Specification

Field of the invention

The invention concerns methods and devices for optical wireless communication, in particular visible light communication .

Background

Optical wireless communication is a form of optical communication in which unguided visible, infrared, or ultraviolet light is used to carry a signal, in particul for data transfer. Amongst other aspects, high data throughput is a key to the success of optical wireless communication.

It is therefore desirable to provide an enhanced optical wireless communication with enhanced data throughput.

Summary

This goal is achieved by methods of optical wireless communication and corresponding devices according to the independent claims.

Regarding the methods, a method of sending optical wireless data comprises parallelizing a digital serial data stream to output a plurality of time synchronized parallel data streams, superposition encoding the plurality of time synchronized parallel data streams to generate a plurality of data signals, summing up the plurality of data signals to form a first signal, sending the first signal as optical wireless data on an optical wireless data link.

Preferably the method comprises spreading and interleaving the plurality of time synchronized parallel data streams to generate the plurality of data signals, summing up the plurality of data signals by varying the plurality of data signals depending on at least one power factor to generate a plurality of output data signals, summing up the

plurality of output data signals to form the first signal. Preferably different power factors are assigned to

different data signals of the plurality of data signals.

Preferably a digital quadrature amplitude modulation produces the digital serial output data stream from encoded user data.

Preferably the first signal is determined as superposition with plurality of layers k:

wherein y _A first signal,

K number of layers,

P _k Power of data signal s _k ,

s _k data signal in layer k.

Preferably the first signal is pre-coded with a pre-coding vector or a pre-coding matrix to generate a plurality of pre-coded signals, and wherein the plurality of pre-coded signals is transmitted as the optical wireless data.

Preferably the method further comprises receiving wireless optical data from at least one sender of optical wireless data, and, depending on the received optical wireless data, determining a channel quality of a channel to the at least one sender of optical wireless data and/or determining the precoding vector or the pre-coding matrix for sending the optical wireless data to the sender of optical wireless data .

Preferably the first signal is sent by a plurality of visible light communication transmitters emitting light of a first frequency or of a first set of frequencies to form a first beam, the first beam having a main steering

direction for sending the first signal on the optical wireless data link to a first visible light communication receiver.

Preferably the first beam is formed so that the light emission of the first frequency or of the first set of frequencies has a minimum in a direction for interference suppression, light of a second frequency or of a second set of frequencies is emitted to form a second beam, the second beam having the direction for interference suppression as main steering direction for sending a second signal to a second visible light communication receiver.

Preferably the method further comprises measuring a

radiation direction of the at least one sender of optical wireless data depending on received optical wireless data, and determining the direction for interference suppression depending on the radiation direction.

Regarding the methods, a method of receiving optical wireless data comprises receiving a receive signal, superposition decoding the receive signal to determine a plurality of time synchronized parallel receive data streams, superposition decoding the plurality of time synchronized parallel receive data streams individually to generate a plurality of receive data signals, serializing the receive data signals to create a serial output data stream.

Preferably the method comprises detecting data in the receive signal, executing a Gaussian approximation based on data detected in the receive signal to determine the plurality of time synchronized parallel receive data streams, de-interleaving and de-spreading the plurality of time synchronized parallel receive data streams

individually to generate the plurality of receive data signals . Preferably the receive signal is determined as

superposition with plurality of layers k:

wherein

Y ' A receive signal,

K number of layers,

P _k Power of data signal s _k ,

Sk data signal in layer k.

Preferably, a feedback signal is determined from one of the receive data streams by de-interleaving the one of the receive data streams to form a de-interleaved signal, by de-spreading the de-interleaved signal to form the receive data signal corresponding to the one of the receive data streams, by determining a difference between a de-spread signal and the de-interleaved signal to form a difference signal, and by interleaving the difference signal.

Preferably the serial output data stream is demodulated by a digital quadrature amplitude de-modulation to determine demodulated output data.

A sender for sending optical wireless data comprises a serial to parallel converter adapted to parallelize a digital serial data stream to output a plurality of time synchronized parallel data streams, a plurality of

superposition encoder (SEC _k , SPE _k ) adapted to superposition encode (208, 210, 310, 312) the plurality of time

synchronized parallel data streams (d _k ) to generate a plurality of data signals (s _k ) , an adder adapted to sum up (212, 316) the plurality of output data signals (o _k ) to form a first signal (y _A ) , and a transmitter adapted to send the first signal as optical wireless data on an optical wireless data link.

Preferably the sender comprises a plurality of spreaders adapted to spread the plurality of time synchronized parallel data streams and a plurality of interleavers adapted to interleave the output of the plurality of spreaders to generate the plurality of data signals, a plurality of multipliers adapted to vary the plurality of data signals depending on at least one power factor to generate a plurality of output data signals, wherein the adder is adapted to sum up the plurality of output data signals to form the first signal.

Preferably the plurality of multipliers is adapted to assign different power factors to different data signals the plurality of data signals.

Preferably a Digital quadrature amplitude modulator is adapted to produce a digital quadrature amplitude

modulation from encoded user data as the digital serial output data stream.

Preferably the sender is adapted to determine the first signal as superposition with plurality of layers k:

wherein y _A first signal,

K number of layers,

P _k Power of data signal s _k ,

Sk data signal in layer k.

Preferably the sender comprises a pre-coder adapted to pre- code the first signal with a pre-coding vector or a pre- coding matrix to generate a plurality of pre-coded signals, and wherein the plurality of pre-coded signals is

transmitted as the optical wireless data.

Preferably the sender comprises a receiver adapted to receive wireless optical data from at least one sender of optical wireless data, and, depending on the received optical wireless data, determine a channel quality of a channel to the at least one sender of optical wireless data and/or determine the precoding vector or the pre-coding matrix for sending the optical wireless data to the sender of optical wireless data.

Preferably the sender comprises a plurality of visible light communication transmitters adapted to emit light of a first frequency or of a first set of frequencies to form a first beam for sending the first signal, the first beam having a main steering direction for sending the first signal on the optical wireless data link to a first visible light communication receiver. Preferably the sender is adapted to form the first beam so that the light emission of the first frequency or of the first set of frequencies has a minimum in a direction for interference suppression, wherein the device is adapted to emit light of a second frequency or of a second set of frequencies to form a second beam, the second beam having the direction for interference suppression as main steering direction for sending a second signal to a second visible light communication receiver. Preferably the sender is further adapted to measure a radiation direction of at least one sender of optical wireless data depending on received optical wireless data and to determine the direction for interference suppression depending on the radiation direction.

A receiver for receiving optical wireless data comprises a superposition decoder adapted to receive a receive signal, superposition decode the receive signal to determine a plurality of time synchronized parallel receive data streams, superposition decoding the plurality of time synchronized parallel receive data streams individually to generate a plurality of receive data signals, and a

parallel to serial converter adapted to serialize the receive data signals to create a serial output data stream.

Preferably the receiver comprises an elementary signal estimator adapted to receive the receive signal, detect data in the receive signal, execute a Gaussian

approximation based on data detected in the receive signal to determine the plurality of time synchronized parallel receive data streams, a plurality of de-interleavers adapted to de-interleave the plurality of time synchronized parallel receive data streams, and a plurality of de- spreaders adapted to de-spread the output of the plurality of de-interleaver individually to generate the plurality of receive data signals.

Preferably the receiver is adapted to determine the receive signal as superposition with plurality of layers k: wherein receive signal,

K number of layers,

P _k Power of data signal s _k ,

Sk data signal in layer k.

Preferably the receiver is adapted to determine a feedback signal from one of the receive data streams by de- interleaving the one of the receive data streams to form a de-interleaved signal, by de-spreading the de-interleaved signal to form the receive data signal corresponding to the one of the receive data streams, by determining a

difference between a de-spread signal and the de- interleaved signal to form a difference signal, and by interleaving the difference signal.

Preferably the receiver comprises a de-modulator adapted to demodulate the serial output data stream by a digital quadrature amplitude de-modulation to determine demodulated output data.

Further developments of the invention can be gathered from the dependent claims and the following description. Brief description of the figures

Figure 1 schematically depicts an exemplary visible light communication system, Figure 2 schematically depicts a first flow diagram for transmitting data

Figure 3 schematically depicts a second flow diagram for transmitting data,

Figure 4 schematically depicts an exemplary assignment of power to signals,

Figure 5 schematically an example of a multiple input

multiple output visible light communication system.

Description of the embodiments Optical wireless communication that operates in the visible band is referred to as visible light communication. The visible band in this context refers to light with a

wavelength between 375 nm and 780 nm.

Optical wireless communication that operates in the

infrared band uses for example a frequency band between 780 and 1600 nm. Optical wireless communication that operates in the ultra violet band uses for example an ultraviolet band between 200-280 nm. The range of the wavelengths that is used in aforementioned definitions of the visible band, the ultra violet band and the infrared band is exemplary. The person of skill in the art readily recognizes that the general concept is

applicable to other definitions of the named bands with different ranges for the wavelengths as well.

The invention is described below for an exemplary

embodiment using visible light communication in the visible band. The person of skill in the art readily recognizes that the principles described below apply to other forms of optical wireless communications as well.

Figure 1 depicts an exemplary visible light communication system 100. The visible light communication system 100 comprises at least one visible light communication

transmitter 102. Each of the at least one visible light communication transmitter 102 comprises for example at least one light emitting diode. The at least one light emitting diode is for example adapted to emit light in the visible band that is pulsed at very high speeds without noticeable effect on the lighting output and human eye.

The visible light communication system 100 comprises at least one visible light communication receiver 104. Each of the at least one visible light communication receiver 104 comprises for example at least one photodiode. The at least one photodiode is for example adapted to receive lighting input in the visible band that is pulsed at very high speeds by the light emitting diodes. The visible light communication system 100 depicted in Figure 1 is adapted for a multi-user multiple input

multiple output visible light communication. This enables parallel data transmission for multiple users. This enhances the data throughput.

In particular, the visible light communication system 100 comprises a matrix 106 of multiple visible light

communication transmitters 102. The visible light

communication system 100 comprises a transmitter 108. All visible light communication transmitters 102 of the matrix 106 may be synchronized by the transmitter 108 with each other and all may contribute to the data transmission for all users in an access area of interest. In some cases, not all of the visible light communication transmitters 102 may be synchronized or used.

In the example of Figure 1, all of the at least one visible light communication transmitters 102 in the matrix 106 are arranged in a plane 110.

The transmitter 108 in the example is adapted to control the matrix 106 for spatial division multiple access.

Spatial division multiple access in this context means that a beam of visible light having the same frequency or the same set of frequencies is used for transmitting data to an individual of the at least one visible light communication receiver 104. The same visible light frequency or set of visible light frequencies may be re-used by the transmitter 108 in another beam to another of the at least one visible light communication receiver 104 in the access area of interest if both are separated by an allowable distance.

As will be described below, different small regions of the access area of interest can make use of the same visible light frequency or set of visible light frequencies if they are separated spatially by the allowable distance. Small regions of the access area of interest that are not

separated by the allowable distance may make use of different visible light frequencies or different sets of visible light frequencies. This way multiple signals are transmittable simultaneously to multiple of the visible light communication receivers 104 in parallel with little or no interference. In Figure 1 a first receiver A and a second receiver B are depicted as examples for the at least one visible light communication receivers 104.

Visible light emitted by different of the at least one visible light communication transmitters 102 of the matrix 106 arrives at the first receiver A in different angles. A main steering direction Θ for transmitting a signal from the matrix 106 to the first receiver A is depicted in

Figure 1 schematically as solid arrow from a center 112 of the matrix 106 through the first receiver A. A first beam 114 for transmitting a first signal y _A to the first

receiver A has a maximum visible light emission at a first frequency or a first set of frequencies in the main

steering direction Θ. The first beam 110 for transmitting the first signal y _A is depicted in Figure 1 as dash-dotted line .

A second signal y _B is transmitted accordingly along a direction for interference suppression θ + φ. The direction for interference suppression θ + φ is depicted in Figure 1 schematically as dashed arrow from the center 112 of the matrix 106 through the second receiver B. The allowable distance is in this example defined by means of an angular difference φ.

The first receiver A comprises a first photodiode facing the plane 110. The second receiver B comprises a second photodiode facing the plane 110. The photodiodes may be facing the plane 110 in parallel or at an angle. The photodiodes are adapted for receiving the first signal y _A or the second signal y _B respectively.

The first beam 112 is shaped to provide a minimum visible light radiation at the frequency or set of frequencies used for the first signal y _A in the direction for interference suppression θ + φ. This reduces the interference with a second beam for the second signal y _B and hence increases the data throughput in a multi-user environment. In the example, a first channel between one of the at least one visible light communication transmitters 102 and the first receiver A and a second channel between the same of the at least one visible light communication transmitters 102 and the second receiver B have different

characteristics. The characteristics depend for example on a distance to the first receiver A or the second receiver B, or on a special geometry of the first receiver A or the second receiver B. Therefore, channel gains of different users are uncorrelated to each other. The first receiver A may by integrated in a first device that includes a first sender. The second receiver B may be integrated in a second device B that includes a second sender. Figure 1 depicts schematically exemplary signal powers in dB for signals sent by the first sender or the second sender respectively. This is depicted as circles with increasing radius from -3dB, -6dB, -9dB, -12dB that are concentric to the respective sender. In this case the matrix 106 may include one or more photodiodes for detecting the signals sent by the first sender or the second sender. In this case the photodiodes may be

connected to a receiver for receiving data transmission from the first sender or the second sender.

The first signal y _A is determined as described below as a Gaussian approximation, so that both the spectral

efficiency and the robustness are enhanced.

In the context of this description, superposition is data overlapping and coding corresponds to spreading,

repetition, interleaving, and other not-mentioned known coding mechanisms. If both are combined together, it is referred to as superposition coding.

Superposition coding allows multiple data streams to share the same resource in time, frequency and/or space. Spreading, repetition or interleaving in a multi-user scenario correspond to a user signature within the

superposition encoding, which enables a receiver to

separate data streams at a receiver. Joint superposition encoding and joint superposition decoding refer to processing or buffering more than one block of a data stream at the time. For example, when forward error correction blocks are used in coding of a data stream, more than one forward error correction block is buffered and processed in joint superposition encoding. For example more than one forward error correction block is buffered and processed by means of allocating different power levels to the data streams. Non-joint superposition encoding refers to individual buffering and processing. For non-joint superposition encoding the spreading/repetition and stream-specific interleaving are processed before the superposition. Joint superposition decoding and non-joint superposition decoding analogously refer to the respective decoding .

A first method for transmitting data of a first user from the transmitter 108 to the first receiver A is described below referencing Figure 2. In a step 202 input data is received or read, e.g. from storage, in particular from transmitter 108.

Afterwards, in a step 204, the input data is encoded by an encoder ENC to generate an encoded data stream es for use in a digital quadrature amplitude modulation modulator Mod. Afterwards, in a step 206, the encoded data stream is modulated by the digital quadrature amplitude modulation modulator Mod. The digital quadrature amplitude modulation modulator Mod is adapted to produce a digital serial output data stream ds .

Afterwards, in a step 208, the digital serial output data stream ds is encoded by a joint superposition encoder SEC and parallelized by a serial to parallel converter S/P. The serial to parallel converter S/P is adapted to output K time synchronized parallel data streams d _k for K data signals S _k in layers k=l, K.

The K time synchronized parallel data streams d _k are individually processed in a step 210 by K individual, i.e. non-joint, superposition encoder SEC _k to generate K data signals S _k -

The data signals S _k are summed up in a step 212 to create the first signal y _A . The first signal y _A is in this example with K layers k :

wherein y _A first signal,

K number of layers, S _k data signal in layer k.

The data signals S _k correspond to K layers. The more layers K overlap, the more precise is the approximation. The number K of layers may be selectable depending on

requirements.

Afterwards the first signal y _A is pre-coded in K parallel steps 214 with the individual elements of the pre-coding vector w _A to generate a plurality of pre-coded signals p _n for n=l, N. In Figure 2 a property of visible light communication channels is multiplied in K parallel steps 216 by individual elements of a channel vector h _A .

Depending on the number N of elements of the matrix 106, for the first receiver A the pre-coding vector w _A = [w _1A , w _N _ _1A , W _{N A} ] is used with the channel vector h-A ⁼ [h-i,A>■■■> h _N _ _1A , for the first receiver A.

The pre-coding vector w _A is for example determined to compensate effects of channels h _A using a linear minimum mean square error determination or zero forcing. This is particularly efficient in a static environment where the first receiver A and the matrix 106 are in determined positions or not moving relative to each other.

As depicted in Figure 2 resulting signals ph _n for n=l, ... N, are summed up in a step 218 and sent as optical wireless data o _ws on physical layer in particular by the transmitter 108 controlling at least one visible light communications transmitter 102, e.g. one or more light emitting diodes, of the matrix 106. Due to additional noise n that is added, the optical wireless data o _ws will result in a receive signal y' _A that contains the additive noise n. This is depicted in Figure 2 by an adder 220 in the signal path. The at least one visible light communications receivers 104 are adapted to receive the receive signal γΆ· In the example the first receiver A, e.g. the photodiode, is adapted to receive the optical wireless data signal o _ws sent on physical layer. Due to the pre-coding, the at least one visible light communications receivers 104 receive in a step 222 the receive signal y' _A that is equivalent to the signal y _A .

The receive signal y' _A is for example received by a joint superposition decoder SDEC. The joint superposition decoder SDEC is adapted to use the knowledge about the

approximation to determine K time synchronized parallel receive data streams rs _k based on data detected in the receive signal y' _A . The K time synchronized parallel receive data streams rs _k are individually processed in parallel steps 224 by K individual superposition de-coder SDEC _k to generate K receive data signals rd _k . In the example, feedback signals fs _k are fed back from the individual superposition de-coders SDEC _k to the joint superposition decoder SDEC. A feedback signal fs _k provides for example extrinsic information about the receive data signal rd _k for the superposition decoder SDEC. For example the signal rd _k is fed back.

Due to the time synchronous transmission in optical communication for the first receiver A any otherwise required repetition coding is replaced by the

aforementioned superposition encoders and superposition decoders .

The receive data signals rd _k are serialized in a step 226 by a parallel to serial converter P/S to create a received serial output data stream ds ' .

Afterwards, in a step 228, the received serial output data stream ds ' is demodulated by a digital quadrature amplitude modulation demodulator DeMod to determine received

demodulated output data es ' .

Afterwards, in a step 230, the received serial demodulated output data es ' is decoded by a decoder DEC for use 232 by the transmitter 108, e.g. as output or stored in storage. A second method for transmitting data of a first user from the transmitter 108 to the first receiver A is described below referencing Figure 3.

In a step 302, the data of the first user is received or read from storage in particular by the transmitter 108 as a data stream.

Afterwards, in a step 304, the data is encoded by the encoder ENC to generate an encoded data stream es for use in the digital quadrature amplitude modulation modulator Mod.

Afterwards, in a step 306, the data is modulated by the digital quadrature amplitude modulation modulator Mod. The digital quadrature amplitude modulation modulator Mod is adapted to produce the digital serial output data stream ds .

Afterwards, in a step 308, the received digital serial output data stream ds ' is parallelized by a serial to parallel converter S/P. The serial to parallel converter S/P is adapted to output K time synchronized parallel data streams d _k for K data signals S _k in layers k=l, K. The K time synchronized parallel data streams d _k are individually processed in a step 310 by K spreader SPE _k and in a step 312 by K interleaver nk to generate K data signals S _k - The data signals S _k are multiplied in a step 314 individually with K power factors. The K power factors in the example are determined as the square root of K

individual power factors Pi, ... P _K . An exemplary assignment of power factors P _k to data signals s _k is depicted in

Figure 4.

As depicted in Figure 4, for each of the K data signals Si, s _K a different power factor Pi, ... P _k is assigned. In the example, the power factor P _k increases starting from P ₁ for data signal Si with increasing values of k to a maximum power factor P _K for data signal s _K . Other power factor assignments may be used as well.

The resulting output data signals o _k are summed up in a step 316 to create the first signal y _A . The first signal y _A is in this example determined as superposition with K layers k:

wherein y _A first signal,

K number of layers,

P _k Power of data signal s _k ,

s _k data signal in layer k. The data signals Sk correspond to K layers for the Gaussian approximation. The more layers K overlap, the more precise is the Gaussian approximation. The number K of layers may be selectable depending on requirements. Afterwards the first signal y _A is pre-coded in a step 318 with a pre-coding vector w _A to generate a plurality of pre- coded signals p _n for n=l, N. In Figure 3 a property of visible light communication channels is indicated by a channel vector h _A .

Depending on the number N of elements of the matrix 106, for the first receiver A the pre-coding vector w _A = [w _1A , w _N _ _1A , W _{N A} ] is used with the channel vector h-A ⁼ [h-i,A>■■■> h _N _ _1A , for the first receiver A. The pre-coding vector w _A is for example determined to compensate effects of channels h _A using a linear minimum mean square error determination or zero forcing. This is particularly efficient in a static environment where the first receiver A and the matrix 106 are in determined positions or not moving relative to each other. Afterwards in a step 320 resulting signals ph _n for n=l, ... N, are summed up and sent as optical wireless data ows on physical layer in particular by the transmitter 108 controlling at least one visible light communications transmitter 102, e.g. one or more light emitting diodes, of the matrix 106.

The at least one visible light communications receivers 104 are adapted to receive the sent signal. In the example the first receiver A, e.g. the photodiode, is adapted to receive the optical wireless data signal ows sent on physical layer. Due to the pre-coding, the at least one visible light communications receivers 104 receive in a step 322 a receive signal y' _A that is equivalent to the signal y _A . The signal y' _A may contain additive noise n.

The receive signal y' _A is for example received by an elementary signal estimator ESE. The elementary signal estimator ESE is adapted to use the knowledge about the Gaussian approximation to determine K time synchronized parallel receive data streams rs _k based on data detected in the receive signal y' _A .

The K time synchronized parallel receive data streams rs _k are individually processed in a step 324 by K de- interleaver n _k ^_1 and in a step 326 by K de-spreader DES _k to generate the K receive data signals rd _k -

In the example, feedback signals f _k are feed back to the elementary signal estimator ESE. The feedback signals f _k are individually determined by K interleavers n _k that correspond to the interleavers n _k of the transmitter 108. The input to each interleaver n _k is the difference between the de-spread receive data signals rd _k and the output of the de-interleaver n _k ^_1 in each layer k. Extrinsic information that is detected by the elementary signal estimator ESE may be exchanged with the de- nterleavers n _k ^_1 and the de-spreaders DES _k as well.

Due to the time synchronous transmission in optical communication for the first receiver A any otherwise required repetition coding is replaced by the spreaders SPE _k and de-spreaders DES _k .

The receive data signals rd _k are serialized in a step 328 by a parallel to serial converter P/S to create a serial output data stream os.

Afterwards, in a step 330, the received serial output data stream ds ' is demodulated by a digital quadrature amplitude modulation demodulator DeMod to determine demodulated output data es ' .

Afterwards, in a step 332, the received serial demodulated output data es ' is decoded by a decoder DEC for use 334 in particular by the transmitter 108, e.g. as output or stored in storage.

The creation of the first signal y _A has been described above. The second signal y _B is for example determined in similar manner. For different users, the definition of spreading by the spreader SPE _k , repetition in the interleaver n _k or the selection of the number of layers K may be different.

The at least one visible light communications transmitter 102 and the at least one visible light communications receiver 104 have been described above for a single user referencing Figure 2 or 3. In the multi-user environment signals for all users may be transmitted accordingly. Visible light communication is used for example as a wireless local area network, a wireless personal area network a car to car or car to infrastructure network.

Visible light communication is used for example for

communication between a first device and a second device. The first device and the second device may be permanently installed at different fixed locations in an infrastructure or environment. The first device may be installed at a fixed location and the second device may be movable with respect to the fixed location in the infrastructure or environment.

An example of a multiple input multiple output visible light communication system using a three dimensional visible light communication array forming the matrix 106 of visible light communication transmitters 102 and using a plurality of visible light communication receivers 104 will be described below referencing Figure 5. The position of the plurality of visible light communication receivers 104 is fixed with respect to the position of the three

dimensional visible light communication array. Each of the visible light communication receivers 104 is connectable to the visible light communication array by an individual visible light communication sub-channel. Each of the individual visible light communication sub-channel is regarded as time-invariant flat channel. This results in an enhancement of overall data throughput.

Preferably the position of individual visible light

communication receivers 104 with respect to each other is selected to reduce interference. This means that the position of the individual visible light communication receivers 104 and a main steering direction Θ of the beam for each individual visible light communication receiver 104 is selected to be in a direction for interference suppression θ + φ with respect to all other beams the visible light communication array produces.

In the previous examples it is assumed that all parameters related to the optical wireless data transmission are previously known. Optionally the receiver is adapted to receive wireless optical data from at least one sender of optical wireless data, e.g. the first sender of the first device that comprises the first visible light communication receiver A and/or the second device that comprises the second visible light communication receiver B. The receiver in this case may be adapted to determine a channel quality of a channel to the at least one sender of optical wireless data depending on the received optical wireless data. The receiver in this case may be adapted to determine the precoding vector w _A or the pre-coding matrix for sending the optical wireless data o _ws to the sender of optical wireless data depending on the received optical wireless data .

Optionally a radiation direction of the at least one sender of optical wireless data may be measured depending on received optical wireless data. In this case the direction for interference suppression θ + φ may be determined depending on the radiation direction. A user of the data transmitted via this visible light communication system may connect with a universal serial bus interface, a local area network cable or the like to any of the individual visible light communication receivers 104.

The visible light communication receivers 104 are adapted to have the universal serial bus interface, a local area network interface or the like. The visible light

communication receivers 104 are adapted to receive data as described above for the user, reconstruct the data and forward it to the user via at least one of these

interfaces .

The performance of the visible light communication system may be represented by an overloading factor p.

The overloading factor p is determined by a superimposed number of layers K and wide sense code R _W , e.g. a spreading rate R _S PE and a repetition rate RREP : P- ^R sm ^" ^REP ^{' K}

v

For different wide sense code rates R _w and different layers K the overloading factor p is for example: Wide sense code rate R _w 1/2 1/4

Layers K 12 36

Overloading factor p 600% 900%.

The description and drawings merely illustrate the

principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly

described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor (s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to

encompass equivalents thereof.

The functions of the various elements shown in the figures, including any functional blocks, may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual

processors, some of which may be shared. Moreover, explicit use of the term 'processor' should not be construed to refer exclusively to hardware capable of executing

software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC) , field programmable gate array (FPGA) , read only memory (ROM) for storing software, random access memory (RAM) , and nonvolatile storage. Other hardware, conventional and/or custom, may also be included.

It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow chart represents various processes which may be

substantially represented in a computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

A person of skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and

magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods.