Transmitting and receiving device and method for continuous outer-loop power control while in DTX mode in a CDMA mobile communication system

A device and method for continuous outer-loop power control on a physical channel which transmits only power control bits and no data while in discontinuous transmission (DTX) mode in a CDMA mobile communication system is disclosed. In the power controlling device according to one aspect of the present invention, a frame error detector detects an error from a frame of predetermined length and generates an error signal indicating whether an error has been generated. A closed-loop power controller compares a threshold with the signal-to-noise ratio (SNR) in each power control group (PCG) in a plurality of periods of the frame and generates power control information according to the comparison result. An outer-loop power controller increases the threshold in order to generate power control information that commands a power increase in response to an error signal indicating the existence of a frame error, and decreases the threshold in order to generate power control information that commands a power decrease in response to an error signal indicating the absence of a frame error. An offset controlling unit, which is connected to the outer-loop power controller, receives gating information about the gated transmission of data in a frame at a predetermined rate, and generates an offset signal, which indicates an offset corresponding to a changed gating rate if the gating rate is changed.

PRIORITY

This application claims priority to an application entitled “Transmitting/Receiving Device and Method for Continuous Outer-Loop Power Control in DTX mode of CDMA Mobile Communication System” filed in the Korean Industrial Property Office on May 29, 1999 and assigned Serial No. 99-19648, as well as application Serial No. 99-21946, filed in the Korean Industrial Property Office on Jun. 12, 1999, the contents of both of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a device and method for outer-loop and closed-loop power control of a CDMA (Code Division Multiple Access) mobile communication system in DTX (Discontinuous Transmission) mode, and in particular, to a device and method for continuous outer-loop power control of a physical channel which transmits only power control bits (PCBs) without data.

2. Description of the Related Art

In the IS-2000 standard, packet transmission is implemented in three ways: the P1 option using a fundamental traffic channel and a supplemental channel (SCH), the P2 option using a fundamental traffic channel and a dedicated control channel (DCCH), and the P3 option using a fundamental traffic channel, a DCCH, and an SCH. A traffic channel and a DCCH transmit control information about packets and a signaling message and an SCH transmits packet data. The control information and the signaling message are generated discontinuously. In the absence of data traffic, the fundamental traffic channel transmits null traffic. A forward DCCH transmits only power control bits and a reverse DCCH transmits only pilot symbols and power control bits if there is no data traffic to be transmitted. That is, the DCCH only transmits data when there is data to transmit. This is called a DTX mode.

Meanwhile, in comparison with the W-CDMA (Wideband-CDMA standard according to the 3GPP, the Third Generation Partnership Project), the Japanese and European IMT-2000 (International Mobile Telecommunications 2000) standard, the conventional IS-95 CDMA mobile communication system that mainly provides voice service releases a channel once the data is completely transmitted and requests a channel and connects to the channel when necessary. However, the conventional method cannot provide other high quality services like packet data service because it involves many delay factors such as reconnection delay time. Therefore, other services including packet data service should be provided in a new method. In many cases, data is intermittently transmitted during packet data service such as Internet access and file download. As a result, a non-transmission period is interposed between packet data transmission periods. According to the conventional technology, a dedicated data channel is released or maintained for the non-transmission period. In the former case, a long time is taken to reconnect a channel, making it impossible to provide a corresponding service; whereas, in the latter case, channels which are transmitting no data, are maintained, drastically reducing usage efficiency of the system. This problem can be solved by establishing a DCCH between a base station and a mobile station to transmit and receive a control signal associated with a dedicated data channel for a transmission period, and to be maintained when the dedicated data channel released for a non-transmission period, so that channels can be used efficiently and channel reconnection occurs rapidly upon generation of transmission data. This state is termed the control only substate.

An outer power control loop and a closed power control loop are used together for power control in a DTX mode. The closed power control loop controls power in power control group (PCG) units using a threshold fixed for each frame, while the outer power control loop varies a threshold depending on the presence or absence of frame errors and feeds the threshold to a closed-loop power controller. In the case of using both the outer power control loop and the closed power control loop while in DTX mode, a closed-loop power control is executed using a threshold determined in the outer power control loop upon generated of frames, and using the previous threshold in the absence of frames to transmit.

There will be given a description of the outer-loop power control and the closed-loop power control in a DTX mode.

FIGS. 1A and 1Bare block diagrams of a transmitter in a typical CDMA mobile communication system. Insertion of PCBs in the DTX mode will be described referring toFIGS. 1A and 1B.

A control message buffer111is a memory for temporarily storing a control message transmitted for communication of a control message on a DCCH. The message buffer111is configured to have a capacity enough to store one or more frames. The control message buffer111interfaces a control message between a higher layer processor and a MODEM controller113. The higher layer processor stores a control message added with header information to identify a frame according to a message type in the control message buffer111, sets a flag to notify the storage, reads the control message from the control message buffer113, and clears the flag to notify the read, thereby preventing over-write and over-read.

The MODEM controller113reads the control message from the control message buffer111, the MODEM controller113determines a message type by analyzing the header of the control message, and outputs a payload to be transmitted on a DCCH according to the message type and a corresponding control signal. The control message is variable in duration according to the analysis result, usually 5 or 20 ms. The MODEM controller113determines whether there is a control message to transmit and controls transmission of the DCCH. That is, the MODEM controller113generates a first gain control value for signal Gc in the presence of a control message to be transmitted and a second gain control value for signal Gc for blocking signal transmission on the DCCH in the absence of a control message. The gain control signal Gc is for controlling the transmission power of the DCCH. While the gain controller is located at the front end of a spreader, the same effect can be produced even if it is at the rear end of the spreader.

The MODEM controller113controls transmission of the DCCH while in DTX mode. That is, the MODEM controller113performs a DTX mode control according to the capacities of the data service signals and MAC (medium access control) related messages communicated on the DCCH, to thereby use channel capacity efficiently. Since voice traffic and signal traffic are multiplexed in IS-95, both a voice channel and a signaling channel should be opened all the time for data service. However, the DCCH operates in the DTX mode and thus need not be opened for a control signal If no signaling information to be transmitted exists, a DTX gain controller reduces transmission power for efficient use of radio resources.

A CRC (Cyclic Redundancy Check) generator115adds a CRC to the control message received from the MODEM controller113to allow a receiver to determine the quality of a frame, that is, the presence or absence of a frame error. The CRC generator115outputs a control message with the CRC under the control of the MODEM controller113. A 40-bit control message with a 16-bit CRC is generated for a 5 ms-frame, and a 184-bit control message with a 12-bit CRC for a 20 ms-frame.

A tail bit generator117analyzes the output of the CRC generator115and adds corresponding tail bits to the output of the CRC generator115, for terminating an error correction code. Here, the tail bit generator117generates 8 tail bits.

An encoder119encodes the output of the tail bit generator117at a code rate of ⅓. The encoder119can be a convolutional encoder or a turbo encoder. An interleaver121permutes the bit sequence of encoded symbols received from the encoder119in frame units to protect the data from burst errors.

The CRC generator115, the tail bit generator117, the encoder119, and the interleaver121form a control message generator150for generating a control message and transmitting it on a physical channel. While the control message generator150processes a control message for a frame inFIG. 1A, it can be contemplated that the MODEM controller113selects a control message generator corresponding to the length of a frame to transmit among as many control message generators as the frame lengths of control messages transmitted on the DCCH. In this case, each control message generator should be provided with a CRC generator, a tail bit generator, an encoder, and an interleaver according to the frame length of a control message processed in the control message generator.

A signal mapper123maps 1s and 0s of the interleaved symbols to −1s and 1s, respectively. A gain multiplier125performs a DTX mode function by establishing a path for transmitting the DCCH control message or blocking the path depending on which gain control message is received from the MODEM controller113.

A PCB inserter127inserts a PCB into a signal received from the multiplier125. A serial-to-parallel converter (SPC or S/P)129multiplexes control message symbols received from the PCB inserter127and distributes the multiplexed symbols to carrier spreaders. Here, three carriers are used by way of example. For the three carriers, six channels are produced from three carrier frequencies and two phases (I and Q channels) of each carrier. The PCB can be used for controlling the reverse link power of a mobile station.

FIG. 1Bis a block diagram of a spreader for spreading symbols received from the PCB inserter127. A forward link transmitter includes as many as spreaders as carriers. One spreader corresponding to one carrier is shown inFIG. 1B. Referring toFIG. 1B, an orthogonal code generator135generates a DCCH orthogonal code which can be a Walsh code or a quasi-orthogonal code. Multipliers131and133multiply I- and Q-channel signals of the forward DCCH control message by the orthogonal code, for orthogonal spreading.

A modulator137PN-spreads the orthogonally spread I- and Q-channel signals received from the multipliers131and133with PN codes PNi and PNq received from a PN sequence generator (not shown). A complex multiplier can be used as the modulator137.

The above embodiment is a 3× multi-carrier system and can be applied to a transmitter in a 1× or 3× DS (direct sequence) system. Thus, a description of the 1× or 3× DS system will be omitted.

FIG. 2is a block diagram of a reverse link transmitter which operates in a DTX mode for the general CDMA mobile communication system. As shown inFIG. 2, the reverse link transmitter is similar to the forward link transmitter in structure. Therefore, a description of the same components will be omitted.

An orthogonal spreader207generates a Walsh code. A first multiplier209multiplies a transmission signal received from a signal mapper205by the Walsh code received from the orthogonal spreader207, for orthogonal spreading. A gain multiplier221outputs no data upon receipt of a gain control signal0from a MODEM controller203if there is no transmission message and outputs data upon receipt of a gain control signal1from the MODEM controller203if a transmission message exists. A summing device223forms a DCCH signal by summing the transmission signal received from the gain multiplier221and a pilot/PCB channel signal. A PN spreader225complex-PN-spreads the DCCH signal.

FIG. 25Ais a block diagram of a base station transmitter in a typical asynchronous IMT-2000 system. A description of the same components as inFIG. 1will be omitted. InFIG. 25A, a rate converter2517changes the rate of the output signal of an encoder2515to that of the input signal of an interleaver2519by repeating or puncturing the output of the encoder2515when the rate at the output of the encoder2515is different from that at the input of the interleaver2519. A multiplexer2523time-division-multiplexes a gain-controlled dedicated physical data channel (DPDCH) and a dedicated physical control channel (DPCCH) and feeds the multiplexed signal to a signal mapper2525.

FIG. 26Ais a block diagram of a mobile station transmitter in the typical asynchronous IMT-2000 system. As shown inFIG. 26A, the mobile station transmitter is similar to the base station transmitter in structure. Therefore, a description of the configuration and operation of the mobile station transmitter will be omitted herein.

There will be given a description of the structures and operations of forward and reverse link receivers for performing an outer-loop power control and a closed-loop power control using a reverse pilot channel and a PCB received on a forward DCCH, respectively, with reference toFIGS. 3 and 4.

FIG. 3is a block diagram of a reverse link receiver in a DTX mode for the general CDMA mobile communication system.

Referring toFIG. 3, a first despreader301is a PN despreader for PN-despreading a received signal. A second despreader303is a DCCH Walsh despreader for despreading a DCCH signal included in the PN-despread signal received from the first despreader301with a Walsh code. A channel estimator305detects a fading component using a pilot channel included in the PN-despread signal received from the first despreader301. A third despreader307is a pilot channel Walsh despreader for despreading the pilot channel signal included in the PN-despread signal received from the first despreader301with a Walsh code.

A multiplier314multiplies the complex conjugate of the fading component received from the channel estimator305by the DCCH signal received from the second despreader303in symbol units, for error compensation. A PCB extractor317extracts a PCB from the error-compensated DCCH signal received from the multiplier314. A bit energy measurer309measures bit energy Ebfrom the PCB received from the PCB extractor317and the fading component received from the channel estimator305. A noise measurer311measures noise energy Ntfrom the symbol value of the pilot channel received from the third despreader307and the fading component from the channel estimator305. An SNR calculator313calculates an SNR from the noise energy Ntand the bit energy Eb. For details of an Eband Ntmeasuring method, see “Forward Link Closed Loop Power Control Method for cdma 2000-(Rev. 1)”, Stein Lundby, Contribution to TR45.5.3.1./98.12.08.28.

A decoder319decodes the output of the PCB extractor317and a CRC error detector321performs a CRC error check on the decoded signal received from the decoder319. The output of the CRC error detector321is True (1) or False (0). Since the DCCH channel is transmitted in the DTX mode, the receiver calculates a CRC from a frame if the frame has transmission data to determine whether a frame error has occurred. For details of a method of determining whether a DCCH has frame data or not while in DTX mode, see Korean Application Serial No. 98-04498. A frame detector322detects whether a frame exists or not. A data detector323receives frame data and a CRC error check result from the CRC error detector321and generates an on/off control signal to a MODEM controller325. The MODEM controller325is activated by the on/off control signal to detect a control message from the decoded data received from the decoder319and to store the control message in a control message buffer327.

If the receiver performs closed-loop power control alone, a closed-loop power controller315compares the SNR of each PCB received from the SNR calculator313with a fixed threshold and controls power according to the comparison result. If the receiver performs closed-loop power control and outer-loop power control together, an outer-loop power controller329is further provided to the receiver. The outer-loop power controller329determines a threshold and then the closed-loop power controller315performs a closed-loop power control using the threshold. The outer-loop power controller329is activated upon receipt of a frame existence flag from the data detector323and determines the threshold from the CRC check result received from the CRC error detector321.

Referring toFIG. 6, a closed-loop power control method in the above reverse link receiver will be described.

In step601, the SNR calculator313calculates an SNR from Ntand Ebmeasured by the noise measurer311and the bit energy measurer309, respectively. Upon receipt of the SNR from the SNR calculator313, the closed-loop power controller315compares the SNR with a fixed threshold in step603. If the SNR is greater than the threshold, the closed-loop power controller315transmits a power-down command (PCB=0) to a mobile station in step607. If the SNR is equal to or greater than the threshold, the closed-loop power controller315transmits a power-up command (PCB=1) to the mobile station in step605.

FIG. 4is a block diagram of a forward link receiver in a DTX mode in the general CDMA mobile communication system. The structure and operation of the forward link receiver will be described referring toFIG. 4.

InFIG. 4, a squarer401squares an input signal in sub-chip units. An accumulator403sums sub-chip energies for one PCG. The sum is estimated as noise energy. A matching filter405filters the input signal in sub-chips in chip units. A first despreader407PN-despreads the output of the matching filter405and outputs the PN-despread signal to a second despreader409, a channel estimator411, and a third despreader413. The third despreader413despreads a pilot channel signal included in the PN-despread signal with a Walsh code. An accumulator415sums chip energies of the Walsh-spread signal. A squarer417squares the sum and outputs the square to an SNR calculator417. The output of the squarer417is estimated as bit energy. The other components are the same as their counterparts shown inFIG. 3in structure but labeled with different reference numerals. The reverse link receiver also performs a closed-loop power control in the same manner as shown inFIG. 6.

FIG. 5illustrates DCCH transmission on a forward link and on a reverse link while in DTX mode according to the IS-95C standard. The forward DCCH transmits data discontinuously and PCBs continuously regardless of the presence or absence of data. Also on the reverse link, data is discontinuously transmitted on the DCCH. If no data to be transmitted exists, pilot symbols and PCBs are transmitted on a pilot channel. Hence, the DCCH transmits no PCBs.

In the case of a traffic channel which continuously transmits frames, a receiver can perform outer-loop power control continuously to obtain an intended frame error rate (FER). However, since the DCCH transmits in DTX mode, the outer-loop power control can be used only when transmission frames are present.

FIG. 7is a flowchart illustrating a general outer-loop power control method. The outer-loop power control method will be described with reference toFIGS. 3and7.

As shown inFIG. 7, upon receipt of frame data, the outer-loop power controller329determines whether a frame error has been generated based on a CRC error check result received from the CRC error detector321in step701. If a frame error exists, the outer-loop power controller329receives a frame existence flag from the data detector323. If the frame existence flag indicates existence of a frame, the outer-loop power controller323increases a threshold in step703. If the frame existence flag indicates the absence of a frame, the outer-loop power controller323decreases the threshold for power control in step705. Procedures other than the above one can be employed for the outer-loop power control.

When the outer-loop power control method and the closed-loop power control method are used concurrently, a threshold updated for each frame in the outer-loop power control method is used as a reference SNR value in the closed-loop power control method.

FIG. 18Ais a block diagram of a mobile station receiver for processing a DPCH received in a DTX mode in an asynchronous IMT-2000 system employed in Japan and Europe. InFIG. 18A, a channel separator1805separates a DPCCH from an input DPCH. A channel estimator1809obtains information about channel status from the DPCCH received from the channel separator1805, using pilot symbols. An SNR measurer1807calculates pilot energy Eband noise energy Ntfrom pilot symbols. A bit energy measurer1813receives a DPDCH and the DPCCH, compares their energies, and outputs the comparison result to a data detector. The other components have been described before.

FIG. 18Bis a block diagram of a base station receiver for processing a DPCH received while in DTX mode in the asynchronous IMT-2000 system. As shown inFIG. 18B, the base station receiver is similar in structure to the mobile station receiver. Hence, its description is omitted.

As described above, the conventional outer-loop power control method is not applied when no frame exists during a DTX mode on a channel like DCCH since an outer-loop power control is performed based on a determination whether a received frame has an error or not. Therefore, if no frame is transmitted in DTX mode, a threshold set for a previous frame is used.

As a result, when frame transmission resumes and the previous threshold is higher than a threshold which should be set for receiving the current frame without errors, unnecessary transmission power is consumed. On the other hand, if the previous threshold is lower than the desirable threshold, frame errors are increased. The increase of frame errors and transmission power dissipation decrease communication quality and base station capacity.

SUMMARY OF THE INVENTION

It is, therefore, a first object of the present invention to provide a device and method for implementing outer-loop power control while in DTX mode regardless of presence or absence of data in a CDMA mobile communication system.

It is a second object of the present invention to provide a device and method for implementing outer-loop power control while in DTX mode, regardless of the presence or absence of data, by tabulating FERs versus data service types and determining whether frame errors exist referring to the table upon absence of transmission data in a CDMA mobile communication system.

It is a third object of the present invention to provide a device and method for implementing outer-loop power control while in DTX mode, regardless of the presence or absence of data, by determining whether frame errors exist using a specific threshold upon absence of transmission data in a CDMA mobile communication system.

It is a fourth object of the present invention to provide a device and method for compensating for an offset threshold according to state transition to reduce the time required to change a threshold set in the previous state to a threshold set in a state transitioned from the previous state during outer-loop power control in a CDMA mobile communication system.

It is a fifth object of the present invention to provide a device and method for minimizing the transmission power of a control channel when only the control channel is transmitted in a gated mode and ensuring the reception capacity of a traffic channel when the traffic channel is transmitted by controlling the transmission power gains of the control and traffic channels in a control hold state in a CDMA mobile communication system.

It is a sixth object of the present invention to provide a device and method for preventing consumption of transmission power when data transmission resumes in a CDMA mobile communication system.

It is a seventh object of the present invention to provide a device and method for minimizing frame errors increased when data transmission resumes in a CDMA mobile communication system.

It is an eighth object of the present invention to provide a device and method for increasing communication quality and base station capacity in a CDMA mobile communication system.

These and other objects can be achieved by providing a power controlling device. In the power controlling device according to one aspect of the present invention, a frame error detector detects an error from a frame of a predetermined length and generates an error signal indicating whether an error has been generated. A closed-loop power controller compares a fixed threshold with the signal-to-noise ratio (SNR) in each of power control groups (PCG) in a plurality of periods of the frame and generates power control information according to the comparison result. An outer-loop power controller increases the fixed threshold to generate the power control information commanding power increase in response to the error signal indicating the existence of a frame error and decreases the fixed threshold to generate the power control information commanding power decrease in response to the error signal indicating the absence of a frame error. An offset controlling unit is connected to the outer-loop power controller, receives gating information about gated transmission of data in the frame at a predetermined rate, and generates an offset signal indicating an offset corresponding to a changed gating rate if the gating rate is changed.

According to another aspect of the present invention, there is provided a power controlling method in a CDMA mobile communication system. In the power controlling method, an offset controller receives an offset table with offsets versus state transitions through a higher layer message from a base station upon state transition and stores the offset table in an offset table storage. The offset controller also receives information about a pre-transition gating rate and a post-transition gating rate through the higher layer message and reads a corresponding offset from the offset table. An outer-loop power controller performs an outer-loop power control operation by adding a previous threshold to the offset received from the offset controller and outputs a fixed threshold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

An outer-loop power control operation of the present invention is executed by use of information about the presence or absence of frame errors if frames exist and by estimating the presence or absence of frame errors if no frames exist. The present invention enables continuous outer-loop power control on a DCCH transmitted in a DTX mode.

FIG. 8is a block diagram of a receiver in a mobile station for outer-loop power control while in DTX mode. The same components as shown inFIG. 3will either be described briefly or not be described.

Referring toFIG. 8, a CRC error detector821determines whether frame data received from a decoder819has errors and outputs a CRC error check result to a data detector823and a frame error detector824. A frame detector822measures the energy of a DCCH to determine whether frame data exists or not and feeds the measured energy to a data detector823. If the measured energy is greater than a predetermined level, the data detector823determines that frame data exists and outputs a frame existence flag set to 1 to the frame error detector824. If no frame exists, the frame existence flag is set to 0. Upon receipt of the CRC error check result from the CRC error detector821and information indicating the frame existence from the frame detector822, the data detector823outputs an on/off control signal to a MODEM controller826and the frame error detector824. The data detector823will later be described in more detail in connection withFIG. 11.

An SNR calculator813calculates an SNR from noise energy Ntreceived from a noise measurer809and bit energy Ebreceived from a bit energy measurer811.

The frame error detector824receives the SNR from the SNR calculator813, the CRC error check result from the CRC error detector821, and the flame existence flag message from the data detector823and determines whether frame errors have been generated. The means of determination will be described in detail with reference toFIG. 10A. If it turns out that frame errors exist, the frame error detector824outputs a frame error indicator to an outer-loop power controller825.

The outer-loop power controller825performs an outer-loop power control in the procedure shown inFIG. 7and outputs a threshold to a closed-loop power controller815. Then, the closed-loop power controller815performs a closed-loop power control using the threshold.

The following description will be conducted with the appreciation that a channel state measuring portion includes a channel estimator, a noise measurer, and a bit energy measurer, a frame decision portion includes a frame detector and a data detector, and an outer-loop power control portion includes a frame error detector and an outer-loop power controller.

FIG. 9is a block diagram of a base station receiver for outer-loop power control in a DTX mode according to an embodiment of the present invention. Referring toFIG. 9, a decoder923outputs frame data to a CRC error detector925and a MODEM controller933. The CRC error detector925determines whether the frame data has errors and outputs a CRC error check result to a data detector927and a frame error detector929. A frame detector924measures the energy of a DCCH to determine whether frame data exists or not and feeds the measured energy to the data detector927. If the measured energy is greater than a predetermined level, the data detector927determines that frame data exists and outputs a frame existence flag set to 1 to the frame error detector929. If no frame exists, the frame existence flag is set to 0. Upon receipt of the CRC check result from the CRC error detector925and the frame existence information from the frame detector924, the data detector927outputs an on/off control signal to the MODEM controller933and the frame error detector929. The data detector927will later be described in more detail with reference toFIG. 11.

An SNR calculator919calculates an SNR from Ntmeasured from an input signal in sub-chip units by a squarer905and an accumulator907and bit energy Ebmeasured from the output of a third Walsh despreader913by an accumulator915and a squarer917.

The frame error detector929receives the SNR from the SNR calculator919, the CRC error check result from the CRC error detector925, and the frame existence flag message from the data detector927, and determines whether frame errors have been generated. A determination method will be described in detail with reference toFIG. 10B. If it turns out that frame errors exist, the frame error detector929outputs a frame error indicator to an outer-loop power controller931.

The outer-loop power controller931performs outer-loop power control in the procedure shown inFIG. 7and outputs a threshold to a closed-loop power controller921. Then, the closed-loop power controller921performs closed-loop power control using the threshold.

A frame error detector according to the present invention can operate in many ways. In the following description, two ways will be presented. The same components in the forward and reverse link receivers will be described referring toFIG. 8.

Now, an embodiment of the frame error detector according to the present invention will be described referring toFIGS. 10A and 10B.FIG. 10Aillustrates input and output of the frame error detector according to the embodiment of the present invention andFIG. 10Bis a detailed block diagram of the frame error detector.

Referring toFIG. 10A, the frame error detector (824or929) outputs a frame error indicator indicating the presence or absence of a frame error, for the input of an SNR, a CRC error check result, and a frame existence flag message.

InFIG. 10B, the frame error detector includes a frame error estimator1003, a random number generator1001, a look-up table1004, and a switch1005. The look-up table1004tabulates FERs versus SNRs (Eb/Nt) as shown inFIG. 14B. The random number generator1001generates a random number NR under the control of the frame error estimator1003. As shown inFIG. 14A, the random numbers range from 0 to 1. The frame error estimator1003, receives an SNR from the SNR calculator (813or919), adds a predetermined offset value to the SNR to achieve a real SNR, reads an FER corresponding to the resulting SNR with the offset (dB) added from the look-up table1004, and stores the FER in a buffer (not shown). Then, the frame error estimator1003controls the random number generator1001to generate a random number and determines whether the generated random number is greater than the stored FER. If the random number is not smaller than the FER, the frame error estimator1003considers that no frame errors have occurred and outputs a frame error message ‘0’ to the outer-loop power controller (825or931). If the random number is smaller than the FER, the frame error estimator1001considers that frame errors have been generated and outputs a frame error message ‘1’ to the outer-loop power controller. The switch1005is switched by the frame existence flag message received from the frame detector (823or927). If the frame existence flag message is 1, the switch1005is switched to the CRC error check result and if it is 0, the switch1005is switched to the frame error estimator1003.

FIG. 11is a flowchart illustrating the operation of the data detector (823or927) for switching the switch1005shown inFIG. 10B.

Referring toFIG. 11, the data detector823determines whether frame energy has been received from the frame detector822in step1101. Upon receipt of the frame energy, the data detector823determines whether the frame energy is a predetermined level or greater in step1103. If it is, the data detector823outputs a frame existence flag set to 1 to the switch1005in step1105. If the frame energy is smaller than the predetermined level, the data detector823outputs the frame existence flag set to 0 to the switch1005in step1107.

FIGS. 12A and 12Billustrate embodiments of a method of measuring the SNR for one frame in the frame error estimator1003shown inFIG. 10B. In the first embodiment, upon receipt of Ntand Ebin PCG units in step1201, the frame error estimator1003obtains an average Eb(Eb, ave) and an average Nt(Nt, ave) for the entire frame in step1203and calculates an average SNR (SNR, ave) from Eb, ave and Nt, ave in step1205. In the second embodiment, the frame error estimator1003calculates an SNR (=Eb/Nt) for each PCG in step1213and an average SNR (SNR, ave) for one frame in step1215. The average SNR in the first and second embodiments can be calculated respectively bySNRave=Eb⁢⁢(1)+Eb⁢⁢(2)+…+Eb⁢⁢(N)Nt⁢⁢(1)+Nt⁢⁢(2)+…+Nt⁢⁢(N)(1)SNRave=(Eb⁢⁢(1)Nt⁢⁢(1)+Eb⁢⁢(2)Nt⁢⁢(2)+…+Eb⁢⁢(N)Nt⁢⁢(N))/N(2)
where N is the number of PCGs in one frame.

The SNR of one frame can be calculated in other ways.

If no frames have been received, a frame error can be estimated in many ways, which will be described below.

FIG. 13is a flowchart illustrating an embodiment of a frame error estimation method when no frames have been received. Referring toFIG. 13, the frame error detector824calculates an effective SNR by adding an offset value to an SNR calculated by Eb/Ntin step1301. Since the measured SNR is different from an SNR on the look-up table to some extent, this difference is compensated for by the offset.

In step1303, the frame error detector824reads an FER (FERT) corresponding to the SNR from the look-up table1004and stores the FER in the buffer. In the look-up table, FERs are listed with respect to SNRs. Here, the SNRs or the FERs can be arranged in predetermined intervals. In step1305, the frame error estimator1003controls the random number generator1001to generate a random number (FERR). Upon receipt of the random number, the frame error estimator1003compares the random number with FERγin step1307. If the random number is smaller than FERT, the frame error estimator1003outputs a frame error message ‘1’ to the outer-loop power controller825in step1309. If the random number is not smaller than FERT, the frame error estimator1003outputs a frame error message ‘0’ to the outer-loop power controller825in step1311.

FIG. 14Aillustrates the range of random numbers generated with the same probability by the random number generator. InFIG. 14A, the marked portion indicates a uniform distribution of random numbers.

The table shown inFIG. 14Bis made by calculating FERs versus SNRs in an additive white Gaussian noise (AWGN) channel environment. It is obvious that the table can be formed in other ways. An example of the FER tables in the AWGN channel environment is shown below. Here, the table size (i.e., the number of rows in the table) is 51.

The size of Table 1 can be changed when necessary. SNRs and FERs can be arranged at predetermined intervals. A mobile station acquires the table in many ways. Hereinbelow three of them will be described.

(1) A base station transmits the table to the mobile station on a common channel like a broadcast channel and then the mobile station stores it in a look-up table storage.

(2) The base station transmits the table to the mobile station on a dedicated channel which transmits a power control message and then the mobile station stores it in the look-up table storage.

(3) The look-up table is stored in an internal memory of the mobile station in a manufacturing process.

Meanwhile, offset values used to compensate SNR measurements vary with radio configurations (RCs), that is, code rates, and gating rates. Offset values versus gating rates in a specific RC can be listed as shown below.

Such a table as Table 2 can be given for each RC. The mobile station can acquire the above table in many ways. Four of them will be presented below.

(1) A base station transmits the table to the mobile station on a common channel like a broadcast channel and then the mobile station stores it in an offset table storage.

(2) The base station transmits the table to the mobile station on a dedicated channel which transmits a power control message and then the mobile station stores it in the offset table storage.

(3) The base station transmits a state transition command message including an offset for corresponding state transition to the mobile station and the mobile station applies the offset.

(4) The offset table is stored in an internal memory of the mobile station in a manufacturing process and a corresponding offset is applied according to state transition.

FIG. 15is a flowchart illustrating another embodiment of the frame error estimation method when no frames have been received. In the second embodiment, a frame error is estimated by comparing an SNR measured in frame units with a fixed threshold or an externally received threshold. That is, if the measured SNR is smaller than the threshold, it is determined that frame errors have been generated. If the SNR is greater than the threshold, it is determined that no frame errors have been generated. The comparison is performed in step1501. The frame error estimator1003outputs the estimate to the outer-loop power controller825in steps1503and1505

The threshold in the second embodiment is changed according to RCs and gating rates. Thresholds versus gating rates in a specific RC are listed below.

Such a table as Table 3 can be made for each RC. The mobile station can acquire the above table in many ways. Four of them will be presented below.

(1) The base station transmits the table to the mobile station on a common channel like a broadcast channel and then the mobile station stores it in a threshold table storage.

(2) The base station transmits the table to the mobile station on a dedicated channel which transmits a power control message and then the mobile station stores it in the threshold table storage.

(3) The base station transmits a state transition command message including a threshold for each corresponding state transition to the mobile station and the mobile station applies the threshold.

(4) The threshold table is stored in an internal memory of the mobile station in a manufacturing process and a corresponding threshold is applied according to state transition.

FIG. 16is a flowchart illustrating a third embodiment of the frame error estimation method when no frames have been received. In step1601, the frame error estimator1003compares an SNR measured in PCG units with a first threshold or externally received. In step1603, the frame error estimator1003increases by one the count number (N) of SNRs in PCGs smaller than the threshold if the SNR is smaller than the threshold. The frame error estimator1003determines whether SNRs are completely measured in all PCGs of one frame in step1605and, if they are completely measured, the frame error estimator1003compares the count value (N) with a second threshold (Threshold2) in step1607. If the count value is greater than the second threshold in step1607, the frame error estimator1003determines that frame errors have occurred and outputs a frame error message ‘1’ to the outer-loop power controller825in step1609. If the count value is not greater than the second threshold in step1607, the frame error estimator1003considers that no frame errors have been generated and outputs a frame error message ‘0’ to the outer-loop power controller825in step1611. The thresholds can be preset or received from the transmitter in advance.

The thresholds used in the above third embodiment vary with RCs and gating rates. A method of making a threshold table for the third embodiment and acquiring the threshold table in the mobile station is the same as that in the second embodiment.

The mobile station can acquire the threshold table in many ways. Three of them will be presented below.

(1) The base station transmits the table to the mobile station on a common channel such as a broadcast channel and then the mobile station stores it in a threshold table storage.

(2) The base station transmits the table to the mobile station on the dedicated channel that transmits a power control message and then the mobile station stores it in the threshold table storage.

(3) The threshold table is stored in an internal memory of the mobile station in a manufacturing process and a corresponding threshold is applied.

FIG. 17illustrates gated transmission while in DTX mode according to an embodiment of the present invention. Case8-1shows transmission at a gating rate of1, case8-3shows transmission at a gating rate of ½, and case8-5shows transmission at a gating rate of ¼. PCBs are also gated at a corresponding gating rate on a forward link. Even though gating occurs, the same effects as produced from a no-gated transmission case are observed except that the number of PCBs to be calculated is reduced. Therefore, the above-described outer-loop power control methods can be applied to the gated mode. That is, the method of changing a threshold by adapting an outer-loop power control based on the determination whether a real frame error is present or not only in a frame transmission period can be applied to the gated mode, and the method of performing an outer-loop power control using the determination whether a real frame error is present or not in a frame transmission period and estimating the presence or absence of a frame error in a non-frame transmission period can be applied to the gated mode. Or the outer-loop power control may not be applied in the gated mode.

FIG. 20illustrates transmission of a DPCH while in DTX mode in an asynchronous Japanese and European IMT-2000 system. DPCHs include a DPDCH for data transmission and a DPCCH for recovering the DPDCH. The DPDCH in turn includes a DCCH for logic control and a DTCH (Dedicated Traffic Channel) for transmission of voice information. The DPCCH has a pilot symbol for providing channel information and a TPC (Transmission Power Control) for power control. There are four cases in the figure: (i) transmission of both the DPDCH and the DPCCH; (ii) non-transmission of DCCH information; (iii) non-transmission of DTCH; and (iv) transmission of DPCCH only without DPDCH. It is noted from the four cases that the DPCCH is continuously transmitted. Therefore, a continuous outer-loop power control is possible using pilot symbols of the DPCCH, as stated before.

FIG. 19Ais a block diagram of an embodiment of a reverse link receiver which performs continuous outer-loop power control on a DPCH while in DTX mode in an asynchronous IMT-2000 system according to the present invention. The receiver is different from that shown inFIG. 18Ain that a frame error detector1925and an outer-loop power controller1927are further provided. The frame error detector1925outputs frame error information to the outer-loop power controller1927, for the input of an SNR, a CRC error check result, and information about the presence or absence of data (DPDCH). The operation of the frame error detector1925is shown inFIGS. 10 and 11, and the operation of the outer-loop power controller1925inFIG. 7.

FIG. 19Bis a block diagram of an embodiment of a forward link receiver which performs continuous outer-loop power control on a DPCH while in DTX mode in an asynchronous IMT-2000 system according to the present invention. The receiver is different from that shown inFIG. 18Bin that a frame error detector1969and an outer-loop power controller1971are further provided. The frame error detector1969outputs frame error information to the outer-loop power controller1971, for the input of an SNR, a CRC error check result, and information about the presence or absence of data (DPDCH). The operation of the frame error detector1969has been described in connection withFIGS. 10 and 11, and the operation of the outer-loop power controller1971in connection withFIG. 7.

As described above, data communication is conducted in several states according to the communication environment. For example, there are multiple states, including a packet signal transmission state, a control signal only transmission state, and a state where neither a packet signal nor a control signal is transmitted. In the first two states, transmission power is controlled by closed-loop power control and outer-loop power control.

A packet signal is transmitted according to a data communication state as stated above. Data communication in an IMT-2000 system is comprised of an active state, a control hold state, a dormant state, and so on. The above-described transmission control method is used in the active state and the control hold state. Specifically, a pilot signal and PCBs are transmitted in a gated mode in the control hold state. According to gating rates ½, ¼, and ⅛, many states can be defined. This is also applied to an active state and a control hold state in an asynchronous IMT-2000 system.

Power control at a gated transmission mode in the communication states and the control hold state can be implemented in the following two embodiments.

First Embodiment

When a communication state transitions to another communication state, a threshold in the previous state is maintained in the transitioned state and then changed to a new threshold fit for the transitioned state through an outer-loop power control operation. For example, if a threshold incrementing step is predetermined and the difference between a threshold before state transition and a threshold after state transition is greater than the step size, an outer-loop power controller changes the previous threshold to the threshold for the transitioned state in a predetermined time.

FIG. 21Ais a block diagram of a mobile station receiver capable of performing outer-loop power control with a reduced time for updating a previous threshold for a transitioned state in a synchronous CDMA mobile communication system according to an embodiment of the present invention. The same components as shown inFIG. 8will not be described.

An offset table storage2133includes an offset table as shown Table 4 in which offsets are listed with respect to pre-transition and post-transition. The offsets are obtained empirically.

Table 4 can be made for each RC.

The reason for the difference in value and sign between the offsets for transition of an active state to a ½ gated transmission state and for transition of the ½ gated transmission state to the active state is that a margin is added to an optimal threshold offset to ensure reception performance in producing a lower threshold with an offset.

The offset table can be obtained in many ways. Four of them will be presented below.

(1) A base station transmits the table to the mobile station on a common channel like a broadcast channel and then the mobile station stores it in an offset table storage.

(2) The base station transmits the table to the mobile station on a dedicated channel which transmits a power control message and then the mobile station stores it in the offset table storage.

(3) The base station transmits a state transition command message including an offset for corresponding state transition to the mobile station and the mobile station applies the offset. In this method, an offset table is not created at the mobile station. Instead, the base station transmits the offset required for each corresponding state transition.

(4) The offset table is stored in an internal memory of the mobile station in a manufacturing process and a corresponding offset is applied according to state transition.

An offset controller2135receives a higher layer message including information about a pre-transition state and a post-transition state from a higher layer processor, reads an offset according to corresponding state transition from the offset table storage2133, and feeds the offset to an outer-loop power controller2137. The offset controller2135receives an offset table from a base station through an upper layer message and stores it in the offset table storage2133. The offset controller2135stores the received offset table only in an initial state and does not store later received offset tables. Or it updates the offset table in handoff and stores the updated offset table. In addition, if the base station transmits only an offset for the corresponding state transition, the offset controller2135detects the offset from a higher layer message and directly output it to the outer-loop power controller2137.

The outer-loop power controller2137adds the offset received from the offset controller2135to a pre-transition offset and outputs a fixed threshold to a closed-loop power controller2119.

FIG. 21Bis a block diagram of a mobile station receiver capable of performing outer-loop power control with a reduced time for updating a previous threshold for a transitioned state in an asynchronous CDMA mobile communication system according to an embodiment of the present invention. The same components as shown inFIG. 8will not be described.

The mobile station receiver for the asynchronous CDMA mobile communication system is the same on structure as that for the synchronous CDMA mobile communication system shown inFIG. 21A. An offset table storage2181includes an offset table as shown in Table 4. Upon receipt of state transition information through an upper layer message from a higher layer processor, the offset table storage2181reads a corresponding offset from the offset table and outputs the offset to an outer-loop power controller2185. Then, the outer-loop power controller2185adds the offset received from an offset controller2183to a pre-transition threshold and outputs a fixed threshold to a closed-loop power controller2171.

FIG. 22Ais a block diagram of a base station receiver in the synchronous IMT-2000 system according to an embodiment of the present invention. The components of the base station receiver except for an offset controller2239are the same as those shown inFIG. 9. The offset controller2239operates in the same manner as the offset controller2135shown inFIG. 21A. An offset table for the offset controller2239of the base station is stored in a memory or received from a system network.

FIG. 22Bis a block diagram of a base station receiver in the asynchronous IMT-2000 system according to an embodiment of the present invention. Due to the nature of the asynchronous IMT-2000 system, the base station receiver operates in the same manner as the mobile station receiver shown inFIG. 21B. An offset controller2281operates in the same manner as the offset controller2183shown inFIG. 21B. An offset table such as mentioned in reference toFIG. 22Ais used.

Second Embodiment

Gated transmission aims at reduction of interference and power consumption by transmitting only a control signal (pilots and PCBs) in a gated mode when no traffic signals to be transmitted exist in a control hold state. Traffic signals to transmit are seldom generated in the control hold state. Accordingly, only control signals are transmitted in a gated mode in most cases. To ensure the reception performance of a traffic signal transmitted in the gated transmission mode, the transmission power of a control signal and the traffic signal should be set higher than in an active state. In an embodiment of the present invention, the transmission power of a control signal transmitted in a gated mode is maintained the same as in an active state. In this state, when a traffic signal to transmit is generated, the gain of the transmission power of the traffic signal is controlled, and, when no traffic signals exist, the transmission power is minimized. Consequently, the reception performance of the traffic signal is ensured.

FIG. 23is a block diagram of a transmitter in a synchronous IMT-2000 base station operated in a gated transmission mode in a control hold state according to an embodiment of the present invention. A description of the same components as shown inFIG. 1will be omitted.

Referring toFIG. 23, a gain adjustment table2329has a gain adjustment table in which gains are listed with respect to transmission power levels of a traffic signal to be controlled according to communication states and gating rates. The gain adjustment table can be empirically obtained and shown as Table 5 by way of example.

Table 5 can be made for each RC.

A gain adjustment controller2305reads a transmission power gain adjustment value for a traffic signal from the gain adjustment table storage2329based on information about a communication state and a gating rate received from a higher layer processor and feeds the gain adjustment value to a multiplier2323which acts as a gain adjuster. The gain adjuster2323adjusts the transmission power gain of the traffic signal with the gain adjustment value received from the gain adjustment controller2305, while establishing a path for transmitting a control message or blocking the control message from being transmitted according to a gain control signal received from a MODEM controller2303as stated earlier with reference toFIG. 1.

FIG. 24is a block diagram of a transmitter in a synchronous IMT-2000 mobile station operated in a gated transmission mode in a control hold state according to an embodiment of the present invention. A description of the same components as shown inFIGS. 2 and 23will be omitted.

Referring toFIG. 24, a gain adjustment table storage2431may acquire a gain adjustment table in one of the four ways described referring toFIG. 21A.

FIG. 25Bis a block diagram of a transmitter in an asynchronous IMT-2000 base station operated in a gated transmission mode in a control hold state according to an embodiment of the present invention. A description of the same components as shown inFIG. 23will be omitted.

Referring toFIG. 25B, the rate converter2517changes the rate of the output signal of the encoder2515to that of the input signal of the interleaver2519by repeating or puncturing the output of the encoder2515when the rate at the output of the encoder2515is different from that at the input of the interleaver2519.

FIG. 26Bis a block diagram of a transmitter in an asynchronous IMT-2000 mobile station operated in a gated transmission mode in a control hold state according to an embodiment of the present invention. A description of the same components as shown inFIGS. 24 and 25Bwill be omitted.

As described above, the present invention is advantageous in that (1) since an outer-loop power control is possible even for a non-data transmission period while in DTX mode, an accurate threshold for outer-loop power control can be obtained when a data frame is generated; (2) transmission power can be saved and frame errors can be decreased due to the accurate threshold; (3) time required to converge a pre-transition threshold to a post-transition threshold in an outer-loop power control operation is reduced through threshold compensation; (4) the decrease of the convergence time prevents power consumption involved in the convergence and reduces frame errors; and (5) transmission power is minimized in the absence of a traffic signal to be transmitted in a gated transmission mode and in the presence of a traffic signal to be transmitted, the reception performance of the traffic signal is ensured.