LED Display Cluster Control System Based on Wireless Communication

Abstract

This invention relates to the field of general control or adjustment system technology, specifically to a wireless communication-based LED display cluster control system. The main controller extracts the pixel difference matrix and regional change rate between the current frame and the previous frame from the video source data, dividing the display screen into high-change and low-change regions, and performing full pixel encoding and incremental pixel encoding respectively. The main controller calculates the multicast transmission rate based on channel state information and maps the full-encoded data and incremental-encoded data onto subcarriers of an orthogonal frequency division multiplexing (OFDM) system for transmission. The slave control node receives multicast data packets, and according to the region mapping identifier carried in the packet header, merges the full-encoded data with the corresponding region data of the previous frame cached locally to reconstruct the complete current frame data, and adjusts the local display clock according to the global timestamp carried in the multicast data packets. This invention reduces the wireless channel transmission load and avoids delays caused by channel congestion.

Description

Technical Field

[0001] This invention relates to the field of general control or regulation system technology, and more specifically to an LED display cluster control system based on wireless communication. Background Technology

[0002] Currently, LED displays are typically deployed in clusters for outdoor advertising, stage performances, and other similar applications. In wireless communication-based LED display cluster control systems, the main controller needs to synchronously transmit video image data to multiple slave nodes distributed across the physical space. Conventional wireless control schemes employ a full-frame data broadcast transmission mechanism. Within each display frame period, the main controller packages the grayscale data of all pixels in the entire image and transmits it to all slave nodes in the cluster via wireless communication links in a broadcast or multicast manner. After receiving the complete pixel data packet, the slave nodes directly write the data to their local buffer and refresh the display. To ensure image continuity, this transmission mechanism relies on a fixed wireless transmission rate and a fixed physical layer modulation scheme, treating the entire display frame as an indivisible whole for channel resource allocation and transmission.

[0003] In the aforementioned conventional full-frame broadcasting mechanism, when a video image undergoes rapid local changes, the pixel data in most areas of the image remains static. However, the main controller still sends a full frame containing a large amount of static redundant data to the wireless channel. This transmission method, which separates the spatiotemporal characteristics of the display content from the physical layer transmission mechanism, results in a large amount of wireless channel bandwidth being occupied by useless redundant data. When redundant data occupies the channel bandwidth, the pixel data that has actually changed faces transmission delays, causing wireless channel congestion. This leads to a misalignment in the time when the slave nodes within the cluster receive the current frame data, causing frame desynchronization and image tearing between the displays in the cluster. Summary of the Invention

[0004] The purpose of this invention is to provide a wireless communication-based LED display cluster control system, which can solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A wireless communication-based LED display cluster control system includes a main controller and multiple slave nodes connected to the main controller via wireless communication links. The main controller receives video source data, extracts the pixel difference matrix and regional change rate of the current frame and the previous frame from the video source data, divides the display screen into high-change regions and low-change regions according to the pixel difference matrix and the regional change rate, performs full pixel encoding on the high-change regions, and performs incremental pixel encoding on the low-change regions. The main controller establishes a multicast group with the multiple slave nodes through a wireless communication module, calculates the multicast transmission rate of the current time slot based on channel state information, and maps the full-encoded data corresponding to the full pixel encoding and the incremental-encoded data corresponding to the incremental pixel encoding onto the subcarriers of the orthogonal frequency division multiplexing system for transmission. The slave nodes receive multicast data packets containing the full-encoded data and the incremental-encoded data, merge and reconstruct the full-encoded data with the data corresponding to the low-change region of the previous frame in the local cache according to the regional mapping identifier carried in the header of the multicast data packet to generate complete current frame data, and adjust the local display clock according to the global timestamp carried in the multicast data packet.

[0006] Preferably, the main controller divides the current frame and the previous frame into multiple image blocks according to a preset grid size. For each image block, it calculates the absolute difference between the gray values ​​of each pixel in the current frame and the gray values ​​of each pixel in the previous frame. The absolute differences are summed to generate the block difference value of the image block. The pixel difference matrix is ​​formed by the block difference values ​​of all the image blocks. The number of image blocks whose block difference values ​​are greater than a preset difference threshold is counted. The number is divided by the total number of image blocks to generate the region change rate.

[0007] Preferably, the main controller compares the region change rate with a first preset change rate threshold and a second preset change rate threshold, respectively. When the region change rate is greater than the first preset change rate threshold, the corresponding image block is classified as the high change region. When the region change rate is less than the second preset change rate threshold, the corresponding image block is classified as the low change region. The main controller performs Huffman coding on the image blocks in the high change region to generate the full encoded data, extracts the pixel coordinates and corresponding grayscale differences of the image blocks in the low change region, and performs run-length coding on the pixel coordinates and the grayscale differences to generate the incremental encoded data.

[0008] Preferably, the slave control node sends pilot signals to the master controller according to a preset period. The master controller receives the pilot signals and calculates the signal-to-noise ratio (SNR) of each orthogonal frequency division multiplexing (OFDM) subcarrier in the wireless communication link. For each OFDM subcarrier, the SNR is substituted into the Shannon capacity calculation formula to calculate the instantaneous channel capacity. The sum of the instantaneous channel capacities of all OFDM subcarriers is obtained, and the sum is multiplied by a preset scaling factor to generate the multicast transmission rate of the current time slot.

[0009] Preferably, the main controller determines the target modulation order by querying a preset rate modulation mapping table based on the multicast transmission rate, allocates the full-quantity coded data to the orthogonal frequency division multiplexing subcarriers with a high signal-to-noise ratio (SNR), and allocates the incremental coded data to the orthogonal frequency division multiplexing subcarriers with a low SNR. For the orthogonal frequency division multiplexing subcarriers allocated with the full-quantity coded data, constellation mapping is performed using the target modulation order. For the orthogonal frequency division multiplexing subcarriers allocated with the incremental coded data, constellation mapping is performed using a down-order modulation method lower than the target modulation order.

[0010] Preferably, the slave control node parses the header of the multicast data packet to obtain the high region coordinate set corresponding to the high change region and the low region coordinate set corresponding to the low change region. The slave control node extracts historical pixel data from the local cache that is within the low region coordinate set in the previous frame, reads the grayscale difference sequence contained in the incremental encoded data, performs pixel-by-pixel addition on the historical pixel data and the grayscale difference sequence to generate updated pixel data, fills the updated pixel data into the position corresponding to the low region coordinate set, and directly fills the full encoded data into the position corresponding to the high region coordinate set to generate the complete current frame data.

[0011] Preferably, the preset grid size is determined as follows: the main controller obtains the scanning mode and pixel array arrangement parameters of the LED display screen connected to the slave control node; when the scanning mode is static scanning, the physical size of a single LED light-emitting module is used as the basic grid size; when the scanning mode is dynamic scanning, the physical size is divided by the scanning duty cycle to obtain the basic grid size as the preset grid size; when the area change rate is within a preset fluctuation range, the image blocks corresponding to four adjacent basic grid sizes are merged to generate an enlarged image block, and the block difference value is recalculated using the enlarged image block as the unit.

[0012] Preferably, before transmitting the pilot signal, the slave control node performs a discrete Fourier transform on the pilot signal to extract the frequency domain channel response matrix, quantizes the complex elements in the frequency domain channel response matrix to generate a quantization index matrix, executes a preset compression algorithm on the quantization index matrix to generate compressed channel state information, encapsulates the compressed channel state information in a reverse link control frame and sends it to the master controller, the master controller executes a decompression algorithm on the compressed channel state information to restore the quantization index matrix, and performs spline interpolation calculation on the quantization index matrix to restore the signal-to-noise ratio of all the orthogonal frequency division multiplexing subcarriers in the wireless communication link.

[0013] Preferably, when allocating the orthogonal frequency division multiplexing (OFDM) subcarriers, the main controller obtains the highest frequency index of the OFDM subcarriers in the high signal-to-noise ratio (SNR) range and the lowest frequency index of the OFDM subcarriers in the low SNR range. A preset number of virtual subcarriers are inserted between the highest and lowest frequency indices. The frequency domain data corresponding to the virtual subcarriers is set to zero. The OFDM subcarriers containing the full-quantity coded data, the virtual subcarriers, and the OFDM subcarriers containing the incremental coded data are concatenated into a complete frequency domain sequence. An inverse fast Fourier transform is performed on the complete frequency domain sequence to generate time-domain OFDM symbols.

[0014] Preferably, the slave node writes the generated complete current frame data into the write buffer of a preset double-buffered queue, extracts the global timestamp carried in the multicast data packet, reads the local clock count value generated by the real-time clock counter inside the slave node, calculates the clock deviation value between the global timestamp and the local clock count value, inputs the clock deviation value into a preset proportional-integral controller to generate a clock adjustment voltage, outputs the clock adjustment voltage to the voltage control terminal of the local voltage-controlled crystal oscillator to adjust the clock frequency of the local display clock, and when the double-buffered queue completes the pointer exchange between the write buffer and the read buffer, triggers the LED driver chip to latch the complete current frame data in the read buffer according to the adjusted local display clock.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention extracts the pixel difference matrix and regional change rate between the current frame and the previous frame, dividing the display screen into high-change and low-change regions. Full pixel encoding and incremental pixel encoding are then performed on these regions respectively. Combined with the multicast transmission rate calculated based on channel state information, the two types of encoded data are mapped onto subcarriers of the orthogonal frequency division multiplexing (OFDM) system. The slave nodes merge and reconstruct the full-encoded data with the locally cached data from the previous frame based on the region mapping identifier. This method eliminates static redundant data, reduces the wireless channel transmission load, avoids channel congestion caused by redundant data occupying bandwidth, eliminates end-to-end transmission delay fluctuations caused by congestion, and ensures that each slave node in the cluster completes the merging, reconstruction, and output of the current frame data within the same clock cycle based on the global timestamp, thus solving the problems of frame asynchrony and screen tearing.

[0016] 2. By dividing the image into blocks according to a preset grid size and calculating the block difference value, Huffman coding and run-length coding are performed in combination with the first and second preset change rate thresholds to achieve data compression of image content with different change amplitudes; by sending pilot signals from the control node to calculate the signal-to-noise ratio of each orthogonal frequency division multiplexing subcarrier and determining the target modulation order, the full-quantity encoded data is allocated to the high signal-to-noise ratio subcarrier and constellation mapping is performed using the target modulation order, and the incremental encoded data is allocated to the low signal-to-noise ratio subcarrier and constellation mapping is performed using a reduced-order modulation method to improve the matching degree of channel resources and transmission reliability; by calculating the clock deviation value between the global timestamp and the local clock count value and inputting it into the proportional-integral controller to generate a clock adjustment voltage, the clock adjustment voltage is output to the voltage control terminal of the local voltage-controlled crystal oscillator to adjust the clock frequency of the local display clock, eliminating the inherent crystal oscillator frequency deviation between the master and slave nodes and maintaining the clock edge alignment when the double-buffered queue pointers are exchanged. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the overall operation of the LED display cluster control system of the present invention. Figure 2 This is a flowchart of the pixel difference matrix and region change rate calculation of the present invention; Figure 3 This is a flowchart illustrating the region division and differentiated coding execution process of the present invention. Figure 4 This is a flowchart of the channel state detection and multicast transmission rate calculation of the present invention; Figure 5 This is a flowchart of the OFDM subcarrier allocation and time-domain symbol generation process of the present invention; Figure 6 This is a flowchart of the frame data reconstruction and clock synchronization control of the present invention. Detailed Implementation

[0018] refer to Figure 1In one embodiment, the wireless communication-based LED display cluster control system includes a main controller and multiple slave nodes connected to the main controller via wireless communication links. The main controller is equipped with a video input interface, a frame buffer unit, a frame difference processing unit, a region division unit, an encoding unit, a wireless communication module, a multicast group management unit, a channel state calculation unit, and a subcarrier mapping unit. The slave nodes are equipped with a wireless receiving unit, a data packet parsing unit, a frame reconstruction unit, a local buffer unit, a clock synchronization unit, and an LED driver interface. The main controller receives video source data through the video input interface. The video source data is serial digital pixel data corresponding to the total resolution of the LED display cluster. The grayscale value of each pixel is stored in a fixed-width quantization format. The complete pixel data of the previous frame is stored in the frame buffer unit of the main controller. The frame buffer unit adopts a double-buffered structure, and read / write conflicts of frame data are avoided through time-division switching of read / write pointers.

[0019] The frame difference processing unit extracts the pixel difference matrix and region change rate between the current frame and the previous frame from the video source data. The current frame and the previous frame are two consecutive display frames with the same pixel resolution and data storage format. The pixel difference matrix is ​​a two-dimensional matrix representing the degree of pixel change at corresponding positions between the current frame and the previous frame, and the region change rate is a quantized parameter representing the overall pixel change range of the current frame. The region division unit divides the display screen into high-change regions and low-change regions based on the pixel difference matrix and the region change rate. High-change regions correspond to screen intervals where pixel grayscale values ​​change significantly over a large range, while low-change regions correspond to screen intervals where pixel grayscale values ​​remain static or only change slightly over a small range.

[0020] The encoding unit performs full pixel encoding on high-change areas and incremental pixel encoding on low-change areas. Full pixel encoding involves lossless encoding of the grayscale values ​​of all pixels in high-change areas, preserving all pixel information within the area. Incremental pixel encoding encodes only the relevant information of pixels whose grayscale values ​​change in low-change areas, discarding redundant data corresponding to static pixels that have not changed. The master controller establishes a multicast group with multiple slave nodes through the wireless communication module. During the establishment of the multicast group, the master controller generates and sends a multicast group join invitation frame. The invitation frame carries the unique identifier of the multicast group, cluster synchronization reference parameters, and access authentication information. After receiving the invitation frame, the slave nodes complete the access authentication process and return a join confirmation frame. After receiving the join confirmation frames from all target slave nodes, the master controller completes the establishment of the multicast group. All slave nodes in the multicast group share the same wireless transmission time slot and frequency domain resources and receive multicast data packets sent by the master controller.

[0021] The channel state calculation unit calculates the multicast transmission rate of the current time slot based on channel state information. Channel state information consists of frequency domain parameters characterizing the transmission quality of the wireless communication link, including channel gain, signal power, and noise power information for each subcarrier. This channel state information is periodically fed back to the master controller from the slave nodes within the multicast group. The multicast transmission rate is the maximum transmission rate adapted to the current wireless channel quality, ensuring stable data reception by all slave nodes within the multicast group. The subcarrier mapping unit maps the full-value encoded data corresponding to full pixel encoding and the incremental encoded data corresponding to incremental pixel encoding onto the subcarriers of the orthogonal frequency division multiplexing (OFDM) system. The OFDM system contains multiple mutually orthogonal subcarriers, each capable of independently carrying data and undergoing modulation configuration. The subcarrier mapping unit allocates the two types of encoded data to subcarriers with corresponding characteristics according to their transmission requirements. After completing the mapping from data to frequency domain resources, the frequency domain data is converted into a time domain radio frequency signal and transmitted to the wireless channel via the radio frequency front-end of the wireless communication module.

[0022] The control node's wireless receiving unit receives multicast data packets containing both full-encoded and incremental-encoded data. The data packet parsing unit parses the multicast data packets, obtaining the region mapping identifier carried in the packet header. This identifier includes the coordinates of high-change and low-change regions on the displayed screen, the encoding type identifier, and the corresponding data length. The frame reconstruction unit, based on the region mapping identifier, merges and reconstructs the full-encoded data with the data from the corresponding low-change region of the previous frame stored in the local cache, generating complete current frame data. The local cache unit's historical frame buffer stores the complete display frame data of the previous frame. The frame reconstruction unit reads the pixel data of the previous frame corresponding to the low-change region from the historical frame buffer, updates this data by combining it with the incremental-encoded data, and then aligns and concatenates it with the decoded full-encoded data of the high-change region to generate complete current frame data. The clock synchronization unit adjusts the local display clock based on the global timestamp carried in the multicast data packet. The global timestamp is the reference time information generated by the main controller corresponding to the display refresh time of the current frame. The clock synchronization unit compares the global timestamp with the real-time count value of the local display clock, calculates the clock deviation between the two, and adjusts the frequency and phase of the local display clock based on the clock deviation to keep the local display clock synchronized with the global reference clock of the main controller.

[0023] The multicast group node access parameter configuration used in this embodiment is shown in Table 1. This table is used to standardize the access behavior, data feedback cycle and synchronization reference parameters of each slave node in the multicast group, so as to ensure the timing alignment and data interaction consistency of each node during multicast transmission.

[0024] Table 1 Multicast Group Node Access Parameter Configuration Table ; In this embodiment, differentiated encoding of the display screen is achieved by extracting and dividing the pixel differences between frames, eliminating static redundant data and reducing the transmission load of the wireless channel; the matching of transmission resources and link quality is achieved by adapting the multicast transmission rate based on channel state information; the complete restoration of the display frame is achieved by merging and reconstructing the area mapping identifier of the multicast data packet and the local cache data; and the display synchronization of each node in the cluster is achieved by adjusting the local clock of the global timestamp, avoiding transmission delay fluctuations and screen asynchrony problems caused by channel congestion.

[0025] refer to Figure 2 In a preferred embodiment, the main controller divides the current frame and the previous frame into multiple image blocks according to a preset grid size. The preset grid size is the number of rows and columns of pixels in the corresponding display screen. Each image block contains the same number of pixels, and all image blocks are arranged in a regular matrix in the display screen, with no overlap or gap between adjacent image blocks. For each image block, the main controller calculates the absolute difference between the gray values ​​of each pixel in the corresponding image block in the current frame and the gray values ​​of each pixel in the corresponding image block in the previous frame. The absolute differences are summed to generate the block difference value of the image block, and the block difference values ​​of all image blocks constitute a pixel difference matrix. The calculation process of the block difference value is implemented through the following formula:

[0026] in, For the first line, number Block difference values ​​of image patches The number of pixels per row in the image block corresponding to the preset grid size. The number of pixels per column in the image block corresponding to the preset grid size. The coordinates in the current frame are The grayscale value of the pixel, The coordinates in the previous frame are The grayscale value of the pixel, The range of values ​​is , The range of values ​​is , The total number of rows in pixels displayed on the screen. This represents the total number of columns in the displayed image.

[0027] The main controller counts the number of image blocks whose difference values ​​exceed a preset difference threshold, divides this number by the total number of image blocks to generate the region change rate. The region change rate is calculated using the following formula:

[0028] in, The rate of change of the region in the current frame. This represents the number of image blocks whose block difference value is greater than a preset difference threshold. The total number of image blocks in the current frame. The preset difference threshold is a pre-defined sum of grayscale differences and a critical value used to distinguish the degree of pixel change in image blocks. The preset difference threshold can be adjusted according to the resolution of the display screen and the display accuracy of the LED display screen.

[0029] The main controller compares the region change rate with a first preset change rate threshold and a second preset change rate threshold, respectively. If the first preset change rate threshold is greater than the second preset change rate threshold, the corresponding image block is classified as a high-change region; if the region change rate is less than the second preset change rate threshold, the corresponding image block is classified as a low-change region. For image blocks whose region change rate is between the first and second preset change rate thresholds, the main controller classifies them according to the classification results of adjacent image blocks. If an adjacent image block is a high-change region, the image block is classified as a high-change region; if an adjacent image block is a low-change region, the image block is classified as a low-change region. This avoids fragmented classification results and reduces the complexity of encoding and transmission.

[0030] The main controller performs Huffman coding on image blocks within high-variability regions to generate full-scale encoded data. Huffman coding is a lossless entropy coding based on the probability of pixel grayscale values. During the encoding process, the main controller first counts the frequency of pixel grayscale values ​​in all image blocks within high-variability regions. Based on this frequency, it constructs a Huffman binary tree, assigning short code lengths to grayscale values ​​with high frequency and long code lengths to grayscale values ​​with low frequency. Then, it encodes all pixel grayscale values ​​based on the constructed Huffman binary tree, generating full-scale encoded data. The full-scale encoded data carries the corresponding Huffman coding table for decoding operations by slave nodes. For image blocks within low-variability regions, the main controller extracts the pixel coordinates and corresponding grayscale differences where grayscale values ​​change. It then performs run-length coding on the pixel coordinates and grayscale differences to generate incremental encoded data. Run-length encoding is a lossless encoding method that compresses consecutively occurring identical values. During the extraction process, the main controller scans image blocks in low-change regions line by line, compares the grayscale values ​​of corresponding pixels in the current frame with those in the previous frame, and records the relative coordinates of the pixel within the image block and the grayscale difference between the current frame and the previous frame when a change in grayscale value is detected. For consecutive unchanging pixel intervals, the run-length is recorded, and for consecutive changing pixel intervals, the coordinate offset and grayscale difference sequence are recorded. Run-length encoding is then performed on the run-length, coordinate offset, and grayscale difference sequence to generate incremental encoded data.

[0031] The preset grid size is determined by the main controller acquiring the scanning mode and pixel array layout parameters of the LED display connected to the slave control nodes. The LED display scanning modes include static scanning and dynamic scanning. In static scanning, each LED in the LED module is controlled by an independent driving channel. In dynamic scanning, multiple LEDs share the same driving channel in a time-sharing manner, and the scanning duty cycle is the reciprocal of the number of LEDs sharing the same driving channel. The pixel array layout parameters include the number of rows and columns of pixels in a single LED module, and the module splicing method. When the scanning mode is static scanning, the main controller uses the physical size of a single LED module as the basic grid size, which is the number of rows and columns of pixels corresponding to that module. When the scanning mode is dynamic scanning, the main controller divides the physical size by the scanning duty cycle to obtain the basic grid size as the preset grid size. This process is achieved through the following formula:

[0032] in, Based on the grid size, This refers to the number of pixels corresponding to the physical size of a single LED light-emitting module. This refers to the scanning duty cycle of the LED display screen. The range of values ​​for the scanning duty cycle is as follows: The static scan corresponds to a scan duty cycle of 1. When the area change rate is within a preset fluctuation range, the main controller merges the image blocks corresponding to four adjacent basic grid sizes to generate enlarged image blocks, and recalculates the block difference value on a per-enlarged image block basis. The preset fluctuation range is a pre-defined area change rate range, corresponding to scenes where the degree of pixel change in the image is at a moderate level. The number of row pixels and column pixels in the merged enlarged image block is twice the basic grid size. By merging image blocks, the amount of calculation required for block difference values ​​is reduced, thus lowering the computational load on the main controller.

[0033] Table 2 shows the compression performance comparison of different grid sizes and encoding methods used in this embodiment. This table compares the performance parameters of the same test video frame after being divided and encoded using different preset grid sizes. It can intuitively show the impact of different grid sizes on the encoding compression effect and provide a reference for the adaptive adjustment of preset grid sizes.

[0034] Table 2. Comparison of Compression Performance for Different Grid Sizes and Encoding Methods ; refer to Figure 3In this embodiment, the degree of pixel change between frames is quantitatively represented by dividing image blocks into pre-defined grid sizes and calculating block difference values; the precise division of high-change and low-change regions is achieved by comparing the regional change rate with dual thresholds; lossless compression of image content with different degrees of change is achieved by using differentiated coding methods of Huffman coding and run-length coding, further reducing the amount of transmitted data; the matching of image block division with display hardware characteristics is achieved by combining the preset grid size determination of LED display scanning method, improving the rationality of region division; and the dynamic adjustment of computational load is achieved through the image block merging mechanism to adapt to different image change scenarios.

[0035] refer to Figure 4 In a preferred embodiment, the slave node sends pilot signals to the master controller at a preset period. The pilot signals are pre-defined, known modulation symbols with a fixed sequence length, used by the master controller for channel estimation and channel state information calculation. The preset period can be adjusted according to the time-varying characteristics of the wireless channel; the stronger the time-varying characteristics, the shorter the preset period. The master controller receives the pilot signals and calculates the signal-to-noise ratio (SNR) of each orthogonal frequency division multiplexing subcarrier in the wireless communication link. The SNR calculation is achieved using the following formula:

[0036] in, For the first The signal-to-noise ratio of each orthogonal frequency division multiplexed subcarrier. For the first The received signal power of each subcarrier, For the first The noise power of each subcarrier, the received signal power, and the noise power are obtained by correlation operation between the received sequence of the pilot signal and the locally known sequence.

[0037] For each orthogonal frequency division multiplexing subcarrier, the main controller substitutes the signal-to-noise ratio into the Shannon capacity calculation formula to calculate the instantaneous channel capacity. This process is achieved through the following formula:

[0038] in, For the first The instantaneous channel capacity of each subcarrier, in bits per second. For the first The bandwidth of each subcarrier is measured in Hz. In an orthogonal frequency division multiplexing (OFDM) system, all subcarriers have the same bandwidth, i.e. , The bandwidth is fixed for a single subcarrier. The main controller obtains the sum of the instantaneous channel capacity of all orthogonal frequency division multiplexing subcarriers, multiplies the sum by a preset scaling factor to generate the multicast transmission rate of the current time slot, and this process is implemented through the following formula:

[0039] in, The multicast transmission rate for the current time slot. This is a preset proportionality coefficient, with a value range of [value range missing]. This is used to ensure a certain link margin for multicast transmission rate and to adapt to the channel quality of all slave nodes within the multicast group. This represents the total number of effective subcarriers in an orthogonal frequency division multiplexing system.

[0040] The main controller determines the target modulation order by querying a preset rate modulation mapping table based on the multicast transmission rate. The rate modulation mapping table is a pre-stored correspondence between transmission rates and modulation orders. Modulation orders include binary phase shift keying (PSK), quadrature phase shift keying (QPSK), 16-quadrature amplitude modulation (QAM), 64-quadrature amplitude modulation (QAM), and 256-quadrature amplitude modulation (QAM). A higher modulation order carries more bits per symbol, resulting in a higher transmission rate and a higher required signal-to-noise ratio (SNR) threshold. The main controller allocates the fully encoded data to orthogonal frequency division multiplexing (OFDM) subcarriers with a high SNR, and allocates the incrementally encoded data to OFDM subcarriers with a low SNR. The high SNR range is defined as the set of subcarriers with an SNR greater than a preset high SNR threshold, and the low SNR range is defined as the set of subcarriers with an SNR less than a preset low SNR threshold. The preset high SNR threshold is greater than the preset low SNR threshold. Full-quantity encoded data consists of complete pixel data in high-variable areas, which has higher requirements for transmission reliability. It is allocated to subcarriers in high signal-to-noise ratio intervals with better channel quality. Incremental-quantity encoded data consists of difference data in low-variable areas, which has a smaller data volume and relatively lower requirements for transmission reliability. It is allocated to subcarriers in low signal-to-noise ratio intervals to achieve a match between channel resources and data transmission needs.

[0041] For orthogonal frequency division multiplexing (OFDM) subcarriers allocated with fully coded data, the main controller uses the target modulation order for constellation mapping. For OFDM subcarriers allocated with incrementally coded data, the main controller uses a reduced-order modulation scheme with a lower modulation order than the target modulation order for constellation mapping. The reduced-order modulation scheme is one with a modulation order lower than the target modulation order. For example, when the target modulation order is 64 quadrature amplitude modulation (QAM), the reduced-order modulation scheme can use 16 quadrature amplitude modulation (QAM) or quadrature phase shift keying (QPSK). The reduced-order modulation scheme has a lower signal-to-noise ratio (SNR) threshold and higher transmission reliability in the low SNR range.

[0042] Before transmitting the pilot signal, the slave node performs a discrete Fourier transform on the pilot signal to extract the frequency domain channel response matrix. This process is achieved through the following formula:

[0043] in, The frequency domain channel response matrix, The time-domain channel impulse response sequence corresponds to the pilot signal. The Discrete Fourier Transform (DFT) is used, and its length is the same as the total number of subcarriers in the orthogonal frequency division multiplexing (OFDM) system. The frequency-domain channel response matrix is ​​a complex matrix, with each element corresponding to the channel gain of a subcarrier, containing amplitude and phase information. The slave node quantizes the complex elements in the frequency-domain channel response matrix to generate a quantization index matrix. Quantization involves uniformly quantizing the amplitude and phase of the complex elements, mapping continuous amplitude and phase values ​​to discrete quantization indices. The number of bits in the quantization index can be adjusted according to the feedback accuracy requirements of the channel state information; a higher quantization bit depth results in higher feedback accuracy but also a larger amount of feedback data. The slave node then executes a preset compression algorithm on the quantization index matrix to generate compressed channel state information. This preset compression algorithm uses lossless compression to remove redundant data from the quantization index matrix, reducing the amount of feedback data for channel state information and decreasing the transmission load on the reverse link.

[0044] The slave node encapsulates compressed channel state information in a reverse link control frame and sends it to the master controller. The reverse link control frame carries the slave node's identification information, frame number, and checksum. Upon receiving the reverse link control frame, the master controller first verifies the frame data's correctness using the checksum. If the verification passes, it performs a decompression algorithm on the compressed channel state information to restore the quantization index matrix. Then, it performs spline interpolation on the quantization index matrix to restore the signal-to-noise ratio (SNR) of all orthogonal frequency division multiplexing (OFDM) subcarriers in the wireless communication link. The spline interpolation calculation, based on the quantized discrete channel response values, fits a continuous channel frequency response curve, thereby restoring the channel gain and SNR of all subcarriers and compensating for the accuracy loss caused by quantization and compression.

[0045] refer to Figure 5When allocating orthogonal frequency division multiplexing (OFDM) subcarriers, the main controller obtains the highest frequency index of the OFDM subcarriers in the high signal-to-noise ratio (SNR) range and the lowest frequency index of the OFDM subcarriers in the low SNR range. A preset number of virtual subcarriers are inserted between the highest and lowest frequency indices, and the frequency domain data corresponding to the virtual subcarriers is set to zero. Virtual subcarriers are subcarriers that do not carry any valid data and are used to isolate subcarriers in the high and low SNR ranges, avoiding inter-symbol interference and inter-carrier interference between subcarriers in different ranges, thus improving the reliability of data transmission. The main controller concatenates the OFDM subcarriers containing fully coded data, the virtual subcarriers, and the OFDM subcarriers containing incrementally coded data into a complete frequency domain sequence. An inverse fast Fourier transform is then performed on the complete frequency domain sequence to generate time-domain OFDM symbols. This process is implemented using the following formula:

[0046] in, For time-domain orthogonal frequency division multiplexing symbols, The concatenated complete frequency domain sequence is generated using IFFT (Inverse Fast Fourier Transform), where the transform length is the same as the total number of subcarriers in the orthogonal frequency division multiplexing (OFDM) system. After generating the time-domain OFDM symbols, the main controller adds a cyclic prefix to the symbol front-end. The length of the cyclic prefix is ​​greater than the maximum multipath delay of the wireless channel, used to eliminate inter-symbol interference caused by multipath effects. The time-domain symbols with the added cyclic prefix are then transmitted to the wireless channel through the radio frequency front-end.

[0047] The subcarrier signal-to-noise ratio range and modulation scheme mapping used in this embodiment are shown in Table 3. This table contains the subcarrier allocation and modulation scheme configuration parameters of the orthogonal frequency division multiplexing system. It can clearly define the data type and modulation scheme corresponding to the subcarriers in different signal-to-noise ratio ranges, and realize the fine allocation and adaptation of channel resources.

[0048] Table 3. Mapping Table of Subcarrier Signal-to-Noise Ratio Range and Modulation Mode ; In this embodiment, the wireless channel transmission capability is quantitatively characterized by calculating the subcarrier signal-to-noise ratio (SNR) of the pilot signal and performing Shannon capacity analysis. The multicast transmission rate is determined based on the channel quality of all nodes within the multicast group, ensuring stable reception for all slave nodes. Differential data allocation and modulation scheme configuration for subcarriers in different SNR ranges achieves precise matching between channel resources and data transmission requirements, improving transmission reliability and resource utilization. Quantization, compression, and feedback of the frequency domain channel response matrix reduce the transmission load on the reverse link. The insertion of virtual subcarriers and the generation of time-domain symbols using inverse fast Fourier transform reduce inter-carrier interference and enhance the anti-multipath capability of wireless transmission.

[0049] refer to Figure 6 In a preferred embodiment, the slave node parses the header of the multicast data packet to obtain the high-region coordinate set corresponding to the high-variable region and the low-region coordinate set corresponding to the low-variable region. The header of the multicast data packet is a fixed-length control field, including frame sequence number, global timestamp, region mapping identifier, data length, encoding method identifier, and checksum information. The region mapping identifier includes the high-region coordinate set and the low-region coordinate set. The high-region coordinate set represents the start and end coordinates of all image blocks in the high-variable region on the displayed screen, and the low-region coordinate set represents the start and end coordinates of all image blocks in the low-variable region on the displayed screen. The slave node extracts historical pixel data from the previous frame that is within the low-region coordinate set from its local cache. The local cache is a random access memory within the slave node, divided into a historical frame cache, a current frame cache, and a double-buffered queue. The historical frame cache stores the complete display frame data of the previous frame, and the data format is consistent with the video source data format issued by the main controller. The grayscale value of each pixel is stored continuously in row and column coordinate order.

[0050] The system reads the grayscale difference sequence from the incremental encoded data from the control node, and performs pixel-by-pixel addition on the historical pixel data and the grayscale difference sequence to generate updated pixel data. This process is achieved through the following formula:

[0051] in, The coordinates are within the low-change region. Update pixel data for each pixel. The coordinates in the previous frame are Historical pixel data of pixels, This represents the grayscale difference between corresponding pixels in the incrementally encoded data. For pixels where the grayscale value has not changed, the corresponding grayscale difference is 0. The slave node fills the positions corresponding to the lower region coordinate set with the updated pixel data and directly fills the positions corresponding to the higher region coordinate set with the full encoded data to generate the complete current frame data. During the filling process, the slave node, according to the row and column coordinate order of the displayed screen, first decodes the full encoded data corresponding to the higher region coordinate set and writes it to the corresponding position in the current frame buffer, then writes the updated pixel data corresponding to the lower region coordinate set to the corresponding position in the current frame buffer. After all coordinate positions in the current frame buffer have been filled with data, the complete current frame data is generated.

[0052] The slave node writes the generated complete current frame data into the write buffer of a preset double-buffered queue. The double-buffered queue contains two independent buffers: a write buffer and a read buffer. The write buffer receives and stores the newly generated complete current frame data, while the read buffer outputs the display frame data to the LED driver chip. The address pointers of the two buffers can be swapped to achieve seamless data switching and avoid screen tearing. The slave node extracts the global timestamp carried in the multicast data packet, reads the local clock count value generated by the slave node's internal real-time clock counter, and calculates the clock deviation between the global timestamp and the local clock count value. This process is achieved using the following formula:

[0053] in, This is the clock offset value. The global timestamp carried in the multicast data packet. The current count value is the local real-time clock counter of the slave node. The global timestamp and the local clock count value use the same time quantization unit, which is an integer multiple of the clock cycle.

[0054] The slave node inputs the clock deviation value into a preset proportional-integral controller to generate a clock-regulated voltage. This process is achieved through the following formula:

[0055] in, Adjust the voltage for the clock. This is the proportionality coefficient. The integral coefficient is... For the first Clock offset value corresponding to each frame period This represents the number of frame periods accumulated through integration. The proportional-integral controller (PIC) responds quickly to the current clock deviation through a proportional element and eliminates static clock frequency deviations through an integral element, achieving error-free synchronization between the local clock and the global reference clock. The slave node outputs a clock adjustment voltage to the voltage control terminal of the local voltage-controlled crystal oscillator (VCO) to adjust the local display clock frequency. The VCO is a crystal oscillator whose output frequency varies with the input control voltage. Its output clock signal serves as the local display clock for the slave node, providing a reference clock signal for the LED driver chip's display refresh, data latching, and local clock counter. When the clock deviation is positive, it indicates that the local display clock is slower than the global reference clock, and the output frequency of the VCO is increased by adjusting the clock voltage. When the clock deviation is negative, it indicates that the local display clock is faster than the global reference clock, and the output frequency of the VCO is decreased by adjusting the clock voltage.

[0056] When the dual-buffered queue completes the pointer exchange between the write buffer and the read buffer, the slave node triggers the LED driver chip to latch the complete current frame data in the read buffer based on the adjusted local display clock. The trigger time for the pointer exchange is determined by the display refresh time corresponding to the global timestamp. When the count value of the adjusted local display clock reaches the refresh count value corresponding to the global timestamp, the pointer exchange of the dual-buffered queue is triggered, switching the write buffer to the new read buffer and the original read buffer to the new write buffer. At the same time, a local latch signal is generated, triggering the LED driver chip to latch the complete current frame data in the new read buffer and output the data to the corresponding LED array for display refresh, ensuring that all slave nodes in the cluster complete the display frame refresh at the same time, achieving frame synchronization.

[0057] The clock adjustment parameters of the proportional-integral controller used in this embodiment are configured as shown in Table 4. This table shows the parameter configuration of the proportional-integral controller and related hardware of the clock synchronization unit, which can clearly define the parameters of the clock adjustment loop and ensure the synchronization accuracy between the local display clock and the global reference clock.

[0058] Table 4. Proportional-Integral Controller Clock Adjustment Parameter Configuration Table ; In this embodiment, precise positioning of different encoded data is achieved through parsing the high-area coordinate set and the low-area coordinate set; accurate updating of pixel data in low-change areas is achieved through pixel-by-pixel addition of historical pixel data and gray-scale difference sequence; efficient reconstruction of complete current frame data is achieved by filling the coordinate correspondence between the full encoded data and the updated pixel data; screen tearing caused by frame data read / write conflicts is avoided through writing to the double-buffered queue and exchanging pointers; quantitative characterization of master-slave node clock deviation is achieved through the deviation calculation between the global timestamp and the local clock count value; and error-free synchronization between the local display clock and the global reference clock is achieved by adjusting the voltage of the voltage-controlled crystal oscillator through the clock generation of the proportional-integral controller, ensuring that the display refresh time of all slave control nodes in the cluster is completely aligned and solving the problem of frame asynchrony.

Claims

1. A control system for an LED display cluster based on wireless communication, characterized in that, It includes a main controller and multiple slave control nodes connected to the main controller via a wireless communication link. The main controller receives video source data, extracts the pixel difference matrix and regional change rate between the current frame and the previous frame from the video source data, divides the display screen into high change area and low change area according to the pixel difference matrix and the regional change rate, performs full pixel encoding on the high change area, and performs incremental pixel encoding on the low change area. The main controller establishes a multicast group with the multiple slave control nodes through the wireless communication module, calculates the multicast transmission rate of the current time slot based on the channel state information, and maps the full-quantity encoded data corresponding to the full-quantity pixel encoding and the incremental encoded data corresponding to the incremental pixel encoding to the subcarriers of the orthogonal frequency division multiplexing system for transmission. The slave control node receives a multicast data packet containing the full encoded data and the incremental encoded data. Based on the region mapping identifier carried in the header of the multicast data packet, it merges the full encoded data with the data of the low-change region corresponding to the previous frame in the local cache to reconstruct the complete current frame data, and adjusts the local display clock according to the global timestamp carried in the multicast data packet.

2. The LED display cluster control system based on wireless communication according to claim 1, characterized in that, The main controller divides the current frame and the previous frame into multiple image blocks according to a preset grid size. For each image block, it calculates the absolute difference between the gray values ​​of each pixel in the current frame and the gray values ​​of each pixel in the previous frame. The absolute differences are summed to generate the block difference value of the image block. The pixel difference matrix is ​​formed by the block difference values ​​of all the image blocks. The number of image blocks whose block difference values ​​are greater than a preset difference threshold is counted. The number is divided by the total number of image blocks to generate the region change rate.

3. The LED display cluster control system based on wireless communication according to claim 2, characterized in that, The main controller compares the region change rate with a first preset change rate threshold and a second preset change rate threshold. When the region change rate is greater than the first preset change rate threshold, the corresponding image block is classified as the high change region. When the region change rate is less than the second preset change rate threshold, the corresponding image block is classified as the low change region. The main controller performs Huffman coding on the image blocks in the high change region to generate the full encoded data. It extracts the pixel coordinates and corresponding grayscale differences of the image blocks in the low change region. It performs run-length coding on the pixel coordinates and the grayscale differences to generate the incremental encoded data.

4. The LED display cluster control system based on wireless communication according to claim 1, characterized in that, The slave node sends pilot signals to the master controller according to a preset period. The master controller receives the pilot signals and calculates the signal-to-noise ratio (SNR) of each orthogonal frequency division multiplexing (OFDM) subcarrier in the wireless communication link. For each OFDM subcarrier, the SNR is substituted into the Shannon capacity calculation formula to calculate the instantaneous channel capacity. The sum of the instantaneous channel capacities of all OFDM subcarriers is obtained, and the sum is multiplied by a preset scaling factor to generate the multicast transmission rate of the current time slot.

5. The LED display cluster control system based on wireless communication according to claim 4, characterized in that, The main controller determines the target modulation order by querying a preset rate modulation mapping table based on the multicast transmission rate, allocates the full-quantity coded data to the orthogonal frequency division multiplexing subcarriers with a high signal-to-noise ratio (SNR), and allocates the incremental coded data to the orthogonal frequency division multiplexing subcarriers with a low SNR. For the orthogonal frequency division multiplexing subcarriers allocated with the full-quantity coded data, constellation mapping is performed using the target modulation order. For the orthogonal frequency division multiplexing subcarriers allocated with the incremental coded data, constellation mapping is performed using a down-order modulation method lower than the target modulation order.

6. The LED display cluster control system based on wireless communication according to claim 1, characterized in that, The slave node parses the header of the multicast data packet to obtain the high region coordinate set corresponding to the high change region and the low region coordinate set corresponding to the low change region. The slave node extracts historical pixel data from the previous frame that is within the low region coordinate set from the local cache, reads the gray-level difference sequence contained in the incremental encoded data, performs pixel-by-pixel addition operation on the historical pixel data and the gray-level difference sequence to generate updated pixel data, fills the updated pixel data into the position corresponding to the low region coordinate set, and directly fills the full encoded data into the position corresponding to the high region coordinate set to generate the complete current frame data.

7. The LED display cluster control system based on wireless communication according to claim 2, characterized in that, The preset grid size is determined as follows: the main controller obtains the scanning mode and pixel array arrangement parameters of the LED display screen connected to the slave control node; when the scanning mode is static scanning, the physical size of a single LED light-emitting module is used as the basic grid size; when the scanning mode is dynamic scanning, the physical size is divided by the scanning duty cycle to obtain the basic grid size as the preset grid size; when the area change rate is within a preset fluctuation range, the image blocks corresponding to four adjacent basic grid sizes are merged to generate an enlarged image block, and the block difference value is recalculated in units of the enlarged image block.

8. The LED display cluster control system based on wireless communication according to claim 4, characterized in that, Before transmitting the pilot signal, the slave control node performs a discrete Fourier transform on the pilot signal to extract the frequency domain channel response matrix, quantizes the complex elements in the frequency domain channel response matrix to generate a quantization index matrix, executes a preset compression algorithm on the quantization index matrix to generate compressed channel state information, encapsulates the compressed channel state information in a reverse link control frame and sends it to the master controller, the master controller executes a decompression algorithm on the compressed channel state information to restore the quantization index matrix, and performs spline interpolation calculation on the quantization index matrix to restore the signal-to-noise ratio of all the orthogonal frequency division multiplexing subcarriers in the wireless communication link.

9. The LED display cluster control system based on wireless communication according to claim 5, characterized in that, When allocating the orthogonal frequency division multiplexing (OFDM) subcarriers, the main controller obtains the highest frequency index of the OFDM subcarriers in the high signal-to-noise ratio (SNR) range and the lowest frequency index of the OFDM subcarriers in the low SNR range. A preset number of virtual subcarriers are inserted between the highest and lowest frequency indices. The frequency domain data corresponding to the virtual subcarriers is set to zero. The OFDM subcarriers containing the full-encoded data, the virtual subcarriers, and the OFDM subcarriers containing the incremental-encoded data are concatenated into a complete frequency domain sequence. An inverse fast Fourier transform is performed on the complete frequency domain sequence to generate time-domain OFDM symbols.

10. The LED display cluster control system based on wireless communication according to claim 6, characterized in that, The slave node writes the generated complete current frame data into the write buffer of a preset double-buffered queue, extracts the global timestamp carried in the multicast data packet, reads the local clock count value generated by the real-time clock counter inside the slave node, calculates the clock deviation value between the global timestamp and the local clock count value, inputs the clock deviation value into a preset proportional-integral controller to generate a clock adjustment voltage, and outputs the clock adjustment voltage to the voltage control terminal of the local voltage-controlled crystal oscillator to adjust the clock frequency of the local display clock. When the double-buffered queue completes the pointer exchange between the write buffer and the read buffer, it triggers the LED driver chip to latch the complete current frame data in the read buffer according to the adjusted local display clock.

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