WO1991007028A1

WO1991007028A1 - System for transmitting data between several subscriber stations in a local communications net

Info

Publication number: WO1991007028A1
Application number: PCT/EP1990/001818
Authority: WO
Inventors: Wolfgang Kemmler; Amer Amin
Original assignee: Siemens Nixdorf Informationssysteme Aktiengesellschaft
Priority date: 1989-11-07
Filing date: 1990-10-31
Publication date: 1991-05-16
Also published as: JPH0793626B2; DE3937096A1; DE3937096C2; JPH04505083A; EP0571366A1

Abstract

The invention concerns a system for transmitting data in half-duplex operation between several subscriber stations (10, 12) in a local communications net, transmission taking place between a subscriber station (10 or 12) and a sub-station (18 or 20) by modulated electromagnetic radiation. The invention calls for data transmission between the sub-stations (18, 20) also by electromagnetic radiation. To transmit binary data, this radiation is impulse-modulated. The sub-stations (18, 20) each emit a pulse in response to the arrival of a pulse. Following arrival of a pulse, the stations (10, 12, 18, 20) are not in a condition to receive at least for a time T equal to the sum of (a) twice the pulse transit time ti between the emitter station and the receiver station located furthest away within emitter range R and (b) the pulse length tp. The new system is highly flexible and can be set up with simple resources.

Description

System for transmitting data between several subscriber stations of a local communication network

The invention relates to a system for transmitting data in half duplex mode between a plurality of subscriber stations of a local communication network via at least two intermediate stations, the data being transmitted between a subscriber station and an intermediate station in each case by means of modulated radiation in the room.

Such a system, which is used for data transmission for a local network in the field of computer-aided manufacturing (CIM), is known from an article "Data transmission with infrared light" in the specialist journal Electronics 24 / 25.11.1988, pages 82 to 90 . Several intermediate stations establish the wireless connection by means of an infrared transmission link to subscriber stations of a flexible transport system in a spacious factory hall. The intermediate stations are connected to each other via lines and connected to a master computer that controls data traffic. The data transmission takes place in half-duplex operation, in which a subscriber station either sends or receives data, however, simultaneous data traffic in both directions is not intended.

In this known system, the intermediate stations usually mounted on the ceiling of the room have to be connected to one another by a permanently installed data line network. If such a system is expanded to a larger hall area or if the transmission system is modified, in which the subscriber stations are assigned new locations, complex installation work for the line network is required.

It is an object of the invention to provide a new system for transmitting data which has a high degree of flexibility and can be implemented using simple means.

This object is achieved for a system of the type mentioned at the outset in that the data transmission between the intermediate stations of the same structure is also carried out by radiation, in that the radiation for transmitting binary data is subjected to pulse modulation in that the intermediate stations each arrive transmit a pulse in response to a pulse, and that the readiness to receive is at least for a time T after the arrival of a pulse, which is equal to the sum of twice the pulse transit time between the transmitting station and the most distant receiving station within the transmission range and the pulse duration .

In the invention, pulse modulation is used for data transmission. In this the pause following a pulse is varied depending on the binary value of the data to be transmitted. A long pause is assigned to the binary value 1, and a short pause to the value 0. The pulse duration itself, ie the The time in which radiation is emitted is such that the intermediate stations switched to receive and the subscriber stations can safely receive the pulse.

This type of modulation means that the radiation energy required for data transmission is minimal, since the information is essentially contained in the length of the pause. By choosing a short pulse duration, the pulse amplitude can be high for a predetermined amount of radiation energy, so that a large transmission range and a high signal-to-noise ratio with respect to the ambient radiation are achieved.

Other types of pulse modulation can also be used. For example, a modulation with a fixed time pattern can be carried out, in which the binary information is encrypted in successive predetermined time segments of constant length. This can be done in such a way that the emission of a radiation pulse is interpreted as binary value 1 within a time period. The absence of such a pulse is then interpreted as a binary value 0.

The pulse, which is generally emitted in all directions, loses intensity as a result of the divergence of the radiation and as a result of scattering and absorption in air and on particles along its path of propagation. Accordingly, a transmission range can be defined for the respective subscriber station or intermediate station, which indicates the distance at which a sufficiently good reception signal is still present. The decisive factor here is compliance with a predefined signal-to-noise ratio to interference signals such as, for example, noise, background radiation and interference radiation. The pulse received by an intermediate station within the range of a transmitting station triggers the transmission of a new pulse, which in turn is received by intermediate stations within its range. These stations then send out further pulses, so that a pulse initially sent out by a subscriber station triggers a large number of further pulses which propagate in the manner of a wave, the intermediate stations sending out the attenuated pulses received in each case again in an increased manner. The wave propagation speed theoretically depends on the speed of light in air. In practice, however, delay times have to be taken into account, which are caused in particular by reaction times and the transient response of the electronic components.

The intermediate stations constructed in the same way generally send their pulses in all directions and can also receive pulses from all directions. This means that after the transmission of a pulse, the intermediate stations receive pulses again from intermediate stations adjacent to them. Without further measures, these impulses would cause new impulses to be sent which are not related to the data to be transmitted and thus interfere with the transmission. In order to suppress these impulses, the invention provides that the readiness for reception of a transmitting station is at a standstill T. During this time, incoming impulses cannot trigger new impulses. The time T is at least the sum of twice the pulse transit time between the sending station and the most distant receiving station within the transmission range and the pulse duration. This measure also ensures that the crosstalk from the sending station or impulses generated by reflection on obstacles in the transmission path are suppressed and consequently no erroneous impulses are received and transmitted again. The readiness for reception of the subscriber stations also rests for the time T, so that their data reception is not disturbed by returning pulses.

Since in the invention the data transmission between the intermediate stations is carried out by radiation, the installation of a line network for the intermediate stations is not necessary. The spatial expansion of an existing data transmission system can therefore be carried out without great technical outlay, since further intermediate stations can be arranged in the room in a simple manner.

Furthermore, the system according to the invention does not require a central control for the data traffic, as is the case with the prior art, since the data transmission can take place asynchronously and the intermediate stations work independently of one another without interfering with one another. The intermediate stations themselves are very simple, since they do not have to perform any storage function or signal processing function. They can be implemented using simple electronic means.

The system according to the invention allows a high transmission speed and data transmission rate, since the transmission of the data from a sending to a receiving subscriber station takes place almost at the speed of light. In addition to the pulse pauses defined by the pulse modulation, the pulse repetition frequency for the transmission is also influenced by the time T during which the stations are ready to receive. In addition to the pulse duration, time T is also determined by the pulse transit time between the stations, which in turn depends on the speed of light in air and the transmission range. The latter can be optimized so that the time T becomes minimal. If pulses with a short pulse duration are used, a high pulse repetition frequency and thus a high data transmission rate can be achieved.

Both visible light and infrared radiation can be used as radiation. The latter has the advantage that with the aid of simpler electronic components, such as light-emitting diodes, a high radiation intensity and thus a long transmission range are achieved in pulse mode. In applications in which the electromagnetic compatibility is not critical, electromagnetic radiation in the radio frequency range or in the micelle range can also be used as radiation.

A preferred embodiment of the invention is characterized in that when the pulse is sent out delayed by a reaction time, the time T is additionally extended by at least this reaction time. The response time is due to the switching time and the delay of inductive and capacitive components of the electronic components in the intermediate stations. Since the unfavorable timing behavior of such components can be compensated for with the aid of the measures mentioned, it is possible to use very simple and inexpensive electronic components with long switching times when implementing the intermediate stations in terms of circuitry.

In a further embodiment of the invention it is provided that the intermediate stations are arranged at equal distances from one another. The intermediate stations then form a connection network composed of equilateral triangles, at the corners of which an intermediate station is arranged. This arrangement ensures that each intermediate station, with the exception of those which are arranged at the edge of the network, is surrounded by six directly adjacent intermediate stations. If one or even more of these stations fails, it is still guaranteed that the pulse emitted by a remaining neighboring station can still be received and further pulse transmission is thus ensured. This means that the system still works very reliably even if individual intermediate stations fail. Furthermore, this arrangement achieves a high and uniform density of intermediate stations in the room, so that data transmission from one subscriber station to another can take place reliably regardless of the location of the subscriber stations in the room.

A further development of the described embodiment provides that the distances are equal to the transmission range. This measure minimizes the number of intermediate stations required and reduces the technical complexity of the system.

An embodiment of the invention is explained below with reference to the drawing. It shows:

FIG. 1 a shows a sequence of pulses after pulse modulation with variable pulse pauses,

Fig. Lb a sequence of pulses with a fixed time pattern,

2 shows an arrangement with two subscriber stations and two intermediate stations, 3 shows a schematic structure of the electronic components of an intermediate station in a block representation,

Fig. 4 test results to determine the

Transmission range shown in one

Diagram,

5 pulse diagrams over time for two intermediate stations, the distance from each other is slightly smaller than the transmission range te,

6 shows the propagation of pulses at a large number of intermediate stations in space,

Fig. 7 pulse diagrams over time for three intermediate stations, which are within a transmission range, and

8 a, b a directional characteristic with a main lobe and two secondary lobes for the radiation emitted by an intermediate station, and a hemispherical directional characteristic.

FIG. 1 a shows pulse sequences over time t for the pulse modulation used to transmit binary data. Radiation pulses with the pulse height H and the duration tp are emitted over time t with different pauses to, tl. A short pause tO corresponds to the binary value 0, a long pause tl is the binary value 1. The pulse duration tp should be as short as possible so that the radiated radiation energy • is low or the pulse height H is large for a given radiation energy. This pulse height H essentially determines the transmission range and the signal-to-noise ratio to interference signals.

Another possible type of pulse modulation is shown in Fig. 1b. With this modulation, a fixed time grid of length t2 is used. If a pulse with the duration tp occurs within a time period t2, this corresponds to the binary value B = 1. If such a pulse is missing within a time period t2, this is interpreted as a binary value B = 0. The duration tp of the pulse may not exceed the length t2 of the time segment. The pulse duration tp is preferably chosen to be considerably smaller than the length t2 in order to obtain a large pulse height H for a predetermined pulse energy.

2 schematically shows the basic structure of the system for transmitting data between two subscriber stations 10, 12 via two intermediate stations 18, 20 in one room. The subscriber stations 10, 12 can be, for example, computer terminals, personal computers with a communication interface, work stations for computer-aided production or automatic cash register stations and are located near the floor of the room. The subscriber stations 10, 12 are mobile, i.e. depending on the application, they can be located in different places in the room.

The subscriber stations 10, 12 each have one

Transmitter-receiver unit 14 or 16, each with a structure corresponding to an intermediate station have, which is described in more detail. The transmitter-receiver units 14, 16 have a spherical directional characteristic 15 for the radiation to be received and emitted and are aligned with the intermediate stations 18 and 20 adjacent to them. This improves the interference immunity of the transmission link between the intermediate station 18 or 20 and the respective subscriber station 10, 12.

The data traffic between the subscriber stations 10, 12 is processed after the half-duplex operation. This means that the subscriber stations 10, 12 alternately send and receive data. To transmit binary data, one of the transmitter / receiver units 14, 16 is activated, which transmits data in the form of modulated radiation pulses which are forwarded in space by the intermediate stations 18, 20. All subscriber stations 10, 12 of the room receive these pulses via their respective transmitter-receiver units 14, 16. The pulses are then evaluated in the respective subscriber stations 10, 12 according to known methods and the corresponding data are further processed.

The ^{'intermediate} stations 18, 20 are arranged on the ceiling 24 of the room at a distance from each other, at least the transmission range of the intermediate stations 18, corresponding to the 20th Infrared radiation with a wavelength of approximately 1 micron typical for semiconductor radiation sources is used as radiation. To suppress background radiation and interference radiation from room lighting, the receiving elements of the intermediate stations 18, 20 and the transceiver units 14, 16 are provided with filters (not shown), the wavelength range of which is matched to the radiation from the semiconductor radiation sources is. The intermediate stations 18, 20 are each supplied with power from a power supply unit (not shown).

The schematic construction of an intermediate station 18, 20 or a transceiver unit 14, 16 is shown in a schematic illustration in FIG. 3. A receiving module 26 equipped with a photodiode detects a pulse 25 which has been emitted by an intermediate station or a transceiver unit of a subscriber station and converts this into an electrical signal. This is fed via a switch arrangement 28 to a preamplifier 30, the impedance of which is matched to the receive module 26 for as low-noise amplification as possible. The output signal of the amplifier 30 is fed to a threshold switch 32, which compares it with a predetermined threshold value 31. If the output signal exceeds this threshold value 31, the threshold value switch outputs a signal 33 by means of which the presence of a valid pulse 25 can be determined. The signal 33 can then be used in a transceiver unit 14, 16 for evaluating the binary information in a subscriber station.

The signal 33 is also fed to a pulse shaping stage 36, which generates a control pulse with the pulse duration tp and thus controls a diode array 38. The diode array 38 consists of a plurality of light emitting diodes (LED) which emit infrared radiation with a wavelength of approximately 1 micrometer. The diodes operate in so-called pulse mode, ie their pulse pause is considerably longer than the time in which they emit radiation. This makes it possible to apply high pulse currents to the diodes, which generate a high radiation intensity. By using several diodes, the total radiated power is enlarged and by different alignment of the diodes, the radiation can be emitted in a large solid angle.

The output signal 33 of the threshold switch 32 is also fed to a timing element 34, which opens the switching path of the switch arrangement 28 for a predetermined time T. During this time T, pulses 25 detected by the receiving module 26 are not forwarded to the preamplifier 30, so that the threshold switch 32 does not emit a signal 33 which signals a valid pulse.

A pulse 40 emitted by the diode array 38 is weakened along its propagation path due to the radiation divergence and the dispersion and absorption of radiation in air. This leads to a limited transmission range of the intermediate stations 18, 20 or of the subscriber stations 10, 12. FIG. 4 shows test results in a diagram for determining the transmission range. About the distance s from the transmitting station 14, 16, 18, 20, the output voltage U of the preamplifier 30 which can be picked up in front of the threshold switch 32 (FIG. 3) is plotted. With increasing distance s, this voltage U drops hyperbolically and, at a distance of s = 13.5 m, reaches a critical value of 0.5 V, below which reliable detection of a pulse is no longer possible. This limit distance is called the transmission range R. The critical value of 0.5 V is used as the threshold value 31 in the comparison in the threshold value switch 32.

5 shows pulse diagrams over time t, which show the transmission of pulses between two Intermediate stations 42, 44 lying within the transmission range R. A pulse 48 emitted by the intermediate station 42 at the time t = 0 reaches the intermediate station 44, but not the station 46 which is further away and lies outside the transmission range R. The pulse 48 arrives with a time delay ti which corresponds to the duration of the radiation Air to station 44 corresponds to station 44. After a reaction time tr, which is due to switching times of the electronic components of the intermediate station 44, the station 44 sends out a pulse 50 in all directions. The pulse 50 subsequently arriving at the previously sending station 42 will be considered in more detail below. It arrives at station 42 after the pulse transit time ti and would trigger another pulse there without further countermeasures. In the further course, this would lead to the stations 42, 44 continuously exchanging pulses at the time interval ti. The transmission of binary information would not be possible.

According to the invention, the readiness for reception of the station 42 is stopped for a time T when its pulse 48 is transmitted, so that pulses arriving during this time T cannot trigger any further pulses. According to the diagram in FIG. 5, this time T must satisfy the relationship T ti + tr + ti + tp. Only then is it ensured that the station 42 does not emit any disturbing follow-up pulses. The pulse 50 sent out by the station 44 is received by the station 46 and triggers a subsequent pulse there. Its intensity is too low to be recognized as a valid pulse at station 42. 6 shows in five representations a) to e) the transmission of data between a plurality of subscriber stations 52 to 58 of a local communication network. The subscriber stations 52 to 58 are identified by a triangle. A large number of intermediate stations identified by circles are provided for data transmission and form a transmission network. The intermediate stations are arranged at equal distances from one another, as indicated by the dashed circle 60 in illustration a). The distances between the intermediate stations are equal to the transmission range R.

In illustration b), the subscriber station 52 sends out a pulse which the intermediate station closest to it receives. This then sends out a subsequent pulse which, according to illustration c), is received by two neighboring intermediate stations. The simultaneous reception of these impulses is marked by a connecting line. This connecting line can be understood as a wave front of propagating impulses.

In the illustration d), this wavefront has advanced by further intermediate stations and in the illustration e) reaches the subscriber station 54 which is furthest away from the subscriber station 52. In order to transmit data from station 52 to station 54, the pulses from the sending subscriber station 52 must therefore be passed on via eight intermediate stations. The subscriber stations 56 and 58 receive the transmitted data after the impulses have been forwarded five times through intermediate stations.

7 shows further pulse diagrams over time t, which provide information about the time "T" required for a station to be ready to receive give if there are several stations in the transmission range R with different distances from the transmitting station. In the upper part of FIG. 7, a station 60, which may be an intermediate station or a subscriber station, transmits a pulse 66 which is well received by both a station 62 and a station 64 further away. To overcome the distance to the station 62, the pulse 66 requires the transit time ti, as does the pulse 68 sent back by the station 62. In this example, the response time tr has been set to zero for a better understanding of the relationships described below.

The pulse 66 requires the transit time ti 'until it arrives at the further distant station 64. The pulse 70 sent back from station 64 to station 60 has the same transit time ti '. For interference-free data transmission, as can be seen from FIG. 7, it is necessary for station 60 to be ready for reception at least the time T, which results from the relationship T> ti '+ ti' + tp. At this time T, the reaction time tr has to be added, which has been neglected in this example. It should therefore be noted that the time T is essentially determined by the pulse transit time ti 'between the transmitting station 60 and the receiving station 64, which is the most distant within the transmission range.

The directional characteristic of the radiation emitted by an intermediate station has a decisive influence on the transmission range R. FIG. 8a shows an exemplary embodiment of an intermediate station 72, the emitted radiation of which has a rotationally symmetrical directional characteristic with a spherical main lobe 74 and two secondary lobes 76, 78. The intermediate station 72 is fastened below the ceiling 24 of the room. The Main lobe 74 has an axis 86 which runs parallel to the surface normal of the ceiling 24. In the radiation area of the main lobe 74 there are preferably subscriber stations which are usually located near the bottom of the surface. The side lobes 76, 78 have axes 82, 80 which run parallel to the ceiling 24. Adjacent intermediate stations are located in the direction of these axes 82, 80. This directional characteristic ensures that the radiated energy is preferably radiated both in the direction of the subscriber stations and in the direction of the intermediate stations, so that on the one hand the energy consumption is minimized and on the other hand a large transmission range is achieved.

In Fig. 8b, the intermediate station 72 has an approximately hemispherical directional characteristic 90, i.e. the radiation intensity radiated into the room - indicated by arrows 91 to 94 - is the same for all solid angles of the half-space. Such a directional characteristic 90 can e.g. by arranging several radiation-emitting semiconductor components, such as LEDs or laser diodes, on a carrier. The components are aligned in such a way that the main axes of their radiation point in different directions and run along normal to the surface of a hemisphere, the central axis of which points towards the interior of the room. The resulting radiation intensity in space is then approximately constant for all solid angles.

Claims

Patent claims

1. System for the transmission of data in half-duplex mode between a plurality of subscriber stations of a local communication network via at least two intermediate stations, the data transmission between a subscriber station and an intermediate station being carried out by modulated radiation in space, characterized in that that the data transmission between the identical intermediate stations (18, 20, 42, 44, 46, 60, 62, 64) takes place by radiation, that the radiation for transmitting binary data is subjected to a pulse modulation, that the Intermediate stations (18, 20, 42, 44, 46, 60, 62, 64) each send out a pulse upon the arrival of a pulse, and that the readiness to receive is at least for a time T after the arrival of a pulse, which is equal to Sum of the double pulse transit time ti, ti 'between the transmitting station (10, 12, 42, 60) and the one furthest away within the transmission range R. receiving station (44, 64) u d from the pulse duration tp.

2. System according to claim 1, characterized in that when the pulse is emitted delayed by a reaction time tr, the time T is additionally extended by at least this reaction time tr.

3. System according to claim 1 or 2, characterized gekenn¬ characterized in that the intermediate stations are arranged at equal distances from each other.

4. System according to claim 3, characterized in that the distances are equal to the transmission range R e.

5. System according to any one of the preceding claims, characterized in that as radiation

Infrared radiation is used.

6. System according to any one of the preceding claims, characterized in that at least one light-emitting semiconductor radiation source is provided for the radiation per intermediate station (18, 20, 42, 44, 46, 60, 62, 64).

7. System according to any one of the preceding claims, characterized in that the of the stations

(10, 12, 18, 20, 42, 44, 46, 60, 62, 64) radiated radiation has a spherical (15) or a hemispherical directional characteristic (90).

8. System according to any one of the preceding claims, characterized in that at intermediate stations (7.2) which are montier¬ bar on the ceiling (24) of the room, the radiated radiation has a rotationally symmetrical directional characteristic with a main lobe (74) and two side lobes (76 , 78), and that the main lobe axis (86) runs parallel to the surface normal of the ceiling (24) and the secondary lobe axes (80, 82) run parallel to the top surface.

9. System according to any one of the preceding claims, characterized in that the subscriber stations (10, 12) each have a transmitter-receiver unit (14, 16) with a directional characteristic (15) for the radiation to be received and emitted and on one of them Adjacent intermediate station (18, 20) are aligned.

10. System according to any one of the preceding claims, characterized in that the of the stations

(10, 12, 18, 20) received radiation is filtered by an optical filter which is tuned to the wavelength range of the radiation emitted by the intermediate stations (18, 20) and the subscriber stations (10, 12).