Date rate conversion using repetition codes

Method for converting signal data rate and transmitter

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 communication system, wherein the signal is transmitted using frames of a given length corresponding to a higher data rate, and the method is grouped into a first block. .

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 communication system, wherein the signal is transmitted using frames of a given length corresponding to a lower data rate, and the method is grouped into a first block .

Background of the invention

The requirements for data transmission systems are constantly growing. This is especially true for wireless communication systems, such as cellular radio systems, for which increasingly diverse services are desired, such as, for example, a variety of data and video services.

Traditionally, wireless communication systems have only been used for voice transmission. The increase in the number of different services to be transmitted, especially in wireless systems, means that the system must be able to transmit signals of different capacities over the radio path, such as • ·

.. speech at a data rate of 8 kbit / s and data at a rate of 64 kbit / s. In addition to this, there is a need to transmit signals of different quality levels, which typically also need different data rates at the same time. A typical example is a video connection where the image requires a high data rate and high^; 30 high quality levels, but audio can be transmitted at a lower data rate and quality level. The data transmission system should therefore be able to operate efficiently. in an environment where transmissions of many different data rates, quality levels, and service types are transmitted.

It is typical for digital communication systems that the transmission of signals takes place in the form of a frame and that the size of the frame is predetermined. When using different data rates, it may not be possible to select just the right size frame for all the data rates to accommodate the symbols to be transmitted, but there is a need to perform a data rate change to transmit the information to be transmitted in the available frames.

The change in data rate can be performed in two directions, either by increasing or decreasing the rate as needed. The best known and simplest way to perform a data rate increase is repetition coding, in which user data symbols are repeated as many times as there are free symbol positions in the frame. Similarly, the reduction in data rate is at its simplest by deleting user data symbols until the remaining symbols fit in the available frame. The problem with the prior art solution is how to distribute the symbols to be repeated or deleted evenly among the symbols to be transmitted.

Brief description of the invention

The object of the invention is thus to implement the method in such a way that the above-mentioned problems can be solved. This is achieved by a method of the type described in the introduction, characterized in that the method comprises steps A1) calculating the number of missing symbols in the frame by subtracting 20 the number of symbols in the first block from the frame length, and B1) repeating the first block every i: s symbol, where i is defined as the largest, or by dividing the number of symbols of the first block by the number of symbols missing from the frame into an equal integer, C1) the first 25 blocks are updated by removing the symbols that have been repeated, D1) is updated * ·._you the number of symbols missing from the frame by subtracting the number of characters repeated from it. the number of symbols, and if the number of missing symbols is greater »· than one, then E1) goes to step B1).

The method according to the invention is also characterized in that ¹ · The method comprises steps A2) calculating the number of symbols that cannot fit in the frame by subtracting the length of the frame from the number of symbols in the first block, and B2) deleting every i-th symbol in the first block, where i is defined as a substantially greater than or equal integer dividing the number of symbols of the first block by the number of symbols that cannot fit in the frame, C2) forming the first block consisting of those symbols that have not been deleted, D2) updating the number of symbols of the volume aphthous in the frame by subtracting the number of symbols repeated from it, and if the number of missing symbols is greater than one, then E2) goes to step B2).

The invention also relates to a transmitter in a digital communication system, the transmitter comprising means for generating a signal having a first data rate and means for generating a signal in frames of a given length corresponding to the second data rate and means for grouping the signal into a first block corresponding 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 number of symbols in the frame and the first block by subtracting the length of the frame from the number of symbols in the first block, and means for smoothing the difference by removing or repeating every i symbol in the first block. the number of symbols in the first block by the absolute value of the calculated difference, the means for updating the number of symbols that cannot fit in the frame by subtracting the number of symbols repeated therefrom, and the means for forming a first block composed of those symbols that have not been repeated or deleted.

Preferred embodiments of the invention are the subject of dependent claims.

Several advantages are achieved with the method and the transmitter according to the invention. With the method according to the invention, the symbols to be repeated or deleted can be selected from the symbols to be transmitted as evenly as possible. In this case, the best possible quality is achieved by coding. The method according to the invention makes it possible to flexibly adjust the speed between different types of data rates. On the other hand, the method according to the invention enables unambiguous reproduction or deletion, whereby the repeated symbols can be deduced by the algorithm at the receiving end for hours.

Brief description of the figures

The invention will now be described in more detail in connection with preferred embodiments, with reference to the accompanying drawings, in which Fig. 1 shows an example of a wireless communication system in which the method according to the invention can be applied, Fig. 2 illustrates a possible structure of a transmitter according to the invention by means of a block diagram; through framework options, Figure 4 illustrates the structure of a second transmitter according to the invention by means of a block diagram.

Detailed description of the invention

Figure 1 illustrates a digital data transmission system in which the solution according to the invention can be applied. It is part of a cellular radio system comprising a base station 100 in two-way communication 102-106 to subscriber terminals 108-112. The digital communication system used as Example 10 is thus a cellular radio system, and in the following the invention will be described when applied to a cellular radio system without being limited thereto, as will be apparent to a person skilled in the art. The invention is also suitable for use in other systems.

It is assumed that in the system, the terminals can transmit information at several different data rates depending on the data transmission capacity required in each case. Figure 2 illustrates a possible structure of a transmitter implementing the solution according to the invention by means of a block diagram. The transmitter comprises a number of data sources 200 to 204, which may be, for example, for voice transmission or various data services. In data sources, channel coding is performed on the information. The signals 206 to 210 of the sources are frame-shaped and differ in data rate. The transmitter further comprises a switch or multiplexer 212 which selects or combines the signal of the currently active data source or data sources on the encoding means 214. The control means 216 control the operation of the switch or multiplexer 212 and other parts of the transmitter. The control and coding means 214, 216 are most preferably implemented in software by means of a processor. The signal 218 output from the encoding means 214 is frame-shaped. In the encoding means 214, the data rates of the signals of the data sources are matched to the frame using either repeat or delete coding by means of the solution according to the invention. It should be noted that the transmitter of Figure 2 comprises only components relevant to the description of the invention. The actual transmitter also has other parts obvious to a person skilled in the art, such as filters and amplifiers, but here they have been omitted for the sake of clarity.

Figures 3a to 3d illustrate the solution according to the invention by means of different frame alternatives. The aim is thus to match the data rate of the transmitted signal to a data rate suitable for the length of the available frame. Let N be the appropriate number of symbols in the frame_Tand the number of symbols of the transmitted signal after channel coding N_c:with. Figure 3a shows a channel data frame 300 and a data source frame 302. In the exemplary situation of Figure 3a, the channel data rate N_T is greater than 5 the information data rate N_c. In this case, repetition coding must therefore be performed in order to fill the channel frame with symbols. Figure 3b shows a channel data frame 300 and a data source frame 304. In the exemplary situation of Figure 3b, the channel data rate N_T is less than the information data rate N_c. In this case, deletion coding must be performed, i.e. puncturing, so that the in10 information can be transferred in the desired frame.

Consider the solution according to the invention in the case of repetitive coding, i.e. the situation of Figure 3a, in which N_T > N_c. Let's form N to be sent_c the first block S of the symbol_o = {d ,, d₂, ..., d_{the so-called}}, Here n_s is a block of S_o number of symbols and at the beginning of the procedure n_s = N_c. Thus, the task is to convert a lower data rate into a higher data rate by repeating

OF_T - N_c symbol from block S_o so that after playback, the block size is N_T symbols. It is preferable to distribute the repetitions as evenly as possible in the frame to be transmitted.

Initially, the number y of symbols missing from the frame is calculated by subtracting the length N of the frame_T the number of symbols in the first block

OF_c. If the number of missing symbols is one, then the first symbol of the block is repeated and the procedure ends. Otherwise, define the term /, such that - y where n_s is then block S_o the number of symbols. That is, / is defined as a substantially greater than or equal integer divided by the number of symbols in the first block by the number of symbols missing from the frame. The first step of repetition coding is performed by repeating block S_o which is the symbol. Number of repeated symbols n_R is determined by determining the nearest 30 or less integer divided by the number of symbols in the block with the term /, i.e.

Next, block S is updated_o by deleting the symbols that have been repeated. The number of symbols missing from the frame to be transmitted is then updated by subtracting the number of symbols repeated therefrom, and the above-described procedure is repeated until the symbol positions of the frame to be transmitted are used.

Consider the solution according to the invention in the case of deletion coding, i.e. puncturing, i.e. the situation of Figure 3b, in which N_T <N_c. Let's form N to be sent_c the first block S of the symbol_o = (d ^ d₂, d_{the so-called}}, Here n_s is a block of S_o number of symbols and at the beginning of the procedure n_s = 10 N_c. Thus, the task is to convert a higher data rate to a lower data rate by removing N_c - N_T symbol from block S_o so that after deletions, the block size is N_T symbols. It is preferable to distribute the depreciation as evenly as possible in the frame to be transmitted.

Calculate the number y of non-frame symbols by subtracting 15 from the number N of symbols in the first block_c frame length N_T. If the number of symbols is one, the last symbol in the block is deleted and the procedure ends. Otherwise, the term / is defined such that i = y

where n_s is a block of S_o the number of symbols. That is, i is defined as an integer greater than or equal to 20 divided by the number of symbols in the first block divided by the number of symbols that cannot fit in the frame. The first step of deletion coding is performed by deleting block S_o which is the symbol. Number of deleted symbols n_R can be found by determining the nearest or equal integer by dividing the number of symbols in the block25 by the term /, i.e.

Next, block S is updated_o consist of those symbols that have not been removed. The number of symbols that cannot fit in the frame to be transmitted is then updated by subtracting the number of symbols removed therefrom, and the procedure described above is repeated until the symbols to be transmitted can fit in the frame to be transmitted.

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Figure 3c shows a channel data frame 300 and a data source frame 306. In the exemplary situation of Figure 3c, the channel data rate N_Tis greater than the information data rate N_c so that

OF_T-OF_C 4 —!----> 1

OF_c that is, the size of the frame to be transmitted is more than twice the number of symbols of the information to be transmitted. In this case, in a preferred embodiment of the invention, each symbol to be transmitted is repeated a sufficient number of times, and the first block S_o is formed from this set of symbols. Then follow the procedure described above.

In the example situation according to Figure 3d, the data rate of the channel

OF_T is less than the information data rate N_c so that • · · • · · • · ·

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where A is some predetermined positive constant between (0,1). For example, A may have a value of 0.2. Figure 3d shows a data source frame 310 and frames 300, 308 of different lengths used in the system, the symbol numbers of which are N_T and N_T1 so that N_T &lt;N_T1. In a preferred embodiment of the invention, when the data rate of the data source is more than a certain threshold higher than the corresponding data rate of the smaller frame, the adaptation is performed by selecting a larger frame for the transmission of the signal to be repeated. In the exemplary situation of Figure 3d, the symbols of the data source frame 310 are not punctured in the shorter frame 300, but a larger frame 308 is selected for use, and repetition coding is performed by the method described previously. This avoids an unnecessarily large amount of deletions that could degrade the signal quality. Another possible alternative in the situation of Fig. 3d 25 is to divide the symbols of the data source frame 310 into two smaller frames 300 in which the repetition coding according to the invention is performed,

Figure 4 illustrates a possible structure of a transmitter implementing the solution according to the invention by means of a block diagram. The figure shows an example of a transmitter utilizing the CDMA multi-use method, but the idea according to the invention can of course be applied to other types of transmitters as well. The transmitter according to the invention thus comprises a number of data sources 456 460, the output signals 400 to 404 of which may have different quality level requirements and data rates, and which data sources may produce signals to be transmitted simultaneously. Typical data transmitters in question are, for example, a speech encoder, a fax machine, a video encoder or some other source of digital information.

The transmitter according to the invention further comprises first encoders 406, 408 performing external coding on at least some of the signals to be transmitted, so that the quality level requirement of the signals thus coded is equal to the lowest quality level requirement of the active data sources. Thus, the same quality level requirement is obtained for all transmitted signals. The coding used can be performed in known ways, and preferably the Reed-Solomon coding method can be used. The transmitter may also comprise first interleavers 410, 412 for interleaving the encoded signals, i.e. changing the position of the symbols of the signal according to some known algorithm.

Signals 400, 416, 418 from all data sources, thus having a common quality level requirement, are applied to multiplexer 414, where the signals are combined in time to equal length frames, the number of bits 15 contained in which frames may vary frame by frame depending on the signals entering the multiplexer. The output of multiplexer 414 is operatively coupled to a second encoder 420 where the signal is internally encoded. This encoder 420 may be any desired encoder, the preferred embodiment using a convolutional encoder to lower the common quality 20 level.

The signal 450 thus encoded is passed to means 422, in which the number of symbols to be transmitted is equalized so that the length of the symbols to be transmitted in each frame is equal to a multiple of a known period of time substantially shorter than the symbol length. When using the CDMA method, it can be a multiple of the bit of the spreading code, i.e. the chip length.

The equalization of the number of symbols can be performed either by repeating the symbols or by deleting the symbols, by the method according to the invention described above. The means 422 may preferably be implemented programmatically by means of signal processing by a signal processor. Means 422 groups the signal symbols into a first block having a length corresponding to the desired smoothed data rate. The means 422 further calculates the difference between the symbols of the frame and the desired number of symbols by subtracting the desired number from the number of symbols of the first block. The difference is equalized in the means 422 by deleting or repeating every i-th symbol of the first block, where i is determined as a substantially greater than or equal integer by dividing the number of symbols of the first block by the calculated difference. Means 422 form a first block of symbols that have not been repeated or deleted and repeat the procedure described above until the desired number of symbols is reached.

In the transmitter according to the invention, frames of different lengths can also be formed, and when the higher data rate is more than a certain threshold than the lower data rate, a larger frame is selected for signal transmission, and repetition coding is performed.

The transmitter according to the invention further comprises a multiplexer 434, 10 which combines symbol-balanced signal frames to be transmitted with information on the frame structure of each frame, such as the bit rate. Said information 426 on the frame structure is first applied to an encoder 432, where the desired encoding is performed to protect the information against transmission errors, and which encoded signal is applied to a multiplexer 434. Said information may comprise, for example, a description of the frame structure of the frame in question or of the next frame to be transmitted. The signal 452 thus combined is passed on to interleaver 436.

The transmitter may comprise a multiplexer 438 in which additional information, such as power control information 428 or reference symbols 430 for coherent reception, is combined with the interleaved signal. In the case of a CDMA transmitter, the combined signal 440 is passed on to a multiplier 442, where the signal is multiplied by a connection-specific spreading code, whereby the signal is spread over the frequency band used. The signal thus multiplied is passed to radio frequency portions, where the signal is converted to radio frequency and amplified by antenna 446 for transmission.

The transmitter according to the invention comprises control means 454 which control the operation of the parts described above, and which means can be implemented, for example, by means of a microprocessor, separate logic circuits or the like. The control means 454 also provides control to the radio frequency components 444 the transmission power of each frame to be transmitted, which may depend on the number of frame symbols 30 after the multiplexer 414.

The transmitter according to the invention naturally also comprises other components, such as filters and transducers, as will be apparent to a person skilled in the art, but for the sake of clarity they have been omitted in Figure 4 and the related description.

Although the invention has been described above with reference to the example according to the accompanying drawings, it is clear that the invention is not limited thereto, but si104673 can be modified in many ways within the scope of the inventive idea set forth in the appended claims.