WO1993025918A1

WO1993025918A1 - A system for the transfer of information comprising several transponders

Info

Publication number: WO1993025918A1
Application number: PCT/SE1993/000543
Authority: WO
Inventors: Staffan Gunnarsson; Jesper Hansson; Lars Egnell
Original assignee: Saab-Scania Combitech Aktiebolag
Priority date: 1992-06-17
Filing date: 1993-06-17
Publication date: 1993-12-23
Also published as: SE9201864D0

Abstract

A system is described for communication by means of signals in form of electromagnetic waves, especially microwaves, within a restricted communication area (3, 7) comprising at least one first unit (4, 6) for emitting a first enquiry signal and receiving a number of reply signals and a number of further units in form of transponders (1, 2, 8) emitting these reply signals when being present in the communication area. The transponders are equipped with modulating means (25, 26) for modulating the arriving enquiry signal with individual reply codes containing information and means for emitting this information as a reply signal. The system is primarily characterized of that each transponder modulating means (26, 72) is adapted to continuously be supplied with its individual reply code from a memory (28) within a first relatively short interval (19) being continuously repeated with relatively long intervals (18), the reply code thus being available to be emitted together with the reply signal in time, completely independent of the enquiry signal. In a preferred embodiment of the system a means is established in the transponder to randomly or pseudorandomly generate said intervals (18).

Description

A SYSTEM FOR THE TRANSFER OF INFORMATION COMPRISING SEVERAL

TRANSPONDERS

The present invention relates to communication systems by means of signals in form of electromagnetic waves, especially microwa¬ ves, within a defined communication area including at least a primary unit for sending a first enquiry signal and receiving a number of reply signals and a number of secondary units i form of transponders emitting these reply signals when being present in the communication area the transponders being equipped with modu¬ lating means for modulating the arriving enquiry signal by indi¬ vidual reply codes including information and means for emitting this information as a reply signal-

Background of the Invention

In microwave based information transmission systems containing transponders a need arises in certain applications of simultane¬ ously reading the information contents of multiple transponders being simultaneously present i the same communication lobe. At the same time there can even exist a need to influence the data content.

An example of this is the passage control of doors when several individuals simultaneously or in close succession are passing through the door. The individuals are each carrying a transponder and the area is scanned by an aerial placed on top of the door. The system may be combined with a time registration, the trans¬ ponder data memory being registered at the same time as the passage time.

As all the transponders being present in the lobe are emitting their own data signal these will be interfering with each other, the reading unit at the best being able to record the strongest transponder signal and the remaining transponder signals being masked off to remain unread.

One way to solve the problem mentioned above is described in the Swedish patent 8903775-8 'Transmission System containing one Enquiry Station and Multiple Reply Stations' . In the patent referred hereinto an interrogator, i.e. the emitter/receiver- unit, is sending a starting code and lets the reply stations, i.e. the transponders, answer with an address related and time delayed reply code. In this way the interrogator can decide which transponders are being present in the communication area for then performing addressed and selective communication with one of the individual transponders at a time.

However, the solution referred to has several drawbacks. By way of example, the emitter/receiver-unit is sending starting codes requiring modulation of the emitted signal. Moreover, the trans¬ ponders are requiring means picking up the emitted signal so that the reply code can be emitted in due time.

A further drawback of the solution referred to is the limitation of the various possible addresses to the number of intervals being possibly permitted within the available communication period, e.g. for passing through a door. An administraion system is then required for allocating a restricted number of addresses to each transponder population, e.g. for a certain working place.

Another solution has been proposed in EP 0 401 192 'Systeme de taxation ou peage automatique pour vehicules routiers ' relating, as the title indicates, to an automatic road toll collect. Even this system is using a transponder reply code time multiplexing, the reply codes still being operated by the emitter/receiver-unit but with the reply time not being address related but instead having a random time delay relatively one of the synchronizing signals emitted by the emitter/receiver-unit. Thus, this system requires also that the emitter/receiver-unit emits starting codes and requires that the transponders have means for picking up the emitted code to generate a relevant reply code after a random controlled delay in relation to the starting code. Purpose and Main Characteristics of the Invention

The purpose of the invention here described is to accomplish an information transmission system with an exact and fast reading of multiple transponders even in the case that they are in the same communication area without any coded signal needed to be sent to the transponders.

Such transmission systems are for example used for identifying individuals at doors and passage gates, for material identifica¬ tion in production and distribution links, as well as for identi¬ fication of animals, vehicles, etc.

An examplifying application is the passage control at a door entry with simultaneous updating of the transponder memory and the passage time. Besides the advantage of several transponders being communicated with simultaneously, such a system is achie¬ ving a simpler installation with reduced wiring. This is due to that the system is able to operate decentralized without communi¬ cation with a primary system, as data are carried from the trans¬ ponder position instead of being transmitted by cable.

An important application is related to the registration of public movements, e.g. i dangerous environments, such as off-shore plat¬ forms, mines, nuclear power stations, petrochemical industry and explosive manufacturing facilities. By automatical registration of a group of individuals quickly passing a passage gate (e.g. an alley way between two platforms) an exact information is received as to those not being rescued during e.g. a fire and the rescue efforts can be optimized considerably.

According to the invention the system of the above mentioned kind is characterized primarily of that each transponder modulating means is adapted to continously receive its individual reply code from a memory within a first relatively short period to be conti¬ nously repeated with relatively large intervals, the reply code thus being kept available to be emitted with the reply signal totally independent in time of the inquiry signal. In a preferred embodiment of the system according to the inven¬ tion the transponders comprise a means randomly or pseudorandomly generating said intervals. Pseudorandomly here means that the in¬ tervals are randomly generated in series being themselves repea¬ ted, but only after that a multitude of intervals have been gene¬ rated.

When a transponder is entering the communication area it is read as sson as it emits its first reply code.

When two transponders are simultaneously entering the communica¬ tion area, each transponder being passive during most of the time and the transponders not being synchronized in between each other, then, with utmost probability the emitted codes from the two transponder, will not interfer. However, should such an in¬ terference occur, then, with utmost probability, the next emitted reply code from the transponder not being read will not interfere as the interval between the transponders are different, being controlled by the random delay distributing function.

When three or more transponders are entering simultaneously the communication area a rather soon reading of all transponders is achieved in the same way as described above.

The procedure is reminding of a data network where several users are sharing the same medium by random process techniques, the medium however not being a physical cable but a non contact microwave link. In a data network, the data transmission period is increasing due to interference probabilites according to a random access function, when many users are simultaneously utili¬ zing the net, this even being the case in a system according to the present invention.

However, interference between reply codes is not a practical problem as not more than a certain number of transponders are being present in the same communication lobe due to physical ■limitations. For example, it is thus not probable to assume more than three to five individuals simultaneously being present in a communication area as well as up to one second is available to perform transactions, i.e. the period required to pass through the communication area.

Many embodiments of the system and the transponders are possible. Conveniently the enquiry signal consists of an essentially conti- nous and unmodulated wave, preferably within the frequency range 0,9 to 25 GHz. The transponders are preferably adapted to reemit reply signals comprising at least one modulated side band fre¬ quency of the enquiry signal frequency. The transponders themsel¬ ves can be equipped with a battery to generate the energy requi¬ red for reemitting the reply signal, in a preferred embodiment, however, the replyu signal is reemitted without any energy being supplied with exception of the one supplied by the enquiry sig¬ nal.

For their internal function, however, the transponders of the type described above are requiring an interntal power supply, by example, for backing up an internal RAM, for driving an internal clock oscillator, e.g. at 455 Hz or 32 kHz, as well as driving an eventually incorporated signal amplifier adapted to amplify a detected video signal when writing data to the transponder by conveniently amplitude modulated microwaves. These internal power requirements can be satisfied in different ways, for example by power supply from a built-in battery, by induction from a relati¬ vely low frequency electromagnetic AC-field, for example of 130 kHz, by receiving an incoming relatively strong microwave signal, for example at 2,45 or 5,72 GHz, or by means of an electric dyna¬ mic generator similar to that of a modern wrist watch of the quartz oscillator type, the transponder application dynamics sto¬ ring power in a chargeable cell.

However, for the external function, i.e. the transponder microwa¬ ve communication, there is normally no need for power supply ex¬ cept that coming from the arriving enquiry signal. This is due to the transponder is acting as a passive modulator with a wave- profile representing data from' its memory which renders the en¬ quiry signal to be reflected in a variable phase and/or amplitude according to the data array to be emitted from the transponder so that sidebands representing the transmitted information are for¬ med in a per se known way on each side of the incoming frequency. The incoming frequency component itself is also reflected, but its power level will then be decreased, partly due to internal losses in the transponder microwave circuits, but partly even due to the power consumption needed for creating said emitted side¬ band.

The transponder being designed for relatively large intervals between emitted reply codes, also a saving of the internal trans¬ ponder power consumption is achieved. As a large part of the in¬ ternal digital transponder circuits need not to be clocked during intervals, less electrical nodes are oscillating between a logi¬ cal zero and a logical one as otherwise would have been the case. As each node represents a capacitance each logical envelope means a power loss of certain power units, the total capacitive flow thereby decreasing in the transponder electronics.

In a preferred embodiment the transponder modulating circuits consist of a microwave diode switched in in connection with its aerial, its backup voltage being varying between discrete values for emitting data as a logical zero or a logical one. The diode blocking layer is thereby changing its reactanse, especially its capacitance, the phase position of the wave reflected/emitted by the transponder thus being varied between distinctive values according to the data beig passed. Thus, by introducing intervals between the emitted reply codes the capacitive power consumption is decreasing even in the backup voltage diode.

Another saving source in the intervals is that the total capaci¬ tive current is decreasing between the conductive tracks from the logical circuits and said diode and the earth.

From this discussion becomes evident that there is a reason to introduce even for saving purposes relatively long intervals between the codes transmitted to the modulator, even if they do ■ not always need to be at random or at pseudorandom. Thus, the in¬ tervals, e.g. in a system where not several transponders are ex¬ pected to communicate simultaneously in the same communication area, can be totally regular with an interval being for example four or sixteen times as long as the reply codes are requiring.

In a special embodiment a sideband suppressing modulator is used in the transponder, the invention, however, not being restricted to this embodiment. In another special embodiment, which is sui¬ ted for especially large communication ranges, a microwave ampli¬ fier is used for the signal emitted from the transponder. The amplifier has then a power supply from said internal power sour¬ ce.

For avoiding negative effects of time interferences between seve¬ ral transponder reply signals, e.g. a missing or wrong interpre¬ tation of the code, the first unit can during reception from several transponders simultaneously emitted, interfering reply signals be adapted not to register these, but to continue to emit the enquiry signal until at least one predetermined part of the various individual reply codes have been correctly received. The thus convenient minimum enquiry signal emitting time is suitably defined by statistical procedures depending on the communication area size and form, the expected number of transponders per period, the expected number of simultaneous transponders in the area, the expected transponder orientation, their reply code length, etc.

If the transponders are adapted to register information emitted by an information signal from the first unit in a memory, the information signal advantageously is comprising an access code being unambiguously defined by the individual reply code being previously emitted as a reply signal from the corresponding transponder. Then, the whole reply code or a part of it from each transponder can be one for each separate transponder unique code, with which said access code is identical or is unambiguously definable. To the extent that transponders are equipped with a memory of the just mentioned type it may be convenient each transponder to comprise means for access control to said information signal so that only that one can be registered in the transponder memory if it contains an access code being a code unambiguously defined to the separate transponder reply code. Thus, each transponder reply code may be one for each transponder unique code, with which said access code is identical or unambiguously defineable. By this procedure is achieved that the transponders can be written in ar¬ rays, even if each transponder is written with individual data and at the same time the risque for unintentional writing into the transponder memories and data damage is eliminated.

In a special embodiment the invention can even be used to selec¬ tively writing data into the transponders, even if several trans¬ ponders are present in the same communication area. This function is especially beneficial when in addition to the reading an upda¬ ting of the transponder memory is asked for, to indicate, for ex¬ ample, the time of communication for debiting a value related saldo to the transponder or a corresponding item.

Considering the need to communicate from said first unit with a relatively large number of transponders being more or less in the shadow of different items or being turned in different direc¬ tions, the system conveniently comprises at least two aerials for emitting said enquiry signal from different aspect angles towards the transponders these thus being irradiated from different directions and thus being able to emit reply signals independent¬ ly of any eventually unsuitable orientation in relation to at least one aerial. These aerials, naturally occasionally being more than two, can either be directly connected to one single first unit, but can also be connected by one or several aerials to each several first unit.

The system may be adapted to automatically register the passage of transponders being carried by individuals passing through a door, a walking passage, a corridor or similar, or transponders being carried on physical objects in a flow, such as gas bottles, material containers, fluid containers, bagage bags, manufacturing objects or similar. The system may even be adapted to write data into the transponders in a flow, such as the passage time, the passage place, the destination, the transaction number, the saldo debiting, etc.

In an embodiment for writing each transponder has an incorporated reading/writing-switch only permitting writing in the beginning of the interval following directly after the transponder accor¬ ding to the previous description having emitted its randomly generated reply code.

The writing sequence is initiated by a writing switch code rela¬ ted to one for the transponder unique part of the transponder reply code and is after reading sent to the transponder for swit¬ ching the reading/writing-switch to the writing position. The transponder memory then can be selectively updated by the wri¬ ting/reading-unit during a directly following interval.

By letting a part of the transponder reply code be unique for the transponder, for eaxample installed during the transponder manu¬ facturing or distribution is achieved that data being related to a specific transponder are only reaching this transponders memory circuits and not any other transponder memories.

The unique code may conveniently be permanently written into the transponder silicon circuits, for example by laser etching, current line burning by means of high voltage, writing into the EEPROM with an eventual following burning of the EEPROM-circuit programming circuits or by any other corresponding procedure.

The writing switch code and writing data emitting time is not requiring any other time relationship than with the reception of the actual transponder reply code and will not interfere with any other signal, the emitted message having no other writing/rea- • ding-signal to' interfere with. If several writing/reading-units are situated close to each other their corresponding emitted wri¬ ting codes, however, can be multiplexed in the time or frequency level according to one of the methods available for this purpose.

A further application is during identification of material in distribution flows, for example of a number of objects on a transportation platform. With a communication zone covering the whole platform carrying area each cargo object transponder code can be picked up, even if the cargo objects are many. The identi¬ fication process is then becoming considerably faster than with each transponder being identified separately.

The system may even be supplemented by an equipment for measuring the transponder position relatively the first unit by comparing the phase position of the reply signal in at least two of the first unit aerials relatively a signal emitted from the first unit, for example according to the American Patent Publication 4,728,955, the emitted enquiry signal conveniently even being used for position measuring and simultaneous registration by means of a video camera or a corresponding optical method of an existing transponder carrier, independently of them implying a transponder communication or not. The system is then designed so that those transponder communications complying a predertermined criterium for access are resulting in that the corresponding optical registrations are eliminated afterwards so that the remaining optical registrations related to a transponder carrier not having performed any approved transponder communication are made available for reporting to a head system.

Naturally, the system can be designed in a corresponding way for the registration of a flow of individuals not being qualified for an actionless passage, for example by prepayment of an entrance fee or by establishing a qualification to pass.

The invention comprises even further applications.

For example it can at automtic road tolls be interesting to com¬ municate with several vehicle transponders in the communication area, for example by means of at least one writing/reading-unit placed across the roadway which covers all the lanes of the road¬ way. In such a system the traffic can float completely unobstruc¬ ted without being hampered by passing a toll gate, this being attractive for reasons of transportation economics and environ¬ mental reasons. For eliminating the risque of vehicles having no approved transponder communication (for example vehicles without any transponder) being able to pass without any fee the system can be provided with a measuring system, for example in accordan¬ ce with US-A-4,728,955. Thus, all passages can be registered be means of e.g. a TV-camera, the vehicle passages not corresponding to an approved transponder measurement initiating a special order.

Description of several embodiments

The invention will now be described in connection with the enclo¬ sed drawings, where

Figure 1 shows a view of a communication area with an emitting-

/receiving unit and individually carried transponders;

Figure la shows schematically a plan view of the system provided with two aerials in a corridor;

Figure 2 shows a view of a communication area and by physically carried transponders with an emitter/receiver-unit carried by hand;

Figure 3 shows an example of how the transponder reply codes can be distributed in time;

Figure 4 shows a simulation result according to a probability calculation generated by transmitting information to a certain number of transponders in the communication area;

Figure 4a shows a further simulation result;

Figure 5 shows a flow chart for a transponder with pseudorandom reply code intervals;

Figure 6 shows a reading unit for transponder communication, eventually also comprising a writing unit;

Figure 7 shows several* signals of importance for the transponder readings; Figure 8 shows in detail a way of generating pseudorandom delays of the transponder reply codes, devided into blocks in figure 5; Figure 9 shows a flow chart for a transponder with pseudorandom reply code intervals, comprising also means for selective writing into a set of transponders; and

Figure 10 shows several signals of importance for the transponder writing.

In figure 1 is shown, how two individuals with each one transpon¬ der 1, 2 are passing the communication area 3 generated in front of a communication unit 4. In an analogous way figure 2 shows, how a freight vehicle with freight objects 5 is passing through the communication area of the communication units 6, the freight objects carrying transponders 8.

From both figure 1 and 2 is to be seen that all transponders being present in the communication area are preferably to be com¬ municated with without interfering with each other. In certain cases one reading of the transponder identity will be sufficient and, moreover, eventually of the identification object linked data, whereas on the other hand it can be neccessary to simulta¬ neously write information into the transponders, for example the passage time, passage location, etc.

In figure la is shown a group of individuals 103, 104, etc. on their way through a corridor 102. Two aerials 100 nd 101 are ins¬ talled in such a way as to essentially increase the chances for noninterfering communication between the aerials and the trans¬ ponders carried by the individuals, in comparison with a system including only one aerial.

The transponders according to the present invention are capable of emitting their reply codes with identity and eventual further data in a randomly time related way in accordance with figure 3. The figure is showing three transponders 9, 10 and 11 being pre¬ sent simultaneously, the corresponding transponder code being in¬ dicated by different arrays. From this figure is evident how the first reading of the reply code 10 will be performed at the time 12. The reading of another transponder code 9 ocurs at the time 13, whereas the transponder code 11 is read at the time 14. The reply code 11 could have been read at the time 15, if this reply would not interfere with the reply code 10 at the same time, however, a data collision occurs resulting in that the communication unit 6, alternatively 4, is rejecting the reply and is waiting for the next code without any collision.

The communication unit detecting of a collision being present can be made in several ways, for example by letting the reply code contain redundance in form of a checking sum according to CRC. Then it is during a data collision probable that at least one bit error occurs in the data received by the communication unit. This is detected by the communication unit CRC-checking and the data is rejected.

Another collision is shown in moment 16, 17, where the codes 9 and 11 are colliding.

By choosing the average reply code interval length 18 relatively, large in comparison with the reply code length 19 the probability of avoiding a collision is relatively high leading to the time 20 being relatively short, when all codes 9, 10 and 11 with a cer¬ tain probability have been read.

The period 20 until all codes have been identified has a probabi¬ lity distribution acording to figure 4.

The involved parameters are the number of all transponders in the communication area, the ratio between the average transponder in¬ terval and reply time as well as the amount of transmitted data and the data transmission velocity.

The result in figure 4 has been achieved by simulating a multitu¬ de of communication attempts, the longest periods for performing. the communication with all transponders being noted for different ratios of time intervals and reply time.

Further, the simulation has anticipated the reply time delay being rectangularly distributed between zero and the double ave¬ rage value. For example, an approximate value to this distribu¬ tion function can be obtained according to the description here below in this part, an embodiment of the random generating cir¬ cuits being shown in detail in figure 8.

In figure 4a the result of a multitude of simulation attempts is shown with up to ten transponders depicted on the diagramme ab¬ scissa axis. On its ordinata axis is shown the time in ms for the performed communication in two cases, one with all transponders having performed a communication with the first unit in 50 per¬ cent of the simulation attempts and the other the time for all transponders having communicated in 99 percent of the simulation attempts.

Figure 5 is a flow chart for a transponder generating reply codes with pseudorandom intervals according to the pattern described previously. A pseudorandom interval is defined by its digital generation and being repeated but first after such a long time as to be significant in this connection.

When the transponder is irradiated by a lighting signal 24 this is received by the transponder aerial means 25 being directly connected to a modulating means 26. The modulating means can have one of two different positions depending on the register data signal 27 being at this moment supplied to the modulating means from the transponder memory register 28.

In figure 5 the memory register 28 is of the serially feedback shift register type, however it is of no significance whatsoever, if the memory is of a serial type or has any other organisation.

The register data signal 27 is by means of the feedback 29 ■ forced to regularly repeat its data sequence, for example 512 data bits, to the modulating and aerial means 26, 25.

The modulating and aerial means 26, 25 will supply the lighting signal 24 with information sidebands and reradiate these in form of a data information sideband signal 30.

The lighting signal can for example be a continous unmodulated wave, for example with the microwave frequency 2,45 GHz and the modulating means can in a per se known way supply a phase, a fre¬ quency or an amplitude modulation to the lighting signal for es¬ tablishing said data information sideband signal.

The sidebands can in an embodiment be symmetrically distributed around the lighting signal and been situated at a distance there¬ from being of the same magnitude as the data transmission veloci¬ ty, with which the transponder reply code is read. In another embodiment one sideband modulation can be performed.

Said modulating forms are adapted to be read by a communication unit of the homodyne type being described further below and il¬ lustrated in figure 6, the invention, however, not being restric¬ ted to any special type of receiver or any special way of modula¬ ting the information sidebands.

The transponder reply codes, however, are not to be emitted con¬ tinously and have instead, according to the previous description, to have certain intervals. For this purpose the transponder is provided with a pseudorandom generator 31 generating a pseudoran¬ dom sequence signal 32 to a coinciding counting net 33 in the transponder.

The coinciding counting net 33 can from the pseudorandom sequence signal 32 generate an activating signal for data shifting 34 per¬ mitting by random intervals the register to shift just one turn.

Figure 7 shows the previously mentioned signals in the time plane. From the pseudorandom^'sequency signal 32 the activating signal for data shifting 34 is generated controlling the register shifting ahead so that the complete register memory contents are present in the register data signal 27.

The register data signal 27 is shown to comprise two parts, a transponder identity part 35 and a data part 36. As can be seen from figure 7 the necessary and randomly controlled intervals are generated between the data codes 35, 36. When the lighting signal 24 is entering the transponder aerial means 25 it will be modi¬ fied so that a data information sideband signal 30 is emitted from the transponder.

Figure 6 shows a communication unit with transponders of the pre¬ viously described type. The communication unit comprises an oscillator 37 generating a signal 38 which after being emitted by an aerial means 39 is the previously mentioned lighting signal 24.

A signal 44 with the same frequency as the oscillator signal 38 is sent to a mixer 45, where even the received information side¬ band signal 30 is carried by the aerial means 39 and the conduc¬ tor 46. The mixers is then transponing the wireless transmitted signal 30 to a lower frequency so that its data contents can be translated in a data decoder net 46 and thereafter written into the communication unit memory in a memory and processor block 42.

In the memory and processor block 42 a check sum control is per¬ formed to decide whether the data received are valid or corrupt. If they should be corrupt this may depend on a data collision between codes from different transponders, the receiving period then to be continued.

In certain cases it is known, how many transponders are simulta¬ neously present in the communication area. This number can then be predeposited in the memory and processor circuits 42 so that a clearance signal can be emitted when all transponders are read in an approved way. Otherwise the communication area and the data transmission periods have to be arranged in such a way that sufficient proba¬ bility is achieved that all transponder reply codes are to be read. For example, it can be anticipated that a restricted number of individuals simultaneously are present in a doorway due to physical restrictions and that these can move through the commu¬ nication area with a limited speed.

The oscillator is controlled via a control signal 40 and is nor¬ mally unmodulated during reading a transponder. For the event that the transponder shall be written a data coding net 41 being controlled by the processor and memory circuits 42 with data from the data conductor 43 will actuate the lighting signal modulation in a way representative of the writing data.

Figure 8 shows more in detail, how the transponder pseudorandom generator 31, the coinciding counting circuit 33 and the data register 34 can be designed. All clocked elements are clocked by the oscillator 50.

A binary pseudorandom sequence is generated by the pseudorandom generator being a n-bit feedback shift register, the number n being determined by the desired length before the sequence is repeated.

The feedback coefficients A(l)-A(n-1) are coefficients in a pri¬ mary polynome g(y) for GF(2) raised by n, i.e.

where A(i) holds the value 0 or 1, and where the coefficients are available from a table-work for primary polynomes.

In figure 8 the numeral 51 is the delay element in this shift register, whereas 52 are EXOR-gates and 53 is the connecting ele¬ ment for the feedback coefficients A(l), A(2), ..., A(n-l), respectively, i.e. the elemnts have connection, or have not con¬ nection, depending on which polynome that has been chosen.

54 is a shift register containing a number of the last generated bits in the pseudorandom sequence 52. The sshift register length is determined by the size of the random delay area asked for and its value can be suupplied at a convenient time into the compari¬ son net 55 via a latch 63.

The comparison net 55 is emitting a clock interval long pulse on the signal line 64 when the values of its inputs are the same.

58 is a delay counter its width being determined by the delay area size. The two counter driving modes, i.e. to count and to stop, are via input 59 controlled by a SR-flip-flop 62.

60 is an address counter counting up to 2x - 2, whereafter it is automatically cleared, x being the number of bits in the memory register 28. The counter is controlled via input 61 and has two driving modes, i.e. to count and to stop.

65 is a net resetting the SR-flip-flop 62, when the address coun¬ ter has stopped counting, i.e. when the data register 28 has been shifted one turn.

Suppose the SR-flip-flop output intially is low implying the delay counter 58 being active and counting forwards. When its outputs 57 have the same value as the outputs 56 of the latch 63 the comparison net 55 emits a pulse on the signal line 64 to the latch enable input and to the SR-flip-flop set input.

The latch is then passing another delay signal 66 from the pseu¬ dorandom generator to the comparison circuit 55. At the same time the SR-flip-flop output becomes high and is stopping and reset¬ ting the delay counter 58 via input 59. The SR-flip-flop is via input 61 activating the address counter 60 so that a number clock pulses 67 corresponding to the register size are passed through the gate 68 from the system clock 50, before the register clock¬ ing is stopped again, the address counter having completed its counting and via net 65 resetting the SR-flip-flop 62. The clock pulses are corresponding to the previous mentioned activating signal for a register data shifting 34.

When the address counter 60 then has counted up to x-1, i.e. the data register has shifted around one turn and has via the regis¬ ter data signal 27 sent its data to the modulating and aerial means the transponder has sent its memory contents and started a new interval controlled by the period the delay counter 58 takes to reach the pseudorandom number existing at the inputs 56 of the comparison net 55.

Figures 9 and 10 are illustrating the writing into the transpon¬ der register.

In figure 9 the pseudorandom generator, the coinciding counter net, the data register and the modulating and aerial means are supplemented with an access control net 71 and a writing/rea¬ ding-switch 70. Furthermore, there is a demodulating function in connection with the aerial means 25, i.e. the modulator/demodula¬ tor 72. Another difference consists of that the coinciding coun¬ ter net even can emit an activating signal for an access control 73.

The reading of the transponder reply code is performed in the same way as previously described, i.e. a lighting signal is supp¬ lied to the transponder aerial and modulating means, the reply code generated with a random interval is emitted by reirradiating a data information sideband signal from the modulating and aerial means to an outer communication unit of the kind previously described.

However, as data even has to be written into the transponder a double way connection is required between the data reister 28 and the modulator/demodulator 72, i.e. the information code line 74. The writing/reading-switch 70 implies that the data register 28 both can shift around with own data and can be supplied with new data. New data, however, can only be supplied under the condition that access has been achieved, i.e. that the new data being supp¬ lied are corresponding a code already existing in the transpon¬ der, thereby prohibiting data correlated to a certain transponder reaching other transponder register memories. This access is made in the access circuit 71, completely controlling the different writing/reading-switch function modes.

In the execution example here described is assumed that each transponder in a system has an unique identity, for example in¬ corporated in the memory register as a non writable part. Figure 10 illustrates how the information sideband signal 75 contains both identity data 76 and user data 77 to be changed from a value 77 to another one 78 by writing it into the transponder.

A writing into the transponder is performed by first reading its data.

A lighting signal approaching the transponder in form of a conti¬ nuous wave 80 during the period 81, the register by means of the register control signal 80 via the writing/reading-switch swit¬ ching means 82 is clocked to the modulator/demodulator means 72 implies that the transponder is read in the way previously men¬ tioned. The switching means 83 in the writing/reading-switch feeds back the regiter data signal 84 also to the register input by means of the register writing signal 85 so that the register data are not changed in the first place.

The transponder identity code 76 is translated in the outer com¬ munication unit according to figure 6 and is directly after rea¬ ding reemitted during the period 86. In principle the identity code can be changed, for example by cryptic writing, only this is made in a unambiguous way. The switching means 82 is switched, initiated by a simultaneously with the from the communication unit generated identity/access code 86 coming activating signal for access control 73 and directly after that the transponder has emitted its reply code 77, via a control signal for access and register data 87 so that a transponder correlated identity/access code via line 88 is reaching the access control net 71.

During the period 89 a comparison is made in the access control net between the transponders own identity code and the identity- /access code received from the communication unit. If the code coincides with the arranged criteria, for example that the code received from the communication unit is in accordance with the identity code emitted from the transponder, a comparison is made by or without means of a crypting algoritm, the access control net will actuate the switch means 83 via the control signal register data 90 so that both switches now are in the lower posi¬ tion in figure 9.

Thus, the signal passage lies open from the aerial means 25 to the memory register 28 so that new data 91 can be written into the register from the outer communication unit. Directly after the registration being completed the switches 82 and 83 are reset to their upper position shown in figure 9 actuated by the control lines 87 and 90.

After data registration a control reading conveniently is perfor¬ med of the data in the previously described way.

By means of the principle here described data with other identi¬ ty/access codes are prohibited to reach other transponders in the communication area than those being read a moment before from a specific transponder.

A test to address the transponder with non valid identity/access code is shown in the sequence 92. Here, the transponder is reached by a foreign identity/access code 93, with the consequen¬ ce that previous data 78 are kept unchanged 94 in the register and so that the transponder is not updated with lighting data 95. As the access control has not provided an approved result the control signal 90 remains unactive so that the switch 83 cannot link data from the communication unit to the register input.

A reading 96 later on shows that the register data have remained unchange .

Claims

C L A I M S

1. A system for communication by means of signals in form of electromagnetic waves, especially microwaves, within a restricted communication area (3, 7) comprising at least one first unit (4,

6) for emitting a first enquiry signal and receiving a number of reply signals and a number of further units in form of transpon¬ ders (1, 2, 8) emitting these reply signals when being present in the communication area, the transponders being equipped with modulating means (25, 26) for modulating the arriving enquiry signal with individual reply codes including information and means for emitting this information as a reply signal, characte¬ rized in that each transponder modulating means (26, 72) is adap¬ ted to continously be supplied with its individual reply code from a memory (28) within a first relatively short interval (19) being continously repeated with relatively long intervals (18), the reply code thus being available to be emitted together with the reply signal in time completely independant of the enquiry signal.

2. A system according to claim 1, characterized in that a means is provided in the transponder to randomly or pseudorandomly generate said intervals (18).

3. A system according to claim 1 or 2, characterized in that the enquiry signal is a generally continuous and unmodulated wave.

4. A system according to any of the claims 1 to 3, characterized in that the electromagnetic waves are having a frequency within the area 0,9 to 25 GHz.

5. A system according to any of the claims 1 to 4, characterized in that each transponder is adapted to reemit a reply signal being one or several thereon modulated sidebands of the enquiry signal frequency.

6. A system according to any of the claims 1 to 5, characterized in that each transponder is adapted to reemit its reply signal without any supply of power other than that being supplied to¬ gether with the enquiry signal.

7. A system according to any of the claims 1 to 6, characterized in that the first unit (4, 6) is during reception of interfering reply signals emitted simultaneously from several transponders adapted to not register these but instead to continue emitting the enquiry signal until at least one predetermined part of the number of individual reply codes are correctly received.

8. A system according to any of the claims 1 to 7, with the transponders being adapted for registration of information being emitted from the first unit in a memory via an information signal from the first unit, characterized in that the information signal comprises an access code (86) being unambiguously defined by the individual reply code (76), previously emitted as a reply signal from the actual transponder.

9. A system according to claim 8, characterized in that the whole or a part of the transponder reply code (76) consists of one for each transponder unique code, with which said access code (86) is identical or unambiguously definable.

10. A system according to any of the claims 1 to 9, with the transponders being adapted for registration of information being emitted from the first unit in a memory via an information signal from the first unit, characterized in that each transponder is comprising a means (71) for access control of said information signal so that it only can be registered in the^' transponder memo¬ ry, when comprising an access code being one for the individual reply code unambiguously defined code.

11. A system according to claim 10, characterized in that each transponder reply code (76) consists of one for each transponder unique code, with which said access code (86) is identical or unambiguously definable.

12. A system according to any of the claims 1 to 11, characteri¬ zed in that it comprises at least two aerials for emitting said enquiry signal from different aspect angles towards the transpon¬ ders so that these are irradiated from different directions and therefore are enabled to emit reply signals independently of an eventually unfavourable orientation in relation to at least one aerial.

13. A system according to any of the claims 1 to 12, characteri¬ zed in that it is adapted to automatically register transponders being caried by individuals passing a door, a walking gate, a corridor or similar.

14. A system according to any of the claims 1 to 13, characteri¬ zed in that it is adapted to automatically register transponders being caried on physical objects in a flow, such as glass bott¬ les, material containers, fluid containers, bagage bags, manufa- turing objects or similar.

15. A system according to claim 13 or 14, characterized in that it is adapted to automatically register data in the transponders in a flow, such as the time for passing, the passage way, the destination, the transaction number, the saldo debiting, etc.

16. A system according to any of the claims 1 to 15, being adap¬ ted by means of the signal emitted from the first unit to regis¬ ter even the transponder position in relation to the first unit and to simultaneously and by means of a video camera to optically register existing transponder carriers independent of them carry¬ ing a transponder communication or not, characterized in that the transponder communications complying with a predetermined crite- rium for access are resulting in that the corresponding optical registrations are eliminated afterwards so that the remaining optical registrations related to transponder carriers not having performed any approved transponder communication become available for a report to a head system.

17. A system according to claim 16, characterized in that it is adapted to register a flow of individuals not being qualified for a passage without any action, for example by prepayment of an entry fee or by establishing an acces to pass.

18. A system according to claim 16, characterized in that it is adapted to register a flow of vehicles not being qualified for a passage without any action, for example by prepayment of a road toll.

19. "A transponder, characterized by any feature indicated in claim 1 to 18.

20. A unit for emitting an enquiry signal and eventually an in¬ formation signal, characterized by any feature indicated in claim 1 to 18.