Preamble

Foshan LPL Spring Finals Wireless Transmission System Analysis and Design
Zhang Le, Li Liang
(Jinan Daily Newspaper Group, Ai Jinan Client, Jinan, Shandong 250000)

Abstract

[Objective] On April 21, 2024, the LPL League of Legends Professional League Spring Finals were held in Foshan, Guangdong. The broadcast required Steadicam stabilizers for mobile camera positions with extensive range of motion, necessitating microwave wireless video transmission. For an event of this scale, the electromagnetic environment within the venue became extremely complex, with high-power audio systems, LED screens, wireless intercom systems, and even security and fire department radios all potentially causing interference to the microwave video transmission. To ensure smooth live broadcasting, the wireless transmission system required careful design, interference analysis, and mitigation strategies. [Method] Optimization was achieved through multiple approaches including antenna design, system redundancy, interference detection, and elimination. [Results] Following these optimization measures, video return quality improved significantly, enabling successful completion of the live broadcast. [Conclusion] Throughout the event, professional-brand walkie-talkies—originally considered the least likely source of interference—proved to be the primary interference source. For broadcast operations with stringent requirements, microwave video transmission should be accompanied by a spectrum analyzer for continuous frequency monitoring to ensure safe transmission.

Keywords: wireless transmission; wireless reverse control; microwave; spectrum monitoring; interference mitigation
Classification Code: G202
Document Code: A
Article ID: 1671-0134(2025)02-146-04
DOI: 10.19483/j.cnki.11-4653/n.2025.02.029
Citation Format: Zhang Le, Li Liang. Analysis and Design of Wireless Transmission System for Foshan LPL Spring Finals [J]. China Media Technology, 2025, 32(2): 146-149.

1. Background and Technical Requirements

On April 21, 2024, the LPL League of Legends Professional League Spring Finals took place in Foshan, Guangdong. As one of the most anticipated events in esports, the tournament featured top-tier teams and players, attracting thousands of live and online spectators. The venue utilized two Steadicam systems for mobile camera positions, both equipped with wireless microwave transmission systems to capture dynamic, high-quality video footage. This configuration allowed camera operators to move freely throughout the venue without cable restrictions. Simultaneously, camera parameters were controlled from the broadcast truck's technical area via OCP (Operation Control Panel), enabling real-time adjustment of aperture, color balance, and other critical video parameters. Since the two microwave systems did not require tally or synchronization signals, the reverse control design remained relatively simple, with camera operators using wireless beltpack intercom systems.

The broadcast truck was parked outside the main venue, making direct SDI coaxial connections impractical. Each system would have required at least four SDI cables spanning 150-200 meters—exceeding the transmission limits of coaxial cable. To address signal attenuation and cabling complexity, a Boyaweiyuan microwave optical transmission system (Model RTP-5) was deployed between the broadcast truck and the venue interior. This system utilized camera hybrid fiber-optic cables, which are standard equipment carried by broadcast trucks as backups. Using these cables ensured both abundance and compatibility, requiring only terminal devices at each end to replace multiple coaxial cables with a single hybrid cable connecting interior and exterior locations.

For this broadcast, the technical team selected the Vislink wireless transmission system, an industry-renowned solution recognized for its reliability and high performance. Operating in the 7GHz band, this system specifically avoids the congested unlicensed 2.4GHz and 5GHz bands commonly used by Wi-Fi, Bluetooth, and Zigbee devices. Each microwave video transmission system comprised an integrated encoder/modulator/transmitter, a receiver/demodulator/decoder, four 7GHz microwave receiving antennas, and four L3025-6471 active downconverters (which convert 7GHz microwave signals to UHF band for SDI coaxial transmission to the receiver). This conversion ensured reliable long-distance transmission without significant attenuation.

The two Steadicam units operated over large areas within a venue filled with numerous LED screens, audio systems, Wi-Fi networks, and intercom equipment, creating a highly complex electromagnetic environment. To ensure successful live broadcasting, the wireless transmission system required meticulous design, thorough interference analysis, and effective mitigation strategies.

2. Design Scheme

The reverse control system utilized Vislink's companion FocalPoint system. Each set included a CCIU (Camera Control Interface Unit) to connect with the camera's native OCP, converting the camera's control protocol to Vislink-compatible format for transmission. The system also comprised an active wireless transmitter and an omnidirectional whip antenna. The CCIU connected to the microwave receiver via a Lemo cable, receiving status information from the camera transmitted back by the microwave transmitter. This information was then sent to the camera's OCP, enabling correct display of technical parameters such as aperture values and color temperature, thereby achieving closed-loop reverse control.

[FIGURE:1]

The movement range of the two Steadicam units is illustrated by the red boxes in [FIGURE:2], with the blue section indicating the player entrance channel. The channel featured an aluminum alloy frame with wooden boards covered by gypsum board and black stickers. Due to the high frequency of the 7GHz band, which exhibits poor diffraction and penetration capabilities, signal transmission performance in this channel would be significantly compromised. Therefore, antenna placement required careful optimization for signal reception in this area.

[FIGURE:2]

To ensure stable video transmission despite the Steadicams' large operating range, the receiver employed a four-antenna diversity reception scheme. Each receiver was configured with four antennas to capture signals from different angles. If interference affected one direction, the remaining antennas could still receive strong signals, preventing signal loss from single-point interference. The antennas were positioned separately to maintain optimal signal reception quality throughout the Steadicams' entire movement path.

Each microwave receiver was equipped with four antennas: two omnidirectional whip antennas and two directional panel antennas. The high gain of directional antennas enabled stronger signal reception in specific directions, particularly in areas with frequent camera movement and partially shielded zones like the player entrance channel. This configuration enhanced anti-interference capability and ensured stable video return. Omnidirectional antennas provided broad signal coverage for areas where cameras might move randomly. The combination of directional and omnidirectional antennas achieved both extensive coverage and signal stability in critical zones. The directional antennas used were Vislink L3490 models with 80° beamwidth in both vertical and horizontal directions. The two directional and two omnidirectional antennas were arranged diagonally to ensure balanced signal strength across all areas.

Due to the poor penetration and diffraction capabilities of 7GHz millimeter waves, signal reception at the player entrance channel required enhancement. A directional antenna was positioned diagonally in the channel to face the entire passage, improving signal reception quality in this area, as shown in [FIGURE:3].

[FIGURE:3]

In [FIGURE:3], red antennas correspond to the left Steadicam position, while green antennas correspond to the right Steadicam position. The yellow lines indicate the beam directions of the four directional antennas. As shown by the blue markers, each side's microwave optical transmitter connected to two antennas for the left Steadicam and two for the right. This cross-connection ensured that even if one microwave optical link failed, the other could maintain diversity reception with at least two antennas for each Steadicam, guaranteeing continuous stable transmission.

At the broadcast truck end, cross-connection was similarly implemented to create hot-standby redundancy between the two microwave optical links, as shown in [FIGURE:5]. The diagram illustrates that directional antennas primarily covered blind spots and enhanced signals in open areas, while omnidirectional antennas provided broad coverage.

Video signals transmitted via microwave typically employ modulation schemes to achieve higher transmission efficiency within limited spectrum resources. The Vislink system supports QPSK (Quadrature Phase Shift Keying) and QAM (Quadrature Amplitude Modulation). QPSK offers lower carrier efficiency, transmitting only one carrier signal, but provides stronger anti-interference capability. Conversely, QAM offers higher carrier efficiency, simultaneously transmitting multiple carrier signals through phase division, but with weaker anti-interference capability. The appropriate modulation scheme should be selected based on application scenarios. For this event, the 7GHz microwave frequency avoided most channel interference, and with directional antenna support, QAM modulation was adopted to ensure efficient high-definition video transmission.

3. Equipment Setup

In large-scale events, any equipment failure can interrupt broadcasting. Therefore, system design must incorporate redundancy and backup mechanisms. As a wireless transmission system, it must also address microwave transmitter roaming coverage and signal transmission performance across different zones, with particular attention to optimizing weak signal areas. The equipment setup diagram is shown in [FIGURE:4].

[FIGURE:4]

Adhering to clean cabling standards and equipment redundancy principles, cross-connection wiring was implemented within the venue. As shown in [FIGURE:4], microwave optical transmitters were positioned at the middle of both upper and lower sides of the stadium. Each side's microwave optical link connected to two antennas for the left Steadicam and two for the right, ensuring that if one link failed, the other could maintain diversity reception with at least two antennas per Steadicam.

At the broadcast truck end, cross-connection similarly created hot-standby redundancy between the two microwave optical links, as shown in [FIGURE:5].

[FIGURE:5]

Since the reverse control system used only one RS485 data line to connect to the microwave optical link, and RS485's limited transmission distance prevented cross-connection between the two reverse control systems, redundancy for reverse control could not be implemented. If the microwave optical system failed, reverse control functionality might be affected, though video transmission would remain unaffected. While this design has limitations for emergency scenarios, it was acceptable for event broadcasting, as stable video transmission remained the priority. Reverse control failure would not directly interrupt the live broadcast; in emergencies, camera operators could be notified via intercom to manually adjust aperture as a contingency measure.

4. On-site Problems and Solutions

The primary on-site issue was electromagnetic interference from diverse sources. Major interference sources included:

High-power audio and LED screen equipment: While these devices don't require wireless transmission, their high operating power generates low-frequency electromagnetic radiation and substantial noise that interferes with microwave transmission systems.

Walkie-talkies and wireless intercom systems: These typically operate in UHF band (400MHz-470MHz). Despite the large frequency difference from the microwave system, their strong penetration and long-distance transmission capabilities create harmonic interference with microwave signals.

Venue Wi-Fi and Bluetooth devices: Although primarily operating in 2.4GHz and 5GHz bands, numerous simultaneous devices generate high-order harmonic interference that affects 7GHz microwave signals.

After equipment installation and commissioning, the rehearsal phase revealed increasingly complex electromagnetic conditions as new equipment was added continuously. The spectrum analyzer showed substantial noise interference near 6.9GHz, and the 450MHz reverse control band experienced heavy walkie-talkie interference. As rehearsals continued over subsequent days with more walkie-talkies and stage equipment occupying wireless frequencies, dedicated personnel had to continuously monitor the MER (Modulation Error Rate, expressed in dB, where higher values indicate better signal quality) on microwave receivers. At any given moment, at least one antenna had to maintain good reception. During Steadicam operation, all antennas were kept at maximum signal strength. If two or more antennas showed MER values below 25dB, technicians used a spectrum analyzer on-site to check for interference near the corresponding antenna frequency. When interference was detected, the receiver, transmitter, or reverse control system frequencies were adjusted to avoid interference bands. Consequently, microwave video transmission and reverse control frequencies were continuously adjusted throughout the rehearsal process.

On the final competition day, the microwave transmission frequencies were set at 6.448GHz and 6.790GHz, with corresponding reverse control frequencies at 463MHz and 443MHz.

Spectrum management plays a crucial role in modern wireless transmission systems. Large events require not only pre-planned spectrum allocation but also real-time monitoring and emergency response. When signal quality degrades in a particular band, technicians must quickly migrate transmission frequencies to less interfered bands. This real-time adjustment strategy proves highly effective in complex electromagnetic environments but demands high agility and experience from the technical team. They must promptly identify interference sources, make rapid judgments, and adjust frequencies according to equipment characteristics—critical capabilities for ensuring uninterrupted live broadcasting.

During the entire event, professional-brand walkie-talkies—originally considered the least likely interference source—proved to be the primary culprit. Walkie-talkies typically operate in the 400MHz-470MHz band, offering optimal penetration and propagation distance. The microwave video transmission operated in the relatively interference-free 6.425GHz-7.125GHz range. Although both bands belong to UHF—one in megahertz and the other in gigahertz—theoretical analysis suggested no possible interference. However, continuous spectrum monitoring revealed that when walkie-talkies operated within the venue, numerous interference spikes appeared between 6.83GHz and 7.1GHz—an unexpected finding from theoretical analysis. Therefore, for broadcast operations with stringent requirements, microwave video transmission should be accompanied by a spectrum analyzer for continuous frequency monitoring to ensure safe transmission.

Additionally, the microwave optical transmission system included redundant links. Even if one fiber link failed, the system could rapidly switch to the backup link, improving overall reliability and providing technical teams with more operational options during emergencies.

Future developments in 5G, artificial intelligence, and advanced antenna technology will significantly enhance wireless transmission systems in terms of transmission quality, anti-interference capability, and automation. These advancements will not only drive progress in live event broadcasting technology but also provide audiences with more immersive viewing experiences.

References

[1] China Communications Standards Association. General Requirements and Measurement Methods for Radio Transmitting Equipment: GB/T 12572-2008 [S]. Beijing: Standards Press of China, 2009: 18-21.

[2] Qin Shunyou. Principles, Operation and Application of Spectrum Analyzers [M]. Xi'an: Xidian University Press, 2014: 7-8, 30-48, 219-241.

[3] National Radio Metrology Technical Committee. Calibration Specification for Spectrum Analyzers: JJF 1396-2013 [S]. Beijing: China Quality Inspection Press, 2013: 1-7.

[4] Hu Siyu. Analysis of Interference from 2.4GHz Wi-Fi and Bluetooth on ZigBee [J]. Science & Technology Vision, 2016(14): 128-129.

[5] Wang Chenhao, Shi Xiaomin. Microwave Coupled Filters and RF Circuit Engineering Design [M]. Beijing: China Petrochemical Press, 2022: 1-16.

[6] Wang Zhitian. Radio Electronics Metrology [M]. Beijing: Atomic Energy Press, 2002: 243-312.

[7] National Institute of Metrology, China. Calibration Specification for Signal Generators: JJF1931-2021 [S]. Beijing: Standards Press of China, 2021: 1-5.

[8] Zhang Zhihai. Analysis of Terrestrial Digital Television Technology in Broadcasting [J]. Integrated Circuit Applications, 2021, 38(1): 94-95.

[9] Deng Changjiang. How to Utilize Digital Microwave Technology in Radio and Television Signal Transmission [J]. West China Broadcasting TV, 2021, 42(1): 202-210.

[10] Howitt I, Gutierrez J A. IEEE 802.15.4 Low Rate-Wireless Personal Area Network Coexistence Issues [C]. Wireless Communications and Networking, 2003, WCNC 2003. 2003 IEEE. IEEE, 2003, 3: 1481-1486.

Author Biographies: Zhang Le (1985—), male, from Jinan, Shandong, New Media Systems Engineer at Jinan Daily Newspaper Group, research interests include new media technology, broadcasting systems, and new media communication. Li Liang (1987—), male, from Jinan, Shandong, New Media Systems Engineer at Jinan Daily Newspaper Group, research interests include new media technology and broadcasting systems.

(Executive Editor: Chen Xuguan)