Evaluate the performance

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Research on OFDM and Initial plans made in the 60s and the 70s. It took more than 25 years for technology to move from research domain to Industry domain. OFDM has also been shown to be effective for digital audio and digital video broadcasting at multimegabit rates in Europe, and it has been incorporated into standards by the European Telecommunications Standards Institute (ETSI). Authentically concept behind is quite simple but, the practicality of implementing it has many complexities. So, a Simulation based project has been under taken.

OFDM depends on Orthogonality principle. The Basic principle of OFDM is to split a high-rate DataStream into a number of lower rate stream that are transmitted simultaneously over a number of subcarriers. It means that cross talk between co-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and receiver, unlike conventional FDM; a separate filter for each sub channel is not required.

  1. Objective:
  2. The main aim of this Project work is to evaluate the Performance of OFDM in Various aspects using Modulations schemes and transformations methods. This research aim is divided into four objectives as discussed in the following sections;

  3. Organization of Dissertation:
  4. History Behind Orthogonal Frequency Division Multiplex (OFDM):

Over from few years, Telecommunication has been rapid growing industry. In next couple of decades this going to be Major industries which make more Revenue in this competitive Market. As we can observe from past 20years it has explosion number of mobile communications subscribers, and it continues into future. In fact, in few countries mobile subscribers will be more than the Population. For the next upcoming years future will be Fourth Generation systems.

Mobile Telephony concept was beginning in 1920's with radiotelephony, by United States Police department. During Second World War in 1930's Frequency modulation (FM) were developed for battle field communication. First generation (1G) Systems were mainly focused on Voice communication, and they succeed in providing it for long time. On other hand it was providing numerous of difficulties. Additional technologies were added to this network to rectify those problems; in addition Implementing of Second generation (2G) systems were the biggest solution.

Second Generation (2G) systems are well established with over two billion users throughout the world. These 2G systems include Global System for Mobile (GSM), Time division multiple access (TDMA) and Code division multiple access (CDMA). The key tributes of 2G Systems are typically Digital Transmission and Voice Capabilities. 2G systems particularly GSM, have come along with initial launch 1992 to provide voice and limited data capabilities. Other further features like packet data using General Packet radio service (GPRS), multimedia messaging service (MMS), High speed circuit switched data (HSCSD), Protocol for browsing like wireless access protocol (WAP) and Enhanced Data rates for GSM Evolution (EDGE) for higher data rate. As 2G Systems have made major success in providing wireless communication coverage outside and inside the building, their success in dedicated in-building deployments has much more limited. Many predictions were made by researchers that deployment of these 2G systems will be widely done in 2015. But, unfortunately 2.5G systems came into existence and deployed soon, it couldn't with stand in the market for longtime. Three generation (3G) Launched in 2000 in many countries. As of now many countries are still running on 2G systems.

In accumulation to be good as 2G system, 3G systems associated 3G services must clearly to offer more over 2G. In practice the main positive differentiators will need to come from air active 3G services. Third generation (3G) system is an extension of Second generation is proposed to introduce after 2000. The system is expected to over ten times of first generation systems. This achievement can be done by Complex multiple access techniques such as Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA).

The telecommunication system has been facing a problem to provide fixed Telephones service in rural areas, where Customer base is small, but the Installation cost is high. The only method to solve the cost of high infrastructure is to use fixed wireless radio network. International Mobile Telecommunications-2000 (IMT-2000) is an Unifying specification, in which enabling mobile and some fixed high speed data services to use one or several radio channels with fixed network platforms for delivering the service.

An advancement of service combining into united Third generation network. Codeless telephony, Private radio systems, Radio paging, Digital and cellular systems and Mobile Satellite etc., will provided by third generation telecommunication systems.

CHAPTER 2:

ORTHOGONAL FREQUENCY DIVISION MULTIPLEX (OFDM):

  1. Introduction:
  2. OFDM depends on Orthogonality principle. The Basic principle of OFDM is to split a high-rate DataStream into a number of lower rate stream that are transmitted simultaneously over a number of subcarriers. It means that cross talk between co-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and receiver, unlike conventional FDM; a separate filter for each sub channel is not required.

                   Orthogonal Frequency Division Multiplexing (OFDM) is a digital multi carrier modulation scheme, which uses a large number of closely spaced orthogonal sub-carriers. Single steam is divided into similar streams on which coded and modulated on to a subcarrier, which used commonly in OFDM systems. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation) at a low symbol rate, maintaining data rates similar to conventional single carrier modulation schemes in the same bandwidth. Therefore the high bit rates seen early on a single carrier is condensed to lower bit rates on the subcarrier.

    In practice, OFDM signals are generated and detected using the Fast Fourier Transform algorithm. OFDM has developed into a popular scheme for wideband digital communication, wireless as well as copper wires.

    Frequency division multiplexing (FDM) is extension of single carrier modulation with single channel using multiple subcarriers. Data rate is divided into various subcarriers and their no need of dividing evenly nor originated. Examples of these FDM are National television systems committee (NTSC) and FM radios. Guard bands are used in between to overcome overlaps.

  3. Specific Application of OFDM:
  4. Because the impact of OFDM in multipath is different from each and every application and it is important to consider the qualities of OFDM on an application-by-application basis.

    1. Broadcasting:
    2. Broadcasting is a quite different application from other wireless applications. This broadcasting has two important characteristics.

      • One-way Transmission.
      • Same signal is generally transmitted from neighboring transmitter sites.

      Transmission in one way means peak-average power ratio will be an issue for OFDM only at transmitter sites. Because there are relatively few of these and minor impact on system cost.

      On the other hand, neighboring sites are somewhat more complex. When we using analog TV transmissions, neighboring transmitters need to use different frequencies even they broadcast the same signal. Otherwise ghost effect will exhibits for receiving more than one signal will result multiple picture on TV screen. To overcome TV transmission use 11 pattern frequencies and transmit a signal at 8-MHz TV channels, 88MHz of spectrum is needed for allocating different frequencies. By using 2048 carriers, the symbol rate is reduced to 2048. In summary, it receives only the nature of broadcast and the desire to avoid using different frequencies on neighboring sites makes OFDM well suited application.

    3. W-LAN:

    Very High data rates has been characterised for these W-LAN for Max 20Msymbols/s. These tend to be use in indoor environment, where multipath signals are present in a time over which they spend is shorter as result of short distance involved. OFDM has proposed 256 carriers with a complexity approach of 10% of that of SCM. Loss in performance is not critical. Hence, the low cost consumption equipments and high data rate makes OFDM suitable for high speed W-LAN solutions.

  5. Features of OFDM:

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