# Transmission of digital signals by multiplexing orthogonal frequency division

In the system multiplexing orthogonal frequency division (MOCR), which uses an external encoder reed-Solomon block interleaving and inner convolutional encoder, after the inner convolutional coding data bits are interleaved by the inner stripe, and then grouped into symbols, each of which has m bits. After grouping the symbols displayed on the complex plane using quadrature amplitude modulation (QAM). Thus, the bits, but not the characters, interspersed through the inner stripe. The receiver performs soft decision, taking into account the value of each bit in each received complex QAM symbol. The technical result is the creation of a system for transmitting high speed digital data in conditions of multipath propagation. 5 C. and 16 h.p. f-crystals, 4 Il., table 1. Technical field the Present invention relates to a digital transmission signal by multiplexing orthogonal frequency division (MOCR), more specifically the invention relates to devices and systems MOCR that are used for the transmission of digital signals.Predoi way broadcast transmission of high speed digital signals, for example, signals of high definition television (HDTV). In systems MOCR one high-speed data stream is divided into several parallel low-speed substream, each substream is used to modulate the corresponding subcarrier frequency.The modulation method used in the systems MOCR, is defined as quadrature amplitude modulation (QAM), which is modulated as the phase and amplitude of the carrier frequency. When modulation QAM many data bits are formed complex QAM symbols, and each symbol includes a real component and imaginary component, and each symbol represents the set of data bits from which it was formed. Many bits QAM transmitted together in a configuration that can be graphically represented using the complex plane. In a typical case, such a configuration is called a "constellation". The use of CAM can improve the efficiency of the system MOCR.Transmitted in the broadcast mode, the signal may be distributed to the receiver in more than one way. For example, the signal from a single transmitter may be distributed to the receiver in a straight line, and after reflection from the Phi is possible spectral efficiency, the received signal may be broadcast more than one transmitter. Therefore, the same signal will be transmitted to the receiver in more than one way. Such parallel propagation of signals as artificial (i.e., caused by transmission of the same signal from more than one transmitter) and natural (i.e., due to reflections), is defined as "multipath". It is clear that, although the cellular digital broadcasting is the spectral effective measures should be taken to account for the effects of multipath propagation.System MOCR using KAM, more effective under the conditions of multipath propagation (which must occur when using a cellular methods broadcast) than the ways of CAM based on using only one carrier frequency. In systems of CAM with one carrier should be used in an integrated equalizer for equalizing characteristics of the channels that have the echo signals, a comparable level with the direct signal propagation, such alignment is difficult to implement. In contrast, in systems MOCR the need for complex alignment can be excluded, just worksout CAM, have the advantage in conditions when there is multipath.As for modern systems MOCR, in assessing the present invention should be aware that in modern systems, the data stream to be broadcast, is encoded twice, first using the encoder reed-Solomon, and then use the schema lattice coding. Note that the present invention is equally applicable to systems in which only one encoding. In a simple trellis encoding the data stream is encoded using a convolutional encoder, and then the serial bits are combined into a group of bits forming a symbol QAM. In the group there are several bits, and the number of bits per group is determined by the integer m (therefore, each group is called with m-ary dimension), usually the value of m is four, five, six or seven, although it may be more or less.After grouping the bits in the multibit symbols are interleaved. "Alternating" means that the character stream is reordered in the sequence, in order to randomize the potential errors caused by distortion in the channel. For illustrative purposes, the distortion in the channel, in such circumstances, even to avoid distortions in the channel, may be lost the whole word, and it may be difficult or impossible to recognize what information was transferred through the lost words.In contrast, if the letters of the five words sequentially reordered (i.e., "alternate") to transfer, and there is interference in the channel, you may lose a few letters, perhaps one letter in the word. However, after decoding reordered letters will be received all five words, although in a few words may be missing letters. It is quite clear that in these circumstances, the digital decoder would be relatively easy, almost completely, to restore the data. After interleaving the m-ary symbols appear on the complex symbols using the aforementioned principles KAM, multiplexed in the respective subcarrier channels, and transmitted.It was found that the modern system MOCR that use the above diagram, trellis coding, in which data bits are grouped into symbols before interleaving, are not sufficiently effective in conditions of multipath propagation, when some of them MOCR in the presence of weakening subcarrier, due to the conditions of multipath propagation. It was also found that the effectiveness of such systems MOCR could be further enhanced by the soft decision receiver when determining the values of the received data.Summary of the invention Accordingly, the present invention is the creation of a system for transmitting high speed digital data in conditions of multipath propagation. Also the present invention is the creation of a system for transmitting high speed digital data using the principles MOCR, which operates relatively effectively with the weakening subcarrier in conditions of multipath propagation. In addition, the present invention is the creation of a system for receiving high-speed digital data, which allows the use of soft decisions on the basis of each subchannel to determine data values. The present invention is a system for transmitting high-speed data, characterized by simplicity and economy in manufacture and maintenance.In one aspect the invention provides a transmitter signal which are through internal striping to grouping bits in the multibit symbols.In another aspect the invention provides a device for transmitter MOCR signal for processing bits of digital data for transmission to the receiver, where the device contains an outer block interleaving for processing data bits; an encoder for encoding the aforementioned processed bits; internal striping for receiving data bits from the encoder and interleaving of data bits; and means receiving the interleaved data bits from the inner stripe and generate symbol that represents m consecutive bits of the internal striping, where m is an integer greater than one.In the transmitter MOCR provided by the device implementing the invention, for processing bits of digital data for transmission to the receiver. In this implementation, the device includes an outer block interleaving, preferably, the stripe symbol reed-Solomon code for processing data bits, and the internal block rotation for receiving the processed output data bits from the outer block interleaving and interleaving of data bits. The device also includes means receiving the interleaved data bits from the inner stripe and generate symbol, representing edocfile, convolutional encoder processes the bits between the inner and outer stripes. In addition, there may be provided a means of display of each character in m-ary signal space, according to a preferred variant implementation, the renderer uses quadrature amplitude modulation (QAM) to generate complex symbols. If m is an odd integer equal to at least five (5), renderer minimizes the sum of the Hamming distances between adjacent symbols in the quadrant signal space.As described in more detail below, a series-parallel Converter handles complex characters in m substream, where m is an integer greater than one. Generator protective period sets the protective period in the signal flow. This device is disclosed in combination with a transmitter MOCR and in further combination with a system MOCR.In another aspect the invention provides a method of transferring bits of digital data using multiplexing orthogonal frequency division (MOCR) that includes convolutional coding bits, interleaving the bits of the group of m bits in parallel, to form himself convolutional coding bits, and then the interleaved bits. Then, the method includes grouping the m bits in parallel to generate an appropriate symbol.The invention also provides a device for a receiver designed to receive n substream signal, multiplexed with orthogonal frequency division (MOCR signal) containing complex is adjusted in phase symbols, where each symbol represents m bits of data, which includes for each substream quantizer soft solutions for determining the binary value of each bit represented by each symbol in the substream. This part of the function of the receiver can accept computer logic device.The invention thus also includes a computer logic device for receiver MOCR signal intended for reception of complex characters in MOCR signal, each of which represents m bits of data, with computer logic device contains computer logical storage device, readable by a digital processing system; and commands that are implemented in a logical storage device, the commands executed by the digital processing system to perform steps of a method for making a soft R the s values for each symbol, moreover, each value in the first set has a binary value "0" in the pre-defined bit; determining, for each symbol, the modulus of the difference between the symbol and each possible value in the first set of possible values; and determining the smallest modulus of the difference, and generating a first signal representing him.The transfer device MOCR signals includes means quadrature amplitude modulation (QAM) to generate QAM symbols. Also, the device includes a display device for displaying characters on m-ary space so that the sum of the Hamming distances between adjacent symbols in space was minimized, where m is an odd integer equal to at least five (5).A brief description of the drawings the features, objectives and advantages of the present invention are explained in the following detailed description, illustrated by the drawings, which show the following: Fig.1 is a block diagram of a transmission system of a digital signal is performed in accordance with the present invention; Fig. 2 is a block diagram of a transmitter constructed in accordance with the present invention; Fig. 3 is a block diagram of a receiver made in accordance with the present invention; and F. the e description of the preferred embodiments In Fig. 1 depicts a system 10 for transmitting high speed digital data to the receiver 12 from one or more essentially identical transmitters 14, 16 through a variety of channels 18, 20 radio interface. High-speed digital signals may represent, for example, signals of high definition television (HDTV). The system 10 is a system multiplexing orthogonal frequency division (MOCR). Accordingly, the transmitters 14, 16 and passed to the receiver 12 of the same signals, and each signal is multiplexed in a set of n subchannels, where n is an integer greater than one (1). In accordance with the principles MOCR, each sub-channel is the corresponding subflow sequence of complex quadrature-amplitude-modulated (QAM) symbols. In turn, each QAM symbol represents m bits of data, where m is an integer greater than one (1). In one of the preferred embodiments the value of m is six (6). In another preferred embodiment, the value of m is seven (7). Although considered an implementation option is described in terms of quadrature amplitude modulation, it is equally applicable to systems of modulation to use the by option exercise. External character encoder error correction, for example, the encoder reed-Solomon 22 receives the bit stream of digital data to be transmitted and encodes the bits according to principles known in the art. Similarly, the outer block interleaving 24, preferably the stripe symbol reed-Solomon, interleaves the data from the external encoder 22 in accordance with principles known in the art. (See for example, G. C. Clark, Jr. and J. B. Cain, "Error-Correcting Coding for Digital Communications", Plenum Press, New York, 1981; S. Lin and D. J. Costello, Jr., "Error Control Coding: Fundamentals and Applications", Prentice-Hall, Englewood Cliffs, N. J. 1983).From the outer block interleaving 24 signal is fed to the convolutional encoder 26, which surtace encodes data bits according to well-known principles. Data bits are then transferred to the indoor unit rotation 28, which interleaves the bits. Then, the interleaved bits are fed to the unit group 30 of the signal space.According to the present invention, the block grouping 30 signal space groups in parallel a sequence of m bits from the inner stripe 28. Thus, the block grouping signal space generates a corresponding symbol that is representative of each of m consecutive bits received from the encoding handles data bits through an internal striping to grouping bits into multi-bit symbols. The applicant found that by using this structure, the transmitter and receiver structure 12, as discussed below, the characteristics of the diversity and efficiency of the system 10 is improved in conditions of multipath propagation, compared with conventional transmitters with lattice encoding that group first data bits into symbols, and then treated with the characters through the inner stripe.As shown in Fig. 2, the symbols of the block grouping 30 signal space is sent to the element 32 of the display signal space. In accordance with the present invention, the element 32 of the display signal space displays each character in m-ary signal space. Preferably, the display element uses quadrature amplitude modulation (QAM), for the implementation of the modulation amplitude and phase on the basis of each symbol, to generate complex symbols.These complex symbols are displayed on the complex plane, sometimes referred to as a QAM constellation. Accordingly, each complex symbol can be otricatelniy units

For even values of m, the mapping on the complex plane is performed using m/2 coded by gray binary digits for the x-coordinates and using the remaining m/2 binary digits (encoded in gray) to represent the y-coordinates. With this display of adjacent bits in the quadrant of the complex plane differ from each other by the value of only one binary value. In other words, the so-called Hamming distance between adjacent bits in quadrant exactly equal to one (1).In contrast, for odd values of m, because the QAM constellation is not rectangular, the QAM symbols can no longer be independently coded by gray in two dimensions. Accordingly, for odd values of m QAM symbols are displayed using quasi-Greensboro code shown in the table below, to minimize the sum of the Hamming distances between the m bits assigned to each distinct pair of adjacent characters in the quadrant (i.e., elements of the same quadrant, which is physically represented in the table as following each other, without any intermediate elements).Specialists will be obvious that the constellation depicted in the t is carried out between the third line and the fourth line and between the third column and the fourth column. According to the present invention two of the m bits of submitted by each QAM symbol, encode quadrant of the symbol.Thus, two of the bits of the characters of CAM in the first quadrant is 00, two bits of each symbol in the second quadrant is 01, two bits of each symbol in the third quadrant is 11 and two bits of each symbol in the fourth quadrant is 10.Accordingly, in the table, the remaining three bits of each character are referred to one of the eight letters a-h. Distribution for the character in the first quadrant are discussed below, but it should be borne in mind that, as shown in the table, the distribution of the same bit is reflected in the other three quadrants. Each letter can be arbitrarily assigned a value of "000"; for example, the letter "a" may represent a binary value of "000". To support the Hamming distance to the neighboring elements in the quadrant is equal to the unit, in the present invention is used, the distribution of b=001, C=010. This, in turn, leads to d=011 & f=111.For the remaining distributions there are two ways of minimizing the amount of inter-symbol Hamming distances in the quadrant. The first is the distribution of g=100 and h=101. In this case, the Hamming distance between all adjacent elements in kVA is the Hamming distance between adjacent elements in quadrant 1, with the exception of Hamming distance between d and g, which is equal to two, and the Hamming distance between b and h, which is equal to two. In both cases, anyway, minimize the sum of the Hamming distances from one neighboring element to another adjacent element in the quadrant.The table is displayed for the case m=5. It should be borne in mind, however, that the principles outlined here are applicable to a large odd values of m. For example, for odd m>5 each point in the table is replaced by a square matrix of the 2

^{(m-5)}points, so that five of the bits of each character are used to identify individual square matrices, and the remaining m-5 bits are used as the two-dimensional gray code to denote the point in a square matrix.After displaying the stream of complex symbols is multiplexed into substreams serial-to-parallel Converter 34. As the Converter 34 multiplexes the symbols, he inserts the symbols of the pilot signal in the n substream d

_{0}....d

_{n-1}(which is represented by block insert 33 symbol of the pilot signal in the transmitter 14, as shown in the drawing). For professionals it is obvious that the pilot signals create a standard amplitude and phase for the receiver, e.g. the After multiplexing substreams is converted into the frequency domain by block 36 fast Fourier transform (FFT). Then the generator 38 of the protective period receives the output signal of the block 36 FFT and generates the output signal protective periods. In a preferred embodiment, the protective periods are created by inserting into the signal cyclic extension of the symbol, which carries information.In Fig.3 shows the essential elements of the receiver 12 corresponding to the present invention. The received signal is sent to the removal unit 40 of the protective period, which removes the protective periods inserted by the transmitter 14 by processing only the energy taken during the period of the useful signal. From the removal unit 40, the signal is sent to the inverse FFT unit 42 for converting the signal back into the time domain.As shown in Fig.3, the inverse FFT unit 42 outputs the substreams received complex data symbolsEach character is combined in the appropriate multiplier 44 with the corresponding vector correction rotation phase e =

^{-j}

^{}where- rotate the phase of the symbol estimate based on the pilot signal, is entered in the transmitter 14.Then the value of bits represented by each complex symbol in vastavatele 46 decode complex characters back into data bits, they respectively represent. The method by which the defined values of the bits of each symbol is described below with reference to Fig.4. As indicated in Fig.3, however, in order to facilitate the adoption of soft decisions, the quantizers 46 take appropriate assessment "R" of the amplitudes of the received signals based on the pilot signals.Of the quantizer 46 substreams of data bits are sent to parallel-to-serial Converter 48 to combine the substreams into a single sequence of data bits. Then the sequence of data bits is sent to the block deinterlacing 50 to reorder the bits in the order in which they were before the implementation of the rotation by the inner stripe 28 of the transmitter. After removal of interleaving the bits are sent to the decoder 52 for decoding the bits in accordance with the scheme convolutional coding is widely known in the art. The variant of implementation of the convolutional decoder 52 is a Viterbi decoder, the construction of which is widely known in the art. The output signal of the decoder 52 is supplied to the external unit decoratiuni 51, which reorder surtace decoded symbols. The reordered symbols is izvestno in the technique.Fig. 4 illustrates the logic of the corresponding present invention quantizer 46 soft decisions when determining the values of the bits that represent the received complex symbol. As follows from Fig.3, each quantizer 46 may be a microprocessor, which, preferably, includes a device 53 data storage, which contains the commands used by the quantizer 46, for the implementation of phases present invention. Accordingly, for professionals it is obvious that the quantizer 46 may include a programmable Central processing unit (CCD) or a programmable chip matrix of gates or specialized integrated circuit.In Fig.4 shows the structure of various embodiments of logic, according to the present invention, as implemented on structures read by the computer logic in the storage device 53 (Fig.3). For professionals it is obvious that Fig. 4 illustrates the logical structure of elements that function according to this invention. Obviously, the invention is implemented in one of the main options for implementation on the basis of the machine component, which implements the logic elements in the form of issuing addicts work corresponding to those shown in Fig.4.These commands can be in logical structures/schemes in the storage device (or realized through these structures), which contains the media data storage, for example in the storage device 53 shown in Fig.3. Machine component can be a combination of logical elements that are implemented in the storage device 53, which may be an electronic constant memory (ROM), or an electronic random access memory (RAM), or other suitable storage device. Alternatively, commands can be implemented in the form of computer software code for semiconductor devices, on magnetic tape, on optical disks, on the matrix of storage devices direct access (SUPD), magnetic tape, conventional hard disk drive, electronic permanent storage device, or an electronic memory device, or other suitable storage device.From block 58, the adjusted phase signal(the value of i denotes the i-th symbol) for each take . the ATEM, in block 56 is defined by a first set of possible values of p

_{i}that may have taken a complex character. The values ofknown in advance, because each of them corresponds to the position in the given geometry of the constellation. This first set includes 2

^{m-1}elements of p

_{i}, each of which has a binary "0" in the k-th bit, k=1,...,m. In other words, in block 56, the first set of possible values is determined for each character, and each value in the first set has a binary value "0" in the bit is set.Similarly, in block 58 is defined by a second set of possible values of p

_{i}that may have taken a complex character. This second set includes 2

^{m-1}elements of p

_{i}, each of which has a binary "1" in the k-th bit, k=1,...,m. In other words, in block 58, the second set of possible values is determined for each character, and each value in the second set has a binary value "1" in the bit is set. Thus, in the constellation of 32 values shown in the table above, sixteen possible values are shown in block 56, and others who regulirovanie phase signaland each expected signal p

_{i}in the first set, and the smallest absolute value is selected as the first signal. Also in block 60 are determined by the absolute value of the difference between the adjusted phase signaland each expected signal p

_{i}in the second set, and the smallest absolute value is selected as the second signal. The output signal of the block 60 has the form:

Although the specific block interleaving bits for multiplexing orthogonal frequency division when the digital signals, described above, provides a solution to the above objectives of the present invention, it should be borne in mind that at the present time is characterized by a preferential option for the implementation of the present invention, representing a broad sense, the essence of the present invention. Thus the present invention encompasses other embodiments of which may be obvious to the experts, i.e. the present invention is limited only by the claims.

Claims

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