WO1996037982A1

WO1996037982A1 - System related to information-carrying signals

Info

Publication number: WO1996037982A1
Application number: PCT/SE1996/000636
Authority: WO
Inventors: Paul Gunnar ROSÉN; Paul Gösta Wilhelm ROSÉN
Original assignee: Rosen Paul Gunnar; Rosen Paul Goesta Wilhelm
Priority date: 1995-05-24
Filing date: 1996-05-23
Publication date: 1996-11-28
Also published as: SE9501943D0; EP0872063A1; AU5849096A; SE9501943L

Abstract

The present invention relates to a system for transmitting information-carrying signals that occur as light-pulses. The system includes a signal-transmitting and/or signal-receiving central unit (1), at least one light-pulse-emitting and/or receiving device (2, 2') and at least one signal-transmitting and/or signal-receiving remote unit (3, 3') wherein the devices (2, 2') are in contact with one another through the medium of a conductor (14). Signals are transmitted between the devices (2, 2') and a remote unit (3, 3') situated in the close proximity thereof via light-pulses in free space, wherein the light-pulses are adapted to convey digital information-carrying signals structured into time frames (4, 4', 4''). Each time frame is divided into a plurality of time slots (50, 51, 52...5n) which, in turn, include a plurality of bit positions. A first type of time slot (50, 51, 52) includes information-carrying bit positions and at least one identification bit position intended for mutually distinguishing first types of time slots in a time frame, and a second type of time slot (5n) intended to synchronize the time frames. This second type of time slot differs unequivocally from the first type of time slots, partly because it lacks the identification bit position/bit positions. The sum of the number of bit positions in the time slots (50, 51, 52...5n) of the first and the second type corresponds to the number of bit positions in a time frame (4).

Description

System related to information carrying signals

FIELD OF THE INVENTION

The present invention relates generally to a system for the transmission of information-carrying signals.

More particularly, the invention relates to a system for sending information between a central unit and a remote unit without the remote unit needing to be in electrical or physical contact with the central unit, so-called cordless communication.

A system which utilizes ultrasound or infrared light (IR) is an example of one type of a cordless communication system to which the invention relates. The present invention is based on the use of coded light-pulse sequences to send information between the central unit and the remote unit.

Systems of this kind are normally used in contexts where there is a need for cordless room-internal communication, because the use of light or acoustic transmission media does not enable long transmission paths to be achieved.

Traditionally, radio waves are used for the cordless transmission of information over long distances, a system which is not included by the concept of the invention.

DESCRIPTION OF THE BACKGROUND ART

Several different designs of systems of the aforedescribed kind are known to the art. The system that lies closest to the present invention is a system designated Both way Infra Red Communication (BIRC). Different versions of BIRC use pulse-width modulated or frequency-modulated IR light to transmit information between a number of people or operators, each wearing a headset which includes, among other things, a receiving and transmitting unit, one or two headphones, and a microphone. BIRC uses a first channel, a call channel, for direct contact between two or more persons, and a second channel for contact with a central unit. The central unit may be an interface to other telesystems, for instance an internal communication system or one or more telephone exchanges.

One of the limitations of BIRC is that the persons or operators connected thereto share a common speech channel, which further¬ more is simple, so-called simplex, meaning that only one operator can talk at a time and that all other operators can hear what is being said.

It should be mentioned here that digital communication also forms part of the earlier standpoint of techniques.

It is known to use pulsated signals to transfer digital informa-^' tion, and to structure this digital information in accordance with standard protocol and therewith enable the information to be decoded. One such standard protocol is found within telephony, using for instance thirty-two channels, of which thirty channels are used for telephone calls and divided into fifteen channels with full duplex, therewith enabling two-way communication to be carried out simultaneously, and of which two channels (channel 0 and channel 15) are used for communication synchronization. A pulse frequency of 2.048 MHz is used in this regard, providing an individual channel sampling frequency of 8 kHz when using 8- bit words.

In the transmission of digital information, system clocks are used to synchronize communication between the various units included in the system. The units that are included may use different transmission speeds. The units include means for synchronizing the transition from one transmission speed to another. It is necessary for synchronization and transition between different system clocks and transmission speeds to function satisfactorily in order to ensure positive communi- cation.

It can also be mentioned that the transmission of digital information through the medium of light-pulses on optical conductors (fibre optics) has long been known in telecommuni- cations systems.

It is also known to transmit digital information from a control unit to a slave unit via light-pulses in space. Examples in this respect are control units in the form of remote control devices used to control slave units, such as diverse audio-visual systems, e.g. acoustic systems and television apparatus.

Communication is only one way in applications of this kind, whereby the control unit is able to send commands, one and one, to the slave unit, whereas the slave unit is unable to send commands to the control unit and only one channel is available.

It is also known to use so-called IR links to transmit digital information by means of IR light in free space between two units, both of which can transmit and receive information. The transmis¬ sion of data between two computers can be mentioned as an example in this regard.

Communication is also one way in this case, even though the two units are both able to transmit and to receive messages. Only one channel is available also in this case, meaning that only one unit at a time can send information while the other unit receives.

It will also be observed that the aforedescribed cordless optical system often has a limited range, because the intensity of light decreases with the square of the distance. This means that transmitter and receiver can seldom be placed more than a few metres apart, and that the transmitter and receiver must be able to "see" each other, either directly or via reflection. The phrase "within sight of one another" will be used in the following description to indicate that a transmitter and receiver can "see"" one another.

It will also be observed that the reason why a cordless optical system often includes only one channel, so-called simplex, is because there is no access to the same signal synchronizing facilities that are available to wire-bound systems, both optical and electrical signal transmission systems, in which common clocking of the signals is often available.

It is also known that in the case of wire-bound communication systems the mobility of an operator is restricted by the conductor or lead that connects him/her with the system, for instance the length of a connection lead between a telephone operator and a telephone exchange unit.

Also forming part of the known prior art in respect of the present invention are wire-bound communications systems in which digital or analog information is transmitted between different units through the medium of electric conductors. With systems of this kind, it is necessary to take into account the electromag¬ netic compatibility (EMC) between the system and the surround¬ ings.

It is also known that wire-borne electric signals are sensitive to an electromagnetically contaminated environment, such as spaces in which strong high-frequency electromagnetic fields are generated. It is also known that wire-borne electric signals generate electromagnetic fields which can disturb the surround¬ ings or which can be listened to on unauthorized equipment.

It is also known that cordless communication effected via electromagnetic fields, radio waves, must take EMC into account. For example, it is forbidden to use mobile telephones on aircraft or in certain hospital wards because of the risk of sensitive instruments being harmed or disturbed by the electromagnetic radiation generated by the mobile telephone.

The requ rements concerning EMC are determined partly by the requirements placed by the system on the surroundings and partly by the requirements placed by the surroundings on the system.

It should also be mentioned that difficulties are experienced with the compatibility between different systems that operate with the transmission of light signals and which are in sight of one another. Such systems must also take account of EMC require¬ ments, although in a wavelength region (light) which is not traditionally considered in the EMC context.

SUMMARY OF THE PRESENT INVENTION

TECHNICAL PROBLEMS

When considering the earlier standpoint of techniques as described above, it will be seen that a primary technical problem resides in the ability to create conditions in which cordless communication can be effected with simple system-related synchronization between a plurality of separate remote units themselves or between a remote unit and a central unit.

It will also be seen that a technical problem resides in the provision of facilities which enable the cordless remote unit in the system to have dedicated significant channels so as to enable any cordless remote unit whatsoever to communicate with any other cordless remote unit within the system, or with another unit permanently connected to the central unit, without further cordless remote units in the same system having access to or being disturbed by said communication. Another technical problem in this regard is one of realizing how the transmission protocol for such a system can be configured to offer an acceptable quality of sound transmission in real time and in full duplex.

It will also be seen that a technical problem resides in the provision of conditions required to enable a selected group having a plurality of cordless remote units within a system that has a larger number of cordless remote units to communicate mutually over a common channel, where all control units within the chosen group have access to all communication within the group without remaining cordless remote units within the same system having access to or being disturbed by said communication.

Another technical problem is one of realizing the advantages of enabling remote units incorporated in the system and located not only far apart but also in separate rooms to communicate with one another.

It will also be seen that a technical problem is one of realizing how conditions can be provided which will enable controlled two- way communication between a plurality of separated remote units to which significant channels have been allocated within a cordless optical communication system.

Another technical problem is one of creating provisions which will enable standard telephony circuits to be used for signal processing within said system.

Another technical problem is one of realizing the possibilities that are afforded when certain remote units can function solely as slave units having a receiving function, that other remote units can function with solely a transmitting function, and that further control units can function both in a transmitting and a receiving mode. A further technical problem in the present context is one of realizing the possibilities that are afforded when the remote units, for instance, can be comprised of a combination of headphones and microphone adapted for speech communication, where said remote unit is adapted both to transmit and to receive information.

Still another technical problem is one of realizing the possibil¬ ities that are afforded when the remote unit, for instance, can be comprised of a control unit for controlling or regulating a process where said remote unit is adapted to operate solely in an information-receiving mode.

In addition to the aforesaid problems, it will be seen that a further technical problem is one of realizing the possibilities that are afforded when the remote unit can be comprised of a measurement data unit intended for collecting measurement data from different instruments or measuring points, and which remote unit is adapted to function solely in an information transmitting mode.

It will also be seen that a technical problem is one of realizing the possibilities that are afforded when cordless remote units of a system are also able to choose whether a central unit shall be in contact with the system via a physical conductor or in a cordless mode.

Yet another technical problem is one of realizing the advantages that are associated with a system which uses two separate information conductors, one intended for conducting information to the remote units information generated by the central unit, and the other intended for conducting to the central unit information generated by the remote units.

It will also be seen that a technical problem resides in realizing how facilities can be created that will allow the transmission of information to include a transfer protocol which will enable all light detecting devices in the system to be fully receptive to light detection without being disturbed by satura¬ tion from closely neighbouring light-emitting devices.

It will also be seen that a technical problem resides in realizing "the possibilities that are created when a transmission protocol used in a cordless communications system according to the present invention is used in a fully wire-bound system.

Another technical problem is one of realizing the conditions required in order for two systems that both operate with the transmission of information-carrying light signals within sight of one another to do so without detriment to one another.

A further technical problem is one of providing a cordless communication system having a plurality of remote units where each unit has its own communication channel and which system fulfils EMC-requirements in environments that are heavily contaminated electromagnetically and/or in environments that are highly sensitive to electromagnetic radiation.

SOLUTION

With the intention of solving one or more of the aforesaid technical problems, the present invention takes as its starting point a system for the transmission of information-carrying signals that occur as light-pulses. Such systems will include a signal-transmitting and/or signal-receiving central unit, at least one light-pulse emitting and/or light-pulse detecting device, and at least one signal-transmitting and/or signal- receiving remote unit.

More specifically, the present invention is based on the concept of enabling signals to be transmitted between the central unit and one or more of said devices via said conductors. The signals are corresponded by electric signals in the central unit, which signals are converted to optical light-pulses in respective light-pulse-emitting devices.

By a central unit is meant a unit which generates those signals that remaining units in the system require to transmit and receive information in phase with one another. It is also through the central unit that the system is configured with regard to which different units shall be in contact with one another and in which way.

With its starting point from the aforesaid earlier known system, the present invention proposes the transmission of signals between said devices and a remote unit located close thereto through the medium of light-pulses in free space. Communication between said central unit and said devices can also be effected through the medium of light-pulses in free space.

The light-pulse-emitting devices may be placed in different rooms or locations in which there is a desire to be able to communicate with different remote units and at a mutual distance between two light-pulse-emitting devices in one room or locality that does not exceed twice the range for communication between a light- pulse-emitting device and a remote unit.

This enables remote units to move freely within those localities to which said devices are allotted and to be available constantly for communication within the system, even with regard to remote units which are not located in the same locality but in a locality to which light-pulse-emitting devices have been allocated.

It is also proposed in accordance with the invention that light- pulses, adapted to convey digital information-carrying signals, are structured to form time frames. A time frame includes a predetermined number of data bits having a predetermined transmission speed. Each time frame is divided into a number of time slots, which in turn include a number of bits. A first type of time slot includes information-carrying bits and at least one identification bit which enables time slots of the first type to be distinguished from one another within a time frame, and a second type of time slot which is intended to synchronize the time frames and which lacks said identification bit/bits.

The sum of the number of bits in the time slots of said first and said second types corresponds to the number of bits in a time frame.

According to one proposed embodiment of the invention, which lies within the scope of the inventive concept, it is proposed that the first type of time slots include ten bits which are divided into a start-bit, eight information-carrying bits, and an end- bit, where the start-bit and end-bit constitute said identifica¬ tion bits.

When the bits are divided in this manner, the start-bit may be comprised of a light-pulse and the end-bit of the absence of a light-pulse, wherein a light-pulse when converted to an electric signal may correspond to a logic one, "1", and the absence of a light-pulse may be corresponded by a logic zero, "0".

It is proposed in accordance with the invention that the second type of time slot must distinguish from the first type of time slot in a characteristic way. This can be achieved, for instance, with a bit combination that statistically cannot occur in the first type of time slot, or at least with a high degree of improbability.

It is also proposed in accordance with the invention that in the case of time slots of a first type, in accordance with the above, a time slot of said second type may, for instance, include at least ten bits where all bits within said time slot of a second type may be comprised of the absence of a light-pulse, corre- sponded by logic zeros, "0", where the time slot also lacks said start-bit and where units belonging to the system are aware that the next arriving bit is the start bit of a first time slot within the next arriving time frame. This enables units included in the system to distinguish between respective time frames and the time slots contained therein.

The end-bit in said first type of time slot is used to provide a given signal transmission margin and therewith ensure unequivo- cal detection of the start-bit belonging to the next arriving time slot.

According to a further embodiment of the invention, it is possible to refrain from including the end-bit in each time slot of said first type, meaning that each first-type time slot will contain only nine bits, wherewith a second-type time slot need only contain nine bits. This bit division provides more time slots per time frame, although it is slightly more difficult to positively detect the start-bit in each first-type time slot.

By adapting the time frames used to telephony standard time frames, which include 256 data bits and extend to 125 μs in time, standard telephony circuits can be used in the system, which offers the requisite bandwidths for acceptable sound transmission quality.

Furthermore, it is proposed that the first-type time slots are divided into two categories so as to obtain full duplex for at least certain remote units. Those time slots used to transmit information from the central unit to the remote units are referred to here as "transmitting time slots" while the time slots used to receive information from the remote units to the central unit are referred to as "receiving time slots".

It is also proposed that a remote unit may be allotted solely a transmitting function, solely a receiving function, or both a transmitting and a receiving function. Requisite time slots of the transmitting and/or receiving type are allocated to respec¬ tive remote units in accordance with how the system is configured and which functions are allocated to different remote units. Each remote unit is therewith allotted its specific setup of one or two time slots and thereby also identification.

Each remote unit is thus allocated its own channel which functions either for one-way communication or two-way communica¬ tion.

The central unit is adapted to generate time frames where the information-carrying bits in the transmitter-type time slots contain information intended for the remote units to which respective transmitter time slots have been allocated. All information-carrying bits in the receiver-type time slots generated by the central unit are free from information and therewith free from light-pulses.

The generated time frames are sent to the devices connected with said conductor, either via the conductor or as light-pulses in empty space, and the devices are allocated light-emitting devices which function to emit the time frames in the form of light- pulses in the room or space in which said devices are located.

According to the invention, the conductor may be either an electric conductor or an optical conductor. When the conductor is an electric conductor, it is necessary for the transition from electrical to optical signals, and vice versa, to take place in respective devices. In the case of optical conductors, the corresponding transition takes place in the central unit.

Optical signals are not sensitive to electromagnetic disturbances and neither do they generate electromagnetic fields which can disturb the surroundings or be detected by non-associated equipment, and consequently optical signals shall be used to the greatest possible extent when high EMC requirements prevail. The use of an optical conductor will mean that all signal transmis- sions within the system take place with optical signals and therewith fulfil very high EMC requirements.

A remote unit located in said room close to a light-pulse 5. emitting device is allocated a light detecting device which functions^* to detect the light-pulses, and the remote unit is adapted to distinguish between detected time frames and to distinguish the transmitted time slot allocated to said remote unit from remaining time slots of the first type, with the aid 0 of second-type time slots and identifying bit/bits within respective first-type time slots.

A remote unit that has been allocated solely a transmitting function or both a transmitting and a receiving function is 5 adapted to generate time frames which, among other things, include receiving-type time slots that contain information- carrying data intended for one or more other remote units or for the central unit. All information-carrying bits within included transmitter-type time slots generated by the remote unit are free 0 from information.

According to the present invention, the remote unit is provided with a light-emitting device whereby time frames in the form of light-pulses are emitted into the room in which the remote unit 5 is located, and a device located in the proximity of the remote unit is allocated light-pulse detecting means which functions to detect the emitted light-pulses.

The light-pulse detecting means then transmits to the central 0 unit the time frames generated by the remote unit.

The central unit is able to distinguish between the various received time slots in the aforedescribed manner. The central unit is able to decide whether the information contained by the 5 information-carrying bits in respective receiver time slots is intended for the central unit itself or whether they shall be sent to an intended remote unit with the aid of information- carrying bits in transmission time slots included in time frames generated by the central unit.

It is also proposed in accordance with embodiments that lie 5. within the scope of the present invention that the remote units may comprise a plurality of different types of unit.

For instance, one type of remote unit may be a headphone and microphone combination adapted for speech communication, 0 therewith enabling a person to work undisturbed while not being restricted by connection leads or by the access to connection points, plug sockets.

Another type of remote unit may comprise a control unit adapted 5 to control or regulate a process from a central unit which stands well-protected in another room, without risk of control data being distorted during its passage from the central unit to the control unit.

0 Another type of remote unit may include a measurement data unit adapted to collect measurement data from different instruments or measuring points where, as in the previous case, the central unit may be installed in another room, without risk of measuring data being distorted during transmission of information between 5 instrument and central unit, and without risk of the central unit or the transmission having a detrimental effect on the objects being measured or assayed.

It is also proposed in accordance with the invention that the 0 central unit is in contact with the light-pulse emitting device via light-pulses in said room, or via the conductor that connects the light-pulse emitting devices.

The conductor may alternatively be comprised of two separate 5 conductors, one intended to conduct generated time frames from the central unit to the remote units, and the other intended to conduct generated time frames from the remote units to the control unit.

With the intention of solving the problem of a saturated light 5. detecting device with possible feedback between a light-emitting device and a light-detecting device belonging to the same unit or to close-by units, it is proposed in accordance with the invention that the transmitting" time slots form a continuous block in time in relation to one another, in that the receiving 0 time slots form a continuous block in time in relation to one another, and that the blocks of receiving and transmitting time slots are followed by a third type of time slot.

This third type of time slot shall be formed by the absence of 5 light from all light-emitting devices in the system and shall be given a time extension that corresponds to a requisite restoring time for light-detecting devices included in the system after such a light-detecting device having been saturated by a light- emitting device. 0

The present invention also provides a further embodiment which will enable two different systems, a first and a second system, which both operate with the transmission of light information- carrying signals, to operate within sight of one another without 5 detriment to each other.

According to this embodiment, the second system synchronizes its time frames to the second time slots belonging to the first system. 0

It is also proposed that the time frames operative within the first system and the second system are given the same configura¬ tion and that first-type time slots used in the first system are not used in the second system, and vice versa. 5 ADVANTAGES

Those advantages primarily associated with an information- carrying signal transmission system in accordance with the invention reside in the provision of conditions in which a communication system can be constructed with simple means to enable diverse remote units to communicate with a central unit and with each other via one-way or two-way communication according to the system configuration, without being physically connected to one another or to the central unit.

The system can cope with very high EMC-requirements, both regarding the ability to operate effectively within electromag¬ netically contaminated environments and regarding the minimum of electromagnetic disturbances that is generated into the surround¬ ing space, such electromagnetic disturbances being in effect practically non-existent. The system can thus be used within heavy industry as well as within sensitive laboratory environ¬ ments or in cases where security against tapping or listening-in is of paramount importance.

The primary characteristic features of an inventive system are set forth in the characterizing clause of the following Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail with reference to exemplifying embodiments of different systems having features significant of the present invention, and also with reference to the accompanying drawings, in which Figure 1 is a very simplified overview of an inventive system and illustrates time frames divided into different types of time slots;

Figure 2 shows by way of example the allocation of available 'data bits to different time slots;

Figure 3 shows another example of the allocation of available data bits to different time slots;

Figure 4 illustrates in more detail the construction of an inventive system;

Figure 5 shows another example of how an inventive system can be constructed;

Figure 6 illustrates an alternative embodiment of a remote unit belonging to the system;

Figure 7 illustrates another alternative embodiment of a remote unit belonging to the system;

Figure 8 shows by way of example how a remote unit may consti¬ tute the central unit of the system;

Figure 9 shows by way of example how a remote unit may consti¬ tute both central unit and a light-pulse emitting device;

Figure 10 shows an example in which the conductor is comprised of two separate conductors;

Figure 11 illustrates an alternative embodiment of allocating different types of time slots within a time frame; Figure 12 is a highly simplified illustration of a system based on the wire-bound connection of the central unit and the remote units; and

Figure 13 illustrates schematically how two separate systems can operate in one and the same room without detriment to one another.

DETAILED DESCRIPTION OF PROPOSED EMBODIMENTS

Figure 1 is a highly simplified illustration of a system for the transmission of information-carrying signals in the form of light-pulses.

The system includes a signal transmitting and/or signal receiving central unit 1, at least one light-pulse emitting device, in the illustrated case two devices referenced 2, 2', and at least one signal transmitting and/or signal receiving remote unit, in the illustrated case two such units referenced 3, 3¹.

By central unit is meant a unit which generates those signals that other units included in the system require in order to transmit and receive information in phase with one another. It is also through the central unit that the system is configured with regard to which different units are in contact with one another and in which way.

Other external units may also be connected to the central unit 1. These external units may be telecommunications lines 11, 11' or cross-connection or jumpering fields, or a telephone exchange unit 12, whereby the system can be configured and further telecommunications lines 13 connected to the system.

These external units will not be described in detail here, since they have no decisive significance to the function of the invention. It can be mentioned, however, that the central unit may include further functions which will not be described in detail but which will enable the central unit 1 to form an interface with other telesystems, for instance to a public telephone system or to an internal communications system.

5. Although only two light-pulse emitting devices 2 and 2' are shown in Figure"1, it will be understood that the system may comprise one or a multiple of such devices in accordance with require¬ ments. These devices will be described in more detail below.

0 In the illustrated case, the system includes two remote units 3 and 3', each being exemplified by a headset carried by an individual and equipped, among other things, with a microphone and one or two loudspeakers.

5 In the illustrated case, the central unit 1 is in contact with the light-pulse emitting devices 2, 2' through the medium of a conductor or lead 14.

Transmission of signals between a device 2 and a remote unit 3 0 located nearby is effected via light-pulses emitted into the room. These light-pulses are adapted to carry digital information-carrying signals.

Also shown in Figure 1 is the manner in which light-pulses are 5 structured to form time frames 4, 4', 4'' which are divided into a number of time slots 50, 51 ... 5n. Each time frame 4 is predetermined to a common size with respect to the number of data bits included thereby. The number of time slots 50, 51 ... 5n that can be accommodated within a time frame 4 is determined by 0 their respective sizes.

Figure 2 shows a time slot 50 which includes a plurality of bits 60, 61 ... 69 that carry information in the form of electric pulses or light-pulses, depending on where in the system the 5 information is located. A first type of time slot 50 includes information-carrying bits 61, 62 and at least one identification bit 60. The identification bit 60 is intended to enable time slots 50, 51 within a time frame 4 to be distinguished from one another. A second type of time slot 5n is intended to enable the time frames 4, 4' to be distinguished from one another. Both the identification bits and the second-type time slots are used by the system units to transmit and receive signals in phase with one another.

According to the invention, the second type of time slot shall differ characteristically from the time slots of the first type. This is achieved with incoming bits that comprise a bit-combina¬ tion which statistically cannot occur in the first-type time slot, or at least only with a high degree of improbability.

This enables a receiving unit, a central unit 1 or a remote unit 3 to mutually distinguish between incoming time frames. The manner in which this is achieved will be described further on.

The sum of the number of bits in the first and second type of time slots correspond to the number of bits in a time frame.

Figure 2 illustrates an embodiment in which respective time slots contain a determined number of bits. It will be seen that a first-type time slot 50, 51 includes ten bits divided into a start-bit 60, eight information-carrying bits 61-68, and an end- bit 69. The start-bit and the end-bit 60, 69 form the identifica¬ tion bits.

In order to enable the system to use the identification bits, the bits are always given the same value in all first-type time slots. If the start-bit 60 has a logic-one, "1", value, which is corresponded by a light-pulse, the end-bit 69 will have a logic- zero, "0", value which is characterized by the absence of a light-pulse. The system thus knows that a time slot 50 will always begin with a light-pulse 60 and end with the absence of a light-pulse 69. The bits located there between and corresponded by the presence or the absence bf a light-pulse represent the information to be transmitted.

The terminating identification bit, the end-bit 69, is used to ensure unequivocal detection of an introductory identification bit, the immediately following start-bit 60a in the next arriving time slot, which therewith enables the system to distinguish positively between respective time slots throughout the whole of the time frame.

The various time frames are distinguished from one another by means of a second type of time slot 5n. The second-type time slot 5n must differ significantly from the first type of time slot 50, 51, which can be achieved, for instance, by allotting to the second type of time slot a doubled bit-frequency in comparison with remaining time slots, thereby enabling unique combinations to be formed. Alternatively, the second type of time slot can be represented by a unique bit-combination which cannot occur in the first type of time slot.

A unique bit-combination is formed when the second type of time slot fulfils the following three conditions:

The second type of time slot 5n does not include the identifi¬ cation bit/bits found in the first type of time slot 50, 51.

- The logic value of all bits 70, 71 ... 7n in the second type of time slot 5n is opposite to the logic value of the first identification bit 60, 60a in the first time of time slot 50, 51.

- The number of data bits in the second type of time slot 5n is equal to or greater than the number of data bits in the first type of time slot 50, 51. These specifications mean that the second type of time slot 5n in the Figure 2 embodiment will include at least ten bits, 70 to 7n, all of which have the logic value zero, "0", corresponded by the absence of a light-pulse.

The second type of time slot need only be one in number, and may be placed last in a time frame.

However, there is nothing to prevent a system being constructed with time frames that include several time slots of the second type and positioning the second-type time slots anywhere within the time frame irrespective of their numbers, provided that all time frames used in the system are standard with respect to the number of time slots and their mutual size and placement.

The system thus knows that when a time slot totally lacks light, the next arriving data bit represented by a light-pulse will be the start-bit in the first time slot of the next arriving time frame. This enables the system to synchronize the various time frames and to distinguish one from the other.

In an alternative embodiment based on the same number of bits within respective time slots, the start-bit 60 can be represented by the absence of a light-pulse, therewith enabling the end-bit 69 to be represented by a light-pulse and all bits in the second- type time slot to be represented by light-pulses.

Figure 3 illustrates a further embodiment which is characterized in that a first type of time slot 50' , 51' includes nine bits 60' to 68' which are divided into a start-bit 60' and eight information-carrying bits 61' to 68'.

In accordance with the aforesaid requirements placed on a second- type time slot, the time slot 5n' of this embodiment, which is a second type time slot, includes 7n' bits, wherein the time slot thus contains at least nine data bits. Similar to the aforegoing, when the start-bit 60' is represented by a light-pulse, all bits in the time slot 5n' are represented by the absence of a light-pulse, and vice versa.

5. The absence of a second identification bit in the time slots of the first 'type 50' , 51' places high demands on the time count and the separation of different time slots in a time frame is made slightly more difficult.

0 To enable the invention to be applied more easily, the aforesaid time frames can be structured to be standard time frames that contain 256 data bits and extend 125 μs in time.

This structuring is not a necessary prerequisite of the present 5 invention, although it will greatly simplify the construction of the system since this time frame size and time frame transmission speed are used in traditional telephony, meaning that when this standard is used the circuits included in the system can be constructed partially by existing standard telephony circuits. 0 This standard also provides an acceptable quality for speech transmission in real time on a number of duplex channels.

However, there is nothing to prevent the use of time frames structured to other sizes and using other transmission speeds. 5

A time frame that included 256 data bits and extends 125 μs in time would enable the Figure 2 embodiment to offer twenty-four first-type time slots 50, 51 and one second-type time slot 5n, which would include sixteen bits. 0

Similarly, the embodiment illustrated in Figure 3 would offer twenty-seven first-type time slots 50', 51' and one second-type time slot 5n' , which would include thirteen bits.

5 These time slots can be distributed between different remote units or between connected external units belonging to the system, in accordance with the system configuration. Figure 1 shows that the first type of time slots are divided into transmitting time slots Al, A2, A3 ... and receiving time slots Bl, B2, B3 ... in relation to the central unit.

Each remote unit 3, 3' is allocated either only a transmitting function Or only a receiving function or is allocated both a transmitting and a receiving function.

A remote unit that is allocated both a transmitting and a receiving function is allocated both a transmitting and a receiving time slot, a control unit that is allocated only a receiving function is allocated a transmitting time slot, while a remote unit that is allocated solely a transmitting function is allocated a receiving time slot.

The information transmission sequence will be illustrated in the following.

The central unit is adapted to generate time frames which include transmitting-type time slots, among other things.

Information intended for a remote unit 3 is stored in the information-carrying bits belonging to the transmitting time slot A3 allocated to the remote unit 3.

All information-carrying bits in the receiving-type time slots Bl, B2, B3 included in said time frames are free from informa¬ tion, meaning that these bits have the logic value zero, "0", this latter being corresponded by the absence of a light-pulse.

Generated time frames are sent, via said conductors, to the light-pulse emitting or radiating devices 2, 2' connected to said conductors. Light emitting arrangements 21 in said devices 2, 2' emit the time frames in the form of light-pulses in the room in which said devices are located. The remote unit 3 for which the information is intended is located in one of the rooms to which a light-pulse emitting device has been allocated, and can therewith detect the emitted light-pulses.

The detecting signals are adapted to the remote unit by means of a converter associated thereto.

The remote unit is adapted to distinguish respective time frames 4, 4', 4' ' and the transmitting time slot A3 allocated to the remote unit 3 from remaining first-type time slots 50, 51 by means of the second-type time slots 5n and by means of identifi¬ cation bit/bits 60, 69 in respective first-type time slots 50, 51, and therewith receive the information originally intended for the remote unit 3.

This can be achieved by providing each unit in the system with a counter which does not start to count until a sufficiently long period of time has lapsed without a light-pulse having been transmitted in the room, or space. This will occur only when a second-type time slot 5n is transmitted, and the unit will therewith know that the next arriving light-pulse constitutes the start-pulse 60 in the first time slot 50 of the next arriving time frame. The counter then counts forward the time slots 50, 51 received until the time slot intended for this particular unit is received, whereafter the information can be detected. Even though no information is contained in transmitting time slots, each first-type time slot 50, 51 will include a start-bit 60, 60a which causes the counter to begin to count when the next arriving second-type time slot 5n is received.

A remote unit 3' which has been allocated solely a transmitting function or both a transmitting and a receiving function and therewith allocated a receiving time slot B3 communicates with another remote unit which is allocated a transmitting-type time slot, referenced A2, and a receiving-type time slot, referenced B2, in the following manner. The remote unit 3' generates time frames which include the time slot B3, among other things. The information intended for the remote unit is stored in the information-carrying bits belonging to the receiving time slot B3. 5.

All information-carrying bits in the transmitting-type time slots Al, A2, A3 of time frames generated by the remote unit 3' are free from information, meaning that these bits have the logic value zero, "0", which is corresponded by an absence of a light- 0 pulse after passage of the signal through an electrooptic converter.

The time frames generated by the remote unit 3' are radiated out in the room in which the remote unit 3' is located, by means of 5 a light-emitting device 32 allocated to the remote unit 3'.

With the aid of the time frames received by the remote unit and the second-type time slots associated therewith, the remote unit is able to transmit the time frames generated by said unit in 0 phase with the time frames transmitted from the central unit 1.

In this way, all time frames generated by all remote units belonging to the system will be transmitted synchronously with the time frames generated and transmitted by the central unit. 5

A light-pulse emitting device 2' situated close to the remote unit 3' includes a detecting device 22 by means of which the device is able to detect the emitted light-pulses, and the device 2 ' then transmits the time frames generated by the remote unit 0 to the central unit 1 on said conductor 13.

When the central unit has received the time frames, the unit is able to distinguish respective time frames 4, 4', 4' ' from one another and the various receiving time slots Bl, B2, B3 from one 5 another with the aid of the second-type time slots 5n and with the aid of identification bit/bits 60, 69 within respective first-type time slots 50, 51, and to determine through the configuration of the system whether the information contained in the information-carrying bits in respective receiving time slot is intended for the central unit itself or whether the informa¬ tion shall be transmitted to a remote unit for which the 5. information is intended, in information-carrying bits in transmitting time slots included in time frames generated by the central unit.

The central unit is adapted to transfer the information stored 0 in the information-carrying bits in time slot B3 to the information-carrying bits in time slot A2 included in a time frame generated by the central unit, this time frame then being transmitted to the remote unit which has been allocated the time slot A2 and for which the information is intended, in accordance 5 with the aforegoing.

Figure 1 and Figure 4 show that the system can be adapted to solely transmit information to different remote units. In this case, the central unit 1 is provided with transmitting circuits 0 15, the light-pulse emitting devices 2, 2' are provided with a light-emitting arrangement 21 and the remote units belonging to the system are provided with a light-detecting arrangement 31.

The system can also be adapted to both transmit and receive 5 information and therewith pass information between different remote units 3, 3', in which case the central unit is provided with both transmitting circuits 15 and receiving circuits 16, the light-pulse emitting devices 2, 2' in the system are provided with both a light-emitting arrangement 21 and light-detecting 0 arrangement 22, and those remote units that are able to both receive and transmit information are provided with both light- detecting arrangements 31 and light-emitting arrangements 32.

The conductor 14 may be any one of a number of different types 5 of conductor depending on the requirements placed on the system, for instance EMC requirements. If the environment in which the system is to be used is not seriously contaminated by electromag- netic disturbances and if requirements on system generated electromagnetic disturbances are low, the conductor 14 may be an electrical conductor.

Each light-pulse emitting device 2 includes a receiving circuit 23 which "receives the signal on the conductor 14, sends the signal to the light-emitting arrangement 23 and to a transmitting circuit 24. The signal that has been received by the light- detecting arrangement 22 is added in the transmitting circuit to the signal that arrives from said receiving circuit 23, whereaf¬ ter said signal is transmitted by the transmitting circuit 24 on the conductor 14.

If high EMC requirements are placed on the system because the environment in which the system operates is highly contaminated electromagnetically or because the environment is highly sensitive and may not at all costs be contaminated electromagnet¬ ically, the conductor 14' may be an optical conductor in accordance with Figure 5.

Accordingly, the central unit 1 is provided with electrooptical and optoelectrical converters respectively.

Transmitting signals will then pass from a transmitting circuit 15' in the central unit 1 to an electrooptical converter 17, from where the signals are transmitted on the optical conductor 14' . Incoming signals to the central unit 1 are received by an optoelectrical converter 18, whereafter the signal is forwarded to a receiving circuit.16' in the central unit 1.

The light-pulses transferred in the optical conductor 14' are converted in the light-pulse emitting devices 2 to an electric signal which then controls the light-emitting arrangements 21 so as to emit the signal in the form of light-pulses in the room. This conversion is effected in an optoelectrical converter 23 ' . Those signals that are received by the light-detecting arrange¬ ment 22 are added to the signal converted by the converter 23' , whereafter the signal is converted by an electrooptical converter 24' to optical signals which are transmitted on the conductor 14'.

As a result of the conversion from optical to electrical signals, and vice versa, the signal occurs electrically in each light- pulse emitting device and also in each remote unit, which means that these devices and units must be screened to ensure that they fulfil the EMC requirements placed on the system.

As a result of the conversion and repetition of the signal effected either by the circuits 23 and 24 in Figure 4 or by the converters 23' and 24' in Figure 5, the signal is amplified and sharpened (enhanced) so as to enable very long conductors to be used and also a large number of light-pulse emitting devices without risk of the signal being distorted as a result of long distances or a large number of light-pulse emitting devices.

A system may include various types of remote units. In Figure 4 and the aforegoing description, the exemplified remote unit 3 has the form of a headset. The headset includes light-detecting and light-emitting arrangements 31, 32, among other things. The unit 3, the headset, also includes a receiving device 33 which receives the signals detected by the light-detecting arrangement 31.

These signals are transferred to a converting arrangement included in the headset and possibly including codec circuit 35 (coder/decoder), which is designed to convert, decode, said standard time frames received by the remote unit 3 into analog speech intended for a loudspeaker 37 in the remote unit 3, and to convert, code, analog speech signals from a microphone 36 in the remote unit 3 to standard digital time frames in accordance with the aforegoing. The coded speech signals, in the form of standard time frames, are transmitted in the form of light-pulses via the light-emitting arrangement 32 out into the room in which the remote unit 3 is located, this transmission being effected in phase with the signals received through the device 33 by a device 34.

5.

A codec circuit can also be used in other remote units or in the central unit when analog signals shall be converted to standard time frames or standard time frames shall be converted to analog signals. 0

Figure 6 illustrates another example of a remote unit that can be included in an inventive system. This remote unit 3'' is solely allocated a receiving function and consequently only light-detecting means 31' are required. Remote units of this kind 5 need not be allocated a receiving time slot, since they are not intended to transmit information.

The remote unit includes a converting arrangement 33 ' which may have a codec circuit or some other electronic device, according 0 to the need to adapt the received signal to the remote unit.

In the case of a remote unit of this construction, the received signal is used to control a valve 38 in a process.

5 Figure 7 illustrates another example of a remote unit 3' ' ' that can be included in an inventive system. This control unit 3''' is adapted solely to transmit information to another unit in the system.

0 The control unit, however, requires both a light-detecting and a light-emitting arrangement 31' ' , 32' ' , since it needs to detect the time frames generated by the central unit in order to transmit its own generated time frames in phase with the time frames transmitted by the central unit. 5

Remote units of this kind, however, need not be allocated an individual transmitting time slot, since they are not intended to receive information, but are allocated a receiving time slot with which the unit can transmit information.

This remote unit also includes a converting arrangement 33 ' ' , which may have a codec circuit or some other electronic device, according^• to whether the signal to be transmitted needs to be adapted for transmission, and necessary devices to enable said signal to be transmitted in phase with the signal generated by the central unit.

In this embodiment, transmitted signals arrive from a measuring instrument 39 in a process.

According to the above example, an inventive system can be adapted to control communication between a plurality of different types of remote units.

The number of remote units is limited by the number of available time slots in a time frame where certain remote units are in need of solely a transmitting time slot or solely a receiving time slot, whereas other remote units are in need of both a transmit¬ ting and a receiving time slot.

The system can be used with light-pulse emitting devices placed in several rooms which are in contact with one another and a system central unit via said conductors. This enables remote units in completely separate rooms to communicate with each other and a movable remote unit, such as a person carrying a headset, is able to move freely within the rooms that are equipped with light-pulse emitting devices.

The central unit 1 has been described in the aforegoing as being stationary and in physical contact with a conductor 14, in accordance with Figure 1.

As shown in Figure 8, however, there is nothing to prevent one of the remote units 1' forming the central unit provided that the remote unit includes the functions necessary for controlling the remainder of the system.

This remote unit can then be comprised of a computer unit according to Figure 1, but without being physically connected to the conductor 14' ' . This conductor is then comprised of a loop which is used to pass the signals between the light-pulse emitting devices 2a, 2b, 2c, 2d in the system, wherein the device 2c located nearest the remote unit 1 ' that constitutes the central unit has a special function of breaking the loop and solely transmitting time frames on the conductor, these time frames being received in the form of light-pulses from the remote unit 1 ' that constitutes the central unit and receives the time frames that arrive at said device on the conductor 14' ' , and send these time frames, as light-pulses, to the remote unit that constitutes the central unit. As with the other remote units, the central unit is provided with a light-emitting and light- detecting arrangement 19.

The remote unit 1' that constitutes the central unit may also be a mobile control unit which controls the nearest light-pulse emitting device at that moment to have the aforedescribed function. According to this embodiment, the device that is located nearest the control unit 1' that constitutes the central unit also has the function of breaking the loop formed by the conductor 14' ' .

Figure 9 illustrates a further embodiment in which a movable remote unit 1' ' forms both central unit and light-pulse emitting device. This embodiment includes only one light-pulse emitting device and the remaining remote units 2e, 2f ... need to be located in the proximity of the central unit, or at least within the range that the system affords. This embodiment is well-suited for use when a guide "G" wearing a headset 1'' which forms a central unit and light-pulse emitting device wishes to move freely together with a public "P", an audience, where each individual wears a headset 2e, 2f ... , constituting remote units in the system, through a room where all of the individuals present are able to communicate with one another through their respective headsets despite the room being extremely noisy.

Although the conductor 14 may consist of a single conductor, it may alternatively consist of two separate conductors 14a, 14b as shown in Figure 10, where one conductor 14a passes the time frames generated by the central unit to the remote units via light-emitting arrangements 21a, 21b connected to the conductor with the aid of necessary electronics, while the second conductor 14b is connected to light-detecting arrangements 22a, 22b having the necessary electronics whereby the time frames generated by remote units in the system are passed back to the central unit, irrespective of whether the central unit is physically connected to the conductor or not. The conductor need not necessarily have the form of a closed loop in this case.

As earlier mentioned, and as illustrated in Figure 1, some units 11, 11', 12, 13 may be connected to the central unit 1 by wires.

It will be seen from Figure 4 that the light-emitting arrange¬ ments 21 and 32 are mounted respectively in the same unit as the light-detecting arrangements 22 and 31. This results in a serious risk of feedback from a light-emitting arrangement 21 to a light- detecting arrangement 22 and there is a risk of a light-detecting arrangement being saturated by light radiating from a closely situated light-emitting arrangement. A given restoring time is required to ensure high sensitivity, or response, of a light- detecting arrangement subsequent to such saturation. Accordingly, the invention proposes an embodiment in which time slots are distributed in a time frame in accordance with Figure 11.

In this embodiment, the transmitting time slots Al, A2, A3 ... are given a common continuous position, the receiving time slots Bl, B2, B3 ... are given a common continuous position within the time frame, and the second type of time slot 5n is given a first position in said time frame. In this Figure, the second type of time slot is positioned first in the time frame, followed by the transmitting time slots, which are followed by the receiving time slots. It will also be seen from the Figure that respective blocks of transmitting and receiving time slots are terminated by a third type of time slot 5pl, 5p2, which is comprised of a number of"bit positions that constitute a delay with no signal¬ ling, i.e. in the absence of light.

This embodiment means that when the transmitting time slots Al, A2, A3 ... are transmitted and respective light-detecting arrangements 22 in the light-pulse emitting devices 2 are still saturated by the light-emitting arrangements 21 in the same device, a restoring time for the light-detecting arrangements 22 is provided during the time required by the third type of time slots 5pl, 5p2. Similarly, the light-detecting arrangements 31 in respective remote units 3 are provided with a restoring time facility subsequent to transmission of the receiving time slots Bl, B2, B3 ..., so as to enable a possibly saturated light- emitting arrangement 31 to be reset in its own remote unit prior to the arrival of the second type of time slot 5n' ' in a following time frame 4' ' .

In order to achieve the technical effect desired, the third type of time slot 5pl, 5p2 shall have a time extension which corre- sponds at least to the time required to restore a light-detecting arrangement that has been saturated by a light-emitting arrange¬ ment in the close proximity thereof.

It will be understood that the aforedescribed manner of distrib- uting different time slots in created time frames so as to enable different units to be allocated a receiving and/or a transmitting function can also be used in a fully wire-bound system as illustrated in Figure 12, where the central unit lb and the remote units 3b, 3b', 3b'' included in the system are all connected to a common electric or optic loop 14b via an electri¬ cal or an optical conductor 2b, 2b', 2b''. This embodiment requires no light-pulse emitting devices connected to the loop for light-detecting and light-emitting arrangements connected to the remote units.

Figure 13 illustrates a further possible embodiment of the present invention. The Figure illustrates how two (or more) separate systems are able to operate in one and the same room without having a detrimental affect on one another.

The Figure illustrates a first system SI and a second system S2 which operate within sight of one another, meaning that a remote unit S13 in the first system SI can detect the light-pulses generated by a light-pulse emitting device S22 belonging to the second system S2, and vice versa.

To prevent disturbance between the two systems, it is proposed in accordance with the present invention that one system, for instance system SI, forms a master system and the other system, system S2, forms a slave system. The master-slave relationship between the two systems means that the light-pulse emitting device or devices S22 that operates/operate in the slave system S2 do not only detect receiving time slots from remote units S23 operating in the system S2, but also the synchronizing time slot in the master system SI. The slave system S2 is herewith synchronized to the master system SI, and the two systems are able to operate without disturbing one another, by configuring the relationship of the time slots to the second type of time slot in respective systems.

For the sake of simplicity, only two systems have been shown operating in close proximity with one another, although it will be obvious to the skilled person that further systems will be able to operate in the same area and in the same way, wherein only one of the systems will form a master system.

It will also be realized that the drawback with this embodiment is that the total number of available channels in all coacting systems will be restricted to the same number of channels as those that would be available in a single operating system. However, the advantages are that different systems which do not utilize their full capacity are able to operate within sight of one another without disturbing each other.

It will also be understood that the invention is not restricted to the described and illustrated exemplifying embodiments thereof and that modifications can be 'made within the scope of the following Claims.

Claims

1. A system for transmitting information-carrying signals which occur as light-pulses, comprising a signal transmitting and/or receiving central unit, at least one light-pulse emitting and/or light-pulse' receiving device, and at least one signal transmit¬ ting and/or receiving remote unit, wherein said devices are mutually in contact through the medium of a conductor, c h a r ¬ a c t e r i z e d in that the transmission of signals between said device and a remote unit situated in the close proximity thereof is effected via light-pulses in free space; in that the light-pulses are adapted to convey digital information-carrying signals structured into time frames which are divided into a plurality of time slots which, in turn, include a plurality of bit positions; in that a first type of time slot includes information-carrying bit positions and at least one identifica¬ tion bit position intended for mutually distinguishing said first type of time slots in a time frame; in that a second type of time slot intended for synchronizing said time frames differs unequivocally from said first type of time slots, partly because it lacks said identification bit position/bit positions; and in that the sum of the number of bit positions in the time slots of said first and said second types is corresponded by the number of bit positions in a time frame.

2. A system according to Claim 1, c h a r a c t e r i z e d in that the first type of time slot includes ten bit positions which are divided into a start-bit, eight information-carrying bits and an end-bit, where said start-bit and said end-bit constitute said identification bit position.

3. A system according to Claim 1 and Claim 2, c h a r a c ¬ t e r i z e d in that the start-bit is comprised of a light- pulse and the end-bit is comprised of the absence of a light- pulse, or alternatively the start-bit is comprised of the absence of a light-pulse and the end-bit is comprised of a light-pulse.

4. A system according to Claim 1, c h a r a c t e r i z e d in that the second type of time slot is one in number and includes at least ten bit positions.

5. A system according to Claim 1, 3 or 4, c h a r a c t e r ¬ i z e d in that all bit positions in the second type of time slot are comprised of the absence of a light-pulse when said start-pulse is comprised of a light-pulse, or that all bit posi¬ tions in a second type of time slot are comprised of light-pulses when said start-bit is comprised of the absence of a light-pulse.

6. A system according to Claim 1, c h a r a c t e r i z e d in that the first type of time slot includes nine bit positions which are divided into a start-bit and eight information-carrying bit positions, wherein said start-bit forms said identification bit position.

7. A system according to Claim 1 or Claim 6, c h a r a c ¬ t e r i z e d in that the start-bit is either comprised of a light-pulse or the absence of a light-pulse.

8. A system according to Claim 1, c h a r a c t e r i z e d in that the second type of time slot is one in number and includes at least nine bit positions.

9. A system according to Claim 1, 7 or 8, c h a r a c t e r ¬ i z e d in that all bit positions in said second type of time slot are comprised of the absence of a light-pulse when said start-bit is comprised of a light-pulse or, alternatively, all bit positions in the second type of time slot are comprised of light-pulses when said start-bit is comprised of the absence of a light-pulse.

10. A system according to Claim 1, c h a r a c t e r i z e d in that said time frames are chosen to represent standard time frames that include 256 bit positions and extend to 125 μs in time.

11. A system according to Claim 1, c h a r a c t e r i z e d in that the first type of time slots are divided into respective transmitting and receiving time slots in relation to the central unit.

5.

12. A system according to Claim 1 or Claim 11, c h a r a c ¬ t e r i z e d in that each remote unit is allocated either solely a receiving or solely a transmitting function or both a transmitting and a receiving function; and in that each remote 0 unit that is allocated solely a receiving function is allocated a transmitting time slot; in that each remote unit that is allocated solely a transmitting function is allocated a receiving time slot; and that each remote unit that is allocated both a transmitting and a receiving function is also allocated both a 5 transmitting and a receiving time slot.

13. A system according to Claim 1, 11 or 12, c h a r a c ¬ t e r i z e d in that the central unit is adapted to generate time frames which, among other things, include time slots of a 0 transmitting type, wherein the information-carrying bits contain information intended for remote units that have been allocated respective transmitting time slots; and in that all information- carrying bits in receiving-type time slots in said time frames are free from information and therewith light-pulses. 5

14. A system according to Claim 1 or Claim 13, c h a r a c ¬ t e r i z e d in that the generated time frames are transmitted to those light-pulse emitting devices that are connected with said conductor; and in that said devices are provided with light- 0 emitting arrangements whereby said generated time frames are radiated in the form of light-pulses in the room in which said devices are present.

15. A system according to Claim 1 or Claim 17, c h a r a c - 5 t e r i z e d in that a remote unit situated in said room in the proximity of said device and allocated a receiving function is provided with a light-detecting arrangement whereby light-pulses can be detected; in that the remote unit is provided with a converting arrangement which functions to convert detected light- pulses to electric signals adapted for the remote unit; in that the remote unit is adapted to distinguish respective time frames from one another and to separate the transmitting time slot allocated to the remote unit from remaining time slots of said first type, by means of time slots of said second type and by means of said identification bit position/bit positions in respective time slots of said first type.

16. A system according to Claim 1, 11 or 12, c h a r a c ¬ t e r i z e d in that a remote unit that has been allocated solely a transmitting function or both a transmitting and a receiving function is adapted to generate time frames which, among other things, include receiving-type time slots containing information-carrying bit positions with information intended for one or more other remote units or for said central unit; in that all information-carrying bit positions in the transmitting-type time slots in said time frame are free from information; in that said remote unit is provided with a light-emitting arrangement, whereby said generated time frames in the form of light-pulses are radiated in the room in which the remote unit is present; in that a light-pulse emitting device in the proximity of the remote unit is provided with a detecting arrangement whereby the light- pulse emitting device can detect said radiated or emitted light- pulses, wherein said device transmits the time frames generated by the remote unit to said central unit.

17. A system according to Claim 1, 13 or 16, c h a r a c - t e r i z e d in that the time frames generated by the remote unit are adapted to contain, among other things, time slots of the second type; in that the remote unit transmits said time frames in phase with the time frames that are generated by the central unit, which is effected with the aid of the time slots of a second type generated by the central unit and the remote unit respectively.

18. A system according to Claim 1, 13, 16 or 17, c h a ¬ r a c t e r i z e d in that the central unit is adapted to distinguish between respective time frames and the different receiving time slots with the aid of said identification bit position/bit positions, and to ascertain through the configura¬ tion of the system whether the information in the information- carrying bit positions in respective receiving time slots is intended for the central unit itself or whether the information shall be sent to a remote unit for which the information is intended, with the aid of information-carrying bit positions in transmitting time slots in time frames generated by the central unit.

19. A system according to Claim 1, c h a r a c t e r i z e d in that the remote unit includes a combination of earphones and microphone adapted for speech communication.

20. A system according to Claim 1, c h a r a c t e r i z e d in that the remote unit includes a control unit adapted to control or regulate a process.

21. A system according to Claim 1, c h a r a c t e r i z e d in that the remote unit includes a measurement data unit adapted to collect measurement data from different instruments or different measurement points.

22. A system according to Claim 1, c h a r a c t e r i z e d in that the central unit is in contact with said light-pulse emitting devices via light-pulses in said room or space.

23. A system according to Claim 1, c h a r a c t e r i z e d in that the central unit is in contact with said light-pulse emitting devices via said conductor.

24. A system according to Claim 1, 13 or 16, c h a r a c ¬ t e r i z e d in that the conductor is comprised of two separate conductors, one of which is intended for time frames sent from the central unit to said remote units, and the other of which is intended for time frames sent from remote units to the central unit.

25. A system according to Claim 1 and Claim 11, c h a ¬ r a c t e r i z e d in that the transmitting time slots form a continuous block in time relative to one another; in that the receiving time slots form a continuous block in time relative to one another; and in that respective blocks of transmitting and receiving time slots are followed by a third type of time slot.

26. A system according to Claim 25, c h a r a c t e r i z e d in that the third type of time slot is comprised of the absence of light from all light-emitting arrangements in the system.

27. A system according to Claim 25, c h a r a c t e r i z e d in that the third type of time slot has an extension in time which is corresponded at least by the time required to restore a light detecting arrangement in the system subsequent to said arrangement having been saturated by a light-emitting arrangement in the system.

28. A system according to Claim 1, c h a r a c t e r i z e d in that said system is comprised of a first system; in that at least a second system operates within sight of said first system; in that said second system synchronizes its time frames with the second type of time slots belonging to the first system; in that the time frames acting in said first system and in said second system have the same configuration; and in that time slots of said first type used in said first system are not used in said second system, and vice versa.

29. A system for transmitting information-carrying signals including a signal transmitting and/or signal receiving central unit and at least one remote unit which transmits and/or receives signals, wherein said central unit and a remote unit are in contact with one another through the medium of a conductor, c h a r a c t e r i z e d in that the signals are structured to form time frames which are divided into a number of time slots containing a plurality of bit positions; in that a first type of time slot includes information-carrying bit positions and at 5. least one identification bit position intended for mutually distinguishing first types of time slots in a time frame; in that a second type of time slot intended for synchronizing the time frames differs unequivocally from^* said first type of time slots, partly by lacking said identification bit position/bit positions; 0 and in that the sum of the number of bit positions in the time slots of said first and said second types is corresponded by the number of bit positions in a time frame.