KR100396287B1 - APPARATUS AND METHOD FOR Power Control IN CDMA SYATEM - Google Patents

Abstract

A forward power control apparatus of a mobile station of a code division multiple access communication system includes a searcher for capturing a specific common channel signal of a received forward link, and fingers for receiving specific common channel signals of at least two paths, the fingers being respectively At least two signal and interferometric fingers for measuring the strength of the signal and the interference signal of a specific common channel received through the corresponding path, combined with the signal and interference of each path output from the fingers through a multipath A signal-to-interference combiner for calculating the received signal-to-noise ratio, and a reverse channel transmitter for transmitting the power control information of the forward link determined using the signal-to-noise ratio.

Description

Apparatus and method for controlling power of code division multiple access communication system {APPARATUS AND METHOD FOR Power Control IN CDMA SYATEM}

The present invention relates to an apparatus and method for controlling power in a code division multiple access communication system, and more particularly, to an apparatus and method for controlling power by measuring a signal-to-interference ratio received on a forward link.

In the W-CDMA system, which is one of the current standards of IMT-2000, a low-speed transmission power control method is adopted. This is briefly described as follows. Under the command of the base station, the normal high speed power control can be stopped and the low speed transmission power control mode can be entered. In this mode, the power of the forward link transmitted to the mobile station is based on the power control ratio transmitted by the mobile station. In this case, the channel of the forward link may be DPDCCH / DPDCH. If there is no message to be transmitted by the mobile station, the transmission of the reverse link may be stopped and resumed to transmit the power control ratio every predetermined time.

The method for measuring the power control ratio of a mobile station currently in use is as follows. The mobile station measures the power of the forward common channel of the base station currently being serviced and calls it Q1. Here, a pilot channel of the forward link may be used as the forward common channel used for the measurement. The mobile station receives a signal of an adjacent base station, and sets this value to Qi (i = 2, ..., n) if this value is greater than a predetermined value Q1 / RSEARCH. Finally, the power control information transmitted from the mobile station to the base station is given by Equation 1 below.

(Q1 + Q2 + ........ + Qn) / Q1

The searcher of the mobile station may be used to measure the power control ratio as shown in Equation 1 above. However, the searcher of the mobile station is not able to search all adjacent base stations, and it is difficult to measure the actual signal-to-noise ratio of the forward link using the searcher information alone.

Meanwhile, the TPC bits are used to transmit the power control ratio on the reverse link. Since one power control ratio is transmitted in one frame, 30 (2BIT * 15 SLOT) TPC bits are used to transmit the power control ratio. Then, a code punctured by two bits in a bi-orthogonal code of (32, 6) is used as a power control command for transmitting a power control ratio. In addition, the normal high speed power control mode may be resumed from the low speed power control mode again by the command of the base station.

As shown in FIG. 1, the conventional power control ratio measurement has some problems. That is, if the mobile station is within a certain distance from the base station as shown in the shaded circle of Fig. 1, it is difficult to capture the signal of the neighboring base station because the signal received at the base station at the closest distance is received too large. Therefore, the power control ratio transmitted by the mobile station to the base station is almost 1 in most cases.

Another problem is the impact of multipath. The performance of the forward link in the code division multiple access scheme depends on what the multipath components are. That is, the performance of the forward link will vary greatly depending on the number of paths in the channel and the power distribution between the paths. However, the existing power control costs could not reflect this.

In FIG. 2, the value of the power control ratio measured using the conventional measuring method is plotted according to the distance from the base station. As the value of the power control ratio shown in FIG. 2, an inverse value was used in Equation 1 described above. However, it can be seen that the conventional measurement method does not reflect the power control ratio due to the change of the multipath.

In addition, in the current mobile communication system, the mobile station measures the performance of the forward link and reports it to the base station, and based on this, the base station can change the data rate of the forward channel or instruct the handoff of the mobile station. Currently, the value measured by the mobile station for this purpose is the ratio of the power of a specific forward common channel of the total received power. In this case, a pilot channel of a forward link may be used as a specific forward common channel. This is called Ec / Io of the pilot signal. As described above, this value is difficult to reflect the performance change due to multipath, and there is little change in the value near the base station.

Accordingly, an object of the present invention is to provide an apparatus and method for efficiently controlling the transmission power of a forward link of a code division multiple access system.

Another object of the present invention is to provide an apparatus and method for accurately measuring performance of a forward link in a mobile station in a code division multiple access communication system.

It is still another object of the present invention to provide an apparatus and method for improving low power control of a forward link channel in a code division multiple access system.

It is still another object of the present invention to provide an apparatus and method for allowing a mobile station to measure the performance of a forward link in a code division multiple access system.

It is still another object of the present invention to provide an apparatus and method for efficiently informing a base station of a channel status of a forward link in varying data rates of a forward link in a code division multiple access communication system.

It is still another object of the present invention to provide a receiver and a method for efficiently measuring a channel state of a forward link so that a mobile station can vary the data rate of the forward link in a code division multiple access communication system.

It is still another object of the present invention to provide an apparatus and method that can determine to perform a more efficient handoff in a code division multiple access communication system.

1 is a diagram illustrating a problem of conventional power control ratio measurement.

2 is a diagram showing a value of a power control ratio according to a distance from a base station when using a conventional measuring method.

FIG. 3A is a diagram showing a configuration for measuring a signal-to-noise ratio of a mobile station receiver in a code division multiple access communication system, FIG. 3B is a diagram showing a configuration of an interference signal measuring instrument in FIG. 3A, and FIG. Drawing

4 is a diagram illustrating a receiver structure of a code division multiple access communication system according to an embodiment of the present invention.

5 is a diagram illustrating a transmitter structure of a code division multiple access communication system according to an embodiment of the present invention.

6 is a diagram for explaining an operation of controlling transmission power according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In an embodiment of the present invention, in the code division multiple access communication system, the mobile station measures the signal-to-noise ratio of the forward common channel (PILOT) of the forward link so that the base station can efficiently control the transmission power of the forward link. Transmitting to the base station, the base station efficiently controls the transmission power of the channel transmitted to the mobile station using the received signal-to-noise ratio of the forward link. In addition, the embodiment of the present invention can be used to determine the handoff or change the data rate of the forward link channel using the received signal-to-interference ratio of the forward link.

First, the embodiment of the present invention proposes a method different from the conventional method for measuring the power control ratio. That is, in the conventional power control ratio, there is a region where it is difficult for the mobile station to capture signals from neighboring base stations, and it is difficult to reflect the situation of the forward channel according to the multipath. Therefore, an embodiment of the present invention proposes a method for measuring a power control ratio of a mobile station that can solve the above problems.

In an embodiment of the present invention, the mobile station measures the signal-to-noise ratio of the forward common channel for low speed power control. In this case, the mobile station may use a pilot channel as a forward common channel to measure the signal-to-noise ratio of the forward common channel. 3A to 3C show a structure of a mobile station receiver capable of measuring a signal-to-noise ratio of a pilot channel proposed in an embodiment of the present invention.

3A is a diagram illustrating a structure of measuring a signal-to-noise ratio in a receiver of a mobile station. That is, FIG. 3A illustrates an embodiment in which only a portion for measuring a signal-to-noise ratio is implemented in the structure of a finger of the mobile station and there is no data demodulator. However, a data demodulator may be added to this finger to add a signal and an interference value to the normal finger. The finger of FIG. 3A may include a time tracking unit.

Referring to FIG. 3A, the multiplier 311 despreads a received signal with a complex scrambling code and outputs the complex signal. The multiplier 313 multiplies the despread signal by a channelization code assigned to a pilot channel to extract a pilot channel signal. The accumulator 315 accumulates the pilot signal output from the multiplier 313 in a predetermined unit (for example, symbol unit), and the signal output from the accumulator 315 is converted into an energy value in the squarer 317 and then accumulates through the accumulator 317. The signal power Pi of the filer channel is output.

In addition, the signal output from the multiplier 311 is applied to the interference signal measuring unit 321 to extract the interference signal, the accumulator 323 is output as the power of the interference signal. 3B illustrates the configuration of the interference signal measuring instrument 321.

3A and 3B, a finger for measuring a signal-to-noise ratio of a mobile station despreads a complex scrambling code of a corresponding path after receiving an input signal, and converts the despread signal into a channel identification code of a pilot channel. Despread to extract the pilot channel signal. Thereafter, the I and Q axes of the despread pilot channel signal are squared to be converted into energy signals, and then the signal size of the pilot channel is measured. The energy of the pilot channel measured in this way can be accumulated asynchronously for a certain period of time. In addition, the interference signal measuring unit 321 inputs a signal despread with a complex scrambling code to measure an interference amount of a corresponding finger. The combiner 341 then combines the power Pi of the pilot signal and the power Ii of the interference signal to generate a signal-to-interference ratio SIR of the pilot channel of the corresponding path i.

According to an embodiment of the present invention, when a mobile station transmits a message on a reverse common channel, after the mobile station transmits a preamble and the base station captures and responds, the base station controls the power of the reverse common channel and the reverse common channel to be used by the mobile station. Allocate a forward channel for In this case, the mobile station receives the channel assignment message to the base station after transmitting the preamble, transmits a message through the assigned channel, and also transmits the message through the allocated forward channel according to the power control command received through the assigned forward channel. Transmit power is controlled.

The configuration for detecting the signal-to-noise ratio as shown in FIG. 3A may be implemented in a finger demodulating the data channel. In addition, other fingers may be implemented separately in addition to the fingers for demodulating the data channel. Figure 4 shows an embodiment of the present invention for measuring the signal-to-noise ratio as described above.

Referring to FIG. 4, the searcher 410 performs a general channel acquision function. Data demodulating fingers 421-42N demodulate the signals of the received data channel to generate data. The data combiner 440 combines the data signals output from the data demodulating fingers 421-42N, and the decoder 442 decodes the combined data signal and outputs the combined data signal. Signal level and interference amount measurement fingers 431-43M measure and output the power of the multipath signal and the power of the interference signal received according to an embodiment of the present invention. The combiner 450 combines the powers P1-PM of the signal output from the fingers 431-43M and the powers I1-IM of the interference signal and outputs the signal-to-interference ratio SIR. Here, the signal-to-interference coupler 450 performs the same function as the combiner 341 of FIG. 3C. The controller 460 receives and processes the signals output from the decoder 442 and the signal-to-interference combiner 450. In particular, the controller 460 generates power control information for controlling the channel transmission power of the forward link of the base station by using the signal-to-interference ratio SIR of the forward link output from the signal-to-interference combiner 450. The transmitter 470 transmits power control information of the forward link output from the controller 460. The transmitter 470 also includes channel transmitters on the reverse link.

In FIG. 4, data demodulation fingers 421-42N denote fingers that demodulate existing data channels. In the embodiment of the present invention, it is assumed that there are N data demodulating fingers. The signal and noise measuring fingers 431-43M mean a finger that does not perform demodulation of the data channel but has a portion for measuring a signal size and an interference amount of a corresponding multipath pilot channel. In the embodiment of the present invention, it is assumed that the fingers 431-43M for measuring the signal component and the interference component of the multipath are added to N data demodulating fingers. Fingers 431-43M for measuring the signal size and the amount of interference are assumed to be composed of a finger which performs only a function of measuring signal components and interference components of the corresponding multipath without demodulating the data channel. Since the existing N signal demodulating fingers include a signal level and interference measuring device, the signal level and interference measuring fingers 431-43M may not be configured. In addition, the signal component and the interference component of the multipath may be measured only by independent M fingers, without the apparatus for measuring the signal component and the interference component of the pilot channel in the N channels for demodulating the data channel.

In the exemplary embodiment of the present invention, there are N data demodulating fingers including the signal level and interference measuring device and M fingers for measuring signal components and interference components of an independent multipath without a data demodulation function. Each finger 431-43M may have a time tracker (not shown), which serves to more precisely find the timing of the complex scrambling code found in the searcher.

In addition, there is a signal-to-noise ratio combiner that finally calculates the signal-to-interference ratio of the forward common channel (pilot channel in the embodiment of the present invention) by using the signal component and the interference component output from each finger.

3C shows a combiner 341 which measures the signal-to-interference ratio of the forward link pilot channel based on the energy and interference amount of the pilot channel received at the finger. The combiner 341 may measure the signal-to-interference ratio in various ways.

If the signal of the pilot channel output from each finger is called Si and the noise measurement of each finger is called Ii, one signal-to-noise ratio measurement method is as follows.

SIR1 = (S1 + S2 + ..... + Sn) / (I1 + I2 + ..... + In)

Another method is as follows.

SIR2 = S1 / I1 + S2 / I2 + ........ + Sn / In

The calculated value can then be passed through a low frequency filter and averaged over a long time to measure the signal-to-noise ratio over a long time.

The fundamental difference between the present invention and the existing method is as follows. In the conventional method, the mobile station allocates the finger to the finger using the search result of the searcher, and the finger measures the signal-to-noise ratio of the corresponding base station. Unlike the past, where the searcher searches for signal components and measures the level of the signal, the searcher performs only a search function, and the signal level and interference amount of the found multipath are measured at the finger. In this case, it is assumed that the measurement of the signal level is performed by measuring the pilot channel of the forward link.

The signal-to-noise ratio is measured and reported to the base station as described above. The method of notifying the base station transmits this information to the TPC transmitted on the reverse link as in the conventional method. Alternatively, you can send this information in a message on the reverse link.

According to an embodiment of the present invention, when a mobile station transmits a message on a reverse common channel, after the mobile station transmits a preamble and the base station captures and responds, the base station controls the power of the reverse common channel and the reverse common channel to be used by the mobile station. Allocate a forward channel for In this case, the mobile station receives the channel assignment message to the base station after transmitting the preamble, transmits the message through the assigned channel and transmits the reverse common channel according to the power control command received through the assigned forward channel. Power is controlled.

5 shows an implementation example of a base station.

Referring to FIG. 5, the demodulator 520 demodulates and outputs a channel signal received on the reverse link. The controller 510 controls the overall operation of transmitting and receiving channel signals of the base station. In particular, the controller 510 analyzes the signal-to-noise ratio of the mobile station output from the demodulator 520 and controls the operation of controlling the channel transmission power of the forward link.

The spreader 541 spreads and transmits the transmission signal of the forward common channel (pilot channel) channel with an orthogonal code assigned to the corresponding channel. The gain controller 543 controls the transmission power of the signal output from the spreader 541 according to the gain control signal of the corresponding channel.

The channel encoder 531 performs channel encoding on the channel signal received from the controller 510, outputs the channel signal, the interleaver 533 interleaves the channel coded data in units of frames, and the signal converter 535 converts the interleaved signal. In this case, the channel encoder 531, the interleaver 533, and the signal converter 535 perform channel encoding, interleaving, and signal conversion functions at the transmission rate determined by the transmission rate control signal output from the controller 510. The spreader 537 spreads the signal output from the signal converter 535 by a channel spreading code assigned to the corresponding channel. The gain controller 539 controls the gain by the gain control signal output from the controller 510 and outputs the signal output from the diffuser 537. Therefore, the gain controller 539 performs a function of controlling the power of the channel signal transmitted by the gain control signal determined by the signal-to-noise ratio transmitted from the mobile station. The adder 545 adds and outputs spread channel signals output from the gain controllers 543 and 539. The spreader 547 spreads the added channel spread signals in a PN sequence and outputs them.

As shown in FIG. 5, the base station receives the power control ratio transmitted by the mobile station and changes the power of the forward link transmitted to the mobile station. One of the easiest implementations is to change the transmit power of the base station to be inversely proportional to the signal-to-noise ratio transmitted by the mobile station. That is, the transmission power of the base station is set as follows.

TX_POWER = Constant / (SIR measured by mobile station)

In this case, the base station controller 510 of FIG. 5 controls the gain of the forward link transmitted to the mobile station.

In addition, the channel state of the base station measured by the above method, that is, the signal-to-interference ratio of the pilot channel is used for handoff of the mobile station or variable data transmission of the forward link. The current handoff or change of the data rate of the forward link is carried out by the mobile station measuring the Ec / Io of the pilot channel, and the base station changes the data rate of the handover or the forward link of the mobile station based on this value. However, as described above, the Ec / Io of the pilot channel does not reflect the influence of multipath, and it is difficult to accurately measure the signal level by capturing a signal from an adjacent base station. In particular, in order to allow a high speed data channel for the forward link, the mobile station should be adjacent to the base station or the forward situation should be good. In this case, it is difficult to capture the signal of the neighboring base station, and the existing search method reflects the influence of multipath. It was hard to do. Thus, in the present invention, the mobile station measures the signal-to-noise ratio of the base station at the finger in the structure of the receiver as shown in Figs.

6 shows an example of how the base station controls the data rate of the forward link. The horizontal axis is the signal-to-interference ratio of the forward link measured by the mobile station. The vertical axis represents the data rate of the data channel allocated by the base station. For convenience of explanation, it is assumed that only two data rates (transmission rate 1 and transmission rate 2) exist. The base station sets two thresholds. This threshold is called SIR_TH2 and SIR_TH1. (SIR_TH2> = SIR_TH1) When the base station transmits on the forward channel at a low transmission rate 2, and the mobile station reports a signal-to-interference ratio greater than SIR_TH2, it transmits at a high transmission rate. When the mobile station reports a signal-to-interference ratio of less than SIR_Th1 while transmitting at a high data rate 1, the base station lowers the data rate to 2.

As described above, the code division multiple access communication system according to the embodiment of the present invention can capture signals of the base station to which the mobile station belongs and adjacent base stations, and measure the signal-to-noise ratio insensitive to the change of the multipath component. This has the advantage that the base station can precisely control the transmit power of the forward link channel by the stable signal-to-noise ratio received from the mobile station. In addition, according to the signal-to-noise ratio received from the mobile station, the transmission rate of the forward link can be variably operated according to channel conditions, and there is an advantage in that the handoff situation can be accurately determined.

Claims (14)

A receiving apparatus of a mobile station in a code division multiple access communication system, A searcher for capturing a specific common channel signal of the forward link received; At least two signals and interferometry having fingers for receiving the particular common channel signals of at least two paths, the fingers respectively measuring the strength of the signal and the interference signals of the particular common channel received via the corresponding path Fingers, A signal-to-interference combiner for combining the signals and interferences of the paths output from the fingers to calculate a signal-to-interference ratio received in multipaths; And a reverse channel transmitter for transmitting the power control information of the forward link determined by using the signal-to-interference ratio to a base station. 2. The power control apparatus of a mobile station in a code division multiple access communication system according to claim 1, wherein said specific common channel is a pilot channel. 2. The apparatus of claim 1, wherein the reverse channel transmitter is a reverse dedicated physical control channel transmitter, and the power control information is transmitted through a TPC. 2. The apparatus of claim 1, wherein the reverse channel transmitter is a reverse dedicated physical channel transmitter, and the power control information is included in a transmitted message and transmitted. delete delete delete delete delete A base station of a mobile communication system having mobile stations which measures signals and interference signals received from at least two paths, respectively, combines the measured signals to calculate a signal-to-interference ratio for a multipath, and reports them to a base station. In the rate control device, A reverse channel receiver for receiving a signal-to-interference ratio transmitted from the mobile station; A rate controller for separating the signal-to-interference ratio from the received reverse channel signal, and controlling the transmission rate of the forward link by comparing the separated signal-to-interference ratio with a preset threshold value; And a forward channel transmitter for adjusting and transmitting a transmission rate of a transmission message according to the transmission control signal. delete A method for controlling transmission power of a forward link in a code division multiple access communication system, the mobile station having fingers for receiving specific common channel signals of at least two paths, the method comprising: Measuring the strengths of signals and interference signals of specific common channels received through respective paths by driving the fingers; Calculating signal-to-interference ratios received in multipaths by combining signals and interferences of the paths output from the fingers; And determining the power control information of the forward link by using the calculated signal-to-interference ratio, and then transmitting the power control information to the base station. delete delete