Mona Aggarwal

Outage and Error Rate Analysis of Network-Coded Coherent TWR-FSO Systems

This letter investigates a two-way relay assisted coherent free space optical system when the optical beam is subjected to gamma-gamma atmospheric turbulence and misalignment errors (pointing errors). A half-duplex relaying system consisting of two terminal nodes and a bidirectional relay is considered. The relay is based on decode-and-forward protocol and employs linear network coding to establish communication between the two terminal nodes in two time slots. Coherent detection with M-ary phase shift keying is employed. Closed form expressions for system outage and error performance for both binary and nonbinary cases are derived in terms of the well known Meijers G-function and are mathematically analyzed.

Dual-Hop Optical Wireless Relaying Over Turbulence Channels With Pointing Error Impairments

In this paper, we present analytical expressions for the performance of dual-hop urban optical wireless communication system under the combined influence of atmospheric turbulence induced-fading and misalignment-fading (pointing errors). The system employs an amplify and forward relay with the assumption that channel state information is available at transmitting as well as receiving terminals. The atmospheric turbulence channels are modeled by independent but not necessarily identically distributed (i.n.i.d) Gamma-Gamma fading statistics with pointing error impairments. Using a tight upper bound for the end-to-end signal to noise ratio of the system, we derive the novel closed form expressions for the moment generating function and probability density function all in terms of Meijers G-function. Based on the aforementioned statistical results, accurate closed-form expressions for average symbol error rate for M-ary phase shift keying modulation schemes, outage probability and the ergodic capacity under four adaptive transmission policies namely optimal rate adaptation, optimal power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate are derived in terms of Meijers G -function function. Finally, the proposed mathematical analysis is accompanied with various numerical examples to demonstrate the effect of different system parameters on the system performance.

Analysis of subcarrier intensity modulation-based optical wireless DF relaying over turbulence channels with path loss and pointing error impairments

The authors consider a subcarrier intensity-modulated relayed optical wireless communication system under the combined influence of path loss, atmospheric turbulence and pointing error impairments. The turbulence-induced fading is modelled by independent but not necessarily identically distributed (i.n.i.d.) Gamma–Gamma fading statistics where the relaying protocol followed by the system is decode and forward (DF). First, the statistics of instantaneous signal-to-noise ratio at the destination is derived, followed by the novel and exact closed-form expression for outage probability of the system. Then using the moment generating function-based approach, the authors evaluate error performance of the system in terms of average symbol error rate (SER) for M-ary phase shift keying modulation schemes. Further, as a special case for M = 2, that is, binary phase shift keying modulation scheme, the exact closed-form expression of average SER is derived in terms of mathematically tractable Meijers G-function and extended generalised bivariate Meijers G-function. Finally, at the end of the paper, various numerical examples are included to demonstrate the effect of different system parameters on the performance of the system and are verified by Monte-Carlo simulations.

Ergodic Capacity of SIM-Based DF Relayed Optical Wireless Communication Systems

In this letter, we consider a dual-hop, subcarrier intensity modulation-based relayed optical wireless communication system under the combined influence of atmospheric turbulence and pointing error impairments. The turbulence-induced fading is modeled by independent but not necessarily identically distributed Gamma-Gamma fading statistics with misalignment fading. The relaying protocol followed by the relay is decode and forward. We first, derive the statistics of instantaneous signal-to-noise ratio at the destination, followed by the novel and exact analytical expressions for ergodic capacity of the system in terms of mathematically tractable Meijers G-function and extended generalized bivariate Meijers G-function.

Analysis of spectrally efficient two-way relay assisted free space optical systems in atmospheric turbulence with path loss

In this paper, we investigate the performance of two-way relay assisted free space optical systems over atmospheric turbulence-induced fading channels affected by molecular absorbtion-induced path losses. A three node, dual-hop, bi-directional, half-duplex relaying system with independent but not necessarily identically distributed channels is considered. Spectral efficiency is achieved by employing network coding to complete data transmission in two-time phases. Closed form expression for system outage performance is derived considering decode-and-forward protocol. Additionally, the error performance in terms of average symbol error rate for M-ary phase shift keying is evaluated. Further, the net achievable capacity of the system is also calculated. Copyright

Multiple user pair scheduling in bi-directional single relay assisted FSO systems

This paper investigates a free space optical (FSO) communication system with multiple user pairs sharing a single relay over atmospheric turbulence induced fading channels effected by path loss. Multiuser diversity is achieved by applying various scheduling schemes at the relay. The performance of various scheduling schemes based on selection combining (SC) diversity and switched diversity are evaluated for the considered dual-hop, bi-directional, half-duplex relay system with network coding. Closed form expressions for the outage performance for different scheduling schemes have been derived.

Asymptotic Analysis of TWR Assisted FSO Links With Partial Dual-Relay Selection

In this letter, a partial-dual relay selection (P-DRS) scheme is proposed for amplify-and-forward protocol based two-way relay (TWR) assisted free space optical (FSO) communication systems. Closed form asymptotic expression is developed for the moment generating function (mgf) of the equivalent signal-to-noise ratio of the system, considering an optical channel that is modeled by the Gamma-Gamma distribution and affected by path losses and pointing errors. Expressions for the outage probability and average error probability are calculated based on the mgf. Finally, the mathematical analysis is accompanied with simulations to demonstrate the effectiveness of the proposed P-DRS scheme.

Partial Dual-Relay Selection Protocols in Two-Way Relayed FSO Networks

In this paper, we present relay selection protocols for parallel relayed free-space optical (FSO) communication network, which consists of two non-line-of-sight terminal nodes and multiple two-way relays (TWR). The TWRs use the two time-phase decode-and-forward relaying protocol to establish a bidirectional link between the terminals. For the considered system, we propose a partial dual-relay selection (P-DRS) scheme, in which two TWRs are selected to participate in the communication process. By using two TWRs, the advantages of cooperative diversity are achieved. For the proposed relay selection scheme and assuming Gamma-Gamma fading channels with pointing errors and path loss, we derive an exact closed form expression for the system outage. Further, we derive an asymptotic expression for average error probability. The diversity order of the system is also presented. It is shown by numerical analysis that by using the proposed P-DRS scheme, the system performance can be significantly improved.

Two-Way Relay Selection in Multiple Relayed FSO Networks

In this letter, a parallel relayed free-space optical (FSO) network is considered. The network consists of multiple half-duplex amplify-and-forward two-way relays (TWRs), that assist in establishing communication between two distant nodes. A single TWR that maximizes the achievable-rate of the network is selected to participate in the communication process. Assuming that the optical channel is affected by path loss, misalignment errors, and atmospheric turbulence, we derive exact and asymptotic closed form expressions for the achievable-rate and the relay with the maximum achievable-rate is selected for communication.

Outage analysis of a variable-gain amplify and forward relayed mixed RF-FSO system

In this work, we present the outage analysis for a variable gain amplify-and-forward relayed dual-hop link that comprises of a radio frequency (RF) first-hop link and a free space optical (FSO) link for the second-hop. We assume that no direct RF and FSO link exists between the source and destination nodes. The RF link experiences a composite multi-path fading and shadowing effects, and is modeled by Generalized-K fading distribution, whereas, the atmospheric turbulent FSO channel follows the Gamma-Gamma distribution statistics. Further, significant pointing error impairments are assumed to be present over the FSO link. The analytical closed form expressions for the outage performance of the system model under consideration are derived and illustrated by numerical plots.