Implementation and simulation of basic structure of the radio over fiber link

Implementation and simulation of basic structure of the receiving set over vul tidy sumized case linkCHAPTER 1 INTRODUCTION1.1 WIRELESS COMMUNICATION SYSTEMS radio converse has g unrivalled through enormous growth in the 1 judgment of conviction(prenominal) ten years. Less than a pct of world population had access to cellular engine room before early nineties, and by the start of this millenary approximately ein truth one in a five people has a mobile phone. In the same period different countries across the globe have increase the mobile net income technology over ninety percent and future forecast says that by the annihilate of 2010 there will be to a greater extent than 1700 million mobiles affairrs across the world. 12Apart from cellular technology WLANs has likewise seen phenomenal growth during the retiring(a) ten years. These WLAN hotspots fundament be utilize in public places such(prenominal) as airports, cafes, hotels and restaurant and so forth YEARWLANFrequ encyModulationBit-Rate (MAX)1997IEEE 802.112.4 gigacycle per secondFrequency Hopping andDirect Spread Spectrum2 Mbps1998ETSI Home RF2.4 gigacycleWide heap FrequencyHopping1.6 Mbps1999IEEE 802.11b2.4 gigahertzDirect Sequence SpreadSpectrum11 Mbps1999IEEE 802.11a5 GHzOFDM54 Mbps2000ETSI HiperLAN25 GHzOFDM Connection-Oriented54 Mbps2003IEEE 802.11g2.4 GHzOFDM compatible with802.11a54 Mbps hold over 1.1 Evolutions of WLAN Standards 3The rapid growth in piano tuner colloquy achieved more fame due the ease of knowledgeability as comp ared to the fixed net produce. The first times (1G) mobile system were analogue, discovered in 1980s. The second generation (2G) know as global system for mobile intercourse (GSM) came on the scene in 1990s, which has been actually successful and has achieved extreme success across the globe. GSM is currently the major mobile communion system which is aimd worldwide. 1The graph above shows the relationship between reportage and capacity of communica tion systems. By looking at the graph the cell size of it of WPAN is of few meters but there transmittal rate may go upto 10 Mbps. While considering 2G and 3G systems, there cell sizes may vary upto some(prenominal) kilometres but that are particular to less than 2Mbps. WiMAX technology rump provide mellowed bit rate mobile ser unrighteousnesss exploitation oftenness span between 2 11 GHz. 6FREQUENCYWIRELESS COMMUNICATION SYSTEMS2 GHzUMTS/ 3G Systems2.4 GHz IEEE 802.11 b/g WLAN5 GHzIEEE 802.11 a WLAN2-11 GHzIEEE 802.16 WiMAX17/19 GHz interior tuner (radio) LANs28 GHzFixed Wireless Access local anaesthetic point to multi point (LMD)38 GHzFixed Wireless Access Picocellular58 GHzIndoor Wireless LANs57-64 GHzIEEE 802.15 WPAN10-66 GHzIEEE 802.16 WiMAXTable 1.2 Frequencies for Wireless Communication Systems 2-51.2 CLASSIFICATION OF WIRELESS NETWORKWireless interlocks stub be categorized into different groups depending on the area they are applied to. As a result amply co me ins of standards have been making to public for the development of new techniques in severalize to increase the spectrum efficiency and perfect utilization of spectrum, which is scarce natural resource.Wireless communicates feces be split into three classes1.2.1 Wireless Private Area Ne cardinalrk (WPAN) Devices of such networks can communicate in the swan of tens of metres. Infrared (IR) and Bluetooth are the two implementation of this principle.1.2.2 Wireless Local Area Network (WLAN)It is computer network that connects devices which are distributed over a local area (e.g office, house, mall, and airport). IEEE 802.11 which is comm unless known as Wi-Fi, is an example of WLAN.1.2.3 Wireless Metropolitan Area Network (WMAN) Such a network covers a geographic area such as city or village. IEEE 802.16 which is commonly known as WiMAX, is an example of WMAN.Depending upon the industriousness, there are licenced and unlicensed oftenness striations in which radio systems ca n operate.1.3 WIRELESS APPLICATIONS Now we will discuss wireless standards along with the overview of their applications1.3.1 Bluetooth WPANBluetooth is a radio standard, which ope pass judgment in the unlicensed Industrial Scientific and Medical (ISM) band at 2.4 2.485 GHz. Frequency Hopping Spread Spectrum (FHSS) is utilise in order to minimize interference and fading. In order to gull the transceiver architecture as simple-minded as assertable, binary modulation is utilize. The bit rate is up to 3 Mb/s. The benefits of Bluetooth include belittled power consumption and low cost, therefore they are utilize in devices such as laptops, mobile phones and PDAs. 7Power ClassMaximum take PowerMinimum Output Power1100mW(20dBm)1mW(0dBm)22.5mW(4dBm)0.25mW(-6dBm)31mW(0dBm)Table 1.3 Bluetooth classes and power levels 71.3.2 Wi Fi WLANThe Wi-Fi alliance, the Institute of Electrical and Electronics Engineers (IEEE) and the European tele communication theory standard Institute (ETSI) are the three organizations which influenced the standardization of WLAN. The IEEE WLAN standard is referred as 802.11. At the moment, the close to apply techniques are defined by the IEEE 802.11a, b and g standards. 8StandardRelease date operate frequenceMaximum Data Rate802.11a19995.15 5.35 GHz5.725 5.825 GHz54 Mbps802.11b19992.4 2.5 GHz11 Mbps802.11g20032.4 2.5 GHz54 MbpsTable 1.4 IEEE 802.11a, b and g standards 81.3.3 WiMAX WMANWiMAX is an abbreviation for Worldwide Interoperability for Microwave Access. The WiMAX Forum is a non clear association. The bugger off and objective of the WiMAX technology is to provide fixed, portable or mobile connectivity to the substance abusers even if they set(p) up to 6 miles away from base carry and it is non necessary to be in line of sight. WiMAX can operate on any frequency below 66 GHz, as operating frequency may change for different countries depending on local regulation. It is possible replacement for mobile/cellular technol ogies such as GSM and CDMA. It has been considered to be the wireless backhaul technology for 2G, 3G and 4G networks. The limitations associated with WiMAX is that it can either provide high info rate or it can transmit data over longer distances but non both simultaneously. 91.3.4 Distributed Antenna Systems and radio receiver Over FiberDistributed Antennas Systems (DAS) are utilize for several applications in the mobiles and wireless communications. It can be set up over indoor and outdoor sites. DAS can be implemented on those areas where there is subscribe of indicates such as tunnels, underground place etc. in order to ex hightail it the coverage of mobile network. Radio over fibre consists of removed(p) unit and primeval unit. Remote unit is kept very simple since it only consists of devices for reception of radio frequency manoeuvres and optoelectronic conversion. All high-ticket(prenominal) and complex equipments are located at central unit and functions such as modulation and up/down conversion etc. are done. This resulted in increase in efficiency and attention cost because as compared to central units, remote units are numerically high in numbers and often remote units are located in sites that are not easy to get in touch with. 10 1.4 FLOW CHART OF THE DISSERTATION1.5 AIMS AND OBJECTIVESThe aim of the dissertation is to implement and simulate the basic structure of the radio over grapheme link victimisation OFDM transceiver with the help of MATLAB/SIMULINK. The MATLAB version 7.8.0 (R2009a) is used for model implementation. Basically two models are designed model number 1 consists of OFDM transceiver linked with a gain which represents the length of the fiber leave. Actually it is based on the a priori fact that fiber has 0.2db loss per kilometre. For example 25km length fiber will be represented as 5 dB(-ve sign to show loss). Later on simulations are carried out by varying the length of fiber and results are deduced. Model 2 co nsist of OFDM transceiver as well but linked with laser diode model, fiber leave model and photodiode model as these are the fundamental components of RoF link. many superfluous parameters of measuring the transmitted and accredited power and bit error rate calculation are also introduced to enhance the diversity of the project.1.6 DISSERTATION OUTLINEThe dissertation consists of six chaptersChapter 1 is the introduction chapter in which wireless communication systems and wireless applications have been discussed briefly.Chapter 2 consist of the theory of radio over fiber which includes the pauperism of RoF system, what RoF technology is, advantages and disadvantages of RoF system and applications of RoF technology.Chapter 3 strictly consist of theory related to OFDM technology. Sub topics include in this chapter are principles of OFDM, history, advantages and disadvantages and applications of OFDM. Fourier trans trope is also discussed in this particular chapter.Chapter 4 con sist of methodology of the dissertation. It consists of the models implemented utilize MATLAB/SIMULINK and the brief study of the essential blocks used in the models.Chapter 5 is the chapter of simulations and results. Chapter 6 includes the conclusion and future work regarding radio over fiber and OFDM.CHAPTER 2 RADIO OVER FIBER2.1 INTRODUCTION Radio-over-fiber (RoF) is a communication technology for delivering broadband applications to wireless users such as satellite communications, mobile-radio communications, broadband access radio, multipoint video scattering and broadband mobile services. RoF technologies make use of ocular and radio communication media for providing above mentioned broadband services. The ocular part is used to transmit cook point outs between a central radio base station and a remote radio feeler and on the other hand radio part provides coverage to wireless users. In RoF system radio frequency (RF) signal is transmitted through an optical network in an easier way by direct modulating the lastingness of the light source with the RF signal to be transmitted and on the receiving end direct detection of the signal at photo detector. The modulating of the laser-diode light intensity with electrical signals at multiple frequencies causes a number of problems such as relative intensity, noise tweedle and inter modulation distortion. The main sources of non-linearity in a system are the laser-diode light source, the optical fiber and the photo detector. 27 2.2 NEED FOR RADIO OVER FIBER SYSTEMSFor the future prerequisite multimedia services and broadband over wireless media, some distinctive characteristics are unavoidable such as cell size reduction in order to accommodate more users and to operate in the millimetre wave (mm-wave) frequency bands to get over spectral clogging. Such a system would demands a prodigious number of base stations to cover large geographical coverage area and base station should be cost impressive as well, then only such a system would be successful in market. In such a competitive market, this necessity has led to the evolution of system architecture where microwave functions such as signal processing, signal routing, handover, modulation, protocols setting and frequency allocation etc. are per songed at central control station (CS) rather than at remote station or base station (BS). This part of centralized arrangement allows complex, nice and pricy equipments to be positioned in safer environment and shared among several BSs or RSs (Remote Stations). Now the question arises how to link the central station (CS) with BS. In such type of radio network, the use of optical fiber is the most suitable choice for the linking of CS with BSs, as fiber is cheaper in cost, has low loss, immune to Electromagnetic Inter Modulation (EMI) and provides wider bandwidth. By charge the BSs as simple as possible and by sharing the resources provided by CS among several BSs, can effectivel y minimizes the cost of entire network and thus maintenance cost. Modulation of RF sub postmans onto an optical carrier over an fiber is known as Radio over Fiber (RoF) technology. Typically RoF network consist of central CS, where functions like switching, routing, medium access control (MAC) and frequency management takes place whereas at BSs functions like optical to electrical and vice versa are performed. 32 2.3 RADIO OVER FIBER TECHNOLOGY Radio over fiber system consists of a Radio Base Station (RBS) and Radio Access Point (RAP) which are connected by an optical fiber link. Optical fiber link is used to distribute RF signals from a RBS to RAP. RAP only contains optoelectronic conversion devices and amplifiers. In GSM technology RBS could be referred as unstable Switching Centre (MSC) and RAP as Base Station (BS). The frequency used by the RoF systems usually lies under GHz region depending on the nature of application. Basically RoF systems were used to transmit microwave signals and to achieve mobility functions in RBS. Therefore modulated microwave signals had to be available at the input end of the system, which are then delivered to the RAP as optical signals. Signals at RAP are re-generated and radiated by antennas. Due to the advancement of technology, RoF systems are designed to perform added radio system functionalities other then witchation and mobility functions. The functions include are data modulation, signal processing and frequency conversion (up and down). The electrical signal at the input of the multifunctional RoF system may be baseband data, modulate IF or actual modulated RF signal for distribution. The modulated optical signal is carried over the optical fiber link to the remote station. At the receiving end, demodulation of the signal is carried out by the photo detector and the optical signal is converted back to electrical signal. 12 132.4 ADVANTAGES OF RADIO OVER FIBER2.4.1 Low AttenuationIt is observed that high frequency signals when transmitted in free space or through transmission lines are expensive and sometimes due to different reasons challenging as well. In free space, losings are directly proportional to frequency due to absorption and reflection. Increase in frequency also gives rise in impedance when signal is delivered through transmission line. Therefore in order to overcome these issues, expensive signal regenerating equipment is required to distribute radio signal electrically over long distances. The cheaper solution is to use optical fibers which offer lower losses. Single Mode Fiber (SMF) made from glass (silica) has attenuation losses below 0.2dB/km and 0.5dB/km in the 1.5um and 1.3um windows respectively. 112.4.2 Larger Potential BandwidthLarger bandwidth is being offered by optical fibers. Larger bandwidth provides high capacity for transmitting high frequency signals and also enables high speed signal processing which is difficult to achieve in electronics systems. Basically the re are three main transmission windows, namely 850nm, 1310nm, and 1550nm wavelengths, which offer low attenuation. Anyhow optical system has to combine with electronic system in order to perform different tasks. But bandwidth mismatch of the systems create problem which is known as electronic bottleneck. The solution to this problem is the use of effective multiplexing techniques such as OFDM, DWDM and SCM. 112.4.3 Easy Installation And MaintenanceThe convinced(p) point of RoF system is the Switching Centre (SC), which are less in numerical quantity because one SC is shared by several Remote stations (RSs), which are equipped with all the expensive and complex equipments and RSs are kept simpler which includes only photo detector, amplifier and an antenna, thus reducing system installation and maintenance cost. 112.4.4 Reduced Power ConsumptionAs discussed earlier centralized SCs are equipped with complex equipment and RSs are kept simpler with less equipments thus resulting in sn ipd power consumption. Thus RSs can be operated in passive mode. 112.4.5 Immune To Interference And CrosstalkAs we know that optical fibers form a nonconductor waveguide therefore there are no concepts as electromagnetic interference (EMI), radio frequency interference (RFI), or switching transients giving electromagnetic pulses (EMP). In fact it doesnt require shielding form EMI. Hence optical signal can be transmitted through electrically noisy environment unaffectedly. The optical fiber can be used underground or overhead as it is not disposed to lightening strike. 112.4.6 Signal SecurityIn RoF system, optical signals are transmitted in the form of light, which doesnt radiate drastically, thus providing high degree of signal security. Therefore it is widely used in military, banking and public data transmission applications. 11 2.5 DISADVANTAGES OF RADIO OVER FIBERRoF systems can be called as analog communication system. Therefore signal impairments such as noise and distortion are worth considering in RoF. These impairments tend to limit Noise Figure (NF) and Dynamic Range (DR) of the RoF links. Chromatic dispersion may limit fiber link length when considering SMFs RoF. Modal dispersion can limit the available link bandwidth and distance when considering MMFs RoF system. congress Intensity Noise(RIN), lasers phase noise, photodiodes shot noise, amplifiers thermal noise and fibres dispersion are few examples of noise sources in analog optical fibre links.10 2.6 APPLICATIONS OF RADIO OVER FIBERListed below are the few applications regarding RoF2.6.1 Mobile Communication Network A mobile network is a useable application of RoF technology. In the past decade the numbers of mobile subscribers coupled with the increasing demand of broadband service have been keeping massive pressure on the mobile service provider to provide vast capacity to the end user. 112.6.2 Video Distribution Systems (VDS)VDS is one of the major applications of RoF systems. In this case the Multipoint Video Distribution Service (MVDS) is used for mobile terrestrial transmission. In MVDS the transmitter serves the coverage area based on tall building. Gunn oscillators and heating plant pipes are used for frequency stabilization while a fiber link can be used for feeding a TWT or solid state amplifiers. This system provides reduction in free weight and wind loading of transmitter. 112.6.3 Cellular Broadband ServicesDue to the very high bit rates of nearly 155 Mbps, carrier frequency is pushed into mm-waves. For this purpose frequency band in 66 GHz frequency band have been allocated. The 62-66 GHz band is used for downlink while 65-66 GHz frequency band can be used for uplink transmission. 112.6.4 Vehicle Control And CommunicationFor vehicle communication and system the frequency band between 63 64 GHz and 76-77 GHz frequency band has been allocated. They are used to provide continuous mobile communication coverage in major areas for the purpose of intelligent tr ansport systems which includes road to vehicle communication (RVC) and inter vehicle communication (IVC). These can be made simple and cost effective by feeding them through RoF system. 11CHAPTER 3 ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING3.1 THE PRINCIPLES OF OFDM outside frequency division multiplexing is a multi carrier technique which divides the bandwidth into several carriers. Each carrier is modulated by a low rate data stream. OFDM has the ability to use the spectrum efficiently by spacing the convey close to to individually one other. Closeness of the guides can result in the interference therefore to counteract interference all carriers are orthogonal to each other which means all carriers are self-directed to each other. 14In FDMA a single channel is allocated to each user to transmit information. The bandwidth of each channel is approximately 10 kHz-30 kHz for voice communications. In order to nix channels from interfering with one another, the allocated bandwi dth is made wider than the minimum amount required. This extra bandwidth or spacing between channels is wasting about 50% of the total spectrum. As the channel bandwidth becomes narrower the problem becomes worst. 14In TDMA multiple users access the same channel or utilized the full bandwidth in different time slots. Many low data rates users can be combined to transmit in a single channel thus bandwidth or spectrum can be used efficiently. There are two problems associated with TDMA. Firstly the symbol rate of each channel is high resulting in multipath delay spread. Secondly at the start time of each user to use bandwidth for data transmission, a change over time has to be allocated in order to prevent from propagation delay variations and synchronization errors. This change over time is a loss, limiting the number of users that can be accommodated efficiently in each channel. 14OFDM is solution to both the problems occurring in FDMA and TDMA. Actually OFDM splits the available ba ndwidth into many narrow sub channels. As the carriers are orthogonal to each other which means they are purely independent of each other therefore they can be spaced very close to each other. Any time full utilization of bandwidth is possible in OFDM, therefore there is no drive for users to be time multiplex and no more switching of the users for bandwidth. Users can send and receive data at any time unlike TDMA. 143.2 OFDM HISTORYThe concept of OFDM was first developed in 1950s. A US copyright was issued in January 1970. The evolution of OFDM took place in order to use the available bandwidth or spectrum more efficiently. 1516OFDM was first implemented in military communications just like CDMA. KINIPLEX 17 and ANDEFT 18 are two examples of OFDM application in high frequency military system. AN/GSC-10(KATHRYN) variable rate data modem was the early application of OFDM which was built for high frequency radio. In 1980s, OFDM had been studied for high speed modems, digital mobile c ommunications and high density recording. OFDM techniques for multiplexed QAM victimization DFT was discover by Hirosaki 19. He has also designed 19.2 kbps voice band data modem which uses QAM modulation. In 1990s, OFDM has been exploited for data communication over mobile radio FM channels, high bit rate digital subscribers lines(HDSL), very high speed digital subscriber lines(VHDSL), digital speech sound broadcasting( splash), digital television, HDTV terrestrial broadcasting and asymmetric digital subscriber lines(ADSL).14OFDM has been considered more towards mobile communication due to its robustness to multipath propagation. Recently OFDM has been put into practice in audio broadcasting applications such as DAB and DVB. And it has been successfully implemented in wireless LAN applications as well. 143.3 FOURIER TRANSFORMThe application of OFDM was not very practical in 1960s. Quite a few numbers of oscillators were needed to generate the carrier frequencies for sub channel tra nsmission. At that time it was a bit difficult to make it practical, that is why OFDM proposal was said to be impracticable.Complexity of the OFDM scheme was eliminated with the evolution of Fourier Transform where harmonically related frequencies are generated by Fourier and Inverse Fourier Transforms used to implement OFDM systems. Fourier Transform can be used in linear systems analysis, antenna studies, optics, random process modelling, probability theory, quantum physics and boundary-value problems.3.4 OFDM REAL PARAMETERSIn the last 10 years, the usage of OFDM has increase to enormous extent. It has been proposed for radio broadcasting such as EUREKA 147 standard and Digital Radio Mondiale (DRM). Some of the useful parameters are listed below 20 Data rate 6Mbps to 48 Mbps Modulation BPSK, QPSK, 16-QAM and 64 QAM Coding Convolutional concatenated with beating-reed instrument Solomon FFT size 64 with 52 sub-carriers uses, 48 for data and 4 for pilots Sub carrier Frequency set 200 MHz divided by 64 carrier or 0.3125 MHz FFT Period / set Period 3.2usec Guard Duration One quarter of symbol time, 0.8usec Symbol time 4usec3.5 ADVANTAGES OF OFDM Overlapping is used for efficient use of spectrum. OFDM systems are more often reluctant to freq selective fading by dividing the channel into narrowband sub channels. Cyclic prefix is used to discard ISI and IFI. The symbols lost due to selective fading can easily be recovered by exploitation channel coding and interleaving. The use of single carrier systems makes channel equalization simpler by using adaptive equalization techniques. With reasonable complexity max likeliness decoding is possible. FFT techniques allow OFDM to be computationally efficient to the functions of modulation and demodulation. It can also be used for DAB systems and partial algorithms can be used for program selection. A channel estimator can easily be discarded with the use of differential modulation. As compared to single carrier system s OFDM is less sensitive to sample timing offset. OFDM gives extra protection concerning parasitic noise and co channel interference. In voiceless multipath orthogonality is preserved. OFDM is used in high speed applications and dynamic packet access is also supported. transmission system and receiving diversity are supported. On the other hand OFDM also supports adaptive antenna arrays, space time coding and power allocation.3.6 DISADVANTAGES OF OFDM The OFDM signal has a noise like amplitude with a very large dynamic range, therefore it requires RF power amplifiers with a high peak to bonnie power ratio. It is more sensitive to carrier frequency offset and drift than single carrier systems. 3.7 PROBLEMS WITH OFDM3.7.1 Peak To Average dimensionPAR is an important OFDM parameter which is defined as the ratio of peak instantaneous value to average time. It can also determine parameters such as current, voltage, phase and power of the signal. Since OFDM is a summation of several c arrier signals therefore results in high PAR. The RF power needs to be increased to overcome the problem of efficiency in PAR. In order to increase the radio frequency power an amplifier is needed which can increase the cost of the system as it is expensive equipment.In order to solve the problems created by PAR, different encoding schemes should be used before the modulation. Also the improvement in the amplification tip of transmitter is needed such as post processing the time domain signal to reduce the peak to mean signal ratio. 21223.7.2 SynchronizationThe performance of OFDM link can be optimized by using two kinds of synchronizations between transmitter and the receiver. Timing Synchronization The timing offset of the symbol is not need to be determined and then the optimal timing instants. Frequency Synchronization The carrier frequency of the received signal must be aligned at the receiving end.Timing sync can easily be achieved because the degree of sync error in OFDM str ucture is more severe. The sync techniques can be achieved by using known pilot tones that are embedded in OFDM signal or by using guard interval. 21223.7.3 Co-Channel InterferenceIn mobile communications co channel interference can be overcome by combining techniques related to adaptive antenna systems. Receiver antenna beam can be focused by beam steering while co channel interferers are attenuated. This is useful as OFDM is sensitive to co- channel interference. 21223.8 APPLICATIONS OF OFDM High frequency modems used for military Voice band modems ADSL HDSL DAB Terrestrial Digital Video Broadcasting (DVB-T) Power line communication systems WLAN Cable modems Wavelength partition MultiplexingCHAPTER 4 METHODOLOGY4.1 INTRODUCTIONThis chapter includes the in depth study of the models built on MATLAB/SIMULINK. MATLAB version 7.8.0 (R2009a) is used for the modelling. Basically two models are designed whic