Optical Wireless Communications: Current and Future Trends

This paper considers the transmission of data over a wireless  channel in which the transmitter converts the message into an optical signal. This optical signal is transmitted over a wireless channel which is commonly known as optical wireless channel (OWC).   The OWC  is still not regulated, i.e., no license is required to transmit over this channel.  In addition, this channel can support communications with very high data rates. Further, in its construction, cheap components like light emitting diode (LED) is normally exploited. These factors attractive both the researchers and the industry field to develop a practical transceivers. In this paper, we initially review the basics of this systems, the benefits of using such a  system.  Then, the current applications are introduced and summarized. Finally, many potential applications are represented. Keywords: Optical Communications, Wireless Communications, Communication Channel

Two-way multiple relays channel: achievable rate region and optimal resources

This paper considers a communication model containing two users that exchange their information with the help of multiple parallel relay nodes. To avoid interference at these common nodes, two users are required to transmit over the different frequency bands. Based on this scenario, the achievable rate region is initially derived. Next, an optimization scheme is described to choose the best relays that can be used by each user. Then, two power allocation optimization schemes are investigated to allocate the proper average power value to each node. Finally, comparisons between these two optimization schemes are carried out through some numerical examples

Capacity of Gaussian Relay Channel with Orthogonal Components and Non-causal Interference at the Source

In this work, we consider a relay channel model, with an out-of-band relay, in which the interference signal is available non-causally only at the source. The case in which the relay operates over different frequency bands with respect to the direct link is investigated. In particular, the source-destination (S-D), the source-relay (S-R) and the relay-destination (R-D) links are designed to be pairwise orthogonal. This may model a communication scenario in which the direct link (S-D) is parallel to the multihop channel (S-R-D). For this channel model, we establish the capacity of the Gaussian relay channel by showing that the developed upper and lower bounds are equal. In particular, the capacity results are obtained in which the relay may operate in either a full-duplex mode or a half-duplex mode. Keywords: Relay Channel, Decode and Forward, Orthogonal Transmission Bands, Gaussian Channel

On Optimal Power Allocation for Gaussian Broadcast Channel

We derive the optimal power allocation for Gaussian two users broadcast channel. To find the optimal power allocation between the two users, two optimization schemes are considered. In each optimization scheme, an analytical expression for the optimal power allocation between the two users is derived. The first optimization criterion finds the optimal power allocation between the two users such that they have equal rates. Then, the optimal power allocation that maximizes the sum rate capacity is studied. In addition, numerical examples are provided to verify the optimality of the derived schemes. Keywords: Gaussian Broadcast Channel, Capacity Region, Optimization

A simple Encoding Scheme to Achieve the Capacity of Half-Duplex Relay Channel

In this paper, the Half-Duplex Relay Chan- nel (HDRC) is thoroughly investigated. Even though this channel model is widely studied, the capacity is not yet fully understood and particularly has not been tightly expressed. In this work, a new capacity ex- pression of the discrete memoryless HDRC is explic- itly established. In particular, a new expression of the achievable rate is derived by taking advantage of the well-known capacity results of both the degraded broad- cast channel and the multiple access channel. Specifi- cally, in order to obtain the achievable rate, the trans- mission from the source to destination is operated over two phases. In the first phase, the broadcast phase, the source broadcasts to both relay and destination. In the second phase, both source and relay transmit to des- tination to form multiple access channel. Then, we prove that the new achievable rate meets the cut-set outer bound such that the capacity of the discrete mem- oryless HDRC is attained. Next, the new derived ca- pacity result is extended to the case of additive Gaus- sian channel. Further, the attained capacity is ana- lytically and then numerically shown to encompass all well-known available findings in the literature. Addi- tional numerical examples are also shown to present the cases in which the relay is beneficial and how the achievable capacity varies with the source-relay and relay-destination channel gain

Geometric Probability Analysis of Meeting Probability and Intersection Duration for Triple Event Concurrency

This study investigates the dynamics of three discrete independent events occurring randomly and repeatedly within the interval [0,T]. Each event spans a predetermined fraction γ of the total interval length T before concluding. Three independent continuous random variables represent the starting times of these events, uniformly distributed over the time interval [0,T]. By employing a geometric probability approach, we derive a rigorous closed-form expression for the probability of the joint occurrence of these three events, taking into account various values of the fraction γ. Additionally, we determine the expected value of the intersection duration of the three events within the time interval [0,T]. Furthermore, we provide a comprehensive solution for evaluating the expected number of trials required for the simultaneous occurrence of these events. Numerous numerical examples support the theoretical analysis presented in this paper, further validating our findings