JP4509296B2 - Mobile radio terminal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mobile radio terminal used in a mobile communication system such as a cellular phone system, and particularly in a feedback transmission diversity communication system.
[0002]
[Prior art]
Feedback type transmission diversity is described in the document “TS25.214 v3.0.0” (page 25) in the 3GPP website (http://www.3gpp.org) as a 3rd generation mobile communication system development activity. Diversity ”.
[0003]
In the feedback type transmission diversity introduced here, the mobile station measures the received signal and performs an operation, and transmits the operation result to the base station as feedback information, and the base station that has received this, based on the feedback information, By controlling the coefficient of the transmission antenna (diversity branch), the strength of the received signal at the mobile station is increased.
[0004]
As a specific method for obtaining the feedback information, for example, when the base station is provided with diversity antennas (hereinafter simply referred to as antennas) ant-A, ant-B, the mobile station is ant-A, ant-B. A pilot signal transmitted as a signal that can be separately separated from B is received, and the vector amount of the received signal from each antenna is obtained.
[0005]
Then, the mobile station performs addition / subtraction of these vector quantities, and based on the result, obtains a combination of the coefficient Wa of the antenna ant-A and the coefficient Wb of the antenna ant-B so as to increase the reception intensity, and this is used as feedback information. To the base station.
[0006]
Such control naturally causes a control delay. That is, in the example of 3GPP, the time is divided into slots of about 666 μs and feedback control is performed for each slot. The mobile station measures the received signal in the Nth slot, calculates feedback information, and transmits it to the base station. In such a case, the information is reflected in the coefficient of the transmission antenna (diversity branch) of the base station only after one slot (N + 1 slot) at the earliest.
[0007]
For this reason, when the mobile station moves during this delay time (one slot), the diversity effect is deteriorated. This deterioration will be described with reference to FIG.
In the following description, the base station includes the antennas ant-A and ant-B described above, the coefficient of the antenna ant-A is Wa, and the coefficient of the antenna ant-B is Wb. Wa is constantly set to +1.
[0008]
In FIG. 5, a waveform “a” indicates signal strength when only a signal transmitted from the antenna ant-A is received by the mobile station, and a waveform “b” indicates that only a signal transmitted from the antenna ant-B is received by the mobile station. In this case, the signal strength is shown.
[0009]
Waveform c shows the signal strength received by the mobile station when the coefficient Wb of antenna ant-B is +1, while waveform d shows the signal strength when coefficient Wb of antenna ant-B is -1. Indicates the signal strength received at the mobile station.
[0010]
The waveform e indicates the signal strength received by the mobile station when the best value is set for Wb. That is, the waveform e indicates a waveform when the larger one of the waveforms c and d can be selected accurately.
[0011]
FIG. 5A shows an ideal state in which the control delay time is zero. FIG. 5B shows a state where the mobile station has moved 0.05 wavelength during the control delay time. In the 3GPP system (wavelength 0.15 m (2 GHz), slot length 666 μs), this corresponds to the mobile station moving at a speed of about 11 m / second (about 40 km / hour).
[0012]
FIG. 5C shows a case where the mobile station has moved by 0.1 wavelength during the control delay time, which corresponds to the mobile station moving at a speed of about 22 m / second (about 80 km / hour). The situation when doing is shown.
[0013]
As can be seen from these figures, compared to FIG. 5A, in FIG. 5B and FIG. 5C, the waveform e drops particularly when the value on the horizontal axis (moving position) is around 5.6 to 5.8 wavelengths. It can be seen that the diversity effect is degraded, and that the diversity effect is greatly degraded as the moving speed of the mobile station increases. In this way, if the diversity effect deteriorates, the probability that the mobile station's reception level will decrease increases, resulting in a loss of communication stability.
[0014]
[Problems to be solved by the invention]
In the conventional mobile radio terminal, the diversity effect is greatly degraded as the moving speed increases. Therefore, there is a problem that the increase in moving speed increases the probability of the mobile station receiving level decrease and impairs communication stability. It was.
[0015]
The present invention has been made to solve the above problem, and provides a mobile radio terminal capable of reducing the degree of deterioration of the diversity effect even when the moving speed is increased and capable of stable communication even during high-speed movement. The purpose is to do.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a mobile radio terminal that performs feedback-type transmission diversity for controlling a weighting factor by which a base station having a plurality of antennas multiplies a signal transmitted from each antenna prior to signal transmission. A signal separating means for detecting transmission signals transmitted from the plurality of antennas of the base station from the received signals, and a plurality of antennas based on the plurality of temporally continuous signals detected by the signal separating means. Prediction means for predicting the reception state of each transmission signal transmitted in the future, weight coefficient generation means for obtaining a weight coefficient value optimum for reception based on the prediction result of this prediction means, and this weight coefficient generation means And a transmission means for transmitting the weighting coefficient obtained in step 1 to the base station.
[0017]
In the mobile radio terminal having the above configuration, a state is predicted for each transmission signal transmitted from each of the plurality of antennas of the base station, and a signal transmitted from each antenna prior to signal transmission on the base station side based on the prediction result The weighting coefficient multiplied by each is controlled.
[0018]
Therefore, according to the mobile radio terminal having the above-described configuration, the weighting factor is controlled based on the predicted state of the transmission signal, so that even when the control delay is shortened and the moving speed is increased, the diversity effect is deteriorated. This makes it possible to reduce the degree of communication and perform stable communication even during high-speed movement.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of a mobile radio terminal and a base station according to an embodiment of the present invention.
[0020]
The mobile radio terminal 1 shown in this figure includes an antenna 11, a pilot separation unit 12, a path trajectory prediction unit 13, a control information creation unit 14, and a control information transmission unit 15.
[0021]
The base station 2 includes information receiving means 20, a weight coefficient control circuit 21, a transmission signal generator 22, multipliers 22a and 22b, and antennas 23a and 23b.
[0022]
The information receiving means 20 receives feedback information from the mobile radio terminal 1 and inputs it to the weighting factor control circuit 21. The weighting factor control circuit 21 analyzes the input feedback information to obtain weighting factors Wa and Wb, inputs the obtained weighting factor Wa to the multiplier 22a, and inputs the weighting factor Wb to the multiplier 22b.
[0023]
The transmission signal generator 22 generates a transmission signal Ta transmitted through the antenna 23a and a transmission signal Tb transmitted through the antenna 23b. The transmission signals Ta and Tb include other common information signals. Includes different pilot signals Pia and Pib, respectively.
[0024]
The transmission signal Ta generated in this way is multiplied by the weighting factor Wa in the multiplier 22a, and is radiated to the space as Ta ′ from the antenna 23a. Similarly, the transmission signal Tb is multiplied by the weighting factor Wb by the multiplier 22b, and is radiated to the space as Tb ′ from the antenna 23b.
[0025]
On the other hand, in the mobile radio terminal 1, the transmission signals Ta ′ and Tb ′ are superimposed and received by the antenna 11 and input to the pilot separation unit 12. The pilot separation unit 12 separates the pilot signals Pia and Pib included in the input reception signal, detects them as independent vectors, and inputs the detection result to the path trajectory prediction unit 13.
[0026]
The path trajectory predicting unit 13 predicts the vector of each pilot signal in the next slot by extrapolating the two vectors detected by the pilot separating unit 12 on the vector plane.
[0027]
As an example of a specific prediction method, the pilot signals Pia and Pib are predicted by linearly approximating a vector of the future, that is, the next slot, based on vectors detected in the present and the past.
[0028]
As a method of predicting the pilot signal vector with higher accuracy, the real axis component and the imaginary axis component of the complex vector are separately approximated by an Nth order equation using the vector detection results of the current and past total (N + 1) points. Then, a method of extrapolating it can be considered.
[0029]
The vector information predicted in this way is input to the control information creating unit 14, and the control information creating unit 14 receives from the base station 2 in the mobile radio terminal 1 based on the predicted vector information. The weighting factors Wa and Wb with the best signal strength are obtained and input to the control information transmission means 15 as feedback information.
The control information transmission unit 15 transmits the input feedback information to the base station 2.
[0030]
Next, feedback-type transmission diversity control operations by the mobile radio terminal 1 and the base station 2 configured as described above will be described.
The transmission signal Ta ′ transmitted through the antenna 23a is scattered by the radio wave reflecting object group indicated by the scattering circle Sa in the vicinity of the antenna 11 of the mobile radio terminal 1 through the propagation path Pa.
[0031]
Similarly, the transmission signal Tb ′ transmitted through the antenna 23b is scattered by the radio wave reflecting object group indicated by the scattering circle Sb in the vicinity of the antenna 11 of the mobile radio terminal 1 through the propagation path Pb.
[0032]
A large number of waves are superimposed on the transmission signals Ta ′ and Tb ′ thus scattered and received by the antenna 11 in a spatial fading state.
The reception signal on which the transmission signals Ta ′ and Tb ′ are superimposed is detected as two independent vectors by the pilot separation means 12 in a state where the pilot signals Pia and Pib are separated.
[0033]
The two vectors of the detected pilot signals Pia and Pib are extrapolated on the vector plane by the path trajectory prediction means 13, and the vector of each pilot signal in the next slot is predicted.
[0034]
This prediction result is input to the control information creating means 14, where the mobile radio terminal 1 obtains the weighting factors Wa and Wb at which the strength of the received signal from the base station 2 is the best, and these are used as feedback information. Then, the information is transmitted from the control information transmitting means 15 to the base station 2.
[0035]
Here, when the weighting factor Wa is constantly set to +1, 1-bit information for controlling only the weighting factor Wb to +1 or −1 may be transmitted to the base station 2 as feedback information. .
[0036]
On the other hand, in the base station 2, the feedback information is received by the information receiving means 20 and input to the weighting coefficient control circuit 21. The weighting factor control circuit 21 analyzes the input feedback information to obtain weighting factors Wa and Wb, inputs the obtained weighting factor Wa to the multiplier 22a, and inputs the weighting factor Wb to the multiplier 22b.
[0037]
As a result, the transmission signal Ta generated by the transmission signal generator 22 is multiplied by the weighting factor Wa by the multiplier 22a, and is radiated to the space from the antenna 23a. Similarly, the transmission signal Tb is multiplied by the weighting factor Wb in the multiplier 22b and radiated to the space from the antenna 23b.
[0038]
2 and 3 show an ideal case using a cheating feedback signal in which the change of the signal due to this movement is known in a situation where the mobile radio terminal 1 moves by 0.2 wavelength before the feedback information is reflected. Mobile radio in the case of performing transmission diversity control, in the case of performing feedback type transmission diversity control based on the prediction result of the pilot signal vector as described above, and in the case of performing conventional feedback type transmission diversity control The received signal strength of terminal 1 and the cumulative rate of received signal strength are shown respectively.
[0039]
In both figures, a broken line L1 indicates a control result when a cheating feedback signal is used, and a thick solid line L2 indicates a control when a result of predicting a pilot signal after movement by a quadratic polynomial according to the present invention is used. A result is shown and the thin continuous line L3 shows the conventional control result.
[0040]
According to FIG. 2, it can be seen that, by performing feedback transmission diversity control based on the prediction result of the pilot signal vector according to the present invention, diversity control extremely close to an ideal state can be performed as compared with the conventional case.
[0041]
Further, according to FIG. 3, for example, when the probability that the reception intensity is equal to or less than the level on the horizontal axis is evaluated at a level of 1% (0.01), that is, a level at which reception can be guaranteed with a probability of 99%, According to the control using the result of predicting the pilot signal after movement, it is found that the deterioration is only about 3 dB as compared with the ideal (cheat), which is about 10 dB higher than the conventional control. .
[0042]
As described above, the mobile radio terminal having the above configuration predicts a future pilot signal vector from past and current pilot signal vectors, and controls the weighting factors Wa and Wb of the base station 2 based on the prediction result. I am doing so.
[0043]
Therefore, according to the mobile radio terminal having the above configuration, feedback-type transmission diversity control is performed using the weighting factors Wa and Wb based on the predicted pilot signal vector.
[0044]
For this reason, even when the moving speed increases, the degree of deterioration of the diversity effect can be reduced and stable communication can be performed even during high-speed movement.
[0045]
The present invention is not limited to the above embodiment. For example, as shown in FIG. 4, when the reflecting object 3 exists, in addition to the propagation paths Pa and Pb similar to those in the above-described embodiment, the delay propagation paths Pa2 and Pb2 reflected by the reflecting object 3 are Through these delay propagation paths, scattering by the radio wave reflecting object group indicated by the scattering circles Sa2 and Sb2 occurs in the vicinity of the antenna 11 of the mobile radio terminal 1.
[0046]
In such a case, there are a direct wave by the propagation paths Pa and Pb and a delayed reflected wave by the propagation paths Pa2 and Pb2. Even in such a situation, the direct wave and the delayed reflected wave are independent of each other. Then, the measurement value of each propagation path is obtained, the optimum weighting factors Wa and Wb are obtained for each propagation path, and fed back to the base station 2.
[0047]
In the above embodiment, the weighting factor Wa is assumed to be a steady value of +1 and the weighting factor Wb is assumed to be either +1 or −1 in order to simplify the description. In order to improve the performance of feedback-type transmission diversity control, there are cases where the weighting coefficient takes four or sixteen values. Even in such a case, it goes without saying that the present invention is applicable, and the same effects are obtained.
[0048]
In the case where the weighting factor takes four values, the four values ((1 + 0j), (0, j), (−1) in which the absolute value is 1 and the phases are 90 ° on the complex plane. , 0j), (0, -j)).
[0049]
The case where the weighting factor takes 16 values is when the absolute value (amplitude ratio) is 2 and the phase is 45 ° on the complex plane.
In addition, it goes without saying that the present invention can be similarly implemented even if various modifications are made without departing from the gist of the present invention.
[0050]
【The invention's effect】
As described above, in the present invention, the state is predicted for each transmission signal transmitted from each of the plurality of antennas of the base station, and transmission is performed from each antenna prior to signal transmission on the base station side based on the prediction result. The weighting coefficient to be multiplied with each signal to be controlled is controlled.
[0051]
Therefore, according to the present invention, since the weighting factor is controlled based on the predicted state of the transmission signal, even when the moving speed is increased, the degree of degradation of the diversity effect is alleviated and the moving speed is increased. Can provide a mobile radio terminal capable of performing stable communication.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a configuration of a mobile radio terminal and a base station according to the present invention.
FIG. 2 is a diagram for explaining improvement in received signal strength by the mobile radio terminal shown in FIG. 1;
FIG. 3 is a diagram for explaining improvement of received signal strength by the mobile radio terminal shown in FIG. 1;
FIG. 4 is a diagram for explaining that the mobile radio terminal shown in FIG. 1 is effective even when a delay propagation path is generated by a reflecting object.
FIG. 5 is a diagram for explaining deterioration of diversity effect due to control delay in a conventional mobile radio terminal;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Mobile radio terminal 2 ... Base station 3 ... Reflective object 11 ... Antenna 12 ... Pilot separation means 13 ... Path locus prediction means 14 ... Control information creation means 15 ... Control information transmission means 20 ... Information reception means 21 ... Weight coefficient control circuit 22 ... transmission signal generators 22a and 22b ... multipliers 23a and 23b ... antennas

Claims (5)

In a mobile radio terminal that performs feedback-type transmission diversity for controlling a weighting factor for multiplying a signal transmitted from each antenna by a base station having a plurality of antennas prior to signal transmission,
Signal separating means for detecting transmission signals transmitted from a plurality of antennas of the base station from received signals,
Prediction means for predicting the reception state of each transmission signal transmitted in the future from the plurality of antennas based on a plurality of temporally continuous signals detected by the signal separation means ;
Weight coefficient generation means for obtaining a value of the weight coefficient to be given in order to optimally receive each transmission signal transmitted in the future based on a prediction result of the prediction means;
A mobile communication terminal comprising: transmission means for transmitting the weight coefficient obtained by the weight coefficient generation means to the base station. The signal separation means detects transmission signals transmitted from the plurality of antennas by detecting pilot signals inherently included in transmission signals transmitted from the plurality of antennas of the base station,
The prediction means predicts a reception state of each transmission signal transmitted in the future from the plurality of antennas based on a locus on a complex plane of a pilot signal detected by the signal separation means. Item 2. The mobile communication terminal according to Item 1.   The predicting means is configured to perform the plurality of operations by polynomial approximation for each component of the real axis component and the imaginary axis component of the locus on the complex plane based on the locus on the complex plane of the pilot signal detected by the signal separation means. The mobile communication terminal according to claim 2, wherein a reception state of each transmission signal transmitted in the future from the antenna is predicted.   The mobile radio terminal according to any one of claims 1 to 3, wherein a code division multiple access (CDMA) system is used as a radio communication system with the base station.   5. The mobile communication terminal according to claim 4, wherein the signal separation unit detects, for each propagation path, a transmission signal transmitted from a plurality of antennas of the base station from the received signal.

Images