JP4231058B2 - Speed estimation apparatus and method in mobile communication - Google Patents

Description

  The present invention relates to an apparatus and a method for estimating a moving speed of a counterpart station in a mobile communication system.

  As a channel multiplexing method in a mobile communication system, a time division multiple access (TDMA) method, a frequency division multiple access (FDMA) method, or the like is conventionally used. However, the development of a scheme with higher frequency utilization efficiency is expected, and in particular, the direct sequence code division multiple access (DS-CDMA) scheme can realize a large communication capacity. It is regarded as promising.

  The DS-CDMA system is a kind of spread spectrum communication. In this method, the transmission side uses the same frequency for multiple channels and multiplies the data signal by a wideband spreading code that is independent for each channel, so that the spectrum of the data signal is widened and transmitted, and the same spreading is performed on the reception side. Multiply the code to restore the data signal for each channel. Multiplication of the spreading code on the receiving side is called despreading. When this DS-CDMA system is applied to mobile communication, a searcher function, a transmission power control function, an absolute synchronous detection function, and the like are indispensable.

  The searcher function is a function that detects the despread code timing, which is the timing for detecting the transmission path and despreading, and the transmit power control function is a near / far problem due to the distance difference between the mobile station and the base station. And a function of changing transmission power against instantaneous fluctuation (fading) due to multipath. The absolute synchronous detection function is a function for performing absolute synchronous detection by adding a pilot signal to a data signal and transmitting it in order to obtain a required BER (bit error rate) with lower transmission power.

  In mobile communication, stable communication is required in a variety of dynamically changing environments such as a process in which a mobile station shifts from a stationary state to a high-speed moving state and a process in which the mobile station transitions from an urban environment to a suburban environment. Is done. In particular, in a multipath environment involving reflected waves and delayed waves that have passed through a plurality of transmission paths, fading (instantaneous value fluctuation) occurs due to interference, so that countermeasures are indispensable in mobile communications. Also in the DS-CDMA system, effective fading countermeasures are desired in connection with the above-described functions.

However, there are the following problems in DS-CDMA mobile communication.
In general, there are optimum values for the parameters of each part of the communication device for fading that occurs during communication. However, since the fluctuation speed of fading varies depending on the moving speed (or fading pitch) of the mobile station, each parameter Is not always set to an optimum value. Therefore, when the parameters are not optimized, the reception characteristics are degraded, and the channel capacity is degraded. Further, in order to optimize each parameter, it is necessary to estimate the moving speed of the mobile station in the base station.

  However, in the DS-CDMA system, since a plurality of channels are multiplexed on the same frequency, the moving speed based on the measurement of the received electric field strength is different from the TDMA or FDMA system known as other multiplexing systems. Is difficult to estimate.

  An object of the present invention is to provide an apparatus and method for estimating the moving speed of a mobile station in spread spectrum type mobile communication such as CDMA.

FIG. 1 is a principle diagram of a speed estimation apparatus according to the present invention. The speed estimation apparatus in FIG. 1 includes an input unit 1, a reception unit 2, a power combining unit 3, and a speed estimation unit 4.
According to the first principle of the present invention, the speed estimation apparatus is used in mobile communication that performs transmission power control between a transmitting station and a receiving station. The input unit 1 inputs a transmission power control command sent from the receiving station to the transmitting station, and the speed estimation unit 4 estimates the moving speed of the receiving station using the transmission power control command and corresponds to the estimated moving speed. Output a control signal.

  The transmitting station and the receiving station respectively correspond to a base station or a mobile station in mobile communication. For example, in the DS-CDMA system, control is performed to optimally set the transmission power with respect to the distance difference between the base station and the mobile station and fading that occurs in the multipath transmission path.

  In this control, a transmission power control command is generated on the reception side and sent to the transmission side. On the transmission side, the transmission power is changed based on the received transmission power control command. Since the value of the transmission power control command changes following instantaneous fluctuations such as fading accompanying movement of the mobile station, the movement speed can be estimated by detecting the change. The speed estimation means 4 estimates the moving speed of the receiving station based on the change in transmission power control command and the accumulated value.

  Further, according to the second principle of the present invention, the speed estimation device is used in mobile communication performed between a transmitting station and a receiving station. The receiving unit 2 extracts a desired wave signal from the received signal, and the power combining unit 3 generates a desired wave power from the desired wave signal. Then, the speed estimation unit 4 estimates the moving speed of the transmitting station using the desired wave power and outputs a control signal corresponding to the estimated moving speed.

  For example, in the DS-CDMA system, the received signal has a spectrum spread state, and a plurality of channels are multiplexed. For this reason, before despreading, a signal subjected to fading from the transmitting station cannot be observed. However, by performing despreading, a desired wave can be extracted, and the moving speed can be estimated by observing the influence of fading.

  The receiving unit 2 despreads the received signal to extract a desired wave signal, and the power combining unit 3 generates desired wave power from the extracted signal. And the speed estimation means 4 estimates the moving speed of a transmitting station based on the sample value of desired wave power.

  Actually, since the base station and mobile station have both functions of the transmitting station and the receiving station, respectively, use the transmission power control command and the desired signal power to estimate the moving speed of the partner station. Can do. Moreover, if the control signal output from the speed estimation means 4 is used, it is possible to set the parameters of the communication device to optimum values for fading.

  For example, the input unit 1 in FIG. 1 corresponds to the TPC command accumulation unit 233 in FIG. 10, the reception unit 2 corresponds to the reception unit 192 and the demodulation unit 193 in FIG. 4, and the power combining unit 3 in FIG. Corresponding to the power combiner 241, the speed estimator 4 corresponds to the fading pitch estimator 231 in FIG. 5, the fading pitch estimator 232 in FIG. 10, and the fading pitch estimator 242 in FIG. 13.

  According to the present invention, it is possible to estimate the moving speed of a mobile station by using a transmission power control function or a despreading function in mobile communication such as CDMA. Further, various parameters of the communication apparatus can be dynamically controlled according to the estimated moving speed, which contributes to improvement of reception characteristics and channel capacity.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In the present embodiment, the moving speed is estimated using the TPC command used in transmission power control (TPC) in the DS-CDMA system and the reception correlation value of the received wave. If the moving speed is obtained, the values of parameters such as the searcher, the transmission power control unit, and the phase estimation unit in the synchronous detection can be set to be optimal for the generated fading.

First, a DS-CDMA communication apparatus will be described. FIG. 2 is a principle diagram showing a concept of a transmitter in the DS-CDMA system, and FIG. 3 is a principle diagram showing a concept of a receiver.
In FIG. 2, transmission data carried on a carrier wave is multiplied by a spreading code from a code generator 11 by a multiplier 12 and transmitted from an antenna 14 through an amplifier 13. As the logic of the multiplier 12, any one such as exclusive OR (EXOR) can be used.

  In FIG. 3, the received signal input from the antenna 21 passes through the amplifier 22, is converted to a baseband signal (digital signal) by the conversion unit 23, and is converted to original data by the demodulation unit 24.

  The demodulator 24 includes a plurality of sets of a code generator 31, a multiplier 32, and a detector 33, and each code generator 31 generates a despread code at a different timing. As the despreading code, the same spreading code used for transmission is usually used. The multiplier 32 multiplies the signal by the despread code to return the spectrum to the original band, and the detection unit 33 detects the despread signal. The adder 34 synthesizes and outputs the outputs of the detectors 33.

  The searcher 25 is provided to match the timing of spreading on the transmission side and despreading on the reception side. The searcher 25 detects the signal delay of each path in the multipath environment from the output signal of the conversion unit 23, and controls the timing of each code generator 31 so that despreading is performed at the timing according to each path. . Thus, the demodulator 24 outputs data synthesized from signals that have passed through a plurality of paths.

  Next, a configuration for estimating the moving speed will be described. Here, the description will be given mainly on the assumption that the moving speed of the mobile station is estimated in the base station, but a similar configuration can be provided in the mobile station. In that case, the relative moving speed of the base station with respect to the mobile station is estimated.

  As a method of estimating the moving speed, there are a method using a TPC command from a mobile station and a method using desired wave power. First, an estimation method using a TPC command will be described. In the DS-CDMA system, for example, transmission power control as shown in FIG. 4 is performed by a transmission power control unit on the reception side with respect to a distance difference between a base station and a mobile station and fading that occurs in a multipath transmission path. Is done.

  4, the antenna 191 corresponds to the antenna 21 of FIG. 3, the receiving unit 192 corresponds to the amplifier 22 and the conversion unit 23 of FIG. 3, and the demodulation unit 193 corresponds to the demodulation unit 24 of FIG. Demodulation section 193 performs despreading and rake combining of the baseband signal from reception section 192, and outputs a reception correlation value. Here, the reception correlation value means a signal after despreading.

  The transmission power control unit 194 includes a SIR estimation unit 195 and a comparison unit 196. The SIR estimation unit 195 estimates a signal-to-interference ratio (SIR) from the received correlation value, and the comparison unit 196 compares the estimated SIR value with the target SIR value. When the estimated SIR is larger than the target SIR, a TPC command for reducing transmission power is generated. When the estimated SIR is smaller than the target SIR, a TPC command for increasing transmission power is generated. Then, it is transmitted to the transmission side to control the transmission power.

  When receiving a TPC command from the reception side, a transmission power control unit (not shown) provided on the transmission side increases or decreases the transmission power value accordingly. According to such control, the transmission power on the transmission side can be controlled so that the SIR on the reception side is optimal.

  Since the TPC command changes following instantaneous fluctuations such as fading, the movement speed can be estimated by detecting the rate of change of the TPC command. However, in the case of very fast fading, the TPC command cannot follow, and in a region where the moving speed is higher than a certain moving speed, the rate of change becomes constant and becomes saturated. This area is usually determined by the variable width and variable time width of the TPC command.

  FIG. 5 shows a configuration for estimating a moving speed using a generated TPC command in a system that performs transmission power control as described above. The fading pitch estimation unit 231 in FIG. 5 is provided on the transmission side, detects a change in the input TPC command, and estimates the moving speed on the reception side.

  For example, when a TPC command for increasing the transmission power is represented by “+1” and a TPC command for decreasing the TPC command is represented by “−1”, the fading pitch estimation unit 231 compares two consecutive TPC commands, and the same The number of times the code data continues twice is counted, and the speed is estimated based on the count value. In general, the sign of the TPC command does not change much when the moving speed becomes slow, and is frequently reversed when the moving speed becomes fast. Therefore, the number of times the same code continues tends to increase as the moving speed decreases and decreases as the moving speed increases.

  For example, the count value (SUM) is 7 in the TPC command sequence shown in FIG. 6, and the count value is 4 in the TPC command sequence shown in FIG. Therefore, it is estimated that the moving speed is faster in the state of FIG. 7 than in the state of FIG. By dividing the range of the count value into several parts, the moving speed can be estimated in a plurality of stages. Further, the moving speed may be expressed as an appropriate function of the count value.

  8 and 9 show other counting methods in the TPC command strings of FIGS. 6 and 7, respectively. Even when such a counting method is used, the moving speed can be estimated in the same manner as in the above-described counting method.

  In such a speed estimation method, when the transmission frequency of the TPC command differs depending on the system, the number of times that the data with the same code is continued twice is not necessarily optimal for speed estimation. Therefore, this method is generalized so that the number of times the data with the same code is repeated N times is counted, and the optimum count value for the system is used for estimation. The greater the frequency of TPC command transmission, the greater the value of N should be.

  Next, FIG. 10 shows a configuration for estimating the moving speed using the accumulated value of the TPC command. The TPC command accumulating unit 233 in FIG. 10 is provided in the transmission power control unit on the transmission side, and sequentially adds the values of TPC commands that are continuously input, and the addition result is used as the accumulated value. On the transmission side, the transmission power value is changed according to the accumulated value. The fading pitch estimation unit 232 receives the accumulated value from the TPC command accumulation unit 233 and estimates the moving speed.

  As shown in FIG. 11, the fading pitch estimator 232 samples the accumulated value of the TPC command at a constant sampling interval, and calculates the absolute value (A, B, C, D, E, F, G, H, I, J, K) are added for a certain time, and the moving speed is estimated from the added value (SUM).

  Since the increase / decrease of the accumulated value becomes more intense as the moving speed is faster, the added value becomes larger. As the moving speed is slower, the increase / decrease of the accumulated value becomes gentler, so the added value becomes smaller. Accordingly, the moving speed can be estimated in a plurality of stages by dividing the range of the added value of the difference between the sample values into several. Further, the moving speed may be expressed as an appropriate function of the added value.

  Further, when adding the difference between the sample values for a certain period of time, a moving average of these values may be taken and the moving speed may be estimated from the average value. By taking the moving average, it is possible to estimate the fluctuation of the moving speed more precisely.

  Further, as shown in FIG. 12, the fading pitch estimation unit 232 can count the number of times that the accumulated value of the TPC command crosses a certain reference value for a certain time, and can estimate the moving speed from the count value (SUM). . Here, the cumulative value crossing the reference value means that the cumulative value exceeds the reference value or the cumulative value falls below the reference value. The count value increases as the moving speed increases, and the count value decreases as the moving speed decreases. Therefore, if this count value is used, the moving speed can be estimated in the same manner as in the case of the added value of the difference between the sample values described above.

  Further, when counting the number of crossings, a moving average of count values for a fixed time may be taken and the moving speed may be estimated from the average value. By taking the moving average, it is possible to estimate the fluctuation of the moving speed more precisely.

  The above is the method for estimating the moving speed using the TPC command. As another method, there is a method using the desired wave power obtained from the reception correlation value. In the DS-CDMA system, the received signal before despreading has a spectrum spread state, and a plurality of channels are multiplexed. For this reason, before despreading, a signal subjected to fading from the target mobile station cannot be observed. However, by performing despreading, the desired wave of the target can be taken out, and the moving speed can be estimated by observing the fading.

  FIG. 13 shows a configuration for estimating a moving speed using desired wave power. The power combiner 241 combines desired wave power from the reception correlation value corresponding to the output of the demodulator 24 of FIG. The fading pitch estimation unit 242 estimates the moving speed based on the combined desired wave power.

  As shown in FIG. 14, fading pitch estimation section 242 measures the reception correlation value and samples the desired wave power at regular intervals. Each sample value (SP1, SP2,..., SPi, SPj) of desired wave power is generated from n consecutive received correlation values (1, 2,..., N).

  By the way, in the detection unit 33 of FIG. 3, phase estimation is required when performing synchronous detection of a signal. When an interpolated synchronous detection circuit is used, phase estimation is performed using a pilot signal, which is a known signal inserted between data signals. As a method of generating the desired wave power from the reception correlation value of the signal including the pilot signal, for example, there are three methods shown in FIGS.

  In FIG. 15, the rake combining unit 243 outputs a reception correlation value of a desired wave corresponding to a specific channel, and the pilot extraction unit 244 extracts a reception correlation value of a pilot signal that is a known signal. The power combiner 241 combines the extracted reception correlation values to generate a sample value of the desired wave power. Here, each of the n reception correlation values is squared, and the sum of the obtained values is taken as a sample value.

  In FIG. 16, the power combiner 241 performs amplitude combination of the extracted reception correlation values to generate a sample value of the desired wave power. Here, an average value of n reception correlation values is obtained and squared to obtain a sample value.

  In FIG. 17, pilot signal extraction is not performed, and power combining section 241 performs power combining of the received correlation values of the pilot signal and data signal output from rake combining section 243 to sample desired wave power. Generate a value. Here, each of the n reception correlation values is squared, and the sum of the obtained values is taken as a sample value. The method of FIG. 17 can be applied to any signal regardless of whether a pilot signal is included.

  The fading pitch estimation unit 242 in FIG. 13 adds the absolute value of the difference between two consecutive sample values for a certain period of time in the same way as the method shown in FIG. 11 based on the sample value of the desired wave power thus generated. The moving speed is estimated from the added value.

  Since the increase / decrease in the desired wave power increases as the moving speed increases, the added value increases. The increase / decrease in the desired wave power decreases as the moving speed decreases, so the added value decreases. Accordingly, the moving speed can be estimated in a plurality of stages by dividing the range of the added value of the difference between the sample values into several. Further, the moving speed may be expressed as an appropriate function of the added value.

  Further, when adding the difference between the sample values for a certain period of time, a moving average of these values may be taken and the moving speed may be estimated from the average value. By taking the moving average, it is possible to estimate the fluctuation of the moving speed more precisely.

  Further, as shown in FIG. 18, the fading pitch estimation unit 242 counts the number of times that the desired wave power sample value intersects a certain reference value for a certain time, and estimates the moving speed from the count value (SUM). it can. The count value increases as the moving speed increases, and the count value decreases as the moving speed decreases. Therefore, if this count value is used, the moving speed can be estimated in the same manner as in the case of the added value of the difference between the sample values described above.

  Further, when counting the number of crossings, a moving average of count values for a fixed time may be taken and the moving speed may be estimated from the average value. By taking the moving average, it is possible to estimate the fluctuation of the moving speed more precisely.

  The estimation method using the TPC command and the estimation method using the desired wave power have been described above, but there is a certain correlation between the estimation results obtained by these two methods. In general, when the moving speed is increased to some extent, transmission power control by the TPC command becomes impossible to follow, so that the rate of change of the TPC command generated on the receiving side becomes constant at a certain speed or higher.

  For this reason, in the method using the TPC command, the estimated speed value obtained based on the rate of change becomes a constant value at a certain speed or higher as shown in FIG. FIG. 19 shows the relationship between the fading pitch (fdT) of the generated fading and the speed estimation value. The fading pitch and the actual moving speed are closely related, and the moving speed increases as the fading pitch increases.

  On the other hand, in the method using the desired wave power, the speed estimated value shows a constant value below a certain speed, contrary to the method using the TPC command. This is because when the moving speed is low, the transmission power control by the TPC command is effective, and the value of the desired wave power becomes a constant value. When the moving speed is increased to some extent, the transmission power control is not effective and fluctuations in the desired wave power appear, so that the speed can be estimated.

  Therefore, it is desirable to estimate the moving speed by using these estimation methods in combination. For example, the estimated value based on the desired wave power is adopted in the region where the estimated speed value based on the TPC command is saturated, and the estimated value based on the TPC command is adopted in the region where the estimated velocity value based on the desired signal power is saturated. do it. By using the two methods in combination, it is possible to compensate for each other's drawbacks and expand the estimated range of the moving speed.

  For example, as shown in FIG. 20, the fading pitch estimation units 231, 232, and 242 described above estimate the moving speed of a mobile station by dividing it into a plurality of speed ranges, and output control signals corresponding to the respective speed ranges. . In FIG. 20, the estimated speeds are 5 (A (stationary state), B (0 to 40 km / h), C (40 to 80 km / h), D (80 to 120 km / h), and E (120 km / h <). Different control signals are output depending on the speed range to which the estimated speed belongs, classified into speed ranges of stages.

  Based on this control signal, the values of parameters such as the searcher, the transmission power control unit, and the phase estimation unit in the synchronous detection can be set to be optimum for the generated fading.

  In the embodiment described above, arbitrary hardware or firmware such as a DSP (digital signal processor) can be used as the circuit for estimating the moving speed and the circuit for setting various parameters of the communication device. Further, the parameters to be controlled are not limited to the parameters of the searcher function, the transmission power control function, and the absolute synchronous detection function, and other arbitrary parameters can be controlled similarly.

  Furthermore, the present invention can be widely applied not only to DS-CDMA communication but also to PSK (phase shift keying), PDC (personal digital cellular), and the like.

It is a principle figure of the speed estimation apparatus of this invention. It is a principle diagram of a transmitter. It is a principle diagram of a receiver. It is a block diagram of the transmission power control part of a receiver. It is a figure which shows the speed estimation by a TPC command. It is a figure which shows the 1st count result of a TPC command. It is a figure which shows the 2nd count result of a TPC command. It is a figure which shows the 3rd count result of a TPC command. It is a figure which shows the 4th count result of a TPC command. It is a figure which shows the speed estimation by the accumulated value of a TPC command. It is a figure which shows sampling of a cumulative value. It is a figure which shows the reference value of the cumulative value of a TPC command. It is a figure which shows the speed estimation by desired wave electric power. It is a figure which shows sampling of a reception correlation value. It is a figure which shows the 1st electric power composition. It is a figure which shows 2nd electric power composition. It is a figure which shows the 3rd electric power composition. It is a figure which shows the reference value of desired wave electric power. It is a figure which shows the relationship between two estimation methods. It is a figure which shows five steps of estimated speeds.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input means 2 Receiving means 3 Power synthesizing means 4 Speed estimation means 11, 31 Code generators 12, 32 Multipliers 13, 22 Amplifiers 14, 21, 191 Antenna 23 Converter 24, 193 Demodulator 25 Searcher 33 Detector 34 Addition 192 Receiver 194 Transmission power controller 195 SIR estimator 196 Comparator 233 TPC command accumulator 231, 232, 242 Fading pitch estimator 241 Power combiner 243 Rake combiner 244 Pilot extractor

Claims (8)

A speed estimation device in mobile communication performed between a transmitting station and a receiving station,
Receiving means for extracting a signal of a desired wave from the received signal;
Power combining means for generating desired wave power from the desired wave signal;
Based on an addition value obtained by sampling the desired wave power at a constant interval and adding a difference between two consecutive sample values for a certain period of time , a control signal corresponding to the estimated movement speed is estimated. A speed estimation device comprising: an output speed estimation means. The speed estimation apparatus according to claim 1, wherein the speed estimation unit obtains a moving average of the difference between the sample values and estimates the moving speed from the moving average. A speed estimation device in mobile communication performed between a transmitting station and a receiving station,
Receiving means for extracting a signal of a desired wave from the received signal;
Power combining means for generating desired wave power from the desired wave signal;
On the basis of the desired signal power to count the number of samples to the sample value crosses the reference value counted a predetermined time at regular intervals, the moving speed is estimated, it outputs a control signal corresponding to the moving speed estimated Speed estimation means to
A speed estimation device comprising: The speed estimation device according to claim 3, wherein the speed estimation unit obtains the count value by a moving average method. Receiving means for extracting a signal of a desired wave from a received signal in mobile communication;
Power combining means for generating desired wave power from the desired wave signal;
The desired wave power is sampled at a constant interval, the moving speed of the transmitting station is estimated based on an added value obtained by adding a difference between two consecutive sample values for a certain time , and a control signal corresponding to the estimated moving speed is output. And a speed estimation means. Receiving means for extracting a signal of a desired wave from a received signal in mobile communication;
Power combining means for generating desired wave power from the desired wave signal;
Based on a count value obtained by sampling the desired signal power at regular intervals and counting the number of times that the sample value crosses the reference value for a certain period of time, a control signal corresponding to the estimated travel speed is estimated. Output speed estimation means and
A receiver comprising: Mobile communication is performed between the transmitting station and the receiving station,
Generate desired signal power from the received signal at the receiving station,
A speed estimation method , wherein the moving speed of the transmitting station is estimated based on an addition value obtained by sampling the desired wave power at a constant interval and adding a difference between two consecutive sample values for a predetermined time . Mobile communication is performed between the transmitting station and the receiving station,
Generate desired signal power from the received signal at the receiving station,
The desired wave power is sampled at regular intervals, and the moving speed of the transmitting station is estimated based on a count value obtained by counting the number of times the sample value crosses a reference value for a certain time.
A speed estimation method characterized by the above.

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