JPH09261082A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the utilizing efficiency of frequencies of the entire communication system as a whole and to increase the channel capacity by adopting a multi-stage filter to a transmission output section of a communication equipment to evaluate and check relation between an excellent filter no load Q and a side band component, thereby suppressing the effect on close frequency bands. SOLUTION: A transmission circuit 12a conducts coding processing and frequency conversion processing or the like of a known digital signal, a power amplifier 12b applies amplification processing to a signal outputted from the transmission circuit 12a to amplify transmission power, and a superconducting filter 12c applies transmission band limit processing to attenuate a side band component caused in the process of power amplification other than the occupied band of the transmission signal; and ad the resulting signal is sent via an antenna wire 11. A multi-sitage filter having a high no load Q and a low insertion loss is adopted for the superconducting filter 12c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system, and more particularly to a communication system in which a transmission output section of a wireless communication device is provided with a filter having a sharp cutoff characteristic to reduce sideband components and improve line capacity. Regarding

[0002]

2. Description of the Related Art A configuration of a transmitting / receiving unit in a conventional wireless communication device (hereinafter referred to as a communication device) will be described below with reference to FIG. In FIG. 6, the signal sent from the transmission circuit 12a is amplified in transmission power by the power amplifier 12b, and then limited by the transmission filter 12c ′ so that only the signal in the predetermined transmission frequency band passes through. It is sent as a transmission signal. The signal received by the antenna line 11 is limited by the reception filter 13c so that only the signal in the predetermined reception frequency band passes, and is input to the reception circuit 13a via the low noise amplifier 13b. As described above, generally, in the antenna input / output stage of the communication device, the transmission filter 12c 'for separating the transmission / reception signal
The duplexer 14 having the function of the reception filter 13c is arranged to limit the input / output of signals other than the desired frequency band.

Next, signal processing in a transmission output section of a conventional communication device will be described with reference to FIGS. 7 and 8. FIG. 7 is a block diagram showing the configuration of the transmission output unit of the communication device, and FIGS. 8A and 8B are diagrams showing signal processing in the transmission output unit. In FIG. 7, the signal A sent from the transmission circuit 12a has a predetermined frequency bandwidth with respect to a predetermined center frequency f, as shown in FIG. Here, the center frequency f, for example, 2000 MHz
, The bandwidth is about ± 5 MHz, that is, about 10 MHz. This signal A has its transmission power amplified by the power amplifier 12b and is sent out as a signal B to the transmission filter 12c '. When amplifying this power,
With respect to the bandwidth W of the signal wave (desired wave) to be used, the signal B has so-called sideband third-order distortion (having a frequency spread three times the bandwidth W) and fifth-order distortion (generally of W An odd-order distortion represented by 5 times) occurs. Among the sidebands of the odd-order distortion, the sideband of the third-order distortion shown in FIG. 8B has a particularly high output level (transmission power), so that another communication device that uses an adjacent frequency band, or There is a problem that distortion is mixed in the frequency band between adjacent lines in one communication device, causing adjacent interference.

FIG. 9 is a conceptual diagram showing a frequency occupation (utilization) state of a communication device having a plurality of lines with a predetermined transmission / reception frequency as a set. In FIG. 9, the transmission frequency band f
_A line is configured with ₁ and the reception frequency band f ₃ as one set,
Further, the transmission frequency band f ₂ and the reception frequency band f ₄ are paired to form a line (f _{1 to} f ₄ : solid line part). Here, it is assumed that the lines and are set close to each other, the sideband components accompanying the transmission frequency bands f ₁ and f ₂ are transmitted from the own device, and the reception frequency band f
The sideband components of ₃ and f ₄ shall be transmitted from another device (sideband component: dotted line part).

In such a configuration, the conventional transmission filter 12c 'limits the signal in the transmission frequency band and sends out the signal C to the antenna line 11, and the reception frequency band f of its own unit.
_This is to prevent the interference given to ₃ and f ₄ , and the processing for reducing the level of the side band component spread in the band (unused band) between the lines has not been performed. However, focusing on the adjacent lines and when the unused band between the lines is set narrow, the transmission signal (f ₂ ) of the line
The sideband component associated with is the reception frequency band f _{3 of the line.}
The phenomenon of overlapping and disturbing occurs. Such a problem is not limited to adjacent lines within the same communication device, but has similar problems not only between adjacent base stations but also between adjacent base stations.

In order to prevent such a problem, for example, between base stations, the frequency of the signal wave to be used later is shifted from the frequency band used in advance, or the signal wave to be used later is accompanied. A method of installing base stations at a distance that the output of the sideband component is sufficiently attenuated, and in the case of a communication device with multiple lines, the unused band is reduced as the level of the sideband component output from one line is sufficiently reduced. A method or the like that is provided in advance and sets the frequency band of an adjacent line is adopted. Therefore, the frequency band occupied by transmission and reception and sideband components in one line is several times the actual transmission frequency bands f ₁ and f ₂ , which causes deterioration of frequency utilization efficiency and reduction of line capacity. . However, the background of such frequency occupancy is that the frequency band to be used does not cause communication trouble due to sideband components until there is a margin in the allocated frequency band until the recent rapid increase in mobile communication. Divide the band sufficiently (for example, provide an unused band 3 to 5 times the bandwidth of the signal wave from the adjacent frequency band to the desired frequency band)
This is because the system could be configured.

[0007]

In recent years, mobile phones, PH
Due to the rapid increase in demand for land mobile communication such as S (Personal Handyphone System) and car telephone, research on highly efficient mobile communication systems has been actively conducted. In particular, with the increase in the number of lines used and the number of telecommunications carriers entering the market, there has been a demand for an effective method of using the line capacity in the same frequency band. In order to realize a filter having such characteristics that the output level is maintained, the desired wave is satisfactorily passed, and the sideband component is satisfactorily cut off, the configuration of the transmission output unit increases, There was a problem that it became complicated and not suitable for practical use.

That is, according to the characteristics of a generally known transmission filter, with an ordinary filter having a low unloaded Q value, the insertion loss increases when the number of filter stages is increased in order to realize a sharp cutoff characteristic. Then, there was a problem that a good output level could not be maintained. In order to keep the insertion loss low even if the number of filter stages is increased, a filter having a high no-load Q value is desired. However, as a generally known no-load Q value of a filter in a high frequency range of MHz to GHz. Is about 100 (300 MHz) at LC resonance, about 1,000 (UHF, microwave) at transmission line resonance, and 5,000 (microwave: 30 at cavity resonance).
0 MHz to 300 GHz), and a filter having desired characteristics could not be realized.

As a technique capable of solving such a problem in the communication system, a filter circuit having a superconducting device with an improved unloaded Q value has been developed in recent years, and its application to the communication system is considered promising. As an example, "MWE'95 Mi
crowave Workshop Digest ", the unloaded Q value is almost 2
It is described that a filter of about 0,000 (10 GHz) can be obtained.

An object of the present invention is to construct a filter circuit having excellent sharp cut characteristics and insertion loss characteristics by using a superconducting device having a high no-load Q value and a low insertion loss, and to apply it to a transmitter of a communication device. By doing so, the emission of unnecessary radio waves other than the frequency band occupied by the desired wave is suppressed, and a good radio wave environment is realized. That is,
Applying to the transmission output section of a communication device to evaluate the relationship between a good filter unloaded Q value and sideband components (adjacent interference waves),
We will study the effects on adjacent frequency bands, improve the frequency utilization efficiency of the communication system as a whole, and increase the line capacity. The present invention is based on CDMA
(Code division multiple access) method, TDMA (t
ime division multiple access) method or FDMA
In many communication systems such as (frequency division multiple access) system, the influence of sideband components is suppressed,
It is possible to increase the number of lines.

[0011]

In order to achieve the above-mentioned object, the invention of claim 1 is a power amplification means for amplifying a signal having a desired frequency band to a desired transmission power, and other than the desired frequency band. In a communication system comprising: a passband limiting unit for limiting the passage of a signal having the desired frequency band; and a transmitting unit for transmitting a signal having the desired frequency band, the passband limiting unit passes the signal of the desired frequency band. At this time, while maintaining the amplified transmission power,
When amplifying the transmission power, it has a sharp cut characteristic for reducing the power of the sideband component generated outside the desired frequency band at the boundary portion of the desired frequency band.

According to a second aspect of the present invention, a second frequency band used for the received signal is set in the vicinity of the first frequency band used for the transmitted signal, the transmission signal is power-amplified, and the desired frequency is obtained. In a communication system that limits the passage of signals outside the frequency band of the first frequency band and transmits the power of the sideband component generated outside the first frequency band due to power amplification of the transmission signal. It is characterized in that the transmission output section after power amplification of the transmission signal is provided with pass band limiting means having a sharp cut characteristic for maintaining the power of the amplified transmission signal.

According to this structure, the pass band limiting means (filter) having the sharp cut characteristic reduces the output level of the side band component generated at the time of power amplification of the transmission signal, and at the same time reduces the frequency band of the transmission signal. Since the electric power can be favorably passed while maintaining the electric power, it is possible to suppress the emission of unnecessary radio waves other than the predetermined frequency band by making the transmission signal into an ideal rectangular shape.

Similarly, it is possible to suppress radio waves outside the transmission frequency band radiated from one line constituted by a set of the transmission frequency band and the reception frequency band.
It is possible to set other lines in close proximity to each other. The filter having the sharp cut characteristic and the insertion loss characteristic applied to the present invention can be configured by a multistage filter having a high unloaded Q value and a low insertion loss, and can be easily utilized by utilizing the characteristics of a superconducting device, for example. Can be realized. Here, a high unloaded Q value is approximately 10 as compared with 5,000 obtained by conventional cavity resonance.
Insertion loss more than double or low means almost 0 dB.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. 1 is a block diagram showing a first embodiment of a communication system according to claim 1 of the present invention. In FIG. 1, the communication system of the present embodiment is a communication device assuming wideband transmission such as a CDMA system, the transmission circuit 12a performs known digital signal encoding processing, frequency conversion processing, etc., and the power amplifier 12b The signal A output from the transmission circuit 12a is subjected to amplification processing to increase it to a desired transmission power, and then the superconducting filter 12c removes sideband components other than the occupied band of the transmission signal generated in the signal B in the process of power amplification. Attenuating transmission band limitation processing is performed, and the signal C is transmitted via the antenna line 11. here,
The power amplifier 12b corresponds to power amplifying means, the superconducting filter 12c corresponds to pass band limiting means, and the antenna line 11 corresponds to transmitting means.

The relation between the good no-load Q value of the filter applied to the transmission output section of such a communication device and the sideband component generated due to the power amplification will be evaluated and examined below.
FIG. 2 shows the signal passing characteristic of the superconducting filter 12c applied to the first embodiment. The center frequency of the passing signal in the superconducting filter 12c is 2000 MHz, the frequency bandwidth is 10 MHz, and the allowable value of the insertion loss of the filter is 0.2.
Assuming dB, the unloaded Q value (Q _u ) of the resonator is 50,0.
For 00, 5 steps, for Q _u = 100,000, 9 steps, for Q _u = 2
At 0,000, a 13-stage filter can be realized. Here, as is well known, the greater the number of filter stages, the better the sharp cut characteristic is obtained. That is, as shown by the solid line in FIG. 2, at Q _u = 200,000, the peripheral band (2000 + 5) indicated by the dotted line at the boundary of the predetermined occupied band (2000 ± 5 MHz: corresponding to the desired wave).
MHz or more and 2000-5 MHz or less: corresponding to a sideband component) is sharply cut.

A signal processing situation in a communication system provided with a transmission output section of the superconducting filter 12c having such a filter characteristic will be examined with reference to FIG. Note that the signal wave (signal A) output from the transmission circuit 12a is equivalent to that shown in FIG. The output signal B from the power amplifier 12b in FIG. 1 has a center frequency of 2000M as shown in FIG.
In addition to the desired frequency of 10 Hz and a bandwidth of 10 MHz, a center frequency of 2
A sideband component of third-order distortion of about 000 MHz and a bandwidth of about 25 MHz is incidentally generated. When the signal B having such an output spectrum is inputted to the superconducting filter 12c having the signal passing characteristic as shown in FIG.
As shown in (b), the transmission power of the desired wave frequency band passes well, the power of the sideband component is attenuated at the boundary of the frequency band of the desired wave, and only weakly remains near the desired wave (signal C). For example, in a trial calculation using a power amplifier with third-order intermodulation of 30 dBc and output of 40 dBm, the power of the sideband component becomes 12.4 dBm if the conditions of the input signal and the filter pass characteristic are appropriately set. When the superconducting filter 12c having a pass characteristic is used, the number of filter stages is 5 (Q _u = 50,000), 5.2 dBm, and the number of filter stages is 9 (Q _u = 100,00).
0) is -5.3 dBm, the number of filter stages is 13 (Q _u =
200,000), it can be reduced to -16.3 dBm. That is, the sideband component that has passed through the superconducting filter 12c has extremely low transmission power,
The transmission signal (desired wave) is transmitted as a signal wave close to an ideal rectangular shape, and unnecessary radiation of radio waves other than the desired wave is suppressed. Therefore, it is possible to improve frequency utilization efficiency without affecting adjacent frequency bands.

As described above, by applying the multistage filter having the characteristics obtained by the superconducting device, that is, the high unloaded Q value, the low electric resistance, and the small insertion loss to the transmission output section. , And an excellent sharp cut characteristic of the side band component is obtained, and also a band pass characteristic is obtained in which the loss of the transmission power of the desired wave is suppressed to be low and the signal is allowed to pass satisfactorily.

Next, a second embodiment of the communication system according to claim 2 of the present invention will be described. Regarding the specific line capacity when the filter having the above-mentioned band pass characteristic is applied to the communication system of the present invention. Evaluate and consider. In Figure 4, CD
1 shows a communication system of MA method. Where system A,
Uplinks A, B and C in frequency bands where B and C are adjacent to each other
And downlinks A, B and C of adjacent frequency bands, respectively, and the downlink of system C (downlink C) is adjacent to the uplink of system A (uplink A) in the frequency band. It is assumed that System A is
The system C is applied to the base station 21, and the system C is applied to the base station 22. The mobile station 23 is in the communication area of the base station 21, and the mobile station 24 is in the communication area of the base station 22.
Shall exist.

In such a state, as described in the prior art, since the radiation of the radio wave (sideband component) in the downlink C other than the transmission frequency band becomes a disturbance source at the time of reception in the uplink A, The line capacity itself of system A decreases. Therefore, for example, a superconducting filter applied to the first embodiment is inserted as a pass band control means having a sharp cut characteristic in the transmission output section of the system C to reduce the line capacity when the radiated power other than the transmission frequency band is reduced. The fluctuations of will be described below.

Table 1 shows the main specifications of the assumed system. These specifications correspond to the first condition arbitrarily set at the installation stage of the communication system such as the base station. The degree of interference given to an adjacent base station was calculated by using the calculation result of the out-of-band radiated power due to the cross modulation product in the power amplifier, and the relation between the out-of-band radiated power and the line capacity was obtained. The calculation method is as follows. 1) is the set of E _b / N _o necessary as the communication channel quality. 2) the received power) / (line usage counts from energy) = (all mobile stations per E _b (bits) / (data rate) 3) N _o (total noise power) = (internal noise of the receiver) + ( other received power from mobile stations) + (received power from other base stations) + (external _{noise) 4) E b / N o} ( required communication line quality) the number of lines used determined by 5) (number of lines) = (Number of lines used) / (Activity (line utilization)) 6) (Received power from other base stations) = (Out-of-band radiated power) x (Power loss due to propagation) x (System gain due to despreading) x (Number of interfering base stations) (However, the out-of-band radiated power varies depending on the filter performance.)

[0022]

[Table 1]

Note that, in the above calculation, the specifications of Table 1 (first
In addition to the (conditions), the following numerical values are assumed with the second condition being conditions such as natural noise, artificial noise, and the installation environment and operating conditions of the communication system such as margins. Natural noise: 300K Artificial noise: 300K Base station feeder loss: 2.5 dB Base station antenna gain: 8 dB Base station internal noise: 5 dB Mobile station feeder loss: 1.5 dB Mobile station antenna gain: 0 dB Activity factor: 50% Location rate margin : 8 dB Multipath margin: 6 dB By such trial calculation, the relationship between the radiated power outside the interference station band and the line capacity as shown in FIG. 5 was obtained. It was found that the line capacity is 17 when the out-of-band radiated power is 10 dBm, the line capacity is 68 when the out-of-band radiated power is 0 dBm, and 101 when the out-band radiated power is -10 dBm, and the line capacity increases as the out-of-band radiated power is attenuated.

That is, by installing a filter having a sharp cut characteristic in the transmission output section, it is possible to suppress radiation outside the occupied band, so that the line capacity can be greatly increased. In particular, a remarkable effect can be obtained by applying a filter having a high unloaded Q value such as a superconducting device. In the present embodiment, the superconducting filter was applied to the transmission output section as a filter showing a high no-load Q value, but the present invention is not limited to this, and a high no-load Q value and a low insertion loss. If the filter is capable of realizing the above, the above effect can be satisfactorily obtained. In addition, in the trial calculation of the line capacity, various conditions were set in detail, but it goes without saying that these conditions are simulations of an example of a communication system. Therefore, although various conditions are set depending on the environment to which the communication system is applied, the relationship between the out-of-band radiated power and the line capacity as shown in FIG. 5 can be similarly obtained by the above trial calculation method. Further, the high no-load Q value in the present invention refers to about 10 times or more as compared with the conventionally obtained value of 5,000 or less, but specific numerical values are the environment in which the communication system is installed and the superconducting filter. It goes without saying that it is appropriately set depending on the nature and the like. When the superconducting filter is applied to the present invention, the electric resistance is extremely small and the insertion loss is almost 0 dB.

[0025]

As described above, according to the first aspect of the present invention, the sideband (particularly, third-order distortion) component generated at the time of power amplification of the transmission signal is reduced to make the frequency spectrum of the transmission signal rectangular. Since it can be shaped, it is possible to suppress the emission of electric power outside the predetermined frequency band.
Therefore, it is possible to set the frequency band of another signal close to the adjacent frequency band, and it is possible to improve the frequency utilization efficiency.

According to the second aspect of the invention, the unused frequency band provided between the lines in the related art in order to suppress the adjacent interference due to the sideband component can be significantly reduced, and the line can be approached close to one line. Alternatively, since another line can be newly set in the unused frequency band, the line capacity can be increased. Further, the characteristics required for the filter applied to the inventions of claims 1 and 2, that is, the sharp cut characteristic and the insertion loss characteristic can be configured by a multistage filter having a high no-load Q value and a low insertion loss. It can be easily realized by utilizing the characteristics obtained by the superconducting device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a communication system according to claim 1 of the present invention.

FIG. 2 is a diagram showing bandpass characteristics of a transmission filter applied to the communication system according to claim 1 of the present invention.

FIG. 3 is a diagram showing signal processing in the communication system according to claim 1 of the present invention.

FIG. 4 is a diagram showing a second embodiment of the communication system according to claim 2 of the present invention.

FIG. 5 is a diagram showing a relationship between out-of-band radiated power and line capacity in the communication system according to claim 2 of the present invention.

FIG. 6 is a block diagram illustrating a configuration of a transmission / reception unit of a communication device according to the related art.

FIG. 7 is a block diagram showing a configuration of a transmission unit of a communication device in a conventional technique.

FIG. 8 is a diagram showing signal processing in a conventional technique.

FIG. 9 is a conceptual diagram showing a frequency occupation state in a conventional technique.

[Explanation of symbols]

 11 Antenna line 12a Transmission circuit 12b Power amplifier 12c Superconducting filter 12c 'Transmission filter 13a Reception circuit 13b Low noise amplifier 13c Reception filter 14 Duplexer 21, 22 Base station 23, 24 Mobile station

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sanya Okazaki, 1767, Shinba-cho, Kohoku-ku, Yokohama-shi, Kanagawa, Ltd.

Claims (2)

[Claims] 1. A power amplification means for amplifying a signal having a desired frequency band to a desired transmission power, and a pass band limiting means for limiting the passage of a signal other than the desired frequency band,
In a communication system comprising a transmitting means for transmitting a signal having the desired frequency band, the pass band limiting means, when passing a signal of the desired frequency band, while maintaining the amplified transmission power, A communication system characterized by having a sharp cut characteristic for reducing the power of a sideband component generated outside the desired frequency band at the boundary of the desired frequency band when the transmission power is amplified. 2. A second frequency band used for a reception signal is set close to a first frequency band used for a transmission signal, and the transmission signal is power-amplified to obtain a signal outside a desired frequency band. In a communication system that limits transmission and transmits, while reducing the power of a sideband component generated outside the first frequency band along with power amplification of the transmission signal at the first frequency band boundary, A communication system characterized in that a pass band limiting means having a sharp cut characteristic for maintaining the power of an amplified transmission signal is provided in a transmission output section after power amplification of the transmission signal.