JPH08316896A - Diversity reception method in mobile communication system - Google Patents

Abstract

PURPOSE: To improve a noise figure for the entire reception system by increasing number of diversity branches without increasing-number of directivity antennas so as to improve the reception sensitivity. CONSTITUTION: The system uses a 4-input 4-output synthesis distribution phase shifter 30 configured in such a way that four output signals are a sum of shifting phases of four input signals and an output signal different based on a difference of phases of each input is obtained at each output. Then reception signals by four 180 deg. directivity antennas 21-24 whose maximum directivity differs from each other by 90 deg. each are given to the synthesis distribution phase shifter 30 to obtain signals equivalent to reception signals by four omnidirectional antennas. The reception signals are given to receivers 71-74, where the signals are demodulated and subject to diversity synthesis thereby realizing 4-branch diversity reception. Moreover, top antennas 25-28 are provided just after the directivity antennas 21-24 and before the synthesis distribution phase shifter 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION In a mobile communication system, communication between mobile stations is performed via a base station or a relay station. A base station device and a relay station device for transmitting and receiving are installed in the base station and the relay station. Although the base station device and the relay station device have a transceiver, the present invention relates to a diversity receiving method in the base station device and the relay station device.

[0002]

2. Description of the Related Art Ideally, a receiving antenna installed in a base station or a relay station is an omnidirectional antenna capable of receiving signals from all directions of 360 °.

The installation position is ideally on the rooftop of a building or the top of a steel tower so that it can be viewed in all directions of 360 °. However, the rooftop of the building has facilities for other purposes and there are space restrictions, the view of the building is impaired, the height of the building becomes high, and problems with the strength of the building occur. Installation is generally rare. Even when installing the tower top, it is not generally adopted because the number of accommodating stations is limited to a small number.

In order to avoid such a problem, 180
Two directional antennas of 90 ° are used, and the maximum directional directions of the two antennas are offset from each other by 180 °. That is, for example, the maximum directional direction of one directional antenna is set to the north direction, the maximum directional direction of the other directional antenna is set to the south direction, and signals received by the directional antennas are combined by hybrid to form one group. An equivalent of the omnidirectional antenna can be constructed, and such a combination method of directional antennas has been conventionally used.

FIG. 4 is a schematic configuration diagram showing an example of a receiving method of 2-branch diversity in a conventional mobile communication system of this type. In FIG. 4, reference numerals 1 to 4 denote 180 ° beam antennas (directional antennas) installed in a base station or a relay station, and are arranged such that the maximum directivity directions are north, south, east, and west. Reference numerals 5 and 6 are hybrids for synthesizing input signals, 7 and 8 are top amplifiers located at the frontmost end of a plurality of stages of amplifiers for amplifying input signals, and 9 and 10 are receivers for demodulation.

The maximum directivity directions of the directional antenna 1 and the directional antenna 2 are north and south, and the output ends of the bidirectional antennas 1 and 2 are input and connected to the hybrid 5. The output terminal of the hybrid 5 is input-connected to the first receiver 9 via the top amplifier 7. Similarly, the maximum directivity directions of the directional antenna 3 and the directional antenna 4 are set to the east and the west, respectively, and the output ends of the bidirectional antennas 3 and 4 are input-connected to the hybrid 6. The output terminal of the hybrid 6 is input-connected to the second receiver 10 via the top amplifier 8.

Next, the operation will be described.

Directional antenna 1 whose maximum pointing direction is north
The hybrid 5 combines the received signal received at 1 and the received signal received at the directional antenna 2 whose maximum pointing direction is facing south. The combined signal combined by the hybrid 5 is amplified by the top amplifier 7 and input to the first receiver 9. The combined signal at this time corresponds to a signal received by one omnidirectional antenna. The omnidirectional antenna is 3
It is an antenna that can receive signals from all directions of 60 °.

Similarly, the received signal received by the directional antenna 3 whose maximum directional direction is east and the received signal received by the directional antenna 4 whose maximum directional direction is west are combined in the hybrid 6. The combined signal combined by the hybrid 6 is amplified by the top amplifier 8 and input to the second receiver 10. The combined signal at this time also corresponds to the signal received by one omnidirectional antenna.

Therefore, in the example of this diversity receiving method, the received signals from the four directional antennas are
It is treated as a received signal in the original omnidirectional antenna, and two-branch diversity reception is performed using these received signals. Further, the amplification of the received signal by the top amplifier is performed after the antenna synthesis by the hybrid.

This conventional diversity receiving method is shown in FIG.
Is considered to be equivalent to the receiving antenna system. In FIG. 5, 1
Reference numerals 1 and 12 are omnidirectional antennas, 13 and 14 are top amplifiers, 15 is a first receiver, and 16 is a second receiver.

The maximum directivity directions of the directional antennas 1 to 4 are set to north, south, east, and west for convenience of description, and there is no need to set north, south, east, and west. The maximum pointing direction of the antenna is 90 °
It suffices if they are staggered and set, of which 18
It suffices to connect the objects separated by 0 ° to the hybrid.

In a mobile communication system, a phenomenon called fading fluctuation in which the envelope and phase of a received signal fluctuate drastically with time occurs due to movement of a mobile station. In that case, the envelope value (voltage amplitude value) sometimes becomes lower than the level of thermal noise inside the receiver. If only a single antenna (corresponding to an omnidirectional antenna) is used for reception, if the signal level becomes lower than the noise level, the signal cannot be discriminated and reception becomes impossible. To avoid this, 2
Reception is performed with one antenna to reduce the probability of signal loss. Correlation of received signals between two antennas is generally small, and it is premised that the signal level at one antenna is extremely low, but the signal level at the other antenna is relatively high. Receiving signals with a plurality of antennas in this way is called diversity reception. In the case of the above-mentioned conventional example, since the antenna is composed of two omnidirectional antennas, the two-branch diversity reception is performed. In diversity reception, the greater the number of diversity branches, the greater the effect (reception sensitivity improves).

In diversity reception, regarding the timing of diversity combining of the received signals (combined signals of north and south and combined signal of east and west) received by each diversity antenna, a method of combining before demodulation and a method of combining after demodulation There is a way to do it. Generally, the diversity combining in the base station and the relay station adopts the latter method after the demodulation. That is, the received signals received by the respective diversity antennas are first demodulated by the separate receivers 9 and 10, and the demodulated signals are diversity-combined by software (not shown). Therefore, when using a 2-branch diversity antenna, two receivers 9 and 10 are required.

[0015]

In the prior art, 18
It has been considered that the number of diversity branches realized by combining a plurality of 0 ° directional antennas is limited by the number of omnidirectional antennas composed of those directional antennas. For example, in the above-mentioned conventional example, two omnidirectional antennas are configured by combining antennas of four directional antennas, and even though two antennas are received by four antennas, up to two branch diversity reception is performed. I could only do it.

When it is necessary to improve the receiving sensitivity, it is possible to increase the number of diversity branches as a countermeasure. As an example, when it is desired to change from 2-branch diversity reception to 4-branch diversity reception, if the conventional way of thinking (two 180 ° directional antennas are used to configure one omnidirectional antenna), In addition to four 180 ° directional antennas, a new 180
° It becomes necessary to install directional antennas in the northeast and southwest to form one omnidirectional antenna, and to install 180 ° directional antennas in the southeast and northwest to form one omnidirectional antenna. A total of eight directional antennas will be required. This not only causes an increase in cost due to the increase in the number of directional antennas installed, but it is practically impossible to newly install four directional antennas at appropriate places in a building or the like.

Further, in the conventional example, since the received signal is amplified by the top amplifier after the antenna combination, the noise figure (NF: Noise Figure) of the entire receiving system is deteriorated (becomes larger). The noise figure NF is (input signal to noise power ratio) to (output signal to noise level ratio), and the smaller the value, the better the performance. The noise figure NF of the entire receiving system is NF up to the top amplifier (first stage amplifier)
Is almost decided by. Even if the NFs of the amplifiers in the second and subsequent stages are slightly worse, the influence on the NF deterioration of the entire system is very small. On the other hand, if there is a loss circuit before the top amplifier, N
F is deteriorated by the loss. In the case of the conventional example, there are loss circuits called hybrids 5 and 6 in front of the top amplifiers 7 and 8. The loss halves each signal,
Since the power gain is 10 log (1/2) ≈3, it is 3 dB. The noise figure NF up to the output of the top amplifiers 7 and 8 is
It deteriorates (becomes larger) than the NF of the top amplifiers 7 and 8 itself, so that the noise figure NF of the entire system also deteriorates accordingly.

The present invention was devised in view of such circumstances, and an object thereof is to increase the number of diversity branches and improve the reception sensitivity without increasing the number of directional antennas. There is. It is also intended to improve the noise figure NF of the entire receiving system.

[0019]

A diversity receiving method in a mobile communication system according to a first aspect of the present invention is a receiving method in a base station apparatus or a relay station apparatus in a mobile communication system, wherein each output signal is An n-input m-output (n, m is a natural number and m ≦ n is a sum of the phase-shifted input signals and is configured to obtain different output signals at each output due to the difference in the phase amount of each input. )
By using a synthetic distribution phase shifter having
A plurality of (m) received signals received by the directional antenna
It is characterized in that it is converted into a reception signal received by an omnidirectional antenna.

A diversity receiving method in a mobile communication system according to a second aspect of the present invention is the diversity receiving method according to the first aspect, in which received signals received by a plurality of (n group) directional antennas are combined and transmitted immediately after each of them. It is characterized in that it is amplified after being amplified by the same number of top amplifiers arranged in front of the phaser.

[0021]

According to the first aspect of the present invention, the received signals from the n directional antennas are converted into the received signals from the m directional antennas (m ≦ n), that is, at most n omnidirectional antennas, and the signals are converted. By diversity-combining received signals of m waves (maximum n waves), diversity reception with m branches (maximum n, that is, the same number as the number of directional antennas) becomes possible. Therefore, the number of diversity branches can be increased without increasing the number of antennas as compared with the conventional example, and the reception sensitivity is improved.

Further, the correlation of the envelopes of a plurality of (n waves) input signals to the combined distribution phase shifter is randomized by passing through the combined distribution phase shifter, and the correlation of a plurality of (m waves) output signals. Also, the reception sensitivity is increased because the noise is reduced.

In the second aspect, since the reception signal amplification by the top amplifier is performed immediately after the directional antenna and before the combining / dividing phase shifter, the antenna reception is performed as compared with the conventional example performed after the hybrid (combining). The power loss until the signal reaches the top amplifier is reduced, and the noise figure of the entire receiving system is improved accordingly.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A diversity receiving method in a mobile communication system according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of a 4-branch diversity receiving method in the mobile communication system of the embodiment. In FIG. 1, reference numerals 21 to 24 denote 180 ° beam antennas (directional antennas) installed in the base station device or the relay station device, and the respective antennas are arranged so that their maximum directivity directions are north, south, east, and west. 25-28
Is a top amplifier connected immediately after the output ends of the directional antennas 21 to 24 and amplifying the received input signal in the first stage. A block 30 surrounded by a dotted line is a 4-input 4-output composite distribution phase shifter, which is 2-input 2-output 3 dB, 9
It is composed of four couplers 31 to 34 of 0 ° phase shift. 41-56 are the terminal parts of each coupler. Between the terminal 43 of the coupler 31 and the terminal 49 of the coupler 33, between the terminal 44 of the coupler 31 and the terminal 53 of the coupler 34,
The terminal 47 of the coupler 32 and the terminal 50 of the coupler 33, and the terminal 48 of the coupler 32 and the terminal 54 of the coupler 34 are connected via cables 61 to 64 of the same length. 71 to 74 are first to fourth receivers for performing 4-branch diversity reception. The output end of the top amplifier 25 is connected to the terminal 41 of the coupler 31, the output end of the top amplifier 26 is connected to the terminal 42 of the coupler 31, and the output end of the top amplifier 27 is connected to the terminal 45 of the coupler 32. The output end of 28 is connected to the terminal 46 of the coupler 32. The terminal 51 of the coupler 33 is connected to the input terminal of the first receiver 71, the terminal 52 of the coupler 33 is connected to the input terminal of the second receiver 72, and the terminal 55 of the coupler 34 is connected to the third receiver 73. Of the coupler 34, and the terminal 56 of the coupler 34 is connected to the fourth receiver 74.

The couplers 31 to 34 have the same structure. FIG. 2 shows a schematic configuration of the coupler 31. 4 inside
There are two routes A to D. Output 1 and output 2 output the addition of input 1 and input 2, respectively. No phase shift occurs when passing through the paths A and B (phase shift 0 °). 9 when passing through routes C and D
A 0 ° phase shift occurs. The power of the signal is reduced by 3 dB (the power level is halved) regardless of which of the paths A to D is passed.

The signal input to the input terminal 41 passes through the path A, so that the power is reduced to ½ while maintaining its phase.
Becomes When the signal input to the input terminal 42 passes through the path D, the phase thereof is shifted by 90 ° and the power becomes ½. These two signals that have reached the output terminal 43 are added and output. In addition, the input terminal 41
By passing through the path C, the signal input to is phase-shifted by 90 ° and the power becomes 1/2. The signal input to the input terminal 42 passes through the path B, so that the power is reduced to ½ while maintaining its phase. These two signals that have reached the output terminal 44 are added and output. The same applies to the other couplers 32, 33, 34.

Next, the operation will be described.

The received signals received by the directional antennas 21 to 24 are individually input to and amplified by the top amplifiers 25 to 28, and the coupler 3 of the combined distribution phase shifter 30.
1 input terminals 41, 42 and coupler 32 input terminal 4
5, 46 are input. These received signals are the coupler 3
By passing through 1 to 34, the output terminals 51, 5
2, 55 and 56 are output as signals having different waveforms. These four output signals are input to the first to fourth receivers 71 to 74, demodulated, and then diversity-combined to perform 4-branch diversity reception.

The operation of the composite distribution phase shifter 30 will be described in detail below.

First, the output terminal 51 of the composite distribution phase shifter 30.
The signal output to will be described. The reception signal received by the 180 ° directional antenna 21 whose maximum pointing direction is north is amplified by the top amplifier 25 and then input to the input terminal 41 of the coupler 31 of the synthetic distribution phase shifter 30. The input signal to the input terminal 41 is a 3 dB coupler 31.
, The power is reduced by 3 dB (1 /
2), and the phase is output as it is to the output terminal 43. The output signal from the output terminal 43 is input to the input terminal 49 of the coupler 33. Input signal to input terminal 49 is 3
By passing through the coupler 33 of dB, electric power is further increased by 3
It is made smaller by dB and reaches the output terminal 51 of the combined distribution phase shifter 30 with the phase unchanged.

The received signal received by the 180 ° directional antenna 22 having the maximum pointing direction facing south is amplified by the top amplifier 26, and then the coupler 3 of the combining / distributing phase shifter 30.
1 is input to the input terminal 42. The input signal to the input terminal 42 passes through the coupler 31 of 3 dB, so that the power is reduced by 3 dB and the phase is shifted by 90 ° and output to the output terminal 43. The output signal from the output terminal 43 is input to the input terminal 49 of the coupler 33. The input signal to the input terminal 49 passes through the coupler 33 of 3 dB, so that the power is further reduced by 3 dB and reaches the output terminal 51 of the combined distribution phase shifter 30 with the phase unchanged.

The received signal received by the 180 ° directional antenna 23 whose maximum pointing direction is east is amplified by the top amplifier 27, and then the coupler 3 of the synthetic distribution phase shifter 30.
It is input to the second input terminal 45. The power of the input signal to the input terminal 45 is reduced by 3 dB by passing through the coupler 32 of 3 dB, and the output terminal 47 with the phase unchanged.
Output to The output signal from the output terminal 47 is input to the input terminal 50 of the coupler 33. The input signal to the input terminal 50 passes through the coupler 33 of 3 dB, so that the power is further reduced by 3 dB and the phase is shifted by 90 ° and reaches the output terminal 51 of the combined distribution phase shifter 30.

The received signal received by the 180 ° directional antenna 24 whose maximum pointing direction is west is amplified by the top amplifier 28, and then the coupler 3 of the composite distribution phase shifter 30.
It is input to the second input terminal 46. The input signal to the input terminal 46 passes through the coupler 32 of 3 dB, so that the power is reduced by 3 dB and the phase is shifted by 90 ° and output to the output terminal 47. The output signal from the output terminal 47 is input to the input terminal 50 of the coupler 33. The input signal to the input terminal 50 passes through the coupler 33 of 3 dB, so that the power is further reduced by 3 dB and the phase is 90
The phase is shifted by ° and reaches the output terminal 51 of the combined distribution phase shifter 30.

As described above, 4
The signals received by the original 180 ° directional antennas 21 to 24 are partially phase-shifted, added together, and output from the output terminal 51. The power of the output signal from the output terminal 51 is
It is the average of the output signal powers of the top amplifiers 25 to 28.
The output signal from the output terminal 51 is input to the first receiver 71, and the signal is used as a reception signal received by one omnidirectional antenna as a reception signal for diversity combination.

When the signals received by the directional antennas 21 to 24 are represented by S _{1 to} S ₄ , and the output signal obtained at the output terminal 51 as a result of the phase shift / synthesis is represented by SO ₁ , SO 1 = S ₁ (0 °) + S ₂ (90 °) + S ₃ (90 °) + S ₄ (180 °).

The output signal from the output terminal 52, the output signal from the output terminal 55, and the output terminal 56 of the composite distribution phase shifter 30.
The same applies to the output signal from the output terminal 51. Output terminals 51, 52, 55, 5
Since the powers of the output signals of No. 6 are the same, the description will be made below focusing on only the phase shift amount of the received signals at the directional antennas 21 to 24.

The output signal obtained at the output terminal 52 is SO2
SO2 = S ₁ (90 °) + S ₂ (180 °) + S ₃ (0 °) + S ₄ (90 °) When the output signal obtained at the output terminal 55 is represented by SO3, SO3 = S ₁ (90 °) °) + S ₂ (0 °) + S ₃ (180 °) + S ₄ (90 °) When the output signal obtained at the output terminal 56 is represented by SO4, SO4 = S ₁ (180 °) + S ₂ (90 °) + S ₃ (90 °) + S ₄ (0 °). However, in the above SO1 to SO4, S ₁ to
The value of S ₄ is a quarter of the original input signal.

As described above, the output signals SO1 from the output terminals 51, 52, 55 and 56 of the combining / dividing phase shifter 30.
SO2, SO3 and SO4 are equivalent to the signals received by the omnidirectional antenna. In addition, these four output signals SO1, SO2, SO3, SO4 are obtained from the synthesis of the signals received by the directional antennas 21, 22, 23, 24 which have undergone different phase transitions. Different signals are input to the first to fourth receivers 71, 72, 73, 74, demodulated, and then diversity-combined softly. Since these four combined signals behave like reception signals received by four omnidirectional antennas, 4-branch diversity reception can be performed. In this case, the gain of the omnidirectional antenna is an amount obtained by averaging the directional characteristics of the directional antennas 21 to 24 in all directions of 360 ° and adding them.

The reception method of FIG. 1 described above can be regarded as equivalent to the reception antenna system of FIG. In FIG. 3, 81 to 84 are omnidirectional antennas, 85 to 88 are top amplifiers, and 91 to 94 are first to fourth receivers.

As described above, by using the four-input, four-output synthetic distribution phase shifter 30, four directional antennas 2
Since it is configured to obtain a reception signal equivalent to the reception of four omnidirectional antennas obtained from 1 to 24, 4-branch diversity reception can be performed. Therefore, compared to the conventional example (FIG. 4), the number of diversity branches is set to 2 without changing the antenna configuration (increasing the number of antennas).
Can be increased from 4 to 4, and the receiving sensitivity can be improved.

Further, the correlation of the envelopes of the four input signals to the combined distribution phase shifter 30 is randomized by the passage of the combined distribution phase shifter 30, and the correlation between the four output signals is reduced. Also, the reception sensitivity can be increased.

Further, since the reception signals are amplified by the top amplifiers 25 to 28 immediately after the directional antennas 21 to 24 and before the combining / distributing phase shifter 30, the reception signals by the top amplifiers are amplified by the hybrid amplifier. As compared with a conventional example which will be performed later, power loss (cable loss, hybrid insertion loss) until the antenna reception signal reaches the top amplifier is eliminated, and the noise figure NF of the entire reception system is improved.

In the above embodiment, the synthetic distribution phase shifter 3 is used.
I used 4 inputs and 4 outputs as 0, but in general,
An n-input m-output (where n and m are the sums of each output signal obtained by shifting the phase of each input signal) and each output is provided with a different output signal depending on the difference in the phase amount of each input. A received signal received by a plurality of (n groups) directional antennas is converted into a received signal received by a plurality of (m group) omnidirectional antennas by using a synthetic distribution phase shifter having a natural number m ≦ n). It may be configured as follows.

[0045]

According to the diversity receiving method in the mobile communication system of the first aspect of the present invention, the received signals at the n directional antennas are equivalent to the received signals at the maximum of n omnidirectional antennas. Will be converted to
A maximum of n-branch diversity reception is possible, the number of diversity branches can be increased without increasing the number of antennas compared to the conventional example, and a plurality of (n-wave) input signals to the composite distribution phase shifter can be obtained. Since the correlation of the envelope of is randomized by the passage of the synthetic distribution phase shifter and the correlation of the plurality of output signals is reduced, the reception sensitivity can be improved.

According to the diversity receiving method in the mobile communication system of the second aspect of the present invention, since the received signal amplification by the top amplifier is performed immediately after the directional antenna and before the combining / dividing phase shifter, a hybrid (combining) method is used. The power loss until the antenna reception signal reaches the top amplifier can be reduced as compared with the conventional example which is performed after), and the noise figure of the entire reception system can be improved accordingly.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a 4-branch diversity reception method in a mobile communication system according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a coupler that constitutes a combined distribution phase shifter used in an example.

FIG. 3 is a schematic configuration diagram of a reception antenna system equivalent to the configuration of FIG.

FIG. 4 is a schematic configuration diagram showing a two-branch diversity receiving method in a mobile communication system according to a conventional example.

5 is a schematic configuration diagram of a reception antenna system equivalent to the configuration of FIG.

[Explanation of symbols]

 21-24 ... 180 ° directional antenna 25-28 ... top amplifier 30 ... synthetic distribution phase shifter 31-34 ... coupler 61-64 ... cable 71-74 ... receiver

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Ken Akiyama 4-3-1, Tsunashima-higashi, Kohoku-ku, Yokohama Matsushita Communication Industrial Co., Ltd.

Claims (2)

[Claims] 1. A reception method in a base station apparatus or a relay station apparatus in a mobile communication system, wherein each output signal is a sum of phase transitions of each input signal, and each output has a phase amount of each input. By using a synthetic distribution phase shifter having n inputs and m outputs (n and m are natural numbers and m ≦ n) configured so that different output signals are obtained according to the difference of A diversity receiving method in a mobile communication system, characterized in that a received signal received by an antenna is converted into a received signal received by a plurality (m) of omnidirectional antennas. 2. The reception signals received by a plurality of (n) directional antennas are amplified after being amplified by the same number of top amplifiers arranged immediately after each of them and before the combining / dividing phase shifter, and then combined. The diversity receiving method in the mobile communication system according to claim 1.