Simplified variant of a base Station receives a respective
`message and forwards the message to the affected mobile
`unit.
`
`16 Claims, 1 Drawing Sheet
`
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`U.S. Patent
`U.S. Patent
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`Jul. 27, 1999
`Jul. 27, 1999
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`5,930,240
`5,930,240
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`FIG. 7
`A MC. 7
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`A V6. 2
`FIG. 2
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`1
`RADIO FREQUENCY COMMUNICATION
`SYSTEM WITH A REPEATER THAT
`OPERATES WITH A TIME DIVISION
`MULTIPLE ACCESS PROTOCOL
`
`TECHNICAL AREA
`The present invention relates to an arrangement for, in a
`digital mobile radio communication System comprising on
`the one hand densely positioned base Stations working with
`a short range and on the other hand mobile units, extending
`the range by means of repeating functions.
`STATE OF THE ART
`In radio Systems, preferably digital radio Systems, which
`are used in local applications, the coverage between a base
`Station forming part of the System and a mobile unit belong
`ing to the base Station is limited to the area of coverage of
`the base Stations. In general public radio-relay Systems, it is
`already known, through patent specification EPA2 092. 237,
`to utilize a repeating function. The repeating function
`repeats a first Sequence of downward time slots, in a first
`time frame, from the first to the Second Station as a Second
`Sequence of downward time slots, in a Second time frame.
`The repeater function also transmits a first Series of increas
`ing time slots to the first Station which answers a Second
`Series of upward time slots received from the Second Station.
`In association with mobile radio Systems belonging to this
`category with poor range in relation to the median in length
`of the radio link, a number of methods have been proposed
`for improving the coverage between the mobile units and the
`base Stations. The proposals which have been put forward
`have, however, resulted in drawbacks with delays of the
`Speech or data connections. No known technology for
`improving the range between mobile units and a base Station
`in local networks which results in high capacity, adequate
`range, Security and quality has previously existed.
`
`DESCRIPTION OF THE INVENTION
`
`TECHNICAL PROBLEM
`The modern local radio Systems of today presuppose the
`greatest possible range between the transmitter and receiver
`of the base Stations and the mobile units at the same time as
`the greatest possible consideration can be given to radio
`Systems being assigned to work in high frequency bands,
`preferably above 100 MHz, which gives a poor range in
`relation to the median attenuation of the radio link. On the
`other hand, a Small part of the radio link has very high
`attenuation. In order to obtain adequate Signal Strength, the
`low attenuation link must therefore be significantly reduced
`as the high attenuation link cannot be changed for applica
`tion reasons.
`The problem can be exemplified with the radio-based
`local network application OMA (area-limited mobile
`access). The application means that the terminated cord
`connection to the subscriber is replaced by radio. The
`telephone exchange is connected to a radio base at a Suitable
`distance from the subscriber, e.g. 500 meters. The radio base
`can connect a large number of Subscribers within the cov
`erage area. The Subscriber, whose usual cord telephone is
`replaced by one or more cordleSS telephones, is offered an
`area-limited mobility. This means that costs for maintenance
`and running cables can be minimized. This presupposes,
`however, that adequate range can be obtained. Ongoing
`testing activity has shown that this type of System gives
`OMA ranges of less than 100 meters. The explanation for
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`this relatively low range is that the Signal Strength is greatly
`damped when the radio wave is to penetrate the building or
`the ground. The invention intends to Solve these problems
`among others.
`In one embodiment of the subject of the invention, the use
`of a time multiplex protocol is utilized, in which protocol
`messages are to be capable of being transmitted in time slots
`divided in time frames in Such a manner that drawbacks with
`delays of Speech or data connections do not arise. The
`invention intends to Solve this problem also.
`In one embodiment of the subject of the invention, an
`influencing function is utilized, in which influencing func
`tion time slots are to be capable of being assigned in Such a
`manner that capacity is increased in the critical coverage
`area of the mobile system. The invention intends to solve
`this problem also.
`In one embodiment of the subject of the invention, the
`repeating function Selects which time slots can be Selected
`for the transmission in which it is engaged. This is to be
`capable of taking place in Such a manner that the mobile unit
`or the base Station can Set up direct connections. The
`invention intends to Solve this problem also.
`In one embodiment of the subject of the invention, the
`radio-based communication System works within an
`assigned frequency band, this frequency band is to be
`applied in Such a manner that it is Suited for local outdoor/
`indoor communication. The invention intends to Solve this
`problem also.
`In one embodiment of the subject of the invention,
`influences of the radio communication System are utilized,
`in which influences the traffic is to be capable of being
`controlled via the repeating function in a manner which is
`favourable and flexible for the system. The invention intends
`to solve this problem also.
`In one embodiment of the subject of the invention,
`transmission of a message in time slots put together to form
`time frames is utilized. This transmission is to be capable of
`being carried out in Such a manner that the quality of Speech
`or data connections is not made worse. The invention
`intends to Solve this problem also.
`In one embodiment of the subject of the invention, said
`repeating function is connected between the respective base
`Station and the respective mobile units, in which connection
`running cable to base Stations is to be capable of being
`avoided.
`
`SOLUTION
`It can primarily be considered to be characteristic of an
`arrangement according to the invention that a repeating
`function is effected/carried out with a simplified variant of a
`base Station. This simplified variant of a base Station is
`positioned between an ordinary base Station and the mobile
`unit. A further characteristic is that the simplified variant of
`the base Station is made in Such a manner that it receives
`each message which is transmitted from an affected base
`station or mobile unit addressed to an affected mobile unit or
`base Station and Subsequently forwards the message to the
`affected mobile unit or base station.
`In one embodiment of the inventive idea, Said repeating
`function of a message is arranged in a digital radio System
`which works in accordance with a time multiplex protocol
`which utilizes the frame structure in TDMA/TDD technol
`Ogy.
`In a further embodiment of the inventive idea, the digital
`radio-based communication System is arranged with time
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`frames divided up into a number of time slots, where half the
`time slots are used for Signalling in a downlink. The other
`half is utilized for an uplink. There, given Selected time slots
`in a respective time frame are assigned for transmitting Said
`message to or from Said repeating function.
`In a further embodiment of the inventive idea, the repeat
`ing function is arranged to influence the number of time slots
`per link in order to increase capacity within critical areas in
`the coverage area of the mobile System.
`In a further embodiment of the inventive idea, messages
`which are transmitted in the radio-based communication
`System can be transmitted from a base Station/mobile unit to
`a mobile unit/base Station without Said repeating function
`being called or activated. This means that the repeating
`function is to determine which time slots can be Selected for
`a transmission in which it is engaged.
`In a further embodiment of the inventive idea, the radio
`based communication System, base Stations and mobile units
`are assigned a frequency, a frequency area, which is Suited
`for local communication outdoors or indoors (greater than
`100 MHz).
`In a further embodiment of the inventive idea, the radio
`communication System can be influenced for reasons of
`capacity in order to make it possible for a user or customer
`to force the System, for a variable time or continuously, to
`transmit all messages between a respective ordinary base
`Station and a respective mobile unit via the repeating func
`tion.
`In a further embodiment of the inventive idea, messages
`which have been received by the repeating function are
`transmitted on to the respective affected mobile unit/
`ordinary base Station within the same time frame but trans
`mitted to the repeating function.
`In a further embodiment, the repeating function is con
`nected cordlessly between an ordinary base Station and a
`mobile unit.
`In a further embodiment of the inventive idea, said radio
`communication System is arranged with one or more mem
`bers for receving or transmitting messages. A further char
`acteristic is that the members can be called from a respective
`base station/mobile unit and that the respective members for
`receiving or transmitting a message are arranged to receive
`a message from a respective base Station/mobile unit. The
`members for receiving or transmitting a message are
`arranged to transmit said message to a respective affected
`(addressed) mobile unit/base Station.
`ADVANTAGES
`By means of what is proposed above, an effective radio
`based local communication System can be established, in
`which a respective mobile unit can move within a larger
`coverage area at the same time as consideration is given to
`the communication System being assigned a frequency
`greater than 100 MHZ, which gives a poor range in relation
`to the median attenutation of the radio link. It should be
`easier/cheaper to cover larger areas as the range of the
`digitally based radio System can be increased greatly. Sub
`Scribers utilizing mobile units in the System obtain greater
`Surface coverage. The arrangement is specially Suited in
`applications when the full capacity of the Systems is not
`required. A typical example of this is DECT (Digital Euro
`pean Cordless Telecommunication) in a local network (often
`called Cordless Local Loop), where the range Sometimes can
`be required to be improved and where covered capacity is
`much greater than what is required.
`DESCRIPTION OF THE FIGURES
`A for the present proposed embodiment of an arrangement
`which has the characteristics which are significant of the
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`invention is to be described below with simultaneous refer
`ence to the attached drawings, in which
`FIG. 1 shows in block diagram form a preferred embodi
`ment of the invention.
`FIG. 2 shows in block diagram form a time frame
`Structure for transmitting messages in a TDMA System.
`FUNCTIONING EMBODIMENT
`In FIG. 1, a mobile telecommunication System comprising
`on the one hand a number of base Stations, one is here
`indicated as 1, working with coverage areas, which are
`indicated as la, and on the other hand one or more mobile
`units, one is here indicated as 2. The mobile communication
`system works with frequencies above 100 MHz and there
`fore has poor range in relation to the median attenuation of
`the radio link. A large part of the radio link has low
`attenuation. On the other hand, a Small part of the radio link
`has very high attenuation. The mobile communication Sys
`tem can be constituted by a System known per Se working
`with a TDMA structure, e.g. DECT, DCS 1800 and DCT
`900. The system which is shown in the figure is a typical
`DECT (Digital European Cordless Telecommuincation in a
`local network), (often called Cordless Local Loop), where
`the range may Sometimes need to be improved, and where
`the capacity of DECT is much greater than is required. The
`base Station 1 shown in the figure is connected, via an
`eXchange-connected connection, to a telephone exchange 4.
`The telephone exchange 4 is a Subscriber exchange (often
`called PABX) connected to the general telephone network 5.
`Conversations/calls to a mobile unit 2 Sought in the System
`come in via the general telephone network 5 and are
`connected to the telephone exchange 4. From the telephone
`eXchange 4, a Search call goes out to the base is Station 1 Via
`the connection of the exchange connection 3. The base
`Station 1 is provided with a transmitting and receiving
`member 6. The information-transmitting and receiving
`member 6 of the base station 1 transmits calls to the mobile
`unit 2 Sought. The mobile unit 2 Sought lies outside the
`coverage area la of the affected base Station 1 and cannot
`therefore directly receive/detect Said calls. A repeating func
`tion 7 is positioned within the coverage area la of the
`affected mobile unit 1 and perceives Said calls. The repeating
`function 7 is in principle a simplified base station 1. The
`repeating function 7 repeats the call/the message which is
`transmitted from the base station 1 on to the affected mobile
`unit which lies outside the coverage area la of the affected
`base Station 1. Repeating of the call/the message takes place
`within the same time frame as the affected base station 1
`transmits the call/the message. In the same manner, the
`repeating function 7 carries out reception and transmission
`of information from the mobile unit 2 on to the transmitting
`and receiving function 6 of the affected base station 1. The
`repeating function 7 does not need to carry out encoding/
`decoding. The transmission of the repeating function 7 takes
`place in four parts of a time frame in the following time
`Sequence: base Station 1 to repeating function 7, repeating
`function 7 to mobile unit 2, mobile unit 2 to repeating
`function 7, repeating function 7 to base station 1. It is the
`repeating function 7 which determines which time slots are
`to be selected for a transmission in which it is engaged. This
`means that it can e.g. be possible for a mobile unit 2 to create
`a direct connection (without the repeating function 7) to the
`transmitting and receiving member 6 of the base Station 1.
`The mobile unit 2 and the base station 1 do not need to be
`modified in order to work with the repeating function,
`provided that they can listen to and follow the desires of the
`repeating function about which time slots are permitted.
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`For reasons of capacity, it may be an advantage also to
`implement given Software in the mobile unit 2 or base
`Station 1, which makes it possible for the user (the operator
`or the customer) to force (where appropriate temporarily)
`the System to utilize the repeating function 7. This means
`that calls on prohibited time slots can be prevented. In the
`event that no extra Software is installed in the mobile unit 2
`or the base Station 1, the repeating function 7 is forced to
`inform the calling mobile unit 2 or base station 1 that another
`time slot is to be used when the repeating function 7
`determines that a communication range between the mobile
`unit 2 and the base Station 1 is too great to reliably close the
`link without using the repeating function 7. The use by the
`repeating function 7 of time slots in the time frames
`increases the range of the System at the cost of a reduced
`total capacity in the network. This is of particular interest as
`far as the introduction of new systems (e.g. DCS 1800,
`DECT etc.) is concerned, where one of the initial problems
`is to keep adequate range.
`In FIG. 2, a preferred TDMA time frame is shown. The
`number of time slots 8 has been selected as 16 (DCT900).
`The time frame is divided into four units 9, 10, 11 and 12.
`Each part of the time frame 9, 10, 11 and 12 contains four
`time slots 8. The first part of the time frame 9 is used for
`transmitting information/messages from the base Station to
`the repeating function. The second part of the time frame 10
`is used for transmitting information/messages from the
`repeating function to the mobile unit. The third part of the
`time frame 11 is used for transmitting information from the
`mobile unit to the repeating function. The fourth part of the
`time frame 12 is used for transmitting information from the
`repeating function to the base Station. The division of the
`time slots 8 in the frame is always to follow the principle in
`the figure. However, the number of time slots 8 per part 9,
`10, 11 and 12 can be selected differently in order in such a
`manner to increase the capacity in critical parts in the mobile
`communication System. For radio-based local network
`applications which are area-limited, transmission from the
`base Station to the repeating function or from the repeating
`function to the base station is the critical part. The TDMA
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`time frame can therefore be divided with regard to this. The
`number of time slots 8 in the time frame can also vary, e.g.
`the mobile communication system DECT can be mentioned
`which has twenty four time slots.
`The Simplified base Station does not need to carry out any
`encoding/decoding of messages from base Station to user
`unit and Vice versa apart from, in case of need, being capable
`of reading or making Small changes to the control field of the
`meSSage.
`Messages which have been received by Said repeating
`function are transmitted on to the respective affected user
`unit/mobile unit/ordinary base station within the same or the
`next time frame as it is transmitted to Said repeating func
`tion. Repeating in the next time frame may, however, only
`take place in one direction, i.e. repeating within the same
`time frame is always to take place towards the user unit
`and/or towards an ordinary base Station.
`The mobile unit can be constituted by a user unit of
`different type to the mobile unit.
`The invention is not limited to the embodiment shown
`above as an example but can be Subjected to modifications
`within the Scope of the following patent claims and the
`inventive idea.
`I claim:
`1. A radio frequency communication System comprising:
`a base Station coupled to a public Switched telephone
`network;
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`a mobile Station configured to communicate with the base
`Station over a wireless two-way communication link
`that operates at frequencies of 100 MHZ or greater; and
`a repeater positioned between Said base Station and Said
`mobile Station, wherein
`Said repeater configured to relay messages between the
`base Station and Said mobile Station without performing
`an encoding/decoding function on non-control field
`portions of Said messages,
`Said wireless two-way communication link using a time
`division multiple access, TDMA, protocol where each
`Segment of Said wireless two-way communication link
`being assigned to Separate parts of a TDMA frame, and
`at least one TDMA time slot within each separate part
`of the TDMA frame hosting at least a portion of said
`non-control field portions of at least one of Said
`meSSages,
`Said repeater being configured to assign, for either con
`tinuous operation or time varying operation, one of the
`Separate parts for relaying Said message in a first
`direction and another of the Separate parts for forward
`ing a reply message in a reverse direction, where Said
`assignment being based on an available traffic capacity
`of a communication coverage area that includes the
`base Station and mobile Station,
`Said repeater configured to relay the message in the first
`direction within a same TDMA frame or in a next
`TDMA frame so as to complete the wireless two-way
`communication link between the base Station and the
`mobile Station, and
`widths of the separate parts of the TDMA frame being
`Substantially equivalent.
`2. The system of claim 1, wherein:
`a first set of contiguous time slots hold the message when
`Sent in the first direction from the base Station to a
`mobile Station and another Set of contiguous time slots
`hold a reply message Sent from the mobile Station to the
`base Station.
`3. The system of claim 1, wherein:
`Said repeater being configured to assign said at least one
`TDMA time slot based on an available traffic capacity
`of traffic handled by said repeater.
`4. The system of claim 1, wherein:
`Said repeater being configured to relay all messages
`between Said base Station and Said mobile Station, and
`all reply messages from Said mobile Station to Said base
`Station.
`5. The system of claim 1, wherein:
`Said repeater is configured to assign the at least one
`TDMA time slot for holding the message when sent in
`the first direction in a Same frame as a reply message
`Sent from the mobile Station to the repeater.
`6. The system of claim 1, wherein:
`Said repeater being arranged to be called to perform the
`repeating operation by at least one of Said base Station
`and Said mobile Station Such that Said repeater performs
`a repeating operation So as to relay the message
`between the base station and the mobile station.
`7. The system of claim 2, wherein:
`Said repeater being configured to assign said at least one
`TDMA time slot based on an available traffic capacity
`of traffic handled by said repeater.
`8. The system of claim 2, wherein:
`Said repeater being configured to relay all messages
`between Said base Station and Said mobile Station, and
`all reply messages from Said mobile Station to Said base
`Station.
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`9. The system of claim 3, wherein:
`Said repeater being configured to relay all messages
`between Said base Station and Said mobile Station, and
`all reply messages from Said mobile Station to Said base
`Station.
`10. The system of claim 2, wherein:
`Said repeater is configured to assign the at least one
`TDMA time slot for holding the message when sent in
`the first direction in a Same frame as a reply message
`Sent from the mobile Station to the repeater.
`11. The system of claim 3, wherein:
`Said repeater is configured to assign the at least one
`TDMA time slot for holding the message when sent in
`the first direction in a Same frame as a reply message
`Sent from the mobile Station to the repeater.
`12. The system of claim 4, wherein:
`Said repeater is configured to assign the at least one
`TDMA time slot for holding the message when sent in
`the first direction in a Same frame as a reply message
`Sent from the mobile Station to the repeater.
`13. The system of claim 2, wherein:
`Said repeater being arranged to be called to perform the
`repeating operation by at least one of Said base Station
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`and Said mobile Station Such that Said repeater performs
`a repeating operation So as to relay the message
`between the base station and the mobile station.
`14. The system of claim 3, wherein:
`Said repeater being arranged to be called to perform the
`repeating operation by at least one of Said base Station
`and Said mobile Station Such that Said repeater performs
`a repeating operation So as to relay the message
`between the base station and the mobile station.
`15. The system of claim 4, wherein:
`Said repeater being arranged to be called to perform the
`repeating operation by at least one of Said base Station
`and Said mobile Station Such that Said repeater performs
`a repeating operation So as to relay the message
`between the base station and the mobile station.
`16. The system of claim 5, wherein:
`Said repeater being arranged to be called to perform the
`repeating operation by at least one of Said base Station
`and Said mobile Station Such that Said repeater performs
`a repeating operation So as to relay the message
`between the base station and the mobile station.
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