Method of controlling mobile communication system, control device, and mobile communication system

A mobile communication system controls switching a transmission diversity system for each channel, and improves the quality of the channel. When the channel type in an uplink is a channel for transmitting voice, open loop transmission diversity is used (steps S1→S3). When the channel type in an uplink is a channel for transmitting a packet, closed loop transmission diversity is used (steps S1→S2). Since the open loop transmission diversity or the closed loop transmission diversity which ever is more appropriate can be used, a transmission diversity system can be appropriately switched for each channel, thereby improving the quality of the channel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of controlling a mobile communication system, a control device, and a mobile communication system, and more specifically to the control of a transmission diversity system in the mobile communication system.

2. Description of the Related Art

Generally, in a mobile communication system, a momentary level fluctuation can occur on a receiving side due to multi-path fading, etc., thereby greatly degrading the uplink reception characteristic in a radio base station and the downlink reception characteristic in a mobile station. There are the technologies for reducing the degradation such as the reception diversity for reception using a plurality of antennas on a receiving side, the transmission diversity for transmission using a plurality of antennas on a base station side, etc. Since the transmission diversity is a method for reducing the level fluctuation without enlarging the circuit (or increasing the number of antennas) on the receiving side, it is common to apply it in downlink mainly. For example, according to “3GPP RAN TS25.214 V3. c. O, March 2003” (herein after referred to as non-patent document 1), there are two types of transmission diversity, that is, open loop transmission diversity (STTD in the non-patent document 1) for obtaining a diversity effect by performing a predetermined symbol conversion using each antenna of a base station, and closed loop transmission diversity (closed loop mode1and closed loop mode2in the non-patent document 1) for allowing a mobile station to transmit a feedback command such that the optimum pattern can be obtained for the amplitude and the phase of signals from each antenna, and allowing a base station to determine the transmission phase and amplitude according to the command.

FIG. 8shows the concept of the open loop transmission diversity (STTD).FIG. 9shows the concept of the control of closed loop transmission power (closed loop mode1or closed loop mode2).

The STTD as an example of the open loop transmission diversity is explained below by referring toFIG. 8. As shown inFIG. 8, in the STTD, an STTD encoder3, an antenna Ant1, and an antenna Ant2are provided on the base station side, and an antenna MS Ant and an STTD decoder4are provided on the mobile station side.

The STTD encoder shown inFIG. 8calculates the complex conjugate of an odd symbol, multiplies an even symbol by a minus sign after the calculation of the complex conjugate, inverts the odd symbol and the even symbol, and performs transmission.

When α1and α2respectively indicate the fading vector of a transmission line from the antenna1(first antenna) to the mobile station, and the fading vector of a transmission line from the antenna2(second antenna) to the mobile station, the signals received by the mobile station can be expressed as follows. For simplicity, the noise is not considered in this example.
r1=α1S1−α2S2*
r2=α1S2+α2S1*  (math 1)

This is calculated in a STTD decoder as follows, and the calculation result Output is output.
Output 1=α1*r1+α2r2*=(|α1|2+|α2|2)S1
Output 2=α2*r2+α1r1*=(|α1|2+|α2|2)S2(math 2)

Thus, the fading from the antennas1and2can be combined at the maximum rate.

The closed loop mode1is explained below as an example of the closed loop transmission diversity by referring toFIG. 9. In the closed loop mode1as shown inFIG. 9, in the closed loop mode1, multipliers5and6, an FBI decoder7, and antennas Ant land2are provided on the base station side. The antenna MS Ant, a data decoder8, and a weight selector9are provided on the mobile station side. The multiplication weight multiplied in the multipliers5and6is transmitted from the mobile station side over a dedicated uplink channel, and is decoded in the FBI decoder7.

The W1shown inFIG. 9indicates a multiplication weight of signals transmitted from the antenna Ant1by which transmission signals are multiplied, and the W2indicates a multiplication weight of signals transmitted from the antenna Ant2by which transmission signals are multiplied. The weight has the following pattern.
(W1,W2)=(1,e×p(jφ))  (math 3)

FIG. 10shows a phase plane of a pattern of the weight W2. The received signals are expressed by the following equation.
r=((α1W1+α2W2)S(math 4)

In the case of the closed loop mode1, as shown by the (math 3) above, W1is fixed to 1. Therefore, in the mobile station, W2is determined to maximize α1W1+α2W2, a positive or negative value of I-axis component of W2is specified by an odd time slot, and a positive or negative value of Q-axis component of W2is specified by an even time slot. In the base station, transmission is performed using the latest I-axis and Q-axis components.

The time slot is constituted by a dedicated physical data channel (DPDCH) and a dedicated physical control channel (DPCCH) as shown inFIG. 10. InFIG. 10, the dedicated physical data channel is constituted by the data unit (Data) of Ndata-bit. The dedicated physical control channel is constituted by an Npilot-bit pilot unit (Pilot), an NTFCI-bit TFCI (transport format combination indicator) unit, an NFBI-bit FBI (feedback information) unit, and an NTPC-bit TPC unit. The weight is updated using an FBI unit (herein after referred to as an FBI bit) assigned to the DPCCH.

In the closed loop data decoder, the following calculation is performed to obtain the original signals. In the equation the noise component is omitted for simplicity.
Output 2=(α1W1+α2W2)r=|α1W1+α2W2|2S(math 5)

The received signals can obtain a gain (beam forming gain) for in-phase, and a larger gain can be ideally obtained as compared with the open loop transmission diversity. However, the above-mentioned FBI bit can erroneously be detected in uplink, and the more states in which the weight used in the base station is different from the weight assumed by the mobile station occur, the more easily the quality is degraded.

To reduce the degradation by the FBI bit error, the mobile station can perform antenna verification to estimate the weight used in the base station with higher accuracy. The Annex A of the non-patent document 1 shows an example of the method. As shown in the above-mentioned example, the determination accuracy is enhanced by assuming a BER (bit error rate) in the uplink of the FBI bit, and including a presumed probability. However, although the antenna verification is correctly performed, there occur the degradation in beam forming gain due to an FBI bit error, and an antenna verification error by mistakenly estimating the weight used by the base station. Therefore, when the FBI bit error rate increases, it is stated that the gain of the closed loop transmission diversity is degraded.

As a conclusion, when the FBI bit error rate is low in the uplink from the mobile station to the base station, a larger gain is obtained by the closed loop transmission diversity than by the open loop transmission diversity, but when the FBI bit error rate in the uplink is high, a gain can be more stably obtained by the open loop transmission diversity than by the closed loop transmission diversity.

The FBI bit error rate depends on the transmission rate of the channel in the uplink, a spreading factor, a transmission time interval (transmission time interval: herein after referred to as a TTI for short), the number of FBI bits, a target error rate and a slot format. Normally, when the transmission rate is high, the FBI bit error rate is low. When the transmission rate is low, the FBI bit error rate is high. An FBI bit is mapped over the dedicated physical control channel DPCCH (dedicated physical control channel), not over the dedicated physical data channel DPDCH (dedicated physical data channel). Therefore, when a comparison is made between a low amplitude ratio of the DPCCH to the DPDCH and a high amplitude ratio, the FBI bit error rate is lower when the amplitude ratio is high.

JP2002-64414A (herein after referred to as patent document 1) describes the technology of applying the closed loop transmission diversity according to the application request information when a predetermined condition is satisfied, for example, when there is no fluctuation of radio transmission line characteristic, etc.

SUMMARY OF THE INVENTION

As described above, the closed loop transmission diversity can obtain a larger gain than the open loop transmission diversity when an FBI bit error rate is low. However, the closed loop transmission diversity can obtain a smaller gain than the open loop transmission diversity when an FBI bit error rate is high.

The FBI bit error rate depends on the channel type of an uplink, or the transmission rate, the spreading factor, the TTI, the number of FBI bits, the target error rate, and the slot format. Normally, when a transmission rate is high, or when the power of the DPCCH is high, the FBI bit error rate becomes low. When the transmission rate is low, or when the power of the DPCCH is low, the FBI bit error rate becomes high.

The present invention has been developed to solve the above described problems of the conventional technology, and the object of the present invention is to provide a method of controlling a mobile communication system, a control device, and a mobile communication system capable of improving the quality of a channel by performing control of switching a transmission diversity system for each channel by applying the closed loop transmission diversity to a channel estimated to have a low FBI error rate in an uplink, and applying the open loop transmission diversity to a channel estimated to have a high FBI error rate.

The method of controlling a mobile communication system according to claims of the present invention includes a radio base station to which transmission diversity of performing radio transmission using a plurality of antennas is applied, and a mobile station for communicating with the radio base station. A transmission diversity system is determined according to the information about a channel in an uplink from the mobile station to the radio base station. Thus, the transmission diversity system can be appropriately switched for each channel, thereby improving the quality of the channel.

In the transmission control method for the mobile communication system according to claims of the present invention, the information about the channel in the uplink is a channel type, open loop transmission diversity is used when the channel type refers to a channel for transmitting voice, and closed loop transmission diversity is used when the channel type refers to a channel for transmitting a packet. Thus, the open loop transmission diversity or the closed loop transmission diversity which ever is more appropriate can be used.

In the method of controlling a mobile communication system according to claims of the present invention, the information about the channel in the uplink is a transmission rate of a channel in an uplink, an amplitude ratio of a control channel to a data channel, a transmission time interval, a target error rate, and a slot format, based on at least one of which a transmission diversity system is determined. Thus, the transmission diversity system can be more appropriately determined.

In the method of controlling a mobile communication system according to claims of the present invention, the transmission diversity system control means uses open loop transmission diversity when the transmission rate of the channel in the uplink is low, and uses closed loop transmission diversity when the transmission rate of the uplink is high. Thus, the open loop transmission diversity or the closed loop transmission diversity which ever is more appropriate can be used.

In the method of controlling a mobile communication system according to claims of the present invention, the information about the channel in the uplink is a signal-to-interference power ratio of a physical control channel of the uplink, and a signal-to-interference power ratio of pilot signals (for example, the pilot unit shown inFIG. 11) based on at least one of which a transmission diversity system is determined. Thus, the transmission diversity system can be more appropriately determined based on the SIR which changes from moment to moment.

The control device according to claims of the present invention controls the execution of transmission diversity of a radio base station for performing wireless transmission with a mobile station using a plurality of antennas, and includes transmission diversity system control means for determining a transmission diversity system according to the information about a channel in an uplink from the mobile station. Using the control device with the above-mentioned configuration, a transmission diversity system can be appropriately switched for each channel, thereby improving the quality of a channel.

In the control device according to claims of the present invention, the information about the channel in the uplink is a channel type, and the transmission diversity system control means uses open loop transmission diversity when the channel type refers to a channel for transmitting voice, and uses closed loop transmission diversity when the channel type refers to a channel for transmitting a packet. With the control device, the open loop transmission diversity or the closed loop transmission diversity which ever is more appropriate can be used.

In the control device according to claims of the present invention, the information about the channel in the uplink is a transmission rate of a channel in the uplink, an amplitude ratio of a control channel to a data channel, a transmission time interval, a target error rate, and a slot format, based on at least one of which the transmission diversity system control means determines a transmission diversity system. With the configuration of the control device, a transmission diversity system can be more appropriately determined.

In the control device according to claims of the present invention, the transmission diversity system control means uses open loop transmission diversity when the transmission rate of the channel in the uplink is low, and uses closed loop transmission diversity when the transmission rate of the uplink is high. With the control device, the open loop transmission diversity or the closed loop transmission diversity which ever is more appropriate can be used.

In the control device according to claims of the present invention, the information about the channel in the uplink is a signal-to-interference power ratio (herein after referred to as a SIR) of a physical control channel of the uplink, and a signal-to-interference power ratio of pilot signals (for example, the pilot unit shown inFIG. 11), based on at least one of which the transmission diversity system control means determines a transmission diversity system. Thus, the transmission diversity system can be more appropriately determined based on the SIR which changes from moment to moment.

The mobile communication system according to claims of the present invention includes a mobile station, a radio base station for performing wireless transmission to the mobile station using a plurality of antennas, and a radio network controller for controlling the mobile station and the radio base station, and controls execution of transmission diversity of the radio base station. The control device according to the claims is provided for at least one of the mobile station, the radio base station, and the radio network controller. With the configuration of the mobile communication system, a transmission diversity system can be more appropriately switched for each channel, thereby improving the quality of a channel.

As explained above, the quality of the downlink, for example, the BLER (block error rate), and a required transmission power can be improved according to the present invention by determining the transmission diversity system based on the channel type of an uplink, the transmission rate, etc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The modes for embodying the present invention are described below by referring to the attached drawings. In the following explanation, a component commonly used in other figures is identified by the same reference numeral.

The modes for embodying the present invention are explained below by referring to the attached drawings.FIG. 1shows an example of the system configuration of the mobile communication system to which the present invention is applied. As shown inFIG. 1, it is assumed that the mobile communication system includes a mobile station10, a base station20for performing wireless communication with the mobile station10using a plurality of antennas, and a radio network controller30for controlling the mobile station10and the base station20.

The present invention controls switching the transmission diversity system of a downlink depending on the channel type of an uplink when the transmission diversity is applied in the downlink, and the descriptions of the components not related to the present invention are omitted.

FIG. 2is a block diagram showing the function of the configuration example of the radio network controller30according to the mode for embodying the present invention. As shown inFIG. 2, the radio network controller30includes a channel setting unit31and a transmission diversity system control unit34for determining the transmission diversity system. The channel setting unit31includes an uplink channel setting unit32and a downlink channel setting unit33.FIG. 2shows only the portion for setting a radio channel and the portion for determining the transmission diversity system related to the present mode for embodying the present invention in the radio network controller30.

In this example, the transmission diversity system control unit34is provided in the radio network controller30, but the transmission diversity system can also be determined by providing the transmission diversity system control unit34in the mobile station10or the base station20.

The channel setting unit31acquires the information about the service type provided for the mobile station10from a core network such as the information about voice communications, a television telephone, packet communications, etc., and sets a parameter of an uplink channel and a parameter of a downlink channel respectively in the uplink channel setting unit32and the downlink channel setting unit33in the channel setting unit31.

The parameter refers to, for example, a transmission rate and a spreading factor, a TTI, the number of FBI bits, a target error rate, the amplitude ratio of the DPCCH to the DPDCH (uplink only), a slot format, etc. The channel setting unit31notifies the transmission diversity system control unit34of the parameter of the uplink set as described above, that is, a transmission rate and a spreading factor, a TTI, a target error rate, the amplitude ratio of the DPCCH to the DPDCH (uplink only), a slot format, etc.

The channel setting unit31can inform about not only the above-mentioned parameter, but also the service type, for example, voice, a television telephone, packet communication, etc. to be transmitted through the uplink.

(Transmission Diversity System Control Unit)

The transmission diversity system control unit34receives from the channel setting unit31the parameter of the uplink, that is, a transmission rate and a spreading factor, a TTI, a target error rate, the amplitude ratio of the DPCCH to the DPDCH, a slot format, etc., or a channel type of the uplink. Then, it determines the transmission diversity system based on at least one of the transmission rate and the spreading factor, the TTI, the target error rate, the amplitude ratio of the DPCCH to the DPDCH, the slot format, etc., or a channel type of the uplink. The determined transmission diversity system is transmitted to the mobile station10and the base station20.

For example, the transmission diversity system control unit34can determine that the transmission diversity system is open loop transmission diversity when the channel of the uplink is a channel for transmitting voice signals, and can determine that the transmission diversity system is closed loop transmission diversity when the channel type of the uplink is a channel for transmitting packet signals.

For example, the transmission diversity system control unit34can determine that the transmission diversity system is open loop transmission diversity when the transmission rate of the channel of the uplink is equal to or less than 32 kbps, and can determine that the transmission diversity system is closed loop transmission diversity when the transmission rate of channel type of the uplink is not equal to or less than 32 kbps.

For example, it also can determine that the transmission diversity system is open loop transmission diversity when the amplitude ratio of the DPCCH to the DPDCH of the uplink is lower than 12/15, and can determine that the transmission diversity system is closed loop transmission diversity when the amplitude ratio of the DPCCH to the DPDCH of the uplink is equal to or higher than 12/15.

It also can determine the transmission diversity system based on both the transmission rate and the amplitude ratio of the DPCCH to the DPDCH of the uplink. For example, it can determine that the transmission diversity system is open loop transmission diversity when the transmission rate is equal to or less than 32 kbps and the amplitude ratio of the DPCCH to the DPDCH of the uplink is lower than 12/15, can determine that the transmission diversity system is closed loop transmission diversity when the transmission rate is equal to or less than 32 kbps and the amplitude ratio of the DPCCH to the DPDCH of the uplink is equal to or higher than 12/15, and can constantly determine that the transmission diversity system is closed loop transmission diversity when the transmission rate is more than 32 kbps.

The transmission diversity system control unit34can determine the transmission diversity system based on the SIR (Signal to Interference Ratio) of the physical control channel of the uplink, or the SIR value of the pilot signals. That is, if the SIR value is equal to or higher than a predetermined threshold, it can be determined that the transmission diversity system is closed loop transmission diversity. If it is lower than the predetermined threshold, it can be determined that the transmission diversity system is open loop transmission diversity. Thus, the transmission diversity system can be more appropriately determined based on the SIR which changes from moment to moment. The SIR value is measured by the base station20, and the measurement result can be notified to the transmission diversity system control unit34in the radio network controller30. Otherwise, in the base station20, the transmission diversity system can be determined from the SIR, and the determination result can be notified to the radio network controller30.

In the explanation above, the transmission diversity system control unit34determines the transmission diversity system using the channel type of the uplink, the transmission rate, etc. However, since the channels of the uplink and the downlink are typically symmetric, the transmission diversity system can be determined using the channel type of the downlink, the transmission rate, etc. instead of the channel type of the uplink, the transmission rate, etc.

(Communication Control Method for Mobile Communication System)

Next, the communication control method for the mobile communication system according to the present invention is explained by referring to the flowchart shown inFIG. 3.

(Transmission Diversity System Depending on Channel Type)

First, in step S1shown inFIG. 3, it is determined whether or not the channel of the uplink transmits voice signals. If it is determined that the channel transmits voice signals, then control is passed to step S3. If it is determined that the channel does not transmit voice signals, then control is passed to step S2.

In step S2, it is determined that the closed loop transmission diversity is applied to the channel as a transmission diversity system.

In step S3, it is determined that the open loop transmission diversity is applied to the channel as a transmission diversity system.

(Transmission Diversity System Depending on Transmission Rate of Uplink)

An other mode of the receiving method using the reception device according to the present invention is described below by referring to the flowchart shown inFIG. 4.

First, in step S11shown inFIG. 4, it is determined whether or not the transmission rate of the uplink is equal to or less than 32 kbps. If it is determined that the transmission rate of the uplink is equal to or less than 32 kbps, then control is passed to step S13. If it is determined that the transmission rate of the uplink is not equal to or less than 32 kbps, then control is passed to step S12.

In step S12, it is determined that the closed loop transmission diversity is applied to the channel as a transmission diversity system.

In step S13, it is determined that the open loop transmission diversity is applied to the channel as a transmission diversity system.

The transmission diversity system can be determined by discriminating whether or not the transmission rate of the uplink is equal to or less than 32 kbps. However, it also can be determined depending on the transmission rate other than 32 kbps.

(Transmission Diversity System Depending on Amplitude Ratio of Control Channel)

Another mode of the receiving method using the reception device according to the present invention is described below by referring to the flowchart shown inFIG. 5.

First, it is determined in step S21shown inFIG. 5whether or not the amplitude ratio of the DPCCH to the DPDCH of the uplink is lower than 12/15. If it is determined that the amplitude ratio of the DPCCH to the DPDCH of the uplink is lower than 12/15, then control is passed to step S23. If it is determined that the amplitude ratio of the DPCCH to the DPDCH of the uplink is not lower than 12/15, then control is passed to step S22.

In step S22, it is determined that the closed loop transmission diversity is applied to the channel as a transmission diversity system.

In step S23, it is determined that the open loop transmission diversity is applied to the channel as a transmission diversity system.

In the process above, the transmission diversity system is determined depending on whether or not the amplitude ratio of the DPCCH to the DPDCH of the uplink is lower than 12/15, but it also can be determined depending on the value other than 12/15.

(Transmission Diversity System Depending on the Transmission Rate and the Amplitude Ratio)

An other mode of the receiving method using the reception device according to the present invention is described below by referring to the flowchart shown inFIG. 6.

First, in step S31shown inFIG. 6, it is determined whether or not the transmission rate of the uplink is equal to or less than 32 kbps. If it is determined that the transmission rate of the uplink is equal to or less than 32 kbps, then control is passed to step S33. If it is determined that the transmission rate of the uplink is not equal to or less than 32 kbps, then control is passed to step S32.

It is determined in step S33whether or not the amplitude ratio of the DPCCH to the DPDCH of the uplink is lower than 12/15. If it is determined that the amplitude ratio of the DPCCH to the DPDCH of the uplink is lower than 12/15, then control is passed to step S34. If it is determined that the amplitude ratio of the DPCCH to the DPDCH of the uplink is not lower than 12/15, then control is passed to step S32.

In step S32, it is determined that the closed loop transmission diversity is applied to the channel as a transmission diversity system.

In step S34, it is determined that the open loop transmission diversity is applied to the channel as a transmission diversity system.

(Transmission Diversity System Depending on SIR)

An other mode of the receiving method using the reception device according to the present invention is described below by referring to the flowchart shown inFIG. 7.

First, it is determined in step S41shown inFIG. 7whether or not the SIR value of the physical control channel of the uplink is equal to or higher than 3 dB. If it is determined that the SIR value is equal to or higher than 3 dB, control is passed to step S43. If it is determined that the SIR value is not equal to or higher than 3 dB, control is passed to step S42.

In step S43, it is determined that the closed loop transmission diversity is applied to the channel as a transmission diversity system.

In step S42, it is determined that the open loop transmission diversity is applied to the channel as a transmission diversity system.

In the above-mentioned receiving method, the transmission diversity system can be more appropriately determined based on the SIR which changes from moment to moment. In the explanation above, the transmission diversity system is determined based on the SIR of the physical control channel of the uplink, but it also can be determined based on the SIR value of the pilot signals (for example, the pilot unit shown inFIG. 11).

CONCLUSION

As explained above, according to the mode for embodying the present invention, the transmission diversity system can be determined based on the channel type of the uplink, the transmission rate, etc. As a result, an appropriate transmission diversity system can be applied to each channel. Therefore, an error rate of each channel can be reduced. When the transmission power control is performed, the transmission power to be assigned to the channel can be reduced.

For example, since a channel for transmitting a packet generally has a higher transmission rate than a channel for transmitting voice, it can be estimated that an FBI bit error rate is high in the case of the channel for transmitting voice, and it is low in the case of the channel for transmitting a packet.

Therefore, the open loop transmission diversity is applied to a channel for transmitting voice while the closed loop transmission diversity is applied to a channel for transmitting a packet, thereby improving the radio characteristic of the channel.

Also, the embodiment described above relates to a wideband Code Division Multiple Access (WCDMA) system in the 3GPP (3rd Generation Partnership Project). However, the present invention is not limited to the WCDMA, but can be applied to another communication system using transmission diversity in a mobile communication system, to the MIMO (multiple input multiple output) system using feedback information, and to an adaptive array antenna system.

The present invention can be used in controlling the transmission diversity system in a mobile communication system.