Antonio García-Zambrana

Error rate performance for STBC in free-space optical communications through strong atmospheric turbulence

In this letter, error rate performance for space-time block coding (STBC) in free-space optical (FSO) communication systems with direct detection operating over strong atmospheric turbulence channels is analyzed. Based on the modification of the Alamouti code presented by Simon and Vilnrotter, a generalized approach is adopted to consider space-time coded on-off keying (OOK) formats with any pulse shape and reduced duty cycle, allowing the increase of the peak-to-average optical power ratio (PAOPR) and, hence, a relevant improvement in error rate performance. Simulation results are further demonstrated to confirm the analytical results

Improving PPM schemes in wireless infrared links at high bit rates

The authors conclude that pulse-position modulation (PPM) with Gaussian pulses provides better performance than classic PPM schemes with rectangular pulses over unguided optical links operating at high bit rates. In this fashion, both intersymbol interference (ISI), induced by multipath propagation, and the phase distortion effects due to the high-pass filter whose function is to suppress interference, are minimized. However, relevant improvement is not achieved if compared with the OOK format with Gaussian pulses and low duty cycle. The above conclusion is validated by the corresponding bit-error rate (BER) computation using Monte Carlo simulations.

Rate-adaptive transmission schemes in the context of runlength-limited-codes for optical wireless communications

In this letter, the performance evaluation of rate-adaptive transmission schemes for indoor unguided optical links has been analyzed in the context of runlength-limited (RLL) sequences. Here, the superiority of on-off keying (OOK) formats with runlength constraints based on silence periods has been corroborated in terms of code efficiency and peak-to-average optical power ratio (PAOPR) compared to a hybrid HHH (1,13) code, variable-rate signalling technique obtained by modifying the RLL (1,13) code specified in the very fast infrared (VFIr) standard by the infrared data association (IrDA). Additionally, the use of very simple decoding schemes based on Boolean logic has been proposed.

Efficient channel model for free space optical communications

In this paper, a novel model for the atmosphere as an optical communication channel is investigated. In this model an unbounded plane wave operating under weak irradiance fluctuation conditions is assumed, considering a second-order Gaussian statistical model as reference. Here, the obtained spectrum is compared with the more physically realistic 1d theoretical equivalent one, generated from the 3d Kolmogorov spectrum. The obtained results show a very good accuracy and a great reduction of computational complexity

Novel block coding method for rate-adaptive optical wireless communications systems

In this paper, a novel rate-adaptive transmission scheme using block codes with codewords of variable Hamming weight is presented. This coding scheme is based on a multiple-pulse position modulation (MPPM) technique, where codewords with different Hamming weight are allowed, including the all-zero one. The performance analysis of this new scheme has been presented by comparing with on-off keying (OOK) formats with memory and the HHH(1,13) code proposed and specified in the Very Fast Infrared (VFIr) standard by the Infrared Data Association (IrDA), but operating under a rate-adaptive transmission environment. The superiority of the block coding method has been corroborated, being the improvement in performance higher as the length of the data block is increased. Additionally, the use of very simple decoding schemes based on ML detection has been proposed as alternative to the procedure based on the Viterbi algorithm. Finally, an improved rate-adaptive capability is provided by the translation table adopted in the block coding here proposed, leading to an attractive adaptation procedure by swapping between proper translation tables

Self-orienting receiver using rate-adaptive transmission based on OOK formats with memory for optical wireless communications

The simultaneous use of a simple rate-adaptive transmission scheme, based on on-off keying (OOK) formats with memory, and a new self-orienting receiver, alternative to conventional angle diversity techniques, is proposed in order to mitigate the effect of large variations of the signal-to-noise ratio in indoor wireless infrared communications. In relation to the rate-adaptive transmission technique, variable silence periods are used for modifying the statistics of the amplitude sequence regarding the statistics of the message sequence, allowing an increase of the peak-to-average optical power ratio (PAOPR). With regard to the new diversity technique proposed, this is based on giving a self-orienting capability to the receiver optical front-end, thus optimizing link quality parameters. It is applied to links operating at an initial bit rate of 200 Mb/s, providing a signaling rate with a wide dynamic range and a relevant improvement in performance with a gradual complexity in implementation, compared with the scheme proposed and specified in the advanced infrared (AIr) standard by the Infrared Data Association (IrDA), which is based on repetition coding and pulse-position modulation.

Comparison of improved OOK formats with pulse-position modulation in indoor unguided optical links at high bit rates

In this paper, on-off keying (OOK) formats with different pulse shapes and pulse-position modulation (4PPM) for indoor unguided optical links and different channel conditions are compared in terms of performance and required complexity, so as to minimize both intersymbol interference (ISI), induced by multipath propagation, and phase distortion effects, due to the interference suppression receiver filter. By means of a direct application of the correlation operator and the corresponding bit-error rate (BER) computation, we conclude that OOK format with Gaussian pulses and duty cycle lower than 50% provides quite good performances compared with the 4PPM scheme, frequently proposed in reported works but with major implementation complexity.