SCM Optical Communication System
Implementation without Optical Isolators
Luís M. M. Mendes ([email protected])
Escola Superior de Tecnologia e Gestão, Alto Vieiro, Morro do Lena, P-2401-951 Leira, Portugal
Henrique J. A. da Silva ([email protected])
Instituto de Telecomunicações, DEE/FCTUC, Universidade de Coimbra, Pólo II, P-3030-290 Coimbra, Portugal
Abstract
OPTICAL LINK PERFORMANCE
This poster describes the design and performance
of a sub carrier multiplexing (SCM) subsystem used in
the optical links between base stations (BS) and the
central node (CN) of a mobile communications system.
The SCM subsystem uses the 1.91-2GHz
bandwidth, with the sub carriers modulated in phase
shift keying (PSK). We demonstrate that there is no
need of optical isolators, allowing a substantial cost
decrease for this kind of systems.
Linear performance
|S22|
|S11|
|S21|
INTRODUCTION
The functional diagram of the downlink is
represented in figure 1, where Tx is the optical
transmitter, APC is the automatic power control
subsystem, and Rx is the optical receiver.
Transmited
signal
RFIN
Tx
E/O
OPT
Rx
O/E
Received
signal
|S21|
Figure 2 – S parameters of the implemented system.
Noise and non linear performance
RFOUT
-115dBm/Hz
50dB
APC
Figure 1 – Block diagram of the implemented system.
The target specifications of the SCM optical
communication system are represented in Table 1.
Figure 3 – a) Noise in the system bandwidth, and
b) intermodulation distortion.
CONCLUSION
From the above results we may conclude that we
have built an almost transparent SCM optical link,
which has the following main properties:
•Negligible linear distortion
•Negligible non linear distortion,
•Gain of approximately 1.5dB
•50 cascade compatible system.
•Links with maximum length of 55.3km.
Table 1 - Overall specifications of the SCM optical
communication system.