JP2015084502A - Method for determining intermodulation product in satellite repeater of satellite communication, and carrier arrangement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for calculating the interference level accurately while taking account of a spread of IM wave on the specific frequency, in a satellite repeater, and to provide a carrier arrangement method based on the interference level.SOLUTION: The IM levels of a combination of two waves or three waves are calculated in all carriers, then the IM levels are summed in unit of slots into which the band of a satellite repeater is divided, and then the C/IM value of each carrier is calculated. The carriers and IM waves are handled as having a spread of frequency according to the normal distribution. For the arrangement of carriers, a removal carrier, where the minimum C/IM value is maximized, is specified, and specification of a slot, where the minimum C/IM value is maximized when the removal carrier is inserted into an idle slot, is repeated until the interference falls within a tolerance.

Description

  The present invention belongs to a technical field related to a placement algorithm of a modulated wave (so-called carrier) in a satellite repeater and a nonlinear distortion of an amplifier in a satellite communication network using geostationary orbit satellites.

  A frequency division multiple access (FDMA) system is generally employed as a method for connecting a large number of satellite communication earth stations through communication satellites. In this method, modulated waves (carriers) transmitted from each earth station accessing the same satellite are arranged on a single or plural repeaters in the satellite by frequency division, and each receiving earth station By receiving a modulated wave addressed to and transmitting a carrier addressed to the station at the same time, a bidirectional line (channel) is formed, and a pair of channels are normally set to each other to perform bidirectional communication. There is also broadcast communication or broadcast communication in which a transmission carrier from one station is received simultaneously by a number of stations. In the case of 1: 1 bidirectional communication, the relationship between channels and carriers is called SCPC (Single Channel Per Carrier) for one channel per carrier, and a pair of modulated waves (carriers) constitutes a pair of channels. Communication. In addition, between the middle and large earth stations, a multiplexing method has been adopted for a long time, where multiple channels are multiplexed and transmitted as one carrier, and the same carrier is received by multiple receiving stations and only the channel addressed to itself is extracted. Has been. One of the features of the recent FDMA communication system is that these channels and carriers are digitized, and the original signal is handled as low-speed or high-speed data instead of the conventional analog telephone channel. This is the generalization of a system in which carriers of different bandwidths corresponding to data rates for transmitting various data rates are mixed (hereinafter referred to as multi-carrier system).

FIG. 1 shows a configuration example of the satellite repeater 100. Usually, a communication satellite repeater includes a low noise reception frequency converter (LNA-Receiver) 101, an I-MUX / BPF (input distributor filter) 102, a transmitter (TWTA) 103, an O-MUX (output combiner / distributor). ) 104 and the like, but when a large number of carriers are commonly amplified by one amplifier, a large number of interference waves (hereinafter referred to as IM waves) called intermodulation are generated due to nonlinear distortion of the amplifier. In a satellite repeater, an IM wave due to such distortion is generated in a transmitter (TWTA) which is the final active element. Of these IM waves, the following IM waves are generated in the same frequency band as the original carrier among the IM waves due to the intermodulation of 2 and 3 carriers, and this is an interference wave for carriers in the same band. It becomes. That is, when the frequencies of the respective carriers are, for example, f ₁ , f ₂ , and f ₃ , they are generated in 2f ₁ −f ₂ and 2f ₂ −f ₁ in the case of intermodulation of two waves of f ₁ carrier and f ₂ carrier 2 IM wave wave, f ₁ in the case of three waves of intermodulation ~f ₃ is _{f 1 + f 2 -f 3,} f 2 + f 3 -f 1 and f ₃ + f ₁ generated -f ₂ 3 waves IM Since the wave is generated in the same frequency band as the original carrier, it becomes an interference wave for the carrier. 2 and 3 show the frequency relationship between these IM waves generated by the two-wave and three-wave intermodulation and the original carrier, including the relationship with the original carrier power of the generated IM wave power ( The actual transmission / reception carrier has a bandwidth because it is a modulated wave, but this figure shows the power of the carrier as a line spectrum, with the power concentrated at the center frequency). These IM waves are generated by the third-order component of TWTA nonlinear distortion, and there are IM waves that depend on higher-order components, but in reality the third-order component described above is dominant. Hereinafter, the third-order IM wave by the combination of the above-described two waves and three waves will be described. The method for obtaining the level of the generated IM wave can be obtained by actually inputting a two-wave or three-wave carrier to the amplifier and measuring the spectrum of the output. The amplitude and phase input / output characteristics are expressed by a mathematical expression by series expansion such as a Bessel function, and the sum of two or three wave carriers is input, and the level of the corresponding IM wave component is calculated from the output wave component of the calculation result. It depends on the method. When a large number of carriers are arranged within the frequency band of one repeater, 2 and 3 IM waves are generated by the combination of all 2 waves and 3 waves of the multiple carriers, respectively. As the number of carriers arranged in the frequency band increases, the number of combinations increases exponentially, and the number of IM waves generated in the repeater band also increases. Therefore, the IM waves generated at the same frequency by combining the two different waves 3 and 3 increase, and the IM waves overlap.
A remarkable feature of the SCPC method is that when a large number of carriers are arranged at equal intervals, most of the IM waves generated by the combination of these two waves or three waves have the same carrier frequency or frequency that can be arranged, As described above, when the number of carriers increases, a large number of IM waves generated at the same frequency are added and added to further increase the level of the interference wave. For example, when 10-wave carriers are arranged at equal intervals, the overlap of IM waves due to the combination of 3 waves generated at the frequency of the 5th or 6th carrier is 26 waves, and the 10th or 11th wave by the 20 wave carrier The overlap of IM waves generated at the carrier frequency reaches 126 waves. Therefore, in a system in which multiple waves are simultaneously arranged, an increase in interference due to the overlap of IM waves has been a problem.

  Therefore, carrier arrangement methods and the like have been studied. As a result, for example, there is a Bubcock arrangement (Non-patent Document 1) as a carrier arrangement method in which the generated IM wave does not overlap with the original arrangement carrier. This method is effective as an arrangement method without interference because the interference wave does not overlap with any of the original arrangement carriers. However, as the number of carriers increases, the total bandwidth required increases rapidly, and several tens or more carriers are obtained. When the arrangement is necessary, an allocated bandwidth of several hundred times or more with respect to the sum of the bandwidths of all carriers is required, which is not realistic. Next, a method called “Deletion-Insertion Method” is a sub-optimal placement method aiming at minimizing the number of overlaps, assuming that an IM wave overlaps with any of the original placement carriers and that the IM waves overlap each other to some extent. (Non-Patent Document 2). This method calculates the number of IM waves overlapping with the carrier frequency for each carrier and the distribution (IM overlap distribution) for each carrier, and finds the frequency with the largest number of overlaps and the number of overlaps. Next, the carrier is removed one by one from the end in order, and the same calculation is sequentially performed under the conditions at the time of removal. Then, a removal carrier having the smallest number of overlaps with respect to the number of frequency overlaps with the largest number of overlaps before extraction is extracted and set as the removal arrangement position (so far, the removal operation). Next, the removed carrier is inserted into the vacant frequency that can be arranged, and the distribution of the IM wave overlap is calculated in the same manner. This rearrangement is sequentially performed to select an insertion frequency slot with the smallest number of overlapping IM waves (insertion operation so far). Up to this point, the removal-insertion operation is repeated with the resulting carrier arrangement as a new arrangement. And it repeats until the frequency of a removal carrier and an insertion carrier corresponds, and the state in which it matched is made into the suboptimal solution. This method is effective in the SCPC system. FIG. 4 shows an example of the effect of improvement by rearrangement in this case. FIG. 4 shows that (a), (b), and (c) and the number of slots are increased and rearranged, so that the number of IM modulation product overlaps can be distributed almost evenly.

W.C. BABCOCK “Intermodulation Interference in Radio Systems Frequency of Occurrence and Control by Channel Selection” Bell Syst. Tech. J, 32, 1, p63 (1963) HIDEO OKINAKA, YUTAKA YASUDA, YASUO HIRATA “Intermodulation Interference- Minimum Frequency Assignment for Satellite SCPC Systems” IEEE Trans Communi. COM-32, 4 pp.462-468 (April 1984)

  However, this “Deletion-Insertion Method” is used when all carriers are allocated at the same bandwidth, basically at the same level as in the SCPC system, and the carriers are allocated in units of the allocated bandwidth of the carrier. The levels of individual IM waves generated by the combination of 2 waves and 3 waves are different depending on the combination of 2 waves and the combination of 3 waves, but are the same level in each. Therefore, since the number of overlaps of IM waves generated at the frequency of each carrier is directly proportional to the interference wave level, the number of overlaps between the two waves of IM waves at each carrier frequency and those due to three waves are counted. Should be weighted to calculate the case where the worst number of overlaps is minimized. However, as described above, when there are many carriers with different bandwidths and the carrier parameters of the bandwidth and level are not uniform as in recent multi-carrier systems, it depends on the bandwidth and level of the original carrier. Since the level and bandwidth of each generated IM wave are different, it is not possible to evaluate the interference level due to the IM wave simply by calculating the number of overlapping IM waves generated at each carrier frequency, and the level difference and bandwidth are included. There was a problem that “Deletion-Insertion Method” could not be applied practically. Furthermore, since the IM wave generally has a wider band than the original carrier, when a wide band carrier and a narrow band carrier are mixed, the carrier may be used when only a part of the band of the IM wave overlaps with the carrier. In addition, there is a problem that it cannot be applied even when it is necessary to obtain and calculate the power density distribution of the IM wave.

  The present invention solves the above-mentioned problems, provides a method for calculating an accurate interference level considering the frequency spread of the IM wave, and further provides a carrier arrangement method for reducing interference based on the accurate interference level. It is to provide. The present invention solves such a problem by the following means using an electronic computer. The feature of this method is that the repeater band is first divided into frequency slots (hereinafter referred to as slots) corresponding to the minimum carrier bandwidth or the minimum assigned frequency step width, and the power of each IM wave is divided into the slot bandwidth units. By obtaining a power density distribution in units of slot bandwidth, each IM wave generated in the repeater in a given carrier arrangement including a number of different bandwidths and carriers of different power Obtained as a level distribution of IM waves with bandwidth as unit bandwidth, and for the overlap of IM waves, add the power of IM waves overlapping in the same slot bandwidth unit to the IM waves in the repeater band By doing so, the level distribution of the added IM wave over the entire repeater bandwidth in the carrier arrangement can be obtained in units of the slot bandwidth. It is obtained by way. Further, for each carrier, the level of the added IM wave of each slot belonging to its own carrier bandwidth is further added to obtain an interference level due to the IM wave of each carrier. An addition level of the IM wave is obtained, and a C / IM value that is a power ratio with the carrier can be obtained. The present invention accurately determines the C / IM value for each carrier with respect to a certain carrier arrangement within the repeater bandwidth, thereby determining the most suitable empty slot to be inserted when arranging a new carrier. By applying the “Deletion-Insertion Method” in the case of multi-carrier by extracting the carrier that has the worst C / IM value by comparing each C / IM value obtained for all carriers by calculation. , Which enables optimal relocation.

By applying the algorithm of the present invention, it is possible to calculate a distributed IM level having a spread in frequency as a power density distribution of IM in units of slot width with reference to the frequency slot width. By adding the IM levels of the slots belonging to the bandwidth of and calculating the ratio with the carrier level, the C / IM value for each carrier can be accurately calculated, thereby accurately evaluating the interference I can do it.
In addition, with the placement or rearrangement algorithm based on the C / IM value thus obtained, the rearrangement that maximizes the worst (minimum) C / IM value can be performed in the entire repeater. Compared to the above, the number of carriers that can actually be arranged in one repeater, that is, the total bandwidth can be greatly increased, and the efficiency of the use bandwidth of the repeater can be improved.

It is a figure which shows the structural example of a satellite repeater. It is a figure showing the frequency relationship and electric power relationship with the IM wave which generate | occur | produces with a 2 wave carrier. It is a figure showing the frequency relationship and electric power relationship with the IM wave which generate | occur | produces with a 3 wave carrier. It is a figure which shows the effect of "Deletion-Insertion Method" in the case of the SCPC system shown by the prior literature. It is an operation | movement flowchart of the IM level calculation method and carrier rearrangement method based on the Example of this invention. It is a figure which shows the relationship between the input / output characteristic of a repeater, an equal level 2 wave IM characteristic, and the value of D. It is a figure which shows how IM by 2 carriers is actually distributed. An example of an actual carrier arrangement example in a satellite repeater calculated by software applying the IM level calculation method and the rearrangement algorithm according to the present invention, and showing the minimum C / IM value every time the rearrangement is repeated It is the graph which plotted the C / IM value of.

The carrier rearrangement method according to one aspect of the present invention calculates the C / IM values of all the remaining carriers when the carrier is sequentially removed from the initial carrier arrangement as a removed carrier one wave at a time. For the removed carrier, the minimum C / IM value of all the remaining carriers is obtained, and the removed carrier having the largest minimum C / IM value when the removed carrier is sequentially changed is extracted. Next, when the removed carrier is sequentially inserted into an empty slot, the C / IM values of all carriers are calculated in the same manner, and the removed carrier is inserted into an empty slot where the minimum C / IM value is maximized. Is a new arrangement. Then, by returning to the removal sequence again and repeating the operation, the bandwidth and power that have not been achieved so far can be obtained by a method of obtaining an optimal arrangement that maximizes the C / IM value of the carrier that exhibits the minimum C / IM value. The optimal arrangement is possible when different carriers are included. Hereinafter, a specific calculation procedure will be described. Although it is also called “Deletion-Insertion Method”, the method described above counts the number of IM waves that overlap the same frequency, and this algorithm minimizes the number of overlaps. The method calculates the power density and distribution of each IM wave and sums the power of all IM waves distributed within the band of each carrier to accurately determine the C / IM value within the band of the corresponding carrier. It can be said that the algorithm is different in purpose and method in that it is an algorithm for obtaining an arrangement in which the minimum value (worst value) of C / IM values is maximized.
In addition, when a new carrier is arranged when operating with a certain carrier arrangement, the new carrier is inserted into an available slot, and the IM wave level distribution and each carrier in each case are inserted. The C / IM value is calculated in the same manner, and the optimum placement is obtained by obtaining the insertion slot when the C / IM value of the carrier showing the minimum C / IM value is the maximum.

Hereinafter, a specific calculation method will be described with reference to the operation flow diagram of FIG. The IM wave, which is a problem caused by the intermodulation product of two or three wave carriers, is generated between the two wave carriers when the original carrier frequencies are f ₁ , f ₂ , and f ₃ as described above ( 2 × f ₁ -f ₂ ) and (2 × f ₂ -f ₁ ), and (f ₁ + f ₂ -f ₃ ), (f ₂ + These are two types of IM waves generated at three frequencies, f ₃ -f ₁ ) and (f ₃ + f ₁ -f ₂ ). To be precise, this IM wave is expressed as f _l −f when the lower limit frequency of the repeater frequency bandwidth is f _l , the upper limit frequency is f _h , and the repeater bandwidth is f _bw (= f _h −f _l ). It occurs in the frequency band between _{bw and} f _h + f _bw . Therefore, it is only necessary to consider the IM wave generated in the repeater frequency band among all the combinations of 2 waves and 3 waves of all carriers, but the center frequency of the IM wave is generated outside the repeater frequency band. Even in this case, since the base of the power density distribution may extend within the repeater band, the IM wave generated outside the repeater bandwidth actually needs to be included in the calculation.

As a procedure, first, the frequency band of the repeater is divided into slots having the minimum carrier frequency band or the bandwidth of the assigned minimum frequency step, and numbers are assigned from the end of the repeater frequency band. The frequency and bandwidth of each carrier are defined by representing the slot number corresponding to the center frequency and the number of slots corresponding to the bandwidth. Next, a combination of 2 waves and 3 waves is sequentially extracted from the end, and the center slot number where the IM wave is generated in each case is obtained. The center slot of this IM wave is calculated by replacing the frequency (f _{1 to} f _n ) with the slot number in the formula for the generated IM wave frequency. Next, for each slot in the band in which each IM wave is distributed, the level (power) for each slot is calculated by the method described later. Specifically, as a table calculation using a matrix, when rows of frequency slots are arranged on the horizontal axis, one row is a combination of two or three carrier waves, and the distribution of IM waves generated by that combination Is obtained as the column level of the corresponding slot in the row (step S101). The number of combinations of 2 waves and 3 waves can be calculated by nC ₂ + nC ₃ when the number of carriers is n. For example, if n is 100, the number of combinations is 980,100. Therefore, it is necessary to perform a table calculation of the number of rows of the number of combinations and the number of columns of the required number of slots. After calculating the IM wave level for each column (each slot) for all rows (combinations), all rows are added for each column to obtain the total IM wave level for each slot (step S102). The distribution becomes the level distribution of IM waves in the entire repeater band. When performing calculations in this way, when a certain carrier is deleted or inserted, only the affected rows are recalculated, and then the addition is performed for each column. Thus, it is possible to recalculate the level distribution of the entire IM wave.
This calculation is also achieved by a method in which the cumulative value is obtained for each slot by sequentially adding the level of each slot each time the level of each slot of the IM wave of each combination is calculated without performing a table calculation. it can.

The power (level) of individual IM waves by the combination of 2 waves or 3 waves is calculated by the following method according to the present invention. First, the IM characteristics of the transmitter of the satellite repeater are equal levels corresponding to the input level on the horizontal axis when the input / output characteristics of the transmitter are expressed in dB linear graphs with the horizontal axis and the vertical axis in dBW. When two-wave carriers are input, the output level of the _two IM waves (2f ₁ -f ₂ and 2f ₂ -f ₁ ) generated outside both carriers separated by the frequency interval of the two-wave carriers is expressed as the input level. Is plotted as the IM wave level corresponding to. In this case, for small signals, the IM level depends mainly on the third-order distortion of the input / output characteristics of the transmitter, so it is basically proportional to the cube of the input level. The characteristics of FIG. 6 shows the input / output characteristics and IM level characteristics of the transmitter (such data is usually provided by the manufacturer as basic characteristics of the transmitter). Next, a straight line obtained by extending the IM level characteristic in this small signal with a gradient 3 (representing a characteristic in which the IM wave level at the time of the small input signal level is proportional to the cube of the input signal level), on the other hand, An intersection with the straight line of slope 1 (which represents the ideal input / output characteristics assuming that the input / output characteristics at the time of a small input signal level where the output level is not saturated continues until the time of a large input signal) The difference between the output level at the third IM intersection in FIG. 6 and the saturation output level of the transmitter at the input signal level at that time is defined as D (dB). Then, if the difference between the transmitter output level and the transmitter saturation output level of each carrier of equal level 2 waves in a small signal is B (dB), the geometrical calculation based on this graph shows that any equal level 2 The level ratio IMR (dB) between the level per wave and the equal level two IM waves for the same level is obtained as 2 (B + D). Next, for IMR when the levels of the two-wave carriers are different, when the center frequency of the two waves is f ₁ and f ₂ , and the value of B corresponding to each level is B ₁ and B ₂ , the frequency 2f IMR for B1 occurring at ₁ -f ₂ ; IMR ₁₂ is expressed as 2 (B ₁ + D) − (B ₁ −B ₂ ) = B ₁ + B ₂ + 2D and occurs at frequency 2f ₂ -f ₁ IMR for B2; IMR ₂₁ is represented by 2 (B ₂ + D) − (B ₂ −B ₁ ) = B ₁ + B ₂ + 2D. (This means that if one carrier level fluctuates from the equi-level two-wave IM, for example, if the f ₁ level fluctuates, the 2f ₁ -f ₂ level fluctuates by twice the fluctuation value (dB), and 2f ₂ The level of -f ₁ fluctuates at the same level as the fluctuation value (dB)). However, these values are relative values to B ₁ and B ₂ , respectively. Therefore, for direct comparison, each IM level is expressed as a relative value with respect to the saturation output level P _os (dBW) of the transmitter.
IMR ₁₂ = P _os −B ₁ − (B ₁ + B ₂ + 2D) = P _os −2B ₁ −B ₂ −2D
IMR ₂₁ = P _os −B ₂ − (B ₁ + B ₂ + 2D) = P _os −2B ₂ −B ₁ −2D

Therefore, let the saturation output power of the transmitter of the satellite repeater be P _os (dBW) (= 10log (p _os (W))), and the output level of each carrier is the power at the output of the satellite repeater of that carrier. _Is defined as the relative power ratio (minus dB value) to Pos. That is, when p _os is the _exact value (W) of P _os and p _i is the power (true value: W) at the repeater output of the carrier in slot i, the relative level P _{i of the} carrier is P _i (dB) = It is defined as 10log (p _i / p _os ). And further slot j, each P _j the relative level of the carrier of k, when the P _k, I the relative levels of IM wave by two waves generated by P _i and P _j in slot (2i-j) in dB _ij and the relative level of the IM wave generated in the slot (2j−i) is the same I _ji, and each of the slots (i + j− _k ), (k + i−j), ( _k ) by three waves P _i , P _j , and P _k When the relative level of the IM wave generated around j + k−i) is the same relative value to P _{os in} terms of dB and I _ijk , I _kij , I _jki , D is used and I _ij = 2Pi + Pj−2D, I _{ji = 2P j + P i -2D} , both the _{I ijk = I kij = I jki} = P i + P j + P k -2D + 6 obtained as a relative value with respect to P _os. When I _ij is expressed by the true value i _ij of the power (absolute value) of the IM wave, the relationship is I _ij = 10 log (p _os / i _ij ). The same applies to other IM levels. Advantage by this way represents the uniquely in addition the level of each IM wave can be calculated in such a simple formula, as a relative value for all levels both P _os of the carrier level and the IM wave When calculating the addition value due to the overlap of IM waves, etc., the relative value for each P _os is converted to a true number and added, and then converted again to 10 times the common logarithm, the added value is again P It can be expressed as a relative value (dB value) to _os, which simplifies the calculation as a whole and speeds up the calculation speed in repetitive calculations.
The value obtained here is the total level of individual IM waves generated in each combination corresponding to the level of each carrier. This relationship is shown in FIGS. 2 and 3 show the original carrier with originally spread frequency and the generated IM wave as a line spectrum with the power concentrated on the center frequency, and the relationship between each frequency (= slot number) and level It represents a relationship. FIG. 2 shows a case of two IM waves, and FIG. 3 shows a case of three IM waves.

Next, the distribution (frequency spread) of each IM wave is obtained by the following method. Today, digital carriers used in satellite communications mainly use PSK (phase shift keying) and APSK (amplitude phase modulation) as modulation schemes, and roll-off filters for waveform shaping. This filter uses the root cosine roll-off characteristic with the symbol frequency width as the equivalent noise band, and it is difficult to say that it is a normal distribution, but it is known that the IM wave generated in the carriers of the roll-off characteristics can be regarded as a normal distribution. . Therefore, if the carrier power density distribution is defined by the standard deviation of the equivalent normal distribution, for example, the standard deviation of the equivalent normal distribution of the power density distribution of each carrier of p _i , p _j , p _k is expressed as σ _i , σ _j , Σ _k , the IM waves are normally distributed, and their standard deviation is the square root of the sum of the standard deviation of the carrier or the square of twice that in the case of the IM wave with two waves, respectively.


In the case of three IM waves, the square root of the sum of squares of each carrier standard deviation


Can be calculated.
Therefore, the power distribution of each IM wave has a total level of i _ij , i _ijk, etc. and a standard deviation of each


The level of each slot is calculated by using an error function as a cumulative distribution function corresponding to the normal distribution as the power density normalized by the slot width. This state is shown in FIG. 7 in the case of two-wave IM.
In addition, the standard deviation of the equivalent normal distribution of the carrier of the roll-off characteristic is assumed that the power of the spectrum of the cosine roll-off spectrum and the spectrum of the normal distribution is equal when the roll-off rate and the symbol frequency are known, When the standard deviation normalized by the cosine roll-off carrier symbol rate is σ ₀ , it is calculated from the following equation.

In Equation 1


Is the complementary error function, and α is the roll-off rate of the cosine roll-off spectrum. For the carrier roll-off rate, it is preferable that the standard deviation of the spectrum distribution in the roll-off characteristics and the standard deviation when the carrier of the same band and the same level is a normal distribution is the standard deviation of the carrier spectrum distribution. In the present invention, since the frequency bandwidth is expressed by the number of slots divided by the slot bandwidth, a value obtained by multiplying the standard deviation normalized by the symbol rate obtained here by the symbol rate and further dividing by the slot bandwidth. Is the standard deviation expressed in slots.

  When the roll-off rate and symbol rate of the carrier are not known, the carrier bandwidth is usually based on the required bandwidth represented by the radio wave type in the Radio Law as the allocated band. Since the required bandwidth is generally determined to be about 1.1 to 1.2 times the normal occupied bandwidth (bandwidth including 99% energy), it can be obtained by back calculation. That is, the power value in the band of ± 2.6 times (2.6σ) of the standard deviation in the case of normal distribution is almost 99%, and if this is considered to correspond to the occupied bandwidth, the equivalent standard deviation is unambiguous. Will be determined. Specifically, the occupied bandwidth of the carrier is set to a value obtained by dividing the necessary bandwidth represented by the radio wave type in the Radio Law by a value between 1 and 1.2, and this occupied bandwidth is set to 5 to 6. A value obtained by dividing a range (range of ± 2.5 times to ± 3 times) by a predetermined constant is preferably used as the standard deviation of the carrier spectrum distribution. Once the standard deviation of each carrier is obtained, the standard deviation of the IM wave is obtained by the method described above.

The calculation of the level distributed in each slot of the IM wave will be specifically described below based on the standard deviation of the IM wave obtained as described above. The level of the IM wave with normal distribution is


The frequency


Is the center of the distribution and the standard deviation is

The spectrum of the power density distribution of the IM wave with respect to the reference level P _os (p _os (W)) is expressed by the following equation using a probability density function (PDF).


Here, ρ _i represents the standard deviation for the IM wave (here, σ represents the standard deviation for the distribution of the carrier itself, and ρ represents the standard deviation for the distribution of the IM wave).
The integrated value for each slot of this probability density function becomes the IM wave level divided into each slot, and is calculated by the following equation.


here,


Is the corresponding slot number. Perform a variable transformation on this equation to obtain the complementary error function


Is represented by the following formula.


Using this formula


Can be calculated for each slot of the IM wave with the center of distribution. Here for convenience


In practice, the calculation can be performed using the slot number corresponding to the frequency. Strictly speaking, the spectrum of IM waves


Is distributed over the range of ± ∞, but the total amount of distribution in the frequency region more than ± 3ρ away from the center is 0.27% (≈−26dB) or less of the total. Therefore, in order to reduce the amount of calculation, there is no problem even if the calculation is performed while ignoring the level of the slot 3ρ or more away from the center.
Calculated here


The value of is a relative integral value per slot with the accumulated total integral value being 1. Therefore, the total level of the individual IM wave described above (the relative value with respect to the saturated output power of the transmitter of the satellite repeater) ) Is multiplied by the true value to obtain the level of the slot as a relative value to the saturation output power of the transmitter of the satellite repeater.

As described above, the level distribution of the IM wave can be obtained for each slot for each of the 2 and 3 individual IM waves for each combination of the 2 waves and 3 waves of the carrier. Then, if the IM wave level in the same slot is sequentially added and accumulated for each IM wave for every combination of 2 waves and 3 waves of all carriers, the total IM wave level of each slot can be obtained, The IM wave level distribution of the entire repeater is obtained. The power addition here is basically a relative value based on the saturation output level of the satellite repeater as a reference (with a true value of 1), but the addition converts the decibel value that is the relative value into a true number. By adding the true number, the addition level for each slot can be obtained. According to the present invention, the level P _{i of} each carrier is expressed as a relative value that is a ratio to the saturation power of the satellite repeater, and the total level I _{ij of the} IM wave is also displayed as a relative value with respect to the saturation power of the satellite repeater. The advantage is that each dB value is converted to a true number as it is, added, then converted to a dB value again, and the relative value of the added value can be obtained in dB, simplifying the calculation. It is in. Thus, with respect to the cumulative value of each slot (true number), expressed in dB after adding the addition value of the slot belonging to each carrier further subtracted from the level of the carrier (e.g. P _i dB), the level of the carrier, The ratio of the added value of the IM level and the C / IM value (dB) are obtained (step S103). The C / IM value of each carrier obtained in this way is the total power within the allocated band for the carrier level, and for the IM level, each IM wave distributed is in slot units and is assigned to each slot. The power level is obtained by decomposition, the power levels of all IM waves belonging to each slot are obtained as a cumulative value, and the power levels of all slots belonging to the assigned band of the carrier are added. It is an accurate C / IM value based on the distribution including the overlap of. In this way, the degree of interference can be evaluated by accurately obtaining the C / IM value in the current carrier arrangement.
When the C / IM value is calculated for all carriers, the carrier showing the minimum C / IM value in the arrangement and the C / IM value can be easily identified.

Now that the C / IM values of each carrier in a fixed arrangement have been accurately determined, the procedure for optimizing the carrier arrangement will be described next.
The rearrangement and optimization method is basically a method similar to the aforementioned “Deletion-Insertion Method”, using the C / IM value for each carrier that can be obtained by the above method. is there. That is, in the initial arrangement, the C / IM value for each carrier is calculated, the carrier showing the worst C / IM value and its C / IM value are obtained, and then each carrier is removed one by one in order from the end, The C / IM value of each carrier in the removed state is calculated. Then, a carrier having an arrangement in which the C / IM value of the carrier having the minimum (worst) C / IM value in each arrangement is maximized is selected and set as a removal carrier (minimum C / IM value maximized removal carrier) ( Step S151). Next, the removed carriers are sequentially inserted into empty slots into which the bandwidths assigned to the removed carriers can be inserted without the frequency of other carriers being assigned, and the C / IM of all carriers is also set for each arrangement. Value is calculated, the insertion slot (minimum C / IM value maximization insertion slot) in which the C / IM value indicating the minimum value (minimum C / IM value after insertion) is maximized is selected, and this is used as the insertion slot for the first time. (Step S152). It is determined whether or not the interference evaluated by the C / IM value is within the allowable range. If the interference is not within the allowable range, the process returns to step S151 and the same process is repeated again. If the interference is within the allowable range, the calculation ends (step S153). . Usually, it is determined that the removal carrier and the insertion slot have been optimized, and interference is within an allowable range. As described above, when the removed carrier and the insertion slot coincide with each other, the optimum rearrangement in the initial arrangement is performed. In addition, considering the case where the number of iterations increases and does not converge easily, a method in which the final arrangement is performed when the minimum C / IM value becomes a predetermined value set, or a fixed number of iterations set Methods of convergence and combinations of these are also possible.

  Further, as another form of relocation according to the present invention, when a certain number of carriers are operated in an arrangement, when adding a certain carrier, new carriers are sequentially inserted into empty slots, It is also possible to calculate the C / IM values of all the carriers in each arrangement, find the arrangement where the minimum C / IM value is maximized, and set the arrangement as the arrangement of additional carriers.

  FIG. 8 is a graph showing how the IM calculation method and the reallocation algorithm are actually realized as computer software and applied to an actual carrier arrangement example to improve the C / IM value. Thus, it was confirmed that the C / IM value of the carrier can be improved by repeating the rearrangement by the algorithm of the present invention.

  The IM level, C / IM value calculation method and carrier relocation method according to the above-described embodiment are the same for each earth station where a satellite operator or a satellite communication network operator shares one satellite repeater in the satellite network. It can be implemented as software for use as a tool for determining the allocation of carrier bandwidth and frequency to each. It is also possible to incorporate software for executing a C / IM value calculation method and a carrier relocation method as a module in a required line assignment (DAMA) device and use it for automatic line assignment.

  The present invention can be realized as software and specifically used for optimization by IM interference level calculation and rearrangement. Thus, the present invention can be effectively used for network control in the satellite communication field.

100 Satellite repeater 101 Low noise reception frequency converter (LNA-Receiver)
102 I-MUX / BPF (input distributor filter)
103 Transmitter (TWTA)
104 O-MUX (output combiner / distributor)

Claims (14)

When relaying a plurality of modulated carriers by a frequency division multiple access method in a satellite repeater equipped in the communication satellite in a satellite communication system that performs communication between a plurality of earth stations via a communication satellite A method for obtaining a level of an IM wave that is an interference wave generated by intermodulation between carriers,
The center frequency of any three of the plurality of carriers is set to f _i , f _j , f _k, and the saturation output power of the transmitter of the satellite repeater is P _os (dBW) (= 10 log (p _os (W ))), And the output power of each carrier at the transmitter of the satellite repeater is p _i (W), p _j (W), p _k (W), respectively, the relative output level of each carrier is P _i (dB), P _j (dB), and P _k (dB) are P _i (= 10 log (p _i / p _os ) dB), P _j (= 10 log (p _j / p _os ) dB), P _{k, respectively.} (= 10 log (p _k / p _os ) dB), and generated at each center frequency (2f _i −f _j ) and center frequency (2f _j −f _i ) by two-wave carriers of center frequencies f _i and f _j. The relative levels of the IM waves are I _ij and I _ji , respectively, and the center frequencies f _i , f _j , f _{It is} expressed in dB values generated at each center frequency (f _i + f _j −f _k ), center frequency (f _k + f _i −f _j ), and center frequency (f _j + f _k −f _i ) by three carriers of _k. When the IM wave levels are I _ijk , I _kij , and I _jki , the output level is not saturated in the input signal level-output signal level characteristics (input / output characteristics) of the transmitter of the satellite repeater. In the ideal input / output characteristics assuming that the input / output characteristics at the time of the small input signal level continue until the time of the large input signal, the input signal level vs. the IM wave level characteristic by the two-wave carrier having the same input level is the IM at the time of the small input signal level. The ideal input at the input signal level when the output signal level of the ideal input / output characteristic is equal to the IM wave level, assuming that the wave level is proportional to the cube of the input signal level. The difference between the output signal level of the output characteristic and the saturation signal output level of the actual transmitter of the satellite repeater is D (dB), and the relative level of the IM wave is I _ij = 2P _i + P _j −2D, I _ji = 2P _J + P _i −2D, I _ijk = I _kij = I _jki = P _i + P _j + P _k −2D + 6 is obtained for all combinations of 2 waves and 3 waves of all carriers in the repeater. To obtain all IM wave levels,
The distribution of the level of each IM wave is divided by a predetermined bandwidth equal to or less than the minimum allocated bandwidth for each carrier to divide the frequency band of the repeater into one slot width, and the slot numbers in order from the end of the repeater band And obtaining the total value for each slot of the IM wave level when the slot is assigned, the method for obtaining the IM wave level distribution of the entire repeater. The step of obtaining a total value for each slot of the IM wave level includes:
The slot number of the slot to which the center frequency of each carrier belongs is the number of that carrier, the carrier has an intensity having a certain spectral distribution, and the standard deviation represented by the frequency of the spectral distribution of the carrier is the slot number. When the value divided by the bandwidth is the standard deviation expressed by the number of slots, and the standard deviation expressed by the number of slots of the carrier corresponding to the slot numbers j, k, and l is σ _j , σ _k , and σ _l , respectively. The standard deviation represented by the number of slots of each IM wave generated by the two-wave carriers of slot numbers i and j and having slot numbers (2j−k) and (2k−j) as the center of the band is represented by ρ _jk , ρ _{When kj}


Generated by three-wave carriers of slot numbers j, k, and l, and the number of slots of each IM wave of three waves centering on slot numbers (j + k−l), (j−k + l) and (−j + k + l) Expressed standard deviation


Where f _i is the slot number of an IM wave with slot number i as the central slot, and ρ _i is the standard deviation expressed by the number of slots of the IM wave, the power density distribution of the IM wave is a probability density function


And the slot number


The integrated value of the level of the IM wave within the slot width of


Is calculated by using a complementary error function as a cumulative distribution function corresponding to the power density distribution, and the relative level of the corresponding IM wave obtained in the step of obtaining all the IM wave levels is expressed as an exact value. Is obtained as a relative value with respect to the saturation level of the transmitter of the satellite repeater of the corresponding slot by multiplying the obtained value, and all combinations of 2 waves and 3 waves of all carriers in the repeater are obtained. The method of claim 1, wherein the method is performed for each IM wave.   The step of obtaining the total value of each level of the IM wave level for each slot converts each of the IM wave levels expressed by a dB value into a true value and sums it for each slot, and then converts it to a dB value. The method of claim 1. Based on the obtained total value of the IM wave level for each slot, the sum of the total values of the IM levels of the slots belonging to the band assigned to each carrier is obtained, and the corresponding carrier Obtaining the C / IM value for each carrier by dividing the output level of
3. The method of claim 2, further comprising: arranging each frequency of the plurality of carriers so that the IM wave level falls within an allowable range based on the obtained C / IM value for each carrier. Method.   In the step of arranging the frequencies of the plurality of carriers, the occupied bandwidth of the carrier is a value obtained by dividing a required bandwidth represented by a radio wave type by a numerical value between 1 and 1.2 in the Radio Law. The method according to claim 4, wherein a value obtained by dividing the occupied bandwidth by a predetermined constant in the range of 5 to 6 is set as the standard deviation of the spectrum distribution of the carrier.   In the step of arranging each frequency of the plurality of carriers, with respect to the roll-off rate of the carrier, the spectrum distribution in the roll-off characteristics and the standard deviation when the carriers of the same band and the same level are normal distribution are The method according to claim 4, wherein the standard deviation of the spectral distribution of the carrier is used. Arranging the frequency of each of the plurality of carriers,
A C / IM value calculation step for each carrier in an initial carrier arrangement for obtaining the C / IM value for each carrier;
When any one of the plurality of carriers is removed as a removal carrier, the one showing the minimum C / IM value is specified as the minimum C / IM value, and the removal carrier is selected from among the plurality of carriers. A minimum C / IM value maximization removal carrier identification step for identifying the removal carrier that maximizes the minimum C / IM value as a minimum C / IM value maximization removal carrier by sequentially selecting;
The specified minimum C / IM value maximized removed carrier is either one slot or a continuous slot into which the frequency assigned to the removed carrier can be inserted without the frequency of another carrier being assigned. By specifying the minimum C / IM value indicating the minimum C / IM value after insertion and sequentially selecting the one slot or continuous slot to which the bandwidth can be allocated A minimum C / IM value maximizing insertion slot specifying step for specifying one slot or a continuous slot having the maximum after insertion as a minimum C / IM value maximizing insertion slot;
5. The method of claim 4, comprising repeating the minimum C / IM value maximization removal carrier identification step and the minimum C / IM value maximization insertion slot identification step until the interference is within an acceptable range.   The repetition of the minimum C / IM value maximization removal carrier identification step and the minimum C / IM value maximization insertion slot identification step in the step of arranging the respective frequencies of the plurality of carriers includes the slot number of the removal carrier. And the minimum C / IM value maximizing insertion slot is executed until the slot numbers are equal.   The repetition of the minimum C / IM value maximization removal carrier identification step and the minimum C / IM value maximization insertion slot identification step in the step of arranging the respective frequencies of the plurality of carriers is performed a predetermined number of times. The method according to claim 7.   The repetition of the minimum C / IM value maximization removal carrier identification step and the minimum C / IM value maximization insertion slot identification step in the step of allocating the respective frequencies of the plurality of carriers is the minimum C / IM after insertion. The method of claim 7, wherein the method is performed until the value is greater than or equal to a predetermined value.   8. The method according to claim 7, wherein in the multi-carrier FDMA communication system based on the demand assignment system that allocates a new carrier each time a request for a new carrier allocation occurs, a carrier that has been newly requested for allocation is the removed carrier. The minimum C / IM value maximizing insertion slot is identified and placed there. When relaying a plurality of modulated carriers by a frequency division multiple access method in a satellite repeater equipped in the communication satellite in a satellite communication system that performs communication between a plurality of earth stations via a communication satellite A program for causing a computer to execute a method of arranging to reduce interference generated by intermodulation between carriers, the method comprising:
The center frequency of any three of the plurality of carriers is set to f _i , f _j , f _k, and the saturation output power of the transmitter of the satellite repeater is P _os (dBW) (= 10 log (p _os (W ))), And the output power of each carrier at the transmitter of the satellite repeater is p _i (W), p _j (W), p _k (W), respectively, the relative output level of each carrier is P _i (dB), P _j (dB), and P _k (dB) are P _i (= 10 log (p _i / p _os ) dB), P _j (= 10 log (p _j / p _os ) dB), P _{k, respectively.} (= 10 log (p _k / p _os ) dB), and generated at each center frequency (2f _i −f _j ) and center frequency (2f _j −f _i ) by two-wave carriers of center frequencies f _i and f _j. The relative levels of the IM waves are I _ij and I _ji , respectively, and the center frequencies f _i , f _j , f _{It is} expressed in dB values generated at each center frequency (f _i + f _j −f _k ), center frequency (f _k + f _i −f _j ), and center frequency (f _j + f _k −f _i ) by three carriers of _k. When the IM wave levels are I _ijk , I _kij , and I _jki , the output level is not saturated in the input signal level-output signal level characteristics (input / output characteristics) of the transmitter of the satellite repeater. In the ideal input / output characteristics assuming that the input / output characteristics at the time of the small input signal level continue until the time of the large input signal, the input signal level vs. the IM wave level characteristic by the two-wave carrier having the same input level is the IM at the time of the small input signal level. The ideal input at the input signal level when the output signal level of the ideal input / output characteristic is equal to the IM wave level, assuming that the wave level is proportional to the cube of the input signal level. The difference between the output signal level of the output characteristic and the saturation signal output level of the actual transmitter of the satellite repeater is D (dB), and the relative level of the IM wave is I _ij = 2P _i + P _j −2D, I _ji = 2P _J + P _i −2D, I _ijk = I _kij = I _jki = P _i + P _j + P _k −2D + 6 is obtained for all combinations of 2 waves and 3 waves of all carriers in the repeater. To obtain all IM wave levels,
The distribution of the level of each IM wave is divided by a predetermined bandwidth equal to or less than the minimum allocated bandwidth for each carrier to divide the frequency band of the repeater into one slot width, and the slot numbers in order from the end of the repeater band And calculating the total value for each slot of the IM wave level,
Based on the obtained total value of the IM wave level for each slot, the sum of the total values of the IM levels of the slots belonging to the band assigned to each carrier is obtained, and the corresponding carrier Obtaining the C / IM value for each carrier by dividing the output level of
And arranging each frequency of the plurality of carriers so that the IM wave level falls within an allowable range based on the obtained C / IM value for each carrier. The step of obtaining a total value for each slot of the IM wave level includes:
The slot number of the slot to which the center frequency of each carrier belongs is the number of that carrier, the carrier has an intensity having a certain spectral distribution, and the standard deviation represented by the frequency of the spectral distribution of the carrier is the slot number. When the value divided by the bandwidth is the standard deviation expressed by the number of slots, and the standard deviation expressed by the number of slots of the carrier corresponding to the slot numbers j, k, and l is σ _j , σ _k , and σ _l , respectively. The standard deviation represented by the number of slots of each IM wave generated by the two-wave carriers of slot numbers i and j and having slot numbers (2j−k) and (2k−j) as the center of the band is represented by ρ _jk , ρ _{When kj}


Generated by three-wave carriers of slot numbers j, k, and l, and the number of slots of each IM wave of three waves centering on slot numbers (j + k−l), (j−k + l) and (−j + k + l) Expressed standard deviation


Where f _i is the slot number of an IM wave with slot number i as the central slot, and ρ _i is the standard deviation expressed by the number of slots of the IM wave, the power density distribution of the IM wave is a probability density function


And the slot number


The integrated value of the level of the IM wave within the slot width of


Is calculated by using a complementary error function as a cumulative distribution function corresponding to the power density distribution, and the relative level of the corresponding IM wave obtained in the step of obtaining all the IM wave levels is expressed as an exact value. Is obtained as a relative value with respect to the saturation level of the transmitter of the satellite repeater of the corresponding slot by multiplying the obtained value, and all combinations of 2 waves and 3 waves of all carriers in the repeater are obtained. The program according to claim 12, which is executed for each IM wave. Arranging the frequency of each of the plurality of carriers,
A C / IM value calculation step for each carrier in an initial carrier arrangement for obtaining the C / IM value for each carrier;
When any one of the plurality of carriers is removed as a removal carrier, the one showing the minimum C / IM value is specified as the minimum C / IM value, and the removal carrier is selected from among the plurality of carriers. A minimum C / IM value maximization removal carrier identification step for identifying the removal carrier that maximizes the minimum C / IM value as a minimum C / IM value maximization removal carrier by sequentially selecting;
The specified minimum C / IM value maximized removed carrier is either one slot or a continuous slot into which the frequency assigned to the removed carrier can be inserted without the frequency of another carrier being assigned. By specifying the minimum C / IM value indicating the minimum C / IM value after insertion and sequentially selecting the one slot or continuous slot to which the bandwidth can be allocated A minimum C / IM value maximizing insertion slot specifying step for specifying one slot or a continuous slot having the maximum after insertion as a minimum C / IM value maximizing insertion slot;
The program according to claim 12, comprising: repeating the minimum C / IM value maximization removal carrier identification step and the minimum C / IM value maximization insertion slot identification step until the interference is within an allowable range.