Md. Zoheb Hassan

Subcarrier intensity modulated wireless optical communications with rectangular QAM

The average symbol error rate is studied for subcarrier intensity modulated wireless optical communication systems employing general order rectangular quadrature amplitude modulation. We consider three different turbulence channel models, i.e., the Gamma-Gamma channel, the K-distributed channel, and the negative exponential channel with different levels of turbulence. Closed-form error rate expressions are derived using a series expansion of the modified Bessel function. In addition, detailed truncation error analysis and asymptotic error rate analysis are also presented. Numerical results demonstrate that our series solutions are highly accurate and efficient.

Performance of Non-Adaptive and Adaptive Subcarrier Intensity Modulations in Gamma-Gamma Turbulence

We investigate a variable-rate, constant-power adaptive subcarrier intensity modulation employing M-ary phase shift keying and rectangular quadrature amplitude modulation for optical wireless communication over the Gamma-Gamma turbulence channels. The adaptive schemes offer efficient utilization of optical wireless communication channel capacity by adapting the modulation order according to the received signal-to-noise ratio and a pre-defined target bit-error rate requirement. Novel closed-form series solutions are presented for the achievable spectral efficiency, average bit-error rate, and outage probability using a series expansion approach of the modified Bessel function. In addition, asymptotic bit-error rate and outage probability analyses are presented. Our asymptotic bit-error rate analysis shows that the diversity order of both non-adaptive and adaptive systems depends only on the smaller channel parameter of the Gamma-Gamma turbulence. Numerical results demonstrate high accuracy of our series solutions with finite number of terms and improved spectral efficiency achieved by the adaptive systems without increasing the transmitter power or sacrificing bit-error rate requirements.

Ergodic capacity comparison of optical wireless communications using adaptive transmissions

Ergodic capacity is investigated for the optical wireless communications employing subcarrier intensity modulation with direct detection, and coherent systems with and without polarization multiplexing over the Gamma-Gamma turbulence channels. We consider three different adaptive transmission schemes: (i) variable-power, variable-rate adaptive transmission, (ii) complete channel inversion with fixed rate, and (iii) truncated channel inversion with fixed rate. For the considered systems, highly accurate series expressions for ergodic capacity are derived using a series expansion of the modified Bessel function and the Mellin transformation of the Gamma-Gamma random variable. Our asymptotic analysis reveals that the high SNR ergodic capacities of coherent, subcarrier intensity modulated, and polarization multiplexing systems gain 0.33 bits/s/Hz, 0.66 bits/s/Hz, and 0.66 bits/s/Hz respectively with 1 dB increase of average transmitted optical power. Numerical results indicate that a polarization control error less than 10° has little influence on the capacity performance of polarization multiplexing systems.

Effective Capacity of Coherent POLMUX OWC Impaired by Atmospheric Turbulence and Pointing Errors

Effective capacity is defined as the maximum constant traffic arrival rate that a communication channel can support in order to guarantee a certain statistical delay constraint. We investigate the effective capacity performance of the optical wireless communications employing the coherent detection and polarization multiplexing over the Gamma-Gamma turbulence fading channels with pointing errors. We consider two different power adaptation techniques, namely, independent power adaptation and joint power adaptation. Closed-form effective capacity expressions are developed for both power adaptation schemes. Asymptotic analyses provide the increments of the effective capacities in the high signal-to-noise ratio regimes, in both nonstringent and stringent statistical delay constraints, for every 1 dB increase of the average transmit optical power. Our analysis reveals the superiority of the joint power-adaptation technique in order to support the stringent statistical delay constraint services over the optical wireless communication channels impaired by the strong turbulence fading and/or large pointing errors. However, the numerical results demonstrate that the performance gap between the joint and independent power adaptations becomes significantly reduced as the statistical delay constraints become loose and/or the channel impairments (i.e., turbulence fading and/or pointing error) become weak.

Error rate analysis of subcarrier intensity modulation using rectangular QAM in Gamma-Gamma turbulence

Subcarrier intensity modulation is analyzed for general order rectangular quadrature amplitude modulation over the Gamma-Gamma turbulence channels. Closed-form expressions of average symbol error rate are derived using a series expansion of the modified Bessel function and a moment generating function approach. Truncation error analysis and asymptotic error rate analysis are also presented. Numerical results demonstrate that our closed-form expressions are highly accurate.

Statistical Delay-QoS Aware Joint Power Allocation and Relaying Link Selection for Free Space Optics Based Fronthaul Networks

We propose a statistical delay quality-of-service (QoS) aware joint power allocation and relaying link selection scheme for uplink of a multichannel coherent free space optical communication-based fronthaul network. The proposed scheme assigns suitable relays and aggregation nodes to the remote radio heads and allocates transmit power among the orthogonal optical channels. Specifically, the proposed scheme maximizes total end-to-end effective capacity of a fronthaul network subject to certain transmit power budgets at both remote radio heads and relay nodes. The joint power allocation and relaying link selection are formulated as a mixed integer non-linear programing problem. We obtain near optimal solution to such an optimization problem by using Lagrangian dual decomposition and minimum weight matching techniques. Our analysis reveals that in order to maximize the aggregate end-to-end effective capacity, transmit power allocation and relaying link selection should consider both statistical delay-QoS requirements of the transmitted traffics and channel gains of the transmission links. Simulation results demonstrate that our proposed scheme improves statistical delay-QoS aware throughput in presence of atmospheric turbulence fading and pointing error.

QoS-aware and energy-aware adaptive power allocations for coherent optical wireless communications

We investigate a quality-of-service-aware and energy-aware adaptive power allocation scheme for a point-to-point and line-of-sight optical wireless communication system employing the coherent detection and polarization multiplexing. The proposed power allocation scheme minimizes the average transmit power and provides the delay aware quality-of-service guarantee through maintaining a required effective capacity over the fading channels. The power allocation scheme is formulated as a convex optimization problem, and using the sub-gradient method, a fast convergent algorithm for the optimal power allocation is proposed. Numerical results demonstrate the advantages of the proposed power allocation algorithm in terms of the energy saving for the case of having strict statistical delay constraints.

QoS-aware joint power allocations and relay selection for NLOS coherent optical wireless communications

In order to improve the energy efficiency of the optical wireless communications, a joint power allocation and relay selection scheme is proposed for a relay assisted non-line-of-sight optical wireless communication system employing coherent detection with a dual optical channel multiplexing technique. The proposed joint power allocation and relay selection scheme aims to improve energy efficiency of the optical wireless communication system by minimizing the total average transmit power, and provides the delay aware quality-of-service guarantee through maintaining a minimum required effective capacity over the atmospheric turbulence fading channels. The joint power allocation and relay selection problem is formulated as a non-convex and combinatorial optimization problem, and the solution of this optimization problem is obtained using a time-sharing relaxation technique. Subsequently, a fast-convergent algorithm is proposed for the joint power allocation and relay selection by considering the delay aware quality-of-service requirements of the services transmitted over the optical wireless communication channels. Numerical results demonstrate the advantages of the proposed joint power allocation and relay selection scheme in terms of the energy saving for different statistical delay constraints.

Statistical Delay Aware Joint Power Allocations and Relay Selection for NLOS Multichannel OWC

In order to improve the delay quality-of-service aware throughput performance of the optical wireless communications, a joint power allocation and relay selection scheme is proposed for a relay assisted multichannel coherent optical wireless communication system. The proposed joint power allocation and relay selection scheme provides the delay aware quality-of-service guarantee by maximizing the end-to-end effective capacity under the average transmit power constraints at both source as well as relay nodes. The joint power allocation and relay selection problem is formulated as a non-convex and combinatorial optimization problem, and the solution of this optimization problem is obtained using a time-sharing relaxation technique. Subsequently, a fast convergent algorithm is proposed for the joint power allocation and relay selection by considering the delay aware quality-of-service requirements of the services transmitted over the optical wireless communication channels. Numerical results demonstrate that the proposed joint power allocation and relay selection scheme provides the strict statistical delay aware quality-of-service with an improved throughput without increasing the transmit power requirements.

Effective Capacity Performance of Coherent POLMUX OWC with Power Adaptation

Effective capacity is defined as the maximum constant traffic arrival rate that a communication channel can support in order to guarantee a certain statistical delay constraint. We investigate the effective capacity performance of the optical wireless communications employing the coherent detection and polarization multiplexing over the Gamma-Gamma turbulence fading channels for two different power adaptation techniques, namely, independent power adaptation and joint power adaptation. In a polarization multiplexing system, independent power adaptation allocates transmit power to a particular channel considering only the signal-to-noise ratio statistics of that particular channel whereas the joint power adaptation allocates transmit power to a particular channel considering the joint signal-to-noise ratio statistics of both channels. Our analysis reveals the superiority of the joint power adaptation technique in order to support the stringent statistical delay constraint services over the strong turbulence fading channels compared to an independent power adaptation technique. However, the numerical results demonstrate that the performance gap between the joint and independent power adaptations gets significantly reduced as the statistical delay constraints become loose and/or the turbulence fading gets weaker.