DK176714B1

DK176714B1 - Wireless digital telephone system and method for transmitting RF signals therein

Info

Publication number: DK176714B1
Application number: DK200101860A
Authority: DK
Inventors: Scott David Kurtz; David Kaewell John Jr
Original assignee: Interdigital Tech Corp
Priority date: 1990-02-02
Filing date: 2001-12-12
Publication date: 2009-04-14
Also published as: DK27890D0; DK174255B1; DK200101860A; DK27890A

Description

i DK 176714 B1in DK 176714 B1

Den foreliggende opfindelse angår dels en fremgangsmåde til transmission af RF-signaler i et trådløst digitalt telefonsystem med i det mindste to stationer, hvoraf én er en emuleret basisstation, 5 som er en modificeret abonnentstation, dels et trådløst digitalt telefonsystem til transmission af RF-signaler mellem i det mindste to stationer på én blandt flere til rådighed stående frekvenser.The present invention relates partly to a method of transmitting RF signals in a wireless digital telephone system with at least two stations, one of which is an emulated base station 5 which is a modified subscriber station and partly to a wireless digital telephone system for transmitting RF signals. between at least two stations on one among several available frequencies.

Vore dages telefonsystemer benytter generelt i 10 stigende grad trådløs teknologi til opkald over store afstande og i visse tilfælde er der påbegyndt brug af digital teknologi; imidlertid har intet system, der er i almindelig brug i dag, været i stand til at tilvejebringe en effektiv og virksom trådløs 15 digital teknologi til lokale opkald til og fra individuelle abonnenter. En sådan teknologi er omtalt i forskellige nyere patenter, der indehaves af nærværende ansøgnings indehaver, såsom f.eks. i US patent nr. 4 644 561 af 17. februar 1987 og US patent 20 nr. 4 675 863 af 23. juni 1987. Den teknologi, der er omtalt i disse patenter, tilvejebringer basis-stationer, der kommunikerer med såvel en central som adskillige abonnentstationer under brug af digitale trådløse tidsdelte kredsløb, hvori der er 25 gentagne sekventielle timeslot-positioner i en transmissionskanalbitstrøm, idet hver timeslot er tilknyttet en bestemt abonnent.Today's telephone systems generally use 10 increasingly wireless technology for long distance calls and in some cases digital technology has begun to be used; however, no system in general use today has been able to provide efficient and effective wireless digital technology for local calls to and from individual subscribers. Such a technology is disclosed in various recent patents held by the present application holder, such as e.g. in U.S. Patent No. 4,644,561 of February 17, 1987 and U.S. Patent No. 4,675,863 of June 23, 1987. The technology disclosed in these patents provides base stations communicating with both a central and several subscriber stations using digital wireless time-shared circuits in which there are 25 repeated sequential timeslot positions in a transmission channel bit stream, each timeslot being associated with a particular subscriber.

Basisstationerne, der benyttes i ovennævnte tidsdelingssystem, er relativt komplekse og dyre, 30 men økonomisk egnede i et stort system, der betjener et stort antal abonnenter; for relativt små systemer, der betjener et relativt lille antal abonnenter, kan det imidlertid være økonomisk uegnet.The base stations used in the above time-sharing system are relatively complex and expensive, but economically useful in a large system serving a large number of subscribers; however, for relatively small systems serving a relatively small number of subscribers, it may be economically unsuitable.

DK 176714 B1 2DK 176714 B1 2

Yderligere benytter et sådant system et par frekvenser, en til transmission og en til modtagelse, og med henblik på den begrænsede mængde af kanaler, der er tilgængelige i spekteret, ville det være 5 særdeles fordelagtigt, hvis blot en enkelt frekvens kunne benyttes effektivt.Further, such a system uses a few frequencies, one for transmission and one for reception, and for the limited amount of channels available in the spectrum, it would be extremely advantageous if only a single frequency could be used effectively.

Fra US-A-4549293 kendes der endvidere et internt walkie-talkie system. Der er ikke tale om et telefonsystem. Systemet er et fordækt synslinje 10 TDMA-kommunikationssystem. En af walkie-talkierne arbejder som den ledende walkie-talkie og kommunikerer med de andre indenfor en given afstand. Alle arbejder på samme frekvens, som ikke er tildelt dem af den ledende walkie-talkie, men forud tildelt til 15 alle walkie-talkierne. Den ledende walkie-talkie rundsender sekventielt et broadcast, hvorefter de øvrige walkie-talkier svarer sekventielt på samme frekvens.US-A-4549293 also discloses an internal walkie-talkie system. This is not a telephone system. The system is a hidden line of sight 10 TDMA communication system. One of the walkie-talkies works as the leading walkie-talkie and communicates with the others within a given distance. Everyone works on the same frequency, which is not assigned to them by the leading walkie-talkie, but pre-assigned to all 15 of the walkie-talkies. The leading walkie-talkie sequentially broadcasts a broadcast, after which the other walkie-talkies respond sequentially to the same frequency.

Det er derfor en hensigt med nærværende opfin-20 delse, at tilvejebringe det, der kan kaldes en simuleret eller emuleret basisstation, som effektivt kan erstatte en faktisk basisstation i visse situationer .It is therefore an object of the present invention to provide what may be called a simulated or emulated base station which can effectively replace an actual base station in certain situations.

Denne hensigt opnås ifølge den foreliggende op-25 findelse med en fremgangsmåde af den indledningsvis nævnte art som er ejendommelig ved trinnene, (a) at initiere en synkroniseringsproces i den emulerede basisstation, hvilken synkroniseringsproces indbefatter tildeling af en frekvens og en 3 0 timeslot i en ramme på den udvalgt frekvens, idet hver ramme er opdelt i fire timeslots, (b) via den tildelte frekvens at transmittere et første RF-signal fra den ene station til den an- DK 176714 B1 3 den station i en tildelt timeslot, (c) at modtage et RF-signal i en anden tildelt timeslot i den samme ramme på den samme tildelte frekvens, og 5 (d) at gentage trinnene (b) og (c) for efter følgende RF-signaler indtil den ene eller den anden af stationerne afslutter.This object is achieved in accordance with the present invention by a method of the kind mentioned initially by the steps of (a) initiating a synchronization process in the emulated base station, which synchronization process includes assigning a frequency and a 30 timeslot to a (b) transmitting, via the assigned frequency, a first RF signal from one station to the other station in an assigned time slot, (c) at the selected frequency. ) receiving an RF signal in another assigned time slot in the same frame at the same assigned frequency, and 5 (d) repeating steps (b) and (c) to follow the following RF signals until one or the other of the stations exit.

Tilsvarende opnås denne hensigt med et trådløst digitalt telefonsystem af den indledningsvis nævnte 10 art som er ejendommeligt ved at den ene station, der er en emuleret basisstation, som er en modificeret abonnentstation, og som da kommunikerer med de andre stationer på én blandt flere til rådighed stående frekvenser, og som omfatter 15 (i) midler til at initiere en synkronise ringsproces, der transmitterer synkroniseringsinformation indbefattende tildelingen af en frekvens og en time-slot i en ramme på den tildelte frekvens, idet der i det mindste tildeles en første og 20 en anden timeslot i rammen, (ii) midler til at transmittere et RF-signal til en anden station i en første tildelt timeslot på den tildelte frekvens, og (iii) midler til at modtage et andet RF-25 signal fra den anden station i en anden tildelt timeslot på den tildelte frekvens, og at den anden station omfatter (i) midler til at modtage synkroniserings-informationen og identificere tildelingen af fre- 30 kvensen og timeslot'ene i rammen på den tildelte frekvens, og (ii) midler til at modtage det transmitterede RF-signal fra basisstationen i en yderligere DK 176714 B1 4 tildelt timeslot i rammen på den tildelte frekvens, og (iii) midler til at transmittere det andet RF-signal til basisstationen i endnu en yderligere 5 tildelt timeslot i rammen på den tildelte frekvens.Similarly, this intention is achieved with a wireless digital telephone system of the type mentioned initially, which is peculiar in that one station, which is an emulated base station, which is a modified subscriber station, and which then communicates with the other stations at one among several is available. standing frequencies, comprising 15 (i) means for initiating a synchronization process which transmits synchronization information including the assignment of a frequency and a time slot in a frame of the assigned frequency, at least a first and 20 a. (ii) means for transmitting an RF signal to a second station in a first assigned time slot on the assigned frequency; and (iii) means for receiving a second RF-25 signal from the second station in a frame. second assigned time slot on the assigned frequency, and the second station comprises (i) means for receiving the synchronization information and identifying the assignment of frequency. and (ii) means for receiving the transmitted RF signal from the base station in an additional time slot in the frame of the assigned frequency, and (iii) means for receiving the transmitted RF signal from the base station. transmit the second RF signal to the base station for a further 5 assigned timeslots in the frame at the assigned frequency.

En anden hensigt er, at tilvejebringe et system, som kan benyttes af adskillige abonnenter, men som fungerer på blot en enkelt frekvens.Another object is to provide a system which can be used by several subscribers but which operates on just a single frequency.

Andre hensigter vil fremgå af den følgende be-10 skrivelse og kravene.Other intentions will become apparent from the following description and claims.

Essentielt benytter systemet ifølge nærværende opfindelse det, der faktisk er en modificeret abonnentstation, til at fungere som en simuleret eller emuleret basisstation, hvorved de totale omkostnin-15 ger ved og kompleksiteten af systemet mindskes væsentligt. Denne emulerede basisstation afviger i det væsentlige kun fra abonnentstationen ved at være i stand til at initiere synkroniseringsprocessen, medens abonnentenheden kun er indrettet til at 20 skandere RF signalerne, der udsendes af den emulerede basisstation, indtil den finder den frekvens og den timeslot, der er tildelt den. I intervallerne mellem transmissioner af RF signalerne er den emulerede basisstation indrettet til at modtage RF 25 signaler fra abonnentenhederne. På denne måde kan abonnentenheden enten tale med den emulerede basis -station, som så fungerer som en anden abonnentstation, eller den kan tale med en anden abonnent station, som er synkroniseret dermed af den emulerede 30 basisstation.Essentially, the system of the present invention utilizes what is actually a modified subscriber station to function as a simulated or emulated base station, thereby substantially reducing the total cost and complexity of the system. This emulated base station essentially deviates from the subscriber station only in being able to initiate the synchronization process, while the subscriber unit is only designed to scan the RF signals emitted by the emulated base station until it finds the frequency and time slot that is assigned to it. In the intervals between transmissions of the RF signals, the emulated base station is arranged to receive RF signals from the subscriber units. In this way, the subscriber unit can either talk to the emulated base station, which then functions as another subscriber station, or it can speak to another subscriber station synchronized therewith by the emulated base station.

Opfindelsen forklares nærmere i det følgende ved hjælp af udførelseseksempler under henvisning til tegningen hvor, DK 176714 B1 5 fig. 1 viser et blokdiagram af et totalt system ifølge opfindelsen, fig. 2 et skitse af RCC bølgeformen, der benyttes i standardbasisstationen, 5 fig. 3 en skitse af RCC bølgeformen, der benyt tes i forbindelse med nærværende opfindelse, fig. 4 en skitse, der viser de positive flanker for amplituden af det modtagne signal, der benyttes ved grovsynkronisering ifølge opfindelsen, 10 fig. 5 et blokdiagram af kredsløbet til opnåel se af grovsynkronisering ifølge opfindelsen, fig. 6 et blokdiagram af modtager-AGC-kredsløbet, der benyttes ifølge opfindelsen, fig. 7 et blokdiagram af frekvensregenererings-15 kredsløbet, der benyttes ifølge opfindelsen, fig. 8 en skitse af en trådløs telefonsystemkonfiguration ifølge opfindelsen, fig. 9 en skitse svarende til fig. 8, men som viser et dobbeltabonnentsystem, 20 fig. 10 en skitse af rammeformatet i dobbelt abonnent sy s ternet i fig. 9, fig. 11 en skitse af rammeformatet for adskillige dobbe11abonnent sys temer.The invention will now be explained in more detail by way of example with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a total system according to the invention; FIG. 2 is a sketch of the RCC waveform used in the standard base station; FIG. 3 shows a sketch of the RCC waveform used in connection with the present invention; FIG. 4 is a diagram showing the positive flanks of the amplitude of the received signal used in coarse synchronization according to the invention; FIG. 5 is a block diagram of the circuit for obtaining coarse synchronization according to the invention; FIG. 6 is a block diagram of the receiver AGC circuit used in accordance with the invention; FIG. 7 is a block diagram of the frequency regeneration circuit used in accordance with the invention; FIG. Fig. 8 is a sketch of a wireless telephone system configuration according to the invention; 9 is a sketch similar to FIG. 8, but showing a dual subscriber system; FIG. 10 is a sketch of the double subscriber frame format shown in FIG. 9, FIG. 11 is a sketch of the frame format for several double subscriber systems.

Den totale interne funktion af systemet 10 er 25 vist i blokdiagramform i fig. 1. I dette system taler en person i telefonen 12 under en telefonsamtale og talesignalet sendes til den lokale telefonin-terfaceenhed 14. Signalet digitaliseres af codec1 en 16 og den resulterende digitale datastrøm føres til 30 taleprocessoren 18, som komprimerer taledataene til en lavere datahastighed. De komprimerede data føres så til modemet 20 via linien 22 og den dobbelte omskifter 24, idet modemet er indrettet til at kon- DK 176714 B1 6 vertere datastrømmen til et spektralt effektivt analogt signal. Dette analoge signal føres til radioen 26 via linien 28. Radioen opkonverterer signalet til et radiofrekvenssignal (RF) og transmit-5 terer dette RF-signal via antennen 30.The overall internal function of the system 10 is shown in block diagram form in FIG. 1. In this system, a person in the telephone 12 speaks during a telephone conversation and the voice signal is sent to the local telephone interface unit 14. The signal is digitized by codec1 16 and the resulting digital data stream is fed to the speech processor 18 which compresses the speech data to a lower data rate. The compressed data is then fed to modem 20 via line 22 and dual switch 24, the modem being adapted to convert the data stream into a spectrally efficient analog signal. This analog signal is fed to the radio 26 via line 28. The radio converts the signal to a radio frequency signal (RF) and transmits this RF signal through the antenna 30.

I intervallerne mellem transmissioner af RF-signalerne er enheden indrettet til at modtage RF-signaler fra en abonnentenhed. Radioen 26 nedkonverterer hvert af disse RF-signaler til et IF-10 signal og afgiver dette IF-signal til modemet 20 via linien 32. Modemet 20 demodulerer IF-signalet for dannelse af et digitalt signal, som føres til taleprocessoren via omskifteren 24 og linien 36. Taleprocessoren er dernæst indrettet til at ekspan-15 dere signalet til et digitaliseret talesignal og dette digitaliserede signal føres dernæst til codec 'en 16, som afgiver et analogt talesignal til telefonen 12 via telefoninterfacen 14.In the intervals between transmissions of the RF signals, the device is arranged to receive RF signals from a subscriber unit. Radio 26 downconverts each of these RF signals to an IF-10 signal and outputs this IF signal to modem 20 via line 32. Modem 20 demodulates the IF signal to generate a digital signal which is fed to the speech processor via switch 24 and line 36. The speech processor is then arranged to expand the signal to a digitized voice signal and this digitized signal is then fed to the codec 16 which delivers an analog speech signal to the telephone 12 via the telephone interface 14.

Datatransmissionsmodusen svarer til det ovenfor 20 beskrevne bortset fra, at telefonen erstattes af en dataterminal eller computer 38 og telefoncodec'en og taleprocessoren forbikobles ved hjælp af den anden position af omskifteren 24, som så er koblet til terminalen 38 via linierne 40 og 42.The data transmission mode is similar to that described above except that the telephone is replaced by a data terminal or computer 38 and the telephone codec and speech processor are bypassed by the second position of switch 24, which is then connected to terminal 38 via lines 40 and 42.

25 Modemet 20 og radioen 26 er begge forbundet med en styreenhed 44. Styreenheden 44 er fra starten sat til en forudbestemt timeslot, en modulations-og træningsmodus for modemet og til en forudbestemt RF-frekvens og effektniveau for radioen. Imidlertid 30 kan disse parametre justeres af abonnentenheden i tilfælde af, at de ikke er tilstrækkelige til at give en tilfredsstillende modtagelse ved abonnentstationen.The modem 20 and the radio 26 are both connected to a controller 44. The controller 44 is initially set to a predetermined time slot, a modulation and training mode of the modem, and to a predetermined RF frequency and power level of the radio. However, these parameters may be adjusted by the subscriber unit in case they are not sufficient to provide a satisfactory reception at the subscriber station.

DK 176714 B1 7 I et system, der benytter en faktisk basisstation, såsom f.eks. systemet beskrevet i det førnævnte US-patent nr. 4 675 863, er den transmitterede bølgeform opdelt i mangfoldige (dvs. 45) ms 5 rammer. Hver ramme er dernæst opdelt i fire 11,25 ms timeslots. Basisstationen transmitterer i alle fire timeslots for at generere en 100% duty cycle modulationsbølgeform, idet den eneste undtagelse er radiostyrekanalen (RCC). RCC timeslot'en er lidt 10 kortere end 11,25 ms og dette bevirker et lille gab i modulationen ved begyndelsen af hver ramme. Dette gab er kendt som et AM hul. Et diagram, af bølgeformen for RCC kanalen i den faktiske basisstations format er vist i fig. 2. I systemet ifølge nærvæ-15 rende opfindelse er der imidlertid ikke nogen transmission af en 100% duty cycle bølgeform. I stedet transmitteres kun én timeslot pr. ramme (en 25% duty cycle bølgeform), som vist i fig. 3. Dette modificerede rammeformat nødvendiggør ændringer i 20 grovsynkronisering automatisk forstærkningsstyring (AGC) og frekvensregenerering. Disse ændringer er indikeret i den følgende beskrivelse:In a system using an actual base station, such as e.g. system disclosed in the aforementioned U.S. Patent No. 4,675,863, the transmitted waveform is divided into multiple (i.e., 45) ms 5 frames. Each frame is then divided into four 11.25 ms timeslots. The base station transmits in all four time slots to generate a 100% duty cycle modulation waveform, with the only exception being the radio control channel (RCC). The RCC timeslot is slightly 10 shorter than 11.25 ms and this causes a small gap in the modulation at the beginning of each frame. This gap is known as an AM hole. A diagram of the waveform of the RCC channel in the actual base station format is shown in FIG. 2. In the system of the present invention, however, there is no transmission of a 100% duty cycle waveform. Instead, only one hour slot is transmitted per day. frame (a 25% duty cycle waveform), as shown in FIG. 3. This modified frame format necessitates changes in 20 coarse synchronization automatic gain control (AGC) and frequency regeneration. These changes are indicated in the following description:

Eftersom systemet ifølge nærværende opfindelse kun benytter en 25% duty cycle bølgeform overvåger 25 det amplituden af det modtagne signal og søger efter positive flanker i amplitudesignalet. Disse positive flanker er vist i fig. 4. Abonnentenheden justerer sin rammetidsstyring til at stemme overens med forekomsten af disse positive flanker.Since the system of the present invention uses only a 25% duty cycle waveform, it monitors the amplitude of the received signal and searches for positive flanks in the amplitude signal. These positive flanks are shown in FIG. 4. The subscriber unit adjusts its frame time management to match the occurrence of these positive flanks.

30 Kredsløbet til opnåelse af den ovenfor nævnte type grovsynkronisering er vist i blokdiagramform i fig. 5, hvor det modtagne signal er vist tilført en amplitudeberegningsenhed 50, som genererer et com- DK 176714 B1 8 puteramplitudesignal, som dernæst afgives til en komparator 52, hvor det sammenlignes med et forudbestemt tærskelsignal, hvorved der dannes et digitalt signal (1 = signal tilstede, 0 = intet signal 5 tilstede). Dette digitale signal føres til en flankedetektor 54, som afgiver en strobe, for at indikere detektionen af en positiv flanke.The circuit for obtaining the above-mentioned type of coarse synchronization is shown in block diagram form in FIG. 5, where the received signal is shown applied to an amplitude calculation unit 50 which generates a computer amplitude signal, which is then output to a comparator 52, where it is compared with a predetermined threshold signal, thereby forming a digital signal (1 = signal present, 0 = no signal 5 present). This digital signal is fed to a flank detector 54 which emits a strobe to indicate the detection of a positive flank.

25% duty cycle modulationen kræver en bestemt type modtage-AGC kredsløb, som undgår sporing, når 10 der ikke er noget signal tilstede. En langsom stigende, hurtigt faldende AGC er derfor tilvejebragt.The 25% duty cycle modulation requires a certain type of receive AGC circuit which avoids detection when 10 no signal is present. A slow-rising, rapidly decreasing AGC is therefore provided.

Denne er vist i fig. 6, hvor det modtagne signal føres til en amplitudeberegningsenhed 56, som kan være en forprogrammeret ROM, hvorfra et resulteren-15 de ampiitudesignal føres til en komparator 58, hvori det subtraheres fra en forudbestemt tærskelværdi for dannelse af et differenssignal. Dette differenssignal føres, via en af to skalerende multiplikatorer 60 og 62, til et lavpasfilter, der om-20 fatter en additionsenhed 64 og en forsinkelse 66, der er forbundet via en sløjfe 68. Den ene eller den anden af de to multiplikatorer benyttes i overensstemmelse med fortegnet for differenssignalet.This is shown in FIG. 6, where the received signal is fed to an amplitude calculator 56, which may be a pre-programmed ROM, from which a resultant amplitude signal is fed to a comparator 58, where it is subtracted from a predetermined threshold for generating a difference signal. This differential signal is passed, via one of two scaling multipliers 60 and 62, to a low pass filter comprising an addition unit 64 and a delay 66 connected via a loop 68. One or the other of the two multipliers is used in in accordance with the sign of the difference signal.

Hvis differenssignalet er positivt implementeres 25 det langsomme fald i AGC styresignalet. Hvis differenssignalet er negativ implementeres en hurtig stigning i AGC styresignalet. Udgangssignalet fra filteret er så det forstærkningssignal, som føres til forstærkningsstyreenheden 44, vist i fig. 1.If the difference signal is positive, the slow decrease in the AGC control signal is implemented. If the difference signal is negative, a rapid increase in the AGC control signal is implemented. The output of the filter is then the gain signal applied to the gain control unit 44 shown in FIG. First

30 På grund af 25% duty cycle rammeformatet er det ikke nødvendigt at udføre frekvensregenerering under slukketiden (75% nul tid) og eftersom rammetidsstyringen ikke er kendt på det tidspunkt, hvor DK 176714 B1 9 frekvensregenerering udføres, er der tilvejebragt en modificeret form for frekvensregenereringskredsløb, som vist i fig. 7. I dette kredsløb føres det modtagne signal til en beregningsenhed 70 til be-5 regning af en diskret fourier transformeret (DFT), som afgiver højbåndsenergien (energien i frekvensbåndet over centerfrekvensen) og lavbåndsenergien (energien i frekvensbåndet under centerfrekvensen).30 Due to the 25% duty cycle frame format, it is not necessary to perform frequency regeneration during the off time (75% zero time) and since the frame time control is not known at the time when DK 176714 B1 9 frequency regeneration is performed, a modified form of frequency regeneration circuit is provided. , as shown in FIG. 7. In this circuit, the received signal is fed to a computing unit 70 for calculating a discrete fourier transform (DFT) which emits the high band energy (the energy in the frequency band over the center frequency) and the low band energy (the energy in the frequency band below the center frequency).

Højbåndsenergiudgangssignalet subtraheres fra lav-10 båndsenergiudgangssignalet i additionsenheden 72 og udgangssignalet derfra føres til en blander eller multiplikator 74. Det modtagne RF-signal afgives også til et amplitudedannende middel 76, som fjerner fortegnet fra signalet (negativt eller posi-15 tivt), hvorved det kun bestemmer amplituden af signalet. Amplitudesignalet føres dernæst til et filter 78, som udglatter signalet ved middelværdidannelse. Udgangssignalet fra filteret 78 føres via forstærkeren 80 til multiplikatoren 74.The high band energy output signal is subtracted from the low band energy output signal in the addition unit 72 and the output signal therefrom is fed to a mixer or multiplier 74. The received RF signal is also output to an amplitude generating means 76 which removes the sign from the signal (negative or positive) where only determines the amplitude of the signal. The amplitude signal is then fed to a filter 78 which smoothes the signal by averaging. The output of filter 78 is passed through amplifier 80 to multiplier 74.

20 Det primære formål med kredsløbet via 76, 78 og 8 0 er at forhindre støj i at indvirke på udgangssignalet, medens selve signalet fremhæves. Eftersom støj sædvanligvis har en lille amplitude, frafil-treres den i denne sammenhæng effektivt ved udglat-25 ningsprocessen. Eftersom det faktiske signal sædvanligvis har en relativt stor amplitude, bliver dette på den anden side fremhævet, ved at tilføje det udglattede eller filtrerede signal til blanderen 74.The primary purpose of the circuit via 76, 78 and 80 is to prevent noise from affecting the output signal while emphasizing the signal itself. Since noise usually has a small amplitude, in this context it is effectively filtered out by the smoothing process. On the other hand, since the actual signal usually has a relatively large amplitude, this is highlighted by adding the smoothed or filtered signal to the mixer 74.

30 Det skalerede signal, der forlader blanderen 74 er balanceret mellem høj- og lavenergifrekvenser, og dette balancerede signal, som er proportionalt med korttidsmiddelamplituden af det modtagne signal DK 176714 B1 10 føres til et lavpasfilter, der omfatter en additionsenhed 82 og en forsinkelse 84, som er sløjfet ved 86. Forsinkelsen 84 gør, at det afgivne signal 88 til VCXO styring repræsenterer udgangssignalet 5 umiddelbart før udgangssignalet faktisk føres til lavpasfilteret. VCXO-styringen benyttes til at justere frekvensen af hovedoscillatoren i systemet.The scaled signal leaving the mixer 74 is balanced between high and low energy frequencies, and this balanced signal proportional to the short-term average amplitude of the received signal DK 176714 B1 10 is fed to a low pass filter comprising an addition unit 82 and a delay 84, which is looped at 86. The delay 84 causes the output signal 88 for VCXO control to represent the output signal 5 immediately before the output signal is actually fed to the low-pass filter. The VCXO control is used to adjust the frequency of the main oscillator in the system.

Efter at indledende eller grovsynkronisering er udført, er systemet i en tomgangstale modus men er 10 helt sat op til taledrift. Hvis telefonen i den ene ende tages af, vil telefonen i den anden ende ringe, indtil den ringende telefon besvares, eller den initierende telefon lægges på.After initial or coarse synchronization is performed, the system is in idle mode but 10 is fully set up for voice operation. If the phone is removed at one end, the phone at the other end will ring until the ringing telephone is answered or the initiating phone is hung up.

Opkaldene opsættes af et talekodeord (VCW) ved 15 begyndelsen af hver tale-timeslot, idet dette kodeord indikerer en "røret taget af tilstand" i den initierende station. Når dette forekommer, vil stationen, der fungerer som en emuleret basisstation, fra centralen (CO) synes selv at overgå til til-20 standen "røret taget af", hvorved den opretter en forbindelse med centralen. Den initierende abonnentstation fortsætter så med at færdiggøre opkaldet ved at dreje det ønskede nummer. Når den initierende abonnentenhed lægger røret på, informeres 25 den emulerede basisstation herom ved VCWen og ser fra centralen ud til at gå i en tilstand med røret på.The calls are set up by a voice code word (VCW) at the beginning of each talk time slot, this password indicating a "tube taken out of state" in the initiating station. When this occurs, the station which acts as an emulated base station from the switchboard (CO) itself seems to switch to the "tube taken off" state, thereby establishing a connection with the switchboard. The initiating subscriber station then proceeds to complete the call by rotating the desired number. When the initiating subscriber unit puts the tube on, the emulated base station is informed of this at the VCW and from the control panel appears to be in a state with the tube on.

Når den emulerede basisstation detekterer et ringesignal fra centralen, bringes abonnentenheden 30 til at ringe ved hjælp af den tilsvarende vCW fra den emulerede basisstation. Når abonnentenheden derefter tager røret af, informeres den emulerede basisstation herom via den tilsvarende VCW og ser DK 176714 B1 11 fra centralen ud til at være i tilstanden "røret taget af".When the emulated base station detects a ring signal from the switchboard, the subscriber unit 30 is called by the corresponding vCW from the emulated base station. When the subscriber unit then takes the tube off, the emulated base station is informed of this via the corresponding VCW and DK 176714 B1 11 from the control panel appears to be in the "tube taken off" state.

Den omtalte type trådløs telefonsystemkonfiguration er eksemplificeret i fig. 8, hvor abonnent-5 enheden 90 er vist i trådløs kommunikation, via antenner 92 og 94, med den emulerede basisstation 96. Stationen 96 er i trådløs kommunikation, via linien 98 og interfacen 100, med centralen.The mentioned type of wireless telephone system configuration is exemplified in FIG. 8, where the subscriber unit 90 is shown in wireless communication, via antennas 92 and 94, with the emulated base station 96. The station 96 is in wireless communication, via the line 98 and the interface 100, with the switchboard.

Det ovenfor beskrevne system kan anvendes i 10 forbindelse med et dobbeltabonnentarrangement, som vist i fig. 9. I dette system er hver kanal i stand til at betjene to komplette konversationer uden behovet for at benyttet en duplexer. Med henblik herpå er en dobbeltabonnentenhed 102 med ledninger 104 15 og 106 forbundet med et par abonnenttelefoner 108 og 110. Abonnentenheden 102 kommunikerer trådløst, via antenner 112 og 114, med en emuleret dobbelt basisstation 116. Enheden 116 er forbundet med centralen, via ledningsforbindelser 118 og 120.The system described above can be used in conjunction with a dual subscriber arrangement, as shown in FIG. 9. In this system, each channel is capable of operating two complete conversations without the need to use a duplexer. To this end, a dual subscriber unit 102 with wires 104 and 15 is connected to a pair of subscriber telephones 108 and 110. The subscriber unit 102 communicates wirelessly, via antennas 112 and 114, with an emulated dual base station 116. The unit 116 is connected to the central, via wired connections 118 and 120.

2 0 De to separate abonnenter 108 og 110 benytter et timeslot-arrangement, som omtalt i det førnævnte US-patent nr. 4 675 863, hvori hver abonnent er tildelt en separat timeslot. Rammeformatet for dette arrangement er vist i fig. 10, hvor fire time-25 slots er vist nummererede 1, 2, 3 og 4, idet de første to timeslots benyttes af den emulerede basisstation og de sidste to benyttes af de to abonnenter .The two separate subscribers 108 and 110 use a timeslot arrangement, as disclosed in the aforementioned U.S. Patent No. 4,675,863, wherein each subscriber is assigned a separate timeslot. The frame format for this arrangement is shown in FIG. 10, where four hour-25 slots are shown numbered 1, 2, 3 and 4, the first two time slots being used by the emulated base station and the last two being used by the two subscribers.

Adskillige dobbeltabonnentsystemer kan fungere 3 0 på forskellige kanaler uden duplexere ved at syn kronisere alle de emulerede basisstationstransmis-sioner. Dette er illustreret ved rammeformatet, der er vist i fig. 11, hvor kanal 1 er vist øverst og DK 176714 B1 12 kanal n (hvilket indikerer et vilkårligt antal kanaler ind imellem) er vist forneden. På hver kanal er de første to timeslots til transmission og de sidste to til modtagelse.Several dual subscriber systems can operate on different channels without duplexers by synchronizing all the emulated base station transmissions. This is illustrated by the frame format shown in FIG. 11, where channel 1 is shown at the top and channel n (which indicates any number of channels in between) is shown below. On each channel, the first two timeslots are for transmission and the last two for reception.

5 En emuleret basisstation kan benyttes i forbin delse med adskillige forskellige abonnenter en ad gangen. I et sådant arrangement overvåger abonnenterne kontinuerligt transmissionerne i radiostyre-kanalerne (RCC) for modtagelse, hvilket er mere ud-10 førligt beskrevet i det førnævnte US-patent nr. 4 675 863, indtil en bestemt abonnent søges af den emulerede basisstation ved hjælp af abonnentens ID nummer (SID). Efter modtagelse af en søgning, initierer abonnenten en transmission tilbage til den 15 emulerede basisstation under brug af den ovenfor beskrevne synkroniseringsproces. For initiering af et opkald transmitterer abonnentstationen på RCC en under brug af den tidligere beskrevne synkroniseringsproces .An emulated base station can be used in conjunction with several different subscribers one at a time. In such an arrangement, subscribers continuously monitor the transmissions in the radio control channels (RCC) for reception, which is more fully described in aforementioned U.S. Patent No. 4,675,863 until a particular subscriber is searched by the emulated base station by means of subscriber ID number (SID). Upon receiving a search, the subscriber initiates a transmission back to the emulated base station using the synchronization process described above. To initiate a call, the subscriber station on the RCC transmits an in-use synchronization process previously described.

Claims

A method of transmitting RF signals in a wireless digital telephone system with a central (CO) communicating with at least two stations 5 (90, 96), one of which is an emulated base station (96) which is in communication with the switchboard (CO) and which is a modified subscriber station characterized by the steps, (a) initiating a synchronization process in the emulated base station (96), which synchronization process includes assigning a frequency and a time slot in a frame on it. selected frequency, each frame being divided into four time slots, (b) transmitting via the assigned frequency a first RF signal from one station to the other station (90) in an assigned time slot, (c) receiving an RF signal in another assigned time slot in the same frame at the same assigned frequency, and (d) repeating steps (b} and (c) for subsequent RF signals until one or the other of the stations (90, 96) ) quits.

Method according to claim 1, characterized in that each frame is subdivided into four hour slots.

Method according to claim 1 or 2, characterized in that an RF signal is transmitted in a first time slot and received in a second time slot.

Method according to any one of claims 1 to 3, characterized in that each time slot has substantially the same duration.

5. Wireless digital telephone system for transmitting RF signals between a central (CO) and at least two stations (90, 96) on one of several available frequencies, characterized in that one station which is an emulated base station (96), which is a modified subscriber station, which then communicates with the other stations at one of several available frequencies, and which comprises (i) means for initiating a synchronization process which transmits synchronization information including the allocation of a frequency and a time slot in a frame of the assigned frequency, at least a first and a second time slot in the frame are assigned; <ii) means for transmitting an RF signal to another station (90) in a first assigned timeslot 15 on the assigned frequency, and (iii) means for receiving a second RF signal from the second station (90) in a second assigned timeslot on the assigned frequency, and a station (90) comprises 20 (i) means for receiving the synchronization information and identifying the assignment of the frequency and time slots in the frame of the assigned frequency, and (ii) means for receiving the transmitted RF signal from the base station (96) and (iii) means for transmitting the second RF signal to the base station (96) in a further assigned time slot in the frame of the assigned frequency.

Wireless digital telephone system according to claim 5, 30, characterized in that the frame of the assigned frequency has four time slots. 35