WO2023242135A1

WO2023242135A1 - A method of uplink resource allocation in an optical wireless communication system

Info

Publication number: WO2023242135A1
Application number: PCT/EP2023/065684
Authority: WO
Inventors: Nancy Yushan LEE; Haimin Tao; Matthias Wendt; Andries Van Wageningen; Conrad DANDELSKI
Original assignee: Signify Holding B.V.
Priority date: 2022-06-16
Filing date: 2023-06-12
Publication date: 2023-12-21

Abstract

A method (100) for allocating uplink radio resource to a plurality of end devices to access an Access Point, AP (200), according to an Orthogonal Frequency Division Multiple Access, OFDMA, and/or a Multi-user Multiple-Input Multiple-Output, MU-MIMO technology, in an optical wireless communication system, the method (100) comprising: assessing (S101) by the AP (200) light intensity received from each of the plurality of end devices; grouping (S102) the end devices based on an assessment of light intensity; wherein more than one end device is assigned to a same group when total light intensity received by the AP (200) from the more than one end devices belonging to the same group is below a first threshold; and allocating (S103) the more than one end devices belonging to the same group to transmit simultaneously.

Description

A method of uplink resource allocation in an optical wireless communication system

FIELD OF THE INVENTION

The invention relates to the field of optical wireless communication, such as LiFi communication. More particularly, various apparatus, systems, and methods are disclosed herein related to an uplink resource allocation in an optical wireless communication system.

BACKGROUND OF THE INVENTION

To enable more and more electronic devices like laptops, tablets, and smartphones to connect wirelessly to the Internet, wireless communication confronts unprecedented requirements on data rates and link qualities, and such requirements keep on growing year over year, considering the emerging digital revolution related to Internet-of- Things (loT). Radio frequency technology like Wi-Fi has limited spectrum capacity to embrace this revolution.

In the meanwhile, optical wireless communication (OWC) is drawing more and more attention with its intrinsic security enhancement and capability to support higher data rates over the available bandwidth in visible light, Ultraviolet (UV), and Infrared (IR) spectra. Depending for example on the wavelengths used, such techniques may also be referred to as coded light, Light Fidelity (LiFi), visible light communication (VLC) or firee- space optical communication (FSO). OWC or LiFi is directional and shielded by light blocking materials, which provides it with the potential to deploy a larger number of access points, as compared to Wi-Fi, in a dense area of users by spatially reusing the same bandwidth. These key advantages over wireless radio frequency communication make OWC or LiFi a promising secure solution to mitigate the pressure on the crowded radio spectrum for loT applications and indoor wireless access. Other possible benefits of LiFi may include guaranteed bandwidth for a certain user, and the ability to function safely in areas otherwise susceptible to electromagnetic interference. Therefore, LiFi is a very promising technology to enable the next generation of immersive connectivity.

In the legacy releases of Wi-Fi / IEEE802.11 the access of the medium is primarily based on CSMA contention based carrier sensing, hence, a best effort protocol. The medium is occupied by only one user at a time, or a few users (Limited by number of antennas on the access point) when MU-MIMO is supported. A key feature of the new generation Wi-Fi 6 / 802.1 lax is orthogonal frequency-division multiple access (OFDMA), which is equivalent to cellular technology (i.e., LTE) applied into Wi-Fi. With this technique, multiple clients are assigned with different Resource Units (RUs) in the available spectrum.

“Distributed Multiuser MIMO for LiFi in Industrial Wireless Applications”, BOBER KAI LENERT et al, relates to a medium access control protocol based on space division multiple access with evaluation results demonstrating the advantages of joint transmission from adjacent optical frontends and the dynamic switching between spatial diversity and multiplexing.

SUMMARY OF THE INVENTION

To allow efficient use of optical spectrum, it is beneficial to adopt Uplink (UL) Orthogonal Frequency Division Multiple Access (OFDMA) and/or Multi-user Multiple-Input Multiple-Output (MU-MIMO) for optical wireless communication. In the meanwhile, to achieve good uplink communication performance in an OFDMA and/or MU- MIMO based system, signals from non-access point (AP) stations (STAs) or end devices (EDs) with simultaneous transmission need to be received by the AP with a similar power level. In a radio frequency (RF) based system, such as an 802.11 (Wi-Fi) system, this can be accomplished by the AP instructing the non-AP STAs to adjust their transmission power. However, in an optical wireless communication (OWC) system, the optical transmission power is constrained by the requirement to keep a light source in a linear operating region and, potentially, also by the presence of a mixer. Thus, an alternative solution is needed for an OWC system as compared to the typical RF solution.

In view of the above, the present disclosure is directed to methods, apparatus, and systems for providing improved uplink communication in an optical wireless communication system. More particularly, the goal of this invention is achieved by a method for allocating uplink radio resource as claimed in claim 1, by an optical access point as claimed in claim 10, and by a computer program as claimed in claim 13.

In accordance with a first aspect of the invention a method for allocating uplink radio resource is provided. A method for allocating uplink radio resource to a plurality of end devices to access an Access Point, AP, according to an Orthogonal Frequency Division Multiple Access, OFDMA, and/or a Multi-user Multiple-Input Multiple-Output, MU-MIMO technology, in an optical wireless communication system, the method comprising: assessing by the AP light intensity received from each of the plurality of end devices; grouping the end devices based on an assessment of light intensity; wherein more than one end device is assigned to a same group when total light intensity received by the AP from the more than one end devices belonging to the same group is below a first threshold and a difference in light intensity between any two end devices out of the more than one end devices is below a second threshold; and allocating the more than one end devices belonging to the same group to transmit simultaneously.

In IEEE 802.1 lax, UL MU-MIMO is adopted to improve uplink capacity by enabling multiple spatially separated clients to access the channel at the same time and is especially useful in scenarios where the STAs have limited number of antennas, which is the case for a typical smartphone. In UL MU-MIMO, also known as Uplink Spatial Division Multiple Access (UL-SDMA), a receiver at the AP side is able to receive uplink signals from multiple spatially separated users simultaneously by using an antenna array. The receiver can separate the different users based on a channel transfer function vector.

OFDMA is a multi-user version of the digital modulation scheme orthogonal frequency-division multiplexing (OFDM). Multiple access is achieved in OFDMA by assigning subsets of subcarriers to individual users. Here, each subset of subcarriers belonging to a same timeslot is called a Resource Unit (RU). Resource Unit is also a terminology used in 802.1 lax WLAN, which defines a group of 78.125 kHz bandwidth subcarriers (tones) used in both Down Link (DL) and Up Link (UL) transmissions. With OFDMA, different transmit powers may be applied to different RUs. There are maximum of 9 RUs for 20 MHz bandwidth, 18 in case of 40 MHz and more in case of 80 or 160 MHz bandwidth.

Although OFDMA maximize the usage of radio resource, allowing different devices to transmit simultaneously on different subcarriers in the same timeslot may result in interference among these devices. For example, in uplink OFDMA for OWC, concurrently transmitting end devices may sacrifice the channel SNR as photons of all end devices in view will add up in the detector of the access point and weak end devices may not have sufficient signal in the combined amplified signal going to the digital demodulation stage, especially because RU leakage from other end devices increases the noise floor and results in interference among end devices in the uplink.

An optical communication system is typically based on intensity modulation and direct detection (IM/DD). With intensity modulation, the transmitting signal is conveyed by varying current that drives the optical front end of a transmitter. This causes the intensity of the light transmitted by the optical transmitter to vary over time. This is different from RF communication. For RF communication, a frequency band (e.g., 5 GHz) is divided into channels that are directly mapped from corresponding channels in the baseband signal. In an optical communication system, the optical band is not divided into channels. By adopting a standard Wi-Fi chipset in optical communication, the conventional IEEE 802.11 channels are only defined at baseband. Each baseband channel is conveyed as varying intensity of light across the entire bandwidth of the optical transmitter.

For simultaneous transmission from multiple EDs or non-AP STAs in UL- OFDMA and UL MU-MIMO, photons of all these multiple EDs in view will add up in the detector of an AP. Considering that the uplink optical transmission power is constrained by the requirement to keep a light source of an ED or a non-AP STA in a linear operating region and cannot be tuned freely by the AP according to a conventional uplink power control mechanism as used by a RF based communication system, it is important to provide a solution to avoid the AP being saturated by the cumulative optical power.

The first threshold is used by the AP in the assessment of a total light intensity received from the more than one end devices belonging to the same group. It may be dependent to a hardware limitation of the AP, a configuration of the AP, a data rate or Quality-of-Service (QoS) requirement of an end device, or an external input from a network installer. The first threshold may also be preconfigured or adjusted according to a real-time uplink reception performance. Thus, the values of the first threshold used by two neighboring APs may be different.

Beneficially, the first threshold is determined by a maximum input power limit of a trans-impedance amplifier, TIA, of an optical transceiver of the AP in a given gain setting.

A TIA is a type of current-to-voltage converter, which is commonly used with sensors, when they have a current response that is more linear than a voltage response. TIAs are very often used as a first stage amplifier to condition the received signals of a photodiode or photo detector in an optical receiver. Because the output electrical signal from a photodiode is typically small and therefore difficult to process further, amplification of the signal from the photodiode to a larger signal is beneficial for further processing.

A single TIA may have configurable gain settings, and each is optimized for certain input signal levels. Therefore, the maximum input power limit may also be different for the same AP, depending on a certain gain setting adopted. Preferably, the assessment of light intensity is made by a measurement on received signal strength from each end device when transmitting individually.

Since the uplink optical signals received from multiple end devices will be added together at the AP when end devices are transmitting simultaneously, a more accurate assessment of light intensity for determining grouping among the plurality of end devices is preferably to be done when each end device is transmitting individually.

The received signal strength may be evaluated by measuring the DC level of the received signal or by measuring the high frequency component of the received signal.

The measurement of the high frequency component of the received signal can be done digitally, such as via received signal strength indicator (RS SI) provided by the baseband or done in the analog domain via an RMS detector. Some baseband chipsets may provide RSSI information directly.

Alternatively, the assessment of light intensity is made by a measurement of received DC power from each end device when transmitting individually.

This is a very low-cost approach, but sometimes it may have reduced accuracy due to interference from the environment, such as daylight interference.

In one option, the method further comprises only assigning one or more stationary end devices to a group for transmitting simultaneously.

End devices with highly variable signal strengths are preferably excluded from any group for using either uplink MU-MIMO or OFDMA scheme. It is known that when an end device uses optical wireless communication, the AP will typically experience more rapid and larger signal strength variations than what will happen when the end device uses RF communication, because of changing distances and changing orientations between the AP and the end device.

Preferably, an end device is identified as a stationary end device according to one or more of: a predefined configuration in the AP, an indication received from the end device, a detection by the AP according to an observation of a variation in received DC power or received signal strength over time from the corresponding end device.

A predefined configuration in the AP may be set during an installation of stationary end device in a factory. An indication from the end device to the AP may be provided by the end device during an association procedure. It may also be learned by the AP by monitoring RSSI or DC power received from the STA for a certain period of time. For example, a STA is determined to be stationary if its SNR or DC power changes by less than a certain level, e.g., less than 10% over say 1 second. Beneficially, the method further comprises only assigning one or more end devices with a same type of light sources to a group for transmitting simultaneously.

Different light sources may be adopted by the end devices depending on an application requirement. For example, an end device may use a LED-based transmitter or a laser-based transmitter. This information may be included in the subscription information from an end device or inferred by the AP according to the bandwidth of the end device, since lasers are capable of much larger bandwidths than LEDs. It is also known that the efficiency of LEDs falls off at higher frequencies, and thus LED-based transmitters usually use higher transmission power at higher subchannels to compensate this effect.

Advantageously, in an optical wireless communication system according to MU-MIMO technology, the method further comprises a step of only assigning one or more end devices without an overlapping coverage area to a group for transmitting simultaneously on a same frequency channel.

In this example, only spatially separated and non-overlapping end devices are selected for participating in a UL MU-MIMO transmission. The AP may have a plurality of optical front ends or optical receivers, which are spatially separated or pointing in different directions. Non-overlapping among the one or more end devices means that the signals transmitted by the end devices are received by different optical front ends or optical receivers of the AP. In this way, the multiple, concurrent uplink signals are decoupled from each other and do not interfere each other. In this way the utilization of the medium is optimized.

Beneficially, the method further comprises a step of assigning one or more end devices to a group for transmitting simultaneously only when a difference in light intensity between any two end devices out of the more than one end devices is below a second threshold.

Although OFDMA and MU-MIMO are treated under the same framework of multiuser uplink transmission in the IEEE 802.1 lax standard, the two technologies have different criteria. Since UL MU-MIMO share the exact same channel, the unequal power among more than one non-AP STA will only result in increased noise floor (so, unfair to the more distant STA) due to coupling between RX channels, but there is no RU leakage problem as in OFDMA. So equal receiving power is more critical for UL-OFDMA than for MU-MIMO.

The first threshold is used to evaluate the total light intensity, while the second threshold is used to evaluate the difference in light intensity from different end devices. The selection of the first and the second threshold are related to the methods used in measuring light intensity, respectively, such as based on either the DC level of the received signal or by measuring the high frequency component of the received signal, as disclosed above.

When both thresholds are measuring light intensity the same way then the second threshold must be lower than the first threshold. But it may also be the case that grouping is based on a total DC power (for the first threshold) and a difference in RSSI (for the second threshold).

Preferably, the method further comprising repeating the steps to regroup the plurality of end devices when a received signal quality of one or more end devices drops below a third threshold.

The method to regroup the end devices may be triggered when the transmission quality of one or more end devices drops below a certain level, such as defined by the third threshold. The third threshold is configurable. The third threshold may also be different for different end devices, depending on a data rate or QoS requirement related to the link between the AP and a certain end device.

In one option, the method further comprising informing the plurality of end devices about uplink radio resource allocation via a triggering frame according to an IEEE 802.11 standard.

According to the IEEE802.11 standard, the triggering frame may be a dedicated Trigger Frame or a frame carrying a triggered response scheduling (TRS) control subfield. As an example, with a High efficiency (HE) PHY in the IEEE802.11 standard, a HE AP may send a Trigger frame to initiate UL MU operation using UL OFDMA or UL MU- MIMO transmissions or a frame containing a TRS Control subfield to initiate UL OFDMA transmissions. The frame initiating these transmissions in the uplink direction is a triggering frame. The triggering frame identifies non-AP STAs participating in UL MU operation and assigns RUs and/or spatial streams to these STAs.

In accordance with a second aspect of the invention, an access point is provided. An Access Point, AP, for allocating uplink radio resource to a plurality of end devices according to an Orthogonal Frequency Division Multiple Access, OFDMA, and/or a Multi-user Multiple-Input Multiple-Output, MU-MIMO technology in an optical wireless communication system, the AP comprising: an optical transceiver configured to carry out optical wireless communication with the plurality of end devices; a controller configured to: assess light intensity received from each of the plurality of end devices; group end devices based on an assessment of light intensity; wherein more than one end device is assigned to a same group when total light intensity from the more than one end devices belonging to the same group is below a first threshold and a difference in light intensity between any two end devices out of the more than one end devices is below a second threshold; and allocate the more than one end devices belonging to the same group to transmit simultaneously.

The optical wireless communication may be carried out in visible light, Ultraviolet (UV), and Infrared (IR) spectra. Thus, the optical wireless communication may also be called a LiFi communication or a Visible Light Communication (VLC). The optical transceiver may comprise at least a light source for optical data transmission and a light detector for optical data reception. The light source or light emitter may be one of a lightemitting diode (LED), a laser diode, a vertical -cavity surface-emitting laser (VCSEL), or an Edge Emitting Laser Diode (EELD). Preferably, the light source comprises at least one of a LED and a VCSEL. The light detector, also called photo detector or photo sensor, is a photodiode, which may be a PIN diode, an Avalanche Photo Diode (APD), or a photomultiplier.

The uplink resource allocation method may be carried out by the controller upon information obtained via the optical transceiver.

Beneficially, the controller is further configured to assign one or more end devices to a group for transmitting simultaneously only when a difference in light intensity between any two end devices out of the more than one end devices is below a second threshold.

Preferably, wherein when the optical wireless communication system is according to MU-MIMO, the controller is further configured to assign only one or more end devices without an overlapping coverage area to a group for transmitting simultaneously on a same frequency channel.

Beneficially, the optical transceiver is configured to inform the plurality of end devices about uplink radio resource allocation by sending a triggering frame according to an IEEE 802.11 standard.

In accordance with a further aspect of the invention, a computer program is provided. A computing program comprises code means which, when the program is executed by an AP according to the present invention to cause the AP to execute the steps of the method according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the same parts throughout the different figures. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

FIG. 1 illustrates an OFDMA based uplink transmission;

FIG. 2 shows a block diagram of a method for allocating uplink radio resource to a plurality of end devices;

FIG. 3 illustrates a typical received analog signal with intensity modulation; and

FIG. 4 shows a block diagram of an optical access point.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

It is commercially interesting to make use of standard WLAN chipsets with OFDMA support and/or MU MIMO support (Wi-Fi 6, 802.1 lax) for optical wireless communication. This allows an optical wireless communication system, such as a LiFi system, to make optimal use of UL-OFDMA and/or UL MU-MIMO features in IEE 802.1 lax compliant baseband chips. These features (used separately or together) can significantly reduce scheduling delay and increase spectral efficiency by allowing multiple users to use the same spectrum at the same time.

To achieve good UL-OFDMA performance at the AP, signals from all participating end devices with simultaneous transmission need to be received at the AP with a similar power level. With RF-based technologies such as 802.11 (Wi-Fi), this can be accomplished by the AP instructing the end devices to adjust their transmission power, such as uplink power control. However, for optical wireless communication, the optical transmission power is constrained by the need to drive the light source at a specific DC current offset in order to stay in the linear operating region, and due to the presence of the mixer, the dynamic range of the transmission power is limited. Thus, a different solution for an AP in an optical wireless communication system is needed.

Furthermore, a solution is needed to prevent oversaturating the optical receiver in the AP with the cumulative optical power from simultaneous transmission from multiple end devices in UL-OFDMA and UL MU-MIMO. This limitation is resulted from the use of intensity modulation in an optical wireless communication system.

To optimize the uplink resource allocation, the present invention discloses a method of an optical access point to allocate resource units (RUs) to a plurality of end devices by taking light intensity received from end devices into account. This allows the AP to group the plurality of end devices in a more efficient and also improved manner. The proposed adaptations can help to improve total throughput of the system or to reduce an average uplink access latency of the end devices.

In an example of an optical wireless communication (OWC) system, ceiling mounted OWC access points (APs) may be integrated with luminaires with general lighting functions. This may be a good placement for an AP function as luminaries are also preferably placed to illuminate a space homogeneously and completely. To guarantee the coverage, the beams from adjacent APs will have overlap regions, and end devices (ED) located in such overlapping regions may experience interferences when the adjacent APs transmit simultaneously. Similarly, those ED may also produce overlapping beams at an AP side and result in interferences to each other in the uplink.

In the legacy releases of Wi-Fi / IEEE802.11 the access of the medium is primarily based on carrier-sensing multiple access (CSMA), which is a best effort protocol. Since the introduction of OFDMA the access of the medium can also be based on frequency/sub -channel division. OFDMA takes place under control of the AP which determines which subchannels to use for which STAs. The advantage of OFDMA is that medium use can be more efficient, especially when many smaller frames are present in the communication.

FIG. 1 illustrates an OFDMA based uplink transmission. The AP indicates which subchannel(s) can be used by which STA in a triggering frame. Low-data-rate users may be able to send continuously with low transmission power instead of using a "pulsed" high-power carrier. Thus, shorter access delay may be achieved for those users. A new mechanism for uplink transmission (UL) from multiple non-AP stations simultaneously to AP station is introduced in 802.1 lax which is called Triggered Uplink Access (TUA). This new mechanism relies on a triggering frame from the AP station, for example using a new type of 802.11 MAC frame called a Trigger Frame. This frame identifies non-AP stations participating in the UL MU transmissions and assigns RUs to these stations. Each non-AP station receiving the triggering frame sends its own frame back to AP using the assigned RUs. They may send Null-Data frames if there is no actual data to send at that moment. A triggering frame may also be a frame carrying a triggered response scheduling (TRS) Control subfield.

FIG. 2 shows a block diagram of a method 100 for allocating uplink radio resource to a plurality of end devices to access an Access Point (AP) 200 according to an Orthogonal Frequency Division Multiple Access, OFDMA, and/or a Multi-user Multiple- Input Multiple-Output, MU-MIMO technology, in an optical wireless communication system. The method 100 comprises: assessing in step S101 by the AP 200 light intensity received from each of the plurality of end devices; grouping in step SI 02 the end devices based on an assessment of light intensity; wherein more than one end device is assigned to a same group when total light intensity received by the AP 200 from the more than one end devices belonging to the same group is below a first threshold; and allocating in step SI 03 the more than one end devices belonging to the same group to transmit simultaneously.

The end devices grouped together are then allowed to transmit at the same time (e.g., the AP may schedule grouped end devices in the same triggering frame). Different groups may be sequentially activated in a polling mechanism. Certain end devices with either very low or very high received power levels at the AP may not be put in any group and may not be allowed to transmit simultaneously with other end devices.

Fig. 3 illustrates a typical received analog signal with intensity modulation. It can be seen that the information of the signal is carried by high frequency component on a DC bias.

In one option, the grouping of non-AP STAs or end devices for purposes of UL-OFDMA and/or UL MU-MIMO is based on a received DC power (average light intensity) or DC bias, per end device received at the AP while ensuring that the total received power of each group does not exceed the first threshold, such as the limit set by a TIA in the optical receiver of the AP.

In another option, the AP groups end devices based on received signal strength of a high frequency component of the signal, which may be measured as the received baseband signal power, via RSSI, when the end device is transmitting individually (in normal single user scheduling without UL-OFDMA or UL MU-MIMO). This can be done using existing measurement capabilities in a commercial Wi-Fi baseband chip.

In another example, the AP 200 only groups stationary end devices. That is, end devices with highly variable signal strength are excluded from UL MU groups. It is known that when an end device uses optical wireless communication, the AP will typically experience more rapid and larger signal strength variations than happens when the end device uses RF communication, both due to travelling (e.g., moving from one room to another) and due to changing orientation of the STA.

In a further example, the AP groups end devices according to the type of light sources used in the end devices, such as by whether the ED uses a LED-based transmitter or laser-based transmitter. This information could be included in subscription information, added to capability information exchange, or inferred from the end device’s bandwidth capability, since lasers are capable of much larger bandwidths than LEDs. It is known that the efficiency of LEDs falls off at higher frequencies, so a LED-based transmitter needs higher power at higher subchannels to compensate this effect.

In an UL MU-MIMO based system, end devices may also be grouped based on the signal path property. Only spatially separated and non-overlapping end devices are selected for participating in any given UL MU-MIMO transmission. Non-overlapping means that the signals transmitted by different end devices are not received by a same optical receiver of the AP. In this way, the multiple, concurrent uplink signals are decoupled from each other and does not interfere each other. In this way the utilization of the medium is optimized. The end devices can be arranged in groups based on this non-overlapping criterion, and then

• In the case of AP having a single baseband processing chain (the signals need to be merged and the separation in the optical domain is cancelled), end devices can be scheduled by the AP to individually access the medium (in time or frequency), i.e., schedule in separate RUs.

• In the case of AP having multiple baseband processing chains, groups nonoverlapping end devices can be scheduled in the same RUs (in time and frequency). UL-OFDMA can be used for groups containing multiple end devices, applying embodiments for grouping for UL-OFDMA.

• In the case of AP having multiple baseband processing chains, groups of partially overlapping end devices can be scheduled at the same timeslot but with RUs on different frequencies.

In UL OFDMA for OWC, concurrently transmitting EDs may sacrifice the channel SNR as photons of all EDs in view will add up in the AP detector and weak EDs may not have sufficient signal in the combined amplified signal going to the digital demodulation stage because a same gain is usually applied by the receiver to all the RUs, and furthermore RU leakage from other EDs increases the noise floor and results in interference among EDs in the UL. In a further example, only MU-MIMO is enabled in multi-user UL transmission (OFDMA disabled). In this case, power difference between end devices is less critical and end devices with different power levels are allowed to simultaneously participate in the MU-MIMO-only uplink transmission, as long as the total light intensity is below the first threshold.

In a further option, the AP uses learning based on evaluating performance metrics to determine the optimal number of power groups, number of end devices in a group, and/or what ranges of received baseband signal strength are beneficial to group together. Various performance metrics could be used singly or in combination, for example:

• RS SI measured in baseband processor;

• DC power measured in the OFE.

Beneficially, such learning cycles may be triggered automatically when the transmission quality of one or multiple end devices drops below a (configurable) threshold and a regrouping of end devices may be beneficial.

FIG. 4 shows a block diagram of an optical access point 200. The AP 200 comprises at least an optical transceiver 210 configured to carry out optical wireless communication with the plurality of end devices; and a controller 220 configured to assess light intensity received from each of the plurality of end devices; group end devices based on an assessment of light intensity; wherein more than one end device is assigned to a same group when total light intensity from the more than one end devices belonging to the same group is below a first threshold; and allocate the more than one end devices belonging to the same group to transmit simultaneously.

The optical transceiver 210 may comprise at least a light source for optical data transmission and a light detector for optical data reception. The light source or light emitter may be one of a light-emitting diode (LED), a laser diode, a vertical -cavity surfaceemitting laser (VCSEL), or an Edge Emitting Laser Diode (EELD). Preferably, the light source comprises at least one of a LED and a VCSEL. The light detector, also called photo detector or photo sensor, is a photodiode, which may be a PIN diode, an Avalanche Photo Diode (APD), or a photomultiplier.

The methods according to the invention may be implemented on a computer as a computer implemented method, or in dedicated hardware, or in a combination of both.

Executable code for a method according to the invention may be stored on computer/machine readable storage means. Examples of computer/machine readable storage means include non-volatile memory devices, optical storage medium/devices, solid-state media, integrated circuits, servers, etc. Preferably, the computer program product comprises non-transitory program code means stored on a computer readable medium for performing a method according to the invention when said program product is executed on a computer.

Methods, systems, and computer-readable media (transitory and non- transitory) may also be provided to implement selected aspects of the above-described embodiments.

Claims

CLAIMS:

1. A method (100) for allocating uplink radio resource to a plurality of end devices to access an Access Point, AP (200), according to an Orthogonal Frequency Division Multiple Access, OFDMA, and/or a Multi-user Multiple-Input Multiple-Output, MU-MIMO technology, in an optical wireless communication system, the method (100) comprising: assessing (SI 01) by the AP (200) light intensity received from each of the plurality of end devices; grouping (SI 02) the end devices based on an assessment of light intensity; wherein more than one end device is assigned to a same group when total light intensity received by the AP (200) from the more than one end devices belonging to the same group is below a first threshold and a difference in light intensity between any two end devices out of the more than one end devices is below a second threshold; and allocating (SI 03) the more than one end devices belonging to the same group to transmit simultaneously.

2. The method (100) of claim 1, wherein the first threshold is determined by a maximum input power limit of a trans-impedance amplifier, TIA, of an optical transceiver of the AP (200) in a given gain setting.

3. The method (100) of claim 1 or 2, wherein the assessment of light intensity is made by a measurement on received signal strength from each end device when transmitting individually.

4. The method (100) of claim 1 or 2, wherein the assessment of light intensity is made by a measurement of received DC power from each end device when transmitting individually.

5. The method (100) of any one of previous claims, the method (100) further comprising only assigning one or more stationary end devices to a group for transmitting simultaneously.

6. The method (100) of any one of previous claims, the method (100) further comprising only assigning one or more end devices with a same type of light sources to a group for transmitting simultaneously.

7. The method (100) of any one of previous claims, wherein in an optical wireless communication system according to MU-MIMO technology, the method (100) further comprises a step of only assigning one or more end devices without an overlapping coverage area to a group for transmitting simultaneously on a same frequency channel.

8. The method (100) of any one of previous claims, the method (100) further comprising repeating the steps to regroup the plurality of end devices when a received signal quality of one or more end devices drops below a third threshold.

9. The method (100) of any one of previous claims, the method (100) further comprising informing the plurality of end devices about uplink radio resource allocation via a triggering frame according to an IEEE 802.11 standard.

10. An Access Point, AP (200), for allocating uplink radio resource to a plurality of end devices according to an Orthogonal Frequency Division Multiple Access, OFDMA, and/or a Multi-user Multiple-Input Multiple-Output, MU-MIMO technology in an optical wireless communication system, the AP (200) comprising: an optical transceiver (210) configured to carry out optical wireless communication with the plurality of end devices; a controller (220) configured to: o assess light intensity received from each of the plurality of end devices; o group end devices based on an assessment of light intensity; wherein more than one end device is assigned to a same group when total light intensity from the more than one end devices belonging to the same group is below a first threshold and a difference in light intensity between any two end devices out of the more than one end devices is below a second threshold; and o allocate the more than one end devices belonging to the same group to transmit simultaneously.

11. The AP (200) of claim 10, wherein when the optical wireless communication system is according to MU-MIMO, the controller is further configured to assign only one or more end devices without an overlapping coverage area to a group for transmitting simultaneously on a same frequency channel.

12. The AP (200) of any one of previous claims 10-11, wherein the optical transceiver is configured to inform the plurality of end devices about uplink radio resource allocation by sending a triggering frame according to an IEEE 802.11 standard.

13. A computing program comprising code means which, when the program is executed by an Access Point, AP (200), according to any one of claims 10-12 to cause the AP (200) to execute the steps of the method (100) according any one of claims 1-9.