RU2153227C2 - Method and device for reliable multimode wireless optical communication - Google Patents

Abstract

FIELD: optical communication equipment. SUBSTANCE: method involves establishing connection between stations using header, which is stable to physical noise and can be recognized by all participating stations. Said header at least has preamble, which consists of frames which provide periodic pulse sequence, number of slots for frame and frame content, which is known to participating stations. Preamble is used for relative synchronization and carrier detection by receiving stations. In addition, header has unique synchronization word, which is used for absolute synchronization of receiving stations. Said synchronization word follows control field, which has fixed length and known structure. Said control field provides possibility for receiving stations to get information about modulation method used for data transmission. In some circumstances, it is useful to get another control information in control field in order to keep communication channel and network control protocol. In addition, it is possible to exchange information in order to negotiate or adapt data transmission rate used for data transmission. EFFECT: increased throughput depending on conditions of data transmission in channel. 38 cl, 14 dwg

Description

 The invention relates to multi-mode wireless optical communication systems and to communication and / or coexistence of communication between different types of devices operating in different modes within such communication systems.

State of the art
With the rapid increase in the number of workstations and personal computers (for example, desktop or laptop computers) in all areas of business, administration, production, etc., the need for flexible and simple interaction of such systems increases. There is a similar need for the connection and interaction of peripheral devices such as keyboards, computer mice, printers, plotters, fax machines, scanners, monitors, modems, etc. With the increase in the number of systems connected to each other, the problem of using electrical interconnections arises, including in many cases when it is often necessary to change the location of systems or the configuration of subsystems. Therefore, for such systems it is necessary to increase flexibility by eliminating electrical interconnects and use wireless communication instead.

 The use of optical signals for the wireless transfer of digital data between systems and devices in recent years has attracted increased interest and led to their use in commercial products. One example is the optical remote control of electronic user devices. Another example is the relationship between information systems in office equipment. In an optical communication system, digital data that must be transmitted from a transmitting system to a receiving system is converted into modulated optical signals that are emitted by a light source (in particular, an infrared (IR) light source) of a transmitting system and received, converted into electrical signals and then into digital data using a receiving system. Optical signals can directly go to the optical receiver of the receiving system or can go directly to the receivers after a series of changes in the direction of light propagation due to effects like reflection or scattering on media surfaces. Currently, the latter option is implemented in laptop computers and peripheral devices, where there is data transfer between the optical transmitter and receiver, which are located close to each other at a distance of about 1-3 m and are correctly aligned. The latter case is typical for applications in office equipment, where noiseless transmission of optical signals between transmitters and receivers that are in direct line of sight and located a few meters from each other is impractical or even impossible due to the inevitable deviations of the optical signals from the rectilinear path of light propagation. According to one known approach to achieving a high degree of flexibility, optical signals sent from a transmission system must be emitted towards the ceiling or walls of the office from which they are reflected or diffusely scattered. Thus, the radiation is distributed in a certain area around the transmitter. The distribution of optical signals reflected from the ceiling depends on numerous details that are characteristic of the particular equipment in question. However, it is essential in this context that the transmission range, that is, the distance between the transmitting system and the receiving system, is limited by a certain final value, which is hereinafter referred to as the transmission range, since the energy flux of the transmitted radiation decreases with increasing propagation distance, while receiver sensitivity is limited due to the minimum signal to noise ratio. Typical known systems operating at optical energy levels, which are limited by embodiments of light sources and safety requirements for optical radiation, have operating transmission ranges of several meters for a data transfer rate of the order of 1 Mbit / s.

 The last example illustrates the main features of wireless optical communication and shows the applications where it is used in contrast to another competing wireless method, radio frequency (RF) transmission. Wireless optical communication allows data transmission over short distances, while RF transmission can potentially be used over long distances. In addition, optical wireless communication in the office environment is localized, because typical office boundaries, such as walls and ceilings, are not transparent to light, as is the case with RF waves. Therefore, it is easier to control the interference between different communication systems, and in a simpler way to provide data protection for a wireless communication system that is based on optical radiation and not on RF transmission. In addition, RF transmission is limited by communication and licensing rules, while optical wireless communication systems are not.

 The determining parameters of the efficiency of the wireless optical communication system are the used data transfer rate and the distance between the data exchange systems. In an office environment, it may be necessary to transmit data over distances exceeding the transmission range of a single optical transmitter. However, the transmission range of a single optical transmitter can be expanded within the concept of wireless communication, for example, by introducing optical repeaters. One example of such an expanded system is disclosed in US Pat. No. 4,402,090, entitled “Communication System in which Data are Transferred Between Terminal Stations and Satellite Stations by Infrared Systems "). This patent describes a system that provides for a plurality of satellite stations, that is, stations usually mounted on the ceiling of a large room. Terminals can optically interact with satellites within their transmission range, and data can be distributed via inter-satellite communications, thereby allowing data to be distributed over distances exceeding the transmission range of a single transmitter.

 When designing a wireless optical communication system, it is necessary to take into account the inevitably present ambient light, such as daylight or lamp light, which always hits the optical detectors, if the application of the system is not limited to its use in a completely dark environment. The energy of infrared radiation (IR) in ambient light (fluorescent (fluorescent) and incandescent lamps, light of the sun) can lead to a predominance of noise in the optical receiver. Thus, ambient light affects the signal-to-noise ratio of the receiver and therefore affects the transmission range. Additional information on the effect of ambient light is given in PCT Patent Application PCT / EP 94/01196, published October 26, 1995 (Publication Number WO 95/28777). The manifestation of ambient light is usually statistical in nature and often difficult to control, and its intensity can vary significantly, as happens, for example, when the lamps are turned on or off or in sunlight. An additional real effect, which statistically affects the signal-to-noise ratio and, thus, the transmission range, is the appearance of obstacles in the optical path, which affect the operation of the receiver. In an office environment, for example, during the movement of users, as well as under the influence of the inevitably present ambient light, the intensity of the transmitted signals can change.

 In modern wireless communication systems based on the transmission of light, the first attempts were made to solve some problems of the presence of ambient light. Typically, signals that change in time with a low frequency (≤ 500 kHz), which may be present in normal room lighting, are suppressed using electric filters after converting the light into electrical signals. Optical filters are used to limit the spectrum of unwanted ambient light. However, the spectrum of a significant part of daylight is in the same range as the optical radiation of light sources operating in wireless communication systems.

 As described in the aforementioned PCT patent application PCT / EP 94/01196, and in another PCT patent application PCT / EP 94/00577 published August 31, 1995 (Publication No. WO 95/23461), an infrared wireless communication system can be implemented , which effectively allows you to solve basic problems, such as the presence of ambient light incident, for example, from commercially available systems. PCT / EP 94/01196 discloses a circuit that allows dynamic optimization of wireless optical communication systems that are exposed to ambient light with varying light levels.

 Specialists working in this technical field have developed and implemented various schemes for wireless optical communication. This has led to the use of various optical communication methods that are not compatible. For example, it is usually not possible to connect a computer from a first manufacturer with a printer from a second manufacturer using a wireless optical channel, because in most cases they work in different modes, and the hardware of the transmitter-receiver is not compatible.

 Part of the incompatibility problem is caused by independent and unrelated developments by various companies. In addition, there are various applications for which, taking into account the specifics of the work, various transmission schemes (modes) are required to achieve an adequate data rate and range. Typical examples are directional high-speed data channels for desktop computers and peripheral devices, local area networks (LANs) with fixed or variable data rates using diffusely scattered radiation, remote control systems, low-speed paging functions and access channels to wired systems and wireless radio frequency (RF) systems, for example, such as cordless phones. Obviously, the characteristics of these types of systems are dictated by the application itself.

 This means that various optical communication schemes will always coexist, which must be interfaced with multi-mode systems. However, it can be expected that over time the differences caused by independent and unrelated developments will disappear, or that at least such a standard will be developed that most systems can communicate with each other. An example of such a standard is the existing lrDA (Infrared Data Technology Association) standard. Work is ongoing to expand this standard. Details are given in the article "Facilitated file transfer using the lrDA protocol of infrared data transfer technology." Bill Travis, EON, Journal of Electronic Industry Projects, July 1995, pp. 17-22 (Ease File Transfer With lrDA-Protocol Wireless Infrared, Bill Travis, EON, The Desiqn Magazine of the Electronics Industry, July 1995, pp . 17-22). This article also describes the modulation method defined using the lrDA standard.

 A solution that satisfies the various requirements and needs of modern and future communication systems based on light transmission and guarantees their coexistence and / or compatibility within a common working environment (for example, within the working area of a large office) is currently lacking.

 Thus, an object of the present invention is to provide a wireless optical communication system that allows multi-mode operation.

 Another objective of the present invention is to develop a method and apparatus for wireless multi-mode optical communication systems.

 An additional objective of the present invention is to solve typical problems of a modern optical communication system, namely, to assess channel quality, frame / symbol synchronization, etc.

 Another objective of the present invention is to develop a method and apparatus for wireless multi-mode optical communication systems that operate even under extremely poor channel conditions.

SUMMARY OF THE INVENTION
The present invention is intended to solve these problems. It provides a method and apparatus for providing wireless optical communication between a transmitting station and a first receiving station capable of receiving data that modulate using the first modulation method, and a second receiving station capable of receiving data that modulate using the second modulation method. For this purpose, a new, physically stable header (RPLH) proposed in the invention was used. According to the present invention:
1. the transmitting station performs a preamble containing frames that form a periodic sequence of pulses, that is, a sequence of pulses with a certain period, the number of slots (L) per frame and the content of the frames, which is known to each of the receiving stations,
2. the transmitting station transmits an optical sequence of pulses,
3. each said receiving station performs carrier detection based on a sequence of received pulses,
4. each receiving station determines the period of the pulse train to obtain relative synchronization,
5. each receiving station corrects its clock with the phase of the slot of the received pulse sequence, and synchronizes the input pulse sequence through the shift register,
6. the transmitting station transmits a unique synchronization word aligned with the preamble period,
7. each of the receiving stations correlates the pulse sequence in the shift register with the unique synchronization word known to this station in order to ensure absolute synchronization with the transmitting station after recognizing the synchronization word,
8. the transmitting station indicates in the control field of a predetermined length which modulation method will be used in the additional data / subsystem field so that receiving stations that are capable of supporting the corresponding modulation method expect data to be transmitted in this data / subsystem field.

 It should be noted that the sequence of the above steps is not mandatory. Some of the steps can be performed in parallel.

 Depending on the particular embodiment, it is advantageous if the transmitting station additionally indicates in the control field the length of such an additional data field / subsystem that the receiving station can retrieve information that determines the duration of the suppression of its own transmitter in order to avoid a conflict of the signal with the ongoing transmission (reading virtual carrier). In some circumstances, it is also useful to obtain other control information in said control field for a communication channel and network control. In addition, it is possible to exchange information that will allow for coordination and / or adaptation of the transmission rate. This will optimize the throughput depending on the conditions (quality) of the channel. An advantage is also the possibility of obtaining information with priority access, which makes it possible for the coexistence of picocells within the same communication cell.

 Further advantages of the present invention and further examples of information that can be exchanged using a physically stable title of the invention are described in detail below.

 The present invention can also be used to maintain communication within a system using a single mode of operation, that is, to communicate between stations supporting the same modulation method or to communicate in a multi-mode system. In order to guarantee the possibility of multi-mode communication, it is necessary to provide the appropriate hardware according to the present invention, and it is necessary to initiate any communication according to the above steps.

Brief Description of the Drawings
The invention is further disclosed with reference to the accompanying drawings, in which:
FIG. 1 is a table of various coexisting IR subsystems (SI-S4) and a selection of typical applications;
FIG. 2 is an example of a receiver of a multi-mode receiving station according to the present invention for operation within subsystems SI, S2 and S3;
FIG. 3 is an example of a schematic representation of multi-mode stations supporting communication within a communication cell according to the present invention (where Sx is a subsystem, SxR is a relay for the Sx subsystem);
FIG. 4A is a packet structure with a physically stable header according to the present invention;
FIG. 4B is an example of a control field stable at the physical level of the header and an exemplary modulation method in the data / subsystem field (4-PIM in the SI system) according to the present invention;
FIG. 5 is a block diagram of an optical wireless communication system operating in a single mode according to the present invention;
FIG. 6 is a block diagram of a system with an adaptive data rate (variable data rate), showing in particular functional blocks for evaluating channel quality and frame / symbol synchronization (recognition of a synchronization signal), according to the present invention;
FIG. 7 is a simplified state transition diagram of the main state machine (FIG. 6) for a system using a data rate reduction of RR = 1, 2, 4, and 8;
FIG. 8 is a data rate interaction mechanism according to the present invention, in conjunction with the standard CSMA / CA (Carrier Control Multiple Access and Conflict Prevention) protocol;
FIG. 9 is an example of a set of data rate connectivity tables according to the present invention;
FIG. 10 - user network information obtained from data rate connection tables (FIG. 9);
FIG. 11 is a block diagram of a portion of a receiving station for frame / symbol synchronization (key 123 in FIG. 12) according to the present invention;
FIG. 12 is a block diagram of a portion of a receiver according to the present invention;
FIG. 13 is a simplified state transition diagram of a receiver containing a function (FIG. 12) for a system using RR = 1, 2, 4, 8 through RR _max ;
FIG. 14 is a schematic illustration of a sync word for 4-PIM according to the present invention, which is composed using two sync words.

general description
A system for wireless optical communication typically comprises at least one station that serves as a transmitter and a second station that serves as a receiver. The transmitter contains a light source, for example, a light emitting diode (LED) or a laser diode, and the receiver contains a photodiode. The word "station" is hereinafter used as a synonym for all types of computers, terminals, repeaters, peripheral devices, etc., which can communicate with each other. The present invention can also be used for communication within a single-mode communication system, however, it should be noted that the present invention is particularly well suited for communication in single-mode systems.

 Typically, infrared (IR) optical radiation is used for wireless optical communication, and the term "infrared communication" is also used in this description, although the present invention is not limited to a specific optical spectrum.

 1) Sustainable title of the invention.

 The present invention provides a header (described in more detail below) that is robust in the sense that it can be recognized and decoded using all receivers located within the same communication cell (for example, in an office space) even under conditions when communication is impossible. In addition, the invented stable header allows you to maintain communication between different stations coexisting in the same communication cell, that is, communication between stations operating in different modes is valid, it is supported and coordinated. The inventive robust header contains a preamble for obtaining synchronization, carrier detection, and relative synchronization at a receiving station. It additionally contains a unique synchronization sequence to guarantee absolute synchronization of the transmitter and receiver after recognizing the synchronization sequence in the receiver. In addition, it contains a fixed-length control field that is transmitted after the synchronization word. This control field is used to obtain information on the supported and / or expected user data rate, data block size, modulation method, and other relevant information about the (sub) system at the receiving station. In particular, it may also contain information that is used to identify the recipient (s) (address list) of the data or information that follows the persistent header.

 2) Compatibility / coexistence of various transmission schemes.

 Currently, in multi-mode systems, signals transmitted by a transmitter of a transmitting station in a certain mode (for example, system S1, see Fig. 1) cannot be received or recognized by receivers of any receiver module in another mode (for example, subsystem S2) and vice versa.

 As indicated below, a new resilient header, which is also referred to as a physically stable header (UHF), is designed to eliminate the incompatibility of coexisting systems. In addition, the structure of the UFUZ, the methods of its application, the respective transmitters and receivers, and the resulting multi-mode wireless optical communication system are described.

 This is important because each station participating in the communication within the communication cell transmits the UHF, and if necessary transmits a data or control packet. Each station inside this cell belongs to a set of stations forming a subsystem (Sx) corresponding to a specific application, as shown in FIG. 1. If the station is equipped to participate in more than one type of communication subsystem, then it is an element of all relevant subsystems. An example of a multi-mode receiver 35 according to the present invention, a station supporting the subsystems SI, S2 and S3, is shown schematically in FIG. 2. It contains an amplifier 30 and a photodiode 36, which form part of an analog data preprocessing device and three band-pass filters 31-33, for example, to filter the corresponding signals received via the optical communication channel 14. Filter 31 (WBW) is designed to isolate the signals used for communication of subsystem S2, filter 32 (VBW) is used to communicate subsystem SI and filter 33 (SBW) for subsystem S3. The outputs of these filters 31-33 can be connected to the digital processing module 34.

 Station 41 (A) (Fig. 3) belongs to the subsystems SI and S2, where, for example, SI consists of stations 41, 42, 43, 44, 46 (A, B, C, D and F), and S2 consists of stations 41 and 42 (A and B). A station may also provide repeater functionality for some subsystems. Station 46 (F) (Fig. 3), for example, performs only the relay function for S1, which is denoted by S1R, station 42 (B), in addition, is able to function inside S1, S2 and S3 as a terminal and also acts as a relay for SI (SIR). The size of the communication cell 40 is determined using the maximum achievable transmission distance of the most stable of the participating subsystems. Usually, it is a subsystem operating at the lowest data rate, for example, the S4 subsystem, which provides pager functions.

 The Invented Sustainable Header (UFS) 50 is shown in FIG. 4A. UFZ 50 allows a virtual carrier reading (BCH) mechanism based on a channel time conservation scheme. The title 50 of the invention at least comprises a preamble field 52 and a synchronization field 53, which carry a preamble and a synchronization word, respectively. In addition, it contains a control field 59 of a given length. This control field 59 may contain information supporting systems with an adaptive (variable) data rate, as described in pending application PCT / EP 94/01196, published October 26, 1995. Further details on persistent header fields are provided below.

 The network with the participating stations on the basis of UFUZ (multi-mode terminals and repeaters) is controlled by stations that are part of the subsystem with the highest data transmission capabilities over the network. This set of stations is called a dispatch network (DC). In FIG. 3 DS is formed by stations 41, 42, 43, 44 and 46 (A, B, C, D and F), that is, a network with a variable data rate is used as a DS in the example under consideration. Each station inside the UFZ-based communication cell that will participate in wireless optical communication should be at least equipped with a receiver data preprocessing device that allows you to receive and recognize UFS in the modulation scheme used by stations forming the DS.

 The transmission of the UHFS according to the present invention is mainly carried out in two phases.

 Phase 1. Each station within the UFZ range (communication cell 40) has its own data preprocessing device activated to receive the header. A station that wants to transmit data is in a standby state until the DS channel goes into an inactive state, then it sends a UHF, preferably including information for the BCH and the operating mode. Other stations located inside the said cell of communication expect this message and process the transmitted information. If the modulation method is indicated in the stable header control field 59, which is capable of supporting the station, then it stores the BCH information and remains active for two phases. On the other hand, it can set timeout counters based on information received by the BCH and, for example, switch to power saving mode. The BCH information, that is, the reserved time for the wireless channel, is obtained from the data rate, block size, and operation mode information indicated by the transmitting station by transmitting the control field 59.

 Phase 2. Stations in the active reception mode switch their receiver data preprocessing devices to the mode indicated in the received control field 59 and determine the received destination address (destination) transmitted in the mentioned information field 59 to determine if the message is intended them. All stations that do not have a destination go into power saving mode and, for example, wait until the reserved channel time has elapsed. Station (s) - the destination can now communicate with the initiating (transmitting) station in its own mode for as long as the channel has been reserved.

 As described above, the present concept not only takes into account reliable reading of the carrier in all receivers of the communication cell, including those with the lowest signal-to-noise ratio (SNR) resource, but they are also informed how long the channel will be occupied by the data block that will be transmitted. This method, known as Virtual Carrier Reading (BCH), has been adapted and optimized for use with the current concept of a robust header.

 3) Stable header for systems with phase-pulse modulation (PIM).

 Further details of the robust header are provided as an example. UFUZ 50 (Fig. 4A) should be transmitted in a format corresponding to the modulation method of the DS. UFUZ 50 should decode each station intended for work inside the communication cell based on UFUZ. In addition, a stable header should help to reduce the so-called hidden problems of the terminal, that is, a header structure must be defined that is subordinate to the appropriate modulation method of the DS and which is suitable for operation even under such critical conditions when the DS (for example, DS = S1 ) directly becomes inoperative for data exchange, while some of the subsystems (for example, pager functions with a low data rate) remain operational.

 An example embodiment of a sustainable header in accordance with the present invention.

 For a system with a variable data rate, PIM is the circuit with the highest efficiency. Consequently, the structure of UFUZ is described for a system based on PIM, with specific problems associated with it and proposed solutions. Details of the corresponding control field 59 are shown in FIG. 4B. The following description assumes a communication system based on a specific FIM data symbol format (i.e. 4-FIM symbol, where two information bits are transmitted by one symbol), however, with appropriate adjustments, the method is equally applicable to a system using different data symbol formats (for example, L -FIM characters, where log2 (L) information bits are transmitted per character).

 In this embodiment, various parts of the stable header field 50, coding methods, and the number of transmitted symbols are given for a variable data rate system based on a 4-FIM symbol format. The SI subsystem (Fig. 1) functions as a DS.

1. PREAMBLE 52
Preamble 52 is used to obtain relative receiver timing. To achieve this, transmit the preamble 52, which is a periodic sequence of pulses. The receiving station, which knows how many slots are contained in each frame, after a certain period of time can detect the period of the mentioned sequence of pulses. In addition, the receiving station adjusts its slot clock phase (clock recovery) using a clock recovery circuit (phase lock PLI cycle). It is recommended to use a pulse sequence, which leads, if possible, to a quick adjustment of the phase of the slot clock. For this purpose, pulse sequences 10001000 ... or 10000010 ... are proposed, each of which can be used for both 16-FIM and 4-FIM formats. The use of different sequences also allows for simple (controlled) transmission of information through a single preamble.

2. SYNC 53
The sync word 53 may comprise an encoded binary sequence (e.g., a 32-bit sequence) with selective autocorrelation and low cross-correlation with the preamble sequence 52. In the present example, each bit is placed in four slots to maintain the same duty cycle as the preamble sequence 52: if the bit is “1”, then the pulse is on the first slot of the 4-FIM symbol: if it is “0”, the pulse is placed in the third slot. Both slots are checked during reception for impossible bit combinations in order to improve the result of processing the clock signal (for example, correlation). Further details are described with reference to FIG. 6 and 7. Another synchronization word composed of two separate synchronization words is shown in FIG. 14.

3. USP (Decrease in transmission rate) 54
The USP field 54 is a word (e.g., four-bit) containing the USP parameter to reduce the data rate of the next data / subsystem field 51 (i.e., data containing the field) when the subsystem uses repetition coding. The data rate reduction parameter shows how often each pulse phase modulation symbol of the data field 51 / subsystem 51 is repeated.

 For other subsystems, it can serve, for example, as an indicator of the data transfer rate. The USP field 54 is transmitted as two characters in 4-FIM format using repetitive coding.

4. USP ^* (Recommended data rate reduction) 55
USP * field 55 is a word (for example, four-bit) containing the recommended USP * coefficient for reducing the data transfer rate, as obtained from the estimated channel quality (error repetition rate) while receiving the last data block (for subsystems supporting channel quality estimation). It can be encoded in the same way as USP.

5. RB (Block size) 56
The block size subfield 56 contains a series of data blocks that will be transmitted in the data / subsystem field 51. To reduce costs, only a limited number of different block sizes can be determined, for example, 16 different block sizes can be detected by a corresponding mapping of four bits. Block size subfield 56 may be encoded in the same manner as USP symbols.

6. Mode 57
The subfield 57 of the operating mode gives signals to the receiver (s), in what modulation manner the data will be transmitted in the data / subsystem field 51 and whether the data / subsystem field 51 will be transmitted further through the repeater. The number of bits of the operating modes is chosen large enough to fit future subsystems. Symbols can be encoded in the same way as USP symbols.

 The information transmitted in the USP field 54 and the RB field 56 can be used to determine how long data will be transmitted in the data / subsystem field 51. This information is important for receiving stations that are not in the address list, because they should be aware of how long the optical channel will be occupied, that is, how long they will remain in silent mode.

 To minimize the effects of direct current or low-frequency components, analog pre-processing devices for IR receiver data are usually designed to operate on alternating current. Therefore, a changing symbol duty cycle will require an expensive (analog) means of restoring the DC component. In addition, the amplitude of the transmitter pulse and the duty cycle of the symbol should be selected in accordance with the average and peak power limits imposed on IR light sources, which are usually light emitting diodes (LEDs) or laser diodes emitting in the IR spectral range.

 The UFUS, proposed as an example, uses a timing pulse diagram with the same duty cycle as the 4-FIM data symbols to limit power. The same duty cycle can also be performed in the synchronization field 55, rather than using a different duty cycle, as is usually done. An additional advantage when using UFUS is that DC signal recovery is not used, as suggested above. If the resulting DC signal offset affects the operational efficiency to the extent that compensation seems to be necessary, then the threshold control method illustrated in FIG. 12.

 Depending on the transmission scheme used, you can use an algorithm that determines the quality of the channel so that you can get the highest possible data rate. Since the beginning of the data field / subsystem is precisely known to all actively receiving stations of the communication cell (s), these stations can determine the quality of the channel by analyzing the data received in the data / subsystem field 51. The maximum possible data rate and other information related to the state inside the communication cell can be displayed in such a way that the user will receive information at what speed he can transmit data.

 According to the present invention, it is possible for a stable header to be used as such to exchange information between certain stations in a multi-mode communication cell if other communication methods are not acceptable. In this case, the transmission capacity of information is very limited, however, some information can be transmitted.

 In some cases, it may be preferable to transmit access priority information within the control field 59, which is needed to distinguish the information of the first communication cell from the information of the second, interfering communication cell. Such a measure makes it possible to ensure the coexistence of various simultaneously active communication cells (picocells) within a single cell 40, each of which requires full channel capacity, ignoring the information on reading the virtual carrier contained in the UHF that comes from other picocells. This can be done because the signal intensities inside such a picocell are high enough to permit the capture of a communication channel, and thus remain unaffected by interference from other remote picocells. A picocell may contain two or more mobile or fixed stations and may also contain a station for accessing wired local area networks (LANs).

 In FIG. 5 shows a first embodiment of the present invention. According to this embodiment, the UHFD is generated if the payload (binary data) or information needs to be transmitted through the optical channel 14. The UHFD is generated by the header generator 10, while the binary data is processed and encoded by a suitable encoder 11 used to display the binary data in FIM characters. In addition, you can use a system with forward error correction (not shown).

 In a first embodiment, the encoder is a phase-pulse modulated (PIM) encoder 11. The excitation device 12 of the light emitting diode is excited by signals that must be transmitted to the LED 17. The excitation device 12 of the LED can have up to eight devices output, generating a total optical peak power, for example, up to 2 watts. A photodiode 18 (or matrix of photodiodes) is provided on the other side of the optical channel 14, which receives signals from the LED 17. The signal at the output of the photodiode 18 processes an analog device 13 for preprocessing the data of the receiver, for example, containing an amplifier and an automatic gain control (AGC) circuit. It is preferable that the analog data preprocessing device 13 be designed with a safety latch in place to prevent ambient light from entering with high intensity, and the AGC circuit has a large dynamic range within 70 dB. Excluding soft demodulation in order to avoid complex multi-bit processing, the amplitude of the controlled analog signal obtained using the data preprocessing device 13 of the present embodiment is supplied to the threshold device 15 (comparator), which generates a binary, time-continuous, output signal. The output signal is then processed by digital processing module 16. The latter, at least, performs such functions as carrier registration (carrier detection), restoration of slot synchronization and the corresponding ones, as well as absolute synchronization of the data symbol by analyzing the fields 52 and 53 of the UHF. Depending on the information transmitted in the UHFD control field 59, the digital processing module 16 may also include retrieving the user data rate and data block size, decoding the data, and estimating the quality of the channel. An example of a receiver digital processing module 16 is described in the description with reference to FIG. 6.

In FIG. 6 shows details of an embodiment of a digital receiver processing module 16. After receiving the preamble frame from the comparator 15, the first clock signal of the slot is restored by means of a digital phase synchronization circuit 60 (DFS) with a variable gain loop and preprocessing, in order to better cope with the PIM noise signals. The phase estimates and the subsequent phase adjustments are based on n-one-time (for example, n = 8) over-quantization by means of a quantizer 61 of the slot from the binary evaluated signal obtained by the threshold device 15. The DSP gain circuit is controlled by the ground state machine (MOS) 63. The operation of the MOC 63 is shown in FIG. 7. It is preferable that the gain is high at the beginning of the reception of the preamble in order to obtain a fast phase capture and reduce the likelihood of disconnecting the DSC 60. To protect the local phase of the clock from the standby mode while tracking the received phase of the signal, the loop gain is changed to a lower value after the carrier and the preamble data are correctly detected by the carrier registration scheme according to the present embodiment. The DSC 60 is blocked at the leading edge of the input signal, and the reconstructed clock (for example, 4 MHz) of the slot is delayed to serve as a reference signal for the slot quantizer 61. A phase resolution of 45 ^o clock quantization is sufficient to quantize a slot without compromising performance. The remaining parts of the circuits are synchronized with the restored slot clock (for example, 4 MHz). Symbol synchronization is performed in two stages. The sequence of events follows from the simplified state diagram of the MOC 63 (Fig. 7). Following the detection of the carrier, the carrier registration circuit searches for the configuration of the corresponding preamble and informs the MOC 63 when a valid pulse sequence of the preamble 52 has been found. In turn, the MOC 63 unlocks the symbol clock circuit inside the clock recognition unit 62 by receiving a trigger signal aligned with the preamble phase (position of the preamble pulse), in accordance with the first slot of a specially encoded synchronization word. From this point in time, the frame synchronization circuit, which is part of the sync pulse recognition unit 62, stores the information found in consecutive 32 symbol frames in a 32-bit shift register inside block 62, the output signals of which are supplied to the correlator (it should be noted that in the present example it is assumed that the sync word has 32 bits). Further details of the clock recognition module 62 are shown in FIG. 11. If the received pulse train, which is fed into the shift register, is subsequently detected by the same and known receiver, then absolute synchronization is achieved, that is, MOC 63 assumes that the start of the fixed-length control field 59 only before the block of FIM-encoded data was found in order to show that absolute synchronization has been achieved, a sync flag is received in the output line 67 of block 62.

 Similarly, you can also use the algorithm and the appropriate sync word 53, which allows you to perform absolute synchronization, even if the received sync word is partially destroyed. An example of such a synchronization word is shown in FIG. 14, and the corresponding receiver hardware is shown in FIG. 11. For example, if the final result of the correlator 112, calculated for each period of the symbol frame where the synchronization pulse can be expected, exceeds a certain threshold Ths (see block 113), then MOC 63 assumes that the beginning of field 59 is found. Sync word 53 may also carry yourself additional information that is addressed later.

 If the beginning of the fixed-length control field 59 is found, then the beginning of the data / subsystem field 51 is also known. Following the present example, where the data / subsystem field 51 is FIM-encoded, all of the following characters are interpreted as FIM-characters. Each field 54-57, as shown in FIG. 4B, is accumulated like a frame (for example, 16 times) in a pulse accumulator 64 and evaluated using a suitable symbol estimation circuit 65. The same procedure can be used to detect data in the data / subsystem field 51, in accordance with the USP information obtained in the control field 59. There are various possible methods for decoding and transmitting information that is transferred to the control field 59. In this case, it is necessary to design the receiver accordingly.

 If the entire data / subsystem field 51 is correctly received, then a trigger signal can be generated to increment the bandwidth measurement circuit, and the data rate counter of the successful packet is reset.

The channel quality estimator 66 monitors the error rate on the IR channel 14. In the present embodiment, a digital channel quality estimator 66 is used because determining the SNR using an analog circuit or measuring the data rate of successful packets is either expensive or too slow and thus less suitable. The channel quality estimator 66 monitors the error rate on the IR channel 14. From this estimated error transmission rate, it is possible to determine the recommended data rate reduction coefficient (USP ^* ) for future data fields 51 / subsystems.

 For a quick feedback response to the transmitter of the transmission station, transmission error counting can be performed at the level of the PIM symbols, and not at the level of the data field / subsystem. Obviously, incorrect PIM symbols (i.e., 0, 2, 3, ... pulses per frame) are counted by observing each individual received symbol. The ratio of the observed symbol errors to the total number of symbols received in the data / subsystem field 51 is then taken as a quantitative measure of the instantaneous error transmission rate on the IR channel 14.

 The following examples show patterns for matching data rates. The maximum possible data rate, which essentially reaches the transmission of a packet free of errors (erroneous packets are repeated at the level of the average access control protocol), can vary over a wide range in a short period of time.

 Stations that can adapt their data rate need to mutually exchange their current suitable data rates. In order to prevent retransmissions, this data rate information exchange can be performed inside the error feedback message.

According to the proposed method of coordinating the data transfer rate, each station transmits the recommended decrease parameter (USP ^* ) of the data transfer rate, based on the last received data frame in the corresponding UFZ field. This is shown in FIG. 8, as a procedure for negotiating the data rate that can be performed in the CSMA / CA protocol (multiple access with carrier control and conflict prevention) using send-to-send / confirmation-readiness-transfer (STP / GWP). The proposed data rate matching is based on the following principles:
Channel quality is estimated based on all received data and control frames for which the total number of L-PIM symbols exceeds 128.

 The data transfer rate, especially for control frames, is coordinated (adapted) with a large margin in order to prevent unnecessary retransmissions caused by damaged GWP frames or acknowledgment frames (MTFs). Relays are appropriate when conflicts occur and when the SNR parameter (signal to noise ratio) is high. In cases of low SNR channel, repetition coding (i.e., an increase in USP) is more efficient.

 A frame with a mandatory PDT is introduced to transmit the recommended symbol for reducing the data rate and to ensure that only one relay of the data block will be needed.

 To alleviate the carrier registration problem, a network allocation method (similar to the method in IEEE 8.2.11) can be used. The reserved information must be transmitted with the highest possible redundancy. For an adaptive data rate transmission system, it is proposed to calculate the actual channel reservation time using a data rate symbol (USP), and transmit the data block size (RB) in the control field 59.

 The initialization of the network inside the communication cell (see, for example, Fig. 3) can occur as follows. One station with S1 is able to initiate a network start by transmitting a special control frame that is defined for each subsystem. This occurs first for S1, then the initiating station is in a standby state until it receives responses from all other stations S1. The initiating station continues to operate in the same manner for S2 and S3. Upon completion, all other stations continue to work in the same way - each for its respective subsystems according to the protocol of access to the selected channel. At the end, all stations transmit their list of approved connections to each station on their list. Using this method, each station receives a status map of each possible connection in the network, including initial channel quality information. These cards are referred to here as data rate / connectivity state cards. Based on this information, terminals hidden inside a communication cell can be identified. In addition, information that is important to known receiving stations can also be transmitted during network initialization. The length of the control field 59, details on the subfields of the control field 59, and the like can be determined during network initialization.

 Both for user information and for network management, it is necessary to store in each station and display to the user in an effective way some types of tables 90-92 data rate / connectivity (TSS). The information of such a data rate / connectivity table can also be made available to the application if necessary. Examples of TCC 90-92 are shown in FIG. 9, these tables are composed of data rate / connectivity state maps. TCC can be used for user information, as shown in FIG. 10, network recognition, alternative routing through repeaters. In addition, TCC helps to increase network bandwidth, since the original data transfer rates are known. After some time, TCC may be required for further updating, because some station S1 adapted to the data rate, physically moving stations or new stations try to connect, for example, to the network. In the latter case, you can perform a different initialization procedure.

 An example of the displayed user network information for station D is shown in FIG. 10, it shows that station B cannot receive station D, that is, station D is a hidden terminal for station B. In the presented example, the display device 101 shows a corresponding message recommending correction of the situation. In addition, the display device 100 shows that communication between stations D and A is limited by a relatively low data rate. As shown in the second display device 101 (FIG. 10), it follows that it takes two minutes to fully transfer a 1.6 MB file. Thus, user D has a recommendation to move closer to station A.

 In high data rate systems, overhead overhead can be avoided as follows. Stations operating in a subsystem that uses low-speed transmission (for example, the S4 pager function) require much lower SNR and, thus, have higher noise immunity to noise (higher than 20 - 30 dB) than the selected DS (DS = S1 ) When using repetitive coding algorithms and a suitable symbol synchronization scheme, it is possible to develop a UFUS that has a sufficiently high error tolerance for low-speed data transmission. However, the required length of such a header will significantly reduce the efficiency of the DS and other high-speed subsystems. An example of such a header with a longer synchronization word used to obtain higher stability is described with reference to FIG. fourteen.

 Studies of the relationship of complexity (cost) and transmission efficiency to system error tolerance led to a dual-mode UFZ scheme. The so-called low-speed mode with a decrease in UFUZ (N-UFUZ) supports a decrease (USP) of data transfer rates up to eight in the transmission mode of the DS. The more expensive mode of high-speed reduction of UFUZ (V-UFUZ) allows you to maintain communication with the maximum value of USP 64. V-UFUZ supports subsystems operating at SNR up to 20 dB, which is lower than the required SNR necessary to maintain an acceptable probability of success for a packet over the DS channel working without reducing the data transfer rate (i.e., USP = 1). The networks in the DS (S1) and with the high-speed (S2) transmission mode usually use N-UFUZ, and activate the B-UFUZ when the low-speed transmission (S3) and / or the remote control function (S4) is detected inside the communication cell. Using this scheme, and assuming a stable direct carrier registration scheme, activation occurs in V-UFUZ stations, with each station within the V-UFUZ range, the upcoming N-UFUZ traffic can be announced, even in the case where the header itself cannot be correctly decoded. Network initialization and initial channel quality assessment for DS stations are performed in the B-UFU mode.

 To achieve high reliability (error tolerance), receiving stations can determine the heading mode (N-UFUZ) or (B-UFUZ) by analyzing the periodic pattern of the received preamble using the pulse averaging method, which makes up the average procedure (this is not the main use of the preamble, according to this invention). For example, averaging a stream with a received preamble up to sixteen times or more allows reliable detection of the mode with a decrease to SNR equal to 0 dB (where reliable detection of the data field 51 requires an RR of 64). For example, the pulse train of the preamble 10001000 ..., which has a period of eight slots (two 4-FIM characters), can be used to transmit a signal whose header mode is B-UHF, and the pulse train of the preamble 10000010 ..., also having a period equal to eight slots, can transmit a signal, the heading of which is H-UVB. The same scheme used on the receiver side for detecting the header mode can be used for stable detection with direct carrier registration.

 Frame synchronization is required to determine the beginning of the control field 59 and the beginning of the next (possibly encoded repetition) data / subsystem field 51. It is also the basis for proving the boundaries of PIM symbols if the transmission of encoded FIM is used. For these purposes, immediately after preamble 52 (see FIG. 4A), a special pulse pattern 53 can be transmitted. General solutions use forbidden FIM symbols (for example, more than one pulse per symbol) in order to make synchronization word 53 uniquely detectable, or they detect a suitable binary sequence (showing the necessary correlation properties) through a correlator circuit. However, it may be required that a single synchronization word 53 operating under B-UHF conditions be excessively long, requiring a correspondingly long correlator circuit. An additional problem is that the synchronization word 53 must be inside the selected PIM format in order to comply with the average power limit imposed by the IR light source (duty cycle) and maintain continuity at the received DC signal level.

 A solution that maintains a duty cycle, avoids shifting the level of the DC signal and reduces the required correlator length under the conditions of the B-UFUS, will be described below with reference to FIG. 11. To compose a suitable longer sync word, it is better to use two relatively short sync words than a long single sync word 53. The first of them is placed inside the selected PIM symbol format in such a way that the corresponding first correlator 110 produces ideally, that is, in the absence of noise, an output signal corresponding to the second determined synchronization word. The output of this first correlator 110 is then used as an input to the corresponding second correlator 112, which provides symbol / frame synchronization information after applying threshold operation 113 to its output. This circuit significantly reduces hardware overhead for synchronization detection. In addition, this scheme is compatible with the (N-UFUZ) or (B-UFUZ) dual header transmission mode.

The two-stage synchronization scheme described below can be expanded so that additional information can be transmitted along with the synchronization information. For example, the second synchronization word is used in 4 different ways (for example, B ₁ = {+ 1, + 1, - 1, + 1, - 1}, B ₂ = {- 1, + 1, - 1, + 1, + 1}, B ₃ = {- 1, - 1, + 1, - 1, + 1}, B ₄ = {+ 1, - 1, + 1, - 1, - 1}) so that there are 2 different two-stage correlators can distinguish 4 resulting composite synchronization sequences (that is, in this case, it is assumed that each version of the second synchronization has an additional version). Four resulting sequences at the output of the first correlator should have good autocorrelation and cross-correlation characteristics. Using this scheme, 2 bits of information can be transmitted along with synchronization information. Similarly, a circuit can be generalized, for example, by including the first synchronization word in it to transmit additional bits of information.

 Below are additional details on a possible two-step synchronization scheme and symbol / frame synchronization for low SNR. In FIG. 11 shows the aforementioned two-stage correlation scheme for a frame and a synchronization symbol in the case of low SNR. In this example, the first correlator 110 is configured to respond to a binary-valued first synchronization word. The output of the first correlator 110 is estimated threefold (+ 1, 0, - 1) using the circuit 111 and provides an input for the second correlator 112. The second output of the correlator is evaluated binary (0, + 1) using the circuit 113 and the memory element 114 controlled by using the clock pulse of the FIM system slot, and the Sync-pulse-flag signal at the output 67 represents synchronization information.

 Another embodiment of a receiver according to the present invention and corresponding to a state diagram is shown in FIG. 12 and 13. This receiver has the necessary properties to obtain a fast (in an environment with high SNR), as well as stable (with a low SNR) carrier detection function. In FIG. 12, two threshold detectors 121 and 124 are shown. The last threshold detector is for fast carrier detection, while the first threshold detector is for stable detection of 123 headers, as well as for detecting 122 data. The robust header detector 123 provides a Preamble_flag signal in a function block 126 that provides a carrier protection signal to protect the Speed_Carrier_flag signal generated by the fast carrier detector 125. Although the Speed_Carrier_ flag signal provides quick carrier detection by the average of good SNRs, the Preamble_flag signal provides a slower signal for carrier detection at low SNR. Combined together two signals (Speed_Carrier_flag, Preamble_flag) provide stable as well as fast carrier detection. Block 126 generates a Carrier_ Flag signal (indicating successful carrier detection) from these two signals. In cases where the Preamble_flag signal is absent within a certain period of time after the excitation of the Speed_Carrier_flag signal, an incorrect alarm appears and the signal Speed_Carrier_ flag (and thus the signal Carrier flag) is returned to its initial state through the signal Speed_Carrier_Reset.

 The persistent header detector 123 generates flag Header_flags. Block_size, Clock_flag, USP, L (mode) and possibly others depending on the fields transmitted in the control field 59 with other receiver functions (not shown).

Since knowledge of the USP after receiving the control field 59 inside the stable header 50 indicates the quality of the channel (SNR), this information, together with information about the modulation method, can be used to adjust the threshold value V _{TH2 of the} comparator 121 to the optimal value when receiving the data / subsystem field 51. (N-bit feedback from 123 to 120). Threshold V _{Th1 of} comparator 124 is selected for optimal fast carrier detection.

 In FIG. 14 shows a synchronization word that consists of two shorter synchronization words (sequence 1 and sequence 2). This drawing shows how a PIM transmitter according to the present invention composes such a long synchronization word from the first word (S) and the second word (B). It is further shown in which order the synchronization word is transmitted within the frames of the 4-FIM symbol. This long sync word is composed of two shorter as well as similar sync words that are suitable for use if the quality of the transmission channel is poor. Thus, this symbol / frame synchronization method is well suited for performing a robust header in practice. Correct synchronization is possible (due to the detection of correlation) even in the case when only a part of the synchronization word is received correctly.

 According to the present invention, the user can transmit encrypted data within 51 data fields / subsystems, however, the robust header 50 will never be encrypted so that all stations can understand when it is received from any participating station. The concept of the invention allows encryption of information transmitted in the data / subsystem field 51, since there are no restrictions on which data / subsystem field should look the same.

 However, it also makes sense to include in the subfield control field 59 (similarly, access priority information or operation mode fields), which can be used to display the destination (receiving station), and possibly other stations that follow the d field data / subsystems will be transmitted in encrypted mode (usually encryption is performed on top of the physical layer).

 In a more general form, it is possible to define in the control field 59 the “common” subfield that is known to each station from those available there (including position and length), but the value of this content is known only to a subset of the stations. The inclusion of such a common subfield in the control field 59 of the stable header 50 shows that the concept of a stable header allows even a certain individual degree of freedom without compromising the main intention, namely, what can be understood by everyone and, in particular, under very poor channel conditions.

 The following are examples of various embodiments of the present invention.

 1. The hardware according to the present invention can, for example, be integrated into a computer board that can be connected to the computer bus by installing it inside the computer case, or which can be connected to a connector (for example, as a board of the International Board Manufacturers Association standard memory for personal computers (PCMCIA)) provided in the said case.

 2. Similarly, a real transmitter / receiver, which should later be connected to a computer, can be implemented in a separate case.

 3. In addition, the transmitter / receiver according to the present invention can be integrated into a peripheral device (for example, a printer). In some cases, a lite version is sufficient, since usually a peripheral device, such as a printer, for example, only receives data. Only a limited amount of information usually goes back to the station that requested the print job. In such cases, it may be sufficient only to transmit a header that is physically stable and some information in the header control field.

 4. The circuit in accordance with the invention can also be made in the form of microcode that runs a digital signal processor or other machine having special-purpose hardware.

Claims (38)

 1. A method for providing wireless optical communication between a transmitting station and a first receiving station capable of receiving modulated data using the first modulation method, and a second receiving station capable of receiving modulated data using the second modulation method, characterized in that the transmitting station performs the preamble containing frames that form a periodic sequence of pulses with a certain period, the number of slots per frame and the content of the frame, which is known receiving stations and the transmitting station optically transmits a train of pulses, the receiving stations detect the carrier based on the sequence of received pulses, each receiving station determines the period of the train of pulses to obtain relative synchronization and each receiving station sets its clock to the phase of the slot of the received train of pulses and synchronizes the incoming a sequence of pulses through the shift register, the transmitting station ne gives a unique synchronization word aligned with the period, and a unique synchronization word is known to the receiving stations, each receiving station correlates the pulse sequence in the shift register with a unique synchronization word known to this station to ensure absolute synchronization with the transmitting station after recognizing the synchronization word, the transmitting station indicates a control field of a predetermined length and structure that the first or second modulation method will use n for data transmission in the data / subsystem that all receiving stations which are able to maintain an appropriate modulation method is waiting for the data.  2. The method according to claim 1, characterized in that the receiving station supports various modulation methods and switches its receiver to the modulation method specified in the control field.  3. The method according to claim 1, characterized in that the control field or data field / subsystem contains a list of data destinations.  4. The method according to claim 1, characterized in that as the modulation method for data transmission using phase-pulse modulation.  5. The method according to claim 4, characterized in that the control field contains a data rate reduction field that indicates to the receiving station how often each phase-pulse modulation symbol of the data field / subsystem will be repeated.  6. The method according to claim 1, characterized in that the control field contains a recommended data rate reduction field for transmitting a recommended data rate reduction, which is used to agree on the data rate that is most suitable for communication.  7. The method according to claim 6, characterized in that the recommended decrease in the data rate is determined on the basis of pre-established rules that take into account the actual transmission rate of errors that occur during communication between the transmitting station and the receiving stations.  8. The method according to claim 1, characterized in that the control field comprises a block size field that indicates the number of data blocks to be transmitted in the data / subsystem field.  9. The method according to claim 1, characterized in that the control field contains an operating mode field that contains information used to indicate to the receiving station which modulation method will be used.  10. The method according to claim 9, characterized in that the modulation method is a 4-slot phase-pulse modulation, 16-slot phase-pulse modulation or modulation methods defined in the standard of the Association for infrared data transmission technology.  11. The method according to claim 1, characterized in that the control field contains information indicating to the receiving station whether said data will be transmitted by this receiving station.  12. The method according to claim 1, characterized in that the control field contains information that allows anyone who is not addressable or unable to support the modulation scheme specified in the control field of the receiving station to determine how long the data transfer will take place in order to ensure such received stations in silent mode during this transmission.  13. The method according to claim 1 or 4, characterized in that each receiving station uses a synchronization word recognition algorithm even in the presence of potential errors caused by damage to the optical connection.  14. The method according to item 13, wherein the synchronization word consists of two synchronization words, and recognition at the receiving station can be divided into two stages.  15. The method according to claim 1, characterized in that the receiving station and / or transmitting station determine the speed at which data will be transmitted.  16. The method according to claim 1, characterized in that the receiving station determines the recommended data rate of the data, taking into account the current quality of the communication channel between the transmitting station and the receiving station, and the recommended data rate is determined based on accurate knowledge, the moment the control field ends and thus the start of the data field / subsystem.  17. The method according to p. 15 or 16, characterized in that information about the data transfer rate and / or recommended data transfer rate is available to the application program or end user.  18. The method according to claim 1, characterized in that the control field contains access priority information that allows at least two coexisting communication subcells to be inside the communication cell.  19. The method according to claim 1, characterized in that the control field contains information that supports data encryption.  20. System for wireless optical communication, adapted to use multi-mode packets for wireless optical communication between the transmitting station and the first receiving station with the ability to receive data that are modulated using the first modulation method, and the second receiving station with the ability to receive data that is modulated using the second modulation method, characterized in that the multi-mode packet contains a data field / subsystem of phase-pulse modulation, which carries data e, which will transmit, and the preceding physical-stable header that can be decoded with all receiving stations, said physical-stable header containing a preamble with frames forming a periodic sequence of pulses with a certain period, the number of slots per frame and the content of frames that is known to the receiving stations, a unique synchronization word known to the receiving stations, a control field with a predetermined length and structure, the contents The present operation mode information indicating which modulation method is used for data transmission, and the field of reducing the data rate, which indicates the receiving stations, how often to repeat each symbol pulse-position modulation Data field / subsystem.  21. The system for wireless optical communication according to claim 20, characterized in that in the multimode package the control field or data / subsystem field contains a list of destinations for the data.  22. The system for wireless optical communication according to claim 20, characterized in that in the multimode package the control field contains a recommended data rate reduction field for transmitting recommended information on reducing the data rate, which is used to agree on the data rate that is best suited for communication.  23. The system for wireless optical communication according to claim 20, characterized in that in the multimode package the control field contains a block size field that shows the number of data blocks that will be transmitted in the data / subsystem field.  24. The system for wireless optical communication according to claim 20, characterized in that in the multi-mode packet the control field contains information that indicates to the receiving station whether the data will be relayed by this receiving station.  25. The system for wireless optical communication according to claim 20, characterized in that in the multi-mode packet the control field contains information that allows all receiving stations that are not addressed or incapable of supporting the modulation scheme indicated in the control field to determine how long they will execute data transmission, in order to ensure that these receiving stations are in silent mode during this transmission.  26. The system for wireless optical communication according to claim 20, characterized in that in the multimode package the control field contains information that supports data encryption.  27. A transmitter for wireless optical communication with a first receiving station with the ability to receive data that is modulated using the first modulation method, and with a second receiving station with the ability to receive data that is modulated using the second modulation method, said communication initiating the use of physical the level of the header, which can be decoded using all the receiving stations, characterized in that it contains a header generator that generates a preamble, i a part of a header that is stable at the physical level, with frames forming a periodic sequence of pulses with a certain period, the number of slots per frame, and the content of the frames that is known to the receiving stations, means for obtaining a unique synchronization word that is part of a header that is stable at the physical level and is known to the receiving stations, a means for obtaining a control field with a fixed length and known structure, which is part of a physically stable the header, while the control field indicates the appropriate modulation method that will be used to transmit the data, means for modulating the data to be transmitted, and means for transmitting the pulse train, followed by a unique synchronization word aligned with the pulse train, control field and modulated data.  28. The transmitter according to claim 27, characterized in that it comprises means for obtaining a list of recipients for the data that will be transmitted, the list of recipients being received inside the control field or the data / subsystem field.  29. The transmitter according to claim 27, characterized in that it comprises means for generating a data field using a previously obtained recommended decrease in the data rate, and transmits to the control field its own recommended decrease in the data rate used to coordinate the data rate, which is better just suitable for communication.  30. The transmitter according to claim 27, characterized in that it comprises means for indicating the number / size of data to be transmitted.  31. The transmitter according to claim 27, characterized in that it comprises means for transmitting a signal to the receiving station whether the data will be relayed using the receiving station.  32. A receiver for wireless optical communication in a multi-mode communication cell with a transmitting station, characterized in that it transmits a physically stable header that can be decoded using all receivers in the multi-mode communication cell and which contains a preamble with frames forming a periodic pulse sequence with a certain period, the number of slots per frame and the content of the frames, which is known to the receiver, a unique synchronization word that is known to the receivers, the control field with a fixed the length and known structure, showing the appropriate modulation method that can be used to transmit data, while the receiver contains means for determining the period of the pulse sequence based on the number of slots per frame and the content of the frames, which it becomes known to obtain relative synchronization, means for detecting a carrier based on a sequence of pulses, means for adjusting a clock of a receiver with a phase slot of a sequence of received pulses, means To synchronize a sequence of pulses received through a shift register, the length of which is determined using a unique synchronization word, means for correlating a sequence of pulses in a shift register with a unique synchronization word known to it in order to achieve absolute synchronization with a transmitting station after recognizing a unique synchronization word, means for determining from the control field whether the receiver supports an appropriate modulation method that will be used A data transmission interface, a means that determines from the received information whether the receiver is a legitimate recipient of the data, and means that allows the receiver to receive data immediately after the end of the control field.  33. The receiver according to p, characterized in that it contains means for switching between one, two or more modulation methods.  34. The receiver of claim 32, wherein the means for achieving absolute synchronization comprises first and second correlators, such that a synchronization word generated using two synchronization words can be recognized in two stages.  35. The receiver according to p, characterized in that it contains means for determining the recommended decrease in the data rate obtained from the channel quality assessment, used to agree on the data rate that is best suited for data transfer.  36. The receiver according to claim 32, characterized in that it comprises means for determining the number / size of the expected data and analyzing the information transmitted in the control field.  37. The receiver according to p, characterized in that it contains means for relaying data if the received information indicates that a relay is required.  38. A multi-mode wireless optical communication system comprising at least one transmitter according to claim 27 and one receiver according to claim 32.

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