CA1251875A - Method of and arrangement for synchronising the receiver arrangements in a digital multiplex transmission system - Google Patents
Method of and arrangement for synchronising the receiver arrangements in a digital multiplex transmission systemInfo
- Publication number
- CA1251875A CA1251875A CA000505481A CA505481A CA1251875A CA 1251875 A CA1251875 A CA 1251875A CA 000505481 A CA000505481 A CA 000505481A CA 505481 A CA505481 A CA 505481A CA 1251875 A CA1251875 A CA 1251875A
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- CA
- Canada
- Prior art keywords
- symbols
- synchronizing
- code
- synchronising
- channels
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/08—Access point devices
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J13/00—Code division multiplex systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0602—Systems characterised by the synchronising information used
- H04J3/0614—Systems characterised by the synchronising information used the synchronising signal being characterised by the amplitude, duration or polarity
Abstract
ABSTRACT:
In digital multiplex transmission systems, more specifically in a digital radio transmission system, a plurality of message transmission channels are operated in time-division, code-division or frequency-division multiplex. When using the code-division multiplex or frequency-division multiplex method, separating the indi-vidual message transmission channels is erected with the aid of different sets of data symbols. The messages trans-mitted through the individual message transmission channels of the multiplex transmission systems more specifically the symbols (data and synchronising symbols) are trans-mitted time-synchronously with each other. At the beginning of each frame and sub-frame (in a time division multiplex transmission system) the synchronising information is transmitted at the beginning of a frame and the length of the message is equal to the period of time between two synchronising symbols. Particularly in a digital radio transmission system, because of the multi-path propagation, a fail-safe synchronisation of the receiver arrangements is a prerequisite for evaluating the message content in the mobile radio station. So as to enable accurate syn-chronisation of the receiver arrangements in wide-band transmission, synchronising symbols are inserted at defined intervals between the data symbols which symbols are transmitted simultaneously in several message transmission channels and are equal to each other. Consequently, the synchronising symbols are received with a significantly higher energy than the data symbols, the multi-path profile can be measured and a sure synchronisation can be rendered possible.
In digital multiplex transmission systems, more specifically in a digital radio transmission system, a plurality of message transmission channels are operated in time-division, code-division or frequency-division multiplex. When using the code-division multiplex or frequency-division multiplex method, separating the indi-vidual message transmission channels is erected with the aid of different sets of data symbols. The messages trans-mitted through the individual message transmission channels of the multiplex transmission systems more specifically the symbols (data and synchronising symbols) are trans-mitted time-synchronously with each other. At the beginning of each frame and sub-frame (in a time division multiplex transmission system) the synchronising information is transmitted at the beginning of a frame and the length of the message is equal to the period of time between two synchronising symbols. Particularly in a digital radio transmission system, because of the multi-path propagation, a fail-safe synchronisation of the receiver arrangements is a prerequisite for evaluating the message content in the mobile radio station. So as to enable accurate syn-chronisation of the receiver arrangements in wide-band transmission, synchronising symbols are inserted at defined intervals between the data symbols which symbols are transmitted simultaneously in several message transmission channels and are equal to each other. Consequently, the synchronising symbols are received with a significantly higher energy than the data symbols, the multi-path profile can be measured and a sure synchronisation can be rendered possible.
Description
8'~
PHD ~5-320 1 10-02-1986 ~lethod oE and a~ran~enent for synchro~is~ng the receiver arr~nge-nPnts in a digital ~,ultiple~ transmission system.
The invention relates to a method of synchronis-ing the receiver arrangements in a digital multiplex transmission system as claimed in the introductory part of the paten-t Claim 1.
For the transmission of messages via a trans-mission means (for example lines, radio-channels) which is used in common by a plurality of subscribers, three basic methods are known, namely the code-division mul-tiplex method, the frequency-division multiplex method and the time-division multiplex method.
In the code-division multiplex method the different messages conveyed through a common transmission means are, for example, modulated on a sub-carrier by basic modulation and -the resultant signal which, compared with the chann0l bandwidth, is a narrow-band signal is spectrally distri-buted over the channel bandwid-th by multiplex modulation with the aid of a code word characterising the receiver.
I`he code-division multiplex channel (message transmission channel) thus obtained is not limited, neither in time nor within the bandwidth, bu-t is limited relative to the power density. Recognising the signal is not effected by selec-tion on -time or fre4uency basis but on -the basis of spec-tral coding. The plurality of spectrally encoded mes3agest superposed in the code-division multiplexed channel, are selected in the receiver on the basis of the code word assigned thereto. For the two-stage modulation (basic and multiplex modulation) phase shift keying (PSK) or frequency shift keying (FS~) are often u-tilized in radio trans-mission systems.
The first stage receives, for example, the digi-tized speech signal (after having been converted in an analog-to-digital converter) which includes9 for example, a multiplicative mixer. In the multiplicative mixer th~
supplied digitized speech signal is combined with a code-word assigned to this transmitter, which results in a spectral distribution. In the second modulation stage of the transmitter the wide-band signal (modulated, binary 5 character sequence) is converted into a frequency position suitable for the transmission.
Recovering the message at the receiver side is effected in the above-described code-division multiplex method by a sequence of basic demodulation and multiplex demodulation. Coversion to a frequency position (for ex-ample baseband position~ suitable for the multiplex de-modulation is effected in the basic demodulation stage by multiplying the signal by the reference sub-carrier. With the aid of a code word generator arranged in the receiver and also a code synchronising circuit the spactral dis-tribution is cancelled, after the code word has been synchronised in the ~pprop~ab0 p~ge Wl~h ~he r~ceivsr code word. As a result thereof, the signal energy which has previously been spectrally distributed over -the entire transmission band is compressed to the original frequency band, whilst the adjacent characters entering the receiver with a different multiplex modulation remain in the spec-trally dlstributed state and can be suppressed by a band-pass filter having a bandwidth corresponding to the band-widthof -the non-distributed signal.
The system-determined residual interference in the multiplex demodulation produced by the other signals is lower according as the values of the cross-correlation functions between the codewords used are lower and the distribution factor is larger. A non-zero value of the cross-corralation function reduces the signal-to-noise ratio. The signal-to-noise ratio and the synchronising period are determined by the cross-correlation and auto-correlation function.
In the frequency-division multiplex method the total bandwidthavailable for message transmission is sub-divided into narrow frequency bands which each correspond 7~
PHD ~5-320 3 10-02-1986 to a message ~ransmission channel. Such a narrow frequency band is available to the subscriber for the duration of the ratio transmission.
In the time-division multiplex method each subscriber has the disposal of a total bandwidt of a single ratio channel which the subscriber may only utilize for short periods of time. The characters or character se-quences of different subscribers are interleaved and are transmitted with correspondingly higher bit rates through the single radio channel, each time a channel assigned to a subscriber being repeated periodically with the frame period duration.
DE-OS 25 37 683 discloses a radio transmissàon system having stationary radio stations and mobile radio stations in which different channel accessing methods with asynchronous time-division multiplex, code-division multiplex and frequency-division rnultiplex are used.
~or codeword synchronisation an incoherent sub-carrier demodulation is used. A code generator generates sequentially one of the nine differen-t codes, which char-acteri~e the sta-tionary ground-based radio stations. After this code h&s been synchronised with the receiver signal the IF-signal is multiplied, causing the wide spectrum in the message bandwidth to be transformed. Subsequent there-to the received message can, for example, be recovered using a DPSK demodulator. Eor the pu~pose of synchronisa--tion its own code sample, having a length of, for example 15 bits, is used, which precedes the mes~age.
Also combinations of the above-mentioned methods and their use in a digital radio transmission system are known. "Nachrichtentechnik, Elektronik ~ Telematik 38 (1984), Vol. 7, pages 264 to 268" describes for example a digital radio transmission system in which the time-divi-sion multiplex method is used in combination with ~ode distribution. In the time channel for speech and/or data transmission (communication channel TCA) there are sequen~
ially transmitted a bit sequence for determining the bit clock (synchronous), a frame synchronising word (leader) ~J~ 5 PHD. 85-320 4 and the bit sequence of the message itself. The time channel for message transmission (3 x 20 TCA) are combined with the control channels (3 CCH) to form a time-division multiplex frame having a duration of 31.5 msec. If the speech signal must be transmitted as the message, then the adaptive delta modulation can be used for analog-to-digital conversion. The message characters (bi-ts) then obtained ha~e a code superposed on them in the transmitter.
It has been found to be advanta~eous to combine individual message characters in blocks of four bits each and to distribute the block thus obtained by means of an ortho-gonal alphabet. The distribution factor used therewith is a compromise to combine the advantages of band distribu-tion with the requirements as regards economical use of the frequencies. In addition, a message transmission method has been proposed in which a different modula-tion method is utilized in the forward and return directions of the message transmission channels. For message transmission the mobile radio stations access one of a plurality of message channels. In the direction from the stationary radio station to the mobile radio stations assigned thereto, each message channel is distributed by means of distribution modulation. The distributed message channels are super-posed on each other and the wide-band sum signal thus obtained is transmitted in a common frequency band. In -the direction from the mobile radio stations -to the stationary radio station the message transmission is effected in separate, narrow-band frequency channels.
For the transmission of speech, in the direction from the stationary radio station to the mobile radio stations, the distribution modulation employed in -the mobile radio station is selected by the stationary radio station and reported during the connection set-up of the mobile radio station. For the transmission of signalling information to the mobile radio station assigned to the stationary radio station a distribution modulation is used which is common to all -the mobile radio s-tations, in the 3~ t'7~;;
PHD &5 320 -5~ 86 direction from the stationary radio station to the mobile radio stations.
To distinguish between stationary radio stations in ad-jacent radio cells, these stations transmit, from the stationary radio stations to the mobile radio stations, in different frequency bands. The stationary radio stations include narrow-band receivers which during operation can be switched to a plurality of frequency channels. The number of transmission frequencies switchable in the mobile ratio station is less than the number of receiver frequencies switchable in the stationary radio station. It is, for example, possible to effect in the stationary radio station a switch-over to 1,000 frequencies and a switch to 40 frequencies in themobile radio station.
In each stationary radio station the receiver frequencies used there are managed on the basis of the interference situation.
In the case of interferences in the reception, the relevant connection, from the mobile radio station to the stationary radio station, is switched to a different, non-disturbed frequency channel, to which both the stationary radio station and the mobile radio station can switch. The receiver arrangement in the stationary radio station towards the wire network of the public telephone system continues to par-ticipate in the connection.
Synchronising the receiver arrangement is very important when the block-wise transmission of messages of opted for, as in the case of incorrect synchronisation the entire block and the message contained therein are mutilated. ~lore specifically, in a radio trans-mission system in which the connection is effected via propagation paths which are subjected to obstruction and in which reflection frequently occurs, errors often occur in the received signal and result in disturbances in the connection. The connection disturbances whose duration and frequency depend on the transmission rate and correspond to a Rayleight distribution, are based on a transmission path-dependent field strength distribu-tion, which in dependence on the reflection c oe fficients of the environment result in error rates of well over 1 %, briefly substantlally 50 %.
The invention has for its object to provide a message transmission method in which the synchronisation of the receiver arrangements can be effected free from disturbances.
This objec-t is accomplished by the characteristics of the c~e'~5 PH~ SS 320 -6- 11-2-19~6 Patent Claim 1.
In the method according to the invention, the same syn-chronising symkols are gated into the code levels (code-division multiplex transmission system) or frequency levels (frequency-division multiplex transmission system). This may accomplish that the synchro-nisation symkols transmitted by the(central transmission station (stationary radio station) do not disturb each other. The synchro-nising symbols which are simultaneously transmitted in all the message transmission channels are received in all the receiver arrangements with a significantly higher energy compared with the useful information.
When the m~thod according to the invention is used in a digital radio transmission system, adjacent stationary radio stations can be dis-tinguished by different frequencies or different code words. The syn-chronising symbols can be received substantially interference-free and be utiliæed in the receiver arrangement for a fail -safe survey of the multipath profile. By gating the synchronising symbols into the continuous data stream of the useful information, spaced, for example, by one ms, utilising the multi-path reception is possible also at high vehicle speeds. The method according to the invention can then also be 20 used in different transmission methods (for example 2-PSK) or different multiplex methcds (for example CDM: Code Division Multiplex ).
The method as claimed in Patent Claim 2 has the advantage that ~ecause of the phase-locked (not necessarily equal phase) addition of the synchronising symkols a (non-controlled) opposite triggering of the in themselves identical synchronising symbols in the individual message -transmission channels is prevented.
For distributing the synchronising symbols and the data symbols it is possible to use the same distribution codes in the code levels. If in accordance with patent claim 3 different code sets are 30 used, an erroneous synchronisation in the receiver arrangement can be excluded with certainty. The same holds when a code-division multiplex method is used for the clata symkols and different frequencies for the synchronising symbols.
If, in accordance with patent claim 4, the data and synchro-35 nising symbols of the different message transmission channels aretransmitted in code-division multiplex, the noise-immunity of the synchronisation can ke in~roved to a still greater extent, as the mutual interferences of different message transmission channels which are typical PH~ ~5 320 -7- 11-2-1986 for the code-division multiplex method are not present in the synchro-nising sym~ols.
If, in accordance with patent claim 5, the receiver ar-rangement is matched to the channel properties on the basis of the supervised multi-pa~h profile, then the accuracy of a goo~ transmission can be further increased. The matching operation can be effected by tracking the samplir.g instants or by adaptive equalization.
The method as claimed in patent claim 6 has the advantage that the synchronisation in the receiver arrangement, more specifically the circuit cost and design effort required therefor, can be reduced in a simple way and manner.
If in accordance with patent claim 7 the block length is a multiple of the distance between the synchronising sym~ols, then the synchronising method in the receiver can be simplified. The aim must then be a compromise between the receiver cost and circuit cost in the control arrangement for effecting the synchronisation. In the method as claimed in patent claim 8 a lower receiver cost and design effort is indeed required but on the other hand a more complicated synchronisation method is necessary.
For the embcdiment defined in claim 9 of a circuit arrange-ment for performing the metho~ as claimed in claim 1, an additional circuit cost and design effort are required, as a number of arrange-ments already present in the stationary and mobile radio stations can be utilized.
The method according to the invention will now be described in greater detail with reference to the em~cdiments shcwn in the accompanying drawings. Therein:
Fig. 1 illustrates for the case in which the method is used in a code-division multiplex transmission system, a first embodi-ment of the synchronising method accordirg to the invention, Fig. 2 illustrates the code sets used for the application shown in Fig. 1, Fig. 3 illustrates for the case in which the method is used in the combined code-division multiplex/frequency-division multiplex transmission system, a second embcdiment of the synchronising metllod according to the invention, Fig. 4 illustrates for the application in a code~division multiplex/time-division multiplex transmission system a third embodiment ~ ~J~ ~3'~ 5 PHD 85 320 -8- 11~2-1986 of the synchronising method according to the invention, and Fig. 5 shows the different code sets used in the application illustrated in Fig. 4.
Fig. 6 is a block circuit diagram of an embcdiment for the transmitter Fortion of the stationary ra~io station and Fig. 7 is a block circuit diagram of an embodiment for the receive portion of the mobile radio station for performing the method according to the invention.
Fig. 1 illustrates a code~division multiplex transmission system in which the individual transmission channels are separated from each other by using different sets of code symbols. ~ecause of the predetermined, selected code sym~ols for the distribution, such as, for example, pseudo~random orthcgonal or quasi-orthogonal code-words, the simultaneous transmission of messages in code-division multiplex is possible. In the emkcdiment shcwn in Fig. 1, eight ir.dividual distribution codes are used which evidence a distribution of 31, that is to say a length of 31. A distribution of 31 is only possible when used in a digital radio transmission system because all the code-division multiplex channels of the transmitter in the stationary radio sta-tion are transmitted with equal pcwers and time-synchronously. By using four symbols in each code division multiplex channel, two bits of the useful signal can be combined in one symbol.
As a result thereof the symbol rate is reduced by half relative to the baseband bit rate.
In the method according to the invention synchronising symkols s are inserted ketween the data symbols with defined spacings, these symbols being transmitted in all the message transmission channels in time-parallel and in synchronism, from the stationary radio station (BS). For the synchronisation two symbols cO, cO are required which are the same for all the code-division multiplex channels. Two of these symbols can be represented by an anti-pcdal distribution code-word and the relevant receiver arrangement must be capable of recog-nising three different anti-pcdal code words. Six different symbols are available for encoding the base-band signals and the synchronising symkols, two of which are exclusively used for synchronisation. As the message transmission is effected simultaneously in eight ccde-division multiplex channels, different code w~rds must be used in the transmitter 17 whilst for accessing the message tIansmission channel P~ 85 320 -9~ 2-1986 only three different code words are necessary in the receiver arrange-ment.
If in the digital multiplex transmission system three different code sets are used, then each receiver arrangement must be capable of setting its correlator to 51 different code w~rds, for which a maximum of three correlators are required. The synchronising symbol s is independent of the modulation of the signal ar.d encoding OL the message transmission channel, so that a synchronisation in the receiver direction is possible, without decoding and demcdulating the actual message. In the method according to the inventic,n no synchro-nisation of the transmitter is required in the multiplex transmission system (as shown in Fig. 3 between different sub-carrier frequencies of adjacent stationary radio stations BS1 to BS3). Only the message transmission channels separated by the code division multiplex method within a sub-carrier are synchronized. The synchronising sym~ols s which are transmitted simultaneously through the eight parallel code-division multiplex channels are received in all the receiver arrange-ments with a significantly higher energy than the data symbols.
If the voltage phases are correctly added together in the transmitter each individ~lal receiver arrangement receives the synchronising in-formation approximately 18 dB above the normal level. In addition, the ca~mon-channel interferences caused by the code-division multiplex-operated transmission channels of the same carrier disappear. As a result thereof a fail-safe synchronisation can be effected.
The receiver arrangement first synchronises itself with the frequency of the non-coherently received synchronising symbols s, the polarity of the synchronising symbols s (c0, c0) not being taken into account. As shown in Fig. 1 or Fig. 3 the synchronising symbols s are transmitted at defined ti~e distances, for example every millisecond, so that the synchronisation procedure of the bit synchronisation ends relatively quickly.
In the second step, the coherent demcdulation and conse-quently the recognition with the correct sign of the received symbo]s is rendered possible. Each synchronising symbol s pro~uces at the correlator output a positive or a negative pulse, corresponding to the logic state "1" or "0", respectively. The synchronising symbols s are encoded with positive or negative signs~ respectively, such that any sign reversal by a phase shifted thrcugh 180 can be de-tected PHD ~5 320 -10- 11-2-1986 therefrom, so that the synchronising m~ethod according to the invention can also be utilized for frame synchronisation in a cornbined ccde division multiplex-time division multiplex transmission system (see Figs. 4 and 5).
In the method according to the invention the synchronising symbol s can also be used f~r measuring the multi-path profile. To ensure that measuring the multi-path profile is as error-free as possible, the synchronising symbol s is transmitted at adequately short distances, for example every millisecond. Because of the sig-nificantly higher power campared with the data symbols the synchronising symbol s is received in the receiver arrangements sufficiently inter-ference-free. As a result thereof, m~lti-paths can be cancelled with a sufficient degree of accuracy and fading effects can be avoided to a very large extent.
The synchronising method according to the in~ention is also suitable for use in a cambined code-division multiplex/frequency-divisic,n multiplex transmission system. For the case in which the methcd is used in a digital radio transmission system, the stationary radio stations BS1 to BS3 are separated from each other by the use of different RF-carriers with different frequencies f. Each stationary radio station BS to BS3 supplies a cell group (cluster) formed by C-cells. Investigations have proved tha-t for the transmission direction from the stationary radio station to the receiver arran~ements a 3-cell cluster is sufficient for suppressing common-channel frequencies.
So as to render it possible to increase the transmission capacity in a digital radio transmission system still further additional message transmission channels are created in each code level using the time-division rnultiplex method. If eight individual distribution code levels with faur time-staggered channels are forned, then 32 individual channels up to 16 kbit/s each can be transmitted, which after code distribution are mcdulated on a cammon RF-carrier. When 4-phase mcdulation is used, a bandwidth of 1.25 l'~z is obtained for the 32 indiviclual channels. The non-coincidence in time and conse-quently t~ number of message transmission channels per distribution 3s code level depend on the bit rate required for each message trans-mission charmel. Because of the fact that each time two bits are cornbined to form one of four possible symbols, the syrnbol duration, which is 25/us, is adequately long to avoid intersymbol interferences 5 ~ ~3 ?'~7 5 produced by multi-path reception and on t~e other hand the cost in the receiver arrangements for the correlators is lcw. The 16 distribution codes used within a stationary radio station B~ for separating the code levels must be pairwise orthogonal for the case of an identical position in time, whilst in different stationary radio stations BS
having equal carriers the different synchronising symbols s must have the lowest possible cross-correlation products at any time shifts.
Distribution codes satisfying these conditions are what are commonly referred to as Gold codes. A change in the distribution code does not affect the receiver arrangements since these arrange-ments have programmable correlators which are always reset from con-nection to connection on the basis of indications supplied by the stationary radio station BS. Yor the transmission of such setting data and for separating the individual time channels in the time-division multiplex frame ZR, a control channel ACCH is provided inthe time-division multiplex frame ZR.
As will be obvious from Figs. 4 and 5, the synchronising symbols s in the time~division multiplex frame ZR are inserted with defined spacings between the data symbols and encoded with positive or negative signs such that therefrom any sign reversal by a phase shifted through 180 can be recognised and it may be decided~hat a frame starts. The receiver arrangement now only resets a bit counter and as a result thereof also the frame synchronisation is ensured. For a framelength of 20 milliseconds for -the time-division multiplex frame the time for the overall synchronisation procedure is oE the order of 100 ms. The 25/us sy~bol period of the distribution code word has been chosen so large that symbol interferences can be avoided to a very large extent or occur only with small amplitudes.
The chip duration is obtained at a distribution of 31 to 0.806 ns and the chip rate to 1.24 ~cps. Consequently, also the chip duration is small enough to allcw an adequate cancellation of the multi-paths and to avoid fading mfluences to the highest possible extent. Each code level allows a maxLmum gross bit rate of 76 kbit/s including 2kbit/s for a control channel ACCH assigned to each codeword and including 2 kbit/s for the transmission of synchronising information.
Fig. 6 is a block circuit diagram of the transmitting portion of the stationary radio station BS. The data/voice stream transmitted in the baseband is assembled as follows. The digitized 3e'~
PHD 85 320 -12~ 2-1986 speech of each individual channel is first converted in a code conver-ter 1 from PCM to the transmission methcd with correspondingly lcwer bit rate, required for the radio transmission. A data source can be connected in the interface B-s. In a channel code arrangement 2 5 connected to the data source and, converter, respectively, a special channel coding is added to protect significant bits from transmission errors in the transmission channel. Depending on the service -trans-mitting the information the channel coding can be different. In a multiplexer 3 connected to the channel coding arrangement 2 t~le signalling information accompanying the connection and the synchroni-sation information originating from the synchronising circuit 4 are inserted in the data stream. Consequently, the TDM-signal (Time-Division-Multiplex-signal) at the output of the TDM-multiplexer 3 comprises in the embcdiment shown in Fig. 4 four voice/data channels, a signalling channel (for a TDM channel bundle) and also the synchronising bits required for the synchronisation in the mobile radio station MS. The synchronising signals are gated into the TDM signal.
The TDM signal at the output of the multiplexer 3 is multiplied by each codeword produced by the code generator 5, always two bits being combined into one sym~ol and being distributed with the desired code. The code generator 5 is connected to a control arrangement 15 and controlled by the control arrangement 15 inserts synchronising symbols instead of data symbols into the continuous data stream occurring at the output of the ~ ultiplexer 3. A mo~ulation ~lethod adapted to the pro~erties of the radio transmission channel is applied to the distributed signal, for example the phase of a carrier signal originating from an oscillator 6 is then keyed by the distributed signal, a BPSK (Binary Phase Shift Keying) signal which is m~dulated at a low intermediate frequency and is combined with the information and the codeword being produced. The mcdulated CDM-signal is applied to an adder 7 whose output is connected to a bandpass filter 8. After having been added together and passband filtering, eight of these modulated CDM signals form an overall signal with ~,ulti-stage amplitude which finally is converted to the output fre-quency.
To that end a synthesizer 9 is provided as a mixeroscillater which, within the frequency range of the digital radio transmission system can be switched by corresponding stages. The ~P
PHD 85 320 -13~ 2-1986 synthesizer 9 is only designed for the few, possible frequencies of the TDM-stage (Frequency-Division Multiplex stage). Mixing the CDM signal with the corresponding frequency produced by the synthesizer 9 is effected in an arrangement 10 connected to a band-pass filter 11. The 5 output of the bandpass filter 11 is connected to a pcwer amplifier 12, and the filtered-out and amplified transmission signal is applied to the antenna 14~ via a transmitter coupler 13. The transmitter coupler 13 is completely omitted in the case of small stationary radio stations BS having up to 32 message transmission channels.
The channel and code generator setting, the appropriate selection of the channel code and inserting reports in the control data stream is effected by means of the control arrange~ent 15 provided in the stationary radio station BS. The selected radio transmission channel may then be a TDM channel in a CDM plane.
Fig. 7 is a block circuit diagram of the receiver portion of the mobile radio station ~S. The signal received from a com~on transmit/receive antenna 16 is applied to the input stage 18 of the receiver via a receive filter of a duplexer 17. The requirements to -be satisfied by the receive filter of the duplexer 17 are compara-tively low, so that also for mobile radio stations MS with a lcw service requirement, for example, a simple data radio set, a lcw-cost solution is possible. The signal is amplified in the input stage 18 and is then mixed with a syn-thesizer frequency received from the synthesizer 19 on an intermediate frequency.
The intermediate frequency is applied to an IF-portion 20, in which the signal is further amplified and filtered. A simple low-cost synthesizer can be used for synthesizer l9 and for the synthesizer 9 of the stationary radio station. The IF-portion 20 includes filters which have for their object the ad-jacent-channel selection for shielding frGm adjacent broadband channels and suppressing mixed products, respectively. The actual noise filtering action is effected in the correlato~s`23 to 25. An ampli-tude-control circuit 21 which raises the output signal of the IF-portion 20 to an appropriate level for driving the subsequent circuits and prevents the risk of these circuits from being overdriven, is connected to -the IF-portion 20. The amplitude control circuit 21 equalizes different radio field attenuations and le~rel fluctuations due to shadowing, so that in the subsequent arrangements of the mobile radio ~r~ e~3~
PHD ~5 320 -14~ 11 -2-1986 station MS a linear processing operation can be performed. The control time constant of the amplitude control circuit 21 is basically deter-mined by the shadow effects.
The pcwer-controlled IF-signal at the output of the amplitude control circuit 21 is converted in the baseband in a de-m~dulator 22 connected to the amplitude control circuit. This can, for example, be effected by using a BPSK mcdulation of the Costas loop principle, so that also the frequency and the phase are taken into account. Ambiguities and integral multiples of 180 can be recog-nized and compensated for on the bas~s of the polarity of the synchro-nising word received.
Three correlators 23, 24 and 25, which are adjusted by a control arrangement 26 to the codes 1 and 2 then valid and to a synchro-nising code valid in the radio zone for the overall channel bundle, are connected to the demcdulator 22. By means of the control arrange-ment 26 the received control data stream is evalua-ted in that the data of the service desired by the subscriber and the data for the device-specific radio transmission channels are read, a radio transmission channel which in the control data stream is indicated as being free and which is switchable in the mobile radio station MS is selected, and subsequently an access slgnal is transmitted to the stationary radio station BS.
The output signal of the correlators 23 to 25 is used for deriving the symbol clock, the frame clock and the bit clock, and is also used to measure the instantaneously valid multi-path profile.
As a uniform synchronising ccde with correspandingly higher level is radiated into the overall channel h mdle at the same instant, an unambiguous synchronisation detection and mul-ti-path profile measure-ment is obtained.
The cutputs of the correlators 24 and 25 are connected to sampling circuits 27~ 28 which sample the outpu-t signals of the correlators 24 and 25 and apply each sampling result to a decision stage 29. The results of the sampling operations which are perEormed synchronously with the echos of the multi-path prcpagation are weighted in the decision stage 29 proportionally to the echo amplitude (using an arrangement 30. The decision stage 29 has for its object to estimate the transmitted code and the polarity of the code. The est~imated value consequently allows the selection of the symbols which are mlost PHD 85 320 -15~ 2-1986 probably transmitted.Pfter the sym~ol to-bit conversion in the decision stage 29 the Cltput signal is transmi-tted to a TDM demulti-plexer 31 connected to the decision stage 29. The demul~iplexer 31 is connected to a channel decoder 32 at whose output the transmitted data stream is available again. In digital speech transmission the digital speech signal is decoded in a speech deccder 33 and applied to a D/A converter and a loudspeaker connected thereto.
If, for example, the data service type of service is provided in the mobile radio station MS, then the data p~oduced at the cutput of the ch~nnel decoder 32 can directly, for example/ be sh~n or expressed.
~0
PHD ~5-320 1 10-02-1986 ~lethod oE and a~ran~enent for synchro~is~ng the receiver arr~nge-nPnts in a digital ~,ultiple~ transmission system.
The invention relates to a method of synchronis-ing the receiver arrangements in a digital multiplex transmission system as claimed in the introductory part of the paten-t Claim 1.
For the transmission of messages via a trans-mission means (for example lines, radio-channels) which is used in common by a plurality of subscribers, three basic methods are known, namely the code-division mul-tiplex method, the frequency-division multiplex method and the time-division multiplex method.
In the code-division multiplex method the different messages conveyed through a common transmission means are, for example, modulated on a sub-carrier by basic modulation and -the resultant signal which, compared with the chann0l bandwidth, is a narrow-band signal is spectrally distri-buted over the channel bandwid-th by multiplex modulation with the aid of a code word characterising the receiver.
I`he code-division multiplex channel (message transmission channel) thus obtained is not limited, neither in time nor within the bandwidth, bu-t is limited relative to the power density. Recognising the signal is not effected by selec-tion on -time or fre4uency basis but on -the basis of spec-tral coding. The plurality of spectrally encoded mes3agest superposed in the code-division multiplexed channel, are selected in the receiver on the basis of the code word assigned thereto. For the two-stage modulation (basic and multiplex modulation) phase shift keying (PSK) or frequency shift keying (FS~) are often u-tilized in radio trans-mission systems.
The first stage receives, for example, the digi-tized speech signal (after having been converted in an analog-to-digital converter) which includes9 for example, a multiplicative mixer. In the multiplicative mixer th~
supplied digitized speech signal is combined with a code-word assigned to this transmitter, which results in a spectral distribution. In the second modulation stage of the transmitter the wide-band signal (modulated, binary 5 character sequence) is converted into a frequency position suitable for the transmission.
Recovering the message at the receiver side is effected in the above-described code-division multiplex method by a sequence of basic demodulation and multiplex demodulation. Coversion to a frequency position (for ex-ample baseband position~ suitable for the multiplex de-modulation is effected in the basic demodulation stage by multiplying the signal by the reference sub-carrier. With the aid of a code word generator arranged in the receiver and also a code synchronising circuit the spactral dis-tribution is cancelled, after the code word has been synchronised in the ~pprop~ab0 p~ge Wl~h ~he r~ceivsr code word. As a result thereof, the signal energy which has previously been spectrally distributed over -the entire transmission band is compressed to the original frequency band, whilst the adjacent characters entering the receiver with a different multiplex modulation remain in the spec-trally dlstributed state and can be suppressed by a band-pass filter having a bandwidth corresponding to the band-widthof -the non-distributed signal.
The system-determined residual interference in the multiplex demodulation produced by the other signals is lower according as the values of the cross-correlation functions between the codewords used are lower and the distribution factor is larger. A non-zero value of the cross-corralation function reduces the signal-to-noise ratio. The signal-to-noise ratio and the synchronising period are determined by the cross-correlation and auto-correlation function.
In the frequency-division multiplex method the total bandwidthavailable for message transmission is sub-divided into narrow frequency bands which each correspond 7~
PHD ~5-320 3 10-02-1986 to a message ~ransmission channel. Such a narrow frequency band is available to the subscriber for the duration of the ratio transmission.
In the time-division multiplex method each subscriber has the disposal of a total bandwidt of a single ratio channel which the subscriber may only utilize for short periods of time. The characters or character se-quences of different subscribers are interleaved and are transmitted with correspondingly higher bit rates through the single radio channel, each time a channel assigned to a subscriber being repeated periodically with the frame period duration.
DE-OS 25 37 683 discloses a radio transmissàon system having stationary radio stations and mobile radio stations in which different channel accessing methods with asynchronous time-division multiplex, code-division multiplex and frequency-division rnultiplex are used.
~or codeword synchronisation an incoherent sub-carrier demodulation is used. A code generator generates sequentially one of the nine differen-t codes, which char-acteri~e the sta-tionary ground-based radio stations. After this code h&s been synchronised with the receiver signal the IF-signal is multiplied, causing the wide spectrum in the message bandwidth to be transformed. Subsequent there-to the received message can, for example, be recovered using a DPSK demodulator. Eor the pu~pose of synchronisa--tion its own code sample, having a length of, for example 15 bits, is used, which precedes the mes~age.
Also combinations of the above-mentioned methods and their use in a digital radio transmission system are known. "Nachrichtentechnik, Elektronik ~ Telematik 38 (1984), Vol. 7, pages 264 to 268" describes for example a digital radio transmission system in which the time-divi-sion multiplex method is used in combination with ~ode distribution. In the time channel for speech and/or data transmission (communication channel TCA) there are sequen~
ially transmitted a bit sequence for determining the bit clock (synchronous), a frame synchronising word (leader) ~J~ 5 PHD. 85-320 4 and the bit sequence of the message itself. The time channel for message transmission (3 x 20 TCA) are combined with the control channels (3 CCH) to form a time-division multiplex frame having a duration of 31.5 msec. If the speech signal must be transmitted as the message, then the adaptive delta modulation can be used for analog-to-digital conversion. The message characters (bi-ts) then obtained ha~e a code superposed on them in the transmitter.
It has been found to be advanta~eous to combine individual message characters in blocks of four bits each and to distribute the block thus obtained by means of an ortho-gonal alphabet. The distribution factor used therewith is a compromise to combine the advantages of band distribu-tion with the requirements as regards economical use of the frequencies. In addition, a message transmission method has been proposed in which a different modula-tion method is utilized in the forward and return directions of the message transmission channels. For message transmission the mobile radio stations access one of a plurality of message channels. In the direction from the stationary radio station to the mobile radio stations assigned thereto, each message channel is distributed by means of distribution modulation. The distributed message channels are super-posed on each other and the wide-band sum signal thus obtained is transmitted in a common frequency band. In -the direction from the mobile radio stations -to the stationary radio station the message transmission is effected in separate, narrow-band frequency channels.
For the transmission of speech, in the direction from the stationary radio station to the mobile radio stations, the distribution modulation employed in -the mobile radio station is selected by the stationary radio station and reported during the connection set-up of the mobile radio station. For the transmission of signalling information to the mobile radio station assigned to the stationary radio station a distribution modulation is used which is common to all -the mobile radio s-tations, in the 3~ t'7~;;
PHD &5 320 -5~ 86 direction from the stationary radio station to the mobile radio stations.
To distinguish between stationary radio stations in ad-jacent radio cells, these stations transmit, from the stationary radio stations to the mobile radio stations, in different frequency bands. The stationary radio stations include narrow-band receivers which during operation can be switched to a plurality of frequency channels. The number of transmission frequencies switchable in the mobile ratio station is less than the number of receiver frequencies switchable in the stationary radio station. It is, for example, possible to effect in the stationary radio station a switch-over to 1,000 frequencies and a switch to 40 frequencies in themobile radio station.
In each stationary radio station the receiver frequencies used there are managed on the basis of the interference situation.
In the case of interferences in the reception, the relevant connection, from the mobile radio station to the stationary radio station, is switched to a different, non-disturbed frequency channel, to which both the stationary radio station and the mobile radio station can switch. The receiver arrangement in the stationary radio station towards the wire network of the public telephone system continues to par-ticipate in the connection.
Synchronising the receiver arrangement is very important when the block-wise transmission of messages of opted for, as in the case of incorrect synchronisation the entire block and the message contained therein are mutilated. ~lore specifically, in a radio trans-mission system in which the connection is effected via propagation paths which are subjected to obstruction and in which reflection frequently occurs, errors often occur in the received signal and result in disturbances in the connection. The connection disturbances whose duration and frequency depend on the transmission rate and correspond to a Rayleight distribution, are based on a transmission path-dependent field strength distribu-tion, which in dependence on the reflection c oe fficients of the environment result in error rates of well over 1 %, briefly substantlally 50 %.
The invention has for its object to provide a message transmission method in which the synchronisation of the receiver arrangements can be effected free from disturbances.
This objec-t is accomplished by the characteristics of the c~e'~5 PH~ SS 320 -6- 11-2-19~6 Patent Claim 1.
In the method according to the invention, the same syn-chronising symkols are gated into the code levels (code-division multiplex transmission system) or frequency levels (frequency-division multiplex transmission system). This may accomplish that the synchro-nisation symkols transmitted by the(central transmission station (stationary radio station) do not disturb each other. The synchro-nising symbols which are simultaneously transmitted in all the message transmission channels are received in all the receiver arrangements with a significantly higher energy compared with the useful information.
When the m~thod according to the invention is used in a digital radio transmission system, adjacent stationary radio stations can be dis-tinguished by different frequencies or different code words. The syn-chronising symbols can be received substantially interference-free and be utiliæed in the receiver arrangement for a fail -safe survey of the multipath profile. By gating the synchronising symbols into the continuous data stream of the useful information, spaced, for example, by one ms, utilising the multi-path reception is possible also at high vehicle speeds. The method according to the invention can then also be 20 used in different transmission methods (for example 2-PSK) or different multiplex methcds (for example CDM: Code Division Multiplex ).
The method as claimed in Patent Claim 2 has the advantage that ~ecause of the phase-locked (not necessarily equal phase) addition of the synchronising symkols a (non-controlled) opposite triggering of the in themselves identical synchronising symbols in the individual message -transmission channels is prevented.
For distributing the synchronising symbols and the data symbols it is possible to use the same distribution codes in the code levels. If in accordance with patent claim 3 different code sets are 30 used, an erroneous synchronisation in the receiver arrangement can be excluded with certainty. The same holds when a code-division multiplex method is used for the clata symkols and different frequencies for the synchronising symbols.
If, in accordance with patent claim 4, the data and synchro-35 nising symbols of the different message transmission channels aretransmitted in code-division multiplex, the noise-immunity of the synchronisation can ke in~roved to a still greater extent, as the mutual interferences of different message transmission channels which are typical PH~ ~5 320 -7- 11-2-1986 for the code-division multiplex method are not present in the synchro-nising sym~ols.
If, in accordance with patent claim 5, the receiver ar-rangement is matched to the channel properties on the basis of the supervised multi-pa~h profile, then the accuracy of a goo~ transmission can be further increased. The matching operation can be effected by tracking the samplir.g instants or by adaptive equalization.
The method as claimed in patent claim 6 has the advantage that the synchronisation in the receiver arrangement, more specifically the circuit cost and design effort required therefor, can be reduced in a simple way and manner.
If in accordance with patent claim 7 the block length is a multiple of the distance between the synchronising sym~ols, then the synchronising method in the receiver can be simplified. The aim must then be a compromise between the receiver cost and circuit cost in the control arrangement for effecting the synchronisation. In the method as claimed in patent claim 8 a lower receiver cost and design effort is indeed required but on the other hand a more complicated synchronisation method is necessary.
For the embcdiment defined in claim 9 of a circuit arrange-ment for performing the metho~ as claimed in claim 1, an additional circuit cost and design effort are required, as a number of arrange-ments already present in the stationary and mobile radio stations can be utilized.
The method according to the invention will now be described in greater detail with reference to the em~cdiments shcwn in the accompanying drawings. Therein:
Fig. 1 illustrates for the case in which the method is used in a code-division multiplex transmission system, a first embodi-ment of the synchronising method accordirg to the invention, Fig. 2 illustrates the code sets used for the application shown in Fig. 1, Fig. 3 illustrates for the case in which the method is used in the combined code-division multiplex/frequency-division multiplex transmission system, a second embcdiment of the synchronising metllod according to the invention, Fig. 4 illustrates for the application in a code~division multiplex/time-division multiplex transmission system a third embodiment ~ ~J~ ~3'~ 5 PHD 85 320 -8- 11~2-1986 of the synchronising method according to the invention, and Fig. 5 shows the different code sets used in the application illustrated in Fig. 4.
Fig. 6 is a block circuit diagram of an embcdiment for the transmitter Fortion of the stationary ra~io station and Fig. 7 is a block circuit diagram of an embodiment for the receive portion of the mobile radio station for performing the method according to the invention.
Fig. 1 illustrates a code~division multiplex transmission system in which the individual transmission channels are separated from each other by using different sets of code symbols. ~ecause of the predetermined, selected code sym~ols for the distribution, such as, for example, pseudo~random orthcgonal or quasi-orthogonal code-words, the simultaneous transmission of messages in code-division multiplex is possible. In the emkcdiment shcwn in Fig. 1, eight ir.dividual distribution codes are used which evidence a distribution of 31, that is to say a length of 31. A distribution of 31 is only possible when used in a digital radio transmission system because all the code-division multiplex channels of the transmitter in the stationary radio sta-tion are transmitted with equal pcwers and time-synchronously. By using four symbols in each code division multiplex channel, two bits of the useful signal can be combined in one symbol.
As a result thereof the symbol rate is reduced by half relative to the baseband bit rate.
In the method according to the invention synchronising symkols s are inserted ketween the data symbols with defined spacings, these symbols being transmitted in all the message transmission channels in time-parallel and in synchronism, from the stationary radio station (BS). For the synchronisation two symbols cO, cO are required which are the same for all the code-division multiplex channels. Two of these symbols can be represented by an anti-pcdal distribution code-word and the relevant receiver arrangement must be capable of recog-nising three different anti-pcdal code words. Six different symbols are available for encoding the base-band signals and the synchronising symkols, two of which are exclusively used for synchronisation. As the message transmission is effected simultaneously in eight ccde-division multiplex channels, different code w~rds must be used in the transmitter 17 whilst for accessing the message tIansmission channel P~ 85 320 -9~ 2-1986 only three different code words are necessary in the receiver arrange-ment.
If in the digital multiplex transmission system three different code sets are used, then each receiver arrangement must be capable of setting its correlator to 51 different code w~rds, for which a maximum of three correlators are required. The synchronising symbol s is independent of the modulation of the signal ar.d encoding OL the message transmission channel, so that a synchronisation in the receiver direction is possible, without decoding and demcdulating the actual message. In the method according to the inventic,n no synchro-nisation of the transmitter is required in the multiplex transmission system (as shown in Fig. 3 between different sub-carrier frequencies of adjacent stationary radio stations BS1 to BS3). Only the message transmission channels separated by the code division multiplex method within a sub-carrier are synchronized. The synchronising sym~ols s which are transmitted simultaneously through the eight parallel code-division multiplex channels are received in all the receiver arrange-ments with a significantly higher energy than the data symbols.
If the voltage phases are correctly added together in the transmitter each individ~lal receiver arrangement receives the synchronising in-formation approximately 18 dB above the normal level. In addition, the ca~mon-channel interferences caused by the code-division multiplex-operated transmission channels of the same carrier disappear. As a result thereof a fail-safe synchronisation can be effected.
The receiver arrangement first synchronises itself with the frequency of the non-coherently received synchronising symbols s, the polarity of the synchronising symbols s (c0, c0) not being taken into account. As shown in Fig. 1 or Fig. 3 the synchronising symbols s are transmitted at defined ti~e distances, for example every millisecond, so that the synchronisation procedure of the bit synchronisation ends relatively quickly.
In the second step, the coherent demcdulation and conse-quently the recognition with the correct sign of the received symbo]s is rendered possible. Each synchronising symbol s pro~uces at the correlator output a positive or a negative pulse, corresponding to the logic state "1" or "0", respectively. The synchronising symbols s are encoded with positive or negative signs~ respectively, such that any sign reversal by a phase shifted thrcugh 180 can be de-tected PHD ~5 320 -10- 11-2-1986 therefrom, so that the synchronising m~ethod according to the invention can also be utilized for frame synchronisation in a cornbined ccde division multiplex-time division multiplex transmission system (see Figs. 4 and 5).
In the method according to the invention the synchronising symbol s can also be used f~r measuring the multi-path profile. To ensure that measuring the multi-path profile is as error-free as possible, the synchronising symbol s is transmitted at adequately short distances, for example every millisecond. Because of the sig-nificantly higher power campared with the data symbols the synchronising symbol s is received in the receiver arrangements sufficiently inter-ference-free. As a result thereof, m~lti-paths can be cancelled with a sufficient degree of accuracy and fading effects can be avoided to a very large extent.
The synchronising method according to the in~ention is also suitable for use in a cambined code-division multiplex/frequency-divisic,n multiplex transmission system. For the case in which the methcd is used in a digital radio transmission system, the stationary radio stations BS1 to BS3 are separated from each other by the use of different RF-carriers with different frequencies f. Each stationary radio station BS to BS3 supplies a cell group (cluster) formed by C-cells. Investigations have proved tha-t for the transmission direction from the stationary radio station to the receiver arran~ements a 3-cell cluster is sufficient for suppressing common-channel frequencies.
So as to render it possible to increase the transmission capacity in a digital radio transmission system still further additional message transmission channels are created in each code level using the time-division rnultiplex method. If eight individual distribution code levels with faur time-staggered channels are forned, then 32 individual channels up to 16 kbit/s each can be transmitted, which after code distribution are mcdulated on a cammon RF-carrier. When 4-phase mcdulation is used, a bandwidth of 1.25 l'~z is obtained for the 32 indiviclual channels. The non-coincidence in time and conse-quently t~ number of message transmission channels per distribution 3s code level depend on the bit rate required for each message trans-mission charmel. Because of the fact that each time two bits are cornbined to form one of four possible symbols, the syrnbol duration, which is 25/us, is adequately long to avoid intersymbol interferences 5 ~ ~3 ?'~7 5 produced by multi-path reception and on t~e other hand the cost in the receiver arrangements for the correlators is lcw. The 16 distribution codes used within a stationary radio station B~ for separating the code levels must be pairwise orthogonal for the case of an identical position in time, whilst in different stationary radio stations BS
having equal carriers the different synchronising symbols s must have the lowest possible cross-correlation products at any time shifts.
Distribution codes satisfying these conditions are what are commonly referred to as Gold codes. A change in the distribution code does not affect the receiver arrangements since these arrange-ments have programmable correlators which are always reset from con-nection to connection on the basis of indications supplied by the stationary radio station BS. Yor the transmission of such setting data and for separating the individual time channels in the time-division multiplex frame ZR, a control channel ACCH is provided inthe time-division multiplex frame ZR.
As will be obvious from Figs. 4 and 5, the synchronising symbols s in the time~division multiplex frame ZR are inserted with defined spacings between the data symbols and encoded with positive or negative signs such that therefrom any sign reversal by a phase shifted through 180 can be recognised and it may be decided~hat a frame starts. The receiver arrangement now only resets a bit counter and as a result thereof also the frame synchronisation is ensured. For a framelength of 20 milliseconds for -the time-division multiplex frame the time for the overall synchronisation procedure is oE the order of 100 ms. The 25/us sy~bol period of the distribution code word has been chosen so large that symbol interferences can be avoided to a very large extent or occur only with small amplitudes.
The chip duration is obtained at a distribution of 31 to 0.806 ns and the chip rate to 1.24 ~cps. Consequently, also the chip duration is small enough to allcw an adequate cancellation of the multi-paths and to avoid fading mfluences to the highest possible extent. Each code level allows a maxLmum gross bit rate of 76 kbit/s including 2kbit/s for a control channel ACCH assigned to each codeword and including 2 kbit/s for the transmission of synchronising information.
Fig. 6 is a block circuit diagram of the transmitting portion of the stationary radio station BS. The data/voice stream transmitted in the baseband is assembled as follows. The digitized 3e'~
PHD 85 320 -12~ 2-1986 speech of each individual channel is first converted in a code conver-ter 1 from PCM to the transmission methcd with correspondingly lcwer bit rate, required for the radio transmission. A data source can be connected in the interface B-s. In a channel code arrangement 2 5 connected to the data source and, converter, respectively, a special channel coding is added to protect significant bits from transmission errors in the transmission channel. Depending on the service -trans-mitting the information the channel coding can be different. In a multiplexer 3 connected to the channel coding arrangement 2 t~le signalling information accompanying the connection and the synchroni-sation information originating from the synchronising circuit 4 are inserted in the data stream. Consequently, the TDM-signal (Time-Division-Multiplex-signal) at the output of the TDM-multiplexer 3 comprises in the embcdiment shown in Fig. 4 four voice/data channels, a signalling channel (for a TDM channel bundle) and also the synchronising bits required for the synchronisation in the mobile radio station MS. The synchronising signals are gated into the TDM signal.
The TDM signal at the output of the multiplexer 3 is multiplied by each codeword produced by the code generator 5, always two bits being combined into one sym~ol and being distributed with the desired code. The code generator 5 is connected to a control arrangement 15 and controlled by the control arrangement 15 inserts synchronising symbols instead of data symbols into the continuous data stream occurring at the output of the ~ ultiplexer 3. A mo~ulation ~lethod adapted to the pro~erties of the radio transmission channel is applied to the distributed signal, for example the phase of a carrier signal originating from an oscillator 6 is then keyed by the distributed signal, a BPSK (Binary Phase Shift Keying) signal which is m~dulated at a low intermediate frequency and is combined with the information and the codeword being produced. The mcdulated CDM-signal is applied to an adder 7 whose output is connected to a bandpass filter 8. After having been added together and passband filtering, eight of these modulated CDM signals form an overall signal with ~,ulti-stage amplitude which finally is converted to the output fre-quency.
To that end a synthesizer 9 is provided as a mixeroscillater which, within the frequency range of the digital radio transmission system can be switched by corresponding stages. The ~P
PHD 85 320 -13~ 2-1986 synthesizer 9 is only designed for the few, possible frequencies of the TDM-stage (Frequency-Division Multiplex stage). Mixing the CDM signal with the corresponding frequency produced by the synthesizer 9 is effected in an arrangement 10 connected to a band-pass filter 11. The 5 output of the bandpass filter 11 is connected to a pcwer amplifier 12, and the filtered-out and amplified transmission signal is applied to the antenna 14~ via a transmitter coupler 13. The transmitter coupler 13 is completely omitted in the case of small stationary radio stations BS having up to 32 message transmission channels.
The channel and code generator setting, the appropriate selection of the channel code and inserting reports in the control data stream is effected by means of the control arrange~ent 15 provided in the stationary radio station BS. The selected radio transmission channel may then be a TDM channel in a CDM plane.
Fig. 7 is a block circuit diagram of the receiver portion of the mobile radio station ~S. The signal received from a com~on transmit/receive antenna 16 is applied to the input stage 18 of the receiver via a receive filter of a duplexer 17. The requirements to -be satisfied by the receive filter of the duplexer 17 are compara-tively low, so that also for mobile radio stations MS with a lcw service requirement, for example, a simple data radio set, a lcw-cost solution is possible. The signal is amplified in the input stage 18 and is then mixed with a syn-thesizer frequency received from the synthesizer 19 on an intermediate frequency.
The intermediate frequency is applied to an IF-portion 20, in which the signal is further amplified and filtered. A simple low-cost synthesizer can be used for synthesizer l9 and for the synthesizer 9 of the stationary radio station. The IF-portion 20 includes filters which have for their object the ad-jacent-channel selection for shielding frGm adjacent broadband channels and suppressing mixed products, respectively. The actual noise filtering action is effected in the correlato~s`23 to 25. An ampli-tude-control circuit 21 which raises the output signal of the IF-portion 20 to an appropriate level for driving the subsequent circuits and prevents the risk of these circuits from being overdriven, is connected to -the IF-portion 20. The amplitude control circuit 21 equalizes different radio field attenuations and le~rel fluctuations due to shadowing, so that in the subsequent arrangements of the mobile radio ~r~ e~3~
PHD ~5 320 -14~ 11 -2-1986 station MS a linear processing operation can be performed. The control time constant of the amplitude control circuit 21 is basically deter-mined by the shadow effects.
The pcwer-controlled IF-signal at the output of the amplitude control circuit 21 is converted in the baseband in a de-m~dulator 22 connected to the amplitude control circuit. This can, for example, be effected by using a BPSK mcdulation of the Costas loop principle, so that also the frequency and the phase are taken into account. Ambiguities and integral multiples of 180 can be recog-nized and compensated for on the bas~s of the polarity of the synchro-nising word received.
Three correlators 23, 24 and 25, which are adjusted by a control arrangement 26 to the codes 1 and 2 then valid and to a synchro-nising code valid in the radio zone for the overall channel bundle, are connected to the demcdulator 22. By means of the control arrange-ment 26 the received control data stream is evalua-ted in that the data of the service desired by the subscriber and the data for the device-specific radio transmission channels are read, a radio transmission channel which in the control data stream is indicated as being free and which is switchable in the mobile radio station MS is selected, and subsequently an access slgnal is transmitted to the stationary radio station BS.
The output signal of the correlators 23 to 25 is used for deriving the symbol clock, the frame clock and the bit clock, and is also used to measure the instantaneously valid multi-path profile.
As a uniform synchronising ccde with correspandingly higher level is radiated into the overall channel h mdle at the same instant, an unambiguous synchronisation detection and mul-ti-path profile measure-ment is obtained.
The cutputs of the correlators 24 and 25 are connected to sampling circuits 27~ 28 which sample the outpu-t signals of the correlators 24 and 25 and apply each sampling result to a decision stage 29. The results of the sampling operations which are perEormed synchronously with the echos of the multi-path prcpagation are weighted in the decision stage 29 proportionally to the echo amplitude (using an arrangement 30. The decision stage 29 has for its object to estimate the transmitted code and the polarity of the code. The est~imated value consequently allows the selection of the symbols which are mlost PHD 85 320 -15~ 2-1986 probably transmitted.Pfter the sym~ol to-bit conversion in the decision stage 29 the Cltput signal is transmi-tted to a TDM demulti-plexer 31 connected to the decision stage 29. The demul~iplexer 31 is connected to a channel decoder 32 at whose output the transmitted data stream is available again. In digital speech transmission the digital speech signal is decoded in a speech deccder 33 and applied to a D/A converter and a loudspeaker connected thereto.
If, for example, the data service type of service is provided in the mobile radio station MS, then the data p~oduced at the cutput of the ch~nnel decoder 32 can directly, for example/ be sh~n or expressed.
~0
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a digital multiplex transmission system com-prising a base radio station having a transmitter and a plurality of mobile radio stations each having a receiver, channels for transmission of data symbols (dl ... dn) from the transmitter to the respective receivers being established by employing different code distributions of such data symbols in respective channels, such data sym-bols being transmitted in time-synchronism with each other;
a method of synchronizing the base station transmitter with the mobile station receivers, comprising:
insertion of respective synchronizing symbols (Sl ...
Sn) between successive data symbols transmitted in each of said channels, the synchronizing symbols in all channels being identical and the synchronizing symbols in each channel all being spaced at the same time intervals; and simultaneously transmit-ting the speech symbols in a plurality of said channels.
a method of synchronizing the base station transmitter with the mobile station receivers, comprising:
insertion of respective synchronizing symbols (Sl ...
Sn) between successive data symbols transmitted in each of said channels, the synchronizing symbols in all channels being identical and the synchronizing symbols in each channel all being spaced at the same time intervals; and simultaneously transmit-ting the speech symbols in a plurality of said channels.
2. A method as claimed in Claim 1, characterized in that the data symbols of the individual message trans-mission channels are transmitted with a defined mutual carrier phase.
3. A method as claimed in Claim 1, characterized in that synchronizing symbols (sl ... sn) are used which differ from all the data symbols (dl ... dn).
4. A method as claimed in Claim 1, characterized in that data and synchronizing symbols (dl ... d, sl ... sn) of the different message transmission channels are trans-mitted in accordance with a code-division multiplex method.
5. A method as claimed in Claim 1, characterized in that each receiver determines on the basis of the received synchronising symbols (sl ... sn) the instantaneous trans-mission factors of the message transmission channel and the receiver adapts its properties continuously to such transmission factors.
6. A method as claimed in Claim 1, characterized in that the synchronising symbols (sl ... sn) are transmitted at regular time intervals which are known to the receiver.
7. A method as claimed in Claim 1, characterized in that the data symbols are transmitted block-sequentially, the synchronizing symbols are transmitted as either of at least two different symbols (co, co), the sequence and time positions of the symbols (co, co) being known to the receiver, and that from the instants of reception of received blocks of data symbols and the sequence of the received symbols (co, co) the receiver determines the time position of the beginning of each block of data symbols.
8. A method as claimed in Claim 1, characterized in that the data symbols are transmitted block-sequentially, the synchronizing symbols are transmitted at time intervals in relation to the transmitted data blocks which are known to the receiver, and from the time positions of the received synchronizing symbols the receiver determines the time position of the beginning of each block of data symbols.
9. In a digital radio transmission system in which a plurality of message transmission channels are established between a stationary radio station transmitter and a plur-ality of mobile radio station receivers by a combination of time-division multiplex, code-division multiplex and frequency-division multiplex transmission; a circuit arrangement for performing a method as claimed in claim 1, such arrangement being characterized in that:
the stationary radio station transmitter comprises a control arrangement (15) and a synchronizing cir-cuit (4) connected thereto, such control arrangement inserting successive synchronizing symbols (sl ... sn) produced by the synchronizing circuit (4) between successive data symbols (dl ... dn) transmitted in each channel, the synchronizing symbols in each channels being spaced at the same time intervals; and a code generator (5) connected to and controlled by the control arrangement (15), such code generator selecting the synchronizing symbols from a store of such symbols contained therein; and each of the mobile radio station receivers comprises a plurality of sampling circuits for sampling received data symbols;
a control arrangement (26) for synchronizing said samp-ling circuits with received synchronizing symbols; and an echo signal amplitude detector connected to said sampling circuits for weighting the sampled received data symbols in proportion to the amplitudes of received echoes of the data symbols.
the stationary radio station transmitter comprises a control arrangement (15) and a synchronizing cir-cuit (4) connected thereto, such control arrangement inserting successive synchronizing symbols (sl ... sn) produced by the synchronizing circuit (4) between successive data symbols (dl ... dn) transmitted in each channel, the synchronizing symbols in each channels being spaced at the same time intervals; and a code generator (5) connected to and controlled by the control arrangement (15), such code generator selecting the synchronizing symbols from a store of such symbols contained therein; and each of the mobile radio station receivers comprises a plurality of sampling circuits for sampling received data symbols;
a control arrangement (26) for synchronizing said samp-ling circuits with received synchronizing symbols; and an echo signal amplitude detector connected to said sampling circuits for weighting the sampled received data symbols in proportion to the amplitudes of received echoes of the data symbols.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19853511430 DE3511430A1 (en) | 1985-03-29 | 1985-03-29 | METHOD FOR SYNCHRONIZING THE RECEIVING DEVICES IN A DIGITAL MULTIPLEX TRANSMISSION SYSTEM |
| DEP3511430.4 | 1985-03-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1251875A true CA1251875A (en) | 1989-03-28 |
Family
ID=6266678
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000505481A Expired CA1251875A (en) | 1985-03-29 | 1986-03-27 | Method of and arrangement for synchronising the receiver arrangements in a digital multiplex transmission system |
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| Country | Link |
|---|---|
| US (1) | US4688210A (en) |
| EP (1) | EP0196723B1 (en) |
| JP (1) | JP2532835B2 (en) |
| AT (1) | ATE66326T1 (en) |
| AU (1) | AU580857B2 (en) |
| CA (1) | CA1251875A (en) |
| DE (2) | DE3511430A1 (en) |
| DK (1) | DK165091C (en) |
| FI (1) | FI80365C (en) |
| NO (1) | NO170446C (en) |
| ZA (1) | ZA862054B (en) |
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-
1986
- 1986-03-18 US US06/841,134 patent/US4688210A/en not_active Expired - Lifetime
- 1986-03-19 ZA ZA862054A patent/ZA862054B/en unknown
- 1986-03-20 DK DK128986A patent/DK165091C/en active
- 1986-03-26 FI FI861323A patent/FI80365C/en not_active IP Right Cessation
- 1986-03-26 EP EP86200506A patent/EP0196723B1/en not_active Expired - Lifetime
- 1986-03-26 AT AT86200506T patent/ATE66326T1/en not_active IP Right Cessation
- 1986-03-26 JP JP61066100A patent/JP2532835B2/en not_active Expired - Fee Related
- 1986-03-26 NO NO861228A patent/NO170446C/en unknown
- 1986-03-26 DE DE8686200506T patent/DE3680805D1/en not_active Expired - Lifetime
- 1986-03-27 AU AU55310/86A patent/AU580857B2/en not_active Ceased
- 1986-03-27 CA CA000505481A patent/CA1251875A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NO170446C (en) | 1992-10-14 |
| NO861228L (en) | 1986-09-30 |
| JPS61227439A (en) | 1986-10-09 |
| AU5531086A (en) | 1986-10-02 |
| NO170446B (en) | 1992-07-06 |
| FI861323A0 (en) | 1986-03-26 |
| FI861323A (en) | 1986-09-30 |
| DK165091C (en) | 1993-02-22 |
| JP2532835B2 (en) | 1996-09-11 |
| ATE66326T1 (en) | 1991-08-15 |
| DE3511430A1 (en) | 1986-10-02 |
| DK128986A (en) | 1986-09-30 |
| FI80365B (en) | 1990-01-31 |
| US4688210A (en) | 1987-08-18 |
| AU580857B2 (en) | 1989-02-02 |
| DK128986D0 (en) | 1986-03-20 |
| ZA862054B (en) | 1987-10-28 |
| EP0196723B1 (en) | 1991-08-14 |
| DK165091B (en) | 1992-10-05 |
| EP0196723A3 (en) | 1987-10-07 |
| EP0196723A2 (en) | 1986-10-08 |
| DE3680805D1 (en) | 1991-09-19 |
| FI80365C (en) | 1990-05-10 |
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