HK1058585B

HK1058585B - Mobile communication system

Info

Publication number: HK1058585B
Application number: HK04101149.4A
Authority: HK
Inventors: 佐藤俊文
Original assignee: 日本电气株式会社
Priority date: 1996-05-30
Filing date: 2004-02-18
Publication date: 2005-12-02

Description

Mobile communication system

Technical Field

The present invention relates to a mobile communication system having a transmission power control circuit for controlling transmission power, and more particularly to a car phone or a portable phone suitable for being provided with a direct diffusion code division multiple access system.

Background

Conventionally, various systems have been used for car-mounted or portable telephone systems as cellular systems. Those known systems include the standard system of japan (PDC: RCR STD27), the north american standard (TIAs 54), and the european standard system, which use a time division multiple access scheme (TDMA), and another north american standard system (TIA IS95), which uses a Code Division Multiple Access (CDMA).

A cellular system using code division multiple access is arranged to cause two or more mobile telephones to connect to a base station via a carrier of one frequency. Such cellular systems require that the base station be provided with channel transmit power control techniques so that the signal power from multiple mobile phones are equal to each other. This will be described below. For example, assume that the power received from one mobile phone is 10 times the power received from another mobile phone. The former one gives a channel interference that is 10 times greater than the received power of the other mobile. In other words, the channel interference brought by the former mobile phone corresponds to 10 times the normal mobile phone. Where the power received from one mobile phone is 10 times as large as the power received from the other mobile phones, the number of mobile stations simultaneously coupled to a base station is reduced by 9 compared to the base station receiving the same power from each of all the mobile phones connected to it.

Cellular systems using Code Division Multiple Access (CDMA) systems require control of the transmit power so that the base station can receive the same power from each mobile phone to which it is connected. This drawback of control disadvantageously results in a significant reduction in the number of channels being connected as system capacity.

The control of the transmit power of the uplink channel implemented in the north american standard system using code division multiple access IS described in detail in paragraphs 6 and 7 of ITA/EIA/IS-95-a published by the TIA. The mobile phone transmit power is controlled by either an open loop power control or a closed loop power control. In open loop power control, a mobile phone measures the received power on a downlink channel, estimates the propagation loss from the difference between the received power and the power transmitted by a base station, and determines the transmission power of the mobile phone itself based on the propagation loss. (the "estimated open-loop output power" of 6.1.2.3.1 of publication TIA/EIA/IS-95-A and the "open-loop estimate" of 6.1.2.4.1 therein, published by TIA.) in this open-loop power control, the downlink channel has a different frequency than the uplink channel, so that the downlink transmission loss does not have to coincide with the uplink transmission loss. Therefore, this open loop power control alone cannot accurately control the transmission power.

Returning to the closed loop power control, the base station measures the received power in a 1.25 millisecond (ms) slot unit and determines the magnitude of the received power based on a reference value. In the subsequent downlink information time slot, the base station indicates to the mobile phone that the power transmitted by the mobile phone has changed by-1 dB in the case where the base station determines that the received power is greater than the reference value. In the case where the base station determines that the received power is less than the reference value, the base station gives an indication to the mobile phone that the power transmitted by the mobile phone has changed by +1 dB. In response to an indication from the base station regarding a change in transmission power, the mobile phone changes the transmission power in the time slot next to the time slot in which the indication is given. (see TIA published closed loop correction of TIA/EIA/IS-95-A6.1.2.4.2 and "power control sub-information" of 7.1.3.1.7 therein).

The north american standard system using CDMA supports a variable rate voice vocoder (voice encoder). That is, in a conventional Telecommunication Channel (TCH), the bit rate is 9600 bits/second, and in an interval where no speech occurs (no speech interval), the bit rate is reduced from half to 1/8 in order to reduce the generated interference to another channel. Specifically, a 20 ms frame structure is divided into 16 slots, each of which is 1.25 ms in length. Half of these time slots through 1/8 are variably selectively transmitted using a pseudo-random, while the other time slots are not transmitted to achieve variable rate transmission. The base station indicates a change in transmission power according to the foregoing procedure without regard to whether or not the current time slot has been transmitted, while the mobile phone changes the transmission power only according to an indication of a changed transmission power of the time slot actually transmitted.

The foregoing description shows that if the variation of the transmission loss, i.e., the attenuation or shadowing, is generated stepwise, the open-loop power control and the closed-loop power control can be used to control the received power from the mobile station to the base station within ± 1 dB.

As described in the aforementioned publication (TIA published "inverted CDMA channel signal" of 6.1.3.1 for TIA/EIA/IS-95-a), the uplink channel IS 64ary quadrature modulated and sync detected. Then, the resulting signal is subjected to RAKE combining and antenna diversity combining. The received power is obtained by measuring these combined powers.

In a closed loop control system used in a north american standard system with CDMA as described above, when a base station measures the power transmitted by a mobile phone in the nth slot, the base station changes an instruction to the mobile phone to change the transmission power in the N +2 th slot, and then the mobile phone changes the transmission power in the N +3 th slot. That is, control extends three slots. Assuming that one slot is 1.25 milliseconds, control is delayed by 3.75 milliseconds.

In such control of the transmission power, if the variation of the transmission path is a control delay much slower than 3.75 msec, i.e., 1/267Hz, this control is effective. If this change is rapid, the control of the transmit power is ineffective. Especially, if a high frequency of 2GHz is used, the change of the transmission path may be fast. This may be uncontrollable.

In north american standard systems using CDMA, the control delay (3 slots ═ 3.75 milliseconds) is greater than the control period (1 slot ═ 1.25 milliseconds). Therefore, when the transmission path is gradually changed, oscillation occurs at a period 4 times the control period (12 slots 15 msec). Furthermore, when the transmission path is changed quickly, the control is not able to keep up with the quick change. Therefore, the power control disadvantageously causes it to rise erroneously and higher than without any transmission power control.

Also, such systems use variable rate services. As described above, the disadvantage is more pronounced if intermittent transmission is performed. As the number of slots to be thinned out increases, the control interval is lengthened, so that the control cannot keep up with the faster change of the transmission path.

The alternation and error correction is effective if the decay following closed loop power control is fast. Thus in north american standard systems using CDMA, a combination of closed loop power control alternation and error correction codes is used to maintain a constant reception quality regardless of how fast the fading is. The combination of the alternation and the error correction code is effective in improving the quality of the main channel while the combination does not result in an increase in interference to other channels from an increase in average transmission power caused by a control error of the transmission power.

Disclosure of Invention

An object of the present invention is to provide a mobile communication system for controlling transmission power, which is configured to use CDMA (code division multiple access) as in the aforementioned north american standard system and reduce interference of a main channel with other channels by reducing control errors of transmission power of an uplink channel.

Another object of the present invention is to provide a mobile communication system for controlling transmission power, which is designed to suppress an increase in transmission power control error with respect to a fast fading and an oscillation phenomenon with respect to a very flat fading, suppress an increase in transmission power control error with respect to a variable-rate intermittent transmission, reduce interference of a main channel with other channels, increase the number of channels simultaneously used in one frequency band, and increase the number of admitted users as system capacity.

According to a first aspect of the present invention, a mobile communication system comprises: a base station having means for detecting carrier signal points represented by an in-phase component and a quadrature component at regular intervals, means for correcting the amplitude of the carrier signal point detected by the detecting means based on the previous transmission power control value, for when the next transmission power control is implemented by using the carrier signal point whose amplitude is corrected by the correcting means, means for predicting the carrier signal point at a certain point in time, means for comparing the electric power of the carrier signal point measured by the predicting means with a predetermined reference value, means for comparing the electric power of the carrier signal point with the reference value, means for generating a transmit power control value at a point in time when a next transmit power control is implemented, a memory for storing the control value of the transmission power generated by the generating means and providing the previous transmission power control value to the correcting means, and means for transmitting the transmission power control value; and a plurality of mobile devices; and a plurality of mobile devices are connected to the base station by radio waves of a certain frequency and controlled according to the control value of the transmission power transmitted from the base station so as to keep the power of the electric signals received by the base station equal to each other.

The mobile communication system has a carrier signal point detector for detecting carrier signal points represented by an in-phase component and a quadrature component, and correcting the amplitude of the carrier signal point detected by the detector based on a previous power control value, and predicting the carrier signal point of the next power control from the corrected amplitude by the action of a prediction unit. Then, the power of the predicted carrier signal point is compared with a predetermined reference value. A power control value for the next power control is generated based on the comparison result and then transmitted to the mobile phone. By doing so, each mobile phone can control the transmission power so that all the power received by the base station from the mobile phone is equal to each other.

According to a second aspect of the invention the mobile communication system according to the first aspect of the invention is characterized in that the means for detecting carrier signal points are arranged to detect carrier signal points on the basis of detecting pilot code symbols inserted at regular periods.

According to a third aspect of the present invention the mobile communication system according to the first aspect of the present invention is characterized in that the means for detecting the carrier signal point is arranged to detect the carrier signal point by detecting an M-valued quadrature modulated data signal point. M-ary orthogonal modulation is a system for selecting one of M-code sequences orthogonal to each other according to information to be transmitted and transmitting the selected code. If M is 2M, M bits of information may be transmitted with one code. This is employed in the conventional north american standard system (tias 95).

According to a fourth aspect of the present invention, the mobile communication system according to the first aspect of the present invention is characterized in that the prediction means is arranged to derive the prediction value from the amplitude correction values inserted into the two last received carrier signal points.

According to a fifth aspect of the present invention, the mobile communication system according to the first aspect of the present invention is characterized in that the prediction means is arranged to derive the prediction value from the last received carrier signal point amplitude correction value by least squares linear prediction.

According to a sixth aspect of the present invention, the mobile communication system according to the first aspect of the present invention is characterized in that the prediction means is arranged to obtain the prediction value from the amplitude correction values of the plurality of carrier signal points received last by least squares linear prediction. That is, the mobile communication system according to the fifth aspect of the present invention performs a linear approximation that minimizes the root mean square error of the straight-line case, while the mobile communication system according to the sixth aspect of the present invention performs a minimum square root prediction that generally does not result in a linear approximation.

According to a seventh aspect of the present invention, a mobile communication system comprises: a base station having means for detecting carrier signal points composed of an in-phase component and a quadrature component of a path at regular intervals, detecting means prepared for each path of a plurality of radio signals, means for correcting the amplitude of the carrier signal point detected by the detecting means based on a previous transmission power control value, correcting means prepared for each path and corresponding to the detecting means for predicting the position of a carrier signal point when next control is made on transmission power using the carrier signal point whose amplitude is corrected by the correcting means, the predicting means being provided in correspondence with each correcting means, means for synthesizing electric power of the carrier signal point detected by the predicting means, means for comparing the electric power synthesized by the synthesizing means with a predetermined reference value, means for generating a transmission power control value in performing next transmission power control based on the comparison result given by the comparing means, means for storing the transmission power control value generated by the generating means and providing the control value as a previous transmission power control value to the correcting means, and a control circuit for controlling the transmission power, the control circuit having means for transmitting the transmission power control value; and a plurality of mobile units connected to the base station by radio waves of one frequency and controlled according to the transmission power control value from the base station to keep the power of the electric signals received by the base station equal to each other.

A mobile communication system according to a seventh aspect of the present invention relates to a method for controlling transmission power when RAKE combining is performed in a direct diffusion code division multiple access (DS-CDMA) system. In mobile communications, radio signals are reflected on objects such as buildings or mountains. That is, the radio signal travels multiple paths to reach the receiver. When using a direct-diffusion cdma system, paths may separate if the inter-path delay is different by more than a small fraction of the diffusion code. Therefore, in the case of using a direct-diffusion code division multiple access system, RAKE synthesis (to be described later) is often used to enhance the reception characteristics of each path. Such a mobile communication system is provided with a "carrier signal point detector", "amplitude corrector", and a "prediction unit" on each path. After the "synthesizer", RAKE synthesis is performed. Only one combination of these components is required. This is similar to the mobile communication system according to the first aspect of the invention.

According to an eighth aspect of the present invention, a mobile communication system comprises: a base station having a radio wave receiving means for receiving a radio band signal and converting the signal into a complex baseband signal, an inverse diffusion means for extracting a main channel signal by copying a spread code of the code division and multiplexed complex baseband signal after the conversion, a demultiplexing means for separating an output of the inverse diffusion means into pilot symbols and data symbols, a means for performing in-phase addition of adjacent pilot symbols received from the demultiplexing means in time series, a means for correcting an amplitude of the in-phase added pilot symbols according to a previous transmission power control value in order to increase a signal/noise power ratio, a means for predicting a reception signal point of the pilot symbol when next transmission power control is performed by the pilot symbol whose amplitude is corrected by the correcting means, a means for comparing an electric power of the pilot symbol predicted and received by the predicting means with a predetermined reference value, means for generating a transmission power control value at the time of performing the next transmission power control based on the comparison result of the comparing means, storing means for storing the transmission power control value generated by the generating means and supplying the control value as the previous transmission power control value to the correcting means, and a circuit for controlling transmission power, the circuit having means for transmitting the transmission power control value; and a plurality of mobile units connected to the base station by radio waves of one frequency, the mobile units being controlled in accordance with the transmission power control value so as to keep the power of the electric signals received by the base station equal to each other.

That is, the mobile communication system according to the eighth aspect of the present invention is another embodiment of the second aspect of the present invention.

According to a ninth aspect of the present invention, a mobile communication system comprises: a base station having radio wave receiving means for receiving a radio frequency band signal and converting the signal into a complex baseband signal, inverse diffusion means for extracting a main channel signal by copying a spread code of the code division multiplexed complex baseband signal after conversion, quadrature modulation means for calculating a correlation value of the complex baseband signal with each M quadrature code (M is a positive integer), means for selecting one of the M correlation values so that the selected correlation value gives a maximum electric power, means for correcting the amplitude of the correlation value selected by the selecting means based on the previous transmission power control value, means for predicting a signal point when next transmission power control is performed by the amplitude-corrected correlation value, means for comparing the amplitude of the predicted signal point with a predetermined reference value, means for generating a transmission power control value when next transmission power control is performed based on the comparison result given by the comparing means, a memory for storing the transmission power control value generated by the generating means and a control value provided to the amplitude correcting means as a previous transmission power control value, and a circuit for controlling the transmission power, the circuit having means for transmitting the transmission power control value; and a plurality of mobile units connected to the base station by radio waves of a frequency, which are controlled in accordance with a transmission power control value transmitted from the base station to keep the power of the electric signals received by the base station equal to each other.

That is, the mobile communication system according to the ninth aspect of the present invention is another embodiment of the third aspect of the present invention.

As previously indicated, the mobile communication system according to the first to ninth aspects of the present invention is provided with a carrier signal point detector for detecting carrier signal points represented by an in-phase component and a quadrature component at regular intervals, and operates to correct the amplitude of the detected carrier signal point based on the previous transmission power control value and to predict the carrier signal point at the next power control by the action of the prediction unit. Then, the power at the predicted carrier signal point is compared with a predetermined reference value. Based on the comparison result, a power control value is generated at the next power control point and sent to the mobile phone. The transmission power is realized by using a predetermined value so that the control of the transmission power can keep up with the faster attenuation to reduce the control error of the transmission power. A smaller control error of the transmission power reduces the influence of the main mobile phone on other mobile phones having other channels of the same frequency, thus enhancing the efficiency of the utilization of the frequency.

The mobile communication systems according to the first to ninth aspects of the present invention are arranged to correct the foregoing control influence of the transmission power for preventing the oscillation phenomenon generated with respect to the transmission power control that is attenuated very gently. In addition, these mobile communication systems use this prediction. So if the control interval is longer, the control can keep up with the decay. Therefore, the increase of the transmission power control error with respect to the intermittent transmission at the variable rate is effectively suppressed. The mobile communication system according to the seventh aspect of the present invention is provided with a "carrier signal point detector", an "amplitude corrector", and a "prediction unit" at each path. Thus, the present invention can be applied to a receiver that performs RAKE combining.

This and other objects, features and advantages of the present invention will become apparent from the drawings and the detailed description that follow.

Drawings

Fig. 1 is a block diagram of a transceiver unit of a base station in a mobile communication system according to an embodiment of the present invention;

fig. 2 is a block diagram of a mobile telephone transceiver unit in a mobile communication system in accordance with an embodiment of the present invention;

FIG. 3 is a diagram illustrating the data exchange between a mobile phone and a base station in a mobile communication system, and the operation timing of the base station loop according to an embodiment of the present invention;

FIG. 4 is an illustrative diagram showing amplitude correction and prediction in the Gaussian plane in accordance with an embodiment of the invention;

fig. 5 is a block diagram of a receiving unit of a base station included in the first variation of the present invention;

fig. 6 is a block diagram of a receiving unit of a base station included in a second variation of the present invention.

Detailed Description

The present invention will be described in detail by way of examples.

Fig. 1 shows a transceiving part of a base station included in a mobile communication system of an embodiment of the present invention. The mobile communication system performs data transfer between the base station and each mobile phone by the function of the code division multiple access system.

The transceiver portion 100 of the base station comprises: an antenna 101, an duplexer 102 connected to the antenna 101, typically includes a transmit part 104 of a radio transmitter 103 and a receive part 106 of a radio receiver 105.

A radio receiver 105 included in the receiving section 106 performs conversion of a signal received over a wireless frequency band into a complex baseband signal. The complex baseband signal is composed of an in-phase component and a quadrature component. The complex baseband signal is applied to an inverse diffusion circuit 111. The inverse diffusion circuit 111 reproduces the code division multiplexed complex baseband signal for extracting the main channel signal. The output of the inverse diffusion circuit 111 is applied to the demultiplexing circuit 112. Demultiplexing circuitry 112 performs the separation of the input signal into a pilot symbol (PL) and data. The pilot symbols are applied to a pilot symbol in-phase addition circuit 113.

The preamble symbol in-phase addition circuit 113 is for increasing the power signal-to-noise ratio of the preamble symbol by in-phase addition of a plurality of preamble symbols received sequentially. The output of the preamble symbol in-phase addition circuit 113 is applied to the amplitude correction circuit 114. The amplitude correction circuit 114 is input with the previous transmission power control symbol 116 read out by the memory 115, and corrects the amplitude of the preamble signal according to the control value of the previous transmission power. The transmission power control symbol is a symbol for indicating an increase or decrease in the transmission power of the mobile phone. The prediction circuit 117 performs extrapolation or linear prediction of the preamble symbols whose amplitudes are corrected on the gaussian plane at the time and before for predicting the preamble signal of the time slot when the transmission power is controlled. In the gaussian plane, the in-phase component is represented by a real axis, and the quadrature component is represented by an imaginary axis.

The amplitude of the preamble symbol predicted by the prediction circuit 117 and the amplitude reference value 118 are applied to the comparison circuit 119 for comparison with each other. The comparison result is applied to a transmission power control circuit 121 in which the transmission power control symbol 116 is generated. The symbol 116 is stored in the memory 115.

On the other hand, the data separated by the demultiplexing circuit 112 is added to a pilot symbol interpolation and synchronization detection circuit 122. The circuit 122 operates to interpolate in-phase summed pilot code symbols at the ends of the time slot for obtaining a reference signal for synchronization detection. The detected signal from the detection circuit 122 is added to a determination circuit 124 for determining the signal. Then, the received data 125 is output from the determination circuit 124.

On the other hand, the transmission section 104 is provided with a multiplexing circuit (MUX)133 to which transmission data 131 and transmission power control symbol 116 are input. The multiplexing circuit 133 time-division multiplexes the three inputs and then applies the result to the diffusion circuit 135. The diffusion circuit 135 spectrally diffuses the diffusion code. The output of the diffusion circuit 135 is applied to the wireless transmission section 103, and the baseband signal is converted into a wireless band signal and amplified in the wireless transmission section 103. The resulting signal is transmitted by the antenna 101 via the duplexer 102.

The comparison circuit 119 performs comparison of the signal power received from the prediction circuit 117 with the reference power. As in the prior art code division multiple access scheme as used in north american standard systems, the received signal to power (sum of noise power and interference power) ratio is compared to a predetermined reference value. The determination circuit 124 can determine whether the data is "0" or "1" according to the polarity of the signal. To enhance communication quality, a combination of deinterleaving and error correction for the determination (for an error correction soft decision (viterbi) decoder based on a multivalued signal) can be made.

Fig. 2 shows a transceiving part of a mobile phone included in the mobile communication system according to this embodiment. The transceiver portion 200 includes an antenna 201, an antenna duplexer 202 connected to the antenna 201, a transmit portion 204 typically including a wireless transmitter 203, and a receive portion 206 typically including a wireless receiver 205.

The wireless receiver 205 of the receiving section 206 converts a signal received in a wireless frequency band into a complex baseband signal. The complex baseband signal is composed of an in-phase component and a quadrature component. This complex baseband signal is applied to an inverse diffusion circuit 211. The despreading circuit 211 despreads the code-divided and multiplexed composite baseband signal for extracting a signal of the main channel. The output of the inverse diffusion circuit 211 is applied to a first demultiplexing circuit 212. The first demultiplexing circuit 212 operates to separate the input signal into a pilot symbol (PL) and data. The preamble symbols are applied to a preamble symbol in-phase adder circuit 213.

The preamble symbol in-phase addition circuit 213 is a circuit for increasing the signal-to-noise power ratio of the preamble symbol according to the in-phase addition of the preamble symbols received in time sequence.

On the other hand, the data separated by the first demultiplexing circuit 212 is applied to a pilot symbol interpolation and synchronization detection circuit 222. Circuit 222 interpolates in-phase added pilot symbols at both ends of the slot to extract the reference signal for synchronization detection. The detected signal output from the interpolation and synchronization detection circuit 222 is applied to a second demultiplexing circuit 223 where the detected signal is separated into a data portion and a transmit power control symbol portion. The data portion is applied to a first determination circuit 224 where it is determined. The circuit 224 then outputs the received data 225. The transmit power control symbols are applied to a second determination circuit 226 where the symbols are determined. Circuit 226 then outputs transmit power control symbols 227.

The transmitting section 204 includes a multiplexing circuit (MUX) that inputs the transmitted data 231 and the preamble symbol 232. Multiplexing circuit 233 time-multiplexes the two inputs and then adds the result to diffusion circuit 235. The spreading circuit 235-spectrally spreads the spreading code. The output of the diffusion circuit 235 is applied to an adjustable amplifier 236. The adjustable amplifier 236 increases or decreases the transmission power according to the transmission power control symbol 227 output from the second determination circuit 226. The adjustable amplifier 236 may thus include an adjustable attenuator. The output of the adjustable amplifier 236 is applied to the wireless transmitter 203. The wireless transmitter 203 converts the baseband signal into a wireless frequency band signal and amplifies the wireless frequency band signal. The amplified signal is transmitted by the antenna 201 through the duplexer 202.

Fig. 3 shows the operation timing of the circuits for transmitting data and base station settings between the mobile phone and the base station in the mobile communication system of the present embodiment. For simplicity of illustration, fig. 3 shows the case of a single transmission of two time slots, i.e., the case where the transmitted and received data are at half the maximum bit rate. In fact, the mobile communication system of the present embodiment is capable of connectively transmitting and transferring data at a bit rate lower than half the maximum bit rate. This can likewise be represented graphically.

Transmission signal 301 in each time slot transmitted by a mobile phone₁、301₃A received signal 302 at each time slot of the base station₁、302₃And a transmission signal 303 for each time slot transmitted by the base station₂、303₄The footers "1", "2", "3", etc. represent the number of time slots. As can be seen from fig. 3, each slot format of signals 301 to 303 is such that there are preamble symbols (PL) at both ends of each slot and data between the preamble symbols. This format is used to facilitate preamble symbol interpolation synchronization detection.

The transmission power control delay is specified as 2 time slots and the transmission from the base station is converted to approximately one time slot for the mobile phone transmission. Received signal 302 in the first time slot of the base station₁Separated into pilot symbols and data by the action of demultiplexing circuitry 112. The pilot code symbols at both ends of the slot are added in phase with each other. The result of addition is represented by "r 0" and "r 1" in the first slot of fig. 3, like "r 2" and "r 3" of the third slot. With respect to the fifth or subsequent time slot, although not shown, the result of addition is similarly represented.

In the case where the symbol frequency is much faster than the transmission path fading frequency, it can be considered that there is substantially no variation in carrier phase and amplitude between adjacent preamble symbols. Thus, by performing in-phase addition of adjacent preamble symbols, the signal-to-noise power ratio of the resulting preamble symbol is improved from the added symbols. These in-phase added preamble symbols "r 0, r1, r2, r 3." can be viewed as signals representing (in-phase and quadrature components) the carrier amplitude and phase on the gaussian plane as each preamble symbol is received.

Without any power control of the transmission and the power transmitted by the mobile phone is constant at each time slot, it can be indicated that the received preamble symbols represent a change of the transmission path. If the spacing between the preamble symbols, i.e., the length of the time slot, can be considered to be much shorter than the fading frequency, the trajectory of the preamble symbols describes a flat curve. However, mobile phones with cdma systems operate to control the transmit power. Therefore, the trajectory of the received preamble symbol cannot be represented by a smooth curve.

In order to eliminate the adverse effect on the mobile phone transmission power control and thus represent only the change in the transmission path, the mobile communication system of the present embodiment operates to correct the amplitude of the received preamble symbol based on the history of the previous transmission power control. For example, in the third slot shown in fig. 3, a change of a transmission path in the fifth slot is predicted by using the pilot signals "r 0" and "r 1" in the current slot (here, the third slot) and a slot two slots before the current slot, i.e., in the first slot, using the pilot signals "r 2" and "r 3".

If set at the current time slot, i.e. in the third time slot, the power transmitted by the mobile telephone is 1dB lower than the power transmitted by the mobile telephone in the first time slot two time slots earlier. In this assumption, by correctly changing the pilot signals 'r 0' and 'r 1' received at the third slot to 'r 0' and 'r 1' whose amplitudes are increased by 1dB, it is possible to eliminate the adverse effect of the transmission power control on all the pilot codes used for prediction. The pilot signals "r 0 '" and "r 1'" and the pilot signals "r 2" and "r 3" whose amplitudes are corrected are points for deducing or linearly predicting a pilot signal on the gaussian plane at a time slot two slots later than the third time slot, i.e., the fifth time slot. By comparing the predicted power value with the reference value, the transmission power control symbol 116 is generated in such a manner that the difference is reduced to the minimum value. This transmit power control symbol 116 is transmitted from the base station to the mobile phone in the next slot to the third slot, i.e., the fourth slot. The mobile phone operates to increase or decrease the transmit power in the next slot to the fourth slot, i.e., the fifth slot, in accordance with the indication given by the received transmit power control symbol.

Fig. 4 is an explanatory diagram showing the amplitude correction and prediction on the gaussian plane in the present embodiment. In fig. 4, the axis of abscissa represents the component I as an in-phase component, and the axis of ordinate represents the component Q as a quadrature component. A circle 401 indicated by long and short lines alternately indicates a reference value for transmission power control. The preamble symbols (in-phase added symbols) are denoted by "r 1" and "r 2" in the first slot. The preamble symbol at the third slot is represented by "r 3" and "r 4". The transmit power is controlled between the first and third time slots. This control results in a change in the transmit power of the mobile telephone. Thus, the amplitudes "r 2" and "r 3" of the preamble symbols are discontinuous.

In fig. 4, assuming that the preamble symbols "r 1 '" and "r 2'" are amplitude corrected preamble symbols "r 1" and "r 2", the power transmitted by the mobile phone in the first time slot is equal to the power transmitted by the mobile phone in the third time slot. By correcting the amplitude, the adverse effects of the mobile phone transmit power control can be eliminated. The trace of the preamble symbol shown by the continuous arrow in fig. 4 is a smooth curve. "r 5 #" and "r 6 #" are preamble symbols predicted by using the preamble symbols "r 1", "r 2", "r 3", and "r 4" at the fifth slot. These pilot symbols "r 5 #" and "r 6 #" greatly exceed the reference values represented by circle 401. Therefore, the transmission power of the mobile phone in the fifth time slot is reduced by controlling. This control thus enables the pilot code symbols "r 5" and "r 6" actually received at the fifth slot to approach the reference values indicated by crosses on the circle 401. The transmission power is controlled by using a conventional code division multiple access system so that the received level is measured only at the third time slot, the magnitude of the measured value is compared with the magnitude of the reference value, and the power transmitted by the mobile phone is corrected according to the comparison result. Assuming that this conventional method is applied to the case shown in fig. 4, the pilot code symbols "r 3" and "r 4" approximately coincide with points on the circle 401, and thus the received level at the third slot also coincides with the reference value. Therefore, an indication that the transmission power is not changed is given in the fifth slot. As a result, the power received in the fifth slot is changed to values indicated by pilot symbols "r 5 #" and "r 6 #", which are greatly deviated from the reference value. Therefore, the power actually received in the fifth slot severely interferes with another channel.

In addition, different methods may be used to predict the preamble signal in the next slot using the amplitude-corrected preamble symbol in the next slot, and the mobile communication system of the present embodiment uses the method (1) mentioned below but may use the methods (2) and (3) instead.

(1) A prediction method by linear extrapolation using pilot code symbols located at both ends of a slot.

(2) A method of prediction by obtaining a straight line whose most recently received amplitude is the minimum mean square error of the corrected N-directed code symbols and extrapolating the straight line.

(3) A prediction method of linear prediction by using N pilot symbols whose latest received amplitude is corrected. This method uses the minimum mean square error of the preceding short time pilot code symbols.

Hereinafter, these methods will be described. To simplify the description, it is assumed that in-phase-added preamble symbols are obtained at regular intervals. The nth pilot symbol is "r (n)", and the predicted value is "r (n #"). "r (n)" and "r (n) #" are complex numbers. Therefore, to represent these components separately, the index I is added to the in-phase component and the index Q is added to the quadrature component. That is, these complex numbers are expressed as follows:

r(n)＝r_I(n)+j×r_Q(n)

r(n)#＝r_I(n)#+j×r_Q(n)#

prediction can be easily performed using linear extrapolation of the pilot code symbols located at both ends of a slot, as shown in (1) of the present embodiment.

r(n)#＝2×r(n-1)-r(n-2)

The description will be directed to a prediction methodThe method is implemented by obtaining a straight line of the minimum mean square error of the most recently received amplitude-corrected N-directed code symbols and extrapolating the straight line, as shown in (2). This straight line of least squares error is obtained by reducing the following value to a minimum_I、b_I、a_QAnd b_QTo obtain the final product. That is, for the in-phase component (I component) and the quadrature component (Q component), the abscissa axis is time and the ordinate axis is the in-phase and quadrature components. On this plane, a linear approximation of least mean square is performed. The straight line obtained has a at the point in time n_I(or-a)_Q) Gradient of (a) and (b)_I(or b)_Q) The value is obtained.

∑_i＝1-N{r_I(n-i)-(a_I×i+b_I)}²

The predicted values can be expressed as follows:

r_I(n)#＝b_I＝6/N(1-N)×∑_i＝1-N{r_I(n-i)×-(i-(2N+1)/3}

r_Q(n)#＝b_Q＝6/N(1-N)×∑_i＝1-N{r_Q(n-i)×-(i-(2N+1)/3}

if N is "2", this is in accordance with the extrapolation method shown in (1) of the present embodiment.

Next, description will be made with respect to a linear prediction method using the N preamble symbols whose latest received amplitude is corrected. The predicted values in this approach can be expressed as follows:

r(n)#＝-∑_i＝1-N{ai×r(n-1)}

where "a 1, a 2.. aN" are linear prediction coefficients and are used to reduce the expected value of the minimum mean square error. This expected value is expressed as follows:

E[|r(n)-r(n)#|²]

＝E[|E_i=0-N{ai×r(n-i)}|]

＝E_i＝0-N∑_j＝0-nai^*×aj×E[r(n-i)^*×r(n-j)]

wherein "a 0" is 1 and^*represents the conjugate value of x.

The linear prediction coefficient can be obtained by solving only the following N-dimensional homogeneous equation (ordinary equation).

E_i＝0-N{ai×E[r(n-j)^*×r(n-i)]}＝0；j＝1-N

Since the short-time transmit path is considered stable, the following expected values can be replaced with short-time averages.

E[r(n-j)^*×(n-i)]

First transformation of

Figure 5 shows the receiving part of a base station provided in a first variant of the invention. The structure of the transmitting part of the base station and the mobile phone are the same as those of the foregoing embodiment shown in fig. 1 and 2. Therefore, the structure will not be explained here. Code division multiple access systems can achieve multipath diversity by using the multipath characteristics of the transmit path. The receiving section 501 assists the receiver in multipath diversity (so-called RAKE receiver).

The receiving section 501 comprises a radio receiver 503 for converting a radio band received signal 502 into a complex baseband signal consisting of an in-phase component and a quadrature component. The complex baseband signal is provided to an inverse diffusion circuit 505. The despreading circuit 505 is operated to despread the code division and multiplexed composite baseband signals in order to extract the main channel signal. The output of the inverse diffusion circuit 505 is provided to a demultiplexing circuit 506. The demultiplexing circuit 506 is operative to separate the input signal into a pilot symbol (PL) portion and a data portion. The pilot symbols are input to a pilot symbol in-phase adder circuit 507.

The pilot symbol in-phase addition circuit 507 operates to add pilot symbols received in time series in-phase to enhance the signal-to-noise power ratio of the pilot symbols. The output of the pilot symbol in-phase addition circuit 507 is supplied to an amplitude correction circuit 508. The previous transmission power control symbol (TPC symbol) 511 obtained from the memory is input to the amplitude correction circuit 508, and the amplitude of the correction pilot symbol is operated in accordance with the control value of the previous transmission power.

The preamble signal prediction circuit 512 operates to extrapolate or linearly predict preamble symbols whose current and previous amplitudes are corrected on the gaussian plane for slot prediction for controlling transmit power.

The output of the prediction circuit 412 is applied to a first synthesis circuit 513. The first combining circuit 513 operates to calculate the sum of the powers of the bootstrap symbols predicted by multiple RAKE fingers 514, each RAKE finger 514 including an inverse spreading circuit 505, a demultiplexing circuit 506, a bootstrap symbol in-phase adding circuit 507, and a prediction circuit 512, all of which are described above, and a bootstrap symbol interpolation and synchronization detection circuit 521, which will be described below. The output of the first combining circuit 513 is applied to a comparing circuit 515. The comparison circuit 515 operates to compare the sum with a reference value 516. The result of the comparison is supplied to a transmit power control circuit 517, where transmit power control symbols 518 are generated. Symbol 518 represents the increase and decrease in the transmit power of the mobile phone. Symbols 518 are stored in storage 509.

On the other hand, the data separated by the demultiplexing circuit 506 is input to the preamble symbol interpolation and synchronization detection circuit 521. This circuit 521 is operated to interpolate the preamble symbols obtained by in-phase addition of the preamble symbols located at both ends of the slot and use the interpolation result as a reference signal for synchronization detection. The detected signal output from the detection circuit 421 is applied to the second preferred integrated circuit 522. The second combining circuit 522 performs diversity combining on the detected signals from all RAKE fingers 514. The synthesized signal is supplied from the second synthesizing circuit to the determining circuit 523 for detecting the detection signal that has been synthesized. Then, the circuit 523 is operated to output the received data 525.

If the present invention is applied to the RAKE receiver used in the first transform, each RAKE finger performs the same procedure as above.

Second transformation

Fig. 6 shows a receiving section of a base station used in a second embodiment of the present invention. In the description of the foregoing embodiment and the first variation, reference has been made to receiving a signal containing pilot code symbols (PL) buried at both ends of each slot. A second variation of the invention IS to apply the invention to a north american standard system (TIA IS95) having the aforementioned code division multiple access system. In this north american standard system, the signal is orthogonally modulated using 64 or 26 walsh codes 64-ary on the uplink and then spread using PN (pseudo noise) codes. This north american standard system does not add a pilot symbol in every slot. Thus, the system cannot build the pilot symbols based on the prediction. However, 64-ary quadrature modulation using 6 bits as one symbol is used to improve the signal/noise power ratio as one symbol. Which means that prediction based data symbols are feasible. Here, the description about the second transformation of the present invention refers to a signal length of 64. The signal length is not necessarily limited to this value. Generally, larger values will yield better results.

The receiving part 60 of the base station shown in fig. 6 provides a radio receiver 603 for converting the received signal 602 in the radio frequency band into a complex baseband signal consisting of an in-phase component and a quadrature component. The complex baseband signal is provided to the inverse diffusion circuit 605. The code division and multiplexed baseband signal is despread by operating the despreading circuit 605 to extract a signal of a primary channel. The output of the inverse diffusion circuit 605 is applied to a fast hadamard transform circuit 606. The circuit 606 operates to derive a correlation value (64 signal) from the 64 active walsh code. Then, a signal having the maximum power is selected by the selection circuit 607 operating.

Next, the amplitude of the correlation value selected by the selection circuit 607 is corrected by the amplitude correction circuit 608 according to the transmission power control symbol 611. Symbol 611 represents the pre-transmit power control value read out by the reservoir 609. The output of the amplitude correction circuit 608 is input to a prediction circuit 612. The correlation value signal whose current and front amplitude have been corrected on the gaussian plane, in effect, the in-phase component on the real axis and the quadrature component on the imaginary axis, is extrapolated or linearly predicted by the prediction circuit 612, and a signal point is predicted at a slot in which the transmission power is controlled. The amplitude of the predicted signal point is applied to a comparison circuit 613 where the amplitude is compared with a standard value 614. A transmit power control symbol 616 is generated by the transmit power control circuit 615 to indicate an increase and decrease in the transmit power of the mobile phone based on the comparison. This symbol 616 is stored in storage 609. The symbol 611 is used in the amplitude correction circuit 608 and is provided to a transmitting part (not shown) by which it is transmitted to the mobile telephone.

On the other hand, the output of the fast hadamard transform circuit 606 is also input to the squaring circuit 618. The power of each input 64 correlation value is calculated by a squaring circuit 618. The maximum power of the calculated power is detected by the maximum value detection circuit 619 and a list of relevant values of the maximum power is provided. The maximum value and the directory are input to a determination circuit 621 and determined therein. The received data 622 is then output through circuitry 621. The decision circuit 621 includes a de-interleaving circuit and a soft decision viterbi decoder. The list of correlation values is provided to the selection circuit 607 and used as a selection therein.

The mobile communication system of the second transformation is different from the aforementioned embodiment and the first transformation in that a correlation value for the maximum amplitude is used instead of the in-phase-added pilot code symbol. But are identical to them in terms of amplitude correction and prediction. The mobile communication system can be applied to a RAKE receiver as in the first transformation.

Many different embodiments of the invention can be made without departing from the spirit and scope of the invention. It must be understood that the invention is not limited to the particular embodiments described in the specification, which are defined by the appended claims.

Claims

1. A mobile communication system for communicating in a direct spread code division multiple access system; comprises the following steps:

a base station; and

a plurality of mobile devices;

wherein the base station comprises:

radio receiving means for receiving a signal of a radio frequency band and converting the signal into a complex baseband signal;

an inverse spreading means for extracting a main channel signal by copying the code division of the composite baseband signal and the multiplexed spreading code after the conversion;

demultiplexing means for separating the output of said despreading means into pilot symbols and data symbols; means for performing in-phase addition of said adjacent pilot symbols, wherein pilot symbols are received in a time sequence from said demultiplexing means, for enhancing signal-to-noise power ratio;

means for correcting the magnitude of said in-phase added preamble symbols by increasing or decreasing the magnitude of said in-phase added preamble symbols in accordance with an increase or decrease indicated by a previous transmit power control value;

means for predicting a reception signal point of the preamble symbol when next control of transmission power is performed by the preamble symbol whose amplitude is corrected by the correction means;

means for comparing a received electric power of the preamble symbol predicted by the predicting means with a preset reference value;

means for generating said control value for the transmission power when performing a next control of the transmission power according to a comparison result given by said comparing means;

a memory for storing the transmission power control value generated by the generating means and supplying the control value as the preceding transmission power control value to the correcting means; and

a circuit for controlling the transmit power, the circuit having means for transmitting the transmit power control value; and

wherein the plurality of mobile units are connected to the base station by radio waves of a frequency so that the mobile units are controlled and maintain the signal electric powers received by the base station to be identical to each other according to the transmission power control value.

2. A mobile communication system for communicating in a direct spread code division multiple access system and an M-ary quadrature amplitude modulation system; the method comprises the following steps:

a base station; and

a plurality of mobile devices;

characterized in that said abutment comprises:

a radio wave receiving device for receiving a signal of a radio frequency band and converting the signal into a complex baseband signal;

an inverse diffusion means for extracting a signal of a main channel by copying the code division of the composite baseband signal and the multiplexed diffusion code after the conversion;

quadrature modulation means for calculating a correlation value of the complex baseband with each M orthogonal code, M being a positive integer;

means for selecting one of said M-related values such that said selected value produces a maximum electrical power;

means for correcting said magnitude of correlation value selected by said selecting means by increasing or decreasing said magnitude of correlation value in accordance with an increase or decrease indicated by a previous transmit power control value;

means for predicting a signal point when next control of transmission power is performed by the amplitude-corrected correlation value;

means for comparing the amplitude of the predicted signal point with a predetermined reference value;

means for generating a transmission power control value when performing the next control of transmission power, based on a comparison result generated by the comparing means;

a storage for storing the transmission power control value generated by the generating means and supplying the control value to the amplitude correcting means as the previous transmission power control value; and

wherein the plurality of mobile units are connected to the base station by radio waves of a frequency so that the mobile units are controlled and maintain the signal electric powers received by the base station to be identical to each other according to a transmission power control value transmitted by the base station.

3. A method for controlling transmission power in a mobile communication system communicating in a direct spread code division multiple access manner, comprising the steps of:

receiving a wireless frequency band signal and converting the signal into a composite baseband signal;

extracting a signal of a main channel by copying the code-divided and multiplexed spreading code of the composite baseband signal after the conversion;

separating the decimated signal into pilot code symbols and data symbols;

adding adjacent pilot code symbols input consecutively in-phase to increase a signal/noise power ratio;

correcting the amplitude of said in-phase added preamble symbols by increasing or decreasing the amplitude of said in-phase added preamble symbols in response to a previous increase or decrease indicated by the transmit power control value;

predicting a received signal point of the preamble symbol at the time of next control of transmission power by using the corrected preamble symbol;

comparing the predicted received electric power of the preamble symbol with a preset reference value;

generating a transmission power control value when next control is performed on the transmission power according to the comparison result;

storing said generated transmit power control value as said transmit power control value previously; and

transmitting the transmission power control value to a plurality of mobile devices connected by radio waves at a certain frequency and controlling transmission power according to the transmission power control value so that the transmission powers received by the base stations are equal to each other.

4. A method for controlling transmission power in a mobile communication system for communication in a direct-diffusion code division multiple access scheme and an M-valued orthogonal modulation scheme, comprising the steps of:

extracting a signal of a main channel by inversely spreading the code-divided and multiplexed complex baseband signal after the conversion;

calculating a correlation value between the complex baseband signal and each M orthogonal code, M being a positive integer;

selecting a value for obtaining a maximum electric power from the M-related values;

correcting the magnitude of said selected correlation value by increasing or decreasing the magnitude of said selected correlation value in accordance with an increase or decrease indicated by a previous transmit power control value;

predicting a signal point when next transmission power control is performed by using the corrected amplitude-related value signal;

comparing the amplitude of the predicted signal point with a preset reference value;

generating a transmission power control value when controlling the transmission power according to the comparison result;

storing said generated transmit power control value as said previous transmit power control value; and

transmitting the transmission power control value to a plurality of mobile devices connected by radio waves at a certain frequency and controlling the transmission power according to the transmission power control value so that the transmission powers received by base stations are equal to each other.