Analysis of Visible Light Communication Using Wireless Technology

Transcription

1 Analysis of Visible Light Communication Using Wireless Technology P. Krishna Chaitanya M. E. (Radar and Microwave Engineering) Andhra University Vishakhapatnam, Andhra Pradesh Venkata Sujit Electronics and Communication Engineering V R Siddartha College of Engineering Vijayawada, Andhra Pradesh Abstract Recent developments in solid state light emitting diodes and many other fast switching light emitting sources led to new phase of communication methodology and technology. In the light of tremendous efficiency showcased by these fast switching light sources, the present report describes about the new method of wireless visible light communication method and device implementing the same. Keywords- LED(light emitting diodes), emission, Fast Switching light sources, Communication Methodology. I. INTRODUCTION Radio Frequency communication is an incumbent and evolving technology that will have the utility for the indefinite future. However, these are both opportunities with the use of free space optical spectrum and some limitations on the use of Radio Frequency. For the next generation of wireless communication technology with the development of the fast switching light sources like Laser Diodes and LEDs, researchers believe that VLC provides a great supplement supporting these fastest evolving technologies. The present technologies use the LEDs as the fast switching light sources because of their high efficiencies and availabilities of the existing infrastructures. The other prominent advantages of LED are high sensitivity in response and good performance in modulation high emission power without hurting human eyes. No electromagnetic influence, no need to apply for spectrum resources. The present technique also utilizes PD as the receiving elements and an MCU to carry out the decoding unit and other communication units. II. VISIBLE LIGHT COMMUNICATION LINK DESIGN Visible Light Communication links may employ various designs and it is convenient to classify them according to two criteria. This classification scheme is shown in the figure. Classification of simple infrared links according to the degree of directionality of the transmitter and receiver and whether the link relies upon the existence of a LOS path between them. Directed links employ directional transmitters and receivers which must be aimed in to establish a link. In this article for maximizing the power efficiency direct line of sights is employed since it minimizes path loss and reception of ambient light noises. III. CHANNEL MODEL For optical wireless links, the most viable modulation is Intensity Modulation (IM), in which the desired waveform is modulated onto the instantaneous power of the carrier. The most practical down conversion technique is direct detection (DD). The visible light communication channel with IM/DD can be modeled with and Additive White Gaussian Noise (AWGN). In the case that there is little or no background light present, the dominant noise source is produced by the circuitry. The optical channel can be modeled as follows. Y (t) represents the signal current at the receiver. ISSN: IJECCT 765

2 X(t) is the transmitted optical pulse, n(t) is the noise modeled as an AWGN process and denotes convolution, represents the optical to electrical conversion efficiency at the users terminal photo diodes. V. TRANSMISSION WAVELENGTH AND NOISE IV. CHANNEL DC GAIN Geometries used in channel gain calculations: LOS In Visible Light Communication the influence of the direct light is very large which determines mainly the performance of the system. If the transmitted power is P t and P r is the received power then P r =P t H (0) Where, H (0) is the channel DC gain. Where A d = Area of the receiver (Photo Diode) = distance between the transmitter and receiver g (Ψ)= optical concentration gain Optical power spectra of common ambient infrared sources. Spectra have been scaled to have the same maximum value.the most important factor to consider when choosing a transmission wavelength is the availability of effective low cost sources and detectors. The availability of LEDs and photodiode operating in the 800nm to 1000 nm range is the primary reason for the use of this band. Many environments contain intense ambient light arising from sunlight, sky light incandescent and fluorescent lamps and other sources. Represents essentially unmodulated sources that can be received at an average power much larger than the desired signal even when optical filtering is employed. The result is dc photo current which causes shot noise. In visible light communication systems OOK-NRZ (on-off keying Non Return to Zero modulation based on IM/DD is a very suitable modulation owing to its simple implementation. The output current contains a Gaussian noise having a total variance σ2total. That is the sum of contributions from shot noise, thermal noise that is σ 2 total = σ 2 shot + σ 2 thermal The shot noise variance and thermal noise variance have been computed approximately. Where, n = refractive index T (Ψ) = band pass filter gain Ψ = angle of incidence Φ = angle of irradiance M = lambertian pattern order Ψ c = field of view For achieving high directivity, Ashperic lines are used due to the fact that they reduce the spherical aberration to large extent. For the directed line of sight transmitter φ1/2 = 150 corresponding to m = 20. σ 2 shot = 2q Pn σ 2 thermal = 4KTB/R 2 P n,isotropic = p n λ n T 0 A n Where q = Electronic charge (1.6X10-19 C) p n = Spectral irradiance (w/cm 2 nm) = Responsivity (photo diode) (A/W) K = Boltzmann constant T = Temperature B = Bandwidth of operation R = Resistance λ n = band pass filter noise bandwidth ISSN: IJECCT 766

3 T 0 = peak transmission filter gain VI. DESIGN OF THE DEVICE The communication device consists of both the transmitter and the receiver. The modulation technique this device employs is OOK-NRZ modulation based on IM/DD. VII. DESIGN OF THE TRANSMITTER Transmitter consists of the light source which is controlled by the Microcontroller Unit. The beam originating from the light source is made to pass through the aspheric lens and is then transmitted 0. Either one of them can be chosen and typed in the serial monitor window of arduino IDE which is converted into the serial data using the ASCII coding technique by the computer and is then put into the serial port for the microcontroller. MCU unit then adds a start bit whose time length for experimental purposes is chosen as 100 milli seconds and then after a time gap of another 100 milli seconds the data bit is sent which is also of length 100 milli seconds the above values are chosen at random for experimental purposes and there is no significance for them. START BIT (1) DATA BIT (0 or 1) (100 ms) (100 ms) (100ms) The signal appears at an I/O pin of the board which is connected to led in series with a resistor. A. LIGHT SOURCE SYSTEM This system uses LED as the element of source of light and the led is chosen due to the fact that of its high conversion efficiency and its availability. This system further consists of reflector and aspheric lens which increases the directivity of the beam. An analogous arrangement of this system is similar to that of torchlight. IX. DESIGN OF THE RECIEVER B. ARDUINO IDE This is the software which runs in the computer and is a platform where the message is typed into and then this software uses the ASCII coding technique to convert and then sends the message as the serial data which the microcontroller intercepts. C. MICROCONTROLLER UNIT This unit here takes the serial information from the computer and then converts it to the form of a signal as per the modulation technique and then this signal is fed into the led which converts the electrical energy into the optical energy. The microcontroller board used is Arduino uno which is manufactured by arduino and this board uses Atmega 328P as the microcontroller The circuit which is used for connecting the mcu and the led is shown in the picture below The receiver consists of two photodiodes which extracts the data from the surroundings and then fed into the microcontroller which decodes the information and interprets in the arduino s serial monitor. A. PHOTODIODES VIII. ALGORITHM FOR THE FOLLOWING METHOD OF TRANSMISSION OF DATA The source alphabet for the experimeantal purposes choesen to contain two characters which are logic 1 and logic This is the first block of the receiver. This block contains 2 photodiodes for receiving the data. PD is the acronym for photodiodes which act like dependent current sources whose current depends upon the amount of light ISSN: IJECCT 767

4 intensity fallen on it. The arrangement of the PDs is in such a way that the midpoint of the intensified light beam from the transmitter is fallen on the main PD and not on the surrounding noise reduction PD and the distance between the two PDs is d. The two PDs are named as Surrounding noise detection PD (PD 1) Main PD (PD 2) The PDs are connected to the respective resistors in series and the potential drop across the resistors is recognized as the analogous electrical voltages to light intensities. For direct transmission m 20. As Φ= Ψ=0 0 and d=d B. MICROCONTROLLER UNIT This calculates the voltage drops across the resistor using the ADC units of the arduino uno s microcontroller board which uses at mega 328p as microcontroller. The voltage values which are obtained across the resistor of both main pd and surrounding noise reduction pd are subtracted using the subtracting units in the microcontroller board and the value which is the outcome after the subtraction is used to determine the digital logic level which is then interpreted on the arduino serial monitor in the computer. C. ALGORITHM FOR RECEIVER The pd1 and pd2 sensors with the resistors continuously sense the surrounding light intensities and convert them into analogous electrical voltages. These electrical voltages are measured and are converted into the digital values by the adc units of the microcontroller and the digital value corresponding to both the pd1 and pd2 are subtracted and if the subtracted value crosses certain threshold then the mcu interprets it as logic 1. When the mcu detects the presence of a start bit then it automatically shutdowns pd2 sensor for 250 milli seconds and then samples the data. After a lapse of 50 milliseconds again it activates the pd2 and the procedure repeats and depending up on the sampled data it interprets whether the data received is logic 1 or logic 0 in arduino serial monitor window. X. MATHEMATICAL ANALYSIS Hence P 2 = H 2 (0) P and And as P 1 = H 1 (0) P As per the design, the ADC units of MCU are measured which leads to Let P be the power transmitted. Then, the receivedpower for PD 2 is P 2 which is given by P 2 = H 2 (0) P And received power for PD 1 is P 1 which is given by P 1 = H 1 (0) P V 2 (t) and V 1 (t) are the voltages across the resistor in the respective photodiode circuit. The value of n 0 depends upon the change in the resistance values because of manufacturing defect and by difference in the surrounding light intensity levels i.e., non isotropic light conditions. ISSN: IJECCT 768

5 If is greater than certain threshold then the microcontroller decodes the received bit as logic 1 A. RECIEVER SNR In this section we compute the receiver SNR. We assume here that the transmitter transmits using on-off keying (OOK) with NRZ pulses. SNR XI. CONCLUSION VLC is a promising technology which has a wide-variety of prospective applications even it is still in a very early stage of development. It can be applied to solve the Internet last mile inter connectivity problem. It is the unlimited bandwidth solution for the metro urban core of downtown building to building communication, as well as the optimal technology for home- to- home and office- to- office connectivity. REFERENCES [1] T. Taguchi "Technological innovation of high-brightness light emitting diodes (LEDs) and a view of white LED lighting system", OPTRONICS, vol. 19, no. 228, pp [2] M. Ishida "In GaN based LEDs and their application", OPTRONICS, vol. 19, no. 228, pp [3] T. Nakamura and T. Takebe "Development of ZnSe-based white Light emitting diodes", OPTRONICS, vol. 19, no. 228, pp [4] T. Komine, Y. Tanaka, S. Haruyama and M. Nakagawa "Basic Study on Visible-Light Communication using Light Emitting Diode Illumination", Proc. of 8th International Symposium on Microwave and Optical Technology (ISMOT 2001), pp [5] Y. Tanaka, S. Haruyama and M. Nakagawa "Wireless optical transmission with the white colored LED for the wireless home links", Proc. of the 11th Int. Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2000), pp ISSN: IJECCT 769