Hossam A. I. Selmy

Proposal and Performance Evaluation of a Hybrid BPSK-Modified MPPM Technique for Optical Fiber Communications Systems

A hybrid binary phase shift keying-modified multi-pulse pulse position modulation (hybrid BPSK-modified MPPM) scheme is proposed as a new modulation technique to improve the performance of both conventional binary phase shift keying (BPSK) and multi-pulse pulse position modulation (MPPM) techniques in optical fiber communications systems. In conventional BPSK scheme, a consecutive stream of low power BPSK symbols are transmitted. However, in the proposed scheme, a less number of high power BPSK symbols are transmitted in a hybrid frame and their positions are exploited to transmit more bits. That is, the transmitted information is carried in both the positions and phases of the transmitted pulses. The transmission characteristics, transmitter and receiver block diagram, bandwidth-utilization, and optimum decoding process for the proposed scheme are all studied in this paper. Several performance measures are also derived and compared to those of conventional schemes in optical fiber channels. Our results reveal that, under an average power constraint, the proposed hybrid BPSK-modified MPPM scheme achieves much lower levels of bit-error rates and symbol-error rates than those of ordinary BPSK and ordinary MPPM schemes, respectively, for both moderate or high signal-to-noise ratios. In addition, the proposed modulation scheme achieves much higher bandwidth-utilization efficiencies than those of ordinary schemes.

Performance analysis of gradual multi-pulse pulse-position modulation in deep-space optical communications

A gradual multi-pulse pulse-position modulation (gradual MPPM) scheme is proposed as a new modulation scheme to improve both the performance and bandwidth-utilization efficiency of the conventional optical multi-pulse pulse-position modulation (MPPM) scheme in deep-space optical communications. Whereas in the conventional MPPM scheme, a fixed number of optical pulses is transmitted in every signal block, a variable number of pulses are transmitted in the proposed scheme. Information is represented by different combinations of the positions of these pulses. The transmission characteristics, bandwidth utilization, and power requirements for the proposed scheme are studied in this paper. Several performance measures are derived and compared with those of the conventional MPPM scheme in deep-space optical communications. Our results reveal that, at the same average power, the proposed gradual MPPM scheme achieves much lower levels of symbol-error rates than those of the ordinary MPPM scheme, whereas, at the same peak power levels, the ordinary MPPM outperforms the gradual scheme. Also, in terms of bandwidth-utilization efficiency, the proposed modulation scheme achieves higher efficiency than the ordinary MPPM by allowing many more symbols to be transmitted per frame.

Fair resource allocation schemes for cooperative dynamic free-space optical networks

Free-space optics (FSO) presents a promising solution for the last-mile connectivity problem. However, adverse weather conditions like fog, rain, and snow, can significantly degrade the performance of FSO links. Thus, the implementation of reliable FSO networks becomes a significant issue. At the same implementation cost, dynamic (reconfigurable) FSO networks are more robust against severe weather conditions over static ones. In this paper, two resource allocation schemes are proposed for dynamic cooperative FSO networks. Each scheme is formulated as a multi-objective optimization problem, where capacity, reliability- fairness, average transmitted power, and bit-error rate functions are targeted. One scheme prioritizes the reliability-fairness over capacity, while the other does the opposite. The simulation results reveal that the proposed schemes are more reliable and cost efficient than traditional relayed networks, especially under severe weather conditions.

Fair cooperative resource allocation schemes for foggy free space optical network

Two new resource allocation schemes are proposed for foggy reconfigurable free space optical (FSO) networks. The schemes are formulated as multi-objective optimization problems (MOP). The MOP is composed of lexicographic lex-max-min and Lex-min-max optimization. One of these schemes enhances reliability and fairness over network capacity while the other scheme does the opposite. The simulation results reveal that two schemes have higher reliability and fairness over robust static topology (relay network).

Hybrid BPSK-modified MPPM: A scheme for enhancing optical MPPM in optical fiber communications

A hybrid binary phase shift keying-modified multipulse pulse-position modulation (hybrid BPSK-modified MPPM) scheme is proposed as a new modulation technique to improve both the symbol-error rate performance and bandwidth utilization efficiency of conventional optical multi-pulse pulse position modulation (MPPM) scheme in optical fiber communication systems. Whereas in conventional MPPM scheme, unmodulated pulses are transmitted in every signal block, BPSK modulated pulses is transmitted in the proposed hybrid scheme. That is, the information is encoded in both the positions and phases of the transmitted pulses. The transmission characteristics, transmitter and receiver structures, bandwidth utilization, and optimum decoding for the proposed scheme are presented in this paper. Several performance measures are derived and compared to those of conventional MPPM schemes, adopting both coherent and direct detection receivers, under the same data transmission rates. Our results reveal that, at same average power levels, the proposed hybrid BPSK-modified MPPM scheme achieves much lower levels of symbol-error rates compared to those of ordinary MPPM schemes. Furthermore, in terms of bandwidth-utilization efficiency, the proposed hybrid modulation scheme achieves much higher efficiencies than that of ordinary MPPM schemes.

Performance enhancement of QPSK modulation using hybrid QPSK-modified MPPM in optical fiber communications

A hybrid quadrature phase shift keying-modified multi-pulse pulse-position modulation scheme is proposed as a new modulation technique to improve the performance of conventional quadrature phase shift keying (QPSK) modulation in optical fiber communication systems.

Interference Mitigation and Capacity Enhancement Using Constraint Field of View ADR in Downlink VLC channel

The continued increase in several mobile applications forces to replace existing limited spectrum indoor radio-frequency wireless connections with high-speed ones. Visible light communication (VLC) is a promising license free indoor wireless technology that could offer high-speed connections. However, both co-channel interference (CCI) from more neighbour transmitters and inter-symbol interferences (ISI) from multipath reflections limit the performance of VLC downlink channel. In this study, a constraint field of view angular diversity receiver (CFOV-ADR) is proposed to mitigate these limitations. By optimising the photodetectors (PD) field of view (FOV) angle, the line of sight CCI could be totally eliminated and the ISI could be significantly reduced. The optimal range for FOV angle is calculated in a typical indoor scenario. Furthermore, the zero-forcing (ZF) algorithm is applied to the conventional ADR (ADR-ZF) which can significantly eliminate the ISI components. The received optical signal-to-interference-plus-noise ratio (SINR) is tested at various room positions. The simulation results show that the proposed CFOV-ADR can achieve higher SINR performance than single receiver, conventional ADR, and ADR-ZF at all positions and orientations.

Novel modulation scheme for VLC

In this paper, we have proposed a novel modulation scheme for visible light communication (VLC), that has two preprocessing blocks namely, discrete Fourier transform (DFT) block and frequency domain signal shaping block, prior to conventional optical-orthogonal frequency division multiplexing (O-OFDM) modulation. Two variants of proposed scheme namely, with and without DC have been implemented so as to make it compatible with intensity modulation and direct detection (IM/DD). The results of the proposed schemes are compared against their standard O-OFDM counterparts based on peak-to-average power ratio (PAPR) and symbol error rate (SER). Results show that the proposed scheme has significantly lower PAPR and better SER as compared to corresponding O-OFDM counterpart.

BPSK based SIM-FSO communication system with SIMO over log-normal atmospheric turbulence with pointing errors

In this paper, we analyze a bit error rate (BER) as well as outage probability in a free-space optical (FSO) link. Log-normal atmospheric turbulence with an effect of pointing errors (PE) is used to model the FSO channel. Binary phase shift keying based on subcarrier intensity modulation is employed. The BER degradation due to the effect of PE is improved by applying single-input multiple-output (SIMO) technique using maximal ratio combining. The outage probability and BER closed-form expressions are derived for all cases which are confirmed by integral expressions. The numerical results show that the BER can be improved by using SIMO technique. For instance, the BER is 1.884×10−6 at 0 dBm transmitted power in the case of without using SIMO, while the BER become 3.223×10−21 at 0 dBm in the caseof applying the SIMO technique.

Constrained fairness placement scheme in cooperative dynamic free space optical network

In this paper, a new scheme is proposed to obtain the strategic locations of the cooperative transceivers on free space optical node in last-mile network. The scheme is formulated as bi-level multiple-objective linear integer programming (BL-MO-ILP) problem, and solved by exhaustive search method to obtain the optimal solutions. The scheme leads to an increasing in the immunity of network against severe weather conditions at the efficient cost in terms of number of optical transceivers. The numerical results reveal that improvements are obtained in the network performance, reliability and fairness, specially at low visibility conditions.