WO2000033501A2

WO2000033501A2 - Adaptive modem and method for adaptive election of modulation mode

Info

Publication number: WO2000033501A2
Application number: PCT/FI1999/000952
Authority: WO
Inventors: Pauli Lallo; Pekka Peltoniemi; Mauri Sekki; Ilpo Tervapuro
Original assignee: Pauli Lallo; Pekka Peltoniemi; Mauri Sekki; Ilpo Tervapuro
Priority date: 1998-11-17
Filing date: 1999-11-17
Publication date: 2000-06-08
Also published as: FI982479A0; FI982479A; AU1389300A; WO2000033501A3

Abstract

Adaptive modem including modem part which comprises a transmitter and a receiver using digital signal processing and a control unit needed for the control of the modem functions, interface for the telecommunication network, where we have interfaces for the telecommunication network, and the signal amplification and waveform shaping units needed in transmission and receiving process, and the computer bus interface. Digital signal processing includes the calculation algorithms of an application of Fourrier Transform, where the transmitter and receiver functions are made with the algorithms mentioned optimally adaptive to the transmission speed, bit error and/or bandwidth of the available communication channel.

Description

Adaptive Modem and Method for Adaptive Election of Modulation Mode

The invention is focused on the adaptive modem for data transmission and it is defined in the introduction part of the claim one.

In known data modems fixed frequencies, phases and amplitudes are used. In symbol transmission the information corresponds to waveforms according to the different modulation methods. Each waveform means thus one or several bits (binary digit). Table 1 shows ITU-T standard modems III. In the table a symbol equals one, two, etc maximal six bits (64-QAM). In these modems a symbol corresponds one frequency (carrier), one certain phase of the carrier frequency or some amplitude of the carrier frequency on the communication line. Modems are used in all analogy transmission channels for data transmission including radio channels. Restrictions of the technology described above are:

- It uses one carrier frequency, according to the table mostly 1800 Hz.

- Maximal 6 bits correspond to the certain waveform, thus there are a limited number of waveforms to present different symbols, according to the table we have maximal 64 different symbols as a 6 bit presentation with 64-QAM modulation,

- Bandwidth is adjusted to the traditional 300 - 3400 Hz analogy telephone network, according to the table and study the old fashioned FSK technology made slow 1200 bit/s N.23 modem has the narrowest bandwidth 900-2500 Hz.

Nowadays information technology produces only digital two-level data (0 or 1). The need to transmit data has caused the evolution of digital telecommunication networks 121. The public opinion is thus in digital telecommunication using optical or fibre cables, where this digital on/off transmission is sufficient. Study associated with radio communications and digital telecommunication ISDN phones has developed digital modulation methods 131, where the digital state (0 or 1) must be transmitted in analogy form.

Common modems have a very limited number of allowed frequencies, phases (for example 8) and amplitude values, Table 1. A disadvantage of present modems is the limited operational range focused to the certain telephone bandwidth or on the other hand range focused the certain radio equipment and channel. They cannot adapt to different type of channels for example the narrower than standard telephone or radio channel or on the other hand the broader bandwidth. Using present modems we cannot have fast data transmission or proper speech or picture transmission.

The limitation of the present ISDN technology is the fixed standard communication and speed of B- channel 64 kbit/s between the subscriber and the exchange 141. The service offers two B-channels and one C-channel 16 kbit/s.

The adaptive modem can handle much more frequencies, phases and amplitudes than common modems in generation of different waveforms. The adaptive modem is not limited to a fixed modulation method but it adapts to the possibilities of the transmission channel in use. Characteristic for the invention is what is presented in the claims.

Table 1 ITU standard modems 71/ and 73/

The invention includes that waveforms used correspond to the rich symbol file, in theory almost unlimited number of symbols, thus we get the following advantages:

The transmission speed of the telephone subscriber over the Internet or over the common telecommunication network is higher than the present ISDN 64 kbit/s or the modem 33.6 kbit.

The data communication is much faster because waveforms in the adaptive modem algorithm correspond to a larger number of bits than presently. Using the equivalent symbol rate we can transmit much more bits than nowadays.

Based on the adaptive performance the modem suits to most telecommunications systems in use and the bandwidths their communication channels provide (including radio and telecommunication channels), which is a quality the common modems cannot provide. The adaptation to the communication channel available is made by software without any change m the mechanic structure or mterconnection of the adaptive modem In the same way the operation mode can be changed on the radio frequencies By the parameter changes the selections like modulation method, transmission speed and quality of service (bit error rate) are made

The adaptive modem fits its performance to each available channel and transmission environment by optimising automatically the functions according to the criterion selected Cnteπons may be for example the channel bandwidth and frequencies, the bit error rate allowed during telecommunication, transmission speed needed, encryption algorithm, error correction etc Modem uses for waveform generation a calculation algorithm and digital to analogy transform and an interface unit between the processor and the telecommunication network In reception we need similarly an interface unit, an analogy to digital transformer, a calculation algorithm for waveform detection and a processor Between the computer and the modem we have a standard connection

In the following the invention is explamed more exactly referring to the enclosed figures, where

Figure 1 is a block diagram of the software modem card

Figure 2 presents the amplitude modulation

Figure 3 presents the phase modulation

Figure 4 presents the amplitude and phase modulation

Figure 5 presents the sum waveform of several different frequencies

Figure 6 is a block diagram of the modem card of the radio modem

Figure 1 block ώagram left side presents a computer PC, where the software modem mterfaces ISA-, PCI- or USB-bus The modem part on the card gets the power, data- and address signals and the interruption signals through the interface The modem card has buffer circuits for the signals

SIGNAL TRANSMISSION

The mam component of the modem part is the signal processor, which gets the on process or the transmittmg data from the PC data bus In reception the signal processor feeds data to the PC data bus The processor also partly takes care of side tones and echo cancellmg The modem software is loaded through the PC data and address bus Memory is EEPROM type, which can be programmed electrically

The modulated digital data from signal processor is transformed to analogy by digital to analogy converter Its analogy voltage message is connected to an opto isolator unit, which separates galvanic the telecommunication network interface from the converter

The output voltage of the signal is lead to the stepwise controlled amplifier the gam of which is regulated with resistors proper for the telecommunication network The output voltage of the amplifier is connected to the resistor bridge from where the signal proceeds through a rectifier to mcorning call identification and overvoltage protection circuit. From there the modem signal proceeds into the two-wired telecommunication network.

SIGNAL RECEPTION

The modem signal from the telecommunication network goes through the incoming call identification and the overvoltage protection circuit to the rectifier, from where the signal is connected to the resistor bridge. The function of the bridge is to build so called side noise free connection or let the incoming modem signal from the telecommunication network pass but reject at the same time the outgoing modem signal to the telecommunication network to get connected to the amplifier of the reception.

The incoming modem signal proceeds automatically to the level locking amplifier, which identifies the signal magnitude and after that locks the proper amplification factor. This adaptive action assists the error free function of the reception especially then, when the received signal levels are weak. From the amplifier the signal proceeds through the opto isolator unit to the analogy digital converter. It converts the analog voltage message into digital for the signal processor. The signal processor detects or demodulated from the digital signal a message, which is lead to the PC data bus.

OTHER PARTS

The function of the call identification and overvoltage protection circuit is to identify the call from a B-subscriber and inform the call to the PC through the opto isolator unit. The function of the unit is also connect through the transmitting and the receiving modem signal. The overvoltage protection rejects the flashing or other high voltages to cause damage to the telecommunication network interface unit. If the PC user is an A-subscriber the control signal is connected through the opto isolator to line interface, and then the modem card is galvanic connected to the telecommunication network. After that the signal processor builds a call sequence to the B-subscriber, and then the connection is ready. The blocks of the interface parts of the telecommunication network get the power from the interface unit power, which does not load the telecommunication network and its power feeding blocks.

GENERATION OF TRANSMISSION WAVEFORM

The adaptive modem applies the Discrete Fourier Transform 151-161 both in the generation of the waveform and in its detection algorithm. The generally known Fourier transform is applied in some measuring equipment as a Fast Fourier Transform (FFT), where we cannot exploit all the transmitted samples in data transmission but onlu in powers of two thus: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 etc The invention like adaptive modem applies the Discrete Fourier Transform and can use all sample numbers encountered in practical applications 8, 9, 10, 11, 12, 16, 32, 100, 1024, etc, thus we can talk about the adaptive function according to the number of the mark (symbol) length We have to mention that the transmitted symbol contams N samples, and thus we get the tune domam length of the symbol and symbol rate The possible sample rate (Sound blasters max 45 000, dsp 120 000, USB

12 000 000 samples Is) of the available technology has effect on the symbol rate The adaptive modem has not been possible before the technology had developed to the present level

According to the coding method of the analogy signal like speech we get one (adaptive delta modulation), two or more for example 8 (PCM) bits The adaptive modem combmes the bits into symbols, which can have 1, 2, 3 or more bits, a very large number of bits The adaptive modem can transmit the coded speech regardless of the coding method used

With the coded text the adaptive modem offers an analogy transmission counteφart for ASCII-code The equal standard codes get their analogy standard counteφarts, which is not realised in modems on the market Coding can be made mstead of bit coding as present with different symbols saved in the computer memory into the analogy transmission mode using the adaptive modem We will develop new standards for the analogy coding of different digital symbols, text, picture, map etc

In figure 1 we have a low sine wave 0-bιt and a high wave is 1-bit In figure 1 we present only amplitude modulation It is usual that fast direct cable connections use digital transmission, where 1- bit is a voltage value over a threshold and 0-bιt is the voltage value below that threshold In figure 1 we present the letter "H" ASCII code with the most trivial amplitude modulation It has only one wavelength (18 samples), no phase changes and only one bit in every wavelength In figure the vertical axis present the voltage and the hoπzontal axis is time White vertical lines are at every tenth sample

Figure 2 is the same ASCII code and the letter "H" is presented by the pure phase modulation If the wave has no phase change in the beginning, it is 0-bιt If the change is 180 degrees, it is inteφreted as 1 In figure 2 we have thus H = 01001000

If we combme the figures 1 and 2 we get the presentation of figure 3 for amplitude and phase modulation A most simply situation In figure 3 every wavelength transmits two bits The first one is amplitude modulated and the second is phase modulated In figure three we have a message "Ha"

If we are satisfied with the figure 3 presentation, we do not get a very fast lme transmission speed If we use mstead of one wave (carrier) four waves (carriers) as follows the second wavelength is Vz > times the first and the third is ^lΛ times the first and the fourth is 1/8 times the first and we a ow 16 states for amplitude heights and 16 different phase change states, we get the situation m figufe 4 In figure 4 we have quite fast signal, which we can detect with the Discrete Fouπer Transform (DFT) We are looking the sum waveform of several different frequencies The transmittmg modem processor has generated the sum waveform usmg general algorithms

Accordmg to the transmission channel quality we can use for example 20 different frequencies at the same time, 8 bits usmg one wave (earner) and modulation method The number of samples in the basic (first) wavelength (earner) can be for example 64 and the lowest waveform can be selected according to the limits set by the channel Still the frequencies can be compressed for example mto 50 Hz channels and we can still calculate the detection result with the algonthm denved from the Founer transform, this means that all the waveforms mcluded in the sum waveform can be detected with the modem processor unit

DESCRIPTION OF THE ADAPTIVE RADIO MODEM

The block diagram of the software radio modem card is presented m figure 5 The modem card is connected to the PC with ISA, PCI or USB bus accordmg to the version The modem part m the card gets the power, data and address signals and interruption signals via bus For the signals we have buffer circuits on the modem card

The mam component on the modem part is the signal processor, which get the transmittmg data from the PC data bus The processor is also available for the use of the spread spectrum technology The signal processor works usmg a program memory The modem software is loaded via the PC data and address bus The memory is EEPRON type, which can be electrically programmed

The modulated digital data from signal processor is converted to analogy with a digital to analogy converter Its analogy voltage message is connected to the step adjustable amplifier, the gam of which can be set with resistors if needed to proper value for the modulator The output voltage of the amplifier is connected to the modulator, from where the signal proceeds to the RF or radio transmitter The function of the modulator is to put the transmittmg data signal mto the high frequency earner usmg amplitude or/and phase modulation The RF transmitter works as the amplifier for the high frequency and modulated earner, from where the signal is lead to the transmittmg antenna (RX-TX-antenna)

The reception of the signal is made by leading the high frequency modem signal from the receiver antenna to the RF-receiver, which works as the amplifier for the high frequency signal The RF- receiver feeds the demodulator or discriminator, where the data signal is separated from the high frequency earner The modem signal proceeds further automatically to the level locking amplifier, which identifies the magnitude of the signal and after that it locks the proper gam factor This adaptive effect helps the error free function m the reception when the signal levels are weak The signal proceeds further to the analogy digital converter It converts the analogy voltage message mto digital for the signal processor The signal processor in turn detects or demodulates the message from the received digital signal The message is put to the PC data bus

The function of the call identification circuit is to identify the incoming radio data message and inform it to the PC Then PC can be ready for the data signal processed by the signal processor When PC sends data by radio, a control signal is connected to the transmission mterface, and then the RF-transmitter is turned on After that the signal processor generates the data signal for the transmission

A modem system accordmg to the presented principle may be both a data modem needed for data transmission and a digital radio where broadband- or so called frequency hopping transmitter is needed and a detector needed in the receiver The mark, data or symbol waveforms are generally ready saved m the memory and they are detected by calculations with the algonthm based on the Founer transform Here we need a signal processor and memory circuits and the software saved m the memory circuit The essential part of the modem is the mterface, by which the program made or in the memory saved waveform accordmg to the transmitted symbol etc is transferred to the telecommunication network or to the radio channel The applied study of the telecommunication technology, digital signal processmg, computer programming and present electronics and signal processors and analogy-to-digital converters m the adaptive modem creates a whole system, which guarantees the transmission speed faster than the present (common) speed The (data) transmission speed can be adjusted accordmg to the situation It is rejected only through the bandwidth available, the signal-to-noise present and the level of the information technology and electronics at the moment

In the patent application presented adaptive modem is much faster than the known standard modems mentioned in the request accordmg to the tests already made In the known modems the digital data transmission is generated already m the telephone equipment (ISDN phone) or m the first telephone exchange at the other end of the xDSL-subscnber lme (no end-to-end principle) The adaptive modem is quite different to that It is designed to work

- Over narrow voice transmission lines by end-to-end principle and usmg complex even arbitrary selectable waveforms accordmg to each need

- Over existing different analogy channels as modems usmg analogy transmission lmes or even usmg present analogy channels which are made digitally (ISDN phone) as a faster data transmission alternative for the standard modems Design principles are exceptional compared to the common data modem design The function of the adaptive modem is based on the generally known Founer transform and series theory made by Joseph Fourier (1768-1830) Accordmg to the digital signal processmg principles the invention uses the Discrete Founer Transform based calculation algonthm for the calculation of the amplitude and the phase This makes it necessary to sample the analogy signal m reception and to decode the symbol with the calculation algonthm based on the Discrete Founer Transform The known signal processmg and spectrum calculation equipment solutions use the Fast Fourier Transform (FFT) but the adaptive modem uses the Discrete Fourier Transform as a basis for the design of the signal detection and calculation algorithm. This feature is a major part to prove the adaptive modem a real invention and shows its difference to the common designs.

For every carrier used in the multi carrier technology we have calculated in real time their amplitude and phase. So we can detect the transmitted symbol from the so-called signal constellation. The adaptive modem can easily detect more complex signal constellations than the present, in-use, standard or otherwise common modems. We can mention one example of these kind of waveforms n times 1024-QAM. Here n means the number of carriers. The waveform can be adapted to the possibilities offered by the channel, it is - the allowed signal power dynamic range, amplitude max and min limits in volts - the frequency max - min values in Herz - the smallest frequency selectivity in Herz - the smallest amplitude step and - the smallest phase difference.

The achieved data rate can be selected partly according to the above but also by selecting the sample rate and the sample number in the symbol and the resulting symbol rate Bd. These are also some factors which greatly proves the adaptive modem is a real invention and different from the common generally known.

Based on this we have designed a computer assembly language calculation algorithm, which can detect carriers, their amplitudes and phases or detect complex waveforms. Modems having the same functionality is neither presented in publicity nor standardised or known to exist. Thus the adaptive modem is suitable to use over the narrow bandwidth better than any known modem. Examples of these channels are all international over telecommunication network working connected telephone lines, radio telephone connections (NMT, GSM, satellite phone and new voice radio communication systems), military radio communication over different frequency bands (HF, VHF, UHF, etc). The adaptive modem works not only over the narrow band but also as a broad band modem. This is also a factor which greatly proves the adaptive modem is a real invention and different from the common generally known.

Because the computer is interfaced with the radio and the telecommunication network, thus we have designed interfaces for the modem. The interface is a part of the waveform receiver and it includes the signal manipulating circuits needed. The complex waveforms need a very exact level control and synchronism. With the transmission and reception algorithms the system is a complete "adaptive modem" as described in the claim document. This is also a factor which greatly proves the adaptive modem is a real invention and different from the common generally known.

Because the adaptive modem is a method, which uses complex waveforms and each waveform uses several bits in a symbol and the number of bits is much greater than any known .njrrow voice band data modem can do, the adaptive modem has a better data transmission rate than common modems.

REFERENCES

I I CCITT, IX^th Plenary Assembly, Melbourne 14-25, November 1988 _; Blue Book, ITU, Geneva, 1989.

Ill Grundstrόm M., Mickos R., ATM teknϋkkka ja monipalveluverkot, Suomen Atk-kustannus Oy, Espoo, 1997.

βl Proakis J. G., Manolakis D. G., Digital Signal Processing Principles, Algorithms, and Applications, MacMillan Publishing Company. New York, 1992.

74/ Volotinen, V., Tietoliikenne, Verkotja paatelaitteet, WSOY, Porvoo, 1994.

151 Couch II L. W.. Modern Communication Systems, Principles and

Applications,

Prentice Hall, Englewood Cliffs, New Jersey, 1995.

Claims

1. Adaptive modem, which includes

- modem part which has transmitter and receiver units both using digital signal processing and a control unit needed for the modem functional control,

- tele- and radionetwork interface part which has interfaces and signal amplification and waveform shaping units needed in transmission and receiving process,

- computer bus interface, characterized in that digital signal processing includes a calculation algorithm based on Discrete Fourier Transform, analysis of line response based on trigonometric or exponential calculation loops, correction algorithm and control parameters so that modulation of the transmitter and receiver is possible to adapt to optimal with the algorithm mentioned in respect to the data transmission speed, bit eπor rate and/or bandwidth of the communication channel.

2. Adaptive modem according to claim 1 characterized in that the modem includes a program which is used for the receiver operation mode change so that the receiver can detect different digital modulations generated by the transmitter like modulations based on different symbol lengths, different numbers of bits in symbol, several simultaneous carriers (multi carrier) or different combinations of several amplitude levels and phases in puφose specially to speed data communications using ordinary telephone lines.

3. Adaptive modem according to claims 1 and 2 where the transmitter is a radio transmitter and the receiver is a radio receiver and where the modem includes a radio interface unit characterized in that the modem unit includes a program change function which makes it possible to use in spread spectrum mode over the bandwidth desired.

4. A method to select the modulation mode adaptively according to the claim one for each communication route of the adaptive modem, characterized in that the transmitted modulations and modulation methods are selected to different waveforms according to the principle that in reception we get by calculations the wanted or the maximal selectivity of transmitted carrier, amplitude and phase of the modulated waveforms using the algorithm developed from the Fourier Transform and using the wanted sample frequency for the waveforms in data transmission over the telecommunication network interface unit or over the radio interface unit.

5. A method according to claim 4 characterized in that in the method each bit, several bits, ASCII character, symbol, data, message, speech or for example picture equals a specific waveform as a part of the modulation.

6. A method according to claims 4 and 5 characterized in that over the telecommunication network or over the radio channels a message is transmitted as a combined calculated and coded sum waveform of several different waveform modulations which are in reception detected to waveforms and using the code information decoded as a message.