One of the benefit of the Radio-over-Fibre engineering is able to show in long distance communicating that are requires the usage of optical fiber links to administer RF signals from a Central Station ( CS ) to Base Stations ( BS ) . In optical systems affecting RoF engineering, Sub-Carrier Multiplexing ( SCM ) is used to increase optical fibre bandwidth use. In SCM, several microwave subcarriers, which are modulated with digital or linear informations, are combined and used to modulate the optical signal, which is so carried on a individual fibre. On the other manus, Wavelength Division Multiplexing ( WDM ) is a multiplexer at the sender to fall in the signals together, and a demultiplexer at the receiving system to divide them apart. In order to execute RoF system cost-efficient this paper is proposed the public presentation analysis of 150km Single Mode Fiber ( SMF ) that are deploying in the SCM/WDM RoF system. The consequence is present higher bandwidth for long distance communicating system ( SMF, 150 kilometer ) by utilizing SCM/WDM for Radio over Fiber. Therefore, the public presentation of 150km use is expected to be much better than conventional optical SCM.
Keywords: Optical Communication, Cellular Communication, SCM, WDM, SMF, RoF, Wireless Communication
The explosive growing of the cellular communicating and wireless communicating and the success of 3.5G systems with WIMAX have had a brooding impact on our perceptual experience of communicating. The demand of being communicating ( ever on, communicating anytime, anyplace ) has impact on the bandwidth demand. The recent of services in cellular communicating that provided by cellular operator that endeavoring to supply the big bandwidth that dependable to busy the demand of user. In other manus, the operator had to cut down the cost that are rises from the applied or extend the systems.
In order to get the better of of bandwidth restriction in radio and cellular communicating Radio over Fiber has offering engineering that is cost-efficient. RoF engineering requires the usage of optical fiber links to administer RF signals from a Central Station ( CS ) to Distributed Antenna Units ( DAUs ) or Base Station ( BS ) . In optical and wireless communicating, RF signal processing maps such as frequence up-conversion, bearer transition, and multiplexing, are performed at the BS or the Radio Access Point ( RAP ) , and instantly fed into the aerial. RoF makes it possible to centralise the RF signal processing maps in one shared location ( CS ) , and so to utilize optical fiber, which offers low signal loss ( 0.3 dB/km for 1550 nanometer, and 0.5 dB/km for 1310 nm wavelengths ) to administer the RF signals to the DAUs. The centralisation of RF signal processing maps enables equipment sharing, dynamic allotment of resources, and simplified system operation and care.
Figure 1: Position of SCM/WDM RoF Technology
150km SCM/WDM Radio over Fiber Architecture
In this work, we propose the integrating the deploying of 150km SMF into the SCM aa‚¬ ” RoF techniques with WDM to analyse the public presentation of word picture. The ends are to better the optimisation of the SCM and WDM for bandwidth utilizing in the base Stationss ( BS ) and command station ( CS ) . The system modeled by utilizing commercial optical system simulation package, OptiSystem, with sing practical system parametric quantities. The theoretical account was setup in two parts, is the sender and the receiving system.
In linear optical systems including RoF engineering, Sub-Carrier Multiplexing ( SCM ) is used to increase optical fibre bandwidth use. In SCM, several microwave subcarriers, which modulated with digital or linear informations, are combined and used to modulate the optical signal, which is so carried on a individual fiber [ 1 ] , [ 2 ] . This makes RoF systems cost-efficient.
Basically the operation of the bomber bearer multiplexing ( SCM ) was similar to Time Division Multiplexing ( TDM ) , such that TDM is normally used in digital transmittal system. On other manus, SCM play an of import function in linear transmittal system, nevertheless multiplexing more handily carried out in frequence sphere.
The chief thought of the SCM is uniting two-step of transition that is runing at different sphere. First transition occupied at RF portion such that several low bandwidth RF channel transporting parallel or digital signal add up together by utilizing multiplexer. Thus the signal will be really near to each other in the frequence sphere depending to local oscillator frequence that applied in the transition portion. This combined signal really modulated onto higher frequence microwave bearer. The up-converted signals are in different frequence sets hence combined by a microwave power combiner organizing a microwave subcarrier multiplexed composite signal. Second transition occupied at optical sphere, the modulated signal so convert to optical sphere by utilizing optical maser rectifying tube and optical modulator.
The usage of Wavelength Division Multiplexing ( WDM ) for the distribution of RoF signals has gained importance late. WDM enables the efficient development of the fiber networkaa‚¬a„?s bandwidth. However, the transmittal of RoF signals is seen as inefficient in footings of spectrum use, since the transition bandwidth is ever a little fraction of the bearer signal frequence. Therefore, methods to better the spectrum efficiency have been proposed [ 3 ]
Soon, RoF engineering is applied chiefly in SMF-based systems. For MMF-RoF systems, merely the IM-DD attack for WLAN applications has been reported. The reported signals transmitted over such links are by and large below 6 GHz. Therefore, sing the increasing importance of in-building coverage for wireless systems, the demand for high-frequency signal distribution over multimode fiber, which constitutes the chief in-building fiber substructure, becomes every bit of import.
In order to get the better of losingss and fading, SMF was presenting as a anchor for cellular communicating. In this nexus the types of the SMF find how signal travels over the nexus with the degree of quality. Choosing the incorrect and unsuitable fibre into the system can be so much fading and scattering being. Therefore, a individual manner fibre was the perfect lucifer for this system harmonizing to the feature of the fibre. A individual manner fibre conducts merely one manner and capable to extinguish higher order manners. Attenuation in a individual manner fibre is smaller than in a multimode fibre because in the individual manner fibre less light will meet soaking up and scattering effects. However, fading ( macro flexing consequence ) in individual manner fibre additions as operating wavelength additions and flex radius lessenings.
Figure 2: The SCM/WDM RoF System Model Communication Link
In this SCM/WDM RoF system theoretical account, we performs of each IA» contains 16 channel of Phase Shift Keying ( PSK ) with the spot rate is 1.8 Gbps, Mach-Zehnder Modulator with the bandwidth 20 GHz and 1550 nanometer of Laser Diode. The frequence of RF channel has set from 1.8 GHz to 27 GHz. The RF signal is used to straight modulate the optical maser rectifying tube in the Central Station ( CS ) . The ensuing strength modulated optical signal is so transported to the WDM over the length of the fiber to the BS. In the fibre ocular nexus, the signal so pre-amplified by EDFA ( 1-5m ) to gained the better perform in the receiving system. At the BS, the familial RF signal is recovered by direct sensing in the PIN photodetector. The signal is so amplified and radiated by the aerial.
Consequences and Analysis
The systems are designed integrated three portion sphere of the system. Mm-wave spheres are generated by using of RF channels as SCM, Optical signal bearer is bring forthing by Mach Zehnder Modulator and Multiplexing are construct by Wavelength Division Multiplexing. The mm-wave consist of 16 RF channels and separate into 2 SCM group. MZM generates of 20 GHz optical signal. A WDM ideal has 50 GHz channel spacing. Those systems are considered in bandwidth nowadays. By concentrating how to increase the bandwidth, we proposed the combine of SCM techniques applied into WDM engineering. In this simulation the parametric quantities was setup to mensurate the capacity in the systems such as SNR, BER, Number of Carrier, etc. The purpose of the SCM/WDM system afforded the bandwidth capacity of the fibre.
Figure 3 illustrates the SNR public presentation to the some assorted distance links 150 kilometer. In 150 kilometer SNR, some channels of SCM fall down from 30 dubniums closed to 5 dubnium over the distance nexus. It is intending that an mistake chance for SNR is additions harmonizing to the fibre length. SNR in optical nexus communicating was used to measure the minimal energy per pulsation that is required to accomplish a prescribed maximal bit-error rate. SNR depend on the entire noise in the systems. Entire noise is accumulated from changeable noise, thermic noise, shunt noise and series noise. These parametric quantities have an consequence on BER and Q factor. So the Q factor is related to the signal-to-noise ratio required to the desire spot error rate.
Figure 3: The SNR public presentation of PSK Channel in 150km
Figure 4 shows the BER public presentations of all electrical bearer frequence across 1 kilometer until 150 kilometers with length of EDFA 5 m. The SCM-1 is illustrated in Figure 4 ( a ) , for channel 1, 2 and 6 the optimal fibre length is 30 kilometer. For channel 4 and 8 the optimal fibre length is 75 kilometer. Note that the being of EDFA someway affected the public presentation of the system in term of BER. In the SCM-2, the channels are arbitrary ( fluctuate ) in unsystematic line due to highest bit-error rate, as shown in Figure 4 ( B ) . The preamplifier in optical sphere has a primary drawback that call as Amplified Spontaneous Emission ( ASE ) noise. This sort of noise non merely impact the BER but able to degrade CNR of the system.
( a ) BER of 8 PSK-SCM/WDM RoF Channels 1
( B ) BER of 8 PSK-SCM/WDM RoF Channels 2
Figure 4: Minimum of BER of SCM/WDM aa‚¬ ” RoF SMF 150km
The power of standard signal nevertheless were to little and will contributed to the uneccepted Carrier-to-Noise Ratio ( CNR ) . Therefore, an electrical amplifier encounter this job that can be reserved the amplified end product signal as shown in Figure 5 below.
Figure 5: 60 GHz of RF spectrum are detected by PIN exposure sensor
In this portion, we present the attaining of the RF bandwidth results from the SCM/WDM-RoF system. By using an external transition of utilizing Mach-Zehnder Modulation, wholly gain bandwidth of MZM is 20 GHz we derive 60 GHZ of RF bandwidth spectrum as shown in Figure 5. The entire capacity of RF bandwidth was increased by use the figure of channels.
The public presentation of the SCM/WDM for RoF is resolved by many factors such as BER, SNR, Power, deformation and fading. In this works 16 channels of SCM are employed to the WDM over 150km SMF fibre. An external transition of MZ Modulator was utilized to obtain optical bandwidth. And the WDM employed multiplexing/demultiplexing of RF signal that carried by optical signal bearer to decide the immense bandwidth. The results of bandwidth was increased to 60 GHz by using of 16 Channel of SCM combined with WDM in optical fibre nexus.
The writers acknowledge the Ministry of Science, Technology and Innovation Malaysia for the fiscal support through E-Science support 01-01-06SF0064. Our gratitude besides goes to the disposal of Universiti Teknologi Malaysia ( UTM ) particularly for Research Management Centre ( RMC ) for the fiscal support through ballot figure 79026.