GB1562964A - Digital information transmission - Google Patents

Abstract

In this method for handling traffic between subscriber stations and radio concentrators (F1....F7, F'1....F'7) in the coverage area of a radio network, the radio concentrators are disposed in a mutual spatal arrangement with overlapping radio areas (1 ... 7). Radio-organisational information is exchanged in the radio areas via central organisation channels which are constantly polled by the activated subscriber stations. The activated subscriber stations check the quality of the radio link and, taking into account the traffic volume information additionally received from the radio concentrators via the organisation channels, decide on the radio areas to which they wish to allocate themselves, or decide when they wish to change radio areas. <IMAGE>

Description

(54) DIGITAL INFORMAON TRANSMISSION (71) We, SIEMENS AKT1ENGESELL- saiAFT, a German Company, of Berlin and Munich, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method and system for digital information transmission for mobile subscriber stations in the area of a radio network which consists of a plurality of radio concentrators mutually arranged in the manner of a cellular system with overlapping radio ranges, and operating on different frequencies, for example on a frequency distribution plan for the radio concentrators which largely eliminates same-channel interferences in the relevant radio range, and including an extended edge zone, and is an improvement in or modification of the invention the subject of our UK Patent Application No. 54065/77 (Serial No. 1,562,963).

A radio network of this type is described for example in the U.S. Patent 3,310,741.

A whole series of radio networks of differing structures exists for mobile public and private radio services. Generally a differentiation is made between the public mobile ground radio and the prive mobile ground radio. The public mobile ground radio comprises mobile telephone subscribers wha can be connected via radio connections to the dial-operated exchanges of the public telephone network. The sub scribers to the private mobile ground radio include public safety bodies, such as the Police, Fire Brigade, emergency services and catastrophe protection, and also service groups such as taxi and transportation enterprises, industrial radio, commercial radio, building contractors and the like.

The continuously increasing interest in mobile radio and the aassociated increase in the number of subscribers indicates more and more that the system organisation em- ployed in known radio networks is not suitable for large numbers of subscribers. The assignment of the radio subscribers to the various radio concentrators is carried out in part manually in accordance with geographical criteria, and thus does not take into consideration optimum local accessibility. Furthermore it proves disadvantageous that the allocation of free channels, at least during the establishment of the connection from the radio concentrator to the subscriber station, is carried out by the radio concentrator, and thus pays little attention to the radio situation of the subscriber station in respect of same-channel and neighbouring channel interferences.A further shortcoming consists in that the probability of blockage due to the organisation increases very rapidly if, during main traffic periods, heavy accumulations of applications and connection requests occur even when free transmission channels are available.

A further shortcoming of the system organisation conventionally employed in known radio networks consists in that a subscriber station engaged in a connection loses its functioning capacity in respect of the network organisation during the communications transmission.

The aim of the invention is, for radio networks of the type described in the introduction, to provide a traffic handling process which is suitable for large numbers of subscribers.

According to one aspect of the present invention there is provided a system for digital information transmission comprising a plurality of radio concentrators mutually arranged in the manner of a cellular system with overlapping radio ranges and operating channels of different frequencies, each concentrator having transmitting and receiving means for communication with a plurality of mobile subscriber stations, and a plurality of mobile subscriber stallions having transmitting and receiving means for communication with a concentrator, in which each concentrator further includes means for transmitting, on a respective organisation channel, to the subscriber stations, information blocks provided with the radio range identification followed in time-staggered fashion by further radioorganisation-related items of information, in which the subscriber stations include means for receiving these transmissions on an organisation channel for deciding on the basis of their own radio-technical situation and the radio-range-related traffic load of the network which of the radio ranges iliey wish to be assigned to, and in which each concentrator and subscriber station includes respectively, receiving and transmitting means operable 'on said organisation channel, whereby each subscriber station can implement a change of concentrator in a dialogue with the radio concentrators via the organisation channels.

In another aspect the invention provides a method for digital information transmission for mobile subscriber stations in the area of a radio network which consists of a plurality of radio concentrators mutually arranged in the manner of cellular system with overlapping radio ranges and operating channels on different frequencies in which radio-organisation-related information-exchange between the subscriber stations and the radio concentrators which concentrators operate with a superordinate pulse train synchronisation in the radio ranges is carried out via central organisation channels, in which for this purpose in the organisation channels, from the radio concentrators to the subscriber stations which can be detected in respect of radio range, there are periodncally transmitted information blocks provided with the radio range identification, which are followed in time-staggered fashion by further radio-organisation-related items of information, and in which the subscriber stations-where these are activated-listen in to the organisation channels, decide, on the basis of their own radio-technical situation and taking into account the radio-range-related traffic load of the network, which of the radio ranges they wish to be assigned to, and when they wish to carry out a change of radio range and then implement these decisions in a dlialogue with the radio concentrators via the organisation channels.

Preferably the concentrators and subscriber stations operate with superordinate pulse train synchronisation.

The invention is based on the recognition that by means of central organisation channels, the information exchange required for handling the traffic within a radio network can not only be fundamentally simplified but furthermore facilitates a highspeed radio-organisational traffic handling in the case of large numbers of subscribers.

Furthermore, the organisation channels provide the subscriber stations with the possibility of selecting the operating channels which are most suitable on the basis of their own radio-technical situation by means of the items of information which they are transmitted via free channels offered by the radio concentrators.

The conditions become particularly favourable if the information exchange between the radio concentrators and the subscriber stations is carried out in the operating channels and in the organisation channels in duplex operation, Expediently the subscriber stations check the quality of the radio-technical accessibility of the various radio concentrators taking into consideration the neighbouring channel and same-channel interferences with reference to the field strength and/or the phase jitter of the received organisation channels as in practice the entire radioorganisational information exchange takes place between the subscriber stations and radio concentrators and via the organisation channels.

As the subscriber stations make their decisions regarding the selection of a radio concentrator both in dependence upon the radio-technical accessibility of a radio concentrator and its trfaffic 1 oading, it is advantageous for the information blocks which are periodically transmitted in the organisation channels from the radio concentrators to the subscriber stations to comprise not only the radio-range characterisation, but also items of information concerning the traffic state of the radio concentrators so that this information is also constantly available to the subscriber stations in the timing of the frame period of the organisation channels.

In order to ensure as friction-free as possiible an operation, it is preferable for the radio concentrators to constantly check their operating channels from a radio-technical viewpoint, and to transmit, in the relevant organisation channels, to the subscriber stations only those free operating channels whose radio-technical properties are of sufficient quality to execute a transmission process.

In a preferred embodiment of the process in accordance with the invention, a subscriber station applying to the relevant radio concentrator in a radio range will, directly following this procedure, listen in to the free operating channels constantly reported by the radio concentrator in she relevant organisation channel and stores these in a memory which is constantly kept up to date. Not until the occurrence of a connection request does the subscriber station check the operating channels last reported to be free in respect of their radio-technical serviceability and indicate the most suitable operating channel to the radio con centrator for the establishment of the desired connection.

The checking of the freedom of the operating channels reported by the radio concentrator by means of the subscriber station only when a connection request has occurred in fact optimises the period of time available to the subscriber station for listening for a call to itself, but on the other hand extends the length of time which passes from the reception of a call or the occurrence of a connection request on the part of a subscriber station until the desired connection has been established.If the structure of the organisation channels is such that a predetermined interval of time exists between a possible call, it is expedient for the subscriber stations to constantly check on the radio-technical serviceability of the operating channels reported as free by the radio concentrator by way of a precaution, and to keep a number of free operating channels recognised as suitable in a further memory which is likewise constantly kept up to date. If, under these circumstances, a call occurs in the subscriber station or the subscriber station requests a connection, it can immediately propose one or more than one suitable free operating channel to the radio concentrator for the establishment of the desired connection.

In this context it is advantageous for the subscriber station to communicate the request of the operating channel which it requires for the connection establishment via the organisation channel to the radio concentrator and for the radio concentrator to itself acknowledge this request by a return signal in the desired operating channel.

In order to carry out the information exchange which constantly takes place between the subscriber stations and the radio concentrators via the organisation channels in a simple and time-saving fashion, it is preferable if, for the information of the various organisation functions, such as identification, application, re-application, presence check, seizure and call, each radio concentrator is provided with a sum organisation channel which combines these items of information in a t.d.m. frame. The beginning of the frame of the sum organisation channel is marked by the information block. Furthermore, the sum organisation channel may employ a super-frame which extends over two and more frames and the length of which can be adapted to the traffic load which fluctuates relative to time for the presence check.The super-frame takes into account the fact that generally speaking it is sufficient for the presence check of the subscribers to take place in a cycle which is considerably slower than the frame period of the sum organisation channel. Furthermore, the number of subscriber stations which can apply at the maximum to a radio concentrator is generally considerably greater than the number of operating channels made available by the radio concentrator sd that the requisite reporting positions for the greater number applying subscriber stations can be considerably better accommodated in a superframe.

In a radio network having a large number of channels and a large application capacity, it is preferable, in dependence upon the local incidence of traffic, to make available two and more sum organisation channels with the same t.d.m. frame to a radio concentrator. Here the sum organisation channels differ from one another merely in respect of a traffic-loadrelated, differing priority in respect of the subscriber stations applying to the radio concentrator.

In a further development of the invention, if there is made available to the radio network a radio frequency band which possesses a small relative band width, it is possible to dispense with a decentral operating channel allocation in that the radio frequencies of the organisation channels are allotted to the central range of the radio frequency band of the radio network, and that the allocation of free operating channels to the subscriber stations takes place centrally, on request, by means of the radio concentrators. Here it has been assumed that the radio-technical quality of the organisation channels, which has been checked by the subscriber stations, exists at least in first approximation, also in the case of the associated operating channels which possess only a relatively short frequency spacing from the organisation channels.The reception differences which nevertheless exist in reality can be compensated in a simple fashion by the use of the spatial diversity technique at the receiving end of the subscriber stations.

In place of a t.d.m. sum organisation channel with a super-frame for the presence check, the radio concentrators can each possess two or more organisation channels which are assigned the various organisation functions, divided in a suitable manner. In this context it is expedient to provide at least the presence check with a separate organisation channel (message channel) which prepares a time slot for each subscriber station which has applied.

Here the frame period of this message channel amounts to n-times (n is a whole-posi- tive number) of the frame period of the further organisation channel or further organisation channels.

It is expedient to discontinuously adapt the message channel in respect of its frame period to the number of subscriber stations which have applied, which number fluctuates relative to time, in the time sections corresponding to the frame period of the further organisation channel or further organisation channels.

In a first preferred method of procedure, the reduction in the frame period of the message channel in the event of a falling number of applying subscriber stations can be effected by regrouping the subscriber stations who have applied in time slots bearing a high ordinal number into unseized time slots having a low ordinal number.

In a second preferred method of procedure, the adaptation of the frame period of the message channel is carried out aut- matically in dependence upon the number of subscriber stations which have applied, in that the subscriber stations which have applied in the radio range are periodically called up to emit presence reports by the relevant radio concentrator via the message channel with a period which is dependent upon the number of subscriber stations which have applied. Thus if a large number of subscriber stations have applied to the radio concentrator, a cycle of the presence check acquires a longer period than in the event that only a few such subscriber stations have applied to the radio concentrator.

As shown in practice, it is not advisable to request a subscriber station which has applied via a radio concentrator to automatically withdraw from the radio concentrator on deactivation. For this reason it is advisable for the presence of a subscriber station which has applied in a radio range to the relevant radio concentrator to be automatically erased in the memory of the radio concentrator when, within a time interval of a given length, the subscriber station emits no presence message to the radio concentrator via the relevant organisation channel.

In a further development of the invention, for the application and call of subscriber stations in a radio concentrator, within a frame period of the relevant organisation channel, there may be made available a predetermined number of discrete time slots which are seized by each of the subscriber stations as and when required in accordance with a pseudo-random law. In this way it is possible, employing simple means, to reduce the risk of a mutual blockage of subscriber stations on the occurrence of an accumulation of application and call procedures.

In this context it is advantageous for each subscriber station to be provided with a frame-and bit pulse train-synchronised scrambler, which, on request, selects one of the time slots of the relevant organisation channel for seizure.

The invention may also provide the possibility of maintaining the functioning capacity of a subscriber station relative to the network organisation even when this subscriber station is engaged in a connection.

Here it is advisable for the subscriber station which is engaged in a connection to interrupt the transmission in the time intervals in which the information flocks occur in the organisation channels, and to alternately check the operating channel which is assigned to the radio range and which is engaged in the connection for the continued existence of the connection and to in each case listen in to one of the organisation channels alien to the radio lange.

The periodic checking of the operating channel engaged in the connection may ex expediently be carried out by a mutual ex- change of messages between the subscriber station and the radio concentrator. When these message fail to appear over a plurality of checking periods, the clearance of the connection is initiated.

The disturbances experienced by the continuous communications flow as a result of the periodic interruptions in the seized connection during the listening in to the information blocks of the organisation channels by the subscriber station can be substantially eliminated in a simple fashion by increasing the transmission speed on the radio link and in fact in combination with a transmitting-end and receiving-end intermediate storage of the communications signals at the subscribed station and the radio concentrator.

As a subscriber station constantly checks its radio-technical situation during the time it is engaged in a connection by listening in to the organisation channels of the various radio ranges, even in the seized state it is in a position to make a decision as to when a change of radio range is necessary.

For this purpose the subscriber station which is intending to change a radio range firstly listens in to the channel information of the new radio range which has tween recognised, radio-technically, as being suitable, and then applies to the associated radio concentrator stating the free operating channel which has been recognised as suitable. The new radio concentrator acknowledges the application with an acknowledgement which causes the subscriber station to assume a waiting position in which the subscriber station maintains the original connection via the previous radio concentrator.Following the preparation of the switch-over of the existing connection in a dialogue between the previous and the new radio concentrators, the new new radio concentrator informs the subscriber station of the time for the final switchover, at which the new radio concentrator and the subscriber station will then simultaneously carry out the final switch-over.

In order to functionally safeguard this operating process, it is preferable to repeatedly transmit the time for the final switch-over from the new radio concentrator to the subscriber station and in fact in such manner that the subscriber station can still recognise the remaining time difference, and that in the event of a satisfactory reception of one of these communications, the subscriber station implements the switch-over at a given point of time.

The method and system of the invention require a relatively high level of technical intelligence on the part of the subscriber stations, the outlay for which is to be kept within as low as possible limits. This can be achieved extremely advantageously by controlling the sequence of the radio-organisational functions at a subscriber station by a micro-processor.

In the following an embodiment of the invention will be explained in further detail with reference to the accompanying drawings in which: Fig. 1 schematically illustrates a radio network constructed in the manner if a cellular system, Fig. 2 is a view of the distribution of the channel frequencies within a frequency assignment range consisting of seven radio ranges, Fig. 3 schematically illustrates first radioorganisational sequences between a subscriber station and a radio concentrator of the invention, Fig. 4 illustrates a second radio-organisational sequence between a subscriber station and a radio concentrator of the invention Fig. 5 illustrates a third radio-organisational sequence between a subscriber station and a radio concentrator of the invention, Fig. 6 illustrates a fourth radio-organisational sequence between a subscriber station and a radio concentrator of the invention Fig. 7 illustrates a fifth radio-organisational sequence between a subscriber station and a radio concentrator of the invention; Fig. 8 illustrates a sixth radio-organisational sequence between a subscriber station and a radio concentrator of the invention; Fig. 9 illustrates an organisation multichannel structure; Fig. 10 is a block circuit diagram of a radio concentrator for use in the invention; and Fig. 141 is a block circuit diagram of a subscriber station for use in the invention.

In the basic plan, illustrated in Fig. 1, of an extendable mobile radio network in which the radio concentrators are spatially arranged in the manner of a cellular system, the radio concentrators each cover a radio range having a means radius r. The mean radius r will be assumed, for example, to amount to approx. 15 km A cellular radio network of this type is described tor example in the "Jahrbuch des elektrischen Fernmeldewesens", 21st edition, 1970, published by Wissenschaft und Leben, Georg Heidecker, Bad Windsheim, pages 305 to 311, in particular page 308, Fig. 1. The radio network expediently operates with frequency duplex in the UHF range at approx. 450 MHz. The transmitting and receiving bands will be assumed to possess a frequency spacing of > 10 MHz as required for 400% electromagnetic compatibility.

As can be seen in detail from Fig. 1, the radio network is divided into frequency assignment ranges which each possess seven radio concentrators provided with the numerals 1 to 7. In Fig. 1, three differently shaded frequency assignment ranges have been emphasised, the radio concentrators of which are referenced F1 . . .

F7, F'!1 . . .F17 and Flll . . F117. The radio concentrators F1, Fl1 and F111 have been represented by a cross to distinguish them from the other radio concentrators which are marked by a spot. This is to indicate that these radio concentrators have been extended to form radio exchanges for the connection between the various radio ranges and the dial-operated exchanges of the public telephone network.

The frequency assignment ranges with their seven radio concentrators are all of identical construction and possess the same frequency distribution plan. The numbers 1 to 7 of the radio concentrators simultaneously designate the numbers of the radio ranges.

-In order to ensure constant accessibility to the mobile subscriber stations T, of which one is illustrated in the radio range F1, the radio ranges of the radio concentrators possess a mutual overlap. As far as possible no same-channel interference is to occur in the overlap range. Same-channel interference of further removed radio concentrators is possible, taking into account a minimum-channel signal to noise ratio, dependent upon the type of modulation, at the receiving location of a mobile subscriber station. This fact is taken into account by the frequency distribution plan within a frequency assignment range, and in fact taking into consideration the superordinate spatial classification plan of the frequency assignment ranges which adjoin one another.

The frequency assignment to the individual radio concentrators is carried out in such manner that radio concentrators which possess the same range numbers and which here operate with the same radio frequencies possess an adequate mutual minimum spacing. In the represented exemplary embodiment this amounts to approx. 80 km.

A frequency distribution plan which is favourable for the cellular system illustrated in Fig. 1 and which is repeated in each frequency assignment range is shown in detail in the plan of Fig. 2. Accordingly the transmitting and receiving bands X and Y for full duplex operation each comprise 120 channel groups KG each having seven individual channels. The number of radio channels per frequency assignment range amounts accordingly to 840.

Each of the radio ranges 1 to 7 is assigned one channel per channel group, and in fact in such manner that the position of the channels assigned to a specific radio range within the channel groups remains the same. In Fig. 2, the channel group numbers KG, the channel numbers KNr, the radio range numbers FNr and the radio ranges 1 to 7 assigned to a frequency assignment range are plotted in consecutive rows over the transmitting and receiving band XY. Accordingly in Fig. 2 the first channel of a channel group KG is in each case assigned to the radio range 1, the second channel to the radio range 6, the third to the radio range 4 etc. This arrangement ensures that the radio channels employed in each radio range always pos sess a mutual frequency spacing of six channels.Thus the channels of each radio range possess a spacing from one another which is such that neighbouring channel disturbances of transmitters assigned to the range are safely avoided. The frequency assignment, illustrated in Fig. 2, in a frequency assignment range also ensures that the directly neighbouring radio ranges of a frequency assignment range operate with the maximum possible frequency spacings.

As indicated by traffic estimations, a radio concentrator designed for 120 channels possesses a capacity of a maximum of 2400 subscriber stations for which such a radio concentrator will then also be designed.

The radio-organisational functions in a radio network of this kind operating with digital signal transmission, for example binary frequency modulation, in full duplex, are executed with the aid of organisation channels which are specifically assigned to radio ranges and which are listened in to by the subscriber stations, and with the a-d of which the subscriber stations, on the basis of their own radio-technical situation, taking into consideration the traffic loading of the network, apply to a radio range and effect changes of radio range. Furthermore other radio-organisational functions, such as presence check, seizure and call are also carried out via these organisation channels.

Basically there are various possible structures of the organisation channels. On the one hand various radio-organisational functions per radio range can be split up between two or more organisation channels.

This leads to simple and clearly laid out circuit structures for the radio concentrators but means that for the radioorganisational nnformation exchange, the subscriber stations must constantly spring back and forth in respect of frequency between two or more organisation channels which naturally also involves an increased time outlay.

At least in the case of radio networks whose radio ranges are designed for small and average numbers of channels, considered as a whole, it could be more advantageous to combine all the organisation functions in one sum organisation channel.

A combination of this type could be used when a digital technique is employed, inasmuch as in this case the various organisation functions can be easily accommodated in a time division multiplex (t.d.m.) frame structure. This basic construction of an organisation channel can also be applied in the case of large numbers of channels per radio range in that, as already indicated in the introduction, in place of one sum organisation channel. of the kind in question, two or more sum organisation channels are provided in combination with a traffic-load-dependent priority table.

The schematically illustrated, radioorganisational sequences illustrated in Fig.

3 to 8 are based upon a sum organisation channel of this type. As shown in Figs. 3 to 8, this sum organisation channel OK has a frame period T and is divided into time slots ZS possessing an equal width to one another. Overall, there are three different types of time slots, namely the time slots C, A and B. The time slots C always mark the beginning of a basic frame and contain an information block K, which in addition to the characterisation of the radio range, contains items of information concerning the state of seizure of the radio concentrator assigned to the radio range. Different items of information can be transmitted in each of the time slots A and B which follow the time slots C and always alternate with one another. The first letter, possibly together with the following number designating the radio-organisational sequences in accordance with Fig. 3 to 8 over the time T indicate the activated station, namely the subscriber station T, -or a radio concentrator Fi, whereas the second letter-number combination indicates the particular approached organisation or speech channels. In de tail, Fi signifies a radio concentrator, OKi signifies the organisation channel of the radio concentrator Fi, and GKi signifies the selected speech channel of the radio concentrator Fi. The arrows also entered in the illustrations of the radio-organisational sequences indicate the direction in which transmission takes place. The transmitted signal is in each case designated by a letter or a letter combination.

The radio-organisational sequence illustrated in Fig. 3 represents the application process of a subscriber station T, entering into operation, to a radio concentrator. As soon as the subscriber station is connected, it commences to check the organisation channels OK1 to OK7 of the seven radio ranges 1 to 7 in Fig. 1 in respect of their radio-technical suitability. The corresponding activities are indicated in Fig. 3 in the sequences designated T-OK1, T-OK2, T OK3 . . . T-OK7. The checking of the organisation channels has, it is assumed, indicated that the radio range 2 is the most suitable radio range for the subscriber station T on the basis of its radio-technical situation. Therefore at the end of the checking interval of the organisation channel of the radio range 7, the subscriber station jumps back to the organisation channel of the radio range 2 and listens in to the latter.At the beginning of a new frame of the organisation channel of the radio range 2, which is designated F2-OK, the subscriber station receives the information block K in the organisation channel and supplements the bit synchronisation which has already been effected by the frame synchronisation. At the same time it discovers the state of seizure of the radio concentrator from the information block K. The information relating to the state of seizure comprises indications as to the extent of exhaustion of the application capacity, the value of the average degree of seizure of the speech channels, and whether all the speech channels are currently seized or not.

If the application capacity is exhausted and/ or the mean degree of seizure has exceeded a critical value, the subscriber station must change to the next best radio concentrator which it has determined from a radio-technical viewpoint by listening in to the relevant organisation channel. In the exemplary embodiment illustrated in Fig. 3, it has been asumed that the information block K of the organisation channel OK of the radio range 2 is still signalling a free application capacity. In the transmitting path of the organisation channel, the subscriber station subsequently sends a first application signal Ew to the radio concentrator F2 in a time slot A. The radio concentrator F2 of the radio range 2 acknowledges this first application by the application call-up MF in the organisation channel OK of the subscriber station in the following time slot B.

In the next time slot B of the organisation channel OK of the radio concentrator F2, the subscriber station T follows this application call-up by the subscriber application MT. This concludes the application process of the subscriber station to the radio concentrator F2. The subscriber station now constantly listens in to this organisation channel for a call with which it is possibly directed in one of the time slots B or for an item of free channel information in one of the time slots A of the organisation channel. Merely in time slots C in which the information block K is transmitted in the organisation channel, this listening in process is interrupted with every second occurring frame.The subscriber station then jumps to one of the organisation channels of the other radio ranges 1, 3 to 7 and checks the radio-technical accessibility of the latter in constant alternation with the information block K of the radio concentrator F2 of the radio range 2 in which the subscriber station has applied. The results of the radio-technical accessibility occurring in each range are constantly averaged and the mean values are stored in a memory of the subscriber station.

If the subscriber station establishes that the radio-technical accessibility within the applied-for radio range is considerably poorer than the radio-technical accessibility to another radio range, it initiates a change of radio range.

The subscriber station also initiates a change of radio range when it is informed, in the information block K, by the radio concentrator to which it has applied, that the danger of a blockage caused by timefluctuating traffic load exists in the appliedfor radio concentrator, i.e. the mean degree of seizure has exceeded acritical value. The subscriber station implements this exchange, however, only when the prospective radio concentrator not only fulfils the requirement upon its radio-technical accessibility but also possesses a more favourable mean degree of seizure which would justify a change of radio range.

In order that with time accumulations of first application signals, the probability of mutual blockage of subscriber stations simultaneously applying to the same radio concentrator may be kept as low as possible, the subscriber stations are equipped with scramblers. For the first application signals to be emitted by the subscriber stations, the scramblers scramble, in quasi-random fashion, frame time slots A in which the subscriber stations then deposit their first application signals. The scramblers are activated in the same manner when the subscriber stations deposit call signals in the radio concentrators to which they have applied or wish to reapply to a different radio concentrator.

Fig. 4 illustrates the time flow of the establishment of a connection to the subscriber T via the radio concentrator F2 of the radio range 2. Firstly the subscriber receives the information block K in the organisation channel OK of the radio concentrator F2 and continues to listen in to the organisation channel of this radio concentrator to which it has applied. Two time slots later, in time slot A it receives a communication from the radio concentrator regarding the operating channels which it is offering and which it has established as being free. This information is referenced V.

The information V is transmitted in each time slot A in the organisation channel, but for reasons of clarity in Fig. 4 and the further Figs. 5 to 8 it is indicated only where it is necessary for the explanation of the relevant function sequence.

In the next time slot B, the subscriber station receives a call directed to him and referenced RF via the organisation channel OK of the radio concentrator F2. The subscriber station always stores the most recent state of the free operating channels communicated to the subscriber station in the timing of the frame period in the organisation channel so that on the reception of a call it can imediately carry out a hunting sequence FS from the collective of free channels communicated by the radio concentrator. For this purpose it leaves the organisation channel of the radio concentrator F2. At the end of the hunting sequence, the subscriber station informs the radio concentrator in the organisation channel, in a time slot B, of the free operating channel which is most suitable from its own radio-technical viewpoint and simultaneously acknowledges the reception of the call.The radio concentrator acknowledges this message with the signal QF in the proposed speech channel GK of the subscriber station which has meanwhile switched over to this speech channel. The connection is thus established and the communications transmission between the subscriber station and the remote subscriber station who has made the call can thus be carried out via the radio concentrator F2. In Fig. 4 this is indicated by the double arrows in association with the cross-shaded sections of the speech channels for both directions.

Also in the seized state the subscriber station must check the radio-technical accessibility to all the radio concentrators in order on the one hand to be sure that his own connection is still in existence and on the other hand, if there is a fundamental impairment of the radio-technical accessibility, to be able to decide to which radio range it can make a change. This check is again carried out exclusively in the timing of the frame period T in the time slots C determined by the organisation channel. In the first time slot C following the establishment of the connection, the subscriber station receives the message signal MF from the radio concentrator and the radio concentrator receives the message signal MT from the subscriber station.On the reception of this signal, the subscriber station and radio concentrator recognise that on the one hand the frame synchronism is still ensured and on the other hand the speech connection between the radio concentrator and the subscriber station is still in existence. If the subscriber station and radio concentrator receives no message signal Mp and MT respectively over a specific number of time slots C, the speech connection is automatically cleared by the subscriber station and radio concentrator respectively.

In the next time slot C the subscriber station leaves the speech channel and listens in to one of the other organisation channels. In Fig.4 this time section is referenced FP.

The actual communications flow is fundamentally interrupted in the time slots C in the speech channel. This disturbance is eliminated, however, in that the transmission speed on the radio link is increased and at the same time, at the transmitting and receiving ends, both in the subscriber station and in the radio concentrator, inter mediate stores are provided for the communications signals, with the aid of which stores the gaps are bridged. If the conversation is ended by the calling subscriber, the radio concentrator F2 transmits a disconnect signal AF via the speech channel in the following time slot C, which signal is acknowledged in the two following time slots A and B by the subscriber station T with the disconnect signals AT whereby the connection is cleared. If, on the other hand the called subscriber T terminates the conversation, as shown in association with the functional sequence in Fig. 5, the subscriber station T transmits a disconnect signal AT via the speech channel in the following time slot C, which signal is acknowledged in the two following time slots A and B by the radio concentrator with the disconnect signals AF, whereby at least the radio connection is cleared.

The flow plan in Fig. 5 shows the situation in which the subscriber station T who has applied to the radio concentrator F2 of the radio range 2 emits a call for a connection request As the subscriber station T wishes to emit a call, via the organisation channel, in a quasi-random chequered time time slot A, it receives the information V concerning a specific number of operating channels which are free in the view of the radio concentrator and in the following time slot B commences the hunting sequence FS from the collective of channels communicated by the radio concentrator in order to determine the free operating channel which is most favourable from its own radio-technical viewpoint, and subsequently reports upon this channel in the organisation channel to the radio concentrator. This report, in association with the wall, is referenced RT.

The time slot for the emission of the call RT is thus indirectly determined via the quasi-random chequered time slot for listening in to the information V. It then leaves the organisation channel and is switched to the speech channel GK which it has proposed. The radio concentrator F2 acknowledges this call with the signal QT in the speech channel GK. The connection is thus established and the communications exchange can be carried out as already stated in Fig. 4.

If the conversation is terminated by the calling subscriber, in the following time slot C the subscriber station T transmits, via the speech channel, a disconnect signal AT which, in the two following time slots A and B is acknowledged by the radio concentrator F2 with the disconnect signals AT, whereby the connection is cleared. If the called, remote subscriber terminates the conversation, the conversation end state of the remote subscriber can be recognised by the radio concentrator or signalled to the radio concentrator via the rear switching network.

The radio concentrator then transmits a disconnect signal AT via the speech channel in the following time slot C', which disconnect signal is acknowledged in the two following time slots A and B by the subscriber station T with the disconnect signals TT, whereby at least the radio connection is cleared.

The function flows represented in Figs. 4 and 5 have been based upon the fact that for the purpose of a free channel hunting sequence FS, the subscriber station does not leave the organisation channel until a call or a call request is present. As already pointed out, it can be effective to provisionally carry out the hunting from the collective of channels reported as free by the radio concentrator following the reception of an item of information V, in order in this way to achieve shorter times for the connection establishment on the occurrence of a call or a call request.

Each subscriber station which has applied to a radio concentrator must be checked at periodic intervals by the radio concentrator to establish whether it is still attainable.

The corresponding radio-organisational sequence is illustrated in Fig. 6. The subscriber station T firstly receives the infor mation block K in the time slot C in the organisation channel, and a few time slots further receives the message call-up MT in a timeslot B, which it acknowledeXes in the next but one time slot B with the message MT. Within the same frame period it also receives the information V concerning the free operating channels reported by the radio concentrator. At the beginning of the next frame, in the time slot C, it leaves the organisation channel in order to check one of the organisation channels of another radio range in respect of its radio-technical accessibility. This is carried out frame by frame in the described interplay.The message call-up MF does not, on the other hand, take place during each frame period but in fundamentally longer intervals of time. The reason for this is that the possible number of subscriber stations which can apply to a radio concentrator is usually considerably greater than the number of time slots B available for this purpose with in a frame period. The cycle for the message call-up to the subscriber stations which have applied extends, in other words, over a larger number of frame periods, which is in fact permissible, since, in contrast it is generally sufficient-for example for radio.organisational functions such a call, identification and application-for the presence check to be carried out only in the cycle of a plurality of frame periods.

The radio-organisational sequence illustrated in Fig. 7 illustrates the situation in which the unseized subscriber station T which has applied to the radio concentrator of the radio range 2 is compelled to reapply to another radio concentrator. In Fig. 7 it has been assumed that during the course of its routine check, the subscriber station which has applied to the radio concentrator F2 has established that it must reapply to the radio concentrator F7 of the radio range 7 if its radio-technical accessibility is to remain ensured. Therefore at the beginning of the next frame in the time slot C it listens in to the organisation channel of the radio concentrator F7 and receives the information block with the identification and information on the state of seizure. It then immediately switches back to the organisation channel of the radio concentrator F2.

In a later, quasi-random chequered time slot A it feeds the organisation channel of the radio concentrator F7 with the reapplication UM which is acknowledged in the following time slot B with the message call-up MF of this radio concentrator. The subscriber station T acknowledges this with the message MT in the following time slot B and has thus applied to the new radio concentrator F7. The remainder of the sequence corresponds to that shown in Fig. 3. A withdrawal from the radio concentrator F2 is not necessary as the latter automatically erases the subscriber station from its memory if, within a given length of time, it does not respond to the message-call-ups which it receives. However it can be effected by an exchange of signals directly between the radio concentrator F7 and the radio concentrator F2.

The radio-organisational sequence represented in Fig. 8 describes the re-application of a subscriber station engaged in a connection from the radio concentrator F2 to the radio concentrator F7. Below the time slots ZS, the speech channel GK is firstly shown in the direction from the radio concentrator F2 to the subscriber station. The crossed shading indicates the communications flow which is interrupted in the time slots C for the emission of messages MT.

The speech channel GK in the direction from the subscriber station T to the radio concentrator F2 is shown in the fifth position from the top. The subscriber station which has established that it must re-apply and has already selected the radio concentrator F7 for this purpose leaves the speech channel at the beginning of a frame and in the time slot C listens into the information block K in the organisation channel of the radio concentrator F7. It subsequently receives the information V concerning the operating channels which have been reported as free by the radio concentrator F7 in a quasi-random chequered time slot A and then, in the following time slot B, immediately proceeds to check the channels which have been reported as free in respect of their radio-technical suitability. In Fig.

8 this time slot is again referenced FS.

Then, in a time slot A in the organisation channel the subscriber station feeds the radio concentrator F7 with the call RTU for reallocation of the existing connection simultaneously quoting the free operating channel which it requests. The radio concentrator F7 acknowledges this message in the desired speech channel by the waiting message W. These re-application procedures in the time slots A and B produce a short disturbance in the communications flow.

The subscriber station then jumps back to the original speech channel of the radio concentrator F2, and thus maintains this connection. In Fig. 8 this is indicated by the double arrows. At the beginning of each new frame, the subscriber station T listens in, in the time slot C, on the new speech channel with which it has been provided by the radio concentrator F7, to the radio concentrator F7 which transmits the wait signal W in the time slot C until the connection has been switched through from the radio concentrator F2 to the radio concentrator F7.- In the time slot of the wait signal W, the subscriber station transmits the message MT. On reception of the message signals MT transmitted by the subscriber station T in the time slots C, the radio concentrator F7 establishes that the connection to the subscriber station is still maintained.

When the new connection has been established, via the speech channel in the following time slot C the radio concentrator F7 feeds the subscriber station T with the signal C3 which states that the switch-over takes place at the beginning of the next but one frame period. In the time slot C of the following frame, the radio concentrator F7 transmits the signal C2 which indicates to the subscriber station that the switchover will take place at the beginning of the next frame period. At the beginning of the now following frame, the radio concentrator feeds the subscriber station with the signal C1 which represents the instant of the switch-over.

The switch-over is thus completed and the connection continues to be maintained via the speech channel which has been made available by the radio concentrator Fv7.

The signals C3, C2 and C1 represent a type of count down which ensures that even in the case of a faulty reception of the switch-over signal C1, the subscriber station nevertheless switches over when it has received one of the two preceding signals C2 or C3.

Fig. 9 illustrates an exemplary embodiment of a radio network in which the associated radio concentrators possess radio ranges having a large number of channels, wherein the various radio-organisational functions are distributed between a plurality of organisation channels. In the exemplary embodiment shown in Fig. 9, each radio range possesses four organisation channels viz the organisation channel KK for identification and first application, the message channel MK for the presence check of subscriber stations which have applied, the call-transmitting channel RsK and the call-reception channel ReK. Fig. 9 also indicates an operating channel BK in the direction from the radio concentrator F to the subscriber T, and the operating channel BK1 in the opposite direction from the subscriber T to the radio concentrator F.

Of the four organisation channels, the organisation channels KK, RsK and ReK posses the frame period 7 and are divided into 32 time slots, of which the time slot 1 in each case contains the information block K. The message channel MK in fact likewise possesses the information block K in the spacing of the frame period T, but is n (n is a whole, positive number) frame lengths longer than the other organisation channels. This is necessary in order to accommodate the requisite application positions for a maximum number of subscriber stations which can apply to the radio concentrator. Within a frame period 7, the message channel MK contains, excluding the information block K, 124 application positions.The length of the message channel MK is expediently rendered dependent upon the traffic load, i.e. with a falling number of applying subscriber stations application positions of a high ordinal number are transferred to application positions of a low ordinal number so that, in accordance with the incidence of traffic, the cycle of a presence check on the subscriber stations which have applied comprises - a differing number of frame periods.

The call-transmitting channel RsK and the call-reception channel ReK comprise 32 blocks per frame period v in the same way as the organisation channel KK, of which the blocks 2 and 32 can selectively contain calls R or communications B concerning the state of seizure of the radio concentrator. The call reception channel ReK serves to communicate connection requests on the part of the subscriber stations to the radio concentrator. The danger of blockage of the call reception channel ReK in the case of an accumulation of call messages emitted to the radio concentrator by the subscriber stations is prevented, as already mentioned, in that each subscriber station is assigned a scrambler which, for each new call message, reappoints one of the time slots for the emission of the call message.

Finally Fig. 10 and 11 are block circuit diagrams of a radio concentrator and of a subscriber station for digital signal transmission in duplex operation, on the basis of which the practical execution of the process corresponding to the invention will be further explained.

In accordance with the illustrations of a radio network shown in Fig. 1 and 2, the radio concentrator in Fig. 10 possesses 120 speech channels GK, of which the speech channel GK1 is illustrated whereas the speech channels GK2 to 120 have merely been indicated. The speech channels are of course also suitable for the transmission of data and other information. Each speech channel is provided with a transmittingreceiving branching device WE via which the transmitter S and the receiver E are connected to the antenna (not shown in detail). Transmitter and receiver are connected to the synthesiser SY in which the frequencies assigned to this speech channel for both directions of transmission are produced.At the output end, the receiver is connected to the regenerator RG which carries out the regeneration and pulse train inphasing of the received signals. and which is itself adioined by a transit time standardising circuit LN. The function of the transit time standardising circuit is to standardise different reception frame phases which can amount for example to up to + 3 bits to the radio concentrator frame phase. In this way the transmission-dependent phase shifts are eliminated.

The camouflaging device VS which is common to the transmitting and receiving path, takes into account the fact that in radio telephony the telephone secrecy can only be maintained if the communications signals are transmitted in camouflaged form. The camouflaging device VS is connected following a speed transformer (bitrate converter) GW in the receiving path and preceding the latter in the transmitting path. In the direction of transmission, the speed transformer GW increases the bit rate of the items of information to be transmitted for example from 4.8 kbit/s to 5.4 kbit/s. The gaps in the originally continuous communication flow which are thus released and which correspond to the time slots C in the frame of the organisation channel are filled with items of signalling information which are prepared in the data safeguarding device DS.In the receiving path, following the passage of the signal flow through the camouflaging device VS the items of signalling information are separated from the latter and in the speed transformer GW the discontinuous signal flow of 5.4 kbit/s is reconverted into the original continuous signal flow of 4.8 kbit/s.

A data safeguarding device DS in which the items of signalling information for the outgoing signal flow are combined to form signalling blocks and are provided with a fault safeguard, receives the transmitted signalling block in the receiving path, recognises transmission errors and where necessary carries out a correction. A signal processing device SV which is connected to the data safeguarding device DS is responsible for radio-organisational sequences which must be carried out as a routine. It carries out the signal repetition, the clearance recognition and message procedures and only in the event of a change in the operating state reports this fact to the relevant function assemblies cooperating with the main radio concentrator control unit FS. It receives corresponding signals to this effect itself.

The pulse train central control TZ which is merely indicated in Fig. 10 is responsible for the production of the pulse trains and frame structures and for the distribution of the pulse train between the various assemblies of the radio concentrator.

The function assembly ESB serves to calculate the start conditions. At the beginning of the establishment phase of a dialogue between the radio concentrator and a subscriber, it calculates the start con ditions for the camouflaging device VS on the basis of the transmitted subscriber number of the subscriber station. In this way itis possible to avoid extensive storage equipment for the codes of all the subscriber stations present within the radio network.

The function assembly KV is responsible for the operating channel administration of the radio concentrator. The state of seizure or freedom of the 120 channels is recorded and administrated therein. It indicates as free only those channels which neither are in use nor have an impermissibly high interference level. Free, utilisable operating channels are notified via the organisation channel OK to the subscriber stations.

The organisation channel OK is similar to the speech channel GKi but differs from it in respect of its structure by the absence of the camouflaging device VS as the radioorganisational information requires no camouflaging. The organisation channel OK also does not have a speed transformer GW. The information flow in both directions is handled directly via the data safe- guarding device DS.

The function assembly SS serves to control the transmitters. It switches the 120 transmitters S of the speech channels KG1 to GK120 on or off as required.

The function assembly KE produces the information block K which is transmitted in the organisation channel OK at the beginning of each frame to the subscriber stations. The information block comprises the identification block of the radio concentrator and items of information which concern the engaged state of the radio concentrator and which are limited to information as to the extent of exhaustion of the application capacity, information on the aver- age degree of engagement of the speech channels and information as to whether all the speech channels are currently in use.

From the information concerning the aver- age degree of seizure of the speech channels, the subscriber stations derive criteria as to whether-if possible-they should transfer to a different radio concentrator.

The information blocks also feed the subscriber stations with information concerning the frame phase. It is also able to contain other items of information of general interest.

The function assembly RV controls the transmission and reception of calls and the release and application of speaking subscriber stations in association with the establishment and disestablishment of connections.

Finally, the function assembly MN represents a message device via which the booking in of first applications and reapplications and the continuous presence check and the booking out of subscribers is carried out. The booking out takes place when the presence check has been unsuccessfully carried out several times or a booking out command is present in the exchange.

The multiplex device MUX, which is also illustrated in Fig. 10 and is provided for the 120 speech channels GK1 to GK120 forms the bridge to the exchange MSt which is fundamentally composed of the signalling device SE, the switching network KF and the control unit SW. In order to indicate that the exchange MSt cooperates with further function units, the open line links represented by three double arrows have been shown in Fig. 10.

The block circuit diagram of a subscriber station illustrated in Fig. 11 possesses, for the transmitter S and the receiver El, a transmitting-receiving branching device WE via which the two units are connected to the antenna AN1. For the execution of a diversity-receiving operation, the subscriber station is also provided with a second receiver 1,2 which cooperates with the antenna AN2 which is accommodated separately from the antenna AN1. The outputs of the two receivers El and E2 cooperate with the diversity combiner DC which mea- sures the reception level of the two receivers and the signal jitter.

In accordance with the speech channels GK of the radio concentrator illustrated in Fig. 10, the transmitter S and the receivers El and E2 are connected to the synthesiser SY which produces the various required frequencies and for this purpose is controlled by the function assembly SYS. A pulse train central control TZ is synchronised via a regenerator RG connected following the diversity combiner DC. In accordance with the speech channels GK1 to GK120 in Fig.

10, the subscriber stations also possess, commonly for transmitting and receiving-direc- tions, a camouflaging device VS, a speed transformer GW, and a data safeguarding device DS.

For the radio concentrator selection, the diversity combiner DC cooperates with the function assembly FA in which the reception levels and the jitter criteria of the or ganisation channels of the various radio concentrators are gathered and analysed for the selection of the most suitable radio concentrator for first application and reapplication.

The diversity combiner DC continues to cooperate with the function assembly FE in which, on the basis of the radio-technical viewpoint of the subscriber station, items of information concerning free operating channels reported by the radio concentrator in the organisation channel are gathered and kept up to date. In comparison, the selection of the most suitable operating channel is carried out in association with the scanning process to be effected by the subscriber station.

The function assembly RVI controls the transmission and reception of calls and for this purpose is provided with the above described scrambler.

The function assembly MNl is the message device required for the presence check.

It also handles re-applications.

The function assemblies MNl, RVt, SYS, FA and FE cooperate with the superordinate central control unit ZS which is expediently in the form of a micro-processor.

The microphone M and earpiece H of the subscriber station are connected via ana logue digital converters A/D to the relevant input or output of the speed transformer GW. BT represents the engaged tone generator which is controlled by the central control unit ZS and which responds whenever, for radio-technical reasons, a connection connot be established or breaks off. The analogue-digital converter A/D which is connected following the xnicro- phone M cooperates with the ringing tone generator FTO which is likewise controlled by the central control unit ZS. The ringing tone generator RTO which also cooperates with the central control unit ZS possesses an acoustic display L and in this way indicates that a call is being received from the radio concentrator in the subscriber station.

For the manual operation of the subscriber station, a dialling keyboard WT is provided which cooperates with an optical display means AZ, a dialling store WS and a console control BS. The console WS is in turn connected to the central control unit ZS.

For completeness, on the left-hand side of the broken line there is also provided a device for the execution of a data operation which can be carried out in place of the speech operation. This device consists of the data transmission device DU and the data terminal device DE.

WHAT WE CLAIM IS:- 1. A system for digital information transmission comprising a plurality of radio concentrators mutually arranged in the manner of a cellular system with overlapping radio ranges and operating channels of different frequencies, each concentrator having transmitting and receiving means for communication with a plurality of mobile subscriber stations, and a plurality of mobile subscriber stations having transmitting and receiving means for comunication with a concentrator in which each concentrator further includes means for transmitting on a respective organisation channel, to the radio range identification, followed in timestaggered fashion by further radio-organisation related items of information, in which the subscriber stations include means for receiving these transmissions on an organisation channel, and means for deciding on the basis of their own radio-technical situation and the radio-range-related traffic load of the network which of the radio ranges they wish to be assigned to, and in which each concentrator and subscriber station includes respectively, receiving and transmitting means operable on said organisation channel whereby each subscriber station can implement a change of concentrator in a dialogue with the radio concentrators via the organisation channels.

2. A system claimed in Claim 1, which the radio concentrators and the subscriber stations are arranged to communicate, on both the operating channels and the organisation channels, in duplex operation.

3. A system as claimed in Claim 1 or 2, in which the subscriber stations include means for assessing the quality of the radio technical accessibility of the various radio concentrators on the basis of the field strength and/or the phase jitter of the signals received on the organisation channels.

4. A system as claimed in any one of Claims 1 to 3, in which the information blocks which are periodically transmitted in the organisation channels from the radio concentrators to the subscriber stations comprise, in addition to the radio range identification, items of information concerning the traffic state of the radio concentrators.

5. A system as claimed in any one of the preceding Claims, in which the radio concentrators are arranged constantly to check their operating channels from a radiotechnical view-point, and notify the subscriber stations of only those free operating channels in the relevant organisation channels whose radio-technical properties possess a sufficient quality for the execution of a transmission.

6. A system as claimed in any one of the preceding Claims, in which each subscriber station is arranged to, after applying to the relevant radio concentrator in a radio range immediately following this process, listen in to the free operating channels constantly reported as free by the radio concentrator in the relevant organisation channel and store these in a memory which is constantly kept up to date, and in which the subscriber station is arranged to, on the occurrence of a connection request, check the radio-technical serviceability of the operating channels last reported to be free and indicate to the radio concentrator the suitable operating channel for the establishment of the desired connection.

7. A system as claimed in any one of Claims 1 to 5, in which each subscriber station is arranged to, after applying to the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (52)

**WARNING** start of CLMS field may overlap end of DESC **. operating channel is carried out in association with the scanning process to be effected by the subscriber station. The function assembly RVI controls the transmission and reception of calls and for this purpose is provided with the above described scrambler. The function assembly MNl is the message device required for the presence check. It also handles re-applications. The function assemblies MNl, RVt, SYS, FA and FE cooperate with the superordinate central control unit ZS which is expediently in the form of a micro-processor. The microphone M and earpiece H of the subscriber station are connected via ana logue digital converters A/D to the relevant input or output of the speed transformer GW. BT represents the engaged tone generator which is controlled by the central control unit ZS and which responds whenever, for radio-technical reasons, a connection connot be established or breaks off. The analogue-digital converter A/D which is connected following the xnicro- phone M cooperates with the ringing tone generator FTO which is likewise controlled by the central control unit ZS. The ringing tone generator RTO which also cooperates with the central control unit ZS possesses an acoustic display L and in this way indicates that a call is being received from the radio concentrator in the subscriber station. For the manual operation of the subscriber station, a dialling keyboard WT is provided which cooperates with an optical display means AZ, a dialling store WS and a console control BS. The console WS is in turn connected to the central control unit ZS. For completeness, on the left-hand side of the broken line there is also provided a device for the execution of a data operation which can be carried out in place of the speech operation. This device consists of the data transmission device DU and the data terminal device DE. WHAT WE CLAIM IS:-

1. A system for digital information transmission comprising a plurality of radio concentrators mutually arranged in the manner of a cellular system with overlapping radio ranges and operating channels of different frequencies, each concentrator having transmitting and receiving means for communication with a plurality of mobile subscriber stations, and a plurality of mobile subscriber stations having transmitting and receiving means for comunication with a concentrator in which each concentrator further includes means for transmitting on a respective organisation channel, to the radio range identification, followed in timestaggered fashion by further radio-organisation related items of information, in which the subscriber stations include means for receiving these transmissions on an organisation channel, and means for deciding on the basis of their own radio-technical situation and the radio-range-related traffic load of the network which of the radio ranges they wish to be assigned to, and in which each concentrator and subscriber station includes respectively, receiving and transmitting means operable on said organisation channel whereby each subscriber station can implement a change of concentrator in a dialogue with the radio concentrators via the organisation channels.

2. A system claimed in Claim 1, which the radio concentrators and the subscriber stations are arranged to communicate, on both the operating channels and the organisation channels, in duplex operation.

3. A system as claimed in Claim 1 or 2, in which the subscriber stations include means for assessing the quality of the radio technical accessibility of the various radio concentrators on the basis of the field strength and/or the phase jitter of the signals received on the organisation channels.

4. A system as claimed in any one of Claims 1 to 3, in which the information blocks which are periodically transmitted in the organisation channels from the radio concentrators to the subscriber stations comprise, in addition to the radio range identification, items of information concerning the traffic state of the radio concentrators.

5. A system as claimed in any one of the preceding Claims, in which the radio concentrators are arranged constantly to check their operating channels from a radiotechnical view-point, and notify the subscriber stations of only those free operating channels in the relevant organisation channels whose radio-technical properties possess a sufficient quality for the execution of a transmission.

6. A system as claimed in any one of the preceding Claims, in which each subscriber station is arranged to, after applying to the relevant radio concentrator in a radio range immediately following this process, listen in to the free operating channels constantly reported as free by the radio concentrator in the relevant organisation channel and store these in a memory which is constantly kept up to date, and in which the subscriber station is arranged to, on the occurrence of a connection request, check the radio-technical serviceability of the operating channels last reported to be free and indicate to the radio concentrator the suitable operating channel for the establishment of the desired connection.

7. A system as claimed in any one of Claims 1 to 5, in which each subscriber station is arranged to, after applying to the

relevant radio concentrator in a radio range, listen in to the free operating channels constantly reported to be free by the radio concentrator in the relevant organisation channel, and store these in a memory which is constantly kept up to date, and the subscriber station is arranged constantly to check the radio-technical serviceability of the operating channels reported as free by the radio concentrator and stores a number of free operating channels, recognised as being suitable, in a further memory which is likewise constantly kept up to date.

8. A system as claimed in Claim 7, in which each subscriber station communicates the request for the operating channel which it requires for a connection establishment via the organisation channel to the radio concentrator, and the radio concentrator acknowledges this request by a return message in the desired operating channel.

9. A system as claimed in any one of the preceding Claims in which for the items of information relating to the various organisation functions, such as identification, application, re-application, presence check, seizure and call, each radio concentrator is provided with a sum organisation channel, which combines these items of information in a t.d.m. frame, in which furthermore the frame beginning of the sum organisation channel is marked by the information block, and the sum organisation channel for the presence check employs a super-frame which extends over two or more frames and the position of which can be adapted to the traffic load which fluctuates over a period of time.

10. A system a claimed in Claim 9, in which, in dependence upon the local incidence of traffic, two or more sum organisation channels having the same t.d.m.

frame are available to a radio concentrator.

and the sum organisation channels differ from one another merely in respect of a traffic-load-related differing priority as regards the subscriber stations applying to the radio concentrator.

11. A system as claimed in Claim 9, in which the radio frequencies of the organisation channels are established for the central range of the radio frequency band of the radio network, and the allocation of free operating channels to the subscriber stations is carried out on request centrally by the radio concentrators.

12. A system as claimed in any one of Claims 1 to 8, in which one of the organisation channels (message channel) of a radio concentrator serves to carry out the presence check on the subscriber stations which have applied in the radio range, and possesses one time slot for each subscriber station which has applied, and the frame period of this message channel amounts to n-times (where n is a whole, positive number) of the frame period of the further organisation channel or organisation channels.

13. A system as claimed in Claim 12, in which the message channel is discontinuously matched in its frame period to the nuumber of subscriber stations which have applied, which number fluctuates over a period of time, in time sections corresponding to the frame period of the further organisation channel or channels.

14. A system as claimed in Claim 12 or 13, in which a reduction in the frame period of the message channel in the event of a falling number of subscriber stations which have applied, is effected by regrouping the subscriber stations which have applied in the time slots bearing a high ordinal number into vacant time slots bearing a low ordinal number.

15. A system as claimed in Claim 12 or 13, in which the subscriber stations which have applied in a radio range are periodically called up by the relevant radio concentrator via the message channel to emit presence reports with a period which is dependent upon the number of subscriber stations which have applied.

16. A system as claimed in any one of the preceding Claims in which the presence of a subscriber station which has applied to the relevant radio concentrator in a radio range is automatically erased from the memory of the radio concentrator when the subscriber station does not emit a presence report to the radio concentrator via the relevant organisation channel within an interval of time of given length.

17. A system as claimed in any one of the preceding Claims, in which for the application and call of subscriber station to a radio concentrator within a frame period of the relevant organisation channel, there are available a given number of discrete time slots which are seized by each of the subscriber stations, as required, in accordance with a pseudo-random rule.

18. A system as claimed in Claim 15, in which each subscriber station possesses a frame-and bit pulse train-synchronised scrambler which, on request, selects one of the timeslots of the relevant organisation channel for seizure.

19. A system as claimed in any one of the preceding Claims, in which, in the intervals of time in which the information blocks occur in the organisation channels, a subscriber station engaged in a connection interrupts the transmission and alternately checks the operating channel assigned to its radio range which is engaged in the connection in respect of the continued existence of the connection and in each case listens in to one of the organisation channels alien to the radio range.

20. A system as claimed in Claim 19, in which the periodic check of the operating channel engaged in the connection is carried out by means of a mutual exchange of messages between the subscriber station and the radio concentrator, and that when these messages fail to appear over a plurality of check periods, a compulsory clearance of the connection is initiated.

21. A system as claimed in Claim 19, in which the periodic interruptions in the seized connection which occur during the listening in to the information blocks of the organisation channels are substantially eliminated by bit rate converters and intermediate storage means in the concentrators and in the subscriber stations which increase the transmission speed on the radio link and reduce the speed after reception.

22. A system as claimed in any one of the preceding Claims, in which each subscriber is arranged to on the initiation of a requisite change of radio range of a subscriber station engaged in a connection, firstly listen in to the channel information of the new radio range which has been recognised as suitable radio-technically, and subsequently apply to the associated radio concentrator stating the free operating channel which has been recognised as suitable, in which the concentrators are arranged to acknowledge messages with a return message which causes the subscriber station to assume a waiting position, in which the subscriber station maintains the original connection via the previous radio concentrator, and in which the radio concentrators are arranged so that the new concentrator, following the preparation of the switchover of the existing connection, in a dialogue between the previous and the new radio concentrator, informs the subscriber station of the time of the final switch-over, and that at this time the new radio concentrator and the subscriber station then simultaneously carry out the final switchover.

23. A system as claimed in Claim 22, in which each radio concentrator includes means arranged repeatedly to transmit from the new radio concentrator to the subscriber station information as to the time of the final switch-over, in such manner that the subscriber station is able to recognise the remaining time difference, and in which each subscriber station includes means responsive to reception of-one of these items of information to implement the switchover at the given time.

24. A system as claimed in any one of the preceding Claims, in which each subscriber station includes a micro-processor for controlling the radio-organisational functions.

25. A method for digital information transmission for mobile subscriber stations in the area of a radio network which consists of a plurality of radio concentrators mutually arranged in the manner of a cellular system with over-lapping radio ranges and operating channels on different frequencies in which radio-organisation-related information exchange between the subscriber stations and the radio concentrators which concentrators operate with a superordinate pulse train synchronisation in the radio ranges is carried out via central organisation channels, in which for this purpose in the organisation channels, from the radio concentrators to the subscriber stations which can be detected in respect of radio range, there are periodically transmitted information blocks provided with the radio range identification, which are followed in time-staggered fashion by further radio-organisation-related items of information, and in which the subscriber stations where these are activated-listen into the organisation channels, decide, on the basis of their own radio-technical situation and taking into account the radio-range-related traffic load of the network, which of the radio ranges they wish to be assigned to and when they wish to carry out a change of radio range, and then implement these decisions in a dialogue with the radio concentrators via the organisation channels.

26. A method as claimed in Claim 25 in which the information exchange between the radio concentrators and the subscriber stations is carried out in the operating channels and the organisation channels in duplex operation.

27. A method as claimed in Claim 25 or 26 in which the subscriber stations check the quality of the radio-technical accessibility of the various radio concentrators on the basis of the field strength and/or the phase jitter of the received organisation channels.

28. A method as claimed in one of the Claims 25 to 27 in which the information blocks which are periodically transmitted in the organisation channels from the radio concentrators to the subscriber stations comprise, in addition to the radio range identification, items of information concerning the traffic state of the radio concentrators.

29. A method as claimed in any one of Claims 25 to 28 in which the radio concentrators constantly check their operating channels from a radio-technical viewpoint, and notify the subscriber stations of only those free operating channels in the relevant organisation channels whose radio-technical properties possess a sufficient quality for the execution of a transmission.

30. A method as claimed in any one of Claims 25 to 29 in which a subscriber station applying to the relevant radio concentrator in a radio range will, immediately following this process, listen in to the free operating channels constantly reported as free by the radio concentrator in the relevant organisation channel and store these in its memory which is constantly kept up to date, and on the occurrence of a connection request the subscriber station checks the radio-technical serviceability of the operating channels last reported to be free and indicates the suitable operating channel to the radio concentrator for the establishment of the desired connection.

31. A method as claimed in any one of the Claims 25 to 29, in which a subscriber station applying to the relevant radio concentrator in a radio range will, directly following this process, listen in to the free operating channels constantly reported to be free by the radio concentrator in the relevant organisation channel, and store these in its memory which is constantly kept up to date, and the subscriber station constantly checks the radio-technical serviceability of the operating channels reported as free by the radio concentrator and stores a number of free operating channels, recognised as being suitable, in a further memory which is likewise constantly kept up to date.

32. A method as claimed in Claim 31 in which the subscriber station communicates the request for the operating channel which it requires for a connection establishment via the organisation channel to the radio concentrator, and the radio concentrator acknowledges this request by a return message in the desired operating channel.

33. A method as claimed in any one of Claims 25 to 32 in which for the items of information relating to the various organisation functions, such as identification, application, re-application, presence check, seizure and call, each radio concentrator is provided with a sum organisation channel which combines these items of information in a t.d.m. frame, in which furthermore the frame beginning of the sum organisation channel is marked by the information block (K), and the sum organisation channel for the presence check employs a super-frame which extends over two and more frames and the position of which can be adapted to the traffic load which fluctuates over a period of time.

34. A method as claimed in Claim 23, in which, in dependence upon the local incidence of traffic, two or more sum organisation channels having the some t.d.m.

frame are available to a radio concentrator, and the sum organisation channels differ from one another merely in respect of a traffic-load-related differing priority as regards the subscriber stations applying to the radio concentrator.

35. A method as claimed in Claim 23, in which the radio frequencies of the organisation channels are established for the central range of the radio frequency band of the radio network, and the allocation of free operating channels to the subscriber stations is carried out on request centrally by the radio concentrators.

36. A method as claimed in any one of the Claims 25 to 32 in which one of the organisation channels (message channel) of a radio concentrator serves to carry out the presence shock on the subscriber stations which have applied in the radio range and possesses one time slot for each subscriber station which has applied, and the frame period of this message channel amounts to n-times (n is a whole, positive number) of the frame period of the further organisation channel or organisation channels.

37. A method as claimed in Claim 36 in which the message channel is discontinuously matched in its frame period to the number of subscriber stations which have applied, which number fluctuates over a period of time, in time sections corresponding to the frame period of the further organisation channel or channels.

38. A method as claimed in Claim 36 or 37, in which a reduction in the frame period of the message channel in the event of a falling number of subscriber stations which have applied, is effected by regrouping the subscriber stations which have applied in the time slots bearing a high ordinal number into vacant time slots bearing a low ordinal number.

39. A method as claimed in Claim 36 or 37 in which the subscriber stations which have applied in a radio range are periodically called up by the relevant radio concentrator via the message channel to emit presence reports with a period which is dependent upon the number of subscriber stations which have applied.

40. A method as claimed in any one of Claims 25 to 39 in which the presence of a subscriber station which has applied to the relevant radio concentrator in a radio range is automatically erased from the memory of the radio concentrator when the subscriber station does not emit a presence report to the radio concentrator via the relevant organisation channel within an interval of time of given length.

41. A method as claimed in any one of Claims 25 to 40 in which for the application and call of subscriber station to a radio concentrator within a frame period of the relevant organisation channel, there are available a given number of discrete time slots which are seized by each of the subscriber stations, as required, in accordance with a pseudo-randomrule.

42. A method as claimed in Claim 39, in which each subscriber station possesses a frame and bit pulse train-synchronised scrambler which, on request, selects one of the time slots of the relevant organisation channel for seizure.

43. A method as claimed in one of the preceding Claims in which in the intervals of time in which the information blocks occur in the organisation channels. a subscriber station engaged in a connection interrupts the transmission and alternately checks the operating channel assigned to its radio range which is engaged in the connection in respect of the continued existence of the connection and in each case listens in to one of the organisation channels alien to the radio range.

44. A method as claimed in Claim 19, in which the periodic check of the operating channel engaged in the connection is carried out by means of a mutual exchange of messages between the subscriber station and the radio concentrator and that when these messages fail to appear over a plurality of check periods, a compulsory clearance of the connection is initiated.

45. A method as claimed in Claim 43, in which the periodic interruptions in the seized connection which occur during the listening in to the information blocks of the organisation channels are eliminated by increasing the transmission speed on the radio link and in fact in combination with an intermediate storage, at the transmitting and receiving ends, of the communications signals which are to be transmitted, in the subscriber station and the radio concentrator.

46. A method as claimed in any one of Claims 25 to 45 in which, on the initiation of a requisite change of radio range of a subscriber station engaged in a connection, this subscriber station firstly listens in to the channel information of the new radio range which has been recognised as suitable radio-technically, and subsequently applies to the associated radio concentrator stating the free operatting channel which has been recognised as suitable, in which furthermore the new radio concentrator acknowledges the message with a return message which causes the subscriber station to assume a waiting position in which the subscriber station maintains the original connection via the previous radio concentrator, and, following the preparation of the switch-over of the existing connection, in a dialogue between the previous and the new radio concentrator, the new radio concentrator informs the subscriber station of the time of the final switchover, and at this time the new radio concentrator and the subscriber station then simultaneously carry out the final switch-over.

47. A method as claimed in Claim 43, in which the time for the final switch-over is repeatedly transmitted from the new radio concentrator to the subscriber station, in such manner that the subscriber station is still able to recognise the remaining time difference, and in the event of a satisfactory reception of one of these items of information, the subscriber station implements the switch-over at the given time.

48. A method as claimed in any one of Claims 25 to 47, in which the radio-organisational functions are controlled in each subscriber station by a micro-processer.

49. A system for digital information transmission substantially as herein described with reference to the accompanying drawings.

50. A method of digital information transmission substantially as herein described with reference to the accompanying drawings.

51. A radio concentrator substantially as herein described with reference to Figures 1 to 10 of the accompanying drawings.

52. A mobile radio station substantially as herein described with reference to Figures 1 to 9 and 11 of the accompanying drawings.