Wireless Optical Telecommunications

Chapter 6

Indoor Optic Link Budget

“Light is an old friend that has fascinated me ever since I can remember”

Jeff Hecht,

Understanding Fiber Optics,

Prentice Hall, Upper Saddle River, 2002

6.1. Emission and reception parameters

For indoor (propagation limited to contours of a room) or outdoor communication, a detailed analysis of the assessment of connection (link budget) is a very significant step for any system. For example, for the systems with optical fibers, the engineer examines the power which is injected into fiber by the transmitter and then determines all the potential losses and gains until the signal arrives on the reception device. The receiver typically has a specific sensitivity (S_e) to a given throughput. This sensitivity represents the lower limit of the optical level of power rather than the reception for a quality of preset transmission. To guarantee the required quality of service (QoS), it is necessary to make sure that after having withdrawn all the losses, the received power remains above the sensitivity of the receiver. To make the connection more resistant, it is judicious to work on a level of power in reception slightly higher than the necessary minimum capacity: the variation is called margin and constitutes a reserve of power used in the event of degradation of the channel. This step represents the compromise between the distance from transmission and the reliability of the communication.

Like the devices in the field of radio or fiber optics, ...