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A review of communication oriented optical wireless systems

A review of communication oriented optical wireless systems

(3) Error correction: In some scenarios and especially for airborne terminals, size, power and weight con- straints may not allow for multiple transmissions and therefore diversity cannot be implemented. Additionally, diversity systems can get very complex because of issues such as optics alignment, signal synchronization, inter- ference effects, and others. Error correction is a simpler fade mitigation technique that has been shown to give satisfactory results [176] on SISO (single input single output) channels. Forward-error-correction (FEC), in particular, adds additional bit patterns to each coded packet being transmitted, which allows all transmitted bits to be recovered if some are lost due to fading. For example, in a (255,223) Reed-Solomon code that uses 8- bit symbols, there are 255 codeword bytes. Each code- word contains 223 bytes of data and 32 bytes for parity checking. The decoder can correct any 16 symbol errors in the code word: errors up to 16 bytes anywhere in the codeword can be automatically corrected. Still, this method only works well if fades are of short duration. In this example, the fade duration should be limited to 128-bit periods. Unfortunately, the transmission time of a code word in a high data rate OW system is much shorter than even the shortest fades. At 1.25 Gb/s, which is a commercially available OW data rate, 255 bytes takes only 1.6 μ s for transmission. As a result, improved coding and interleaving techniques are being investigated for application in higher rate OW systems.
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Volume 3, Issue 3, March 2014 Page 518

Volume 3, Issue 3, March 2014 Page 518

is the aggregate rate over all TDM channels in the system, while the optical CDM chip rate may be much higher than each user’s data rate. As a result, both the TDM bit rate and the CDM chip rate may be much higher than electronic processing speed, i.e., some part of an end user’s network interface must operate at a rate higher than electronic speed. Thus, TDM and CDM are relatively less attractive than WDM [5], since WDM - unlike TDM or CDM-has no such requirement. Specifically, WDM is the recent favorite multiplexing technology for long - haul communications in optical communication networks since all of the end-user equipment needs to operate only at the bit rate of a WDM channel, which can be chosen arbitrarily, e.g., peak electronic processing speed. Hence, the major carriers today all devote significant effort to developing and applying WDM technologies in their businesses. Research is ongoing to introduce more intelligence in the control plane of the optical transport systems, which will make them more survivable, flexible, controllable and open for traffic engineering. Some of the essential desirable attributes of optical transport networks include real-time provisioning of lightpaths, enhanced network survivability, interoperability functionality between vendor-specific optical sub-networks, and enabling operational protection and restoration capabilities. The research efforts now are focusing on the efficient internetworking of higher layers, primarily IP with WDM layer. The paper discusses about the issues along with the dedicated effort to introduce the new technique termed as ECON, which uses the potential features of ROADM to enhance the OSNR. Section 2 discusses about the theoretical outline of the study followed by Section 3 that discusses about prior research work. Section 4 discusses about the problem identification followed by elaboration of ECON in section 5. Section 6 highlights the design consideration of ECON while research methodology of the study is discussed in Section 7. Section 8 discusses about the algorithms that were implemented to get the result discussed in Section 9. Section-10 gives some of the concluding remarks of the ECON model discussed.
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Saturation in cascaded optical amplifier free space optical communication systems

Saturation in cascaded optical amplifier free space optical communication systems

The past three decades have witnessed the emergence of free-space optical (FSO) communication as a viable approach for terrestrial short range access networks. The catalysts for the development of the FSO communication systems are the rising demands for higher bandwidth and technological developments in optoelectronics such as sensitive detectors and high power transmitters [1-3]. The main advantages of FSO communication systems over the traditional radio frequency (RF) and millimetre wave systems include the large potential bandwidth obtainable, improved security of information and absence of spectrum licensing requirements. The employment of a FSO communication system also eliminates the cost of purchasing and laying the optical fibre which would be needed in optical fibre communication systems [4, 5]. Though FSO systems offers many advantages, their practical implementation is highly susceptible to unpredictable severe atmospheric conditions. For instance, beam attenuation can occur as a result of scattering and photon absorption which is caused by rain, fog, snow, aerosol and atmospheric gases. Also, thermal expansion, earth tremors and wind loads can result in high-rise building sway [1, 6]. Even in clear weather conditions, due to inhomogenities in pressure and temperature changes in the atmosphere, the refractice index varies leading to atmospheric turbulence. The effect of atmospheric turbulence is highly significant because it results in scintillation i.e. fluctuations of the power of the optical signal propagated through the atmosphere [2, 6, 7]. These fluctuations in the received signal power lead to a reduction in system performance. In order to achieve the desired bit error rate (BER), appropriate fade mitigation techniques should be employed [8]. Various techniques that have been proposed in the literature include aperture averaging [1, 9], error correcting codes with interleaving [10], spatial diversity [3, 7, 11, 12], cooperative diversity and multi-hop transmission [13], maximum likelihood sequence detection (MLSD) [14], and the use of a saturated optical amplifier (OA) [15-17].
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Bit Error Rate Performance in Coherent Optical Systems

Bit Error Rate Performance in Coherent Optical Systems

Although a single-filter heterodyne receiver can be used for FSK, it has the disadvantage that one-half of the received power is rejected, resulting in an obvious 3-dB penalty. For this reason, a dual-filter FSK receiver [see Fig. 1] is commonly employed in which 1 and 0 bits pass through separate filters. The output of two envelope detectors is subtracted, and the resulting signal is used by the decision circuit. Since the average current takes values I p and −Ip for 1 and 0 bits, the decision threshold is set in the middle (ID = 0). Let I and I_ be the currents generated in the upper and lower branches of the dual filter receiver, where both of them include noise currents through Eq. (12). Consider the case in which 1 bit are received in the upper branch. The current I is then given by Eq. (12) and follows a Rice distribution with I p = I1 in Eq. (13). On the other hand, I _ consists only of noise and its distribution is obtained by setting Ip = 0 in Eq. (13). An error is made when I’ > I, as the signal is then below the decision level, resulting in
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Bit Manipulation Accelerator for Communication Systems Digital Signal Processor

Bit Manipulation Accelerator for Communication Systems Digital Signal Processor

blocks represent the omitted bits. Interleaving is the oper- ation of shuffling input bits and characterized by the size of the interleaver and an interleaving scheme. Bit stream multiplexing is used to merge encoded data according to the code rates in the convolutional encoder. Although the opera- tions have regular patterns, it is not easy to implement hard- ware which can accommodate different characteristics of var- ious communication standards. However, bit extraction and insertion in arbitrary bit positions are common operations for puncturing, interleaving, and bit stream multiplexing. 2.2. Existing DSP architectures for bit manipulations Figure 4 shows computation units of a general DSP. The data processing unit (DPU) of general DSPs consists of an arithmetic unit, a logical unit, and a shifter. The repetitive shift/XOR operations can be performed using the logical unit and the shifter. First, the data is read from the register. Next, the shifter shifts the data 1 . Finally, the logical unit performs XOR operations 2 . However, conventional DSPs do not sup- port parallel shift and XOR operations on multiple data. In addition, a bit extraction operation is performed by a shift left followed by a shift right, and then, the field in the source is extracted 3 . A bit insertion operation can also be per- formed using shift, AND, or OR operations.
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Bit Error Rate Prediction of Coded MIMO-OFDM Systems

Bit Error Rate Prediction of Coded MIMO-OFDM Systems

Bit error rate (BER) prediction over channel realisations has emerged as an active research area. In this paper, we give analytical signal to interference and noise ratio (SINR) evaluation of MIMO-OFDM systems using an iterative receiver. Using this analytical SINR expression, we propose an accurate BER prediction method based on effective exponential SINR mapping (EESM) method. We show by simulations that our method is independent of the channel realisation and of the MIMO scheme. It is only dependent on the modulation and coding scheme.
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A SIMO one bit time reversal for UWB communication systems

A SIMO one bit time reversal for UWB communication systems

[3]. The TR complexity increases along with the length of the pre-filters and the quantization steps used in the channel estimation process. It is practically very difficult to deploy the pre-filter TR with a very fine quantization steps in rate of several gig symbol per second. Several attempts have been made to reduce the time reversal complexity using only the phase of the channel impulse response (CIR), the so-called one-bit time reversal, to construct the pre-filter [5]. In other word, the transmit filters in one-bit time reversal preserve only the sign information of the CIR. One-bit time reversal ultra wideband (OTR-UWB; also known as channel phase precoding UWB) has shown promising results for improving the system performance [5,6]. To overcome the shortcomings of TR-based UWB systems, CPP UWB transceiver architecture was proposed and showed that the spatial property of time reversal remained, but its delay spread increased [7]. Since the OTR system demands the receiver to estimate and feedback the signs of channel tap coefficients only (rather than the com- plete CIR), its complexity is significantly lower than that of time reversal. At the transmitter end, a more expen- sive linear amplifier is needed in time reversal to pro- vide a larger signal dynamic range as compared with OTR [5,8]. As the data rate goes up, the ISI of OTR sys- tem becomes more severe and it degrades system per- formance more than background noise. We show that using a single input multiple output (SIMO) OTR trans- ceiver, ISI is reduced and the system capacity is increased almost linearly with the number of received antenna. According to authors ’ knowledge, no research work about SIMO OTR-UWB system has been reported so far. In this article, such a system is proposed in order to decrease ISI and improve the system capacity.
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An Iterative Soft Bit Error Rate Estimation of Any Digital Communication Systems Using a Nonparametric Probability Density Function

An Iterative Soft Bit Error Rate Estimation of Any Digital Communication Systems Using a Nonparametric Probability Density Function

In general, performance of communication system receivers cannot be calculated analytically. The bit error rate (BER) is thus computed using the Monte Carlo (MC) simulation (Bit Error Counting). It is shown that if we wish to have reliable results with good precision, the total number of transmitted data must be conversely proportional to the product of the true BER by the relative error of estimate. Consequently, for small BERs, simulation results take excessively long computing time depending on the complexity of the receiver. In this paper, we suggest a new means of estimating the BER. This method is based on an estimation, in an iterative and nonparametric way, of the probability density function (pdf) of the soft decision of the received bit. We will show that the hard decision is not needed to compute the BER and the total number of transmitted data needed is very small compared to the classical MC simulation. Consequently, computing time is reduced drastically. Some theoretical results are also given to prove the convergence of this new method in the sense of mean square error (MSE) criterion. Simulation results of the suggested BER are given using a simple synchronous CDMA system.
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Performance Analysis of Optical Spatial Modulation in Atmospheric Turbulence Channel

Performance Analysis of Optical Spatial Modulation in Atmospheric Turbulence Channel

Abstract: In this paper, spatial pulse position modulation (SPPM) is used as a case study to investigate the performance of the optical spatial modulation (SM) technique in outdoor atmospheric turbulence (AT). A closed-form expression for the upper bound on the asymptotic symbol error rate (SER) of SPPM in AT is derived and validated by closely-matching simulation results. The error performance is evaluated in weak to strong AT conditions. As the AT strength increases from the weak to strong, the channel fading coefficients b ecome m ore d ispersed a nd d ifferentiable. T hus, a b etter error performance is observed under moderate-to-strong AT compared to weak AT. The performance in weak AT can be improved by applying unequal power allocation to make FSO links more distinguishable at the receiver. Receive diversity is considered to mitigate irradiance fluctuation and improve the robustness of the system to turbulence-induced channel fading. The diversity order is computed as half of the number of detectors. Performance comparisons, in terms of energy and spectral efficiencies, are drawn between the SPPM scheme and conventional MIMO schemes such as repetition coding and spatial multiplexing.
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Design of Higher Capability and Reliable long Distance Network and Performance Analysis

Design of Higher Capability and Reliable long Distance Network and Performance Analysis

We can use either EDFA (Erbium Doped Fibre Amplifier) or Raman Amplifier. Erbium doped Fibre Amplifier is the widely used optical amplifier for long range fibre optic communication. It amplifies light in 1.5μm wavelength region efficiently. This is of great importance to Telecom industry where they acquire minimum loss. Its application includes the boosting of the data transmitter power with EDFA amplifier for long distance fibre cable or for the fibre optic splitter which has maximum loss. Eg: Traditional Cable TV system now used, which transmits to several fibre using a single transmitter. Raman amplifier is now mostly attracted because of its smaller noise figure and cheaper than EDFA amplifier.
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Online Full Text

Online Full Text

Optical fibers fall into two major categories, namely: step index optical fiber, which include single mode optical fiber and multimode optical fiber, and graded index optical fiber. Single mode step index optical fiber has a core diameter less than 10 micrometers and only allows one light path. Multimode step index optical fiber has a core diameter greater than or equal to 50 micrometers and allows several light paths, this leads to modal dispersion. Graded index optical fibers have their core refractive index gradually decrease farther from the centre of the core, this increased refraction at the core centre slows the speed of some light rays, thereby allowing all the light rays to reach the receiver at almost the same time, thereby reducing dispersion. Figure 2 gives a description of the various optical fiber modes.
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Improved Adaptive Bit Error Rate Performance
for Fading Channel Communication

Improved Adaptive Bit Error Rate Performance for Fading Channel Communication

The rising demand of multimedia services and the development of Internet related contents lead to increasing curiosity to high speed communications. In the ceaseless search for increased capacity in a wireless communication channel it has been shown that by using MIMO (Multiple Input Multiple Output) system architecture it is possible to increase that capacity considerably. The MIMO is very likely beneficial since it enables support of more antennas and larger bandwidths and it simplifies equalization in MIMO systems. Usually fading is considered as a problem in wireless communication but MIMO channels uses the fading to increase the capacity of entire system. Fading of the signal can be mitigated by different diversity techniques. The data rate and spectrum efficiency of wireless mobile communications have been significantly improved over the last decade or so. Recently, the advanced systems such as 3GPP LTE and terrestrial digital TV broadcasting have been sophisticatedly developed using OFDM and CDMA technology. In general, most mobile communication systems transmit bits of information in the radio space to the receiver. The radio channels in mobile radio systems are usually multipath fading channels, which cause inter-symbol interference (ISI) in the Received signal. To remove ISI from the signal, there is a need of strong equalizer which requires knowledge on the channel impulse response (CIR).[1]Hence, there is a need for the development of novel practical, low complexity equalization techniques and for understanding their potentials and limitations when used in wireless communication systems characterized by very high data rates, high mobility and the presence of multiple antennas.[10]In radio channels, a variety of adaptive equalizers can be used to cancel interference while providing diversity. Since the mobile fading channel is random and time varying, equalizers must track the time varying characteristics of the mobile channel, and thus are called adaptive equalizers. The general operating modes of an adaptive equalizer include training and tracking. First, a known, fixed-length training sequence is sent by the transmitter so that the receiver’s equalizer may adapt to a proper setting for minimum bit error rate (BER) detection.
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Outage Probability and Bit-Error Rate for Communication Systems with Gaussian-Schell Electromagnetism Beams in Non-Kolmogorov Raining Turbulence

Outage Probability and Bit-Error Rate for Communication Systems with Gaussian-Schell Electromagnetism Beams in Non-Kolmogorov Raining Turbulence

Abstract—Two major performance degrading factors in free space optical communication systems are rainfall and atmospheric turbulence. We study the outage probability and bit-error rate for free-space communication links with spatial diversity and Gaussian-Schell electromagnetism beams over the raining turbulence fading channels by double inverse Gaussian distribution proposed in this paper. Assuming intensity-modulation/direct detection with on-off keying and perfect channel state information, we derive expressions of average bit-error rate and outage probability of multiple-input multiple-output free space optical communication systems over double inverse Gaussian model. The effects of scintillation index of raining turbulence, spatially coherence of source, pointing errors and spectral index of non- Kolmogorov turbulence on the outage probability and bit-error rate of multiple-input multiple-output free space optical communication systems are examined.
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Performance evaluation of OFDM using MIMO STTC for AWGN, RAYLEIGH, combined Rayleigh with AWGN and   RICIAN channel for WIMAX and Bluetooth application

Performance evaluation of OFDM using MIMO STTC for AWGN, RAYLEIGH, combined Rayleigh with AWGN and RICIAN channel for WIMAX and Bluetooth application

There are various categories of MIMO techniques. One of the technique aims to improve the power efficiency by maximizing spatial diversity. Such techniques include delay diversity, STBC and STTC. The second one uses a layered approach to increase capacity. In broadband wireless communications, an efficient implementation of space-time coding (STC) improves the performance and diversity gains of the system. The data experiences much impairment during transmission, especially due to the channel noise. The block diagram of M X N MIMO system is represented in figure which consists of M antennas at transmitter side and N antennas at receiver side. In this paper, the effects of using different antenna configuration on the performance of MIMO systems using OSTBC4 over AWGN and Rician channels with Zero Forcing receivers are considered. The impact of antenna selection on the performance of multiple input- multiple output (MIMO) systems over nonlinear communication channels. The author presented improvement in SNR penalty due to nonlinearity of fading channels for the reduced complexity system (Mitalee Agarwal and Yudhishthir
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Optical wireless MIMO communication

Optical wireless MIMO communication

More specifically, this project furthers studies on OW MIMO by providing three infrared MIMO experimental systems using different modulations to describe the detailed process and the experiment methodology in developing the infrared MIMO systems. On-off keying (OOK), serial infrared protocol – return to zero inverted (SIR-RZI) and pulse positon modulation (PPM) are considered. The BERs of three systems are measured and compared, and the advantage and disadvantage of these systems are illustrated and discussed. To the best of the authors’ knowledge, neither the built system nor their experimental results have been published in the literature before. Moreover, using curve fitting, the experimental results of BER are fitted as functions of system parameters to derive some mathematical models that have not been studied before. The results obtained from the specified experiments indicate that the developed system is viable for indoor optical applications as verified by root mean squared error.
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Investigation of optical wireless for employment within a vehicular environment

Investigation of optical wireless for employment within a vehicular environment

LOS systems are capable of high transmission capacity, however they have the problem of alignment in practical communication links. Non-Line-of-sight (NLOS) systems, in contrast, permit roaming but offer lower bandwidths. NLOS communication systems rely on the reflections of light from any diffusely-reflecting surfaces which have been illuminated from elsewhere [98]. However, multipath dispersion arising from surface reflections can degrade the performance of an NLOS system, in terms of SNR and potential data rates. This chapter aims demonstrate that OW systems can operate around confined spaces and corners, and, in order to assess the performance of NLOS systems, the effect of representative different tube configurations were set up, using the types of configurations as below:
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Mathematical modelling of all optical buffering for ultrafast optical time division multiplexed networks

Mathematical modelling of all optical buffering for ultrafast optical time division multiplexed networks

Among the emerging switching technologies highlighted in section 3.2.7 MEMS have emerged as the most popular choice within industry [85]. This is due to their precision, simplicity, small size and low manufacturing cost in high volume. In addition, they exhibit exceptional optical performance with a high reflection coefficient leading to low loss and cross-talk. Unfortunately, these opto-mechanical devices are slow, taking milliseconds to switch, require moving parts and have a limited scalability. The bubble switches considered have the added advantage o f having no movable parts but again the switching process is still slow. Moreover, scalability is limited to about 100 ports because o f the loss and cross-talk at each intersection. The liquid-crystal switches are reliable and well characterised but are slow and difficult to integrate with other optical technologies. The high losses experienced by the optical pulses as they traverse the medium prohibit its uses for packet switching. Electro-holographic switches are very promising especially for WDM technology despite their limited scalability. They are fast and consume negligible amounts o f power, however because o f their limited scalability they are not considered. In summary, these emerging technologies are better suited for circuit switching applications within TONs because o f their slow speeds.
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ACE PI: PAPR Reduction in OFDM Systems Using Constellation Extension with Peak Insertion

ACE PI: PAPR Reduction in OFDM Systems Using Constellation Extension with Peak Insertion

complexity of the system, higher Bit error rate (BER) and transmitted signal power, etc. Also, there is a problem of disturbance in the adjacent channel because of using of clipping technique for power reduction at the initial stage. The high data rates in the communication systems cause an issue in the current communication mechanisms, particularly inter-symbol interference (ISI) in fading channels. To deal with such problem, many solutions were proposed, as coding schemes were used to reduce the ISI and reducing the BER in the communication system. But still, improvements can be done, however, by not only using the coding schemes in the OFDM communication but this can be more improved by introducing the equalization approach in the present systems. This will reduce the variation in the signal at the receiver end and more BER and ISI will be reduced. Therefore, an Active Constellation Extension (ACE) mechanism has been projected that offers improved outcomes in case of several performance parameters such as PAPR and BER. In the proposed model, the equalization approach that can be recommended will be improved by ML equalizer. Novel ACE scheme introduced peak inverse and butter worth band pas filter so that the PAPR can be decreased to an extent by incorporating a relatively high impulse.
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SECURE VOICE COMMUNICATION USING LOW BIT RATE SYSTEM FOR GSM USERS

SECURE VOICE COMMUNICATION USING LOW BIT RATE SYSTEM FOR GSM USERS

Prof.K.Murugesan obtained B.E. and M.E. degrees from Madurai Kamaraj University, Madurai in 1990 and 1994 respectively. He earned his Ph.D from Anna University, Chennai in 2001. He has published more than 40 research papers in National and International journals and reputed conferenes. He has a teaching experience of about 18 years in various educational institutions in India and abroad. presently, he is serving as Principal at Bharathiyar Institute of Engineering for Women, Attur, Salem in India. He is a life member of Indian Society for Technical Education, Fellow of Institution of Engineers, Fellow of Institution Electronics and Telecommunication Engineers. He achieved Best ISTE Chapter Secretary Award (TN & P Section) in 2007. He has authored about eight technical books. His research area include Optical Code Division Multiple Access, Optical Signal Processing, Lightwave Communication Systems, Optical Coding Theory and Biometric Image Processing. He is a reviewer of several international conferences and journals
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Duobinary Modulation Format in Optical Communication Systems

Duobinary Modulation Format in Optical Communication Systems

Abstract This paper presents the environment of the optical fiber and digital information transmission over optical fiber, using signal transformation technique called duobinary modulation technique. We propose a complete duobinary encoder and duobinary decoder that we tested in Matlab simulink R2014B. In the final part, it will be shown a comparison of duobinary modulation technique with on-off keying modulation technique

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