BER Performance Analysis of DIGITAL AUDIO BROADCASTING SYSTEM

BER Performance Analysis of DIGITAL AUDIO BROADCASTING SYSTEM

BER Performance Analysis of DIGITAL AUDIO BROADCASTING SYSTEM

Dissertation Part-1- Submitted byTANMOY PAUL

Reg. No.- 131630410017

Roll No.- 16310513017

M.Tech, E.C.E, 3rd Semester

Under The Guidance of

AVIK CHAKRABORTY, Assistant Professor

Department of Electronics & Communication Engineering

Bengal Institute Of Technology & Management

ContentsI. IntroductionII. Theoretical Background

III. History

IV. Proposed Scope of my work

V. ReferencesAcronyms

Stands forBER

Bit Error RateDAB

Digital Audio BroadcastingISI

Inter-Symbol InterferenceBCH

Bose-Choudhuri-Hocquenghem

OFDM

Orthogonal Frequency Division Multiplexing

COFDM

Coded Orthogonal Frequency Division Multiplexing

ETSI

European Telecommunications Standards Institute

FPGA

Field Programmable Gate Array

FEC Codes

Forward Error Correcting CodesQPSK

Quadrature Phase Shift KeyingI. Introduction

Today we live in a world of digital communication systems and services. These analog standards are now failing to provide the quality of services to the listeners they expect. Now the essential parts of the production processes in radio houses was to change to digital ones in recent times. There are many mass-storage digital medium to offer superior sound quality like CDs, hard disks, digital compact cassettes, Mini-Disks, DVDs etc or streaming & download formats (such as MP3) for distribution via Internet. Consequently, broadcast transmission systems tend to change from conventional analogue transmission to digital. The first steps in the introduction of digital broadcasting services were taken by the BBC for stereo television sound in the VHF/UHF bands), DSR (Digital Satellite Radio, which was already shut down) or ADR (Astra Digital Radio), none were suited to replace the existing conventional services completely, especially for mobile reception. For that reason, the universal digital multimedia broadcasting system Eureka 147 DAB was developed & is now being introduced worldwide.

Following goals were set up for DAB from the beginning with the sole aim of quality audio for mobile reception:

High quality audio comparable to that of the CD;

Suitable for mobile reception in a car, even at high speeds;

Efficient use of frequency spectrum;

Transmission capacity for ancillary data;

Low transmitting power;

Terrestrial, cable and satellite delivery options;

The advantage of the DAB system developed in the European Eureka-147 standard is its ability to deliver high quality audio services to mobile receivers under different channel conditions. This is because of the use of rugged transmission technology called the Coded Orthogonal Frequency Division Multiplexing (COFDM). This is the heart of Digital Audio Broadcasting. COFDM modulation combines the multi-carrier modulation technique OFDM with Convolution Channel Coding in such a way that the system can exploit both time and frequency diversity.II. Theory Related This Paper: BER (Bit Error Rate): What does BER suppose to??? Thebit error rateorbit error ratio(BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER is a unit less performance measure, often expressed as apercentage. Thebit error probabilitypeis theexpectation valueof the BER. The BER can be considered as approximate estimate of the bit error probability. This estimate is accurate for a long time interval and a high number of bit errors. For AWGN channel, the BER as function of Eb/N0 is given by:. [1] Working Principle of DAB System: The working principle of the DAB system is illustrated in conceptual block diagram shown in fig. below. At the input of the system the analog signals such as audio and data services are encoded and through Channel Coder it is being fed to MSC (Main Service Channel) multiplexer, where through FIC (Fast Information Channel) service information is being multiplexed in Transmission Multiplexer to form the DAB frame. After signal passing through Transmission Multiplexer passed to OFDM signal generator. This block is the heart of the DAB system. These technical aspects make the system very reliable, multi- programme, providing robust reception on mobile receivers using simple antenna.[2]

Fig: DAB transmission Block Diagram

MSC: Main Service Channel carries all user data, e.g, audio, multimedia. The MSC consists of Common Interleaved Frames (CIF) which results in a data rate of2.304Mbits/s. FIC: Fast Information Channel contains blocks with 256 bits each.It contains all control information which is required for interpreting the configuration and content of the MSC.[2] OFDM: Orthogonal frequency-division multiplexing(OFDM) is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme forwidebanddigital communication, whether wireless or copper wires, used in applications such as digital television and audio broadcasting, DSL Internet Access, Wireless Networks, Power Line Networks and 4G mobile communications. COFDM is almost the same as like OFDM except here signals are being coded first with FEC methods. This is to overcome errors in the transmission due to lost carriers from frequency selective fading, channel noise and other propagation effects.

OFDM is afrequency-division multiplexing(FDM) scheme used as a digital multi-carriermodulationmethod. A large number of closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data streams/channels. Each sub-carrier is modulated with a conventional modulation scheme (such asquadrature amplitude modulationorphase-shift keying) at a lowsymbol rate, maintaining total data rates similar to conventionalsingle-carriermodulation schemes in the same bandwidth. The primary advantage of OFDM over single-carrier schemes is its ability to cope with severechannelconditions ( e,g attenuationof high frequencies in a long copper wire, narrowbandinterferenceand fadingdue tomultipath) without complex equalization filters.

The main advantage of the DAB system developed in the European Eureka-147 standard is its ability to deliver high quality audio services to mobile receivers under different channel conditions. This is because of the use of rugged transmission technology called the Coded Orthogonal Frequency Division Multiplexing (COFDM). This is the heart of Digital Audio Broadcasting. COFDM modulation combines the multi-carrier modulation technique OFDM with Convolution Channel Coding in such a way that the system can exploit both time and frequency diversity. This is achieved by interleaving data symbols, in the time and frequency domains, prior to transmission.

Additive White Gaussian Noise(AWGN) is a basic noise model used inInformationtheory to mimic the effect of many random processes that occur in nature. The modifiers denote specific characteristics:

'Additive' because it is added to any noise that might be intrinsic to the information system. 'White' refers to idea that it has uniform power across the frequency band for the information system. It is an analogy to the color white which has uniform emissions at all frequencies in thevisible spectrum.

'Gaussian' because it has anormal distributionin the time domain with an average time domain value of zero.

AWGN is often used aschannel modelin which the only impairment to communication is a linear addition ofwidebandorwhite noisewith a constantspectral density& aGaussian distributionof amplitude. The model does not account for fading, frequency selectivity, interference, non-linearity or dispersion. OFDM Symbol Demodulator

The OFDM symbol demodulator block demodulates the OFDM symbols from the synchronized DAB frame. The demodulation is done by removing the null symbol and the phase reference symbol. Generation of BPSK

In Phase Shift Keying technique, the phase of the carrier is changed according to input the data signal. The phase of the modulated signal itself conveys some information; in this case the demodulator must have a reference signal to compare the received signal phase. This is termed as coherent detection. BPSK is the simplest form of phase shift keying (PSK). It uses two phases which are 0 and 180.

Generation of BPSK

To generate a binary PSK signal, we have to represent the binary sequence in polar form with symbols 1 and 0 represented by constant amplitude levels of +Eb & -Eb respectively. The resulting binary wave (in polar form) and a sinusoidal carrier 1(t), whose frequency fc = (nc/Tb) for some fixed integer nc are applied to a product modulator. The carrier and the timing pulses used to generate the binary wave are usually extracted from a common master clock; the desired PSK wave is obtained at the modulator output.

To detect the original binary sequence of 1s and 0s, we apply the noisy PSK signal x(t) (at the channel output) to a correlator, which is supplied with a locally generated coherent reference signal 1(t). The correlator output x1 is compared with a threshold of zero volts. If x1> 0, the receiver decides in favor of symbol 1. On the other hand, if x1