Radio Over Fibre Using Uwb Computer Science Essay

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UWB (Ultra Wideband) is a radio technology which uses very low power for communications in a high data rates (could be 480 Mbps) over a wide bandwidth in a short distance (less than 10 meters). UWB is the ideal solution for wireless streaming multimedia at home or office environment and in a personal area networks PAN, also it can be used in radars.

UWB system is defined by the Federal Communications Commission (FCC) as any radio system that has a bandwidth larger than 20% of its centre frequency, or has a bandwidth equal to or larger than 500 MHz. FCC also allocates the unlicensed frequency band between 3.1 and 10.6 GHz (7.5 GHz) for UWB wireless communication indoor systems. The maximum allowable power spectral density (psd) for UWB transmission is -41.3 dBm/MHz. This means approximately 0.5mW of average transmit power when the entire 3.1-10.6 GHz band is used.

UWB Advantages

UWB has many advantages over the traditional narrowband communication systems as follow:

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The major advantage is the channel capacity improvement. According to Shannon's capacity limit equation shown below, channel capacity increases linearly with the bandwidth while it increases exponentially with the signal power. Because of that UWB is capable on transmitting high data rates with using low power.

Ben Manny & Kevin Kahn. Ultra-Wide-Band / a Disruptive RF Technology? Spring'02 Intel Developer Forum Conference.

As it is shown, UWB is effective in the short range of up to 10 meters.

Another advantage is UWB may be has also lower cost architectures than narrow band radios. Narrow band architectures use high quality oscillators and tuned circuits to modulate and de-modulate information. UWB transmitters, however, can directly modulate a baseband signal reducing some components. On the other hand, UWB receivers may require more complex architectures but it can take advantage of digital signal processing techniques. Implementing digital signal processing techniques with the same low cost CMOS processes used for microprocessors will enable radio solutions that scale in cost/performance with digital technology.

Also, UWB is robust for fading and interference. The wide-band nature of UWB reduces the effects of random time varying amplitude fluctuations. Also, multipath components can be resolved and used to improve signal reception with UWB technology. UWB also promises more robust immunity to co-channel interference and narrowband jammers.

Radio over Fibre using UWB

In general, Radio over Fibre (RoF) refers to a technology whereby light is modulated by any radio signal and transmitted over an optical fibre link and transmitted again as a wireless signal. The term RoF is usually applied when a wireless access is required.

In RoF systems, wireless signals are transported in optical form between a central station and a set of base stations, after that it will be radiated with the needed wireless technique. Each base station can communicate over a radio link with the mobile stations located within the radio range of this base station.

In UWB radio over fibre, there is a challenging problem of low-cost and high performance conversion of high data rates modulated communication signals from optical mode (over single mode and multimode fibre) to radio frequency mode and vice-versa.

UWB over Fibre Architecture

There is much possible architectures to be adopted but the main idea is to connect two or more UWB nodes together with optical fibre. Each node has to have optical to electrical converter (O/E) and electrical to optical converter (E/O). Each node (Access Point) transmits and receives UWB signals to the user's device located at the range of the node. Figure below simplified this concept.

Fig 2 - UWB over fibre architecture

Moshe Ran, Yossef Ben Ezra, Motti Haridim, and Boris. I. Lembrikov, Holon Institute of Technology (H.I.T), Ultra Wideband Radio over Optical Fibre

Aims and objectives

The aim from this dissertation is to study the possibility of connecting UWB user to a far UWB base station using another high bandwidth technique to keep the benefit of UWB high data rates.

The most effective method is to use the high bandwidth optical fibre and implement a radio over fibre to achieve high speeds. Figure below illustrates the block diagram of this idea. The results of the SNR and the BER will show us the possible lengths of the optical fibre which could be used to achieve this target.

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UWB Base station

UWB Access Point

Optical Fibre

UWB User

Wireless

Fig 3 - Optical over Fibre using UWB diagram

The objectives will be

Background studying for UWB (Ultra WideBand) technique.

Background studying for optical fibre.

Background studying for Radio over Fibre.

Designing and implementation for a MatLab code for Optical over Fibre using UWB.

Analyse the results of the system performance.

Writing a whole report about this subject.

Literature review

1) Moshe Ran, Yossef Ben-Ezra, and Boris Lembrikov H.I.T - Holon Institute of Technology, "Ultra-Wideband Radio-over-optical Fibre: technologies and applications"

This paper investigates the concepts, technologies and applications of Ultra-Wideband Radio over optical fibre (UROOF) and provides overview of key results of the funded project UROOF. They studied the theoretical aspects of the UROOF channel, and demonstrate experimentally, key features of this new technology, through a validation platform. UROOF envision that within 3-5 years, fibre optics will be widely spread for indoor residential applications, and the trend of using multimode fibres (MMF) for in-building small-office-home office (SOHO) will increase. The key drivers will be services that are required by the users: distribution of several streams of High Definition TV, rich multimedia content, truly broadband connection to the infrastructure etc. Hence the great opportunity for UROOF technology for range extension applications will be available over the "in-house fibre infrastructure". For this application scenario, WPAN, W-USB devices, Bluetooth 3.0 will be the natural surrounding that is embedded in users devices. As the paper say, UROOF will provide unique technology to enable the range extension of these inherently limited technologies.

2) Zoubir Irahhauten, Homayoun Nikookar, and Gerard J. M. Janssen, "An Overview of Ultra Wide Band Indoor Channel Measurements and Modelling"

In this letter, an overview of reported measurements and modelling of the ultra wide band (UWB) indoor wireless channel is presented. An introduction to UWB technology and UWB channels is provided. Different UWB channel sounding techniques are discussed and approaches for the modelling of the UWB channel are reviewed. The available indoor UWB channel measurement results are consulted and accordingly, the major UWB channel parameters are presented and compared to those of narrowband systems. The novelty of this work is the gathering of different UWB channel parameters, analysis, and comparison. Added with the influence of UWB antenna in channel-modelling, as well as the frequency-dependency of the channel parameters, leads to a conclusion on the UWB radio channel modelling.

3) Jianping Yao, Senior Member, IEEE, Member, OSA, Fei Zeng, Member, IEEE, and Qing Wang, "Photonic Generation of Ultra wideband Signals"

In this paper, techniques to generate UWB pulses in the optical domain have been discussed. These techniques were divided into three categories: 1) PM-IM conversion in a dispersive device, 2) microwave filtering using a photonic microwave delay-line filter having two- or three taps with one negative tap, and 3) optical spectral shaping and frequency-to-time mapping in a dispersive device. The key feature of the techniques in all the three categories is that all could be implemented using all fibre-optic components, which provide the potential for integration using integrated photonic circuits. Compared to the techniques in the second and third categories, the techniques in the first category have a simpler structure, with only a single LD required. The approach based on spectral shaping and frequency-to-time mapping in the third category has more flexibility in generating UWB pulses with arbitrary shapes. The use of an optical pulsed source may make the system more complicated and costly.

4) João Nascimento and Homayoun Nikookar (Senior Member IEEE), International Research Centre for Telecommunications and Radar (IRCTR), Department of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, "On the Range-Data Rate Performance of Outdoor UWB Communication"

Major envisioned commercial Ultra Wideband (UWB) applications are indoor. Nonetheless, the suitability of UWB technology for data communication over longer ranges may also have a relevant role in the outdoor wireless communications. In this paper it is demonstrated that satisfying the FCC outdoor emission limits, IR-UWB is a suitable technology for long range communication at low data rates using the PAM and PPM modulations. In the AWGN channel, better performances are obtained with the use of higher order levels of PPM modulation comparing with the best performance obtained using binary PAM. Consequently, for the limited power system, longer ranges can be achieved for the UWB link with the use of PPM modulation when compared to PAM modulation. Considering outdoor shadowing environments with signal fluctuations present at the receiver, lower range-data rate performance is obtained for the UWB link when compared to the free space environment.

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The huge bandwidth of UWB technique influences signal propagation. The UWB frequency dependency of two different materials utilized for the ground reflection, which are often used in outdoor environments, is incorporated in the two-ray path loss model. Using the UWB frequency dependent path loss model, for the most considered distances there is a slight improvement in the achievable range-data rate performance of the UWB link, when compared to the case of no ground reflection.

For different BER and outage probabilities, tables of achievable range-data rate performance of the UWB link for the free space, lognormal shadowing and the frequency dependent two-ray path loss models are provided. Results of this study can be used in the design of outdoor UWB systems as well as in the analysis of range-data rate trade off of the UWB communication systems.

Experimental/investigative methods to be adopted

In this project, Matlab code could be used to simulate the system and from the required results, we could analyse the performance.

We will simulate the system with 2 parts, wireless part with UWB technique and optical fibre part. The code should contain the matching between the two parts. In this simulation we will examine the SNR and BER for several UWB distances and several optical fibre lengths.

The results will give us an idea about the possible fibre lengths could be used for Optical over Fibre using UWB.

Time plan

Dissertation work should be finished in 16 weeks. The work could be divided into 7 activities from A to G. The activities and their periods are as follows:

A. Background studying for UWB (Ultra WideBand) technique. (2 weeks)

B. Background studying for optical fibre. (2 weeks)

C. Background studying for Radio over Fibre. (2 weeks)

D. Designing and implementation for a MatLab code for Optical over Fibre using UWB. (4 weeks including overlap)

E. Analyse the results of the system performance. (4 weeks including overlap)

F. Writing a whole report about this subject. (9 weeks including overlap)

G. Review and final checking for the analysing and overall report. (2 weeks)

The overall activities can be more illustrated with its overlapping using the following Gantt chart:

Fig 4 - Gantt chart for the dissertation activities

Deliverables or specific outcomes

From the results of the matlab code, the SNR and the BER, we should get the possible fibre lengths to transmit UWB signal over it.