High efficiency modulation control

Abstract

To fully utilize the benefits of adaptive modulation or bit loading in multi-carrier wireless communication systems, a bit loading control method (700) is disclosed to reduce system complexity and signaling overhead by leveraging the properties of the communication channel, which has a channel response that decreases with increasing frequency. The disclosed method (700) estimates the channel response based on a test signal (S703) rather than applying adaptive bit loading on a per-subcarrier basis; and determines (S704) a bit loading scheme for allocating multiple subcarriers to one or more non-overlapping frequency bands based on the estimated channel response. For each frequency band, a separate modulation scheme is allocated, which is shared by more than one adjacent subcarrier contained within the same frequency band. The monotonicity of the channel response is used to accelerate the algorithm and make the control information more compact.

Description

Technical Field

[0001] This invention relates to the field of physical (PHY) layer modulation control in multi-carrier wireless communication systems. More particularly, various methods, apparatuses, systems, and computer-readable media are disclosed herein, relating to methods that assist a pair of transmitters and receivers in performing adaptive modulation control in an efficient manner. Background Technology

[0002] To enable a growing number of electronic devices, such as laptops, tablets, and smartphones, to wirelessly connect to the internet, wireless communication faces unprecedented demands for data rates and link quality, and these demands continue to grow year after year, given the emerging digital revolution associated with the Internet of Things (IoT). Radio frequency (RF) technologies, such as Wi-Fi, have limited spectrum capacity and cannot meet this revolution. Meanwhile, Light Fidelity (Li-Fi) is attracting increasing attention due to its inherent enhanced security and ability to support higher data rates across the available bandwidth of the visible, ultraviolet (UV), and infrared (IR) spectra. Furthermore, compared to Wi-Fi, Li-Fi is directional and shielded by light-blocking materials, making it possible to deploy a larger number of access points in densely populated areas by spatially reusing the same bandwidth. These key advantages compared to wireless RF communication make Li-Fi a promising solution for alleviating the congestion of the radio spectrum for IoT applications. Other benefits of Li-Fi can include guaranteed bandwidth for specific users and the ability to operate safely in areas susceptible to electromagnetic interference. Therefore, Li-Fi is a very promising technology for enabling next-generation immersive connectivity.

[0003] Several related terms exist in the field of lighting-based communications. Visible light communication (VLC) transmits data via intensity-modulated light sources such as light-emitting diodes (LEDs) and laser diodes (LDs), faster than the persistence of the human eye. VLC is typically used to embed signals into light emitted by a lighting source, such as everyday lamps, for example, indoor or outdoor lighting, thus allowing the lighting from the lamp to serve as a carrier of information. Therefore, the light can include a visible lighting component used to illuminate a target environment such as a room (often the primary purpose of light), and an embedded signal used to provide information to the environment (often considered a secondary function of light). In this case, modulation can typically be performed at a sufficiently high frequency to exceed human perception, or at least make any visible transient light artifacts (such as flicker and / or stroboscopic artifacts) sufficiently weak and not noticeable or at least tolerable to humans at a sufficiently high frequency. Therefore, the embedded signal does not affect the primary lighting function; that is, the user only perceives the overall lighting, not the effect of the data modulated into that lighting.

[0004] The IEEE 802.15.7 Visible Light Communication Personal Area Network (VPAN) standard maps anticipated applications to four topologies: peer-to-peer, star, broadcast, and coordinated. Optical Wireless PAN (OWPAN) is a more general term than VPAN, as it also allows communication over invisible light, such as UV and IR. Therefore, Li-Fi is often considered a derivative of Optical Wireless Communication (OWC) technology, which utilizes a broad spectrum to support bidirectional data communication.

[0005] In Li-Fi systems, signals are embedded by modulating the properties of light (typically intensity) using any of a variety of suitable modulation techniques. For high-speed communication, infrared (IR) is often used instead of visible light. Although ultraviolet and infrared radiation are invisible to the human eye, the techniques for utilizing these spectral regions are similar, although variations can occur as a result of wavelength dependence (such as in the case of refractive index). In many instances, using ultraviolet and / or infrared is advantageous because these frequency ranges are invisible to the human eye and can introduce more flexibility into the system. Of course, ultraviolet quanta have higher energy levels than infrared and / or visible light, which in turn may make the use of ultraviolet light undesirable in certain situations.

[0006] Based on modulation, any suitable light sensor can be used to detect information in light. For example, a light sensor can be a photodiode. A light sensor can be a dedicated photocell (point detector), a photocell array possibly with lenses, reflectors, diffusers, or phosphor converters (for lower speeds), or a photocell (pixel) array and lenses for forming an image on the array. For example, a light sensor can be a dedicated photocell included in a dongle inserted into a user device such as a smartphone, tablet, or laptop, or the sensor can be integrated and / or dual-purpose, such as an infrared detector array originally designed for 3D facial recognition. Either way, this allows applications running on the user device to receive data via light.

[0007] In many wireless communication systems, the frequency response of the communication channel is frequency-dependent or frequency-selective. To improve the capacity of the communication channel, adaptive modulation or adaptive bit loading is employed, where the number of bits is allocated to each subcarrier based on the channel characteristics of the subcarrier. If the first subcarrier has better channel characteristics than the second subcarrier, more bits are allocated to the first subcarrier accordingly. For multi-carrier wireless communication systems, such as orthogonal frequency division multiplexing (OFDM) systems, traditional adaptive bit loading methods assign the optimal modulation scheme to each individual subcarrier to maximize channel capacity. Summary of the Invention

[0008] Typically, due to the mobility of terminal devices, wireless channels can change rapidly, and therefore, adaptive modulation schemes may need to be updated frequently due to the dynamic frequency response of the channel. The computational complexity of deriving appropriate modulation schemes on multiple subcarriers, as well as the overhead of signaling exchange for aligning the modulation schemes between a pair of remote transmitters and receivers, can be considerable, potentially undermining the intention to increase effective data throughput on the channel. Furthermore, the complexity and overhead of implementing this approach can also be proportional to the number of subcarriers.

[0009] In view of the foregoing, this disclosure relates to a method, apparatus, system, computer program, and computer-readable medium for providing a mechanism to support an adaptive bit loading control method between a transmitter and receiver pair in a multi-carrier wireless communication system.

[0010] Therefore, to reduce the overhead of implementing adaptive modulation in multi-carrier wireless communication systems, the modulation control method proposed in this invention utilizes the monotonicity of the channel response to accelerate the algorithm, find suitable bit loading schemes for multiple subcarriers, and reduce the signaling overhead of notifying remote devices of these schemes. Based on the channel response, the multiple subcarriers are first divided into frequency bands comprising more than one subcarrier, and a separate modulation scheme is determined for each frequency band rather than each subcarrier. The monotonicity of the channel response is further utilized to simplify the representation or storage of the determined modulation schemes.

[0011] According to a first aspect of the present invention, a bit loading control method is provided. A bit loading control method in a multi-carrier wireless communication system is used to transmit data on a communication channel having a channel response that decreases with increasing frequency. The bit loading control method includes the following steps: sending a request for a test signal by a device; receiving the test signal from a remote device by the device; obtaining an estimated channel response of the communication channel on a plurality of subcarriers based on the received test signal; determining a bit loading scheme for allocating the plurality of subcarriers to one or more non-overlapping frequency bands based on the estimated channel response, each non-overlapping frequency band including more than one adjacent subcarrier, and allocating a separate modulation scheme shared by the more than one adjacent subcarrier to each frequency band, wherein the separate shared modulation scheme is allocated with a modulation order that monotonically decreases with increasing frequency.

[0012] Mobile wireless channels are characterized by variations in channel strength over time and frequency. These variations can be caused by either large-scale fading or small-scale fading. Large-scale fading results from signal attenuation due to propagation over a distance and diffraction around objects in the propagation path. Small-scale fading refers to variations in signal amplitude and phase, which can be experienced as a result of minute changes in spatial positioning between the transmitter and receiver (as small as half a wavelength). Therefore, large-scale fading is more relevant to link budget calculations, such as estimating communication coverage, while small-scale fading is more relevant to the design of reliable and efficient communication systems.

[0013] Channel state information (CSI) is typically used to describe how a signal propagates from the transmitter to the receiver and represents the combined effects of power attenuation with distance, scattering, and small-scale fading. The method of deriving CSI is called channel estimation. Channel estimation can be implemented in data-aided or blind methods. In data-aided methods, channel estimation is based on pilot data or training sequences known to both the transmitter and receiver. In blind methods, estimation is based only on some unknown data received. Typically, data-aided methods are assumed to achieve better channel estimation accuracy at the cost of system-level complexity in defining and transmitting pilot data or training sequences. This invention considers the data-aided method.

[0014] To simplify system design, communication channels are typically modeled as frequency channel response (or simply channel response). Therefore, channel response is included in the concept of CSI, which specifies CSI in the frequency domain.

[0015] Although the present invention is particularly applicable to links in mobile applications, it can also be used to configure static links by explicitly taking into account the channel changes experienced in communication between devices due to environmental variations.

[0016] In intensity-modulated optical communication, small changes in the optical signal on the order of half a wavelength (hundreds of nanometers) may not result in channel variations. In fact, the incoherent nature of photon intensity flux does not allow for cancellation at a single narrow spectral line. Meanwhile, for high-speed modulation, cancellation effects can occur in the modulation domain (e.g., hundreds of MHz or GHz), where the corresponding wavelengths are on the order of a meter. Typically, scattered and reflected light within a room tends to interfere with the signal, resulting in perceived attenuation in the higher portions of the modulation frequency range used, leading to a decreased frequency response. This, along with the observed large surface areas (and thus high capacitance) of transmitters (e.g., LEDs) and detectors (e.g., photodiodes) to trap incident light, contributes to a significant reduction in frequency response in the higher frequency range. The inventors have recognized that these effects, individually or collectively, are characteristic of high-speed optical communication and offer opportunities to improve efficiency specific to optical communication. Meanwhile, other wireless communication channels may also exhibit predominantly low-pass responses. In particular, systems employing wide baseband modulation exhibit this behavior, in contrast to carrier-offset narrowband modulation.

[0017] Note that the characteristic of the channel response decreasing with increasing frequency describes the general trend of the channel response across the entire channel bandwidth. Sporadic spikes are likely to occur in a single subcarrier due to sudden noise or interference.

[0018] The communication channel proposed in this invention is characterized by a channel response that decreases with increasing frequency, meaning that signals passing through the channel experience more attenuation in higher frequency bands / parts than in lower frequency bands / parts. This monotonicity of the channel response provides additional opportunities for system optimization.

[0019] As described above, adaptive modulation or adaptive bit loading is a method to improve channel capacity in a multicarrier system by allocating bits to each subcarrier based on the channel characteristics of the subcarrier. However, applying this method on a per-subcarrier basis can suffer efficiency losses due to additional computational complexity and signaling overhead. Therefore, it is advantageous to allocate multiple subcarriers to one or more non-overlapping frequency bands, where each frequency band includes one or more adjacent subcarriers, and at least one frequency band includes more than one adjacent subcarrier. The calculation of a suitable modulation scheme can then be performed on a per-segment basis. The derived modulation scheme can then be shared by all subcarriers contained in the same segment.

[0020] Preferably, each frequency band includes more than one adjacent subcarrier. However, in some cases, it may be possible that some frequency bands contain only one subcarrier.

[0021] To derive a suitable modulation scheme, modulation control methods can consider factors other than channel response, such as the transmitter's output power and the minimum signal-to-noise ratio (SNR) required for the receiver to demodulate and decode the received data propagating along the channel. However, the transmitter's output power and the minimum SNR requirement for a particular modulation scheme are generally considered predefined or known information. Therefore, channel response is the primary dynamic factor in the evaluation.

[0022] When the communication channel is relatively dynamic or when no local or historical channel information is available, it is preferable to obtain the estimated channel response based on test signals from a remote device. To initialize the process and derive the latest channel response, a request is first sent to the remote device. Then, based on the received test signals, the estimated channel response on multiple subcarriers is obtained. This request can be sent as a separate control or signaling message or carried in a data packet. Similarly, the test signal can be implemented as a training sequence included in a dedicated test packet or carried in another data packet received from the remote device.

[0023] To keep a pair of remote devices up-to-date with channel response information, such test packets or dedicated control or signaling messages can be sent on an event-driven basis, for example, when the propagation channel changes—this could be due to the movement of one of the devices or another device partially blocking the propagation channel. Given a degraded signal quality in recently received packets, one of the remote devices can trigger the process by first sending a request to derive an updated channel response and refresh the bit allocation scheme. This process can also be performed periodically, for example, according to a specific schedule. Alternatively, the remote devices could occasionally utilize idle periods to implement the disclosed method to keep the bit allocation scheme always up-to-date.

[0024] In another option, the request can be sent by the device as a broadcast or multicast message. All remote devices in the vicinity of the device, or a subset of adjacent remote devices, can receive the request. One or more remote devices receiving the request can respond by sending a test signal to the device. In this sense, the device can trigger the process to simultaneously establish a channel response link between each responding remote device and the device.

[0025] This process can be initiated by either the receiver or the transmitter in the intended session. In one example, the receiver first sends a request for a test signal to the transmitter, and then, based on the derived estimated channel response, determines the bit loading scheme to be used in the intended session between the transmitter and receiver. In this sense, for a bidirectional link, the roles of the transmitter and receiver are reversed. Alternatively, such a process can be triggered separately for each unidirectional link. In some cases, a symmetrical bidirectional link state can be assumed. And then, the process may only be triggered once. By assuming a symmetrical bidirectional link state, the transmitter is likely to initialize the process by first sending a request to the intended receiver. And then, the transmitter derives an estimated channel response based on the test signal received from the intended receiver and further determines the bit loading scheme. The transmitter then directly uses the bit loading scheme in subsequent data sessions with the intended receiver.

[0026] In terms of maximizing data throughput, this proposed implementation initially appears suboptimal compared to the per-subcarrier approach. However, if we take into account computational and signaling overhead, the overall system may even be more efficient using the proposed implementation, especially when the channel response is approximately monotonic and does not vary drastically with frequency. In fact, even when the actual frequency response is not strictly monotonic but rather substantially monotonically decreasing, the proposed method remains advantageous due to its approximation of the monotonically decreasing response, particularly taking advantage of the lower system response at high frequencies.

[0027] From a practical perspective, communication standards typically define a finite set of potential modulation schemes in their physical layer (PHY) specifications. In many standards, these potential modulation schemes are also defined in conjunction with coding schemes, collectively known as modulation and coding schemes. Therefore, the modulation schemes proposed in this invention should be understood as being identical to the modulation and coding schemes of those systems. Consequently, the minimum SNR requirement for a receiver to demodulate and decode certain received data, given both the modulation order and coding rate combination, is also specified. Furthermore, PHY layer specifications typically indicate this minimum SNR requirement for a finite set of modulation (and coding) schemes supported by the receiver side, listed in monotonic order. Therefore, considering the similar monotonicity of the channel response across these frequency bands, selecting individual appropriate modulation schemes for one or more frequency bands is further simplified.

[0028] Data transmitted on one or more adjacent subcarriers is modulated using the same assigned modulation scheme. Modulation here should be understood as mapping data bits to symbols. When the modulation scheme is represented by a constellation diagram, this bit-to-symbol mapping is also called constellation diagram mapping. Different modulation schemes can be distinguished by different constellation diagram sizes. Note that channel coding can be applied to the original data bits before the modulation or bit-to-symbol mapping steps.

[0029] In OFDM-based systems, an additional step of OFDM modulation is required, which is achieved by performing an inverse fast Fourier transform (IFFT) to convert parallel frequency domain data on multiple subcarriers into serial time domain data for transmission over the channel.

[0030] Advantageously, the method further includes the step of updating the bit loading scheme when a change in the channel response of the communication channel is detected, wherein the update is performed by maintaining each frequency band with an individual modulation scheme comprising the same number of subcarriers, and shifting the allocation of frequency bands up or down in frequency according to the change in channel response.

[0031] A separate shared modulation scheme assigned to each of one or more non-overlapping frequency bands constitutes a bit loading distribution. When a change in channel conditions is detected, it is also possible to adjust the original bit loading scheme rather than triggering a new process to derive an entirely new bit loading scheme, especially when the observed change in channel conditions is not significant.

[0032] The bit loading scheme is adjusted by horizontally shifting the bit allocation table. For a given modulation scheme, the number of subcarriers contained in each frequency band remains constant, but the allocation of the bands is offset in the frequency domain. The granularity of the offset can be based on each subcarrier. For example, when channel conditions improve, the allocation of one or more frequency bands can be offset to higher frequencies by a first number of subcarriers; when channel conditions deteriorate, the allocation of one or more frequency bands can be offset to lower frequencies by a second number of subcarriers. For each frequency band, the number of subcarriers contained in that band remains constant. Therefore, this is a horizontal offset of the bit loading scheme in the frequency domain.

[0033] For boundary conditions, it is possible that when the bit loading scheme shifts to the right (towards a higher frequency) by a first number of subcarriers, a new segment is generated at the beginning of the frequency band, comprising that first number of subcarriers. This new segment can use a new modulation scheme, which may have a modulation scheme of even higher order than previously supported by the channel. Sometimes, when the actual system does not support even higher order modulation schemes, the new segment can use the same highest modulation scheme as before, which can be equivalent to an extension of the first frequency band under such boundary conditions.

[0034] Similarly, when the bit loading scheme shifts left (towards a lower frequency) by a second number of subcarriers, the first frequency band at the lower band limit can include fewer subcarriers than before, for example, the second number of subcarriers are shifted out. If the first frequency band includes fewer subcarriers than the second number, then the first frequency band can be completely shifted out and is also part of the second frequency band, meaning the channel no longer supports the previous highest-order modulation scheme. In this case, if the system supports it, the last frequency band at the upper band limit can use a lower modulation order. Otherwise, the last second number of subcarriers at the upper band limit may no longer be used for bit loading.

[0035] Alternatively, another update can be made by maintaining the same allocation of one or more non-overlapping frequency bands and shifting the individual shared modulation scheme allocated to each of the one or more non-overlapping frequency bands up or down in frequency, depending on changes in the channel response.

[0036] Therefore, adjustments in another update are made by keeping the allocation of one or more non-overlapping frequency bands or the grouping of subcarriers unchanged, and only shifting the bit loading distribution. Since individual shared modulation schemes are allocated with a modulation order that monotonically decreases as frequency increases, changes in the channel can be easily adapted by simply shifting the individual shared modulation schemes allocated to each frequency band up or down. For example, when the channel deteriorates, the initially allocated modulation scheme may not be suitable for a certain frequency band, and then another modulation scheme initially allocated to another frequency band with a higher frequency may meet the link budget criterion, where that other modulation scheme has a lower modulation order. Depending on the degree of change in the communication channel, the offset may be related to the modulation scheme initially allocated to a frequency band adjacent to or further away from the current frequency. Similarly, when channel conditions improve, this offset is achieved by reusing the modulation scheme initially allocated to a first frequency band with a lower frequency to a new frequency band with a higher frequency.

[0037] Each of one or more frequency bands can also be understood as an offset in the bit loading distribution of another update, which means reducing the modulation order of the individual modulation scheme allocated to each of the one or more frequency bands when the channel response deteriorates; or increasing the modulation order of the individual modulation scheme allocated to each of the one or more frequency bands when the channel response improves.

[0038] In one example, the communication channel is an optical communication channel, and the channel response can be dominated by one or more components in the signal propagation chain. One possible component could be the optical front end of the transmitter, such as a light-emitting diode (LED). Compared to the optical wireless communication spectrum, the modulation bandwidth of commercial LEDs is typically very limited. Due to the dynamic response or carrier recombination process of LEDs, they exhibit power-limited first-order low-pass behavior, which may dominate the channel response of the optical communication channel. Typically, the dynamics on an optical communication channel will only be reflected in the frequency shift of the channel response while maintaining the same channel distribution. Therefore, maintaining the same frequency band allocation and only shifting the bit loading distribution accordingly would be highly efficient compared to alternatives that require reinitializing the entire process to derive a new bit loading scheme.

[0039] In one embodiment, the method further includes the step of sending a bit loading scheme to a remote device for use by the remote device when communicating with the device via a communication channel.

[0040] When the disclosed method is triggered by the receiver, the receiver will first transmit the determined bit loading scheme to the remote transmitter before the transmitter can apply the scheme in subsequent data communications. However, when the disclosed method is triggered by the transmitter or the bit loading scheme is derived by the transmitter, it may not be necessary to transmit the bit loading scheme to the intended remote receiver beforehand. Of course, it is beneficial for the transmitter to also inform the device about the frequency band allocation and the corresponding allocation of each modulation scheme in order to facilitate the remote device to detect data packets using appropriate settings. Otherwise, deriving such information may introduce additional complexity to the remote device side for proper demodulation and decoding of packets. Information related to the bit loading scheme can be included in the same data packet in which the determined bit loading scheme is executed. For example, the transmitter can insert the information into the packet header, or immediately after the packet header and before the payload of the data packet.

[0041] Preferably, the method further includes the step of a local storage bit loading scheme.

[0042] When the pair of remote devices is primarily fixed, the communication channel between the two devices can be stable over a certain period of time, and at least some information contained in the same bit loading scheme, or the original bit loading scheme, can be reused by one or more sessions between the same pair of remote devices. For example, the shift of the bit loading distribution regarding changes in channel response is based on the original bit loading scheme. Therefore, it can be highly beneficial for the devices to store such information locally.

[0043] In a preferred configuration, the test signal is contained in a dedicated field within a dedicated probe group or data or management group.

[0044] To establish a new session between a pair of remote devices and determine the latest bit loading scheme, dedicated control packets or frames can be used. For example, a test signal can be included in a dedicated probe packet or probe frame. When an earlier session already exists between the pair of remote devices, the test signal can be carried in a data or management packet or frame, for example, placed in a dedicated field within the data or management packet. This carrying method may be more efficient than using dedicated probe packets.

[0045] Advantageously, the request for test signals also includes parameters related to dedicated fields in dedicated probe packets or data or management packets.

[0046] The initiator of the bit loading control method—either the transmitter or the receiver—can instruct the responder to prepare a test signal by including configuration parameters in the request. Configuration parameters may include information about the selection between dedicated fields in a dedicated probe packet or another packet, the test signal mode, the test signal duration, or which part of the data or management packet can be used to insert the dedicated field of the test signal.

[0047] In another embodiment, the bit loading scheme is configured to use a format that includes at least one of the following representations:

[0048] - The index of the lowest subcarrier in each frequency band, and the index of the highest subcarrier in any frequency band;

[0049] - The index of the highest subcarrier in each frequency band, and the index of the lowest subcarrier in any frequency band;

[0050] - The index of the lowest subcarrier in any frequency band, and the number of subcarriers included in each frequency band, listed in ascending order of frequency;

[0051] - The index of the highest subcarrier in any frequency band, and the number of subcarriers included in each frequency band, listed in descending order of frequency;

[0052] - The number of subcarriers included in each frequency band, listed in ascending order of frequency.

[0053] The bit loading scheme transmitted to the remote device includes at least information about the allocation of one or more frequency bands. Given the monotonicity of the channel response along a frequency band, individual modulation (and / or coding) schemes can be derived based on predefined lookup tables, such as the Modulation and Coding Scheme (MSC) table defined in the PHY layer specification of a communication standard. Note that the MCS tables defined in the standard are typically developed in ascending order of modulation order and are listed as MCS0, MCS1, MCS2, and so on. In one example, the frequency band with the highest subcarrier frequency can be assigned the lowest modulation order, such as MCS0. And then, each subsequent frequency band with a decreasing subcarrier frequency can be assigned the next higher modulation order in the MCS table. If there is any anomaly in the mapping between the options provided in the MCS table and the modulation orders assigned to frequency bands—for example, skipping one or both options in the MCS table due to a sharp drop in channel response—the modulation control unit can provide additional information. One possibility is that additional information, such as an index of the assigned modulation order for each frequency band in the MCS table, or an index of skipped modulation orders in the MCS table, can be sent to the remote device.

[0054] Further leveraging the monotonicity of the channel response simplifies the representation of adaptive modulation or bit-loading methods, particularly regarding more efficient signaling messages to inform remote devices about the method, and reducing the size of transmitter and / or receiver memories to store relevant information for signal processing, such as modulation and / or demodulation, and encoding and / or decoding. Given the fact that the channel response monotonically decreases with increasing frequency, the assigned modulation order will also monotonically decrease with increasing frequency.

[0055] Because non-overlapping frequency bands are allocated in such a way that each frequency band includes one or more adjacent subcarriers, this bit loading scheme can be represented in a very compact manner. There are several options for this representation, such as in ascending or descending frequency order. One option is to present the information by sequentially indicating the index of the lowest subcarrier that begins each frequency band and the index of the highest subcarrier that includes all frequency bands for each band. Note that here, the lowest or highest subcarrier means either the subcarrier with the lowest subcarrier frequency or the subcarrier with the highest subcarrier frequency. Another option is to present the information by indicating the index of the lowest subcarrier that includes all frequency bands, and the number of subcarriers included in each frequency band, listed in ascending frequency order. Similarly, both of these options can be presented in descending frequency order by starting with the highest subcarrier that includes all frequency bands. Another option is to record the allocation of one or more frequency bands by sequentially listing the multiple subcarriers included in each frequency band, for example, in ascending frequency order. In this option, the range of subcarriers may have already been agreed upon between a pair of remote devices, for example, by defining the first subcarrier index and the last subcarrier index.

[0056] To notify remote devices of one or more frequency band allocations, a compact format for transmitting information can be included in dedicated signaling packets or messages and sent to the remote device before data packet transmission begins. These dedicated signaling messages can be transmitted using the lowest possible modulation order or the most robust modulation and coding scheme to ensure that information is delivered most reliably under given channel conditions.

[0057] Embedding this compact format in the header of each data frame or data packet may be even more beneficial. Note that in communication systems, data packets typically consist of at least two parts: a header and a payload, which are associated with control information and user data, respectively. The control information included in the header can be a preamble, address information, sequencing information, the modulation and / or coding scheme used in the payload, the payload length, and so on. By embedding the compact format in the header of each data packet or data frame, frequency band allocation can be updated in a more dynamic manner.

[0058] When the transmitter initiates the bit loading control method, it can derive an updated channel response based on the ACK from the remote device and then determine a new frequency band allocation, or adopt offsets for various modulation schemes. The remote device receives the update promptly by embedding a compact format conveying the new allocation into the packet header of the next data packet. Therefore, the system is more robust and flexible in handling changes to the communication channel.

[0059] Similarly, when the receiver is the initiator of the bit loading control method, it can derive an updated channel response based on the most recently received data packets and update the bit loading scheme accordingly. The updated compact format can be immediately fed back to the transmitter by piggybacking this information in the ACK of the most recently received data packets.

[0060] In one example, the communication channel is an optical communication channel, and a compact format can be embedded in the header portion of the illumination communication data frame. The illumination communication data frame can conform to the IEEE 802.11 standard or the ITU G.9991 standard for high-speed optical wireless data communication.

[0061] Preferably, each modulation scheme is implemented with a uniform power load in each frequency band.

[0062] For wireless communications, transmitter operations are subject to certain regional or national regulations regarding electromagnetic compatibility (EMC)—such as those set by the Federal Communications Commission (FCC) in the United States or the European Telecommunications Standards Institute (ETSI) in Europe. Therefore, it is beneficial for transmitters to apply a uniform power load or uniform power spectral density (PSD) across every frequency band in a multi-carrier system. This is because it provides the transmitter with the opportunity to utilize the maximum permissible output power across the entire frequency band.

[0063] Alternatively, the transmitter can apply pre-emphasis techniques to compensate for the frequency-selective channel response in order to obtain a uniform received spectral density across the receiver band. Then, the transmitter's output power will be limited initially at higher frequencies, sacrificing channel capacity at lower frequencies. If the fading channel response is fully or significantly compensated by the pre-emphasis filter, the same modulation order or modulation and coding scheme can be applied across the entire band, i.e., multiple subcarriers.

[0064] According to a second aspect of the invention, a bit loading control device is provided. A bit loading control device for assisting in the transmission of data on a communication channel in a multi-carrier wireless communication system, the communication channel having a channel response that decreases with increasing frequency, the bit loading control device comprising: a transmitter configured to transmit a request for a test signal; a receiver configured to receive the test signal from a remote device; a controller configured to obtain an estimated channel response of the communication channel on a plurality of subcarriers based on the received test signal; and a bit loading scheme determined based on the estimated channel response for allocating the plurality of subcarriers to one or more non-overlapping frequency bands, each non-overlapping frequency band comprising more than one adjacent subcarrier, and allocating a separate modulation scheme shared by the more than one adjacent subcarrier to each frequency band, wherein the separate shared modulation scheme is allocated with a modulation order that monotonically decreases with increasing frequency.

[0065] As described above, the bit loading control device can be included in the transmitter or receiver to help the remote device implement the proposed adaptive bit loading or adaptive modulation scheme in an efficient manner, which provides a good balance between throughput enhancement and implementation overhead.

[0066] Advantageously, the bit loading control device also includes a memory for storing derived bit loading schemes, such as one or more allocations of one or more non-overlapping frequency bands, wherein each frequency band includes one or more adjacent subcarriers and a corresponding individual modulation scheme allocated to each of the one or more non-overlapping frequency bands.

[0067] Since one or more allocations derived from the frequency band serving the adaptive bit loading method can be reused by several consecutive data packets destined for the same remote device, it is advantageous to store this information locally in memory. Given the use of a very compact format, it does not place a significant burden on memory in terms of storage space and resources available for reading and writing information.

[0068] In one embodiment, the bit loading control device is further configured to perform wireless communication with a remote device in a multi-carrier wireless communication system, wherein the transmitter is further configured to modulate data transmitted on one or more adjacent subcarriers belonging to the same frequency band using the same individual modulation scheme according to the bit loading scheme; and to transmit the modulated data to the remote device via a communication channel.

[0069] In this embodiment, the bit loading control device operates in a transmitter-initiated manner. Therefore, the transmitter side of the intended session initializes the bit loading control method, and subsequently, the same device applies the determined bit loading scheme when modulating data to be transmitted to a remote receiving device.

[0070] In another embodiment, the bit loading control device is further configured to perform wireless communication with a remote device in a multi-carrier wireless communication system, wherein the receiver is further configured to receive data from the remote device via a communication channel; and to demodulate the data received on more than one adjacent subcarrier belonging to the same frequency band using the same individual modulation scheme according to the bit loading scheme.

[0071] Using this option, the transmitter of the bit loading control device is also configured to send a bit loading scheme to a remote device for use by the remote device communicating with the bit loading control device.

[0072] In this option, the bit loading control device operates in a receiver-initiated manner. Therefore, the receiver side of the intended session initializes the bit loading control method and provides a bit loading scheme to the remote transmitter. Subsequently, the bit loading control device applies the determined bit loading scheme when demodulating data received from the remote transmitter equipment.

[0073] In a preferred system configuration, the communication channel is an optical communication channel, and the bit loading control device further includes an optical front end configured to connect to the transmitter and receiver for transmitting and receiving data on the optical communication channel.

[0074] An optical front end is used to convert an electrically transmitted signal into an output optical signal in the transmitter chain and to convert a received optical signal into an electrical signal in the receiver chain. The optical front end includes at least one light source in the transmitter chain, such as an LED, laser diode (LD), or vertical-cavity surface-emitting laser (VCSEL), and at least one receiving optical sensor or photodiode in the receiver chain. Commercial LEDs typically exhibit power-limited first-order low-pass behavior. When the channel response of an optical communication channel is dominated by an LED, it will exhibit a channel response that monotonically decreases with increasing frequency.

[0075] According to a third aspect of the present invention, a multi-carrier wireless communication system is provided. The multi-carrier wireless communication system has a communication channel with a channel response that decreases with increasing frequency. The multi-carrier wireless communication system includes...

[0076] - According to the first transceiver and remote device of the present invention, the remote device is configured to receive a bit loading scheme from the first transceiver and demodulate data received from the first transceiver according to the received bit loading scheme; or

[0077] - According to the second transceiver and the second remote device of the present invention, wherein the second transceiver is further configured to transmit a second bit loading scheme to the second remote device, and the second remote device is further configured to receive the second bit loading scheme from the second transceiver, and, according to the received bit loading scheme, modulate data transmitted on one or more adjacent subcarriers belonging to the same frequency band using the same individual modulation scheme; and

[0078] In a multi-carrier wireless communication system, modulated data is transmitted to a second transceiver through a communication channel.

[0079] Since the disclosed bit loading control method can be either transmitter-initiated or receiver-initiated, the system can have two configurations. In the first configuration, the system's first transceiver operates in a transmitter-initiated mode; in the second configuration, the system's second transceiver operates in a receiver-initiated mode.

[0080] A transceiver enables wireless communication in multi-carrier systems—such as wireless systems based on orthogonal frequency division multiplexing (OFDM). The wireless channel can reside in different electromagnetic spectra (e.g., radio frequency, microwave frequencies) or optical components (e.g., infrared, visible, or ultraviolet). Therefore, the front-end included in the transceiver can be an analog front-end or an optical front-end. In one example of an optical front-end, LEDs are used to convert electrical signals from baseband into optical signals for transmission over the channel.

[0081] The present invention can also be embodied in a computer program including a code device, which, when executed by a bit loading control device including a processing device, causes the processing device to execute the bit loading control method of the present invention. Attached Figure Description

[0082] In the accompanying drawings, similar reference numerals are used throughout. Figure 1 Generally, the same parts are referred to. Furthermore, the accompanying drawings are not necessarily to scale; instead, the focus is usually on illustrating the principles of the invention.

[0083] Figure 1 An overview of the OWC network and the backbone network connected to it is presented;

[0084] Figure 2 The basic components of a Li-Fi access point are schematically depicted.

[0085] Figure 3 The basic components of a Li-Fi access point with multiple optical front ends are schematically depicted.

[0086] Figure 4 The basic components of a Li-Fi endpoint are schematically depicted.

[0087] Figure 5 The basic components of the optical front end contained in a Li-Fi access point or Li-Fi endpoint are schematically depicted.

[0088] Figure 6 The channel response decreases as the frequency increases;

[0089] Figure 7 The allocation of one or more frequency bands is shown;

[0090] Figure 8 These are the modulation-related parameters defined for OFDM PHY in IEEE 802.11 (2016);

[0091] Figure 9 The data frame format is shown;

[0092] Figure 10 The basic components of the bit loading control device of the present invention are schematically shown.

[0093] Figure 11 The basic components of a bit loading control device according to one embodiment are schematically depicted.

[0094] Figure 12 A flowchart of the bit loading control method is shown;

[0095] Figure 13 An example of an initial bit allocation table is shown;

[0096] Figure 14 Showing relative to Figure 13 The initial bit allocation is the result of shifting the values ​​in the bit allocation table up by two;

[0097] Figure 15 Showing relative to Figure 13 The initial bit allocation is the result of shifting the values ​​in the bit allocation table down by two. Detailed Implementation

[0098] Now, it will be based on an optical wireless communication (OWC) network system 100, or more specifically, on such Figure 1 The Li-Fi network system shown is used to illustrate various embodiments of the invention. For illustrative purposes, Li-Fi network 100 is connected to backbone network 20 via IP router 15 and Ethernet switch 14. In a real system, more routers and switches can be deployed to connect the backbone network to the Li-Fi network. In this example, the connection between the Li-Fi network and the backbone network is referred to as backbone connection 21. The backbone connection is a stable and high-speed link, which can be a wired connection (such as Ethernet) or a radio frequency (RF) or millimeter wave-based wireless connection. The backbone connection can also be another type of optical wireless link, which differs from the link performed by the endpoints in an optical multi-cell wireless network. An example of another type of optical wireless link could be a free-space point-to-point optical link.

[0099] Li-Fi System Overview and Network Architecture

[0100] As a wireless communication technology for local area networking, Li-Fi plays a similar role to Wi-Fi in providing connectivity for the last few tens of meters. A Li-Fi network 100 may include multiple optical access points (APs) 120 and network devices or endpoints (EPs) 110. Each endpoint 110 is selectively associated with and synchronized with a corresponding access point 120. Li-Fi APs 120 may connect to one or more optical front-ends or Li-Fi transceivers (TRXs) 121 to provide access to Li-Fi devices or Li-Fi endpoints (EPs) 110. The trapezoidal shape shown by the dashed line illustrates the field of view (FOV) or coverage area of ​​each Li-Fi transceiver 121. An EP 110 will only be able to receive downlink communication from a Li-Fi AP 120 when it is within the coverage area of ​​that AP 120. By assuming symmetrical uplink and downlink in optical communication, bidirectional optical links can be established under the same conditions. Due to the line-of-sight characteristics of optical communication links, there is no direct optical link between adjacent access points 120, but the endpoint 110 located in the overlapping area of ​​the coverage of adjacent access points 120 can detect optical signals from both access points.

[0101] In one example, the Li-Fi AP 120 can also operate as a domain host with additional functions according to G. hn, ITU G.9960, and G.9961 to manage several Li-Fi EPs 110. In one implementation, a handover occurs when an EP roams from one domain to another. In another implementation, each Li-Fi AP 120 operates as a domain host managing a separate domain hosting multiple Li-Fi EPs, up to 255 in total. Such Li-Fi APs 120 are typically located on the ceiling. They may, but not necessarily, be juxtaposed with lighting fixtures, especially when communication is not based on visible light. The main functions of the Li-Fi AP 120 may include announcing the presence of the AP 120 to surrounding Li-Fi EPs 110, registering and deregistering Li-Fi EPs 110, providing Media Access Control (MAC) scheduling between associated Li-Fi EPs 110, collecting interference reports from EPs 110, adjusting local scheduling in response to interference reports, and / or reporting adjacency relationships to the Li-Fi controller 13. Some functions of the Li-Fi AP 120 (such as MAC scheduling for interference avoidance) can be implemented in a centralized manner by the Li-Fi controller 13.

[0102] Li-Fi EP or Li-Fi device 110 is an end-user modem that facilitates connection of endpoint devices to Li-Fi network 100. Currently, Li-Fi EP 110 is typically a dedicated entity for connecting to laptops or other end devices. In the future, Li-Fi EP 110 may be partially or fully integrated into smartphones, tablets, computers, remote controls, smart TVs, display devices, storage devices, home appliances, or other smart electronic devices.

[0103] There may be multiple Li-Fi controllers or central controllers 13 connected to access points 120 in the Li-Fi network 100. The Li-Fi controllers or central controllers 13 are responsible for centrally controlling the Li-Fi system when necessary, such as deriving information about topology and adjacency relationships, and determining scheduling between different Li-Fi access points (APs) to suppress interference. Furthermore, the Li-Fi controllers 13 can also be used to provide a user interface that allows users or administrators (such as IT managers) to configure scheduling tables among multiple Li-Fi APs, monitor reports from these Li-Fi APs, and / or derive further statistics about system performance. Typically, it is ensured that only one Li-Fi controller 13 is visible to a single AP; this is achieved through network configuration such that traffic to and from the Li-Fi controller 13 is isolated within its own network segment via a virtual LAN (VLAN) or similar. Additionally, protocols such as the Control and Provisioning of Wireless Access Points (CAPWAP) protocol can be used to discover multiple controllers and select one with available resources to host / manage access points joining the infrastructure.

[0104] In one exemplary implementation of the Li-Fi system, a Li-Fi synchronization server 16 is connected to the system, which is responsible for synchronizing (or aligning) the G.vlc Media Access Control (MAC) cycles of different G.vlc domains. This requires aligning some common time slots for detecting adjacent APs 120 and avoiding interference to EP 110 located in the overlapping area of ​​adjacent APs 120. Due to the line-of-sight nature of optical links, adjacent APs 120 typically cannot directly detect each other's signals. However, if adjacent APs 120 are transmitting simultaneously, EP 110 located in the overlapping area of ​​two adjacent APs 120 may experience interference. To avoid this, it may be necessary to keep adjacent APs 120 synchronized with a common time base and prevent them from transmitting at the same time. A preferred option for network synchronization is to use the Precision Time Protocol (PTP), IEEE 1588v2. PTP provides sub-microsecond accuracy, which is sufficiently fair for MAC alignment of mutual G.vlc domains. To maintain the accuracy of PTP, support from Ethernet switches is necessary, and this should also be a capability of PTP. To maintain the accuracy of PTP, every component in the Ethernet network must handle PTP, therefore the switches chosen for any deployment must support and be configured accordingly to operate in PTP mode.

[0105] It is also possible that the Li-Fi system will be deployed on legacy systems where PTP is not supported by the existing infrastructure. Therefore, additional measures should be taken to synchronize neighboring APs 120 in a different and potentially suboptimal manner, and thus a solution should be found for EP 110 to handle the non-ideal synchronization between neighboring APs 120.

[0106] Detailed system description

[0107] Li-Fi AP

[0108] The Li-Fi AP 120 is a key unit for establishing the Li-Fi network 100. In some scenarios, the Li-Fi AP 120 also forms the interface between the existing IT infrastructure and the Li-Fi network 100. Figure 2 The diagram shows a high-level block diagram of the Li-Fi AP 120.

[0109] On one hand, the Li-Fi AP 120 has an interface 124 to the backbone network, which can be a wired connection (Ethernet) or a wireless connection (RF, millimeter wave, or another type of optical wireless than the optical wireless being performed by the Li-Fi AP). On the other hand, the Li-Fi AP 120 has an optical front-end 121 to establish an optical link with one or more Li-Fi APs 110. Furthermore, the Li-Fi AP 120 also performs bidirectional conversion or transformation between data on the backbone network 20 and data on the optical link, in terms of conversion between different modulation schemes and modulation of analog signals. Therefore, the Li-Fi AP 120 also includes at least a digital modulator and demodulator assembly 123 and an analog front-end 122. In the transmission path, the analog front-end (AFE) 122 may include a programmable amplifier, filters, and drivers to modulate and amplify the baseband signal to drive the optical front-end. For the reception path, the AFE 122 may include attenuators, low-noise amplifiers, filters, and programmable gain amplifiers to accommodate the received signal for further digital processing.

[0110] An optical front-end 121, comprising at least a light source and a light sensor, performs the conversion between electrical and optical signals. In the transmitter chain, the optical front-end 121 converts the electrical transmission signal via the light source into an output optical signal. In the receiver chain, the optical front-end 121 converts the received optical signal via the light sensor into an output electrical signal for further signal processing. The optical front-end 121, also known as a Li-Fi transceiver (TRX), enables:

[0111] • Li-Fi transmitter (Tx): Converts the electrical signal obtained from the AFE into an optical signal (e.g., to be emitted by an LED), and

[0112] • Li-Fi receiver (Rx): Converts received optical signals (e.g., from photodiodes) into electrical signals for AFE.

[0113] The Li-Fi AP 120 can connect to a single Li-Fi TRX 121 or multiple Li-Fi TRX 121s, allowing optical signals to be transmitted on different optical paths. When the Li-Fi AP 120 is connected to multiple Li-Fi TRX 121s, the Li-Fi AP can treat them as a coherent signal or as (partially) independent incoherent signals used to establish a communication link. Figure 3 An example of a Li-Fi AP 120 with multiple Li-Fi TRX 121s is shown. A Li-Fi interface component 125 is used to separate or combine data sent to or received from the multiple Li-Fi TRX 121s.

[0114] Li-Fi EP

[0115] Figure 4 A high-level overview of the Li-Fi EP or Li-Fi device 110 is shown. Similar to the Li-Fi AP 120, the Li-Fi EP 110 includes at least an optical front end 111, an analog front end 112, a digital modulator / demodulator 113, and an interface 114 to an end device or processor.

[0116] The Li-Fi EP 110 can be connected to a terminal device as a separate entity via cable, or partially or fully integrated into the terminal device. For many terminal devices (such as laptops, smartphones, and remote controls), Ethernet is the recognized interface in the terminal device's operating system. Alternatively, Li-Fi can also be used to provide a communication interface to the terminal device. To simplify system integration of the Li-Fi EP or Li-Fi device into the terminal device's operating system, USB Ethernet is advantageous. Therefore, in one option, the Li-Fi EP or Li-Fi device 110 can be connected to the terminal device via a standard USB cable or plug. Using USB Ethernet as an example, the Li-Fi EP 110 may include a USB Ethernet interface 114 and connect to the terminal device via a USB cable 115. Similar to the Li-Fi AP 120, the Li-Fi EP 110 can also be connected to one or more client optical TRX 111s. Alternatively, a single optical front end with segmented transmitters / receivers, where each transceiver / receiver points in a different direction, is also conceivable.

[0117] In another example, a different interface 114 can be used to connect the Li-Fi EP to the operating system of the terminal device, and the corresponding interface 114 (USB Ethernet) and / or cable 115 should be replaced accordingly.

[0118] Figure 5Exemplary components are provided for optical front-ends or optical TRX 111, 121 included in or connected to Li-Fi AP 120 and Li-Fi EP 110. Optical TRX 111, 121 include at least a light source 1211, a photosensor 1212, a driver 1213, and an amplifier 1214. The light source 1211 is used to convert an electrically transmitted signal into an output optical signal; it may be a light-emitting diode (LED), a laser diode (LD), or a vertical-cavity surface-emitting laser (VCSEL). The photosensor 1212 is used to convert the received optical signal into an output electrical signal; it may be a photodiode, an avalanche diode, or another type of photosensor. The driver 1213 is primarily used to regulate the power required by the light source 1211. The amplifier 1214 is primarily used to regulate the signal received by the photosensor 1212 to make the signal suitable for further processing in the circuit. In one example, the amplifier 1214 may be a transimpedance amplifier (TIA), which is a current-to-voltage converter implemented using one or more operational amplifiers. The TIA can be located near the receiving optical sensor or photodiode 1212 to amplify the signal with minimal noise.

[0119] Interconnection in Li-Fi systems

[0120] Typically, the Li-Fi AP 120 is deployed on the ceiling. This AP 120 requires power to perform communication activities. Therefore, the connection to the AP 120 involves both power and data. The AP 120 establishes a bidirectional link with the cloud or backbone network 20 on one side via backbone connection 21, and on the other side, the AP 120 communicates with one or more associated EPs 110 via an optical link. The EP 110 typically draws power from an end device, which is coupled to or integrated into the end device, and communicates with the associated AP 120 via an optical link.

[0121] Connect the Li-Fi AP to the backbone network

[0122] The Li-Fi AP 120 can use different options to connect to the backbone network 20.

[0123] In one aspect, data and power can be delivered together to the Li-Fi AP, which can be achieved via a single power cable with power line communication (PLC) or a single Ethernet cable with power over Ethernet (PoE).

[0124] PLCs utilize existing power cables, both for providing trunk power to equipment and for data communication. Popular PLC communication standards (such as HomePlug® or G.hn) utilize Orthogonal Frequency Division Multiplexing (OFDM) technology, which is also used in Li-Fi systems. Therefore, the physical layers (PHYs) of PLC and Li-Fi systems can be very similar, such as the modulation and synchronization methods used in both systems. However, transmission in the optical domain is unipolar, while OFDM typically uses bipolar signals. As a result, some adaptation may be required for transmission in optical networks. A simple solution is to use DC offset, which eliminates the need for demodulation and subsequent remodulation of the OFDM-based PLC signal before optical transmission, or alternatively, to use unipolar OFDM modulation techniques (such as ACO-OFDM, DCO-OFDM, ADO-OFDM, and / or inverted OFDM) for demodulation and subsequent remodulation. Therefore, for the Li-Fi AP 120, which is usually placed alongside ceiling lights, it may be very convenient to obtain a data connection to the backbone network 20 using existing power cables.

[0125] However, it is also recognized that the channels of PLC systems are quite noisy, considering that the trunk power lines may act as antennas, picking up all sorts of unwanted signals that may interfere with the communication signals also present on the trunk power lines. Therefore, it is important to handle this external interference for devices enabling Li-Fi on PLCs. Furthermore, the amount of attenuation experienced by the communication signals on the trunk power lines is unpredictable during manufacturing and may vary throughout the day. Influencing factors include cable lengths varying from building to building, electrical loads that more or less create short circuits at high frequencies, and being switched on or off, etc.

[0126] One known solution to address signal integrity issues introduced by PLC systems is to equip Li-Fi-enabled devices with a PLC decoder to decode PLC communication signals received over the mains power line. Impairments to the communication signal are handled digitally. For example, narrowband interference causes errors only on a single subcarrier of the OFDM modulated signal. Error correction algorithms can be used to correct the reconstructed data. The reconstructed data is then converted back to the analog domain to modulate the LED current flowing to at least one LED. In this way, more robust operating devices can be provided, with reduced data loss, although one drawback of this solution is that the devices become larger, more complex, and more expensive.

[0127] On the other hand, if power can be delivered via Ethernet cables, Li-Fi APs may also be convenient in utilizing existing IT infrastructure to obtain both power and connectivity to the backbone network. Power over Ethernet (PoE) is described in the IEEE 802.3af / at standard and is currently being extended to 4-pair power delivery in the IEEE task group P802.3bt. PoE is designed to supply a 40V to 48V power supply voltage from a power supply equipment (PSE) to a power consumer (PD), alongside data lines for control and communication purposes. PSE devices are also known as PoE switches. In a PoE lighting system, the PD can be a light source, a user interface device, or a sensor. PSEs are typically powered by trunk power, such as according to the IEC / TR 60083 standard. Traditional PoE systems transport data and power through the network and its endpoints, thus between the PSE and the PD.

[0128] Therefore, data can be received by control devices, for example, via an Ethernet connection using the Ethernet protocol. Data is communicated between devices in a Power over Ethernet (PoE) system via the Ethernet protocol. Thus, microchips in the form of Ethernet controllers can be used to establish communication links between devices, supporting the Media Access Control (MAC) and Physical Layer (PHY) of the Open Systems Interconnection (OSI) model.

[0129] Ethernet connections can be, for example, fiber optic cables, electrical wires, or twisted-pair cables, such as Category 3, Category 4, Category 5, Category 5e, Category 6, Category 6A, Category 7, Category 7A, Category 8, Category 8.1, or Category 8.2 cables. An Ethernet connection can have several pairs of cables, such as 2, 3, 4, or more. The cables can be unshielded or shielded, particularly individually or collectively shielded. Power and data can be transmitted via the same fiber optic cable, electrical wire, or cable connected to the Ethernet connection, or via different fiber optic cables, electrical wires, or cables connected to the Ethernet connection. In the case of power transmission via fiber optics, the power can be transmitted in the form of photons, which can be received by the solar cell unit of the data receiving device.

[0130] Data receiving devices in a PoE system may include one or more ports. Each port may include one or more pins. Pins may be configured to receive power, data, or both. Alternatively or additionally, the port may also include one or more solar cell units for receiving power in the form of photons. Because the port can receive power and data via an Ethernet connection, some pins can be powered and others can be provided with data via the Ethernet connection. Alternatively or additionally, a pin may also be powered and provided with data via an Ethernet connection.

[0131] In another aspect, data and power can be delivered to the Li-Fi AP separately, and the option can be either via a power cable and an Ethernet cable (a wired connection to the backbone network), or a combination of a power cable and a wireless link (optical wireless link or free-space optical link) to the backbone network 20.

[0132] Preferably, the Li-Fi system can be integrated into existing wireless communication systems, such as Wi-Fi or cellular systems. Therefore, the Li-Fi AP 120 can be integrated into or directly connected to a Wi-Fi access point or cellular base station. By performing signal conversion or transformation between the Li-Fi AP 120 and the Wi-Fi access point or cellular base station, the existing infrastructure of the Wi-Fi or cellular system can be used to provide the Li-Fi AP 120 with connectivity to the backbone network 20.

[0133] Connect the Li-Fi EP to the Li-Fi AP

[0134] The Li-Fi EP 110 connects to the Li-Fi system via the Li-Fi AP 120, which is typically referred to as the local AP. Several aspects need to be considered regarding the connection between the Li-Fi EP 120 and the Li-Fi AP 110:

[0135] - Coverage: Li-Fi EPs may not always be able to see Li-Fi APs, depending on their location, orientation, the location of the Li-Fi AP, and the size of the Li-Fi EP's transducer / sensor coverage area.

[0136] - Downlink interference: If these Li-Fi APs transmit simultaneously, the Li-Fi EPs in the overlapping coverage areas of multiple optical downlinks will be subject to interference.

[0137] - Uplink interference: When one Li-Fi EP transmits a signal to its associated Li-Fi AP, while another Li-Fi EP is transmitting to the same Li-Fi AP, this causes uplink interference at the Li-Fi AP.

[0138] - Handover: Due to the mobility of Li-Fi EPs, handover is required when a Li-Fi EP moves from the coverage area of ​​one Li-Fi AP to an adjacent Li-Fi AP. That is, when a Li-Fi EP (such as one connected to or contained in a user equipment, client device, mobile phone, etc.) moves from its current cell to an adjacent cell, any active communication must be handed over to the node or access point of that adjacent cell. To minimize interference with any ongoing communication or data transmission, the handover is designed to be performed as quickly as possible and may include a preparation period to facilitate this. When there is insufficient time available to prepare and establish a link to a new Li-Fi AP before the link with the existing Li-Fi AP is disconnected, the Li-Fi EP may experience a period without connection. Considering the relatively small size of Li-Fi cells due to the line-of-sight characteristics of optical links, seamless handover is important for ensuring link quality and user experience.

[0139] Essentially, the Li-Fi EP 110 can connect to the Li-Fi AP 120 via a bidirectional optical link or a hybrid downlink and uplink. Note that here, the downlink represents the communication link from the Li-Fi AP 120 to the Li-Fi EP 110, and the uplink represents the communication link from the Li-Fi EP 110 to the Li-Fi AP 120. The bidirectional optical link achieves a relatively symmetrical connection between the Li-Fi EP 110 and the Li-Fi AP 120. Therefore, both the downlink and uplink enjoy the same advantages of Li-Fi communication as described above. However, in some applications (such as web surfing or video streaming), the link between the Li-Fi AP and the Li-Fi EP can also be a hybrid link, combining an optical downlink from the Li-Fi AP 120 to the Li-Fi EP 110 and a radio frequency (RF) uplink from the Li-Fi EP 120 to the Li-Fi AP 110. RF links can be based on popular short-range wireless communication protocols, such as Wi-Fi, BLE, or Zigbee; or on cellular communication protocols, such as 4G or 5G cellular.

[0140] Referring back to the option of building the Li-Fi AP 120 via a combination of devices supporting Li-Fi AP functionality and Wi-Fi access point or cellular base station functionality, this hybrid link can be seamlessly handled by the controller on the Li-Fi AP side. Since the Li-Fi EP 110 is typically connected to or integrated into an end device (which could be a smartphone, tablet, computer, or other smart device), this end device may already have hardware support for the short-range wireless communication protocol or cellular protocol used in the hybrid link. Therefore, this hybrid link also optimizes the use of existing resources in the end device and provides a simplified solution for the Li-Fi EP, which only requires a receive path and not a transmit path. The cost, power consumption, and form factor of the EP 110 can be further reduced in this way. Accordingly, the Li-Fi AP 120 is also simplified by primarily including an optical transmitter to send data to the Li-Fi EP 110 via an optical downlink, while the RF-based uplink from the Li-Fi EP 110 to the AP120 can be received by optimizing the use of RF receivers in combined devices or cooperatively positioned Wi-Fi access points / cellular base stations, or via a dedicated RF receiver included in the Li-Fi AP 120 itself.

[0141] Scheduling and interference suppression in optical multi-cell wireless networks

[0142] Media Access Control (MAC) becomes necessary for interference-free optical communication when multiple Li-Fi AP 120s are deployed adjacent to each other, or when multiple EP 110s are associated with the same local AP 120 or neighboring AP 120s. Different MAC mechanisms can be employed in optical multi-cell wireless networks, such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Carrier Sense Multiple Access (CSMA), Code Division Multiple Access (CDMA), Space Division Multiple Access, or a combination of one or more of these mechanisms. TDMA is based on a time division multiplexing scheme, where radio resources are scheduled in the time domain, and different time slots are allocated to different transmitters in a typical cyclic repeating frame structure or MAC cycle. FDMA is based on frequency division multiplexing, where different frequency bands are allocated to different devices for simultaneous transmission. Furthermore, in optical communication, FDMA can evolve into wavelength division multiple access (WDMA) based on wavelength division multiplexing. Another advanced variant of FDMA is Orthogonal Frequency Division Multiple Access (OFDMA), where each device can use one or more subcarriers outside the entire frequency band. OFDMA offers greater flexibility in providing different data rates or qualities of service to different users, while maintaining high resource efficiency despite this diversity. CSMA typically employs a "listen-before-talk" approach, where devices verify the presence of any other traffic before transmitting over a shared medium. CSMA is widely used in sparse networks, and further collision avoidance techniques emerge as node density changes. CDMA is typically built on spread spectrum, and a common form is direct sequence CDMA based on direct sequence spread spectrum, where different devices simultaneously transmit messages using different orthogonal spreading codes. Given that the FoV of optical links is generally smaller compared to radio links, spatial division multiple access (SDMA) can also be a very attractive solution here.

[0143] In a TDMA-based multi-cell network with multiple AP 120s, adjacent AP 120s may sometimes lack synchronized MAC cycles due to the lack of direct communication. While the duration of a MAC cycle or superframe is typically the same for all AP 120s in the network, the start time of the MAC cycle can differ for each individual AP 120. Note that the start time of the MAC cycle is used by the AP as its local time base to divide the wireless media into consecutive time slots. Even when a time slot is specifically allocated to an AP 120 for communication with an EP 110 in an overlapping area, this MAC cycle offset between two adjacent AP 120s can still cause interference to the EP 110 located in the overlapping coverage area of ​​these two adjacent AP 120s. Therefore, it is necessary for the AP 120s to synchronize to a common time base. The common time base can be obtained via a synchronization handshake, via a reference clock distributed across the network (such as a synchronized Ethernet clock), or via a dedicated synchronization server in the network, or derived from a common signal (such as the zero-crossing of trunk power). However, due to unpredictable delays or interference in the network, timing synchronization uncertainties between APs and a timing base may still exist. An EP 110 located in the overlapping area of ​​at least two adjacent APs 120 may still need to derive timing information related to the MAC cycles of at least two APs 120 based on downlink communications from these APs, which can be normal data communication links or out-of-band signaling messages. Then, based on the derived timing information related to the MAC cycles of at least two APs 120, the EP 110 can further assist at least one of the two adjacent APs 120 in adjusting its MAC cycle to align with the other.

[0144] High-efficiency modulation control

[0145] OFDM is widely used as a digital multicarrier modulation method in many communication systems because of its significant robustness against adverse channel conditions such as narrowband interference or frequency-selective fading. By dividing the entire frequency band into multiple subcarriers, the system also offers the flexibility to apply different modulation and coding schemes to each subcarrier, which can be used to maximize channel capacity. As discussed in previous chapters, adaptive modulation or bit-loading methods can also suffer from reduced system complexity and signaling overhead, especially as the number of subcarriers increases, resulting in limited overall system performance enhancement. To achieve a more efficient adaptive modulation method, this invention discloses a method that utilizes certain channel characteristics to significantly simplify implementation complexity and reduce signaling overhead.

[0146] The disclosed invention can be applied to any multicarrier wireless system with similar channel conditions to those addressed by this invention. Without loss of generality, the system can be an optical wireless communication system, such as a Li-Fi system. LEDs are used to achieve electro-optical conversion in Li-Fi systems. Although the OWC spectrum is approximately 2600 times larger than the entire radio spectrum, Li-Fi systems may not be able to fully utilize such a spectrum to freely transmit data. Standard lighting LEDs are not designed or optimized for communication purposes, and the modulation bandwidth of commercially available LEDs is typically very limited compared to the OWC spectrum. Due to the dynamic response or carrier recombination process of LEDs, they exhibit power-limited first-order low-pass behavior. This low-pass characteristic of LEDs—especially their junction capacitance—degrades the main part of the spectrum, but these can still contribute to throughput. OFDM allows the use of different portions of the spectrum with specific power and signal constellation diagrams. More robust signals can be used in the more severely attenuated portion of the spectrum containing a relatively larger amount of noise. More robust signals indicate smaller constellation diagrams, carrying fewer bits per symbol depending on the actual signal-to-noise ratio (SNR) level.

[0147] Furthermore, the maximum available LED bandwidth is also dynamic, depending on the distance from the LED to the receiving photodiode, temperature, noise level, and dimming level. Depending on the actual maximum available LED bandwidth, adaptive algorithms may be needed to more effectively distribute output power across frequencies.

[0148] Given the frequency-selective channel response, various strategies have been proposed to distribute power and bit load across different frequency components. Waterfilling is well-known as the optimal strategy for loading power in each frequency band. The number of bits / s / Hz is chosen based on the SNR of the various frequency bands. Waterfilling is based on theoretical Lagrange optimization, which is considered a computationally intensive solution. More practical strategies include uniform power loading with pre-emphasis and uniform bit loading. Uniform power loading transmits the same power across all frequencies but adjusts the constellation size accordingly, while pre-emphasis power loading attempts to transmit the same number of bits on each subcarrier (using the same constellation size) but adjusts the power to reverse channel attenuation.

[0149] Given the significant attenuation in the high-frequency portion of an LED channel, applying preemphasis might mean avoiding highly attenuated high frequencies or using only small constellation sizes. Conversely, adaptive bit loading is more effective if most of the channel is severely attenuated.

[0150] Figure 6An exemplary illustration of such a communication channel is provided, characterized by a channel response that decreases with increasing frequency. Note that the smooth envelope of the frequency channel response shown in the figure is for illustrative purposes only and does not exclude channel conditions with one or more small ripples in the channel distribution. This also means that a monotonic channel characteristic is observed across the entire frequency band, and small deviations may still exist for some subcarriers. This is typical of real-world communication systems.

[0151] Instead of calculating a suitable modulation scheme for each subcarrier, it is advantageous to accelerate the algorithm by first dividing the multiple subcarriers into one or more non-overlapping frequency bands, where each band includes more than one subcarrier. Then, a suitable modulation scheme is assigned to each frequency band and shared by all subcarriers contained within the same frequency band. An example of this allocation of one or more frequency bands is... Figure 7 The diagram shows the frequency bands, indicated by dashed boxes. As shown, the number of subcarriers contained within a single frequency band can vary. This allocation of frequency bands may depend on several factors. On one hand, it depends on channel response characteristics, such as the slope of the channel response or the channel response deviation between adjacent subcarriers. The flatter the channel response, or the smaller the channel response deviation between adjacent subcarriers, the more subcarriers can be included in a frequency band. On the other hand, it also depends on the characteristics of the modulation schemes supported by the system, such as the minimum signal-to-noise ratio required for different modulation orders, or the step size of the minimum signal-to-noise ratio required for adjacent modulation (and coding) schemes as defined in the MCS table of the system's communication standard. Furthermore, it may also depend on the performance trade-off strategy between maximizing throughput and minimizing overhead. The finer the frequency band allocation (fewer subcarriers in a segment), the smaller the channel response deviation between different subcarriers included in a single frequency band, and the greater the potential for increased data throughput; however, this also leads to increased system overhead.

[0152] As an example, one or more non-overlapping frequency bands are allocated in such a way that each band is assigned to a different modulation order or MCS supported by the system. Therefore, the deviation of the channel response between more than one subcarrier in each band is no greater than the step size between the minimum SNR requirements of two adjacent modulation orders or MCSs. For a given system design, the correlation between a specific modulation order and the minimum required SNR is determined.

[0153] For example, for the same coding rate at ½, demodulating a binary phase shift keying (BPSK) modulated signal might require 3 dB SNR, while a quadrature phase shift keying (QPSK) modulated signal might require 5.5 dB, and a 16 quadrature amplitude modulation (QAM) modulated signal might require 12 dB. Therefore, the step size for the minimum required SNR between adjacent modulation orders also differs. And in this example, the step size between BPSK and QPSK is only 2.5 dB, while the step size between QPSK and 16QAM is 6.5 dB. When the channel response varies relatively linearly in dB, the number of subcarriers included in each frequency band will be primarily determined by the difference between the minimum SNR requirements of adjacent modulation and coding schemes. Note that the figures mentioned here are for illustrative purposes only and may vary depending on other system parameters and hardware implementations.

[0154] Figure 8 Another example of an MCS table defined for OFDM PHY in IEEE 802.11 (2016) is provided. It can be seen that the table is organized in ascending order of modulation, and for the same modulation order, in ascending order of coding rate. Therefore, as the index in the table increases, the minimum SNR required for correct demodulation and decoding on the receiver side also increases monotonically. Similar to the previous example, depending on the combination of modulation order and coding rate, the step size of the minimum SNR required for two adjacent MCSs defined in the table may differ by several dB. Therefore, even if the slope of the channel response is very linear, the number of subcarriers included in each frequency band may still be different due to modulation characteristics.

[0155] Since both modulation characteristics and estimated channel response are considered when allocating one or more frequency bands, the mapping between frequency bands and individual modulation schemes becomes straightforward. Therefore, as an option, it is advantageous to only notify the remote device of the allocation of one or more non-overlapping frequency bands and allow the remote device to locally derive the corresponding modulation scheme for each frequency band, since information about the potential modulation orders or MCS tables supported by the system should also be available at the remote device.

[0156] In certain special cases, a larger frequency band can be allocated by skipping one or more potential modulation orders or MCSs. This can happen when a portion of the channel response undergoes drastic changes / attenuation. Another possible scenario is when it is more efficient to merge a higher frequency band with an adjacent higher frequency band that consists of only a few subcarriers, using the same lower modulation order. In this particular case, the transmitter's modulation control unit can provide additional information to the remote device, such as the modulation order or MCS index of the frequency band.

[0157] To further reduce overhead related to storage and signaling, frequency band allocations can be composed in a compact format. This can be particularly beneficial if the transmitter must provide such information to remote devices on a per-packet or per-frame basis. Figure 9 A simplified illustration of a data frame format is provided, comprising two parts: a header and a payload. The packet header relates to control information for packet reception, while the payload contains the actual user data. The packet header may also include several subfields, such as a preamble, address information, sequencing information, the modulation and / or coding scheme used in the payload, and the payload length. Therefore, preferably, a compact format regarding frequency band allocation is embedded in the header of each data packet or data frame. Thus, the proposed adaptive modulation scheme can be updated more dynamically, for example, when receiving earlier packets from a remote device. The bit loading control device can derive the updated channel response and then apply the new frequency band allocation. Therefore, the remote device can obtain timely updates using the compact format, which conveys the new allocation embedded in each data packet, acknowledgment (ACK) packet, or dedicated control packet. As a result, the system is more robust and flexible in handling any changes on the communication channel.

[0158] Figure 10 The basic components of the bit loading control device 1010 of the present invention are schematically depicted. The bit loading control device 1010 includes at least a controller 1011, a transmitter 1012, and a receiver 1013. The transmitter 1012 is configured to send a request for a test signal, and the receiver 1013 is configured to receive the test signal. The controller 1011 is configured to obtain an estimated channel response and derive a bit loading scheme based on the estimated channel response, as disclosed in the bit loading control method 700. The bit loading control device 1010 may also include a memory 1014 for storing at least one or more non-overlapping frequency band allocations for signal processing or communication with remote devices. Depending on the mapping between frequency bands and potential modulation orders or MCSs supported by the system, additional information may be stored to clarify the allocation of modulation orders or MCSs for each frequency band.

[0159] The bit loading control device 1010 can also be configured to perform wireless communication in a multi-carrier wireless communication system after implementing the adaptive bit loading method. When the bit loading control device 1010 is configured to operate in a transmitter-initiated manner, the transmitter 1012 of the bit loading control device 1010 is also configured to modulate data transmitted on one or more adjacent subcarriers belonging to the same frequency band using the same individual modulation scheme according to the bit loading scheme; and transmit the modulated data to a remote receiving device through a communication channel.

[0160] When the bit loading control device 1010 is configured to operate in a receiver-initiated manner, the transmitter 1012 of the bit loading control device 1010 is also configured to transmit a determined bit loading scheme to a remote device, wherein the remote device is the intended transmitter of the data session, and the bit loading control device 1010 is the intended receiver side of the data session. The receiver 1013 of the bit loading control device 1010 is also configured to receive data from the remote transmission device via a communication channel; and, according to the bit loading scheme, demodulate the data received on more than one adjacent subcarrier belonging to the same frequency band using the same individual modulation scheme.

[0161] Therefore, a multi-carrier wireless communication system may include a first transceiver and a remote receiving device. The first transceiver operates as a bit loading control device 1010 using a transmitter-initiated method. The first transceiver is also configured to modulate data transmitted on one or more adjacent subcarriers belonging to the same frequency band using the same individual modulation scheme according to the bit loading scheme; and to transmit the modulated data to the remote receiving device via a communication channel. The remote receiving device is configured to receive the bit loading scheme from the first transceiver and demodulate the data received from the first transceiver according to the received bit loading scheme.

[0162] Here, modulation refers to the mapping from bits to symbols. When the modulation scheme is represented by a constellation diagram, this bit-to-symbol mapping is also called constellation diagram mapping. Different modulation schemes can be distinguished by different constellation diagram sizes. With a combined modulation and coding scheme assigned, the raw data bits are first channel-coded, and then the coded bits are modulated into data symbols. In OFDM-based systems, additional OFDM modulation steps are required to further process the data symbols, and this additional step is performed by executing an inverse fast Fourier transform (IFFT) to convert the parallel frequency-domain data symbols on multiple subcarriers into serial time-domain data for transmission over the channel.

[0163] Therefore, for OFDM-based systems, an early step of processing the data received from the channel for OFDM demodulation is required before data symbol-to-bit demodulation or demapping. The Fast Fourier Transform (FFT) is used to convert the serial time-domain received data into parallel frequency-domain data symbols on multiple subcarriers. Then, the demodulation control unit can use the same determined individual modulation scheme to demodulate data symbols on one or more adjacent subcarriers belonging to the same frequency band.

[0164] As a second configuration, the multi-carrier wireless communication system may include a second transceiver and a second remote transmitting device. The second transceiver operates as a bit loading control device 1010 using a receiver-initiated method. The second transceiver is also configured to send a second bit loading scheme to the remote transmitting device, and the second remote transmitting device is further configured to receive the second bit loading scheme from the second transceiver; modulate data transmitted on one or more adjacent subcarriers belonging to the same frequency band using the same individual modulation scheme according to the received bit loading scheme; and transmit the modulated data to the second transceiver through a communication channel in the multi-carrier wireless communication system.

[0165] The bit loading control device 1010 may optionally include a user interface that can provide users with additional convenience for querying the status of the device or operating it.

[0166] Figure 11 The basic components of a bit loading control device 1010 according to one embodiment are schematically depicted. The bit loading control device 1010 also includes a front end 1050 connected to a transmitter 1012 and a receiver 1013. The front end 1050 is configured to transmit and receive data over a wireless communication channel that may utilize one of several electromagnetic spectra (e.g., radio frequency spectrum, microwave spectrum, or spectral spectrum). Furthermore, it may use a subset of the spectrum (e.g., infrared, visible, or ultraviolet spectrum). In a preferred configuration, the front end 1050 is an optical front end 111, 121, and the front end 1050 may use a front portion and Figure 5 The optical front ends 1050, 111, and 121 are constructed using the sub-blocks disclosed in the diagram. Therefore, the electrical signals generated by the bit loading control device are converted into optical signals for transmission over the optical channel, for example, using LEDs. Similarly, the optical front ends 1050, 111, and 121 receive optical signals and convert them into electrical signals, for example, using photodiodes or other photodetectors.

[0167] In a preferred system configuration, the bit loading control device 1010 may be incorporated as part of either the Li-Fi access point 120 or the Li-Fi endpoint 110. The disclosed method facilitates the application of more efficient adaptive bit loading to the optical link between the Li-Fi access point 120 and the Li-Fi endpoint 110.

[0168] Figure 12The diagram shows a flowchart of modulation control method 700. In step S701, the bit loading control device sends a test signal request; and in step S702, it receives a test signal. In step S703, based on the received test signal, an estimated channel response of the communication channel on multiple subcarriers is obtained. Then, in step S704, a bit loading scheme is determined based on the estimated channel response for allocating multiple subcarriers to one or more non-overlapping frequency bands, each non-overlapping frequency band including more than one adjacent subcarrier, and assigning a separate modulation scheme shared by more than one adjacent subcarrier to each frequency band, wherein the separate shared modulation scheme is allocated in a modulation order that monotonically decreases with increasing frequency.

[0169] Method 700 may further include step S705 of detecting changes in the channel response of the communication channel, and step S706 of updating the bit loading scheme at the time of detection, wherein the update is performed by maintaining the same allocation of one or more non-overlapping frequency bands and shifting the frequency up or down of each of the one or more non-overlapping frequency bands according to the changes in the channel response.

[0170] Given the characteristics of the wireless communication channel proposed in this invention, the distribution of the channel response can remain largely unchanged, while the response can shift in frequency. Since the channel response decreases with increasing frequency, further deterioration of the channel may indicate a shift of the original channel response curve to lower frequencies, and further improvement of the channel may indicate a shift of the original channel response to higher frequencies. Therefore, upon detecting a change in the channel, it may not be necessary to trigger an entirely new process to determine an alternative bit loading scheme. Instead, maintaining the same frequency band and applying the shift in the bit loading distribution to each frequency band based on the shift in the frequency response may be a very efficient solution, especially when the change in the channel response is not significant.

[0171] Optionally, method 700 may further include the step of sending a bit loading scheme for communicating with a remote device via a communication channel. Depending on whether the disclosed method operates in a transmitter-initiated method or a receiver-initiated method, the remote device may be a receiving or transmitting device of the intended data link.

[0172] In another example, method 700 may further include a step of loading a local storage bit scheme for later use.

[0173] The disclosed invention can be incorporated into Li-Fi related standards. Using ITU-T G.9960 and ITU-T G.9961 as examples, this section describes ITU recommendations regarding system architecture and physical layer home networks. To determine how many bits can be loaded for each subchannel, a so-called Bit Allocation Table (BAT) is applied. A frame according to ITU-T G.9960 includes a preamble, header, additional channel estimation symbols, and payload. The frame header indicates the frame type. For data frames, management frames, and acknowledgment (ACK) frames, the applied BAT is represented by a 5-bit identifier, BAT_ID, in the variable portion of the header. To determine the BAT, the receiver measures signal quality based on a test signal transmitted by the transmitter. The test signal can be of one of two types: a probe frame carrying probe symbols in the payload portion, and an ACE symbol added to a data or management frame located between the header and payload portion. The receiver then determines which BATs the transmitter can apply.

[0174] BAT (Block Assignment) can be applied to a portion / region of the MAC cycle. To estimate the channel within a region of the MAC cycle, the receiver can instruct the transmitter to send probe frames in that region of the MAC cycle. Different BATs can be applied to different regions of the MAC cycle. Each group of subcarriers can be divided into 2, 4, 8, or 16 subcarriers. This grouping is very basic, meaning that the grouping is uniform across all subcarriers in the band plan.

[0175] The receiver transmits CE_Initiation.req The transmitter uses a message to initiate a channel estimation protocol. CE_ Initiation.cnf Reply to the message CE_Initiation.req Message. The transmitter can also send... CE_ Initiation.ind The message triggers the receiver to initiate channel estimation.

[0176] When sending CE_Initiation.req When sending a message, the receiver provides the transmitter with the following parameters:

[0177] New BAT-ID

[0178] Minimum value of grouping

[0179] • Channel estimation window (which part of the MAC cycle is estimated)

[0180] Parameters of the probe frame

[0181] The receiver can request probe frames (and can change their parameters). Upon request, the transmitter sends a probe frame. To send a probe frame, the transmitter needs resources in the MAC cycle, which must be obtained from the domain host. The receiver terminates the process by sending a channel estimation result with an update message providing information about the BAT (Block Arrangement Parameter). The receiver then sends... CE_ParamUpdate.req Transmitter CE_ParamUpdate.cnf Reply to the message CE_ParamUpdate.req The transmitter can be used CE_ParamUpdate.ind The message requests a retransmission of the channel estimation results.

[0182] This protocol allows for faster channel adaptation by omitting the initiation process (omitting CE_ParamUpdate.req and CE_ParamUpdate.cnf) and jumping directly to a sub-section of that process.

[0183] Active request – The new BAT is determined by sending an update message CE_ParamUpdate.req containing the following parameters:

[0184] New BAT ID

[0185] ·Band Program

[0186] Grouping

[0187] • BAT Valid Mask – Which BATs are currently valid for the node

[0188] • BAT validity period in the MAC cycle - This allows BAT to be dedicated to the MAC cycle portion.

[0189] • Has non-zero bits (TIDX) MIN …TIDX MAX The range of subcarriers (the range of subcarrier groups).

[0190] • A bit allocation table for each subcarrier or each group of 4 bits (for all subcarriers);

[0191] Partial update request – The new BAT is determined by updating the existing BAT CE_PartialBatUpdate.req, which has the following parameters, such as

[0192] • Old + New BAT ID (The new BAT ID is after the BAT change)

[0193] • Number of BAT entries to be updated

[0194] • Bit allocation table - entries with subcarrier indexes + 4 bits per subcarrier or per group (for a subset of subcarriers);

[0195] Probe Request – Directly requests probe frames CE_ProbeRequest.ind, ACK_CE_CTRL;

[0196] ACE Request — Request to insert ACE symbol CE_ACESymbols.ind

[0197] • The transmitter must add to the ACE symbol count for all frames (between the header and payload).

[0198] The fields in the bit allocation table contained in the CE_ParamUpdate.req message can be compressed. For this purpose, the table is divided into groups (compressed and uncompressed). For compressed groups, the number of instances and bit allocations for the subcarriers within the group are indicated.

[0199] The initial bit allocation can be determined by the receiver and transmitted to the transmitter via the CE_ParamUpdate.req message. If no application packet is applied (G=1), the BAT index represents a subchannel. If an application packet is applied (G>1), the BAT index represents a group of subchannels. Note that for some higher-order subchannels, the BAT value can be zero, which means that the corresponding subchannel (subgroup) is offloaded.

[0200] Once the BAT is fixed, it can be adjusted by changing the BAT value within the BAT. If the signal quality improves, the BAT value is shifted upwards within the BAT (towards higher frequencies).

[0201] Figure 13 An example of an initial BAT is provided. Figure 14 Showing relative to Figure 13 The initial bit allocation results in shifting the values ​​in BAT up by two. Note that the first two BAT entries have the new values, and are related to... Figure 13 Compared to the initial allocation, the range of BAT values ​​with non-zero values ​​has increased by two entries and is located at a higher frequency boundary. If channel conditions worsen, the BAT value shifts down within the BAT range. Figure 15 It shows relative to Figure 13 The initial bit allocation shifts the values ​​in BAT down by two. Note that the last two BAT entries are now zero, and... Figure 13 Compared to the initial allocation, the range of non-zero values ​​has been reduced by two entries, placing it at a higher frequency boundary.

[0202] The ITU-recommended protocol can be extended by defining two new messages:

[0203] • CE_ParamShift.req (see Tables 1 and 2, where the transmitter or receiver determines the new TIDX) MIN and TIDX MAX )

[0204] • CE_ParamShift.cnf (see Table 3)

[0205] Table 1: Format of CE_ParamShift.req message (Variant 1: Transmitter determines new TIDX) MIN and TIDX MAX )

[0206]

[0207]

[0208] Table 2: Format of CE_ParamShift.req message (Variant 2: Receiver determines new TIDX) MIN and TIDX MAX )

[0209]

[0210]

[0211] Table 3: Format of CE_ParamShift.cnf messages

[0212]

[0213] Another extension recommended by the ITU is to allow transmitters to dynamically turn the power of their subcarriers on / off depending on the bit loading scheme. By default, all unshielded subcarriers within the band plan are on. This extension allows transmitters to turn off subcarriers whose corresponding BAT entries are set to zero.

[0214] You can select the following options to enable / disable subcarriers where the BAT entry is set to zero.

[0215] Subchannels adjacent to non-zero BAT entries can remain open.

[0216] Subchannels that are not adjacent to non-zero BAT entries can be turned off.

[0217] Subchannels adjacent to non-zero BAT entries may be shut down, but may be temporarily enabled in the following situations.

[0218] - Transmit probe symbols

[0219] - Transmit ACE symbols.

[0220] The method according to the invention can be implemented on a computer as a computer-implemented method, or in dedicated hardware, or in a combination of both.

[0221] The executable code of the method according to the invention can be stored on a computer / machine-readable storage device. Examples of computer / machine-readable storage devices include non-volatile memory devices, optical storage media / devices, solid-state media, integrated circuits, servers, etc. Preferably, the computer program product includes non-transitory program code means stored on a computer-readable medium for executing the method according to the invention when the program product is executed on a computer.

[0222] Methods, systems, and computer-readable media (transitory and non-transitory) may also be provided to implement selected aspects of the above embodiments.

[0223] The term "controller" is used generally herein to describe various means relating to the operation of one or more network devices or coordinators (among other functions). A controller can be implemented in a variety of ways (e.g., such as with dedicated hardware) to perform the various functions discussed herein. A "processor" is an example of a controller employing one or more microprocessors, which can be programmed using software (e.g., microcode) to perform the various functions discussed herein. A controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) performing other functions. Examples of controller components that can be employed in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, application-specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0224] In various embodiments, the processor or controller may be associated with one or more storage media (generally referred to herein as "memory," such as volatile and non-volatile computer memories, such as RAM, PROM, EPROM and EEPROM, compact disks, optical disks, etc.). In some embodiments, the storage medium may be encoded with one or more programs that, when executed on one or more processors and / or controllers, perform at least some of the functions discussed herein. Various storage media may be fixed within the processor or controller, or may be transportable, such that one or more programs stored thereon may be loaded into the processor or controller to implement various aspects of the invention discussed herein. The terms "program" or "computer program" are used herein in a general sense to refer to any type of computer code (e.g., software or microcode) that can be used to program one or more processors or controllers.

[0225] As used herein, the term “network” refers to any interconnection of two or more devices (including controllers or processors) that facilitates the transport of information (e.g., for device control, data storage, data exchange, etc.) between any two or more devices and / or between multiple devices coupled to the network.

Claims

1. A bit loading control method (700) for transmitting data over a multi-carrier wireless communication system, the communication channel having a channel response that decreases with increasing frequency, the bit loading control method (700) comprising: - A request for a test signal is sent by the device (S701); - The device receives the test signal from the remote device (S702); - Based on the received test signal, obtain (S703) the estimated channel response of the communication channel on multiple subcarriers; - Determine (S704) a bit loading scheme based on the estimated channel response for allocating the plurality of subcarriers to one or more non-overlapping frequency bands, each non-overlapping frequency band including more than one adjacent subcarrier, and assign a separate modulation scheme shared by the more than one adjacent subcarrier to each frequency band, wherein the separate shared modulation scheme is allocated with a modulation order that monotonically decreases as the frequency increases.

2. The method (700) according to claim 1, further comprising: - When a change in the channel response of the communication channel is detected (S705), the bit loading scheme is updated (S706), wherein the update is performed by maintaining each frequency band with a separate modulation scheme comprising the same number of subcarriers, and by shifting the allocation of frequency bands up or down in frequency according to the change in the channel response.

3. The method (700) according to claim 1 or 2, further comprising: - Send the bit loading scheme to the remote device for use by the remote device when communicating with the device through the communication channel.

4. The method (700) according to claim 1, further comprising: - The bit loading scheme is stored locally.

5. The method (700) according to claim 1, wherein, The test signal is contained in a dedicated probe group, or in a dedicated field within a data or management group.

6. The method (700) of claim 5, wherein the request for the test signal further includes parameters related to a dedicated field in the dedicated probe group or the data or management group.

7. The method (700) according to claim 1, wherein the bit loading scheme is configured using information comprising at least one of the following representations: - The index of the lowest subcarrier in each frequency band, and the index of the highest subcarrier in any frequency band; - The index of the highest subcarrier in each frequency band, and the index of the lowest subcarrier in any frequency band; - The index of the lowest subcarrier in any frequency band, and the number of subcarriers included in each frequency band, listed in ascending order of frequency; - The index of the highest subcarrier in any frequency band, and the number of subcarriers included in each frequency band, listed in descending order of frequency; - The number of subcarriers included in each frequency band, listed in ascending order of frequency.

8. The method according to claim 1, wherein, A separate modulation scheme is implemented with a uniform power load in each frequency band.

9. A bit loading control device (1010) for assisting in the transmission of data on a communication channel in a multi-carrier wireless communication system, the communication channel having a channel response that decreases with increasing frequency, the bit loading control device (1010) comprising: Transmitter (1012), which is configured to send a request for a test signal; A receiver (1013) is configured to receive the test signal from a remote device; The controller (1011) is configured as follows: Based on the received test signals, the estimated channel response of the communication channel on multiple subcarriers is obtained, and • A bit loading scheme is determined based on the estimated channel response for allocating the plurality of subcarriers to one or more non-overlapping frequency bands, each non-overlapping frequency band comprising more than one adjacent subcarrier, and a separate modulation scheme shared by the more than one adjacent subcarrier is allocated to each frequency band, wherein the separate shared modulation scheme is allocated with a modulation order that monotonically decreases as the frequency increases.

10. The bit loading control device (1010) according to claim 9, wherein the bit loading control device (1010) is further configured to perform wireless communication with a remote device in the multi-carrier wireless communication system, wherein the transmitter (1012) is further configured to: - According to the bit loading scheme, data transmitted on one or more adjacent subcarriers belonging to the same frequency band is modulated using the same individual modulation scheme; and - The modulated data is transmitted to the remote device via the communication channel.

11. The bit loading control device (1010) according to claim 9, wherein the bit loading control device (1010) is further configured to perform wireless communication with a remote device in the multi-carrier wireless communication system, wherein the receiver (1013) is further configured to: - Receive data from the remote device via the communication channel; and - According to the bit loading scheme, demodulate the data received on more than one adjacent subcarrier belonging to the same frequency band using the same individual modulation scheme.

12. The bit loading control device (1010) according to any one of claims 9 to 11, wherein, The transmitter (1012) is also configured to: - Send the bit loading scheme to the remote device for use by the remote device communicating with the bit loading control device.

13. The bit loading control device (1010) according to claim 9, wherein, The communication channel is an optical communication channel, and the bit loading control device (1010) further includes an optical front end (1050) configured to connect to the transmitter (1012) and the receiver (1013) to transmit and receive data on the optical communication channel.

14. A multi-carrier wireless communication system, wherein the communication channel has a channel response that decreases with increasing frequency, the multi-carrier wireless communication system comprising: According to claim 10, the first transceiver and the remote device are configured to receive a bit loading scheme from the first transceiver and demodulate data received from the first transceiver according to the received bit loading scheme. or The second transceiver and the second remote device according to claim 11, wherein the second transceiver is further configured to send a second bit loading scheme to the second remote device, and the second remote device is further configured to: • Receive the second bit loading scheme from the second transceiver. • Based on the received bit loading scheme, data transmitted on one or more adjacent subcarriers belonging to the same frequency band is modulated using the same individual modulation scheme, and • Transmit modulated data to the second transceiver through the communication channel in the multi-carrier wireless communication system.

15. A computational program including a code means, which, when executed by a bit loading control device (1010) including a processing means, causes the processing means to perform the method according to any one of claims 1-8.

Images