CN1173494C - Indoor Laser Wireless LAN System Based on Ethernet - Google Patents

Abstract

The indoor laser wireless local area network system built on the basis of Ethernet belongs to the technical field of wireless optical local area network. , laser diode drive circuit and light scattering sheet; the laser wireless receiver part contains in turn: hemispherical coating optical concentrator, photodetector, transimpedance preamplifier, secondary amplifier, high-pass filter, low-pass filter, The limiting amplifier and the differential output circuit that the output end is also connected with another Ethernet card through the RJ45 interface. It has the advantages of no need to set up a direct transmission path, saves the cost of wireless Internet access, the movement and occlusion of people and other objects will not affect the signal transmission, and has the advantages of good robustness and mobility.

Description

Indoor Laser Wireless LAN System Based on Ethernet

technical field

An indoor laser wireless local area network system based on Ethernet belongs to the field of wireless optical local area network technology, and in particular relates to a method and system for constructing a laser wireless local area network based on the existing Ethernet.

Background technique

The existing wireless local area network is generally in the radio frequency band, with a carrier frequency of 2.4G, such as Bluetooth, HomeRF, IEEE802.11b, etc., but the wireless system itself has problems such as poor security, easy eavesdropping, interference to other electronic equipment, limited frequency band, and strong power. There is also harm to the human body, which limits its scope of use. As a substitute for wireless local area network, wireless optical local area network has the advantages of good security, no environmental interference, and high system bandwidth, showing broad application prospects. However, the currently known wireless optical local area network cannot replace the wireless local area network indoors due to its low data rate and cannot be compatible with the currently most widely used Ethernet in a subnet. And this system enables users to freely switch between indoor wired and wireless, which is convenient to use.

Contents of the invention

The object of the present invention is to provide an indoor laser wireless local area network system based on Ethernet which is compatible with Ethernet in one subnet.

The indoor laser wireless local area network system based on Ethernet of the present invention is characterized in that it contains: a plurality of laser wireless transceivers connected to the Ethernet card respectively, a computer local area network with a plurality of computers, and each of the above-mentioned computers includes computer rooms. An Ethernet card for communication connection; the laser wireless transmitter part is sequentially composed of: a differential input circuit connected to the Ethernet card through an RJ45 interface at the input end, an operational amplifier circuit, a laser diode drive circuit and a light scattering sheet; among them The laser wireless receiver part consists of: hemispherical coating optical concentrator, photodetector, transimpedance preamplifier, secondary amplifier, high-pass filter, low-pass filter, limiting amplifier and the output terminal is also connected to another via RJ45 interface. A differential output circuit connected to an Ethernet card is connected in series.

Proof of use: It fulfills its intended purpose.

Description of drawings

Fig. 1: The network structure diagram of the laser wireless transceiver of the present invention connected with the original Ethernet.

Fig. 2: The functional block diagram of the wireless laser transmitter of the present invention.

Fig. 3: The functional block diagram of the laser wireless receiver of the present invention.

Detailed ways

In the present invention, a laser wireless transceiver connected to the Ethernet card through an interface is used to replace the traditional twisted pair and coaxial cable, the infrared laser is used as the light source, and the method of optical wireless communication is used to pass the ceiling and the wall. Diffuse reflection system for multipath propagation of optical signals with receivers in laser wireless transceivers pointing arbitrarily and positionally.

Please see Figure 1. When any one of the laser wireless transceivers A, B, and C is used as a transmitter, it must be connected to the 1 (TX+) and 2 (TX-) terminals on the RJ45 interface of the Ethernet card through a twisted pair, and when using the receiver It should be connected to the 3(RX+) and 6(RX-) terminals on it. Both the emitted light and the received light are propagated through the extremely diffuse reflection of the ceiling.

Goodbye Figure 2. The chip MAX4100ESA is used for the differential input circuit, and its input end is connected to the two ends of 1 and 2 in the RJ45 interface through a twisted pair, and the magnification factor is 1. The chip MAX4100ESA used in the operational amplifier circuit is biased. The laser diode (LD) drive circuit with high output current uses the chip SS8050, which drives the laser diode to emit infrared laser. Adjusting the bias voltage and magnification of the operational amplifier circuit can make the output of the third-level drive circuit meet the requirements of the laser diode threshold current and operating current. In this embodiment, four laser diodes are used, the peak output power of each tube is 300mV, the threshold current is 130mA, the working current is 500mA, the model is SLD303, and the working wavelength is 808nm. The gain bandwidth of the operational amplifier circuit is 500MHz. The maximum output current of the laser diode drive circuit is 800mA. Since the output of the laser diode has the characteristics of good monochromaticity and strong directionality, an optical scattering sheet should be placed in front of it, so that the laser can output a uniform spot similar to Lambertian through the optical scattering sheet, expand the area of the light source, and reduce the Light intensity, so that the output of the emitter meets the safety standard of ANSI IEC825-1 Class1 human eyes, in this embodiment, the transmittance of the optical diffuser is 90%.

Goodbye Figure 3. The front end of the receiver is a hemispherical coated optical concentrator, which is made of glass with a refractive index n of 1.80 and has a radius of 2cm. The passband of the coating on the hemispherical surface is 780nm to 820nm. Considering that the central wavelength of the passband of the optical coating varies with the incident angle of light For the phenomenon of shifting to a narrow band, the filter bandwidth is 40nm, which matches the emission wavelength, so as to effectively improve the light receiving efficiency through a larger field of view. The photodetector uses a Si PIN detector with an area of 1cm ² , the peak response wavelength is 960nm, the responsivity is 0.66A/W (at 960nm), the junction capacitance is 40pF (at 70V bias), and the cutoff frequency is 40MHz. for S3590-08. Due to the large junction capacitance of the large-area detector, the preamplifier adopts a transimpedance structure, which has both transimpedance gain and system bandwidth performance. Its gain-bandwidth product is 400MHz, and the transimpedance gain is 1K. Its model is OPA655P. Since the transimpedance of the preamplifier cannot be too large due to the limitation of the system bandwidth, a secondary amplifier is required. The gain-bandwidth product of the secondary amplifier used is 500MHz, and the model is MAX4100ESA. In order to eliminate the DC noise generated by incandescent lamps and sunlight, as well as the high-frequency electrical noise generated by fluorescent lamps and amplifiers at all levels, high-pass and low-pass filters must be used successively. The cut-off frequency of the high-pass filter is 160KHz, and the cut-off frequency of the low-pass filter is 20MHz. The models are RC network respectively. Due to mobility, the distance between the two computers will change. Therefore, the signal power received by the detector will change with the distance, resulting in a changing electrical signal amplitude. In order to make the signal amplitude output by the receiver consistent so as to connect with the network card, the After the low-pass filter, a limiting amplifier is used to clamp. The clamping range is ±1.2V, and its model is OPA689U. The output terminals of the differential output circuit are respectively connected to the two ends of 3 and 6 of the RJ45 interface of the Ethernet card, and its gain-bandwidth product is 500MHz, and the model is MAX4100ESA.

It can be seen that it can use the network card of Ethernet, replace the twisted pair and coaxial cable with laser wireless transceiver, and use the method of diffuse reflection optical wireless communication in a small space to form a laser wireless local area network. There is no need to set up the direct propagation path that is necessary for optical LAN, which saves the cost of wireless Internet access for users. The movement and occlusion of people or other objects will not affect the propagation of signals, and users can freely switch between wired and wireless.

Claims (1)

1. be the indoor laser radio LAN system that the basis is set up with Ethernet, it is characterized in that, it contains: a plurality of laser radio transceivers that are connected with Ethernet card separately, computer local network with a plurality of computers, above-mentioned each computer comprise the Ethernet card that computer to computer communication connects usefulness; Laser radio transmitter portion wherein is successively by difference input circuit that input links to each other with Ethernet card through the RJ45 interface, operational amplification circuit, and laser diode driver circuit and light diffusion sheet serial connection form; Wherein laser radio receiver part is successively by dome-type coated optics concentrator, photodetector, transimpedance preamplifier, secondary amplifier, high pass filter, low pass filter, limiting amplifier and output also form through the differential output circuit serial connection that the RJ45 interface links to each other with another Ethernet card.

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