PCT
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`
`International Bureau
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`
`W0 89/ 08355 (51) International Patent Classification 4 :
`(11) International Publication Number:
`
`H04B 7/26, H04H 3/00
`(43) International Publication Date: 8 September I989 (O8.09.89)
`
`
`
`PCT/SE89/00049
`
`(81) Designated States: AU, DK, FI, JP, NO.
`
`(21) International Application Number:
`
`
`3 February 1989 (os.o2.s9)
` (22) International Filing Date: Published
`
`With international search report.
`
`(31) Priority Application Number:
`8800698-6
`(32) Priority Date:
`29 February 1988 (29.02.88)
`
`SE
`(33) Priority Country:
`
`
`icant: TELEFONAKTIEBOLAGET LM ERICS-
`N [SE/SE]: S-126 25 Stockholm (SE).
`
`P5
`
`(71) A pl
`0
`
`
`
`
`
`(72) Inventors: RAITH, Alex, Krister ; Sorogatan 19, S-164
`41 Kista (SE). UDDENFELDT, Jan, Erik ; Back-
`timjegrand 19, S-162 41 Vallingby (SE).
`
`
`
`(74) Agents: LOVGREN, Tage et a1.; Telefonaktiebolaget
`LM Ericsson, S-126 25 Stockholm (SE).
`
`
`
`(54) Title: CELLULAR DIGITAL MOBILE RADIO SYSTEM WITH PLURAL BASE STATION TRANSMITTERS -
`AND METHOD OF TRANSMITTING INFORMATION IN SUCH A SYSTEM
`7
`
`
`
`
`
`.
`
`(57) Abstract
` The invention relates to a cellular digital mobile radio sys-
`
`
`tem including base stations (Bm, B") and mobile stations (MS,,
`MS3) with transmitters and receivers. The invention also relates
`to a method of transmitting message information digitally be-
`tween mobile and base stations in such a system. In accordance
`with the invention, at least two base station transmitters (Em,
`
`Bm, BM, Bub) at a given transmitting distance from each other
`
`are assigned to each of certain cells (Cm, Cn) within a restricted
`
`geographical area. The base station transmitters which are as-
`
`signed to the same cell transmit digitally modulated radio sig-
`
`nals within the same frequency range at least partially simul-
`
`taneously to the mobile stations of the cell. The radio signals
`
`from different base station transmitters associated with the same
`
`cell are digitally modulated with the same message information
`
`to the mobile stations in the cell. Different base station transmit-
`ters (9A, 9B) preferably transmit the digitally modulated radio
`
`signals with the same message information to a given mobile sta-
`
`tion with a given mutual transmission time shift. Here, the trans-
`
`mission time shift is selected individually for each mobile sta-
`
`tion, such that corresponding digitally modulated radio signals
`
`with the same message information to a given mobile station
`
`from different base station transmitters arrive practically simul-
`
`taneously at the mobile station.
`
`.1
`
`
`
`Petitioners, Ex. 1014, Page 1
`
`
`
`Petitioners, Ex. 1014, Page 1
`
`

`
`FOR IHE PURPOSES OF HVFORMAHON ONLY
`
`Codes used to identify States party to thel’CT onthe front pages ofpamphlets pubfishing internationalappli-
`cations under the PCT.
`
`AT Austria
`AU Australia
`BB Barbados
`BE Belgium
`BG Bulgaria
`BJ
`Benin
`BR Brazil
`CF Central African Republic
`CG Congo
`CH Switzerland —
`CM Cameroon
`DE Germany, Federal Republic of
`DK Denmark
`FI
`Finland
`
`,
`
`France
`Gabon
`United Kingdom
`Hungary
`Italy
`Japan
`Democratic People’s Republic
`of Korea
`Republic ofKorea
`Liechtenstein
`Sti Lenka
`Luxembourg
`Monaco
`Madagascar
`
`ML Mali
`MR Mauritania
`MW Malawi
`NL Netherlands
`NO Norway
`R0 Romania
`SD Sudan
`SE
`Sweden
`SN Senegal
`SU Soviet Union
`TD Cliad
`TG Togo
`US United States of Americ_a.
`
`Petitioners, Ex. 1014, Page 2
`
`

`
`wo 89/08355
`
`PCT/SE89/00049
`
`1
`
`Cellular digital mobile radio system with plural
`base station transmitters and method of transmitting
`information in such a system
`
`TECHNICAL FIELD
`
`The present
`
`invention relates to mobile radio systems. More specifically the
`
`invention relates to a digital, cellular, mobile radio system. The invention also
`
`relates to a method of transmitting information digitally to and from mobile
`
`stations in a cellular mobile radio system.
`
`BACKGROUND ART
`
`The mobile radio systems that were first
`
`taken into common use were of
`
`analogue type,
`
`i.e. message information was transmitted in analogue form to
`
`and from mobile stations by transmitting and receiving analouge-modulated
`radio signals. In such systems it
`is known to have two or more base station
`
`transmitters at a distance from each other simultaneously transmitting radio
`
`signals within the same frequency range-and modulated with the same message
`
`information to the mobile stations. Such mobile radio systems are described in
`
`EP 0040731 and EP 0072479, as well as in the two publications: NTG-
`
`Fachberichte, Bewegliche Funkdienste, Vortréige der NTG-Fachtagung vorn 25.
`
`bis 27 November in Munich, "GLEICHKANALFUNKSYSTEME FUR DIE FRE-
`
`QUENZUKONISCHE VERSORGUNG GROSSER GEBIETE" Berndt Heynisch pp
`
`41-46, VDE-VERLAG GmbH, Berlin, Elektrizitéitswirtschaft, Jg. 8D(l98l), Heft
`6, pp 187-198 "C~)uasissynch1-oner Gleichwellenfunk-ein Gleichkanalfunk-Ver-
`fahren zur Erhbhung der Erreichbarkeit in Mobilfunknetzen.
`
`In known systems of the kind in question here, it is known to transmit message
`
`information from a central station or exchange to the base station transmitters
`
`either via cables or radio signals. It is also known to have equalisers in the fixed
`
`part of the mobile radio system for equalising differences in propagation time
`
`and attenuation in transmission from the exchange to the base station trans-
`
`rnitters. The equalisers can be at
`
`the exchange and/or at
`
`the base station
`
`transmitters. The object of the equalisers is
`
`that irrespective of position in
`
`relation to the exchange the base station transmitters shall transmit the radio
`
`signals simultaneously, and modulated with the same message information.
`
`Petitioners, Ex. 1014, Page 3
`
`

`
`wo 89/08355
`
`PCVSE39/°“°"9°
`
`2
`
`Digital mobile radio systems in which message information is 5transmitted.
`
`digitally to and from mobile stations by transmission and reception of digitally 9
`
`modulatedr signals have been proposed in US 4675863 and "Digital Mobile
`
`Telephone System Using TD/FDMA Scheme", Kota Kinoshita, Masaharu Hata
`
`and Kenkichi Hirade, IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY,
`
`VOL. VT’-31, NO.4, NOVEMBER 1982, pp 153-157.
`
`It has been proposed to have adaptive equalisers in mobile radio stations in
`
`digital radio systems, whereby multi-path propagation of radio signals can be
`
`used to improve signal quality, instead of the multipath propagation acting as
`
`noise. Among the publications on adaptive equalisers in digital mobile radio
`
`systems can be mentioned: "Multi—path Equalization for Digital Cellular Radio
`
`Operation at 300 k. bit/s". K Raith, J~E Sjternvall and J Uddenfeldt, 36th IEEE
`
`Vehicular Technology Conference, pp 268-272, Dallas, Texas, USA May 1986.
`
`"Radio Test Performance of a Narrowband TDMA System", J-E Stjernvall, B.
`
`Hedberg, and S Ekmark, IEEE Vehicular Conference, Tampa, Florida, USA, June
`
`1987, RADIO TEST PERFORMANCE OF A NARROWBAND TDMA SYSTEM-
`
`DMS 90, .]-E Stjervall, B. Hedberg, K Raith, T Béickstrbm and R Lofdahl.
`
`DISCLOSURE OF INVENTION
`
`In mobile radio systems there are problems due to reflections and radio shadows
`
`from natural obstacles such as rocks and hills, as well as structures such as
`
`buildings. These problems are especially troublesome in transmitting informa-
`
`tion requiring great accessibility/reliability and high transmission speed.
`
`In
`
`particular the problems may become large in certain urban environments where
`
`the propagation conditions for radio signals can vary heavily within a small
`
`geographic area, while radio traffic is intensive at the same time. Up to now
`
`attempts have been made to solve these problems by having adaptive equalisers
`
`in the mobile stations and small cells with specially selected positioning of the
`
`base station transmitters. In areas with much traffic it is, however, a desire to
`
`be able to select the size of the cells and their positions in the mobile radio
`
`system cell plan in an optimum way with respect
`
`to the traffic handling
`
`capacity of the system. Reducing the cell size and selecting the positions of the
`
`small cells to avoid radio shadows thus involves a complication. Another
`
`complication resulting from the reduction of cell size to below what
`
`is
`
`necessary for reasons of capacity is that the number of handovers increases.
`
`Petitioners, Ex. 1014, Page 4
`
`

`
`WO 89/08355
`
`PCT/SE89/00049
`
`3
`
`The object of the invention is to solve the above-mentioned problems and
`
`complications, and to provide a method and a cellular digital mobile radio
`
`system which are also suitable for transmitting information requiring great
`
`accessibility/reliability and high transmission speed.
`
`What is distinguishing for a method and a digital cellular mobile radio system in
`
`accordance with the invention, and particularly preferred embodiments thereof
`
`is disclosed in the independent and dependent claims. Somewhat simplified, it
`
`may be said that according to the invention there are utilised at least two base
`
`station transmitters for each of a plurality of cells, these transmitters being at
`
`a distance from each other and at least partially simultaneously transmitting
`
`radio signals within the same frequency range digitally modulated with the
`
`same message information to the mobile stations in the cell. The digital
`
`modulation is changed with a modulation time interval which is adapted to the
`
`greatest transmitting distance between two base station transmitters serving
`
`the same cell
`
`in an area. The mobile stations have adaptive equalizers for
`
`reconstructing the digital modulation in the transmitted signals from the signals
`
`received during a reception time interval, which is also adapted to the greatest
`
`transmitting distance between two base station transmitters serving the same
`cell in an area.
`
`In a preferred embodiment of a method in accordance with the invention, the
`
`digitally modulated signals are transmitted with the same message information
`
`to a given mobile station with a given, mutual transmission time shift from the
`different base stations. The transmission shift
`is then selected such that
`it
`
`counteracts the difference in arrival time for the signals from the different
`
`base station transmitters to this mobile station.
`
`In each mobile station,
`
`there is preferably estimated the arrival timezshift
`
`between the digitally modulated radio signals with the same message informa-
`
`tion from'
`
`the different base station transmitters.
`
`Information about
`
`the
`
`estimated arrival time shift at the respective mobile station is transmitted
`from there to at least one base station transmitter. This estimated arrival time
`
`shift is utilised at the base station for selecting the transmission time shift for
`at least one base station transmitter. A transmission time shift is thus obtained
`
`individually for each affected mobile station, and which is adjusted for this
`
`Petitioners, Ex. 1014, Page 5
`
`

`
`A
`
`particular mobile stations's position in relation to the base station transmitters:
`
`The amount of tranmissions time shift can thus vary from mobile stat~ion:toE”
`mobile station.
`
`According a somewhat different, preferred embodiment, there is estimated in
`
`different base station receivers the reception time shift between corresponding
`
`radio signals with the same message information from the mobile station. This
`
`estimated reception time shift is utilised for selecting the transmission time
`
`shift between corresponding base station transmitters. A transmission time
`
`shift can thus be individually obtained for each affected mobile station such
`
`that it is adjusted to the position of this particular mobile station in relation to
`the base station transmitters. The amount of transmission time shift can thus
`
`vary from mobile station to mobile station.
`
`A preferred embodiment of a mobile radio system in accordance with the
`
`invention has time measurement means for estimating the mutual reception
`
`time shift in a mobile statioin between, on one hand, digitally modulated radio
`
`signals transmitted to the mobile station via a base station transmitter for the
`
`cell where this mobile station is, and, on the other hand, corresponding digitally
`
`modulated signals transmitted to this station via another base station trans-
`
`mitter for the cell.
`
`In this embodiment
`
`the mobile radio system has trans-
`
`mission time shifting means for mutually time shifting the transmission times
`
`for base station transmitters of the same call so that they transmit correspon-
`
`ding digitally modulated signals to the mobile station with greater or less
`
`mutual transmission time shifting in response to estimated reception time shift.
`
`The time measurement means preferably include arrival time comparison means
`
`in at
`
`least certain mobile stations,
`
`for comparing the arrival
`
`times for
`
`corresponding digitally modulated signals transmitted from different base-
`station transmitters for the same cell.
`
`According to a somewhat different, preferred emdiment, the time measurement
`
`means include arrival time comparison means in the stationary part of the
`
`mobile radio system, for comparing the arrival times of digitally modulated
`
`signals transmitted from a mobile station in a cell and received at different
`base station transceivers of the cell.
`
`Petitioners, Ex. 1014, Page 6
`
`

`
`WO 89/08355
`
`PCT[SE89/00049
`
`5
`
`A method and as cellular digital mobile radio system in accordance with the
`
`invention provide substantial advantages. The coverage degree can be made
`
`greater, signifying better opportunities for establishing new connections and
`
`maintaining those already established. The coverage degree can be made
`
`greater without the cell size needing to be reduced, which give greater freedom
`
`in the selection of cell plan and a lesser number of handovers. In preferred
`
`embodiments, the transmission time shift, which is individually selectable for
`
`each mobile station, reduces the risk of noise and interruption of calls in
`
`progress, when a mobile station goes from receiving signals chiefly from one
`
`base station transmitter to receiving signals chiefly from another base station
`
`transmitter. when a mobile station simultaneously receives signals from at
`
`least two base station transmitters of the same cell, the variable transmission
`
`time shift enables the received signals together to be more like the signals
`
`obtained from a single base station transmitter in conjunction with reflections.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`Figure 1 illustrates cells and positioning of transmitters in base stations in one
`
`embodiment of a mobile radio system in accordance with the invention.
`
`Figure 2 illustrates parts of a mobile radio system in accordance with the
`invention.
`
`BEST MODES FOR CARRYING OUT THE INVENTION
`
`A cellular mobile radio system in accordance with the invention has mobile
`
`stations and base stations with transmitters and receivers for radio signals.
`
`Message information is transmitted digitally to and from the mobile stations by
`
`transmission and reception of signals digitally modulated in correspondence
`
`with the message information. The radio signals are transmitted on one of a
`
`plurality of radio channels. Signals can be transmitted in time multiple to and
`from several mobile stations on the same radio channel.
`
`The mobile stations move within and between the cells of the system. The base
`
`station transmitters are assigned to the cells so that there is at least one base
`
`station transmitter for each cell, for transmitting signals to the cell's mobile
`stations.
`
`Petitioners, Ex. 1014, Page 7
`
`

`
`W0 89]08355
`
`PCT/SE89[00049i -
`
`6
`
`Somewhat simplified, there is illustrated in Figure 1 the division of an area into,
`
`cells and the assignation of base station transmitters to the cells inia‘ mobile
`
`telephone system in accordance with the invention. For the sake of simplicity in
`
`Figure 1, all cells CI to C24 are illustrated as regularrhexagones with sides‘ L.
`
`In practice, the cells will probably have different sizes and shapes. In addition,
`
`depending on service conditions, it will often be suitable with overlapping in the
`
`boundary areas between the cells. To a certain extent,
`
`the base station
`
`transmitter can then off—load each other by handling transmission to mobile
`
`stations where such transmission should from a purely geographically point" of
`
`view be performed by the base stations of a contiguous cell.
`
`For each cell Cl-C24 there is an ordinary base station transmitter BS1-B524.
`
`For contiguous cells these transmitters are conventionally colocated in groups
`
`of three. For example, the base station transmitter BS1 for the cell C1 is co-
`located with the base station transmitter BS3 for the cell C3 and the base
`
`the base station
`the cell C5. Correspondingly,
`station transmitter BS5 for
`transmitter B514 for the cell C14 is co-located with the base station trans-
`
`mitter BS16 for the cell C16 and with the base station transmitter B518 for the
`
`cell C18. These co-positioned ordinary base station transmitters are situated in
`
`the boundary areas between the cells to which they are assigned. For example,
`
`the ordinary base station transmitters B52, B54 and B56 are co-located in the
`
`boundary areas between the cells C2, C4 and C6.
`
`Further to the ordinary base station transmitters BS1-BS2-4 the system includes
`
`a number of extra base station transmitters for certain of the cells. Cells C6,
`
`C7, C10, C11, C13, C14, C19 and C20 each has one extra base station
`
`transmitter. For each of the cells C15, C18 and C22 there are two extra base
`
`station transmitters. The extra base station transmitters X56, X57, X510, X511,
`
`X513, XSl5A, XS15B, XS18A, XSl8B, X519, X520 and XS22A are co-located in
`
`groups with three extra base station transmitters in each group in a similar
`
`manner as the ordinary base station transmitters. Accordingly, for example, the
`
`extra base station transmitter XS18B for the cell C15 is co-located with the
`
`extra base station transmitter X519 for the cell C19 and the extra base station
`
`transmitter XS1BA for the cell C18. On the other hand, neither the extra base
`station transmitter X514 for the cell C14 nor the extra base station transmitter
`
`XSZZB for the cell C22 are co-located with any other base station transmitter,
`
`Petitioners, Ex. 1014, Page 8
`
`

`
`WO 89/08355
`
`PCT/SE89/00049
`
`7
`
`but are situated approximately at the centre of the cell with which they are
`associated.
`
`An extra base station transmitter does not need to differ technically from an
`
`ordinary base station transmitter. For a given cell am extra base station
`
`transmitter can thus have technical equipment of the same type as an ordinary
`
`base station transmitter for the same cell. In principle it can also function in
`
`the same way as the ordinary one. If there are two identical base station
`
`transmitters for a given cell,
`
`in certain cases either of
`
`them may be
`
`respectively regarded as ordinary or extra.
`
`The extra base station transmitter or transmitters for a given cell transmit
`
`radio signals which are substantially the same as those sent by the ordinary base
`
`station transmitter of the cell. The radio signals are digitally modulated with
`
`digital message information to the mobile stations in the cell. A mobile station
`in a cell for which there is one or more extra base station transmitter can
`
`therefore receive, at least in certain cases, corresponding radio signals from
`
`more than one base station transmitter approximately simultaneously within the
`
`same frequency range (radio channel). Depending on the mutual,
`
`relative
`
`positions in the cell of the mobile and base stations as well as the transmission
`
`times and propagation paths of
`
`the radio signals from the base station
`
`transmitters to the mobile stations, corresponding radio signals from different
`
`base station transmitter can be received without, or with a given time shift at
`
`the mobile station. The greater
`
`is
`
`the distance between the base station
`
`transmitters associated with the cell, the greater in general can be the time
`
`shift. When the ordinary base station transmitters and the extra base station
`
`transmitters are situated according to Figure 1, the distance between two base
`
`station transmitters for the same cell varies between L and 2L, i.e. between the
`
`side and diameter of the regular hexagones. If, for the sake of simplicity,
`
`reflections are ignored and the assumption made that the transmitters transmit
`
`without mutual time shifting,
`
`the time reception shift at the mobile station
`
`could then attain a maximum of 2L/c, where c is the propagation speed of the
`
`radio signals. C is approximately 300000 km/s.
`
`In Figure 2 there are illustrated parts of a mobile radio system in accordance
`
`with the invention. A mobile radio exchange MSC is connected via cables L1,
`
`Petitioners, Ex. 1014, Page 9
`
`

`
`wo 39/03355
`
`PCT/SE39/“"049 '
`
`8
`
`L2,....Lm, Ln to a- plurality of basestations, of which two,1B
`illustrated in the Figure.
`
`m
`
`and. B6 are’
`
`and,-.Lmb.’to
`The base station Bm has a central unit connected via cables L
`me
`two transceiver units B
`and Bmb situated at a distance from the central unit;
`The central unit of the base station Bm includes a central line and control unit
`1, transmission time shifting means 2A and 2B, one for each of the transceivers,
`
`ma
`
`A
`
`reception time shifting means 3A and 3B, one for each of the transceivers and
`
`line units 4A and 4B, one for each of the transceivers.
`
`Both transceivers in the base station Bm are alike. Each such transceiver
`contains a line and control unit 5A or 58, transmitter means 6A or 6B, receiver
`
`means 7A or 7B, a transmission-reception filter BA or 8B and an antenna 9A or
`9B.
`
`5
`The base station Bn differs partly from station Bm primarily due to its central
`line and control unit 10 being situated in connection with one of its transceivers
`
`Bna. Accordingly, no cable with associated line units corresponding to Lm, Lmb,
`4A-SB is needed for the transceiver Bna, but only to the other transceiver Bnb.
`In addition, no transmission or reception time shifting means are included in any
`
`the corresponding means 2A, 2B, 3A and 3B are
`in B“, but
`central unit
`respectively included in transceivers Bna and Bnb.
`
`The mobile stations M51 and M52 are mutually alike. Each mobile station
`includes sound sensing means 11, encoding means 12, transmitting means 13,
`
`transmit-receive switch 14, reception means 15, equaliser and decoding means
`
`16, sound reproducing means 17, control means 18 and means 19 for feeding in
`
`our out or presentation of digital information.
`
`Apart from the base stations having two transceiver units at a distance from
`
`each other, and having controllable transmision and reception time shifting
`
`means, the mobile radio system in Figure 2 functions in most respects in a way
`
`well-known in cellular mobile radio systems. No complete description of how
`
`the system functions in different respects should therefore be necessary for one
`
`skilled in the art, and it should only be necessary to describe what is unique or
`
`unusual
`
`in the cellular mobile radio system according to Figure 2. One not
`
`Petitioners, Ex. 1014, Page 10
`
`

`
`wo 89/08355
`
`PCT/SE89/00049
`
`9
`
`skilled in the art of cellular mobile radio systems is referred to the technical
`
`litterature and to the publications mentioned under the section "Background
`Art".
`
`Message information that
`
`the mobile radio exchange forwards to a mobile
`
`is transmitted from the mobile
`station in the cell Cm, e.g. the station M51,
`radio exchange via the cable Lm to the line and control unit 1. From the line
`and control unit 1
`the information is transferred via the transmission time
`
`shifting means 2A, line unit 4A, cable Lma and line and control unit 5A to the
`transmitting means 6A. The transmitting means transmits via the transmission
`
`reception filter 8A and antenna 9A radio signals with digital modulation in
`
`correspondence with the message information from the mobile radio exchange.
`
`The message information from the mobile radio exchange is also transferred
`
`from the line and control unit 1 via the transmission time shifting means 2B,
`
`line unit 4B, cable Lmb and line and control unit SB to the transmission means
`6B in the transceiver Bmb. The transmission means 6B transmits via the
`transmission reception filter BB and antenna 98 radio signals with digital
`
`modulation in correspondence with the information from the mobile radio
`
`exchange.
`
`Depending on the delay in transferring the message information to the
`
`transmission means 6A and the corresponding delay in transferring to the
`
`transmission means 6B the radio signals can be transmitted from the antenna
`
`time shifting, or time
`9A of the transceiver unit Bma substantially without
`shifted in relation to the transmission of corresponding radio signals from the
`
`antenna 9B of the other transceiver Bmb.
`
`The signals from the antenna 9A i Elma arrive at a given mobile station in the
`can Cm, e_g_ the mobile station M51, with or without time shift in relation to
`corresponding radio signals from the antenna 9B in Bmb. The possible time shift
`on arrival at the mobile station depends partly on possible time shifting at
`
`transmission from the antennas and partly on possible difference in propagation
`
`time for the radio waves from the antennas. The transmission time shifting
`
`means 2A and 2B have a variable delay and can be controlled by the line and
`
`control unit 1, such that the radio signals are transmitted from the antenna 9A
`
`Petitioners, Ex. 1014, Pae 11
`
`Petitioners, Ex. 1014, Page 11
`
`

`
`10
`
`in Bma time-shifted more or less before or after corresponding‘ radioésignals
`from the antenna 9B in Bm'b. In the preferred embodiment according to,Figure’- '
`2,
`the line and control unit 1 controls the varialbe delays in the transmission»
`
`time shifting means 2A and 2B so that the differences -in:,delay in the cables’
`
`Lma and Lmb as well as the differences in the radio signal propagationtimes‘
`are counteracted. This may also be expressed by saying thatthe line and control
`
`:
`
`;.
`
`unit controls the variables delays in the transmission time shifting‘ means 2A
`
`and 2B, such that the time shift of the radio waves on arrival at the mobile
`
`station is decreased compared if the means 2A and 2B had the same fixed delay.
`
`It could be thought that the ideal case were that the line and control unit
`
`controlled the delays in the time shifting means 2A and 2B so that the digitally
`
`modulated radio signals transmitted from the antenna in Bma arrived at the
`antenna in M81, exactly simultaneously and in phase with corresponding radio
`signals transmitted from the antenna in Bmb. In practice, this is neither striven
`for nor achieved. Reflections occur in the propagation of the radio signals
`
`between the antennas, and the mobile station has an adaptive equaliser. It is
`
`therefore not necessary for the signals from the different transceiver units to
`
`arrive exactly simultaneously to the mobile station. On the contrary, there is
`
`preferably sought a small
`
`time shift
`
`to achieve diversity against Rayleigh
`
`fading. One not skilled in this art and who is desirious of obtaining further
`
`information can find it in the publications mentioned in the section "Background
`
`Art", e.g. "Radio Test Performance of a Narrow-band TDMA System-DMS 90".
`
`In principle, there are at least two conceivable methods of determining how the
`
`line and control unit 1 may control the delay in the transmission time shifting
`
`means 2A and 2B. One method is to estimate in the fixed part of the mobile ~
`
`radio system. the time shift between the mobile station radio signals at one of
`
`the transceivers Bma and the corresponding radio signals at the other trans-
`ceiver Bmb. There is
`thus obtained an estimation of
`the differences in
`propagation time to the mobile station,
`these differences depending on the
`
`position of the mobile station. Remaining differences in delay are related to the
`
`fixed part of the mobile radio system, e.g. differences in length of the cables
`
`Lma and Lmb and are not dependent on the position of the mobile station. In
`the embodiment according to Figure 2, this method can be applied in practice
`
`such that the delays in the reception time shifting means 3A and 3B are
`
`adjusted so that
`
`information received from the mobile station M51 at Bma
`
`Petitioners, Ex. 1014, Pae 12
`
`Petitioners, Ex. 1014, Page 12
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`

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`wo 89/08355
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`PCT/SE89/00049
`
`ll
`
`arrives at the line and control unit 1 simultaneously as corresponding informa-
`
`tion received at Bmb from the mobile station MS1 arrives at the line and
`control unit 1. The delays in the transmission time shifting means 2A and 2B are
`
`subsequently adjusted in correspondence with the optimum delays
`
`in the
`
`reception time shifting means 3A and 3B.
`
`The other method is to estimate in the mobile station the difference in arrival
`
`time or
`
`time shift between the digitally modulated radio signals from one
`
`transceiver Bma and the corresponding digitally mobile radio signals from the
`other transceiver Bmb. Some kind of encoding of the radio signals is required
`for this, which indicates from which transceiver they are transmitted. In TDMA
`
`systems it
`
`is known to transmit special synchronising words. These can be
`
`utilised if they are formed or supplemented so that two base station trans-
`
`mitters for
`
`the same cell do not only have identical synchronising words.
`
`Alternatively, radio signals digitally modulated with special synchronising words
`
`can be transmitted from the base station transmitters soleley to enable the
`mobile station to estimate the differences in arrival times or time shifts. The
`
`mobile station transmits information about the estimated arrival time diffe-
`
`rence or time shift via radio signals to the fixed part of the system, where it is
`
`utilised for controlling the transmission time shifting means 2A and 2B. The line
`
`and control unit 1 then receives, via the respective line units 5A, 4A and 58,
`
`4B,
`
`information about estimated arrival
`
`time difference from the mobile
`
`station in the same way as the line and control unit obtains message infor-
`mation from the mobile station.
`
`It is conceivable per se, but hardly to be preferred, to combine both methods
`
`for controlling the transmission time shift in a mobile radio system according to
`
`Figure 2.
`
`Measuring the difference in arrival time or time shifting for correspoding radio
`
`signals can be performed in a conventional way, e.g. with the aid of correlation.
`
`In the cases where the radio signals conventionally contain predetermined
`
`synchronising patterns (words),
`
`the time difference between these patterns
`
`(words)
`
`in different signals can be measured using conventional methods. A
`
`mobile station control means 18 and/or a base station line and control unit 1,9
`
`possible in combination with the transceivers‘ line units 5A and 58 can then
`
`Petitioners, Ex. 1014, Pae 13
`
`Petitioners, Ex. 1014, Page 13
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`W0 89/03355
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`PCT/SE89/00049‘.
`
`If j ’
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`12
`
`comprise time measurement means for estimating reception‘ timeishiftingori
`
`the arrival time comparison means for comparing arrival times.
`
`When so required, a base station preferably utilises conventionally the same
`
`transmitter means and antenna for transmitting,
`
`in time multiplex within the
`
`same frequency range on the same radio channel,
`
`radio signals digitally
`
`modulated with message information to different mobile stations associated
`
`with the same cell. The radio signals with information to a given mobile station
`
`are then transmitted from different base station transmitter with a possible
`
`transmission time shift which is specially adjusted with regard to the position of ‘
`this particular mobile station. The case can arise where a base station in a
`
`mobile radio system needs to transmit a radio signal with information intended
`
`for
`
`reception by several or all of
`
`the mobile stations in the cell, e.g.
`
`information as to the identity of
`
`the base station/cell. Such signals are
`
`preferably transmitted without mutual time shifting from the transceivers B
`
`ma’
`
`, Ba,
`Bmb and B”
`nb
`Figure 2. The transmission time shifting means are then controlled to a
`
`of the base stations in a mobile radio system according to
`
`balancing state where the delay of information from the line and control unit 1
`
`to the antenna in one transceiver Bma is equally as great as the delay of o
`information from the line and control unit 1 to the antenna in the other
`
`transceiver Bmb. The corresponding situation can apply when a base station‘
`"listens" in unoccupied combinations of time slot and frequency range channel
`
`for calls from mobile stations of unknown positions relative to the transceivers
`
`of the base stations. The reception time shifting means 3A and 3B can then be
`
`controlled to