Modeling and simulation of Digital television using Labview
Charmy Patel1, Parth somaiya2, Dr.G.R.Kulkarni3
1Research scholar Department of Electronics & Communication Engineering, Singhania university,junjuhnu,jaipur- Rajsthan, India
2R &D Engineer, Masibus Automation and Instumentation pvt.ltd. ,Gandhinagar,Gujarat,India
3 Principal of Shri C.U.Shah College of engineering and Technology Vadhvan city - Gujarat, India
Abstract - Digital television broadcasting is present and future of television. With the advent of digital technology, digital audio and video compression and other advanced signal processing, it is possible to transmit and receive broadband data over co-axial cable and through satellite and terrestrial. Digital television is a telecommunication system for broadcasting and receiving moving picture and sound by means of digital signals, in contrast to analogue signals in analogue (traditional) Television. It uses digital encoded data convolute the data and transmit the data with OFDM.
modulation data, which is digitally compressed .DVB-T is a European digital television standard that uses OFDM modulation. DVB-T uses Convolutional interleaver with Reed solemn encoder. Significant performance improvements can be realized by implementing parts of the blocks and create the model of terrestrial digital video broadcasting and simulates the blocks. In this paper, we document the process RS encoder and convolution encoder to implement the model of DVB-T. We use the Lab VIEW graphical data flow programming environment for implement the RS encoder and Convolution encoder.
Keywords- Digital Television; DVB-T; RS encoder; Convolution Encoder; OFDM;
I. INTRODUCTION TO DIGITAL
TELEVISION SYSTEM
One of the major problems with analog system is that it becomes distorted by ‘noise’. This happens when the signal being transmitted experiences interference from other sources, such as power lines, reflections from buildings, conflicting broadcast signal, or distortions in the transmission equipment itself. Once interference creeps in to the signal, not much can be done to remove it. By contrast, a well designed digital television transmission system with transmission content represented by the binary digits 1 and 0 can provide an almost interference free service. Any errors in the signal can be automatically corrected and ‘noise’ becomes a thing of past. With all content in a digital format, picture becomes crystal clear and stereo sound takes on a CD quality. And the narrow bandwidth used means space is free for extra services such as multiple sound tracks covering different language versions.
For digital transmission, the video must be digitized first using and A/D converter. The video is converted in to samples with, for example, 8bits per sample. The data is now simply a bit stream, which can be manipulated by computer.
Phase Alternate Line (PAL) is the analogue TV transmission standard used in the UK, and throughout many parts of the world. An uncompressed PAL TV picture requires a massive 216Mbps, far beyond the capacity of most radio frequency links. The U.S. uses and analogue TV system called NTSC. This system provides less precise color information and a different frame rate.
And uncompressed NTSC signal requires slightly less transmission capacity at 168Mbps.
The situation becomes much more acute when one realizes that high definition TV just around the corner. A high definition television picture requires a raw bandwidth exceeding 1 G bps (1000Mbps).
This kind of bit rate is impossible to achieve in normal life applications and the bandwidth requirement for this much bit rate is much higher the capacity of satellite transponder.
So in order to make digital video transmission possible it is necessary to compress that and have small amount of bit rate. (2.5Mbps)
II. TERRESTRIAL DIGITAL VIDEO BROADCASTING
DVB-T uses coded orthogonal frequency division multiplexing (COFDM), which uses as many as 8000 independent carriers, each transmitting data at a comparatively low rate. This system was designed to provide superior immunity from multipath interference, and has a choice of system variants which allow data rates from 4 M Bit/s up to 24 M Bit/s. One U.S. broadcaster, Sinclair Communications, petitioned the Federal Communications Commission to permit the use of COFDM instead of 8-VSB, on the theory that this would improve prospects for digital TV reception by households without outside antennas (a majority in the U.S.), but this request was denied. (However, one U.S. digital station, WNYE-DT in New York, was temporarily converted to COFDM modulation on an emergency basis for data casting information to emergency services personnel in lower Manhattan in the aftermath of the September 11 terrorist attacks.)
Fig: 1 block diagram of terrestrial digital video broadcasting.
This demo models part of the ETSI (European Telecommunications Standards Institute) EN 300 744 standard for terrestrial transmission of digital television signals. The standard prescribes the transmitter design and sets minimum performance requirements for the receiver.
The purpose of this demo is to Model the transmitter in its
"2k mode," as prescribed in the standard Model one possible receiver design Generate error statistics that will help determine whether the receiver model satisfies the performance requirements.
A. Random data:
the mixing of R,G,B with the digital data is the random intiger input data for RS encoder.
B. Rs encoder:
In coding theory, Reed–Solomon (RS) codes are non- binary[1] cyclic error-correcting codes invented by Irving S.
Reed and Gustave Solomon. They described a systematic way of building codes that could detect and correct multiple random symbol errors. By adding t check symbols to the data, an RS code can detect any combination of up to t erroneous symbols, and correct up to ⌊t/2⌋ symbols.
As an erasure code, it can correct up to t known erasures, or it can detect and correct combinations of errors and erasures.
The original concept of Reed–Solomon coding (Reed &
Solomon 1960) describes encoding of k message symbols by viewing them as coefficients of a polynomial p(x) of maximum degree k − 1 over a finite field of order N, and evaluating the polynomial at n > k distinct input points.
Sampling a polynomial of degree k − 1 at more than k points creates an over determined system, and allows recovery of the polynomial at the receiver given any k out of n sample points using (Lagrange) interpolation. The sequence of distinct points is created by a generator of the finite field's multiplicative group, and includes 0, thus permitting any value of n up to N.
The error-correcting ability of a Reed–Solomon code is determined by its minimum distance, or equivalently, by n
− k, the measure of redundancy in the block. If the locations of the error symbols are not known in advance, then a Reed–Solomon code can correct up to (n − k) / 2 erroneous symbols, i.e., it can correct half as many errors as there are redundant symbols added to the block.
For practical uses of Reed–Solomon codes, it is common to use a finite field F with 2m elements. In this case, each symbol can be represented as an m-bit value. The sender sends the data points as encoded blocks, and the number of
symbols in the encoded block is n = 2m − 1. Thus a Reed–
Solomon code operating on 8-bit symbols has n = 28 − 1 = 255 symbols per block.
The number k, with k < n, of data symbols in the block is a design parameter. A commonly used code encodes k = 223 eight-bit data symbols plus 32 eight-bit parity symbols in an n = 255-symbol block; this is denoted as a (n,k) = (255,223) code, and is capable of correcting up to 16 symbol errors per block.
For any single color
Color television stats with R, G, B and it also end with R, G, and B. To simplify the system if any one color would like to transmit than
n = 2m – 1 28 − 1 = 255 Bit length k= 223 (n,k) = (255,223)
So, it is capable of correcting up to 16 symbol errors per block.
Implementation of RS encoder in lab view
Fig:
2 Implementation of RS encoder in lab view
Fig: 3 Implementation of RS encoder in lab view
Simulation results for Color GREEN
Fig: 4 Simulation result of RS encoder For Color GREEN For color Blue
Fig: 5 Simulation result of RS encoder For Color Blue C. Convolutional encoder
Channel codes (also called error-correction codes) permit reliable communication of an information sequence over a channel that adds noise, introduces bit errors, or otherwise distorts the transmitted signal.
The purpose of a Convolutional encoder is to take a single or multi-bit input and generate a matrix of encoded outputs. One reason why this is important is that in digital
modulation communications systems (such as wireless communication systems, etc.) noise and other external factors can alter bit sequences. By adding additional bits we make bit error checking more successful and allow for more accurate transfers. By transmitting a greater number of bits than the original signal we introduce a certain redundancy that can be used to determine the original signal in the presence of an error.
As any binary code, convolution codes protect information by adding redundant bits. A rate-k/n Convolutional encoder processes the input sequence of k-bit information symbols through one or more binary shift registers (possibly employing feedback). The convolution encoder computes each n-bit symbol (n > k) of the output sequence from linear operations on the current input symbol and the contents of the shift register(s). Thus, a rate k/n convolution encoder processes a k-bit input symbol and computes an n-bit output symbol with every shift register update.
For our illustration we will assume a 5-bit input and rate- 1/2 code (two output bits for every input bit) as shown in fig 6. This will yield a 2x5 output matrix, with the extra bits allowing for the correction
Fig: 6 block diagram of convolution encoder Table 1 Convolusion encoder input/output
Input Output Input Output Input Output Input Output 00000 00000 01000 01110 10000 11100 11000 10010
00000 01010 10100 11110
00001 00001 01001 01111 10001 11101 11001 10011
00001 01011 10101 11111
00010 00011 01010 01101 10010 11111 11010 10001
00010 01000 10110 11100
00011 00010 01011 01100 10011 11110 11011 10000
00011 01001 10111 11101
00100 00111 01100 01001 10100 11011 11100 10101
00101 01111 10001 11011
00101 00110 01101 01000 10101 11010 11101 10100
00100 01110 10000 11010
00110 00100 01110 01010 10110 11000 11110 10110
00111 01101 10011 11001
00111 00101 01111 01011 10111 11001 11111 10111
00110 01100 10010 11000
Implementation of Convolution encoder using lab view
Fig: 7 Implementation of convolution encoder in lab view Simulation result for Blue
Fig: 8 Simulation results of RS encoder and correspondence Convolution encoder For Color Blue For Green
Fig: 9 Simulation results of RS encoder and correspondence Convolution encoder For Color Green.
C. Convolutional interleaver
A Convolutional interleaver consists of a set of shift registers, each with a fixed delay. In a typical Convolutional interleaver, the delays are nonnegative integer multiples of a fixed integer (although a general multiplexed interleaver allows arbitrary delay values).
Each new symbol from the input signal feeds into the next shift register and the oldest symbol in that register becomes part of the output signal. The schematic below depicts the structure of a Convolutional interleaver by showing the set of shift registers and their delay values D(1), D(2),..., D(N). The blocks in this library have mask parameters that indicate the delay for each shift register.
The delay is measured in samples D. OFDM
Orthogonal frequency-division multiplexing (OFDM) is the modulation technique for European standards such as the Digital Audio Broadcasting (DAB) [ETSI, 1997a] and the Digital Video Broadcasting (DVB) [ETSI, 1997b]
systems.
OFDM is a block transmission technique. In the baseband, complex-valued data symbols modulate a large number of tightly grouped carrier waveforms. The transmitted OFDM signal multiplexes several low-rate data streams — each data stream is associated with a given subcarrier. The main advantage of this concept in a radio environment is that each of the data streams experiences an almost flat fading channel. In slowly fading channels, the inter symbol interference (ISI) and inter carrier interference (ICI) within an OFDM symbol can be avoided with a small loss of transmission energy using the concept of a cyclic prefix.
III CONCLUSION
This is simulation of RS encoder and Convolutional encoder for terrestrial Digital video broadcasting television system, so one can do all the necessary changes without practical implementation for better result. The important parameters of television transmission systems like bandwidth requirements signal to noise ratio, modulation techniques, fault simulation, resolution, bit error rate etc can be analyzed. Based on these parameters, modeling and simulation can be done and model becomes over simplified. Transmission would be much more effective.
IV FUTURE SCOPE:
With the help of Rs encoder and convolution encoder the perfect model of DVB-T using OFDM will be developed and specify the bit error rate of the system using lab view.
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