RADIO OVER FIBER (ROF) SYSTEM FOR OPTICAL COMMUNICATION SYSTEM APPLICATIONS

Project ieee format should include the following items (Abstract, Introduction, System block

diagram (or SYSTEM DESIGN), System Advantages, Conclusions and reference. [NOT more

than 5 pages].

Abstract

Radio-over-Fiber (ROF) refers to a technology which use light to modulate electrical signals

(radio signal) and transmit it over an optical fiber link to facilitate wireless access, such as 3G

and WiFi simultaneous from the same antenna. In other words, radio signals are carried

over fiber-optic cable. Thus, a single antenna can receive any and all radio signals (3G, Wifi,

cell, etc..) carried over a single-fiber cable to a central location where equipment then

converts the signals; this is opposed to the traditional way where each protocol type (3G,

WiFi, cell) requires separate equipment at the location of the antenna. ROF technology able

to transport the RF signal over few kilometres with minimal loss. High frequency signal is

more challenging in ROF because it requires high frequency components and large link

bandwidth. This paper portrayed about the ROF architecture and challenges and

development issues of ROF technology.

Keywords: RoF,

3.2 ROF Technology Structure for Outdoor Mobile Communication

In outdoor mobile communication, the mm-band frequency considered for future

mobile communication. The range of Millimeter-band frequency is 60 GHz. Direct

modulation only function within Millimeter -wave frequency. Thus, external modulation or

heterodyning techniques must be used in order to generate the mm-band frequency. In

external modulation, Machzehnder modulator used to optical modulate the RF signal and

optical carrier. The drawback of this system is chromatic dispersion due to double-sideband

transmission. Therefore, the most popular technique can be heterodyning technique.

There are 3 technique for heterodyning modulation. The first technique involve two

DFB laser with the operating range of 1550 nm as a master slave arrangement to produce RF

signal are used in CBS. The main disadvantage of this method is that it is not amendable to

all modulation format or modulation bandwidth and also chromatic dispersion is created in

the signal because of mixing optical carriers with RF signal at the CBS.

In the second technique, similar to first method the RF carrier using two master

slaves DFB. However, in this technique data is not mixed with the RF signal and

upconversion with the data is taken place in the RBS using conventional electrical mixer or

in simpler arrangement using optoelectronic mixer. Therefore, separate pair of laser source

and photodiode is needed to transmit the data and carriers.

3.3 Perspective of ROF Mobile Communication

3.4 Remote Base Station antenna (RBS)

The RBS consists of Eletroabsorbtion modulator, remote antenna, diplexer, high

power amplifier, low noise amplifier and Power supply. However, the trend of ROF system is

simplifying the RBS and changing it to passive unit.

Figure : The block diagram of remote base station (RBS)

FIGURE 1. Simplified schematic of a RoF system. LD: Laser diode. BS: Base Station. RAU:

Remote Access Unit. BPF: Band-pass filter. Amp: Electrical amplifier.

In radio-over-fiber (RoF) systems, optical fibers transmit RF signals between Central

Office (CO) and Remote Access Unit (RAU). This system makes it possible to transmit the RF

signals with much lower loss and broader bandwidth than the coaxial cable, and is very

useful for future high-speed wireless transmission systems. RAUs can be simplified

significantly, as they only need to perform optoelectronic (O/E) conversion and filtering and

amplification functions. In order to increase the capacity and to implement advanced

network features we may use Wavelength Multiplexing Techniques (WDM). This allow lower

cost system operation and maintenance.

The CO and the RAU perform electro-optical (E/O) and opto-electronic (O/E)

conversion of wireless signals respectively. E/O conversion is achieved by employing either

directly modulated laser sources or external electro-optic modulators. O/E conversion is

done employing photodetectors or photoreceivers.

The most successful application of RoF technologies is the transmission of wireless

standards over optical fibre links in centralized architectures, also known as distributed

antenna systems (DAS) for both indoor and outdoor applications. The broad bandwidth of

the optical fibre facilitates standard- independent multiservice operation for cellular

systems, such as GSM, UMTS, wireless LAN (WiFi 802.11 a/b/g/n) and also for emerging

technologies WiMAX and Ultra-wideband (UWB).

Benefits of Radio over Fiber System

The radio over fiber technology has many advantages over the conventional optical

communication system:

(i) Low Attenuation Loss: Commercially available standard Single Mode Fiber

(SMFs) made from glass (silica) have attenuation losses below 0.2 dB/km and

0.5 dB/km in the 1.5 μm and the 1.3 μm windows respectively.

(ii) Reduced Power Consumption: Reduced power consumption at the RAU

because most of the complex equipment keep at the CO

(iii) Large Bandwidth: RoF technology is used to increase optical fiber bandwidth

utilization.

(iv) Immunity to Radio Frequency Interference: EMI is a very attractive property

of RoF technology, especially for microwave transmission.

(v) Easy Installation and Maintenance: In RoF systems, complex and expensive

equipment are kept at the head end, thereby making the Remote Antenna

Unit (RAUs) simpler.

(vi) Multi-Operator and Multi-Service Operation: RoF distribution system can be

made signal-format transparent.

(vii) Dynamic Resource Allocation: In a RoF distribution system for GSM traffic,

more capacity can be allocated to a certain area during the peak times and

then reallocated to other areas when off-peak