Beijing Haite Weiye Technology Co., Ltd. Ren Hongzhuo
1. Project requirements
my country’s FM radio transmission uses the 88-108MHz frequency band, which can only be transmitted under direct viewing and unobstructed conditions. Therefore, the underground parking lot receives poorly received FM radio signals, and some even have no signal at all. This brings problems for parking owners to listen to the radio. Great inconvenience, objective requirements for FM broadcast signal coverage of underground parking lots. In order to solve this problem, Beijing Haite Weiye Technology Development Co., Ltd. adopted the broadcast signal fiber optic remote coverage technology to build an underground parking lot FM radio coverage plan. This technology uses "the same frequency modulation of the radio station + signal fiber remote + broadband antenna transmission". In the combined way, an artificial transmission medium is created in the underground parking lot, so that the radio waves form a continuous coverage without blind areas in the parking lot, so that the purpose of listening to the car can be received by the radio. Beijing Haiteweiye adopts a new architecture and new concept to build an underground parking lot FM broadcast coverage system design scheme, which is suitable for airports, communities, shopping malls, railway stations, airports and other large, medium and small underground parking lots and underground businesses Sites, underground garages, underground pipe corridors.
2. User needs analysis
FM broadcasting (88-108MHz) radio waves have the characteristics of linear transmission and a certain degree of diffraction ability; FM radio is the main coverage object in the tunnel, and the coverage field strength is required to reach 40dBuV/m for good reception. In view of the transmission characteristics and coverage field strength requirements of FM broadcasting, there are currently two main solutions to achieve FM broadcasting signal coverage in underground parking lots, namely, the leakage coaxial cable coverage solution and the transmitting antenna coverage solution. Compared with the leaky coaxial cable coverage solution, the transmitting antenna coverage solution has the characteristics of strong practicability, high cost performance, and cost saving, and is more popular among builders and users.
Beijing Haiteweiye underground parking lot FM broadcast coverage system design scheme adopts the combination of "digital frequency selection + optical fiber remote + antenna coverage" to construct, carry out FM FM underground parking lot FM broadcast signal coverage, and use broadcast remote receiver Distribute the points and cover them with a covering transmitting antenna. Generally, a covering point can cover a radius of about 80-100 meters in diameter (unobstructed).
Three, system principle
1. System schematic diagram
2. System principle
The underground garage broadcast signal supplement point synchronization coverage system. Firstly, the outdoor FM broadcast signal is received through the FM receiving antenna, the broadcast signal is low-noise amplified by the antenna amplifier, and then sent to the broadcast digital frequency selector through the feeder. Then use high-speed sampling, quantization, frequency selection, level difference equalization adjustment for multi-channel FM broadcast signals, and output FM FM broadcast signals with the same frequency, same phase, same modulation degree, and level equalization as the signal source. After the frequency-selected FM broadcast signal is filtered through a band-pass filter to remove the 88-108MHz out-of-band clutter signal, it is sent to the broadcast remote transmitter to convert the FM radio frequency signal into an optical signal, and the broadcast remote amplifier, optical The distributor and optical cable are transmitted to the remote broadcast receiver. Finally, the FM broadcast optical signal is restored to a radio frequency signal, and after linear amplification gain adjustment is performed, it is output to the coverage transmitting antenna for wireless supplement point synchronization coverage of the FM broadcast signal in the underground garage.
Four, system function
■ Automatic rebroadcast: 1-16 outdoor FM broadcast signals can be rebroadcast automatically on the same frequency.
■ Wireless transmission: The FM radio broadcast coverage of the parking lot is realized through the remote broadcast receiver and the coverage transmitting antenna set in the parking lot.
■ Synchronous coverage: the use of balanced digital frequency selection method supports level balance adjustment, which can keep the frequency, phase and modulation of the signal source synchronized with the broadcast program covered in the underground garage.
■ Non-coherent area: The signal source and the underground garage coverage signal realize the "three-in-one", no coherent area will be formed at the entrance and exit of the underground garage, and the radio will not stray when the car passes.
■ Stable and reliable: The system adopts mature and stable digital frequency selection technology and linear amplification technology, and the signal coverage field strength value is very stable.
■ Emergency handover: In case of emergency, the underground parking lot can broadcast emergency broadcast signals in the full frequency band of 88-108MHz for evacuation broadcast.
■ Status monitoring: Reserve an interface for monitoring the working status of the radio remote receiver of the underground parking lot and covering the quality of the signal.
5. Scheme design
1. FM signal reception
Set up an FM receiving antenna outside the underground garage at a relatively open and high altitude location to receive the 87-108MHz open-circuit FM broadcast signal. The received FM broadcast signal is amplified by the low-noise antenna amplifier and sent to the computer room. When the antenna is far away from the machine room, the radio frequency optical transmitter is used for electrical-to-optical conversion and sent to the machine room of the parking lot management center through an optical cable.
2. Signal digital frequency selection output
The open-circuit FM broadcast signal sent to the computer room is selected by the broadcast digital frequency selector to select the FM frequency to be covered. 1-16 FM broadcast frequencies can be selected according to the needs, after high-speed sampling quantization, level difference digital dynamic equalization , Output "three-in-one" (same frequency, same phase, same modulation degree, equalization level) FM FM broadcast signal. The broadcast digital frequency selector has an emergency cut-in interface, which can realize the forced switching of the supplementary coverage frequency in case of emergency; it has a debugging and monitoring interface, which can realize software operations such as frequency selection and parameter setting of the broadcast digital frequency selector.
3. Optical fiber remote transmission
The FM broadcast coverage signal output by the broadcast digital frequency selector is filtered by a band-pass filter to remove the out-of-band clutter in the 88-108MHz frequency band. The radio frequency signal is converted into an optical signal by the remote broadcast transmitter and sent to the remote broadcast amplifier pair. The optical signal undergoes erbium-ytterbium multi-channel power amplification and output, and a broadcast remote amplifier can output 4-8 channels of 18-20dB optical signals, which are then distributed through the optical splitter and transmitted to the broadcast remote optical receiver.
4. FM coverage terminal design
The signal input to the remote broadcast receiver is firstly converted from an optical signal to an electrical signal in the 88MHz～108MHz FM frequency band, and then subjected to linear fast-band amplification, gain adjustment, and output to the coverage transmitting antenna, wirelessly forwarding the FM radio signal to the underground In the parking lot, FM broadcast signal coverage of the underground parking lot is realized. The coverage of each fiber optic repeater is 30-50 meters in radius, and the FM radio frequency modulation broadcast signal reaches 40dBuv or more to meet the coverage requirements.