CZ288913B6 - Method and apparatus for implementing a bi-directional wireline transmission connection - Google Patents

Abstract

The invention concerns a method and apparatus for implementing a wireline transmission connection, especially a transmission connection by making use of a digital subscriber's line with a very high data transmission rate (VDSL). The transmission connection is implemented in electric form so that a separate frequency range is reserved for either transmission direction. To allow efficient filtration of radio-frequency interferences by using as simple an apparatus as possible, the frequency band of a transmission line (13) is divided into sub-bands limited by international radio amateur frequency bands (AB1...AB6) and the transmission connection is implemented in at least some of these sub-bands (a) by generating for each sub-band to be used a carrier wave (C1, C3, C5, C6) with its own modulator (A1 through An) for each sub-band used and (b) by dividing the bits of the bit stream (DATA_IN) to be transmitted between the modulators (A1 through An) of the transmission direction in question s

Description

Technical field

The invention generally relates to the implementation of an electrical wired line transmission link, and in particular to a transmission connection using very high bit rate (VDSL) digital subscriber line technology.

BACKGROUND OF THE INVENTION

Of course, fiber optics are very often chosen as a transmission medium for long-distance and long-distance network lines, as such long-distance connections very often require high transmission capacity, transmission distances are very long and existing routes are often occupied by cables. Even for subscriber connections (that is, the line between the local exchange and the respective subscriber), the situation is changing very quickly, as different services provided by different means of transmission and requiring high data rates are becoming common everyday services also for private users.

However, no significant cost savings can be expected in building future networks offering broadband services, as these costs mainly stem from the increasing cost of cable installation. However, it would be desirable to build as many fiber optic cables as possible in subscriber networks as well, as it is obvious that this will be needed in the future. The costs of renewal of subscriber networks are very high, but the work can only be completed in decades. Indeed, high costs are the most serious obstacle to the distribution of fiber optics to subscriber networks.

For the above reasons, far more effective measures have been taken than before to find and find out how to use conventional subscriber lines (metallic two-line lines) to transmit data at high speed, that is to say at transmission rates that lie entirely clearly above the speed (144 kbit / s) of the basic ISDN access.

Indeed, the known asymmetric digital subscriber line (ADSL) and high bit rate digital subscriber line (HDSL) techniques presently provide new possibilities for high-speed data and video transmission using wired telephone lines for subscriber terminals.

A transmission connection made using an asymmetric digital subscriber line (ADSL) is asymmetric in that the transmission rate from the network to the subscriber is substantially higher than the transmission rate from the subscriber to the network. This is due to the fact that the asymmetric digital subscriber line (ADSL) technique is designed primarily for so-called 'on-demand services'.

In practice, for an asymmetric digital subscriber line (ADSL) transmission link, the transmission rate from the network to the subscriber is of the order of 2 to 6 Mbit / s, while the transmission rate from the subscriber to the network is of the order of 16 to 640 kbit / s (conventional control channel).

The transmission technique utilizing a high-bit rate digital subscriber line (HDSL) refers to the transmission of a digital system at 2 Mbit / s using a two-line metallic line. The high-bit rate digital subscriber line (HDSL) is a symmetrical technique, that is, the transmission speed is the same in both directions.

The individual high-bit rate digital transceiver (HDSL) combined transceiver system incorporates transceiver units

And receivers which employ echo cancellation technology and which are interconnected through two-way transmission paths formed by a wired pair.

In a transmission system using a high-bit rate digital subscriber line (HDSL), the number of the above-mentioned individual transceiver systems may be one or two or three connected in parallel, while in the case of two or three pairs connected in parallel, the rate which can be used for each parallel transmission link is 2 Mbit / s sub rate, 784 kbit / s when three pairs are connected in parallel, and 1 168 kbit / s if two pairs are connected in parallel.

International Recommendations specify how 2 Mbit / s signals are transmitted with a High Bit Rate Digital Subscriber Line (HDSL) system, such as SDH sewn VC-12 signals or 2,048 kbit / s signals in accordance with CCITT G recommendations .703 / G.704.

Since only the bit rates typically in the order of 1 to 2 Mbit / s can be achieved with the above solutions, a technique has been sought for subscriber line cables that would allow the bit rates to be achieved at ATM level. The specification for the very high bit rate digital subscriber line (VDSL) equipment was in fact implemented by the European Telecommunications Standards Institute (ETSI).

The intention is that transmission links using a very high bit rate (VDSL) digital subscriber line and performed using dual-line metallic lines of the telephone network will be able to transmit ATM units between the telephone network and the subscriber terminal.

Using the very high bit rate digital subscriber line (VDSL) technology, subscriber lines in the telephone network will start to use such high frequencies that the high frequency interference induced on the subscriber line, which is usually a unshielded wired pair, becomes a serious problem.

It has been suggested that radio frequency interference could be eliminated, for example, by means of an adaptive channel equalizer arranged in the receiver. In this case, however, it is necessary to use a very accurate and expensive AD-converter, since the interference, which must also be converted to digital form, can be very strong.

In addition, it may be very difficult to set up the channel equalizer as the interference occurs very quickly and their frequency changes very quickly.

Another known way to eliminate strong radio frequency interference is to use a multi-carrier modulation method where several carrier waves are fed into a single modulation process (e.g., DMT-Discrete Multitone or DWMTDiscrete Wavelet Multitone), that the bits to be transmitted are not all assigned to those carrier waves that have interference.

DMT-Discrete Multitone is a method of making connections using an asymmetric digital subscriber line (ADSL), defined by the American National Standards Institute (ANSI), where multiple such sub-channels (carriers) are fed into the same modulation process while being equally spaced across the domain frequency and have the same width.

If it is desirable to eliminate interference caused by solid sources, such as radio amateur transmissions, then those sub-channels that are located on interference bands (such as radio amateur bands) are completely disconnected from use. Such a solution is described, for example, in PCT International Application WO-A-95/28773.

-2GB 288913 B6

The basic drawback of this solution is that this leads either to complex and costly implementation, or to inefficient and inefficient use of the frequency range. This is due to the fact that the efficient use of the discontinuous frequency range requires narrow sub-channels, whose number is high. The added number of subchannels for a given part makes the system much more complex.

The bandwidth efficiency and efficiency is also reduced by the condition that the DMTDiscrete Multitone subchannels partially exceed the domain frequency, and to avoid interference, out-of-band carrier waves that are also exposed to interference must also be decommissioned. Implementing modulation methods with a large number of carrier waves is also complex and complicated (signal generation and detection are very complex processes).

Another drawback of the DMT-Discrete Multitone solution is that padding bits (the so-called cyclic prefix) must be added to the data to be transmitted in order to eliminate the distortion that could be caused by the channel. So the DMT-Discrete Multitone solution also wastes capacity even in domain time.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the above-mentioned drawbacks by providing a solution which allows very simple execution of a transmission link, in particular a transmission link using a very high bit rate (VDSL) digital subscriber line whose operation will be of high quality.

This object has been achieved on the basis of the solution object of the present invention as defined in the independent claims.

The present invention is based, firstly, on the view that although the use of a large carrier wave modulator (DMT) is defined as a transmission method for, for example, using an asymmetric digital local loop, it could constitute an obvious alternative also for making a similar but high speed connection. that is, a connection using a very high bit rate (VDSL) digital subscriber line is not the most efficient or simplest way of making a transmission link where the available frequency bands are discontinuous, but certain narrow frequency bands are not used.

Secondly, the invention is also based on the view that the radiofrequency interference caused by amateur radio stations is particularly very strong, since amateur radio stations are usually located near subscriber lines of telephone networks.

For the above reasons, the present invention is not based on the idea that it is necessary to first generate many carrier waves across the entire frequency band and then decommission some of them, since the available bandwidth is divided by means of the bands with the worst expected interference (i.e. to clearly separated subbands, each having its own modulation process of a single carrier wave or modulator to which the high-speed bitstream to be transmitted is supplied.

Thus, in this context, a sub-band represents a transmission band that borders an international amateur radio band at least at one of its edges.

The idea is that, with the help of international amateur radio bands, the frequency bands reserved for connection are divided into sub-bands into which the relevant data is modulated. Each carrier wave is generated by its own modulator. So in domain

The channels are separated from each other and can be independently manipulated. The band reserved by each channel can thus be set independently using carrier frequency and symbol ratio.

In the method of the present invention, some simple modulation procedures may be utilized, preferably for example a QAM or a CAP-free modulation.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further elucidated by way of example with reference to the accompanying drawings, in which:

Fig. 1 illustrates a transmission system using a very high bit rate (VDSL) digital subscriber line connection;

Fig. 2 illustrates a frequency distribution for use in a very high bit rate (VDSL) digital subscriber line connection;

Fig. 3 illustrates a transmission principle in accordance with the present invention;

Fig. 4 shows the sub-band split between transmission directions in accordance with a preferred embodiment of the present invention;

Fig. 5 illustrates a basic form of a device for making a connection using a very high bit rate (VDSL) digital subscriber line according to the present invention; and Fig. 6 shows a preferred embodiment of the device shown in Fig. 5.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned earlier, the European Telecommunications Standards Institute (ETSI) is implementing the specification of very high bit rate digital subscriber line (VDSL) equipment.

Fig. 1 shows a structure of a system using a very high bit rate (VDSL) digital subscriber line connection. The design of this system complies with the so-called FTTC structure (fiber in sheath or cable). The sheath or cable 11 receives data via a high-speed fiber optic connection 12.

Existing metallic lines, such as copper twin cables, also pass through the same sheath or cable from the exchange to the subscriber. These copper pairs may form a transmission line 13.

With an on-board optical network unit (ONU), high-speed data is combined on the subscriber line so that the subscriber can still use the old POTS / ISDN narrowband services, but in addition a full-duplex high-speed data connection is already available .

These narrowband and broadband services are separated by a passive filter that performs frequency separation of digital subscriber line signals

-4GB 288913 B6 with very high bit rate (VDSL) and narrowband signals. A very high bit rate (VDSL) digital subscriber line connection is established between the optical network unit (ONU) and the network terminal (NT).

The network terminal (NT) is typically located in the user or subscriber's home and is connected to a subscriber terminal, such as a conventional analog telephone or ISDN telephone 15, or to a TE terminal using broadband services, such as a microcomputer 16.

The network terminal ensures the connection of the INT 1 user to the network (UNI) in accordance with the relevant standards. The very high bit rate (VDSL) digital subscriber line (INT2) broadband connection is provided by an optical network unit.

Since the present invention relates only to a very high bit rate (VDSL) digital subscriber line connection to be made between an optical network unit (ONU) and a network terminal (NT), the system will not be described in any detail in this context, as shown in Fig. 1. A very high bit rate digital subscriber line (VDSL) connection system is described in greater detail and detail in, for example, the European Telecommunications Standards Institute (ETSI) report DTR / TM-03068, where the reader can find much more detailed information. description, if interested.

On a provisional basis, the European Telecommunications Standards Institute (ETSI) has approved the following bit rates for transmission with the help of a very high bit rate (VDSL) digital subscriber line:

- downwards (from network to subscriber): 52, 26, 13 and 6.5 Mbit / s;

- upwards (from subscriber to network): 26.13, 6.5 and 2.3 Mbit / s.

Frequency distribution is performed in accordance with the illustration in Fig. 2, leaving a low frequency space for existing POTS or ISDN services (frequency band A). The very high bit rate digital subscriber line (VDSL) channels are transmitted to frequency band B, whose lower cutoff frequency is typically 300-600 kHz, while the upper cutoff frequency is preferably around 18 MHz, as discussed below. The sub-band splitting between the different transmission directions of the connection using a very high bit rate (VDSL) digital subscriber line will be described in more detail below.

In accordance with the present invention, a bit stream transmitted by a very high bit rate (VDSL) digital subscriber line is subdivided into a plurality of carrier waves that are located in the frequency band so as to be located on the sub-bands designated for international amateur radio bands. Thus, the transmitter has several parallel modulators that utilize some suitable known modulation method, for example, the method of quadratic amplitude modulation (QAM). An individual frequency is used for each modulator so that the corresponding carrier wave is located in the desired subband.

The international amateur radio bands are listed in Table 1 below, whose left column indicates the lower bandwidth of the band, while the right column indicates the upper bandwidth of the band.

It follows from the frequency values given in Table 1 that, in the method according to the invention, the carrier waves are located in sub-bands whose lower and upper cut-off frequencies are determined in accordance with the amateur radio bands (see Table 2).

-5GB 288913 B6

Fig. 3 illustrates a transmission principle in accordance with the present invention by indicating the power spectral density (PSD) of a signal received from a very high bit rate (VDSL) digital subscriber line connection using six different carrier waves C1 to C6 (or sub-bands 1-6 above) modulated by quadratic amplitude modulation, with the two lowest ones being reserved for upward transmission while the remaining ones are reserved for downward transmission.

Radio amateur bands AB1 to AB6 are represented by rectangles. The values shown in Fig. 3 correspond to a computer calculation performed for a link distance of 400 m. The power density of the VDSL connection was -60 dBm / Hz and additional white Gaussian noise (AWGN). was at -115 dBm / Hz. The height of the rectangles of the amateur radio bands AB1 to AB6 corresponds to the calculated interference size, assuming the transmission power is equal to 0 dBm, and assuming that the bandwidth is 4 kHz.

The transmission rates of the above connection using a very high bit rate (VDSL) digital subscriber line may be implemented using six lower subbands (subbands 1 to 6). It is advantageous to use the lowest sub-band (sub-band 1) downwards, since these low frequencies are also used in this direction in a system using a very high bit rate (VDSL) digital subscriber line.

In this way, signal penetration (NEXT) is prevented, even if both asymmetric digital subscriber line (ADSL) and very high bit rate digital subscriber line (VDSL) connections are in accordance with object of the invention in the same cable.

The Shannon law test of the subscriber line showed that the above transmission rates and target link distances reported in the above-mentioned report of the European Telecommunications Standards Institute can best be achieved when selecting subband transmission directions in accordance with the data in Table 3.

Shannon's law

C = B x log2 (1 + S / N) indicates the theoretical maximum information transmission capacity of a C channel whose bandwidth is B and whose signal to sum ratio is S / N.

This division of transmission directions was determined using Shannon's law to first calculate capacities of different subbands at different link distances (300m, 500m and 1500m) and then selecting subbands for transmission directions according to their total capacity and the appropriate bit rate required for a given transmission direction.

It should be noted that since attenuation or attenuation of the signal in the cable increases rapidly with increasing frequency, the band at lower frequencies has a correspondingly better signal-to-noise ratio and, in accordance with Shannon's law, also has a higher information transmission capacity than higher frequencies. With regard to the transmission capacity, it is thus not possible to change, for example, the directions between the sub-bands 3 and 4, although these bands have almost the same width.

The above-described distribution is also very advantageous in that it can be used for symmetrical and asymmetric connections, where there can be connections of each type in the same cable, without penetrating signals from one connection to another. This preferred frequency distribution is also shown in FIG. 4, with the upstream sub-bands shaded.

-6GB 288913 B6

Similar tests have shown that if only symmetric operation or, alternatively, only asymmetric operation is sufficient, the connection with the very high bit rate (VDSL) digital subscriber line can also be made by pointing upwards to the sub-bands of the lower end of the frequency band (zone B in Fig. 2), while the downward direction is given to the sub-zones of the upper end.

If only symmetrical connections can be used, the amateur radio band 3.5 to 3.8 MHz is a good cutoff frequency for splitting the upper or lower channel. If, on the other hand, asymmetric operation is considered important, it should be stated in a similar way that the amateur radio band 1,810 to 2,000 MHz represents a suitable interruption frequency. By placing the cross frequency on the 3.5 to 3.8 MHz frequency band, it allows achieving a symmetrical bit rate of 26 Mbit / s and downstream bit rates of 52 Mbit / s.

Fig. 5 shows the basic form of the device according to the invention. In this Fig. 5, both ends of the connection with a very high bit rate (VDSL) digital subscriber line are viewed in one direction of the transmission. The high-speed bit data DATA_IN (its speed is in accordance with what has been said above, for example 52 or 26 Mbit / s) to be transmitted by a transmission link using a very high bit rate (VDSL) digital subscriber line is supplied to symbol generating means 41 which form bit symbols and divide these symbols into different carrier waves by supplying them to modulator means 42. comprising a number of n parallel modulators A1, A2 to An for quadratic amplitude modulation operating at different carrier frequencies , in accordance with FIG. 3.

The symbol generating means 41 directs the symbol created here directly to the input of its corresponding modulator. Since the signal-to-noise ratio varies from carrier to carrier, a different number of bits per symbol can be used with different modulators. The better the signal-to-noise ratio of the carrier wave the more bits can be used (density structure diagram).

When using the most preferred embodiment in accordance with FIG. 4, it is preferable to use the device to select a symbol ratio, for example, that upwardly the carrier or carrier wave C4 has twice as high a ratio of the carrier or carrier wave C2, in the downward direction, carriers C3, C5 and C6 have twice the symbol ratio as compared to the carrier CL carrier 3. The carriers C3 and C4 may not have the same symbol ratio because the transmission occurs in different directions.

If, on the other hand, the channel distribution is up or down in the amateur radio band 3.5 to 3.8 MHz, the same symbol ratio can be selected for each carrier or carrier in both the up and down directions. If the limiting frequency in the amateur radio band is 1.81 to 2.0 MHz, then only one subband is used upwards. In this case, the downward symbol ratios may be selected such that in bands having frequencies exceeding 3.8 MHz, a symbol ratio that is twice as high as that in the lowest band of 2.0 to 3.5 MHz is used.

When the aforementioned adaptive bit allocation for different carriers or carriers is used in a transmitter, it is advantageous to provide a short trial period for the initial phase of the connection to determine how many bits are recommended to use per symbol for each carrier or carrier.

The quadratic amplitude modulation (QAM) modulators modulate signals to different carrier frequencies that are located in any of the aforementioned subbands 1 to 9, preferably in each case substantially at the center of the respective frequency band.

-7EN 288913 B6

Since the amplitude modulation (QAM) quadrature method is currently the most widely used modulation method, for example in cable modems, this method will not be described in further detail in the present context. A more detailed description of quadratic amplitude modulation (QAM) can be found, for example, in William Webb, Lajos Hanzo: Quadrature Amplitude Modulation Modem, Pentech Press, IEEE Press, New York, ISBN 0-7803-1098-5.

The output signals from the modulators are fed to the adder 43 where they are digitally summarized. The digital sum signal is further supplied to the line adapter 44, which typically comprises a sequential DA converter or digital-to-analog converter, a filter for removing harmonic components occurring in the digital signal, a line driver circuit to raise the output signal level to the correct level, separation of the transmit and receive branches, a line transformer and a (passive) filter (POTS / ISDN interrupter) for separating the POTS / ISDN signals and the very high bit rate digital subscriber line (VDSL) signals. The filter output is connected to a channel (wired pair).

At the receiving end, the signal is first connected to a line circuit adapter 45 comprising the above-mentioned (passive) filter (POTS / ISDN interrupter), a plug for separating the transmit and receive branches, an adjustable amplification stage, a filter stage and an AD converter. The filter stage is preferably provided with so-called serrated filters operating in amateur radio bands.

Since the adder 43 and the add-on line adapter 44 and 45 can be operated in accordance with known conventional procedures, their structure will not be described in further detail in the present context.

The digital words received from the line circuit adapter 45 are further coupled to a demodulation unit 46 comprising n parallel QAM demodulators B1 to Bn, where n modulator / demodulator pairs (e.g., carrier waves C1, C3, C5) are formed. and C6 wherein n = 4).

Word symbols based on the outputs of the demodulators are supplied to the symbol identification circuit 47 that generates an original bit stream of the DATA_OUT symbol baseband word symbols.

Since different carrier wave delays cause problems in the reconstruction of the original signal, these delays can be measured individually for each wave in the initial connection stage, and this information can be used on reception to ensure the correct received order of symbols.

The aforementioned and presented apparatus may be further modified, for example in accordance with its preferred embodiments, which will be described in more detail below.

According to the method it is advantageous to use grid coded modulation (TCM), since in this way coded amplification can be achieved and the differences between the carrier waves can thus be compensated. Grid coding is also a very advantageous choice also because it is well known to be a very useful coding method, especially in the case of transmission over telephone lines.

FIG. 6 illustrates an embodiment of the present invention wherein the symbol creation unit 51 also performs grid coding. Since this grid coding is generally known per se, it will not be described in further detail in the present context. A more detailed description can be found, for example, in William Webb, Lajos Hanzo, supra:

-8EN 288913 B6

The Ouadrature Amplitude Modulation Modem, Pentech Press, London, IEEE Press, New York, ISBN 0-7803-1098-5.

Since lattice encoding is performed at the transmitting end, a decoding such as Viterbi decoding is used at the receiving end, since it is a conventional decoding method used in connection with lattice encoding. Thus, in this embodiment, the symbol identification unit 52 is provided with a Viterbi decoder.

The Viterbi algorithm is described in both William Webb and Lajos Hanzo: Ouadrature Amplitude Modulation, Pentech Press, IEEE Press, New York, ISBN 0-7803-1098-5, as well as in Benedetto, Biglieri, Castellani: Digital Transmission Theory, Prentice-Hall Inc, ISBN 0-13-214313-5 025.

It is also possible to compensate for differences between the carrier waves using the so-called amplification standardization method, i.e., using different transmission levels for different carrier waves. In practice, the overall power of the transmitter may be limited to a certain value (e.g., 10dBm), and it is preferable to scale the transmit powers of the different carriers so that the bit error rate is the same for all carriers.

For the above purposes, each modulator output is provided with an adjustable amplifier AMP1 to AMPn in accordance with the illustration in FIG. which allows the transmitter control portion 48 to individually adjust the gain of each carrier wave. In the initial situation, the receiver then informs the transmitter of the signal-to-noise ratios that have been measured, and based on these measured values, the transmitter control section 48 adjusts the gain of the adjustable amplifiers AMP1 to AMPn so that the bit error rates are the same for each carrier.

Although the subject matter of the invention has been described above with reference to the exemplary embodiments shown in the accompanying drawings, it is to be understood that the invention is not limited to the exemplary embodiments, since it may be varied within the scope of the inventive idea described above. , which is specified in the following claims.

For example, an embodiment of the present invention has been described in the above description wherein each subband has one carrier wave. Although this is the most preferred embodiment of the present invention, it is in principle also possible to use multiple carrier waves for one subband.

Although amateur radio bands are international, the limits of some bands may vary somewhat in different countries, which means that given band limits (which are generally used at least in Europe) may not necessarily be considered as strict limits.

Table 1

Lower bandwidth (MHz) band Upper bandwidth (MHz) band 1,810 2,000 3,500 3,800 7,000 7,100 10,100 10,150 14,000 14,350 18,068 18,168 21,000 21,450 24,890 24,990 28,000 29,700

-9EN 288913 B6

Table 2

Sub-band no. Lower cut-off frequency (MHz) Upper limit frequency (MHz) 1 0.3 1,810 2 2,000 3,500 3 3,800 7,000 4 7,100 10,100 5 10,150 14,000 6 14,350 18,068 7 18,168 21,000 8 21,450 24,890 9 24,900 28,00

Table 3

Sub-bands no. Direction of transmission 1 down 2 up 3 down 4 up 5 down 6 down

PATENT CLAIMS

Claims (10)

A method of making a bi-directional wired line transmission link, wherein the transmission link is made in an electrical form such that different frequencies are reserved from the frequency band of the transmission line (13) for different transmission directions, characterized in that the frequency band of the transmission line (13) is divided into sub-bands defined by the amateur bands (AB1 to AB6), and the transmission link is made in at least some of these sub-bands (a) by generating a carrier wave (C1, C3, C5, C6) with its own modulator (A1 to An) ) for each subband used, and (b) splitting the bit stream bits (DATA_IN) to be transmitted between the modulators (A1 to An) of the respective transmission direction such that each carrier waveform (C1, C3, C5, C6) modulated by some bits, each carrier having a frequency range that is independent on the corresponding subband frequency bands reserved for other carrier waves. Method according to claim 1, characterized in that one to two carrier waves (C2, C4) are used in the direction from the subscriber to the network, and one to five carrier waves (C1, C3, C5, C6). Method according to claim 2, characterized in that of the available subbands, the six lowest subbands are used such that data is transmitted from the subscriber to the network to -10GB 288913 B6 sub-bands whose upper cut-off frequencies are 3.5 MHz and 10.1 MHz, with data being transmitted from the network to the subscriber on sub-bands whose upper cut-off frequencies are 1.81 MHz, 7.0 MHz, 14 , 0 MHz, and 18.068 MHz. Method according to claim 1, characterized in that only one carrier wave is used between the amateur radio bands, wherein more symbol ratios than one are used in carrier wave modulation. Method according to claim 1, characterized in that adaptive bit allocation is used for different carrier waves. Method according to claim 1, characterized in that different transmission power levels are used for different carriers of the same transmission direction. Method according to claim 1, characterized in that lattice-coded modulation is used in the transmitter. The method of claim 1, wherein the transmission link is a very high bit rate (VDSL) digital subscriber line connection. An apparatus for making a bi-directional wired line transmission link in electrical form, the apparatus comprising for each transmission direction (a) means (41) for generating input bit symbols (DATA IN), and (b) modulator means (42) for modulation carrier symbols using generated symbols, the apparatus utilizing different frequencies for different transmission directions, characterized in that the modulator means (42) comprise n parallel modulators (A1 to An) whose frequencies are selected to produce several carrier waves (C1) , C3, C5, C6), each of which is located in its own sub-band in the transmission band frequency band, each of which is adjacent to the international amateur radio band (AB1 to AB6) at least at one end thereof. Device according to claim 9, characterized in that each modulator (A1 to An) is provided with an adjustable amplifier (AMP1 to AMPn) for individually adjusting the power level of each carrier wave.