Free space optics with the increased noise stability.
ABSTRACT
Author: Michailov I.V.
Topicality of the work
One of basic problems at construction of modern digital networks (it can be LAN, telephone networks, etc) is the problem of a channel equipment choice. One of perspective, but at the same time not enough explored, variants is use of wireless communication technology, FSO (Free Space Optics). FSO technology has the following advantages:
- Data transfer speed can reach several Gbit/s
- bit error frequency (BER) is from 10e-10 to 10e-9
- In one of the countries the license for use of a range of frequencies is not required
- Practically absolute protectability from radio noise (radio noise can influence only directly the terminal equipment)
- Small (about several hours) time of installation
- Smaller in comparison with other similar on throughput decisions cost
Lack of presents FSO is the high bottom limit of system cost. Cheapest on the today's moment FSO ÁÎÊÑ - 10ÌË (50 – 250m, 10Mb/s) has cost $1200. In Europe or America price is on the order higher .(Flight Path 20/200, 200m, up to 20 Mbit/s, $24000). It is explained to that at present majority FSO are offered as main network devices.
Other constraining factor is the mistrust to FSO, that is explained by novelty of technology and dependence on weather conditions. For its overcoming it is necessary to use various methods of increase of FSO reliability, in particular to use protective coding , cryptographic protection etc.
Thus there is a question on development reliable and functional, but in this time cheap FSO.
Research and development purpose
The following requirements to the developed equipment FSO are put:
- FSO cost should not exceed $ 1000. Optimum cost is about $ 200 - $ 500.
- Range of communication is 200 - 300 m. Probably up to 1 km.
- It is necessary to realize one of the basic advantages all modern FSO transparency for the network protocols of a channel level. In this case the most simple way of introduction FSO in structure of a network inclusion of optical system in break of hard-wire channel is possible.
- The FSO terminal devices should have the allocated structurally block of the agreement with hard-wire channel parameters.In this case it is possible without changing in realization of other part of FSO, but offering various variants of the agreement block , it is possible to realize interfaces with various hard-wire channels (10BASE-T, 100BASE-T, 10BASE-FL, RS-232, USB etc.)
Separately there is a question on research of various methods of increase of FSO noise stability, in particular of noiseproof coding and control above integrity of the transmitted data.
Structure of FSO hardware
The following structure of the terminal device (TD) of FSO channel was developed.
The module of noiseproof coding (MNC) carries out logic transformation of the data. Structurally MNC can be realized as the microcontroller or FPGA.
The interface module are intended for the agreement of network signals with the bus of MNC.
The modulator is intended for light waves oscillator management in according to signals acting from MNC.
For the control of a condition and work of FSO control module is bring in.
The further work
As result of development will be FSO, that satisfy to the above described requirements. A some intermediate researches is necessary for achievement of this purpose.
The construction of program model of environment is necessary for the further modeling of FSO.
It will allow to determine at a theoretical level successful circuit technique decision and algorithms.
After that testing the chosen decisions on a breadboard model and realization of the final device is possible. |
