Pulse or digital communications – Systems using alternating or pulsating current
Reexamination Certificate
1998-10-22
2001-12-18
Chin, Stephen (Department: 2734)
Pulse or digital communications
Systems using alternating or pulsating current
C375S225000, C375S240000
Reexamination Certificate
active
06332005
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for converting a signal data rate from a lower data rate to a higher data rate in a digital data transmission system, wherein a signal is transmitted by using frames of a given length, which length corresponds to the higher data rate, in which method the signal is grouped to a first block the length of which corresponds to the lower data rate, and wherein symbols to be transmitted are subjected to repetition coding.
The invention also relates to a method for converting a signal data rate from a higher data rate to a lower data rate in a digital data transmission system, wherein a signal is transmitted by using frames of a given length, which length corresponds to the lower data rate, in which method the signal is grouped to a first block the length of which corresponds to the higher data rate, and wherein symbols to be transmitted are subjected to removal coding.
BACKGROUND OF THE INVENTION
The requirements set for data transmission systems continue to increase. This concerns especially wireless data transmission systems, such as cellular radio systems, which are required to provide more and more varied services, including different data and video services.
Traditionally, wireless data transmission systems have been used to transmit only speech. The increasing number of different services to be transmitted means especially in wireless systems that a system must be able to transmit signals with different capacities over the radio path, for example to transmit speech at the data rate of 8 kbps and data at the rate of 64 kbps. It is also necessary to transmit signals with different quality levels, which typically require different data rates simultaneously. A typical example is a video connection where the image requires a high data rate and a high quality level, but the voice can be transmitted at a lower data rate and with a lower quality level. Therefore, a data transmission system should be able to operate effectively in an environment where transmissions of several different data rates, quality levels and service types are forwarded.
It is typical of digital data transmission systems that signals are transmitted in frames and that the size of a frame is predetermined. When different data rates are used, it is not always possible to select for all data rates a frame which is exactly of the correct size and which has space for the symbols to be transmitted, but it is necessary to change the data rate so that the information to be transmitted can be forwarded in the available frames.
A data rate can be either increased or decreased, as required. The best known and the simplest method of increasing the data rate is repetition coding, wherein user data symbols are repeated as many times as there are free symbol positions in the frame. Correspondingly, the data rate is decreased in the simplest manner by removing user data symbols until the remaining symbols fit in the available frame. The problem in the prior art arrangement is how to select the symbols to be repeated or removed so that they are distributed evenly among the symbols to be transmitted.
BRIEF DESCRIPTION OF THE INVENTION
The object of the present invention is to implement the method such that the aforementioned problems can be solved. This is achieved with a method of the type described in the preamble, characterized in that the method comprises the steps of D1) calculating the number of symbols missing from the frame by subtracting from the frame length the number of symbols in the first block, and if the number of the missing symbols is greater than one, E1) repeating every ith symbol in the first block, i being determined as the nearest bigger or an equal integer when the number of symbols in the first block is divided by the number of symbols missing from the frame, F1) updating the first block by removing therefrom the symbols that have been repeated, G1) updating the number of symbols missing from the frame by subtracting therefrom the number of the symbols that have been repeated, and if the number of the missing symbols is greater than one, H1) proceeding to step E1).
The method according to the invention is also characterized in that the method comprises the steps of D2) calculating the number of symbols that do not fit in the frame by subtracting the frame length from the number of symbols in the first block, and if the calculated number of symbols is greater than one, E2) removing every ith symbol from the first block, i being determined as the nearest bigger or an equal integer when the number of symbols in the first block is divided by the number of symbols that do not fit in the frame, F2) forming the first block to consist of the symbols that have not been removed, G2) updating the number of symbols that do not fit in the frame by subtracting therefrom the number of the repeated symbols, and if the number of the missing symbols is greater than one, H2) proceeding to step E2).
The invention also relates to a transmitter in a digital data transmission system, comprising means for generating a signal having a first data rate, and means for forming the signal in frames of a given length that corresponds to a second data rate, and means for grouping the signal in a first block the length of which corresponds to the first data rate. The transmitter according to the invention is characterized in that the transmitter comprises means for calculating the difference between the frame and the number of symbols in the first block by subtracting the frame length from the number of symbols in the first block, means for equalizing the difference by removing or repeating every ith symbol in the first block, i being determined as the nearest bigger or an equal integer when the number of symbols in the first block is divided by the absolute value of the difference that was calculated, means for updating the number of symbols that do not fit in the frame by subtracting therefrom the number of the symbols that have been repeated, and means for forming the first block to consist of the symbols that have not been repeated or removed.
The preferred embodiments of the invention are disclosed in the dependent claims.
The method and the transmitter according to the invention provide several advantages. By means of the method according to the invention, the symbols to be repeated or removed can be selected as evenly as possible from among the symbols to be transmitted. In this manner the quality of the coding is the best possible. The method according to the invention enables flexible rate adaptation between data rates of different types. On the other hand, the method according to the invention enables unambiguous repetition or removal, so that it is possible to deduce the repeated symbols at the receiving end if the algorithm is known.
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Finnish Office Action.
Chin Stephen
Ghayour Mohammad
Nokia Mobile Phones Limited
Perman & Green LLP
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