Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Of data transmission
Reexamination Certificate
2001-02-09
2003-04-01
Barnie, Rexford (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Of data transmission
C379S027010, C379S032040, C379S024000, C379S022080, C379S001010, C379S001030, C375S227000
Reexamination Certificate
active
06542581
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for controlling the transmission power in a system for transmitting data via a telephone line by using a digital subscriber line.
TECHNICAL BACKGROUND
Telephone line connections have to fulfil certain requirements to achieve good connection quality. Standardisation organisations, such as The International Telecommunication Union, ITU-T, has constructed recommendations that specify these requirements. Limit values for a number of important transmission parameters together define the quality requirements of a connection between two subscribers.
Basically, it is question about the degree of distortion allowed in the information sent from a sender to a receiver. There are different techniques that can be used to measure how the information is changed. Different transmission parameters can be used as measure values for these measurements.
Modulation is a technique used for both analogue and digital information in which the information is sent as changes in a carrier signal. The unit that performs the modulation and the corresponding demodulation is called a modem, consisting of a modulator and a demodulator. With modulation it is possible to send digital binary information on analogue carrier, such as radio waves. In digital information transmission, wherein the information is sent as a sequence of “0s” and “1s” on a carrier wave, the bandwidth, i.e. the transmission capacity, is given in bits per second, bit/s. The bit rate can be increased on bandwidth limited connections, such as telephone cables and limited frequency bands at radio communication to have as many bits per Hertz as possible in the signal. Examples of such modulation methods are Frequency Shift Keying, FSK or Phase Shift Keying, PSK and Amplitude Shift Keying, ASK and combinations of these. The combination of e.g. PSK and ASK is called Quadrature Amplitude Modulation, QAM and enables more bits per second than any single method. The use of QAM requires a strong signal so that the single bits can be distinguished in demodulation.
The most common quality parameter in digital networks is the bit error rate, BER. The number of erroneously received bits at the receiver is a measure of the quality of the connection, expressed as the average portion of erroneously bits received of the total number of transmitted bits. BER is the number of erroneous bits in one time slot divided by the number of checked bits. In the practice, the bit errors appear in “bursts”, which means that the time aspect has to be taken into consideration in the definition of the quality of the connection. A given number of bit errors can be tolerated as methods for automatic correction of bit errors exist. These methods can handle bit errors to a certain extent.
Noise in the data connections is the most frequent reason for bit errors. No systems can today be made completely without noise, but there are limits for how much noise can be tolerated. The level of noise itself is not so important, instead the ratio between the level of the transmitted signal and the noise, The Signal Noise Ratio (S/N), is decisive for the audibility.
Cross-talk appearing in cable pairs working in opposite directions is another reason for bit errors. Both near-end cross-talk (NEXT) and far-end cross-talk (FEXT) take place in digital systems; NEXT between cable pairs working in opposite directions and FEXT between cable pairs working in the same transmission direction. NEXT is the bigger problem, since it is caused by an outgoing signal that is strong compared to the incoming one in the other cable pair.
Different transmission media are used for transmission, of which the most important are the copper cable (such as the pair cable or the coaxial cable), optical fibers and radio waves.
New transmission systems for copper access have been developed for allocation of different frequency ranges to telephony and data communication, which enables simultaneous telephony and data traffic over the same copper pair. This family of systems is called xDSL, where DSL stands for digital subscriber line.
The acronym xDSL refers collectively to a number of variations of the DSL (Digital Subscriber Line) technology, which aims at utilizing the information transmission capability of ordinary copper wires to the ultimate possible extent. Known variations that go under the umbrella definition of xDSL are at the priority date of this patent application ADSL (Asymmetric Digital Subscriber Line), CDSL (Consumer DSL, registered trademark of Rockwell International Corp.), G. Lite (also known as DSL Lite, splitterless ADSL, and Universal ADSL; officially ITU-T standard G-992.2), HDSL (High bit-rate DSL), RADSL (Rate-Adaptive DSL), SDSL (Symmetric DSL), VDSL (Very high data rate DSL) and even to some extent UDSL (Unidirectional DSL), which is only a proposal, and IDSL (ISDN DSL), which is actually closer to ISDN (Integrated Services Digital Network).
DSL standards sets given limits for the transmission power, which are followed in the implementation level. In general, digital subscriber line system implementations transmit a signal at a predetermined fixed transmission power level, when transmitting data through a telephone line. Preferably, the transmission power level should be sufficiently high so as to maintain a sufficiently high S/N (signal to noise) ratio. The data transfer rate can be kept high and the signal can be kept strong only with a high S/N ratio. On the other hand, the transmission power level should be sufficiently low so as to reduce any influence on the information due to cross talk between the subscriber lines, wherein the cross talk is proportional to the transmission power level.
The problem with having a fixed transmission power is that the transmission power is unnecessary high from time to time. In reality, the lines of the subscribers may have different conditions of noise. Nevertheless, the transmission power level has been fixed so that in some cases, the fixed transmission power level may be lower or higher than the what would be necessary in relation to the prevailing circumstances. As a result, the system may be influenced by cross talk. In order to reduce the negative effects of the cross talk, the data transfer rate must be lowered. This results in a decrease of the transmission capability and an unnecessary waste of transmission power.
In U.S. Pat. No. 6,061,427 there is presented a transmission power control method in an asymmetric digital subscriber line system. In this solution, the asymmetric digital subscriber line system compares a measured noise margin with a reference value, changes a transmission power level of a transmission signal, step by step, beginning from an initial level and sets the transmission power level to a minimum level as long as the measured noise margin is greater than the reference value.
The object of this invention is to control the transmission power in a more flexible and accurate way.
SUMMARY OF THE INVENTION
The method of the invention controls the transmission power for a session in a system for transmitting data via a telephone line by using a digital subscriber line between a user terminal and a central unit. The transmission power is increased or decreased between given limit values so that the power is kept as low as possible, while still providing sufficient transmission quality. The quality criteria according to which the transmission power is controlled consists of the value of the Signal to Noise Ratio (S/N), and the number of bit errors BER within a given time interval.
The advantageous ways of carrying out the invention appears in the following description.
The transmission power is stepwise increased or decreased in accordance with the values of transmission quality and it is controlled independently in the upstream and downstream links but in the most preferable embodiment taking into account the overall cross-effects of these links.
The transmission power is controlled with an algorithm with the aim of adjusting the transmission power to the prevailing circumstan
Rossi Timo
Savolainen Seppo
Sipila Juri
Suonsivu Heikki
Tirri Tomi
Barnie Rexford
Fasth Rolf
Fasth Law Offices
VDSL Systems
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