Effect of the incident angle of a transmitting laser light on the coverage of a NLOS-FSO network

Abstract

In this paper, we propose a model of the coverage and achievable data rates in No Line-of-Sight Free-Space Optical Communications (NLOS-FSOC) as a function of the angle of incidence. NLOS-FSOC uses diffuse reflected light to establish communication between two or more stations that are with or without line-of-sight to each other. Different from free-space optical communications (FSOC), NLOS-FSOC uses a diffuse reflector (DR) between a transmitter and a receiver so that LOS is not required between them but between the station and the DR. Unlike a mirror, the DR reflects the incident light to all directions but to itself and that reflection broadcast the optical channel to all receivers within LOS. The optical broadcast channel establishes a true optical local area network (OLAN). However, the reflected power and the coverage of an OLAN largely depend on the angle of incidence of transmitted laser beam. Therefore, the planning and building of an OLAN with NLOS-FSOC must consider this angle to optimize coverage, to set range, or to estimate the achievable communication data rates.The proposed model and presented analysis center on an outdoor urban setting where mobile stations, represented by cars, travel through a city street. In such scenario, we estimate the average reflected power at the DR, the received power at different locations of the covered area, and their achievable communication data rates for downlink and uplink communications. With the consideration of mobile stations, we identify different displacement configurations that represent the different traveling paths of a mobile station with respect to a DR configuration on the urban scenario. Our extensive numerical evaluations on the different traveling and location scenarios show the effect that the incidence angle has on the coverage, the achievable data rates on an OLAN, and highlight the pros and cons of each different displacement. These results also show the options for the placement and orientation of the DR and ground optical base stations for an effective and extensive coverage and the signal quality of transmissions made by mobile stations traveling through the covered area in an NLOS-FSOC OLAN.