JPS61501670A - Single sideband communication system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Single sideband communication system It relates to digital communication methods for transmitting signals.

A wide variety of modulation formats are used in digital communication systems. commonly used formats in which the elements of the data signal modulate a carrier signal with orthogonal relationships. Ru.

This type of modulation has various names, such as phase shift keying (PSK), quadrature Amplitude Modulation (QAM) and non-coherent. The information carried by the data signal is Of course, there are virtually no limitations, including audio, video, facsimile, etc. Ru. Additionally, there are no restrictions on the transmission channel carrying the modulated carrier, and currently there are no Including wire, wired or fiber optic.

A problem with virtually all communication systems is that the transmission channel is band-limited. It means that there is. In other words, the frequency width used to transmit information is It is finite. This constraint comes from system and/or device requirements. It is. The difficulty of this problem varies from system to system, but for a given frequency range Their ability to transmit large amounts of information is particularly prized.

Information transmission capabilities of digital systems that transmit carrier waves with modulated orthogonal relationships One approach to increasing is to increase the number of possible modulation states. This hand An example of the method is to use 64 QAM instead of a 16 QAM system in an application that requires large capacity. This can be exemplified by the design and widespread use of AM systems. this The problem with the method is to design and develop new modulators and demodulators by changing the number of modulation states. This means that at least one is required. This effort is expensive and the results are Equipment that has been installed can sometimes be used in production systems without significant expense. I can't.

Another approach to increasing system capacity is to use single-sideband signals instead of double-sideband systems. The method is to use This method is relatively simple to implement and requires only a single carrier signal. It has been commonly used to modulate signals. Unfortunately, after single sidebanding, the received Since there is no well-known way to gracefully decode a signal that is It has not been used as a system that utilizes carrier waves.

Summary of the invention The present invention is a digital communication system that modulates a carrier signal in which the elements of a data signal have an orthogonal relationship. Intended for use in systems. To reduce the required bandwidth, The resulting orthogonal carriers are converted to a single sideband signal. transmission After propagating through the channel, the received single sideband signal is the received signal demodulated into elements. Each of these elements is an element of the data signal and a single sideband transform. Therefore, it contains introduced parasitic signals.

To recover the data signal elements, each received signal element is transformed and paired. At least one estimate of the corresponding data signal element is formed. Each thrust formed The fixed value is then compared to the set of allowed data signal element values, and the estimated value is also If the pre-selected conditions are met, the data is output.

According to a feature of the invention, this is realized within an existing digital communication system, Essentially increasing information transmission capacity within a certain predetermined band.

According to another feature of the invention, it can be used in conjunction with conventional demodulation and equivalent techniques. I can do it.

Brief description of the drawing FIG. 1 is an explanatory block diagram of a communication system related to the present invention: Figure 2 is a sample of the signal space diagram of the signal levels transmitted by the communication system in Figure 1. lot; FIG. 3 shows a detailed diagram of the decoder 118 or 119 shown in the communication system of FIG. This is an explanatory diagram.

detailed description FIG. 1 is an example of a QAM communication system related to the present invention. At the transmitter 10 The digital data signal on lead 120 is coupled to QAM modulator 101. . Inside the modulator 101, a parallel to serial converter 121 connects the serial data on lead 120. The data signal is spread out on four paths 131.132.133 and 134. Di A digital-to-analog (D/A) converter 122 appears on leads 131 and 132. quantizes the signal appearing on lead 135 into a number of signal voltages appearing on lead 135. Similarly D/ A converter 132 converts the signals appearing on leads 133 and 134 onto lead 136. quantize into a number of signal voltages coupled to. Multipliers 127 and 128 read The signals on 135 and 136 are passed through Nyquist filters 124 and 125, respectively. receive the signal voltages on leads 135 and 136 after smoothing them respectively with . Multiplier 127 filters the amplitude of the carrier signal generated by oscillator 126. The signal on the lead 135 after this is used for modulation. Similarly, multiplier 128 After smoothing the amplitude of the carrier wave signal with the Nyquist filter 125, the lead 1 36. The second carrier signal provided to multiplier 128 is an oscillator. The carrier signal generated by 126 is shifted by a phase shifter 129 to −π/2 radians It is generated by shifting the phase. Therefore, the voltage applied to multipliers 127 and 128 is The pair of carrier signals transmitted are spatially orthogonal to each other and multipliers 128 and 129 The products given by are each a double sideband signal. Next, the adder 130 The products given by multipliers 128 and 129 are added and this sum is output. , which is a double sideband signal on lead 102.

Looking at the signal processing provided by the transmitter components described above, these The component modulates a carrier wave having an orthogonal relationship with the signal element of the data signal, and A signal appearing on one of the element beams 131.132 or 135.137. Yes, the other element of the data signal is on leads 133.134 or 136.138. It can be seen that this is a signal that appears in Furthermore, if D/A converters 122 and 1 By selecting the number of signal voltages and the allowed values given by 23, the data signal can be Graphically represent all combinations of transmitted carrier signals on rectangular coordinates. I can do it. Such a graph is commonly called a signal space diagram.

Reference is now made to FIG. 2, which shows a signal space diagram for the example transmitter of FIG. lead 137 top The data signal elements that appear in The data signal elements appearing at code 138 are referred to as quadrature elements Q. As shown, ■ The allowed values for the and Q factors are ±1 and ±3 volts, and with these tolerances All possible combinations of values form 16 states as shown at 201 in Figure 2. Ru.

In prior art communication systems, the output of adder 130 transmits information to system receiver 11. is added to the transmission channel propagating to the output of summer 130 to produce a double sideband signal at the output of summer 130. into a single sideband signal, thereby reducing the bandwidth required for signal transmission. child of the second single sideband QAM signal in the frequency band recovered by the reduction of the band of transmission becomes possible. This resulting capacity of two 16QAM single sideband signals is The amount is equivalent to that of a 256QAM double sideband signal. The conversion from QAM to single-sideband degrades the operation of normal QAM receiver circuits and Additional functionality is required to successfully recover the code elements. In this regard, the main It will be appreciated that light can also be used in wireless systems. In this case, add A circuit is often inserted between the adder 130 and the transmission channel to This is manifested in shifting the transmission frequency to a higher band. Furthermore, the present invention provides a QAM system. In fact, it is not limited to phase, amplitude, and pairs of phase and amplitude. Any system that transmits a signal consisting of orthogonally related carrier waves modulated by It can be used in the system.

To understand the principles of the invention, one of the sidebands of the illustrated double-sideband QAM device is used. the resulting single sideband signal through the transmission channel. First of all, we need to think about the effect of sending it out.

The QAM signal at the output of adder 130 is expressed as a function of time 5(t): s(t)=i(tlaIswct q(tldnwct) (1).

here wo is the frequency 1 of the carrier wave generated by the oscillator 126 (tl and q (tl is the The components of the I and Q data signals are each a function of time.

m(t) with a filter with impulse response h(t) to remove one of the sidebands. When passed through the filter 103, the resulting single sideband signal (5 (t)) sss. Here, it is a temporary variable for integration. Next Relationships between trigonometric functions such as cas(we(t-τ))-cos wct ax wcτ+dn w, t m W, τ and brutality (vc (t-τ): 1 = sin vct cas vc Using t-cos w, tdn v, τ (3), equation (2) can be written as follows. Color can be changed.

Equation (4) is then rewritten as follows.

C5(tl) 5Sn=’(1(tl-FQ(t)).wct-”(q(t -1-ki)) corridor WQ t (5) where %) and q(tl are each 1(t ) and q (the Hilbert transform of tl).

Comparing equation (5) with equation (1), one of the sidebands of the QAM signal in equation (1) is excluded. By doing this, 1(1) contains the Hilbert transform of q(tl), and q(t) is mixed with the Hilbert transform of i(t). Therefore, the receiver in Fig. 1 to recover the components of i(tl and q(tl), respectively, q(s) and and 1(t) is required.

Referring again to FIG. 1, transmission channel 105 is diffuse, intersymbol interference (IS) I), inter-rail interference (X rail l5I), and distortion including Gaussian noise (n(tl) Let us consider the general case of introducing . If m (tl sss is normal QAM' When combined through O1 modulator 107, the two received data elements i'(t) and q'(t) are formed on leads 110 and 111. i’(t) and q ’(t) can be derived from the received signal by well-known carrier recovery techniques. This is done by extracting the carrier wave that has on leads 110 and 111 The signal is z'(t) = Ct(tl+order(tl')+ISI+X-rail IS I + nI(t) (6) q’(t) = Cq(tl-’t(tl”l+I SI + X-rail ISI + nQft) (7). where n I(t) and nq(t) are the gases introduced into i(tl and q(t), respectively) represents a raspy murmur.

The ISI and X-rail ISI in equations (6) and (7) are t'(t) and q'(t It acts on l, and (i (tl + plan (t)) and (q (t) - now (t)) are just emotions. normal transversal equalization, configured to treat it as if it were a By combining i'(t) and q'(t) through containers 112 and 113, removed. Equalized signal ig(t) appearing at the output of equalizers 112 and 113 and qE(t) are then sampled by sampler 114 at a baud frequency of 17T. It will be done. The i-th sample, where K is an arbitrary integer, is i for lead 116. (kT) = (1 (kT) +/; 4 (kT)) + n g (kT > ( 8), and for lead 116 QE (kT) = q (kT) i (kT) + nQg (kT) (9) expressed. The formula n (kT) and n, E (k'r) are equal to the posthumous reception g Represents Gaussian noise in the signal component. The sampler 114 uses the normal timing of the receiver. A timing signal on lead 108 provided by a recovery circuit (not shown) is controlled.

In order to recover the information components of 1 (kT) and q (kT), it is necessary to ) must be removed. Life (kT) and’? (kT) only has a finite number of values. The value is given by D/A converters 122 and 123. is a function of the quantized value. In any communication system, △ 1(kT)=-1/2q((k-1)T)+''/2q((k+1)T)(10 ). That is, the Hilbe of 1(t) at the sampling point The root transformation is a function of q(t) at the (k-1) and (k+1) sampling points. and (k-1) and (k+1) sampling time points are respectively The sampling time immediately before and after the sampling time. kth sample The Hilbert transform of (1(tl) at the point in time is (k-1) and (k+1) 1 at the sampling time (tl), (k-1) and (k+1) The sampling points are the samples immediately before and after the sampling point, respectively. This is the time of sampling.

From equations (10) and (11), in the illustrated 16CAM communication system, 1(t) and q(t) can take voltages of ±1 and ±3, and 1(kT) and q(kT) are Can take any value from the set of (0, -1, -2, -3, 1・2.3) Ru.

Therefore, at the sampling time kT, (kT) and Q(kT) have seven types. It can take one of the possible values.

See FIG. 3 for a detailed illustration of the decoder 118 and 1190 circuits of FIG. Let's shine. In the decoder 118, the second sample iB(kT) is It is supplied to seven adders 301, 302, . . . 307, and leads 311 to 31 Form 7 estimates of 1(kT) on 7. Each adder starts from ig(kT) ’&　(t) by subtracting the different seven possible values of Forms one of the fixed values. Each of leads 321-327 is connected to a reference voltage source (not shown). ) from it). Selection circuit with multiple threshold detectors 318 assigns each estimate to a permissible value of 1(t), i.e. ±1 and ±3 volts. Compare and choose an estimate of 1(kT) that is close to any of the acceptable values.

This selected estimated value is output to the board 150. The decoder 119 Perform a similar operation for qF, (kT) and find the most acceptable value of q(t). A close estimate of q(kT) will be output to the board 151 in FIG. figure As shown, leads 150 and 151 have selected estimates of 1(t) and ct(tl to the timing recovery and other receiver circuits for subsequent Used for signal processing.

Ambiguity may arise in the process of forming and selecting estimates. Sunawa If two or more similarly proximate estimates of different possible data element values form may be accomplished. This problem takes one set as a value of 1 (1) and converts it to q(tl This is prevented by using the other set as the O value. For example, as shown in this example For the 16QAM signal arrangement shown in Figure 2, the values of 1(t) are ±1 and ±3 volts. , the value of q(t) is equal to ±1.5 and ±4.5 volts, and the above mentioned To provide a signal state that avoids the problem of obscurity.

The decoders 118 and 119 disclosed herein use parallel signal processing to and q(tl), but the decoder only has one (tl or q (includes only one adder that forms seven estimates of tl in series) It's okay. In this manner, selection circuit 318 selects each estimate as an acceptable value of the data element. any estimate that falls within a predetermined width around each possible value. is output. After selecting the estimate, selection circuit 318 selects the next sample. 114 and prohibits outputting all other estimates.

The present invention is, of course, not limited to the specific embodiments disclosed herein; Understand that many changes are possible in painting without departing from the spirit and scope of Ming. I want to be For example, first if the magnitudes of ISI and X-rail ISI are acceptable If the difference is not large compared to the difference between the data element values, then the receiver uses transversal. Eliminates the need to use filters. This is the transmission of optical fibers and transmission channels. This often holds true in wired systems where the reach function is not time-varying. Second, Nyquist Although the filter is only shown at transmitter 10, a half-Nyquist filter can be used at transmitter 10. 10 and receiver 110.

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Claims (16)

[Claims] 1. The elements of the data signal modulate orthogonal carrier waves, and the carrier waves are single sideband signals. A receiving device used in a digital transmission system that converts signals into The receiving device forms received signal elements by extracting carrier waves having the orthogonal relationship. the received signal element includes means for demodulating the single sideband signal to It differs from the data signal element by being converted into a single sideband signal, and forming at least one estimate of each of said data signals; the data signal by changing one of the received signal components by a defined amount. means for changing the element and then comparing the formed estimate with predetermined conditions. Receiving device including. 2. The apparatus of claim 1, wherein for each of the data signal elements: characterized in that the estimated value formed includes changes in different ones of the received signal components. Receiving device. 3. The apparatus according to claim 2, wherein the recovery means A receiving device forming an estimated value. 4. The apparatus of claim 1, wherein each end of the data signal element has a specific A receiving device characterized in that it has an assigned value. 5. In the device according to claim 4, allocating to all data signal elements A receiving device characterized in that the received values are the same. 6. In the device according to claim 4, the data signal element is assigned to the one data signal element. The received value is different from the values assigned to other data signal elements. communication device. 7. In the apparatus according to claim 4, the predetermined amount is allocated. A receiving device characterized in that the receiving device is a function of a given value. 8. The apparatus of claim 7, wherein the function includes the predetermined quantity. A receiving device characterized in that it forms a set of numbers. 9. The apparatus according to claim 1, wherein each received signal element comprising one data signal element and a nonzero function of another data signal element. Receiving device. 10. The apparatus according to claim 9, wherein the non-zero function is a Hilbert transform. A receiving device characterized by: 11. 4. The apparatus of claim 4, wherein the preselected quantity is algebraic combination of all possible permutations of the assigned value of one of the signal elements A receiving device characterized by being included in a set of numbers generated by taking . 12. In receiving equipment used in digital transmission systems, the elements of the data signal are modulate the intersecting carrier waves, the modulated waves are then converted to single sideband signals, and the received The device extracts the orthogonally related carrier waves from the components of the received signal. demodulating the waveband signal, each received signal element being selected from a selected element of the data signal; a non-zero function of the data signal elements not received; varying each received signal element by a plurality of preselected amounts for the element; by forming sets of values, and then extracting from each set according to predetermined conditions. means for recovering the data signal element by picking up the value of the data signal element; A receiving device comprising: 13. In the apparatus according to claim 12, the non-zero function is a non-selected data. A receiving device characterized in that it is a Hilbert transform of a data signal element. 14. A method for retrieving elements of a data signal, wherein the elements are orthogonally related carriers. In a reception method in which a carrier wave is modulated and the carrier wave is converted to a single sideband signal, the method The method forms the received signal elements by extracting the carrier waves that have the orthogonal relationship. demodulating the single sideband signal in order to for the conversion to the data signal elements, and each of the data signal elements receiving at least one preselected quantity forming at least one estimate; by modifying one signal element, and then subjecting the formed estimate to a predetermined condition. Compare with A receiving method characterized by: 15. In transmitters used in communication systems, the elements of the cheetah signal are orthogonal. means for modulating a carrier signal in a carrier to form a double sideband signal; the double sideband signal; and means for converting the signal into a single sideband signal. 16. In a communication system that includes a transmitter and a receiver, the transmitter A double-sideband signal is formed by modulating a carrier signal that has an orthogonal relationship with the elements of the data signal. means to and means for converting the double sideband signal into a single sideband signal, the receiver comprising: Form a received signal element by extracting the orthogonal carrier waves, and The signal element is different from the data signal element for conversion of the carrier into a single sideband signal. means for demodulating said single sideband signal so as to reduce one of said received signal components; each of said data signal elements by one predetermined amount. form an estimate and then compare the formed estimate with predetermined conditions means for recovering data signal elements by A communication method characterized by including.