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Optoelectronics, IET

Issue 4 • Date August 2009

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Displaying Results 1 - 4 of 4
  • Bit error performance of diffuse indoor optical wireless channel pulse position modulation system employing artificial neural networks for channel equalisation

    Publication Year: 2009 , Page(s): 169 - 179
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (554 KB)  

    The bit-error rate (BER) performance of a pulse position modulation (PPM) scheme for non-line-of-sight indoor optical links employing channel equalisation based on the artificial neural network (ANN) is reported. Channel equalisation is achieved by training a multilayer perceptrons ANN. A comparative study of the unequalised dasiasoftdasia decision decoding and the dasiaharddasia decision decoding along with the neural equalised dasiasoftdasia decision decoding is presented for different bit resolutions for optical channels with different delay spread. We show that the unequalised dasiaharddasia decision decoding performs the worst for all values of normalised delayed spread, becoming impractical beyond a normalised delayed spread of 0.6. However, dasiasoftdasia decision decoding with/without equalisation displays relatively improved performance for all values of the delay spread. The study shows that for a highly diffuse channel, the signal-to-noise ratio requirement to achieve a BER of 10-5 for the ANN-based equaliser is ~10~dB lower compared with the unequalised-soft-decoding for 16-PPM at a data rate of 155 Mbps. Our results indicate that for all range of delay spread, neural network equalisation is an effective tool of mitigating the inter-symbol interference. View full abstract»

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  • Determination of the dispersion curve of the refractive index by the stockwell transform

    Publication Year: 2009 , Page(s): 180 - 186
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (457 KB)  

    The determination of dispersion curves by the Stockwell transform (ST) is proposed. The required numerical data for dispersion curves are produced from the transmittance signal by the ST. The obtained data are then used to estimate the unknown dispersion parameters in Cauchy's formula using the genetic algorithm method through the minimisation problem based on the least-squares curve fitting. The results have shown that the dispersion curve obtained from the ST produced more improved outcomes than those obtained from the continuous wavelet transform. View full abstract»

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  • Adaptive code-division multiple-access system for communications over indoor wireless optical channels based on random optical codes

    Publication Year: 2009 , Page(s): 187 - 196
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (623 KB)  

    The authors have designed an adaptive optical codes-based system for communications over the indoor wireless optical channel when large numbers of users access to the channel simultaneously. This system uses a code-division multiple access (CDMA) scheme based on the named random optical codes (ROC). The authors present the characteristics of this kind of optical codes and several results about its performance over noisy indoor wireless optical channels. Finally, the authors describe a CDMA system which adapts its performance to the number of users which are accessing simultaneously to the channel. The proposed system is able to maintain a target bit error rate adapting its data throughput independently of the number of simultaneous users in the optical environment, whenever certain conditions are accomplished. View full abstract»

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  • Analysis of return-to-zero-on-off-keying over absolute polar duty cycle division multiplexing in dispersive transmission medium

    Publication Year: 2009 , Page(s): 197 - 206
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (954 KB)  

    We propose and investigate a technique to reduce the spectral width as well as increase the tolerance to chromatic dispersion (CD) using improved return-to-zero (RZ) on-off-keying (OOK) over absolute polar duty cycle division multiplexing (AP-DCDM) technique. The proposed channel multiplexing and demultiplexing are performed electrically using only one modulator for n number of users, which is very economical. It is demonstrated that the spectral width occupied by 30 Gb/s RZ-OOK without AP-DCDM measured at -20 dB from the peak power is around 105 GHz whereas, this value can be reduced to around 64 GHz for 30 Gb/s RZ-OOK over AP-DCDM. This amount of saving in the spectral width is a significant achievement, which leads to better tolerance to CD. Its tolerance to CD is in the range of plusmn109 and plusmn155 ps/nm, for the worst and the best users, respectively. These values are higher than that of 30 Gb/s conventional RZ-OOK, which is around plusmn86.5 ps/nm. At 120 Gb/s RZ-OOK over AP-DCDM (the worst user) has pre-amplified receiver sensitivity and optical signal to noise ratio (OSNR) of -22.5 dBm and 28.57 dB, respectively. View full abstract»

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Aims & Scope

IET Optoelectronics covers but is not limited to the following topics: Optical and optoelectronic materials; Light sources, including LEDs, lasers and devices for lighting; Optical modulation and multiplexing; Optical fibres, cables and connectors; Optical amplifiers; Photodetectors and optical receivers; Photonic integrated circuits; Nanophotonics and photonic crystals; Optical signal processing; Holography; Displays.

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