MXPA06004631A

MXPA06004631A - System and method for frequency modulation in a modem

Info

Publication number: MXPA06004631A
Application number: MXPA/A/2006/004631A
Authority: MX
Inventors: Letounov Leonid; Sharayeuski Vladimir; Hryhoryeu Aliaksandr
Original assignee: Nuovotel Properties Avv
Priority date: 2003-10-29
Filing date: 2006-04-26
Publication date: 2006-12-13

Abstract

The invention provides a method for transmitting information across a communication channel, comprising the steps of:- extracting, from a two-directional information flow signal at theside of a first subscriber, information transmitted by the first subscriber;- modulating said extracted information with a carrier frequency f1, for providing a frequency modulated (FM) information signal;- mixing said frequency modulated (FM) information signal into said two-directional information flow signal in said communication channel;- extracting at the side of a second subscriber from the two-directional information flow signal the transmitted frequency modulated (FM) information signal;- demodulating said transmitted extracted frequency modulated (FM) information signal for providing the information as transmitted by the first subscriber;mixing the information into the two-directional information at the side of the second subscriber.

Description

SYSTEM AND METHOD FOR MODIFYING FREQUENCY IN A MODEM Field of the Invention The present invention relates to a system and method for transmitting information through a communication channel. The invention relates more specifically to a system and method for transmitting information through a standard telephone communication channel. BACKGROUND OF THE INVENTION Existing telephone modems using standard protocols such as V.34 or V.90 or V.92 provide the maximum information transmission rates only in high-quality communication lines where the proportion of the the signal to the noise energy (S / N ratio) becomes more than 32 dB for the V.34 protocol and 52 dB for the V.90 and V.92 protocols. The standard for lower quality communication lines, such as a telephone line, is a signal to noise (S / N) ratio of approximately 38-40 dB. In such lines the transmission speed stipulated by the V.34 protocol can still be obtained, but a transmission speed of 56 Kbit / s (V.90 and V.92 protocols) is practically never achieved. In noisy communication lines, i.e. at S / N ratios of up to 20-25 dB that are widely diffused in the world, the transmission speed does not exceed 10-15 Kbit / s. SUMMARY OF THE INVENTION It is an object of the present invention to provide a system and method for transmitting data wherein at least the above disadvantages are obviated and which provide an increased transmission capacity on the communication channel. A further objective of the present invention is to provide a transmission system and transmission method with increased transmission capacity using standard telephone lines and existing systems (including modems, telephones, etc.) and using standard communication protocols (eg V.34, V.90, V.92). According to a first aspect of the invention there is provided a method for transmitting information in a bidirectional flow signal through a communication channel between a first subscriber and a second subscriber, the communication channel comprising a first part and a second part , the method comprising the steps of: extracting from the bi-directional flow signal at the end of the first subscriber of the first part of the communication channel, the information transmitted by the first subscriber; - modulating said extracted information with a carrier frequency fi to provide a frequency modulated (FM) information signal; mixing said frequency modulated information signal (FM) in said bi-directional information flow signal at the end of the first subscriber of the first part of the communication channel; extracting from said bi-directional information flow signal at the end of the second subscriber of the first part of the communication channel the transmitted frequency modulated (FM) information signal; demodulating said extracted frequency modulated (FM) information signal transmitted to provide information as transmitted by the first subscriber; - mixing the information transmitted by the first subscriber in the bi-directional flow signal in the second part of the communication channel. According to a second aspect of the invention there is provided a system for transmitting information through a communication channel, comprising: extracting a bi-directional information flow signal at the end of the second subscriber of the first part of the channel of communication, the information transmitted by the second subscriber; - modulating said additional extracted information with a second carrier frequency f2 to provide a frequency modulated (FM) information signal; mixing said frequency modulated information signal (FM) in said bi-directional information flow signal in said communication channel; - extracting the transmitted frequency modulated information signal (FM) at the end of the first subscriber of the first part of the communication channel of the bi-directional information flow signal; - demodulating said extracted frequency modulated (FM) information signal transmitted to provide the information as transmitted by the second subscriber; mix the information in the bi-directional information at the end of the first subscriber of the first part of the communication channel. As mentioned above, the invention relates to the field of telephone communication and allows the total transmission capacity of a communication channel to be increased by a telephone line when using standard telephone sets and modems by increasing the transmission capacity of that part of the telephone. communication channel that has a relatively low transmission capacity. More specifically, the total transmission capacity of the communication channel is increased by increasing the transmission capacity of the "end" part of the communication channel that is called the "last mile". The method and system allow, under similar conditions, to carry out the transmission of information with greater speed (in comparison with previous channels) due to the fact that in the present method and system the transmission of information through a telephone communication line takes performed by applying a frequency modulation (FM) process, where while a modulation signal is used, the information transmitted by a standard subscriber (telephone, modem), is located at the respective end of a telephone line. At the second end of a telephone line, the transmitted FM signal is demodulated and sent to the second subscriber, in whose role as a rule, the automatic telephone station (ATS) equipment, for example an urban center, acts, but Such a role can also be acted on by a telephone, a modem and so on. Similarly, the transmission of the information from the second subscriber to the first subscriber takes place. The standard subscriber in most cases will be an existing standard subscriber device. The invention therefore ensures an increase in the total transmission rate of a communication channel comprising an existing telephone system, for example formed by an existing standard telephone and an existing standard ATS, by placing the first and second devices in the vicinity of both, the first existing subscriber apparatus and the second existing subscriber apparatus. Preferably the first and second devices are provided in separate housings so that the installation thereof can be performed without having to interfere (e.g. when opening the cover) with the existing subscriber apparatus. In order to provide additional discrimination the carrier frequencies of the frequency modulators are preferably selected so that the frequency bands of the FM signals of the first and second subscribers do not overlap. BRIEF DESCRIPTION OF THE DRAWINGS The features, properties and additional details of the present invention will be elucidated in the following description of several preferred embodiments of the present invention. In the description reference is made to Figure 1 which shows a block diagram of a system embodiment according to the invention and to Figure 2 which shows a diagram of a preferred embodiment of a part of the system, i. e. , a preferred embodiment of a frequency modulator. Figure 3 shows a schematic diagram of one of the preferred arrangements of the first and second devices of the system according to the invention. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows the system that implements the method to increase the transmission capacity of a switched telephone communication channel by increasing the transmission capacity of a communication channel that is called the "last mile". The "last mile" is the part of the telephone communication channel between the subscriber (user) and the part of the telephone station of the telephone communication channel. Usually the last mile is in the form of twisted double-conductor telephone wires. If the length of this part of the communication exceeds 2 km and an information signal with a bandwidth of approximately 4 kHz is applied, that is, as a rule, difficult, if not impossible, to provide a signal-to-noise ratio (S / N) of 52 dB in the last mile, which is the minimum requirement to achieve a transmission speed of at least 56 kbit / s. The remaining parts of the telephone communication channel (trunk lines, telephone station equipment and so on) can have a transmission capacity of 56 kBit / s. The task of increasing the total data transmission capacity through a standard telephone communication channel can therefore be solved by sufficiently increasing the transmission capacity of the last mile. Figure 3 shows a typical installation of a telephone line and the system according to the invention. A first subscriber A connects through a "last mile" section with a first switch (ATSi), while the second subscriber B connects through a "last mile" section with a second switch (ATS). An additional communication channel is present between both switches. According to the modality shown in Figure 3, the system comprises two first devices 1 and two second devices 2, included in the empty spaces of the two-wire telephone lines. The first devices 1 are installed on the subscriber side A and on the subscriber side B, while the second devices 2 are installed at the position of the first ATS and at the position of the second ATS. Although Figure 3 shows first and second devices according to the invention installed at both ends of the communication channel, in another preferred embodiment (not shown) the devices are installed at one end of the communication channel. From the bi-directional information flow coming from the first subscriber side with the help of the directional transformer 1, the information transmitted by the first subscriber is extracted. The frequency modulator 2 is modulated by this information with the carrier frequency fi. The FM signal received with the aid of the differential transformer 3 is routed (mixed) to a two-wire telephone line as a component of the bi-directional FM flow 10. Having passed the telephone line the FM signal coming from the first subscriber with the the differential transformer aid 5 is extracted from the FM flow 11 and is input to the frequency demodulator 6, where the information transmitted by the first subscriber is extracted without (substantial) change in its structure (frequency bandwidth, modulation type) , and so on) . This information with the help of the differential transformer 7 is mixed in the bi-directional information flow 12, which goes to the information input / output of the second subscriber 2. Similarly the information transmitted by the second subscriber 20, with the aid of the differential transformer 7 is introduced to the frequency modulator 8, where it modulates the carrier frequency f2. The FM signal coming from the output of the frequency modulator 8 with the help of the differential transformer 5 is routed to a telephone line as a component of the bidirectional FM flow 11 (the FM flux 11 being identical to the aforementioned FM 10 flow). ). Having passed the telephone line the FM signal from the second subscriber with the help of the differential transformer 3 is extracted from the FM stream 10 and is input to the frequency demodulator 4, where the information transmitted by the second subscriber is extracted without changing the its structure. This information with the aid of the differential transformer 1 is mixed in the flow of bi-directional information 9, which goes to the input / output of information of the first subscriber 1. In order to achieve the speed of 56 Kbit / s it is required that the S / N ratio at the output of the frequency demodulator 4 (or 6, depending on the transmission direction) is not less than 52 dB, as will be explained below. The information samples in the communication channel with a bandwidth of 4 kHz can go with a clock frequency of 8 kHz. Due, in order to achieve a speed of 56 kbit / s, it is required to transmit 7-bit information samples with such a clock frequency. The so-called Shannon formula shows the threshold of the transmission speed C that can be achieved by a signal in a continuous communication channel.

C = B * log2 (Ps + n) / Pn where B is the transmission bandwidth of the communication channel, Ps is the energy of the signal, and Pn is the energy of the noise. In a bandwidth of 4 kHz a speed of 56 kBit / s can be achieved if the expression C = B * log2 (Ps + n) / Pn / could be equal to 14. From this the ratio (Ps + Pn) / Pn is equal to approximately 16000. And then the required signal-to-noise ratio S / N = 10 * logl0 (16000) is approximately equal to 42 dB. In practice, this limit is approximated by applying several coding methods. However, a much higher signal to noise ratio (S / N) is required for the transmission of uncoded 7-bit information with a practically acceptable error probability. For example, in order to provide an error probability of not less than 10 ~ 5, a S / N signal to noise ratio of not less than 52 dB is required. This requirement imposes rather rigid requirements on the level of non-linear distortions in the output of the corresponding frequency modulator (2 or 8), which does not exceed 0.03 - 0.05% (-66 - -70 dB). Such a level of non-linear distortions is provided by the design of frequency modulators 2 and 8 according to Figure 2. The information 18 (20), transmitted by subscriber 1 (subscriber 2) arrives at the first entry of the unit of subtraction 13, in which second input error signal 22 (23) is provided. The error signal 22 (23) is formed by the error signal former 16. The difference between the information 18 (20) and the error signal 22 (23) serves as a modulation signal for the controlled voltage oscillator (VCO) ) 14. The FM signal 19 (21) of the VCO output 14 is transmitted to one of the outputs of the differential transformer 3 (5) and at the same time - to the input of the additional frequency demodulator 15, which is preferably identical to the respective main demodulator 6 (4) of the given address. The output signal of the demodulator 15 is transmitted to one of the inputs of the error signal former 16, for which the second input information 18 (20) is transmitted by the subscriber 1 (subscriber 2), and which has passed the delay line 17. The delay line is necessary to compensate for the signal delay when passing the modulator 14 and the demodulator 15. The error signal 22 (23) at the output of the error signal former 16 is formed as the difference between the output signal of the demodulator 15 and the signal of the delay line 17. The compensation of the non-linear distortions at the output of the frequency modulator in the offered scheme is made possible due to the fact that as the frequency modulator In this scheme, a demodulator is used which is identical to the respective main demodulator of this address 6 (4). If the S / N ratio at the output of the frequency demodulator 4 (6) is 52 - 53 dB, the respective frequency demodulator 2 (8) constructed as shown in Figure 2 will worsen this ratio by no more than 0.5 dB , which is quite acceptable from the point of view of the provision of data transmission speed of 56 kBit / s. The increase of a communication channel transmission capacity with the help of the offered method is based on the fact that the frequency modulation (FM) improves the S / N ratio in the frequency demodulator output not less than 3m2, where m = cOd / Omax - frequency modulation index by the higher modulation frequency, a > d - frequency deviation, Omax - higher modulation frequency. The gain in the S / N ratio at the output of the frequency demodulator will be observed in more than 0.6. If we take m = 5 for Oraay 2p = 3.5 kHz, the advantage in the S / N ratio at the output of the frequency demodulator will not be worse than 18 dB. As a consequence, the maximum speed of the protocol in the described system will be maintained until the maintenance on the line in the bandwidth of a standard telephone signal of S / N ratio not worse than 14 dB for the V.34 protocol and up to the maintenance in the S / N ratio line not worse than 34 dB for the V.90 and V.92 protocols. At this frequency the bandwidth occupied by the FM signal on the telephone line is approximately equal to 35 kHz. The increase of the modulation index m up to 10 increases the gain up to 25 dB in the amplification of the bandwidth of the FM signal up to 70 kHz. The increase in the Modulation Index has its limit due to the threshold effect of frequency demodulation, which starts the influence on the decrease of S / N for the FM signal to a certain critical value. The m limit starts as soon as the quality of a telephone line gets worse in a communication channel. For example, increasing the modulation index to 20 increases the gain up to 30 dB at the demodulator output, but worsens the S / N ratio on one line for the FM signal on a 16 dB line and thus does not allow the use of such an index of modulation in the lines, where the S / N ratio in the bandwidth of a telephone signal does not exceed 20-22 dB. Thus, the application of the FM signal in telephone communication allows to significantly increase the actual capacity of transmission of a communication channel through telephone lines. For this it becomes possible to use all the existing protocols without any change. The system offered is relatively simple in its implementation and economical in production.

Table I Dependence of the data transmission rate C with error probability 10 ~ 6 in the ratio of the energy of the signal to the noise energy (Ps / Pn) in a telephone channel bandwidth for ordinary telephone lines P3 / Pn, dB C, Kbit / s 32 33.6 36 37 41 41 46 46 52 56 Table II Dependence of the data transmission speed C with error probability 10 ~ 6 in the ratio of the energy of the signal to the energy of noise (Ps / Pn) in a telephone channel bandwidth for telephone lines with increased transmission capacity for the frequency modulation index m = 4 Ps / Pn, dB C, Kbit / s 16 33.6 20 37 25 41 30 46 36 56 The present invention is not limited to the preferred embodiments described above; it is intended that the rights be defined by the following claims, within the scope of which many modifications can be visualized

Claims

CLAIMS 1. A method for transmitting information in a bi-directional flow signal through a communication channel between a first subscriber (A) and a second subscriber (B), the communication channel comprising a first part and a second part , the method comprising the steps of: extracting from the bi-directional flow signal at the end of the first subscriber (A) of the first part of the communication channel, the information transmitted by the first subscriber (A); modulating said extracted information with a carrier frequency fi to provide a frequency modulated (FM) information signal; - mixing said frequency modulated information signal (FM) in said bidirectional information flow signal at the end of the first subscriber (A) of the first part of the communication channel; - extracting from said bi-directional information flow signal at the end of the second subscriber of the first part of the communication channel the transmitted frequency modulated (FM) information signal; - demodulating said transmitted frequency modulated (FM) information signal transmitted to provide the information as transmitted by the first subscriber (A);
mix the information transmitted by the first subscriber (A) in the bi-directional flow signal in the second part of the communication channel. The method according to claim 1, further comprising: extracting, from a bidirectional information flow signal at the end of the second subscriber (B) of the first part of the communication channel, the information transmitted by the second subscriber (B); - modulating said extra information extracted with a second carrier frequency f2 to provide a frequency modulated information (FM) signal; - mixing said frequency modulated information signal (FM) in said bi-directional information flow signal in said communication channel; - extracting at the end of the first subscriber of the first part of the communication channel of the bi-directional information flow signal the transmitted frequency modulated (FM) information signal; - demodulating said extracted frequency modulated (FM) information signal transmitted to provide the information as transmitted by the second subscriber; - Mix the information in the bidirectional information at the end of the first subscriber of the first part of the communication channel.
3. The method according to claim 1 or 2, wherein the first carrier frequency fi and the second carrier frequency f2 are selected so as to avoid superposition of the frequency bands of the frequency modulated information signals from the first and second frequencies. subscribers. The method according to claim 1, 2 or 3, which comprises transmitting said information through a standard telephone line. The method according to claim 4, which comprises transmitting said information between a telephone and an automatic telephone station (ATS). 6. The method according to claim 4, comprising transmitting said information between a modem and an automatic telephone system (ATS). The method according to any of the preceding claims wherein the first part of the communication channel has a relatively low transmission capacity and the second part of the transmission channel has a relatively large transmission capacity. The method according to claim 7, wherein the first part of the communication channel is the "last mile" of a telephone communication channel. 9. The method for transmitting information through a communication channel between a first subscriber and a second subscriber, the communication channel comprising a first part with a relatively low transmission capacity and a second part with a relatively high transmission capacity, the method comprising the steps of placing a first device at the end of the first subscriber (A) of the first part of the communication channel and placing a second device at the end of the second subscriber (B) of the first part of the communication channel , the first and second devices being operative in order to perform the steps of extraction, modulation, demodulation and mixing as defined in any of the preceding claims. The method according to any of the preceding claims, wherein the first and / or second subscriber is a telephone apparatus or an existing modem apparatus. 11. The system for transmitting information in a bi-directional flow signal through a communication channel between a first subscriber (A) and a second subscriber (B), the communication channel comprising a first part and a second part, the system comprising a first device to be installed at the end of the first subscriber (A) of the first part of the communication channel and a second device to be installed at the end of the second subscriber (B) of the first part of the communication channel in order to of increasing the transmission capacity of the first part of the communication channel, including the first device: - a first extractor to extract from the bi-directional flow signal the information transmitted by the first subscriber; a modulator for modulating said information with a carrier frequency fx to provide a frequency modulated (FM) information signal; a first mixer for directing said frequency modulated (FM) information signal to the bi-directional information flow signal at the end of the first subscriber (A) of the first part of the communication channel; and the second device including: a second extractor for extracting from said bi-directional information flow signal taken from the end of the second subscriber (B) of the first part of the communication channel the transmitted frequency modulated (FM) information signal; a demodulator for demodulating the information transmitted by the first subscriber from the transmitted frequency modulated (FM) signal; - a second mixer for directing the information transmitted by the first subscriber (A) to the bi-directional information flow signal in the second part of the communication channel. The system according to claim 10, further comprising a third device installed at the end of the second subscriber (B) of the first part of the communication channel and a fourth device installed at the end of the first subscriber of the first channel of communication. communication, including the third device: - a third extractor for extracting additional information, transmitted by the second subscriber from said bi-directional information flow signal of the second subscriber; a second modulator for modulating said additional information with a carrier frequency f2 to provide an additional frequency modulated (FM) information signal; - a third mixer for directing said additional frequency modulated information signal towards the bi-directional information flow signal existing in the communication channel; and the fourth device including a fourth extractor for extracting from the bi-directional information flow signal, existing in the first part of the communication channel, the additional modulated frequency information signal transmitted;

- a second demodulator for demodulating the frequency modulated (FM) information signal to provide additional information as transmitted by the second subscriber; - a fourth mixer for mixing the additional information, transmitted by the second subscriber, to the bi-directional information flow signal at the end of the first subscriber (A) of the first part of the communication channel. The system according to claim 11 or 12, wherein the first part of the communication channel has a relatively low transmission capacity and the second part of the communication channel has a relatively large transmission capacity. 14. The system according to the claims

11 or 12, wherein the first extractor and the fourth mixer, the first mixer and the fourth extractor, the third mixer and the second extractor and / or the third extractor and the second mixer are combined. 15. The system according to any of claims 11-14, wherein the communication channel is a standard telephone line. The system according to any of claims 11-15, wherein the first part of the communication channel is the "last mile" portion of the telephone communication channel. The system according to any of claims 11-16, wherein a mixer comprises a differential transformer to be installed in the communication channel. 18. The system according to any of claims 9-17, wherein an extractor comprises a differential transformer to be installed in the communication channel. The system according to any of claims 9-18, wherein a frequency modulator comprises: - a controlled voltage oscillator having an input and an output; - an additional frequency demodulator having an input connected to the output of the controlled voltage oscillator and an output; - an error signal former having a first input connected to the output of the additional frequency demodulator, a second input connected to the extractor and an output; a subtraction unit having a first input connected to the output of the error signal former and a second input connected to the extractor; wherein the information transmitted by the first and second subscribers originating from the extractor is supplied to a second input of the subtraction unit, to whose first input an error signal is supplied, the error signal being formed by the signal former of error as the difference between the extractor information and the signal at the output of the additional frequency modulator and where the difference between the transmitted information and the error signal serves as a modulating signal for the controlled voltage oscillator and where the output of the Controlled voltage oscillator is transmitted to one of the inputs of the mixer. 20. The system according to claim 19, wherein the additional demodulator is identical to the main demodulator. 21. The system according to the claims

19 or 20, where a delay line is provided for the compensation of the delay when passing the modulator and the demodulator. The system according to any one of the preceding claims, wherein the first and the fourth devices are connected in series to the end of the first subscriber of the telephone line, while the second and third devices are connected in series to the end of the second subscriber. of the telephone line. The system according to any of the preceding claims 11-22, wherein the first and / or second subscriber is a telephone apparatus or an existing modem apparatus. The system according to any of the preceding claims 11-23, wherein the second subscriber is an automatic telephone station (ATS). 25. A method according to any of the preceding claims 1-10, which comprises transmitting the information with a transmission speed of at least 56 kbit / s in the case of a S / N signal-to-noise ratio of at least 36 dB, with a transmission speed of at least 46 kbit / s in the case of a S / N signal to noise ratio of at least 30 dB, with a transmission speed of at least 41 kbit / s in the case of a S / N signal to noise ratio of at least 25 dB, with a speed transmission rate of at least 37 kbit / s in the case of a S / N signal-to-noise ratio of at least 20 dB, and / or with a transmission speed of at least 33 Kbit / s in the case of a signal-to-noise ratio of S / N noise of at least 16 dB. 26. The method or system according to any of the preceding claims, wherein the first and second devices are provided in separate housings.