Microelectronic Implementation of Dicode PPM System Employing RS Codes

Optical fibre systems have played a key role in making possible the extraordinary growth in world-wide communications that has occurred in the last 25 years, and are vital in enabling the proliferating use of the Internet. Its high bandwidth capabilities, low attenuation characteristics, low cost, and immunity from the many disturbances that can afflict electrical wires and wireless communication links make it ideal for gigabit transmission and a major building block in the telecommunication infrastructure. A number of different techniques are used for the transmission of digital information between the transmitter and receiver sides in optical fibre system. One type of coding scheme is Pulse Position Modulation (PPM) in which the location of one pulse during 2M time slots is used to convey digital information from M bits. Although all the studies refer to advantages of PPM, it comes at a cost of large bandwidth and a complicated implementation. Therefore, variant PPM schemes have been proposed to transmit the data such as: Multiple Pulse Position Modulation (MPPM), Differential Pulse Position Modulation (DPPM), Pulse Interval Modulation (PIM), Digital Pulse Interval Modulation (DPIM), Dual Header Pulse Interval Modulation (DH-PIM), Dicode Pulse Position Modulation (DiPPM). The DiPPM scheme has been considered as a solution for the bandwidth consumption issue that other existing PPM formats suffer from. This is because it has a line rate that is twice that of the original data rate. DiPPM can be efficiently implemented as it employs two slots to transmit one bit of pulse code modulation (PCM). A PCM conversion from logic zero to logic one provides a pulse in slot RESET (R) and from one to zero provides a pulse in slot SET (S). No pulse is transmitted if the PCM data is unvarying. Like other PPM schemes, DiPPM suffers from three types of pulse detection errors wrong slot, false alarm, and erasure. The aim of this work was to build an error correction system, Reed Solomon (RS) code, which would overcome or reduce the error sources in the DiPPM system. An original mathematical program was developed using the Mathcad software to find the optimum RS parameters which can improve the DiPPM system error performance, number of photons and transmission efficiency. The results showed that the DiPPM system employing RS code offered an improvement over uncoded DiPPM of 5.12 dB, when RS operating at the optimum code rate of approximately ¾ and a codeword length of 25 symbols. Moreover, the error performance of the uncoded DiPPM is compared with the DiPPM system employing maximum likelihood sequence detector (MLSD), and RS code in terms of number of photons per pulse, transmission efficiency, and bandwidth expansion. The DiPPM with RS code offers superior performance compared to the uncoded DiPPM and DiPPM using MLSD, requiring only 4.5x103 photons per pulse when operating at a bandwidth equal to or above 0.9 times the original data rate. Further investigation took place on the DiPPM system employing RS code. A Matlab program and very high speed circuit Hardware Description language (VHDL) were developed to simulate the designed communication system. Simulation results were considered and agreed with the previous DiPPM theory. For the first time, this thesis presents the practical implementation for the DiPPM system employing RS code using Field Programmable Gate Array (FPGA)

MATLAB Simulation for DiPPM over Diffuse Optical Wireless Communications

In this paper computer simulation is presented for dicode pulse position modulation (DiPPM). DiPPM system offers good performance and operates at only twice the original PCM, thus it is very simple to implement in comparison to other PPM modulations. This makes DiPPM an extremely attractive modulation scheme for indoor optical wireless applications. MATLAB/Simulink has become the universal mathematical and modelling tool in most universities and research laboratories around the world. Studying complex models in optical link communications may be simplified by using simulation models so that real and industrial applications can be approached. The DiPPM is implemented over a diffuse optical wireless link using an LED at a wavelength of 1550nm and data rate of 1Gb/s. The data sequence, coded by using DiPPM coder, is convolved with the diffuse optical link then received and decoded by DiPPM coder to get the original data signal. The indoor diffuse channel model which considers additive white Gaussian noise (AWGN) model as more appropriate for significant background light has been simulated and bit error rate (BER) has been calculated

Optimum reed solomon code using with dicode pulse position modulation system

Dicode Pulse Position Modulation (DiPPM) has been proposed as a more advantageous format than digital PPM with one of its main advantages being that the line rate is twice that of the original data rate, a significant reduction in speed compared to digital PPM. This paper describes the performance of a DiPPM system using a Reed Solomon (RS) code to enhance the sensitivity. Theoretical results are presented at an original data rate of 1Gbit/s, in terms of transmission efficiency, bandwidth expansion, and number of photons per pulse. According to simulation results the Reed Solomon error correction coded system offers an improvement over uncoded DiPPM of 5.12dB, when operating at the optimum code rate of approximately 3/4 and a codeword length of 25 symbols

Improving error performance of dicode pulse position modulation system using forward error correction codes

Dicode pulse position modulation (DiPPM) has been considered as a solution for the bandwidth consumption issue that other existing pulse position modulation (PPM) formats suffer from. This is because it has a line rate that is twice that of the original data rate. This paper considers for the first time forward error correction (FEC) Reed Solomon (RS) codes to improve the error performance of a DiPPM. The results show that the error performance in the system can be improved by using FEC code when the RS is working at its optimum parameters. The error performance of the uncoded DiPPM system has been compared with a RS coded DiPPM system and one using maximum likelihood sequence detector (MLSD) in terms of the number of photons per pulse, transmission efficiency, and bandwidth expansion. The DiPPM with RS code offers superior performance compared to the uncoded DiPPM and DiPPM using MLSD, requiring only 4.5 × 103 photons per pulse, when operating at a bandwidth equal or above to 0.9 times the original data rate. This is with an optimum code rate of approximately ¾, and a codeword length of 25

VLC system performance using Dicode Pulse Position Modulation over an indoor diffuse link

Dicode Pulse Position Modulation (DiPPM) has been proposed as an alternative modulation scheme to digital PPM over optical fibre channels. This paper, for the first time, analyses the receiver sensitivity of the DiPPM system on a diffuse indoor Visible Light Communication (VLC). The system operates at a bit rate of 1Gbit/s and λ = 0.65 μm. A mathematical model of the VLC using DiPPM is presented. The results show the degradation in sensitivity as normalized delay spreads increase. It is shown that with a typical delay spread of 5 ns, the DiPPM system can achieve a sensitivity of -36.47 dBm and -37.5 dBm for the error rates of 10-9 and 10-6, respectively. This represents a sensitivity improvement over a comparable digital PPM system by 3.47 dB and 3.5 dB