EP4515733A1

EP4515733A1 - A method of uplink resource allocation in an optical wireless communication system

Info

Publication number: EP4515733A1
Application number: EP23720891.3A
Authority: EP
Inventors: Matthias Wendt; Nancy Yushan LEE; Andries Van Wageningen; Conrad DANDELSKI; Haimin Tao
Original assignee: Signify Holding BV
Current assignee: Signify Holding BV
Priority date: 2022-04-28
Filing date: 2023-04-20
Publication date: 2025-03-05
Also published as: CN119096486A; WO2023208748A1

Abstract

A method (100) for allocating uplink radio resource to a plurality of end devices to access an Access Point, AP, according to Orthogonal Frequency Division Multiple Access, OFDMA, in an optical wireless communication system, wherein the uplink radio resource comprises a plurality of Resource Units, RUs, distributed on a plurality of timeslots with each RU comprising one or more subcarriers in a single timeslot; the method (100) comprising detecting (S101) mutual interference levels between any two end devices out of the plurality of end devices; detecting (S102) individual requirements of each one of the plurality of end devices; allocating (S103) the plurality of RUs to the plurality of end devices for uplink transmission depending on the mutual interference levels and the individual requirements; wherein RUs belonging to a same timeslot are allocated to more than one end device only when mutual interference levels between any two out of the more than one end device are below a first threshold and the individual requirements of each one of the more than one end device are satisfied.

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 free- 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 carrier sense multiple access (CSMA), 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. For example, a 80MHz channel can be split into multiple Resource Units, so that multiple clients transmit or receive different types of data at different rates over the same spectrum, simultaneously. A Resource Unit (RU) denotes a group of 78.125 kHz bandwidth subcarriers (tones) used in both DownLink (DL) and UpLink (UL) transmissions. With UL 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.

W02022033950A1 is related to a mechanism to improve system performance in an optical wireless communication system by examining whether time slots in time channels are to be scheduled for exclusive use or could be utilized for parallel communication.

WO2021234064A1 is related to an interference handling method and system for an optical wireless communication system, wherein multiple levels and operating modes are provided to flexibly handle partitioning of a coordination functionality between a central entity and distributed entities.

EP3884594A1 is related to a system for interference handling in a wireless optical network comprising multiple coordinators or other access points with overlapping coverage areas.

SUMMARY OF THE INVENTION

To allow efficient use of optical spectrum, it is beneficial to adopt UL OFDMA for optical wireless communication. Thus, standard Wi-Fi chipsets with OFDMA support may be deployed for optical wireless communication (also known as LiFi). However, concurrently transmitting end devices (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, especially because RU leakage from other EDs increases the noise floor.

RECTIFIED SHEET (RULE 91) ISA/EP In view of the above, the present disclosure is directed to methods, apparatus, and systems for allocating uplink radio resource by taking mutual interference among end devices into account. 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 13, and by a computer program as claimed in claim 15.

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 Orthogonal Frequency Division Multiple Access (OFDMA) in an optical wireless communication system, wherein the uplink radio resource comprises a plurality of Resource Units, RUs, distributed on a plurality of timeslots with each RU comprising one or more subcarriers in a single timeslot. The method comprises the steps of: detecting mutual interference levels between any two end devices out of the plurality of end devices; detecting individual requirements of each one of the plurality of end devices; allocating the plurality of RUs to the plurality of end devices for uplink transmission depending on the mutual interference levels and the individual requirements; wherein RUs belonging to a same timeslot are allocated to more than one end device only when mutual interference levels between any two out of the more than one end device are below a first threshold and the individual requirements of each one of the more than one end device are satisfied.

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 maximizes the usage of radio resources, allowing different devices to transmit simultaneously on different subcarriers in the same timeslot may result in interference among these devices. The interference characteristics of OWC are different from those in RF. 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. Therefore, it is important to take mutual interference among the plurality of end devices into account when allocating uplink radio resource according to OFDMA. Only a subset of end devices with mutual interference below the first threshold are assigned to share the RUs belonging to a same timeslot. Otherwise, the communication performance may be degraded.

Furthermore, individual requirements of the end devices shall also be satisfied when applying the OFDMA scheme. For example, by splitting subcarriers among multiple end devices, the data rate to be supported for an individual end device will be lower, but the chance that the end device gets resource allocation will be increased. Therefore, applying OFDMA or not will also depend on the requirements from the end devices.

Beneficially, the mutual interference level is detected by monitoring uplink data communication of the corresponding end devices for a certain period of time, and/or by monitoring a received signal strength and noise floor of one or more RUs used by the corresponding end devices for a certain period of time.

The mutual interference level between two end devices may be affected by different factors, such as the separate distance between two devices, output power, spectrum mask of the signals, and mobility of the end devices. For example, when the end device moves, the link throughput may vary per signal pathloss. To make a correct judgement of RU interference in that case, both signal strength (RSSI) and noise floor of that RU can be monitored. The noise floor will indicate the interference from other devices. It is also beneficial that no dedicated resource is used for obtaining such mutual interference information. Preferably, the mutual interference level is detected by monitoring uplink data communication of the corresponding end devices for a certain period of time, such as by monitoring a received signal strength and noise floor of one or more RUs used by the corresponding end devices.

Preferably, the individual requirement is related to at least one of a latency requirement, a size of a data frame to be transmitted, a data rate requirement, a jitter requirement, and another Quality-of-Service, QoS, requirement.

Since the RU mapping scheme may have a direct impact on the transmission delay and other QoS related parameters of a connection, it is beneficial to take a QoS requirement from an end device into account. Depending on the application, some end devices may require high throughput connections, while others may require low latency and low jitter connections.

For example, an end device requesting a high data rate may be allocated to lower-band subcarriers, where the channel gain is stronger and higher modulation and coding schemes can be supported, while another end device requesting a wide bandwidth may be allocated to a higher-band subcarriers.

In one example, an individual requirement of an end device is detected upon receiving a request from the end device or based on a data flow analysis of one or more previous communication links with the end device.

The individual requirement of an end device may be collected based on an explicit request from an end device. It may also be derived by the access point based on a data flow analysis of one or more previous communication links with end devices, such as an analysis on a received signal quality per RU. With that information (in addition to the collected queue-sizes), the AP calculates which RUs to allocate to which stations (STAs).

For certain end devices that fulfill the requirement to share the RUs belonging to a same timeslot, further measures may be taken to further improve the performance, especially when the mutual interference level is close to the first threshold.

In one option, the method further comprises the step of allocating RUs belonging to a same timeslot on nonadj acent subcarriers to two end devices, when the mutual interference level between the two end devices is below the first threshold and above a second threshold; wherein the second threshold is smaller than the first threshold.

In this case, two end devices with mutual interference above the second threshold but below the first threshold will be scheduled in the same timeslot but assigned to nonadj acent RUs.

The first threshold and second threshold may also be adjusted according to the application scenario, such as the number of end devices in the system, the latency requirement, the data rate requirement, or another QoS related requirement.

It may also be helpful to analyze the usage of subcarriers and keep gaps in the frequency domain between adjacent allocations of RUs whenever RUs are not fully occupied. This also reduces the node-to-node interferences during synchronous transmission.

In another option, the method further comprises the step of allocating RUs in a same timeslot on two adjacent subcarriers to two end devices with the two adjacent subcarriers having an enlarged guard tone, when the mutual interference level between the two end devices is below the first threshold and above a second threshold; wherein the second threshold is smaller than the first threshold.

If there is flexibility in the system, an enlarged guard tone may be adopted to alleviate the mutual interference between two end devices.

Advantageously, the method further comprises the step of requesting an end device out of the plurality of end devices to reduce or switch off its transmitter bias current when it is not transmitting to reduce a leakage output, if there is at least one mutual interference level related to the end device is equal to or above the second threshold.

Beneficially, the method further comprises the step of informing an end device out of the plurality of end devices to reduce its transmission power, when one or more mutual interference levels related to the end device is equal to or above the second threshold.

Preferably, the method further comprises the step of allocating RUs in a further timeslot out of the plurality of timeslots exclusively to an end device out of the plurality of end devices for an uplink transmission, if at least one mutual interference level related to the end device is equal to or above the first threshold.

When at least one mutual interference level related to the end device is equal to or above the first threshold, it indicates that the end device introduces too much noise to other end devices. It is more efficient to assign the end device to a dedicated timeslot without sharing the subcarriers with other end devices. This mimics a TDMA channel management.

In one option, the method further comprises the step of allocating RUs in a further timeslot out of the plurality of timeslots exclusively to an end device out of the plurality of end devices for an uplink transmission when a received uplink signal strength related to the end device is above a third threshold.

It may happen that an end device is located very close to the access point, even if a lowest transmission power is used, the received signal strength is still too high, which also means out-of-channel leakage will also be high. Thus, the end device may cause interference to end devices using adjacent RUs. To prevent this, it is also beneficial to assign the end device to a dedicated timeslot.

Beneficially, the method further comprises the step of assigning a further timeslot out of the plurality of timeslots for assessing a mutual interference level between two or more end devices, wherein only the two or more end devices are allowed to transmit in that further timeslot.

The further one or more timeslots are used dedicatedly for assessing a mutual interference level between two or more end devices. The assessment of the mutual interference level between two or more end devices may be a direct measurement of the mutual interference level. It may also be an indirect assessment by comparing uplink performance of different allocations of RUs to the two or more end devices in that dedicated one or more timeslots.

In one example, the method further comprises 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 to access the AP according to Orthogonal Frequency Division Multiple Access (OFDMA) in an optical wireless communication system, wherein the uplink radio resource comprises a plurality of Resource Units, RUs, distributed on a plurality of timeslots with each RU comprising one or more subcarriers in a single timeslot. The AP comprises an optical transceiver configured to carry out optical wireless communication with the plurality of end devices; a controller configured to detect mutual interference levels between any two end devices out of the plurality of end devices; detect individual requirements of each one of the plurality of end devices; and allocate the plurality of RUs to the plurality of end devices for uplink transmission depending on the mutual interference levels and the individual requirements; wherein RUs belonging to a same timeslot are allocated to more than one end device only when mutual interference levels between any two out of the more than one end device are below a first threshold and the individual requirements of each one of the more than one end device are satisfied.

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 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, 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 allocation of resource units in an optical communication system;

FIG. 4 demonstrates a typical interference scenario for uplink optical wireless communication;

FIG. 5 illustrates an example of allocation of resource units in an optical communication system;

FIG. 6 illustrates another example of allocation of resource units in an optical communication system;

FIG. 7 illustrates another example of allocating RUs alternately between a pair of STAs; and

FIG. 8 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 (Wi-Fi 6, 802.1 lax) for optical wireless communication. 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 mutual interference levels among the plurality of end devices into account. This allows mitigating the subchannel interference issues for neighboring nodes or mitigating the so-called hidden node issue known for optical wireless communication and still make optimal use of RUs. 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) according to Orthogonal Frequency Division Multiple Access (OFDMA) in an optical wireless communication system, wherein the uplink radio resource comprises a plurality of Resource Units (RUs) distributed on a plurality of timeslots with each RU comprising one or more subcarriers in a single timeslot. The method 100 comprises detecting, in step S 101 , mutual interference levels between any two end devices out of the plurality of end devices; detecting, in step SI 02, individual requirements of each one of the plurality of end devices; allocating, in step SI 03, the plurality of RUs to the plurality of end devices for uplink transmission depending on the mutual interference levels and the individual requirements; wherein RUs belonging to a same timeslot are allocated to more than one end device only when mutual interference levels between any two out of the more than one end device are below a first threshold and the individual requirements of each one of the more than one end device are satisfied.

FIG. 3 illustrates allocation of resource units in an optical communication system. As an example of RU mapping scenario 500, 551-567 show exemplarily 17 subcarriers where four end devices with communication nodes STA1-STA4 are mapped to different numbers of subcarriers and time slots. The AP will receive signals from multiple STAs in the same MU UL transmission. The signals are separated in frequency (multiple subchannels). However, RU leakage (ED transmissions outside its intended RUs) will result in interference in the AP, for example between STA1 and STA3 in the 1st transmission.

As shown in FIG. 3, OFDMA offers a huge flexibility in how to allow devices to access the channel. Especially as RUs of varying sizes allow for frequency and time domain multiplexing tailored to users’ traffic. To understand the influence on power consumption as well as quality of service, it can be assumed that the shown exemplary RU mapping repeats in a cyclic pattern. In this example, STA4 gets only 2 RUs: in the 3rd transmission 543 and in the 4th transmission 544. From the power consumption point of view, it means that with this scheduling STA4 can sleep (e.g., deactivate the OWC transceiver) half of the time and need a single wake up for the 3rd transmission. After 4th transmission it can go to sleep again. However, for QoS this means a jitter of packet transmission half of the shown mapping cycle.

For STA3, it gets an RU in each slot, and thus the jitter and transmission delay are lowest. However, data rate varies due to changing number of allocated subcarriers in each time slot in this example. Both STA3 and STA4 are mapped to the highest subchannels so may experience increased error rate due to the high frequency roll off of OWC channels.

STA1 and STA2 both have a missing single transmission slot making a maximal transmission delay during one transmission slot.

However, 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, especially because RU leakage from other EDs increases the noise floor and results in interference among EDs in the UL. FIG. 4 demonstrates a typical interference scenario for uplink optical wireless communication.

In a space 600, two EDs 621 and 622 may send at the same time beams 641 and 642, which they cannot observe as potentially interfering with each other. The AP 610 is in a position where it receives the two independent OWC transmissions 641 and 642. Multiple EDs managed with OFDMA and occupying neighboring RUs with other EDs may suffer from RU spectrum leakage and so reduce SNR at the AP and hence the total uplink throughput. In the AP receiver, these signals are combined and are potentially interfering with each other, degrading the reception signal quality at the AP 610 side.

To monitor the mutual interference level, it is proposed to make direct use of reception quality figures available from the commercial Wi-Fi chipsets. To achieve this goal, in parallel to normal data communication, a monitoring algorithm may request the quality of transmission figures from chipset registers and store these together with the related connections (occupying the related RUs). An optimization run tries to exclude sources of severe interferences, e.g., by pausing certain connections and checking whether or not the transmission for the remaining connections rises more than expected given the ratio of additional RUs available. One of the most important parameters for reaching high throughput is a high constellation (modulation order). The higher the modulation order the more bits can be transported in a single symbol. However high modulation orders of e.g., 256 QAM, 1024 QAM require the noise level (as measured with signal to noise ratio (SNR)) to be low. Improvement on SNR is a key to making use of higher modulation order possible. For example, the connections with a strong negative impact on SNR may be shifted to separate transmission timeslots and hence the interference across frequencies caused by RU leakage will be reduced or eliminated completely.

FIG. 5 illustrates an example of allocation of resource units in an optical communication system. In this example, STA2 gets its own time slots. This may be required if monitoring determines that STA2 is especially sensitive for interferences generated by neighboring nodes. When all subcarriers are devoted to STA2 during some of the transmissions 722 and 724. This mimics a TDMA channel management. All other nodes STA1, STA3, STA4 get the remaining timeslots and are optimized into the available RUs.

Interfering STAs may be scheduled in the same timeslot but are assigned to nonadj acent RUs as shown by STA1 711 and STA4 741 in FIG. 5 to reduce potential interference. Alternatively, interfering STAs may be scheduled in the same timeslot and assigned to adjacent RUs with enlarged guard tones, as illustrated in FIG. 6.

FIG. 6 illustrates another example of allocation of resource units in an optical communication system. Using larger guard tones between RUs may serve the same aim. As schematically depicted in FIG. 6, a two-subcarrier spacing 850 is kept for all transmissions. The transmission of STA2 during 4th slot 824 makes use of an RU with an increased number of subcarriers, which also reduces the chance of interferences.

It is beneficial that stations with larger frames in the buffer get larger RU’s. To achieve this, it may be possible to link the Buffer reports of the stations to the RU allocation algorithm.

Furthermore, the monitoring may also comprise recording a history of interfering ED pairs. The monitoring can support a single AP with multiple EDs connections to generate statistics for each of the EDs for future OFDMA optimization as long as an ED is not moved out of the coverage of the AP.

In a further example, the monitoring adapts the TX power ratio between interfering EDs which also can lead to improved SNR in the subchannels experiencing high interferences. Preferably, the monitoring may be assisted by allocating one or more dedicated timeslots for an interference assessment. Only specified pairs of stations are allowed to transmit in the one or more dedicated timeslots to evaluate the interference they cause to each other. This may beneficially be done by pausing one of the transmissions to have a reference SNR for a non-interfered connection. Therefore, the assessment may not be a direct measurement, but rather an indirect assessment by comparing the results of different allocations of RUs to the EDs during that dedicated one or more timeslots.

In a further example, the subchannel allocation of a pair of STAs (STA1 and STA2) may be alternated to find out the best performance. For example:

1. allocate sub channel- set 1 to STA1 + subchannel-set2 to STA2 (frequency multiplexing);

2. allocate sub channel -set2 to STA1 + subchannel-setl to STA2 (frequency multiplexing);

3. alternately allocate both subchannel-sets to STA1 and to STA2 (time multiplexing).

Then, AP may compare the performance for each of these allocations and decide which is the best. Fig. 7 illustrates these different options of allocations (1, 2, 3) in a small period. In this period the SNR may be determined for each allocation and the performance may be assessed by measuring the SNR levels of the received signals at the AP. However, to better evaluate the performance, it is beneficial to keep each of these allocations over a longer period, which allows time to optimize the modulation schemes for each of the allocations (for example, maximize the constellations for each allocation).

FIG. 8 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 detect mutual interference levels between any two end devices out of the plurality of end devices; detect individual requirements of each one of the plurality of end devices; and allocate the plurality of RUs to the plurality of end devices for uplink transmission depending on the mutual interference levels and the individual requirements; wherein RUs belonging to a same timeslot are allocated to more than one end device only when mutual interference levels between any two out of the more than one end device are below a first threshold and the individual requirements of each one of the more than one end device are satisfied.

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 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 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, according to an Orthogonal Frequency Division Multiple Access, OFDMA, in an optical wireless communication system, wherein the uplink radio resource comprises a plurality of Resource Units, RUs, distributed on a plurality of timeslots with each RU comprising one or more subcarriers in a single timeslot; the method (100) comprising: detecting (S 101) mutual interference levels between any two end devices out of the plurality of end devices; detecting (SI 02) individual requirements of each one of the plurality of end devices; allocating (SI 03) the plurality of RUs to the plurality of end devices for uplink transmission depending on the mutual interference levels and the individual requirements; wherein RUs belonging to a same timeslot are allocated to more than one end device only when mutual interference levels between any two out of the more than one end device are below a first threshold and the individual requirements of each one of the more than one end device are satisfied; wherein when the mutual interference level between the two end devices is below the first threshold and above a second threshold with the second threshold smaller than the first threshold; the method further comprises: allocating RUs belonging to a same timeslot on nonadj acent subcarriers to two end devices; or allocating RUs in a same timeslot on two adjacent subcarriers to two end devices with the two adjacent subcarriers having an enlarged guard tone.

2. The method (100) of claim 1, wherein the mutual interference level is detected by monitoring uplink data communication of the corresponding end devices, and/or by monitoring a received signal strength and noise floor of one or more RUs used by the corresponding end devices.

3. The method (100) of claim 1 or 2, wherein the individual requirement is related to at least one of a latency requirement, a size of a data frame to be transmitted, a data rate requirement, a jitter requirement, and another Quality-of-Service, QoS, requirement.

4. The method (100) of any one of previous claims, wherein an individual requirement of an end device is detected upon receiving a request from the end device or based on a data flow analysis of one or more previous communication links with the end device.

5. The method (100) of any one of previous claims, the method (100) further comprising requesting an end device out of the plurality of end devices to reduce or switch off its transmitter bias current when it is not transmitting to reduce a leakage output, if there is at least one mutual interference level related to the end device is equal to or above the second threshold.

6. The method (100) of any one of previous claims, the method (100) further comprising informing an end device out of the plurality of end devices to reduce its transmission power, when one or more mutual interference levels related to the end device is equal to or above the second threshold.

7. The method (100) of any one of previous claims, the method (100) further comprising allocating RUs in a further timeslot out of the plurality of timeslots exclusively to an end device out of the plurality of end devices for an uplink transmission, if at least one mutual interference level related to the end device is equal to or above the first threshold.

8. The method (100) of any one of previous claims, the method (100) further comprising allocating RUs in a further timeslot out of the plurality of timeslots exclusively to an end device out of the plurality of end devices for an uplink transmission when a received uplink signal strength related to the end device is above a third threshold.

9. The method (100) of any one of previous claims, the method (100) further comprising assigning a further timeslot out of the plurality of timeslots for assessing a mutual interference level between two or more end devices, wherein only the two or more end devices are allowed to transmit in that further timeslot.

10. 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 802.1 lax standard.

11. An Access Point, AP (200), for allocating uplink radio resource to a plurality of end devices to access the AP according to an Orthogonal Frequency Division Multiple Access, OFDMA, in an optical wireless communication system, wherein the uplink radio resource comprises a plurality of Resource Units, RUs, distributed on a plurality of timeslots with each RU comprising one or more subcarriers in a single timeslot; 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 detect mutual interference levels between any two end devices out of the plurality of end devices; o detect individual requirements of each one of the plurality of end devices; and o allocate the plurality of RUs to the plurality of end devices for uplink transmission depending on the mutual interference levels and the individual requirements; wherein RUs belonging to a same timeslot are allocated to more than one end device only when mutual interference levels between any two out of the more than one end device are below a first threshold and the individual requirements of each one of the more than one end device are satisfied; wherein when the mutual interference level between the two end devices is below the first threshold and above a second threshold with the second threshold smaller than the first threshold, the controller (220) is further configured to: allocate RUs belonging to a same timeslot on nonadj acent subcarriers to two end devices; or allocate RUs in a same timeslot on two adjacent subcarriers to two end devices with the two adjacent subcarriers having an enlarged guard tone.

12. The AP (200) of claim 11, wherein the optical transceiver (210) is configured to inform the plurality of end devices about uplink radio resource allocation by sending a triggering frame according to an IEEE 802.1 lax 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 11-12, cause the AP (200) to execute the steps of the method (100) according to any one of claims 1-10.