CHAPTER 1 : INTRODUCTION

Transcription

1 1 CHAPTER 1 : INTRODUCTION 1.1. Introduction to Dual Tone Multi Frequency (DTMF) DTMF is a way for instructing a telephone switching system of the telephone number to be dial, or to concern commands to switch systems or linked telephony equipment. DTMF dialling scheme traces its line to a system "AT&T developed in the 1950s call Multi-Frequency" which was deploy within the AT&T touchtone phone network to direct calls among switching services by in-band signalling. In the early on 1960s, a derived procedure was offered via "AT&T" throughout its Bell System touchtone phone companies as a "modern" way for set of connections customers to position calls. In "AT&Ts Compatibility Bulletin No. 105, it describe the product as a process meant for pushbutton signal as of client stations by means of the voice broadcast lane". The customer product was marketed by AT&T beneath the registered deal name Touch-Tone. Former vendors of like-minded telephone equipment called this alike system "Tone" dialling or "DTMF"[1]. Fig.1.1 4X4 Keypad having frequencies (Low & High) DTMF signalling have numerous applications such as touchtone phone dialling, data way in, credit inspection, and accent mail system organize. A DTMF gesture

2 2 Consists of two superimpose sinusoidal waveforms by means of frequencies selected from a rest of eight harmonized frequencies. These frequencies have to be generate and detect according to the "CCITT" counsel [2-5]. The DTMF arrangement uses eight altered frequency signals transmitted in pairs to signify sixteen altered letters, numbers & symbols. The Fig.1.1 show how the frequencies are structured. The frequencies used be selected to avoid any harmonics as of being the wrong way detected by the receiver as various former DTMF regularity [6-9]. From the fig.1.1 The ABCD tones are simply supplementary DTMF tones so as to might be use in several way the standard (0-9) tones be used. The ABCD tones be used here the U.S. armed forces touchtone phone network, in various ACD systems meant for manage messages in various PBX systems, as well as in various amateur broadcasting auto-patches [10]. During the AutoVon arrangement, unique telephones be prepared by ABCD keys. The ABCD keys be define as such: A Flash B Flash take priority over C Priority contact D Priority overrule At one moment in time it be feasible to employ the ABCD tones to right of entry a special preservation style of the ACD systems use by means of Directory assist operators to bond two callers as one. The use of the Silver Box is to generate the ABCD tones [11] DTMF Generation and Detection This development is of DTMF" recognition through Goertzel algorithm. The initial tap tone telephone mechanism be within DTMF signalling uses voice-band tones

3 3 on the way to remit address signals as well as previous digital information commencing pushbutton telephones along with other devices such as fax machines and modems. Analog DTMF recognition is completed by means of band-pass filter banks by way of axis frequencies at the DTMF sign frequencies. Digital finding of DTMF is finished by quite a few algorithms be fond of notch filter, Goertzel etc [12-15]. The aerial of a DTMF signal at the same time sends single frequency from the high-group as well as single frequency as of the low-group. This couple of signals represent the symbol or the digit exposed at the connection of row with column in Fig For instance, transfer 1209Hz and 770Hz indicate with the intention of the "4" number is being send. The fig.1.2 represent the fundamental DTMF Communication scheme. Fig.1.2 DTMF communication scheme By the side of the aerial, the utmost signal strength of a join up of tones should not go beyond +1 dbm, as well as the minimum strength be dbm intended for the low group frequencies & -8.5 dbm for high-group frequencies. While the deliberately not sending DTMF tones, any seepage of these tones be required to not go beyond dbm. The frequencies generated by the aerial be required to be supposedly in 1.5% of the stated values along with the receiver should not accept signals so as to deviate additional than 3.5% from the settled values.

4 4 The handset is accountable for performing quite a few checks resting on the incoming signal previous to accept the inward signal as a DTMF numeral: Energy as of a low-group and a high-group frequency have to be detect. Energy as of all former low-group and all former high-group frequencies should be not present or else not as much of -55dBm. The energy commencing from the solitary low-group and solitary high-group frequency ought to persevere intended for at least 40ms. There should be an inter digit space have at least 40ms. Here around there is no energy detect at whichever of the DTMF frequencies. The bare minimum duty cycle is 85ms. The handset should obtain the DTMF digit by way of a signal power of at least -25 dbm and no extra than 0 dbm. The energy strong point of the "high-group frequency have to be -8 db to +4 db" qualified to the energy strength of the "low-group frequency the same as measured at the receiver". This jagged broadcast level is branded as the "twist", and various receiving tools may not accurately obtain signals where the "twist" is not implemented accurately. Almost all current DTMF decoders receive DTMF digits rightly in spite of twist error. The handset should accurately perceive and decode DTMF in spite of the occurrence of dial tone, together with the intense case of dial-tone being send by the central agency at 0 dbm. Higher than 600Hz, any erstwhile signals detected by the handset be obliged to be at least -6 db less than the low-group frequency signal strength in favour of proper digit recognition.

5 5 The standards made known be those settled by AT&T in Compatibility announcement 105. On behalf of compatibility by means of ANSI T , the bare minimum inter-digit space shall be 45ms, the smallest amount pulse interval must be 50ms, as well as the smallest amount "duty cycle" meant for "ANSI compliance shall be there 100ms"[16-23] Methods in favour of generate DTMF tones DTMF production be capable of different methods in favour of analog as well as digital systems. Use unique IC to generate DTMF tones. Telephones & Modems employ this scheme. Produce DTMF tones by "soundcard FM synthesizer chip". Load sine wave example to wavetable soundcard remembrance. Play so as to the sample using two instrument channel by the side of altered frequencies. Sample each and every one DTMF tone combination headed & play support these samples as essential. "8 khz at 8 bit resolution" be sufficient meant for that. Generate sample information which is play support by means of software. This research work is concentrating on the look-up table method, because it is the most generic way to do the DTMF generation. By this method every sound card which can play back samples and it is as well suitable for DSP implementation also [24-38] DTMF Generation and Detection - Methods The another methods for the generation of the DTMF tones will be Polynomial approximation Look-up table Recursive oscillator

6 6 Dual tone generation can be done with 2 sine wave sources connected in parallel. Different method can be used for such implementation: DTMF signal must meet certain duration and spacing requirements: 10 Digits are sent per second. Sampling is done via a codec at 8 KHz. Each tone duration must be > 40ms and a spacing of 50ms Minimum between two digits is required. DTMF generator refers to any electronic device capable of generating Dual Tone Multi-Frequency (DTMF) signals used for dialling touch-tone telephones. The DTMF dialling system operates by configuring a keypad in a three column by four row grid representing the numbers 0 through 9 and other special characters such as the # and * keys. The touch pad grid is arrayed by assigning a specific high frequency for each column and a designated low frequency for each row [39-44]. Fig.1.3 DTMF tone generator

7 7 When a user presses a digit on the keypad, a dual tone is generated that represents the intersection of the two distinct frequencies assigned for each column and row on the grid [45]. The equivalent tone generated by the keypad is next transmitted towards the local headquarters of the telephone corporation. Here it is decoded or translated hooked on the appropriate equivalent digits which permit the elected mobile phone number to be dialled [46-48]. For that reason the tones in keypad be generated by captivating one of the occurrence as of the row selector as well as the former frequency commencing the column selector [49-51]. These two frequencies unite as well as provide the twin tone by the side of output. The DTMF tone generator is an initial business application of DTMF producer. The Touch Tone Dialling (TTD) system be evidently quicker as well as more suitable than the automatically base rotary dial beat system which it supplant. After its introduction it be eventually adopted international from United States [52]. Touch-tone dialling permits activation and communication with DTMF-compliant equipment. This type of dialling allows users to control answering machines remotely and to activate and interface with much call routing, voice mail systems, or other auxiliary telephonic devices that can decode signals produced by a DTMF generator [53-57]. Telephones are capable of, by way of DTMF based TTD consent to customers to access their bank account balance, and rescue other information as of organization so as to give a telephonic interface based on top of the DTMF system [58-61].

8 8 Table.1: ITU Standards for DTMF Signals Characteristic Type Specification Frequency Tolerance Operational 1.5% of Hz Non-Operational 1.5% of Hz Signal Duration Operational 40 ms min. Non-Operational 23 ms max. Signal Exceptions Pause Duration 40 ms min. Signal Interruption 10 ms max. Twist Forward 8 db Reverse 4 db Signal Strength Signal-to-Noise Ratio 15 db min. Signal Power -26 db min. A system with a sound card in addition to digital acoustic software is talented of performing as a DTMF producer by produce the twin tone multi frequencies used on touch-tone telephone keypads. The software program interpret the handset digits and generates the proper audio records that obey the rules to the consistent DTMF matching frequency tone [62-72]. The dialling process can be activated either by a mouse click or through keyboard commands. This allows for rapid automated computer dialling of outgoing telephone numbers and is used by many businesses. The ITU values intended for DTMF signals be tabulated over [73-74] Organization of Thesis Chapter 1: This part gives a basic overture about Dual Tone Multi Frequency (DTMF). In this chapter also discussed about DTMF Tone generation & Detection. Methods of generating DTMF tones are clearly explained.

9 9 Chapter 2: Chapter 3: Chapter 4: Chapter 5: Chapter 6: Chapter 7: This chapter deals with Literature Survey of the thesis. The Existing Methods & Proposed Solutions are mentioned in this chapter. This chapter gives on the subject of a brief overview of proposed Architecture Design of DTMF module. This chapter gives the detailed explanation about modules & sub modules of proposed design. This chapter deals with MODELSIM Simulation results of Proposed Architecture Design with a clear explanation. This chapter deals with Synthesis Reports of Proposed Architecture Design. RTL Schematic, Technological Schematic, Xpower, Place & Routes screenshots are showed. And finally tables for all phases are compared This chapter deals with Xilinx ChipScope Results of Proposed Architecture Design to investigation the FPGA inside outcome whereas the logic successively on FPGA. This chapter gives the Conclusion and Future Scope for the Project. 1.6 Conclusion In this chapter the concept of Dual Tone Multi Frequency (DTMF) is explained along with existing generation and detection methods [1-2, 88]. The International Telecommunication Union (ITU) is an agency of the United Nations (UN) and the purpose is to coordinate telecommunication operations and services throughout the world. ITU standards for Dual Tone Multi Frequency signals are tabulated. A clear view of thesis organization also given. The following chapter gives the review of literature about the existing methods of dual tone multi frequency detection and implementation.