Interference-Rejection Coding Method For An Optical Wireless Communication System And The Optical Wireless Communication System Thereof

Abstract

An interference-rejection coding method for an optical wireless communication system and such an optical wireless communication system are provided. The coding method uses delay modulation, block code techniques and filtering to reduce the low frequency interference from light sources. A plurality of codewords from the block codes are reserved for performing digital data recovery. The invention removes the need of analog clock data recovery circuit, and does not require complex hardware for realization. Therefore, it can be applied to a wide range of applications, such as optical WLAN, data transmission of medical facilities, wireless communication in the aircraft, encrypted data transmission network, and low-priced transmission interfaces.

Description

CROSS REFERENCE[0001]This is a continuation application of U.S. patent application Ser. No. 11 / 146,546, filed Jun. 7, 2005, which is incorporated herewith by reference.FIELD OF THE INVENTION[0002]The present invention generally relates to a coding scheme for optical wireless communication systems, and more specifically to an interference-rejection coding method for an optical wireless communication system and the optical wireless communication system thereof.BACKGROUND OF THE INVENTION[0003]As the wireless local area network (WLAN) becomes ubiquitous, the users of portable devices can easily find access points to surf the internet and obtain the information without the restriction imposed by the conventional wiring cables. However, the electromagnetic wave (EM wave) emitted from the wireless communication is potentially harmful to the health, and can also interfere with other electronic instruments. Therefore, its use is usually restricted in the environment where sensitive electron...

AI Technical Summary

Benefits of technology

[0013]Another object of the present invention is to provide such an optical wireless communication system that can use only low-complexity hardware to effectively and stably reject the optical interference.

[0014]To achieve the aforementioned objects, the present invention uses the delay modulation together with block code to modulate the data signals to a high frequency range, and then uses a narrow-band band-pass filter to reject the optical interference. The transmitting end and the receiving end are added with corresponding modulation and demodulation structures, respectively. Hence, the receiving end can correctly demodulate the modulated signals transmitted by the transmitting end.

[0015]The interference-rejection coding scheme of the present invention can be applied to optical WLAN, data transmission of medical facilities, wireless communication in the aircraft, and encrypted data transmission network. As the present invention uses digital modulation and filtering, the present invention can also be used with digital data recovery to greatly reduce the demands on the specification and the cost of analog front-end. Therefore, the present invention can also be used in low-priced transmission interfaces.

Problems solved by technology

However, the electromagnetic wave (EM wave) emitted from the wireless communication is potentially harmful to the health, and can also interfere with other electronic instruments.

Therefore, its use is usually restricted in the environment where sensitive electronic devices are widely used, such as in a hospital or an aircraft.

In addition, because wireless electronic networks are susceptible to eavesdropping or interception, they are unsuitable for applications such as military, government or financial institutes where data security is highly regarded.

This, however, may lead to the distortion of the signals, and generating the additional inter-symbol interference (ISI) effect.

But the conventional methods can only provide 0.2 dB of improvement in filtering the interference of fluorescent light.

The unfiltered fluorescent interference still creates a loss of 17 dB or more, and is unable to reject the interference entirely.

However, these techniques require additional modulation and demodulation mechanisms, and the system complexity is increased.

Although these techniques are simple, the disadvantages include the bandwidth requirement twice of that of conventional non return to zero (NRZ), the increasing received optical noise, transmission distortion, and higher demands on the optical components. FIG. 2 shows a waveform view of various line coding techniques, including NRZ, Manchester, DMI and delay modulation.

These techniques greatly increase the system complexity, transmission bandwidth requirement and impose higher demands on optical components.

The disadvantages of these techniques include the complexity of front-end circuitry and the uncertainty of interference improvement dependent on interference characteristics.

These techniques can improve the change of the signal bias, but are less effective for optical interference and these techniques increase the front-end circuitry complexity.

This, combined with the high propagation attenuation (20-40 dB) of the air, greatly limits the power of the signals received at the receiving end.

In addition, the indoor light sources, such as sun rays, fluorescent light, lamps, infra-red remote controllers, all contribute to the optical interference in the optical wireless communication.

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