JP4354438B2 - Weight determination device and weight determination method - Google Patents

Description

  The present invention generally relates to the technical field of mobile communication, and more particularly, to a weight determination apparatus and a weight determination method for determining transmission weights for a plurality of antennas.

  In the technical field of mobile communication, it is required to improve the radiation efficiency of a communication device from the viewpoints of improving the quality of communication signals and effectively using radio resources. The demand is particularly strong for small mobile stations such as mobile phones. One attempt to improve radiation efficiency is to provide directivity to the beam pattern using a plurality of antenna elements. This intends to realize high radiation efficiency by appropriately adjusting the weight (phase and / or amplitude) of the signal transmitted from each antenna element.

With regard to the weight determination method, in the conventional method described in Patent Document 1, a weighting factor (weight) for reception is determined based on an error between a predetermined reference signal (also referred to as a pilot signal) and a reception signal. Has been. In Patent Document 1, the arrival direction of a desired wave is detected based on a signal received with an optimum weight, and the transmission weight is determined in consideration of the arrival direction.
JP 2004-297663 A

  However, with such conventional techniques, pilot signals must be communicated, which consumes some radio resources. In addition, the adaptive algorithm processing for determining the weight in real time based on the pilot signal is generally complicated, and the calculation burden and power consumption are not small.

  An object of the present invention is to provide a weight determination apparatus and a weight determination method that adaptively set weights for a plurality of antennas without using a pilot signal.

  In the present invention, an apparatus for determining a transmission weight is used. The apparatus includes a measuring means for measuring an instantaneous value of an amplitude ratio and a phase difference over a certain period for each of a plurality of received signals received by a plurality of antennas, and an amplitude ratio and a phase difference having a relatively high frequency of appearance. And a setting means for setting transmission weights for a plurality of antennas based on the derived amplitude ratio and phase difference.

  According to the present invention, weights for a plurality of antennas can be set adaptively without using a pilot signal.

  In one embodiment of the present invention, the instantaneous values (instantaneous weights) of the amplitude ratio and phase difference are measured over a certain period for each of a plurality of received signals received by a plurality of antennas. Amplitude ratio and phase difference having a relatively high frequency of appearance are derived, and a transmission weight is determined based on the ratio.

  A weight optimum for reception is derived by statistically processing a plurality of reception signals received by each antenna element over a certain period. By using a weight immediately derived from this weight at the time of transmission, high radiation efficiency can be realized. Since the weight is derived by simple temporal statistical processing of the received signal, it is not necessary to communicate a special signal such as a pilot signal. Statistical processing may include instantaneous weight appearance frequency measurement, frequent weight selection, determination of the weight with the highest appearance frequency, and the like. Since high radiation efficiency can be realized, it is possible to reduce the power consumption of the device, extend the life of the battery, expand the service area, improve the communication quality, and the like.

  The instantaneous amplitude ratio and phase difference may be calculated by comparing a received signal received by a predetermined antenna with a received signal received by another antenna. Alternatively, the instantaneous amplitude ratio and phase difference may be calculated by comparing some reference value with the received signal received by the antenna.

  Of the combinations (instantaneous weights) of the instantaneous values of the amplitude ratio and the phase difference, those obtained at a frequency higher than a predetermined appearance frequency may be selected. Thereby, the number of samples used for data processing can be reduced while maintaining the calculation accuracy, and the above simple calculation can be made more efficient.

  The transmission weight is set so that the amplitude ratio derived from the reception weight is maintained, and the phase relation derived from the reception weight is reversed. Such a transmission weight can be easily and quickly obtained from the reception weight.

  FIG. 1 shows a weight determination system according to an embodiment of the present invention. FIG. 1 shows a mobile station 10 such as a mobile phone, a first antenna element 11, a second antenna element 12, a receiver 13 and a transmitter 14 connected to the first antenna element, A receiver 15 and a transmitter 16 connected to two antenna elements, and an analysis unit 17 are depicted. In the illustrated embodiment, the mobile station 10 has only two antenna elements, but it may have more than two antenna elements. For convenience of illustration, the receivers 13 and 15, the transmitters 14 and 16, and the analysis unit 17 are depicted as if they are located outside the mobile station 10, but these elements typically move. It is provided inside the station 10.

  The receiver 13 converts the signal received by the first antenna element 11 into an appropriate analog signal or digital signal and outputs it. Conversion to a digital signal may be performed by a receiver or an analysis unit.

  The receiver 15 converts the signal received by the second antenna element 12 into an appropriate analog signal or digital signal and outputs it. Conversion to a digital signal may be performed by a receiver or an analysis unit.

Since the first and second antenna elements 11 and 12 are provided at different locations in the mobile phone 10, the received signals E ₁ (t) and E ₂ (t) having instantaneously different amplitudes and phases are provided. Is output.

  The analysis unit 17 determines the weight of the signal transmitted from each transmitter 14, 16 based on the received signal obtained from each receiver 13, 15. There are two types of weights: reception and transmission. Since the same frequency is used for transmission and reception in the time division duplex (TDD) system, the reception weight and the transmission weight may be equal. However, when different frequencies are used for transmission and reception, the reception weight and the transmission weight are set separately. This is because it has been conventionally known that the frequency characteristics of the reception weight and the transmission weight are very different and should be determined independently. However, the inventors of the present application have a very high frequency correlation between the optimal reception weight and the optimal transmission weight when statistically considered over a certain period, although the frequency characteristics of the reception weight and the transmission weight are very different instantaneously. I found out. In the present invention, the transmission weight is determined from the reception weight by utilizing this property.

  The transmitter 14 converts the signal weighted with an appropriate transmission weight into a radio signal suitable for transmission from the first antenna element 11.

  The transmitter 16 also converts a signal weighted with an appropriate transmission weight into a radio signal suitable for transmission from the second antenna element 12.

FIG. 2 shows a weight determination method used in the weight determination system shown in FIG. In step 21, a signal is received through the first and second antennas 11 and 12. The received signal need not be a pilot signal, but may be a traffic signal. Signals received through the antenna are converted into formats suitable for subsequent signal processing by the receivers 13 and 15 and input to the analysis unit 17. The analysis unit 17 samples the instantaneous amplitude r ₁ (t) and instantaneous phase θ ₁ (t) of the signal received by the first antenna 11. The instantaneous amplitude r ₂ (t) and instantaneous phase θ ₂ (t) of the signal received by the second antenna 12 are also sampled. In the analysis unit 17, an instantaneous amplitude ratio and an instantaneous phase difference are calculated over a certain period. The instantaneous amplitude ratio is calculated based on the instantaneous amplitude ratio (r ₂ (t) / r ₁ (t)) from the first and second antennas. The instantaneous phase difference is calculated based on the instantaneous phase difference (θ ₁ (t) −θ ₂ (t)) from the first and second antennas.

  In step 23, the appearance frequency of various instantaneous values of the amplitude ratio and the phase difference obtained during a certain period (for example, several seconds) is calculated, and the state of the distribution is analyzed. One combination of amplitude ratio and instantaneous value of phase difference is associated with one weight for the two antennas. Among various weights (for example, several thousand or more instantaneous weights), the weight including the most frequently occurring values (instantaneous values of the amplitude ratio and the phase difference) is the optimum (reception) weight. Therefore, the weight corresponding to the peak or the center of gravity in the above distribution is the optimum reception weight. The number of weight samples prepared for obtaining the peak position and the like is appropriately determined depending on factors such as the performance of the analog-to-digital converter used, the clock frequency, and the allowable delay time.

  The optimal reception weight may be derived by averaging weights having a high appearance frequency. The averaging may be an arithmetic average or a weighted average. In addition, an optimal reception weight may be derived based only on a weight that appears at a frequency exceeding a predetermined appearance frequency (threshold).

  In step 25, the optimum transmission weight is determined based on the optimum reception weight. According to the research results of the inventors of the present application, even if different frequencies are used for transmission and reception, if the frequency difference is at most several hundred megahertz, the optimal reception weight and the optimal transmission weight can be calculated by considering statistically over a certain period. (The instantaneous frequency characteristics of the reception weight and the transmission weight are very different). Specifically, the transmission weight amplitude ratio is set to be the same as the optimal reception weight amplitude ratio. The phase difference of the transmission weight is set to the inverted phase difference sign that gives the optimum reception weight. When signals are transmitted from the first and second antenna elements with such transmission weights, the received signal quality on the communication partner side is improved. For example, it is assumed that the optimum reception weight is expressed by an amplitude ratio of +0.3 dB and a phase difference of +10 degrees. The transmission weight in this case is expressed by an amplitude ratio of +0.3 dB and a phase difference of −10 degrees. That is, the amplitude of the signal transmitted from the second antenna element is adjusted to be about twice as large as that from the first antenna element, and the phase relationship is adjusted so that the phase difference is -10 degrees.

FIG. 3 shows an example of a simulation result regarding the appearance frequency of the weight. In FIG. 3, an amplitude ratio (−10 dB to +10 dB) is associated in the radial direction. The phase difference (0 degree to 360 degree) is associated with the angular direction or the circumferential direction. The appearance frequency of various values is expressed in four levels (very few, few, many, very many). Weights that appear very frequently are indicated by black areas in the figure. In this simulation, the optimum reception weight is expressed by an amplitude ratio of 0 dB and a phase difference of -7 degrees. Therefore, the transmission weight is expressed by an amplitude ratio of 0 dB and a phase difference of +7 degrees.

  FIG. 4 is a diagram illustrating a weight determination system according to an embodiment of the present invention. Unlike the system of FIG. 1, in this embodiment, the reception and transmission weights for the three antenna elements are determined. As an example, the amplitude ratio and the phase difference are derived on the basis of a signal received by the first antenna element. Or the reference value of an amplitude or a phase may be set separately irrespective of an antenna element. In the analysis unit, the appearance frequency of the weight is analyzed in the same manner as in the first embodiment. In the present embodiment, by repeating the method described in FIG. 2 for each antenna element, the weight for each antenna element can be set appropriately.

It is a figure which shows the weight determination system by one Example of this invention. 3 shows a flowchart of a weight determination method according to an embodiment of the present invention. The simulation result about the appearance frequency of a weight is shown. It is a figure which shows the weight determination system by one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Mobile station 11, 12 Antenna element 13, 15 Receiver 14, 16 Transmitter 17 Analysis part

Claims (5)

Measuring means for measuring an instantaneous value of an amplitude ratio and a phase difference over a certain period for each of a plurality of received signals received by a plurality of antennas;
A derivation means for deriving an amplitude ratio and phase difference with relatively high frequency of appearance;
Setting means for setting transmission weights for a plurality of antennas based on the derived amplitude ratio and phase difference;
An apparatus for determining a transmission weight characterized by comprising: 2. The measurement unit according to claim 1, wherein the measurement unit compares a reception signal received by a predetermined antenna with a reception signal received by another antenna, and measures instantaneous values of an amplitude ratio and a phase difference. apparatus. The apparatus according to claim 1, wherein the derivation unit selects one obtained from the combination of the instantaneous values of the amplitude ratio and the phase difference with a frequency higher than a predetermined appearance frequency. The apparatus according to claim 1, wherein the setting unit sets the transmission weight such that the derived amplitude ratio is maintained and the leading and trailing relations of the derived phase are reversed. For each of a plurality of received signals received by a plurality of antennas, an instantaneous value of an amplitude ratio and a phase difference is measured over a certain period,
Deriving the amplitude ratio and phase difference that appear relatively frequently,
Setting transmission weights for multiple antennas based on the derived amplitude ratio and phase difference;
A method for determining a transmission weight characterized by:

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