CN103873217A

CN103873217A - Method and device for correcting CQI (channel quality indicator), and user equipment

Info

Publication number: CN103873217A
Application number: CN201210546109.6A
Authority: CN
Inventors: 薛丰廷; 沈旭强
Original assignee: Spreadtrum Communications Shanghai Co Ltd
Current assignee: Spreadtrum Communications Shanghai Co Ltd
Priority date: 2012-12-17
Filing date: 2012-12-17
Publication date: 2014-06-18

Abstract

The invention provides a method and a device for correcting a CQI (channel quality indicator), and user equipment. Better throughput can be obtained by performing more accurate channel quality indication. The method for correcting the CQI comprises the following steps: determining an SIR (signal to interference ratio) according to a receiving signal received from a base station; converting the determined SIR into the CQI; calculating a block error rate of the receiving signal; correcting the calculated CQI according to the block error rate; sending the corrected CQI value to the base station.

Description

Correction method and device for channel quality indication and user equipment

Technical Field

The present invention relates to a High Speed Downlink Packet Access (HSDPA) technology, and in particular, to a method and an apparatus for correcting a Channel Quality Indicator (CQI), and a user equipment.

Background

In a mobile communication system, in order to increase a data transmission rate in a downlink, HSDPA technology is introduced in The 3GPP (The 3rd generation Partnership Project) release R5. HSDPA is a link adaptation technique. When the user approaches the base station and the channel condition is good, the system transmits data at a high rate; when the user is far away from the base station and the channel condition is poor, the system adopts a lower rate instead of increasing the rate by increasing the power. The link adaptation technology is mainly implemented by feeding back a CQI (channel quality indicator) to a base station by a User Equipment (UE), and the base station determines a Modulation and Coding Scheme (MCS) for sending data next time according to the CQI.

HSDPA is mainly composed of two key technologies, which are HARQ (Hybrid automatic repeat Request) technology and AMC (Adaptive Modulation and coding) technology.

The HARQ technology is realized by feeding back ACK/NACK information to the base station to request the base station to retransmit a bad frame. The ACK/NACK is obtained by determining a CRC (Cyclic Redundancy Check) code of the received data, where ACK indicates that the data frame is decoded correctly, and NACK indicates that the data frame is decoded incorrectly.

The AMC technique adaptively adjusts a transmission data rate and a data coding scheme (as shown in fig. 1) according to a CQI value fed back by the UE, thereby compensating for a fading influence on a received signal due to channel variation. According to the 3GPP standard, the BLER (Block Error Rate) of data using AMC should not exceed 10%.

The implementation mode of AMC is as follows: the UE measures SIR (Signal to Interference Ratio) of the downlink channel, calculates CQI from the SIR, and feeds back the CQI to the base station. And the base station determines the MCS of the next data transmission according to the CQI fed back by the UE.

Fig. 2 shows a schematic structure of a UE adapted to the existing AMC technology. A Radio Frequency (RF) radio unit 10 of the UE amplifies and digitally converts a signal transmitted from a base station, and performs resource de-mapping on an RS signal in a PDCCH (Physical downlink control channel), a PDSCH (Physical downlink shared channel), and a PDSCH. The demodulation section 20 demodulates each channel signal after the resource de-mapping process. The rate detection unit 40 detects rate information from the control signal output from the demodulation unit 20. The decoding unit 30 decodes the data signal output from the demodulation unit 20 based on the rate information, and obtains user data that can be subjected to back-end processing. SIR measuring section 50 performs SIR measurement on the RS signal output from demodulation section 20. The CQI converting unit 60 converts the SIR measured by the SIR measuring unit 50 into a CQI. At this time, a unique corresponding CQI value is mapped from the SIR value according to the SIR-CQI mapping table specified by 3 GPP. The CQI transmitting section 70 transmits the CQI value obtained by the CQI converting section 60 to the base station.

The AMC technique is sensitive to CQI errors and delays. Whether the CQI information fed back by the UE accurately reflects the channel condition in real time has a great influence on the correct selection of the MCS. The method of mapping CQI purely according to SIR may encounter the following problems:

1. if the channel environment is too complex, especially in the case of complex external field environment, SIR is likely to be measured incorrectly, and therefore the accuracy of CQI will be affected.

When the fed back CQI value is larger than the actual CQI value, because the system modulates the data transmission rate exceeding the actual receiving capability of the channel for the UE according to the fed back CQI value, the error rate of the data block received by the UE is greatly increased, thereby causing the reduction of the throughput rate of the UE; when the fed back CQI value is smaller than the actual CQI value, the system will allocate too many data transmission resources to the UE, thereby resulting in a decrease in the overall throughput rate of the system.

2. Modulation scheduling strategies of various base station equipment manufacturers and terminal analyzers are various, some base station equipment manufacturers select MCS only according to CQI fed back by UE, and some base station equipment manufacturers can select MCS by referring to ACK/NACK messages fed back according to HARQ technology, so that even if the same feedback CQI value is used, the base station can modulate different data transmission rates, and the actual channel receiving capacity and the data transmission rate of the UE cannot be well matched.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method and an apparatus for correcting channel quality indication, and a user equipment, so as to improve the accuracy of a CQI value fed back by a UE.

The invention provides a method for correcting channel quality indication, which comprises the following steps:

measuring reception environment quality from a downlink signal received from a base station;

generating a channel quality indication corresponding to the measured reception environment quality;

calculating the block error rate of data transmitted by a downlink physical channel;

and correcting the channel quality indication according to the difference value between the calculated block error rate and a preset target block error rate, and sending the corrected channel quality indication to the base station.

The invention provides a correction device of channel quality indication, comprising:

a reception environment quality measurement unit configured to measure a reception environment quality from a downlink signal received from a base station;

a channel quality indicator generating unit configured to generate a channel quality indicator corresponding to the reception environment quality measured by the reception environment quality measuring unit;

a channel quality indicator correction unit for correcting the channel quality indicator according to a difference between the calculated block error rate and a preset target block error rate;

a channel quality indication reporting unit, configured to send the corrected channel quality indication to the base station.

The user equipment provided by the invention comprises the correction device for the channel quality indication.

Compared with the prior art, the correction method, the correction device and the user equipment have the following beneficial effects:

since the embodiment of the present invention corrects the channel quality indicator obtained by the SIR according to the block error rate of the downlink data and transmits the corrected channel quality indicator to the base station, the channel quality indicator can be corrected to an appropriate value according to the reception environment at that time every time the channel quality indicator is generated, and thus more accurate channel quality indicator can be transmitted to the base station. Therefore, better throughput can be obtained, and the actual channel reception capability and data transmission rate of the UE can be better matched.

Drawings

Fig. 1 is a CQI mapping table specified by 3 GPP;

fig. 2 is a schematic diagram of a UE adapted to existing AMC;

fig. 3 is a flow chart of a CQI correction method according to an embodiment of the present invention;

FIG. 4 is a flowchart of the operation of a UE to which the method of the present invention is applied;

fig. 5 is a flowchart of the operation of the BLER calculation method in the embodiment of the present invention;

FIG. 6 is a flowchart illustrating a CQI adjustment step calculation method according to an embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a calibration device according to an embodiment of the present invention;

fig. 8 is a schematic diagram of a UE structure using the calibration apparatus of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.

Fig. 3 is a flowchart of a CQI correction method according to an embodiment of the present invention.

In order to make up for the defects brought by singly adopting SIR to determine CQI, the inventor creatively adopts the transmission quality condition of a downlink signal to correct the CQI value, so that the user equipment can more accurately report the quality condition of a receiving environment to a network side.

The CQI correction method of the specific embodiment of the present invention comprises:

step S301 measures reception environment quality from a downlink signal received from a base station.

Because the signal transmission is carried out between the user equipment and the base station in a wireless communication mode, and various interference factors exist in the communication environment, certain influence is brought to the integrity and the accuracy of the signal.

For better communication, the base station typically adjusts the power or other parameters of its transmitted signal according to the receiving environment of the ue, so as to improve the communication quality. The quality of the reception environment is usually measured by the ue in various ways and reported to the base station.

In the prior art, various techniques exist for measuring the quality of the reception environment. Those skilled in the art will appreciate that the quality of the reception environment can be generally determined according to the transmission of the downlink signal.

One possible way is to calculate the ratio between the power of the downlink signal and the power of the interfering signal, i.e. calculate the SIR, so as to estimate the quality of the receiving environment by the effect of the interfering signal on the downlink signal.

Step S302 generates a channel quality indicator corresponding to the measured reception environment quality.

The CQI is used to indicate the reception environment quality, and is usually generated by the ue and transmitted to the base station in a message reported by the ue to the base station.

Since the CQI is used to characterize the reception environment quality, there is a correspondence between the CQI and the SIR measured from the downlink signal.

In the prior art, the corresponding relationship between SIR and CQI is usually stored in a relationship table, so that the corresponding CQI value can be obtained by looking up the relationship table between SIR and CQI according to the SIR obtained in step S301.

Of course, other ways to record the corresponding relationship between SIR and CQI may also be adopted, which can be understood by those skilled in the art and will not be described herein again.

Step S303, calculates a block error rate of data transmitted by the downlink physical channel.

The block error rate is a way to characterize the correct rate of data transmission, and various ways can be adopted to calculate the block error rate of data transmitted by the downlink physical channel.

There are a number of factors that affect the block error rate of the data, where the inventors have found that the quality of the reception environment has some effect on the block error rate.

Specifically, the block error rate may be obtained by periodically counting the CRC check code of the received data, and a ratio of the number of CRC check errors to the total number of statistical frames is the block error rate in the statistical period.

Step S304, correcting the channel quality indicator according to a difference between the calculated block error rate and a preset target block error rate.

As mentioned above, the block error rate is associated with the reception environment quality, and therefore the block error rate can be used to correct the channel quality indication.

The target block error rate is the lowest block error rate that can be tolerated under the existing channel reception environment quality. This requires that the base station modulated downlink data transmission rate match the existing channel reception environment quality.

If the block error rate calculated in step S303 is greater than the target block error rate, the channel quality indicator fed back to the base station should be correspondingly reduced, and the base station correspondingly reduces the downlink data transmission rate according to the reduced channel quality indicator, so that the block error rate of the data received by the terminal is controlled within the target block error rate.

In contrast, if the block error rate is less than the target block error rate, it is proved that the current channel can accommodate data transmission at a higher rate, and the base station should be instructed to increase the transmission rate of the downlink data.

Step S305, the corrected channel quality indication is sent to the base station.

Generally, the channel quality indicator may be transmitted back to the base station by the ue through an uplink channel, which is understood by those skilled in the art and will not be described in detail herein.

Specifically, in a TDD LTE communication system or an FDD LTE communication system, the report may be sent to the base station through an UL-SCH channel.

For the convenience of understanding the above scheme, the CQI correction method of the present invention will be described below by taking an application in an LTE system as an example.

Referring to fig. 4, the CQI correction method according to the embodiment of the present invention includes the following steps:

in step S401, the UE determines SIR according to the downlink signal of the PDSCH channel.

In the present embodiment, the SIR is obtained from a ratio of RS (Reference Signal) power on the PDSCH channel and interference Signal power.

The reference signal is similar to the pilot signal of CDMA, and is sometimes called a pilot, and is used for downlink physical channel demodulation and channel quality measurement.

The reference signal is obtained from a cell specific reference signal sequence and frequency shift mapping. The RS is essentially a pseudo-random sequence that propagates over the time-frequency domain. At a certain antenna port, the RS has a frequency domain interval of 6 subcarriers.

The RS is discretely distributed in the time-frequency domain, which is equivalent to sampling the time-frequency domain characteristics of the channel, so as to provide reference for downlink channel estimation and signal demodulation.

The data signal power is obtained by measuring the received data signal level, and the interference signal power in the channel is estimated according to the transmitted data level on the basis.

Step S402, calculating CQI value according to SIR obtained by actual measurement.

The calculation of the CQI value can also be done in a number of ways, one possible way being according to the 3GPP standard provided SIR and CQI correspondence table from which the unique corresponding CQI value can be derived from the SIR.

Step S403, calculating a block error rate according to the CRC information of the data frame.

In this embodiment, the block error rate is obtained by periodically counting the ratio of the number of bad frames of the traffic data received from the PDSCH channel to the total number of counted frames.

The PDSCH channel carries actual service data, such as voice data, short message data, and multimedia data during a call. The block error rate of the PDSCH channel is a key indicator for measuring the channel quality.

In one embodiment, the base station may dynamically adjust the TBS (Transmit block size) according to the CQI fed back, and the TBS information is described in the control signal transmitted from the base station, so that the averaging interval should be dynamically adjusted according to the size of the TBS. In this embodiment, the relationship between the statistical total frame number and the TBS is shown in table 1 below:

TABLE 1

TBS（bit）	Count the total frame number
		30000 or more	10
10000-30000	20
		10000 or less	40

Fig. 5 shows a specific flow of calculating the block error rate, which includes:

step S4031, first, obtains relevant data transmission format parameters from the PDCCH channel, for example: coding scheme, modulation scheme, TBS size, etc. Calculating to obtain a total statistical frame number in a statistical period according to the TBS size, and resetting the current frame number and the bad frame number;

step S4032, reading CRC check information of an actual service data frame in a PDSCH channel, and executing an operation of adding one to the current frame number;

step S4033, determine whether the CRC of the current data frame is correct, if the check is incorrect, go to step S4034; if the checking result is correct, executing step S4035;

step S4034, add one to the bad frame number;

step S4035, judge whether the present frame number is already greater than the total frame number that needs to count, if yes, carry out step S4036, otherwise jump back to step S4032;

step S4036, the block error rate BLER is obtained according to the ratio of the counted bad frame number and the counted total frame number.

Step S404, calculating the adjustment step size of the CQI correction value according to the block error rate;

the relationship between the channel reception environment quality and the downlink data transmission rate can be reflected according to the block error rate of the PDSCH channel calculated in step S403.

If the block error rate is far greater than the target block error rate, which proves that the downlink data transmission rate is far beyond the capacity of the channel, the CQI should be adjusted downward by a larger value so as to reduce the data transmission rate by the base station.

If the block error rate is less than or equal to the target block error rate and there is only a small difference, the CQI value only needs to be fine-tuned or not. The CQI correction value adjustment step reflects the magnitude of correction to the CQI.

Fig. 6 shows a specific implementation flow of calculating a CQI correction value adjustment step size, which includes:

step S4041 reads the target block error rate.

In the present embodiment, the target block error rate is set to 10%, i.e., the lowest tolerable block error rate specified by 3 GPP.

Of course, those skilled in the art can select the value of the corresponding target block error rate according to the actual situation and the requirement.

Step S4042, judge whether the block error rate got from step S403 is greater than the target block error rate, if yes, carry out step S4043, otherwise carry out step S4044;

step S4043, sets the CQI correction value adjustment step size to:

(block error rate-target block error rate)/10%;

in the case of a poor channel environment, the block error rate may be much greater than the target block error rate, and at this time, a large adjustment needs to be performed on the CQI, in this embodiment, 10% is used as a first-level adjustment step, for example, when the block error rate is greater than 50% of the target block error rate, the adjustment step of the CQI correction value is 5.

Step S4044, set CQI correction value adjustment step size to 1;

the step is a processing step when the block error rate is smaller than the target block error rate, and the block error rate is smaller than the target error rate, so that the downlink data transmission rate is proved to be basically matched with the current channel environment quality, and only small adjustment needs to be carried out on the CQI.

Of course, a person skilled in the art can select a corresponding step value for small adjustment according to actual conditions and requirements.

Step S405 calculates a CQI correction value according to the CQI correction value adjustment step size.

The CQI correction value adjustment step obtained in step S404 only obtains the correction amplitude of the CQI, and determines the direction of CQI adjustment according to the block error rate and the target block error rate. If the block error rate is greater than the target block error rate, the CQI correction value is a negative CQI correction value adjustment step size, otherwise the CQI correction value is a positive CQI correction value adjustment step size.

Step S406 adds the CQI correction value to the calculated CQI value.

And adding the CQI value calculated in the step S402 and the CQI correction value calculated in the step S405 to obtain a corrected CQI value.

Step S407, the corrected CQI value is transmitted to the base station.

Generally, in the LTE system, the CQI value may be transmitted back to the base station through an uplink UL-SCH channel.

In other communication systems, the corrected CQI may be reported to the base station using a corresponding uplink channel. This is understood by those skilled in the art and will not be described in detail.

Through steps S401 to S407, the CQI correction method according to the embodiment of the present invention further corrects the CQI value by calculating the block error rate of the received data, so that the fed back CQI value better reflects the actual reception environment of the current channel, and the base station modulates the data transmission rate more suitable for the current channel environment.

An embodiment of the present invention also provides an apparatus for implementing the CQI correction method, as shown in fig. 7, the apparatus includes:

a reception environment quality measurement unit 101 for measuring reception environment quality from a downlink signal received from a base station;

a channel quality indicator generating unit 102 configured to generate a channel quality indicator corresponding to the reception environment quality measured by the reception environment quality measuring unit 101;

channel quality indicator correcting section 103 corrects the channel quality indicator.

A channel quality indication reporting unit 104, configured to send the corrected channel quality indication to the base station.

For the understanding of the above devices, the following description will take the actual user terminal UE as an example. Fig. 8 is a diagram showing a structure of a UE using the apparatus, including:

an RX radio unit 10 for receiving the air signals transmitted by the respective channels from the base station;

wherein the channels associated with embodiments of the present invention include RS signals of PDSCH channels for determining SIR; a PDCCH (physical downlink control channel) for receiving various data transmission format parameters; a PDSCH channel for receiving actual service data;

a demodulation unit 20 for demodulating each channel data output from the RX radio unit 10;

a decoding unit 30 for decoding the PDSCH channel data output from the demodulation unit 20;

a rate measurement unit 40 for acquiring a parameter relating to a data transmission rate from the PDCCH channel output from the demodulation unit 20;

the parameters comprise a modulation mode, a coding mode, a TBS size and the like;

reception environment quality measurement section 101 for measuring SIR from the RX signal of the PDSCH channel output from demodulation section 20;

the SIR may be derived from a ratio of a received data signal power of the RX signal and an interference signal power;

a channel quality indicator generating unit 102 for calculating a CQI value based on the SIR measured by the reception environment quality measuring unit 101;

the 3GPP standard provides a corresponding table of SIR and CQI, and a unique corresponding CQI value can be obtained from the SIR through the table;

a CQI value correction unit 103 for further correcting the CQI value obtained from the CQI value generation unit 102 in accordance with the block error rate of the traffic data output from the decoding unit 30.

Wherein the cqi correction unit 103 comprises: a target block error rate storage unit 1031, a block error rate calculation unit 1032, a channel quality indication adjustment step calculation unit 1033, a channel quality indication correction value calculation unit 1034, and a channel quality indication correction value addition unit 1035; wherein,

target block error rate storage unit 1031, which is a nonvolatile memory device, stores a predetermined optimum block error rate, i.e., "target BLER".

Here, as the target BLER, it is assumed that the optimal block error rate "10%" specified by 3GPP is set.

Block error rate calculation section 1032 checks CRC information of data outputted from decoding section 30 to determine an error, and calculates a block error rate BLER, which is a reception error occurrence rate in block units;

a CQI adjustment step size calculation unit 1033 configured to calculate a CQI adjustment step size according to a difference between the BLER obtained by the block error rate calculation unit 1032 and the target BLER;

channel quality indicator correction value calculation section 1034 calculates a CQI correction value for correcting the CQI value calculated by channel quality indicator generation section 102, based on the target BLER, the size of the BLER, and the CQI adjustment step size.

For example, in the case where block error rate calculation unit 1032 calculates that the BLER is 20%, since the BLER is greater than the target BLER (10%) (poor reception environment), the CQI correction value is set to "-CQI adjustment step size". Conversely, in the case where the BLER is 5%, since the BLER is smaller than the target BLER (reception environment is good), the CQI correction value is set to "+ 1".

Channel quality indicator correction value adding section 1035 adds the CQI correction value calculated by channel quality indicator correction value calculating section 1034 to the CQI value calculated by channel quality indicator generating section 102 to calculate a corrected CQI value.

Channel quality indicator reporting section 104 transmits the CQI value corrected by channel quality indicator correcting section 103 to the base station.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. A method for correcting a channel quality indicator, comprising the steps of:

correcting the channel quality indication according to the difference between the calculated block error rate and a preset target block error rate, and

transmitting the corrected channel quality indication to the base station.

2. The method according to claim 1, wherein the calculating the block error rate of the data transmitted by the downlink physical channel comprises: and counting the cyclic redundancy check codes of all the subframes of the downlink physical channel in a counting period, and calculating the block error rate of the received signal according to the ratio of the number of the subframes with cyclic redundancy check code errors to the number of all the subframes.

3. The calibration method according to claim 1, wherein the downlink physical channel is a PDSCH channel.

4. The calibration method according to claim 2, wherein in the step of calculating the block error rate of the data transmitted by the downlink physical channel, the length of the statistic period is dynamically determined according to the size of the transmission block of the downlink physical channel.

5. The correction method according to any one of claims 1 to 4, wherein said channel quality indicator has a plurality of adjustment steps, and said correcting comprises calculating an adjustment step for a channel quality indicator based on a difference between said block error rate and said target block error rate.

6. The calibration method according to claim 5, wherein the calculation method of the adjustment step size of the cqi is specifically: if the calculated block error rate is greater than the target block error rate, the adjustment step size of the channel quality indicator is an integral value obtained by dividing the difference value by the target block error rate; and if the calculated block error rate is less than or equal to the target block error rate, the adjustment step length of the channel quality indicator is a preset value.

7. The correction method according to claim 5, wherein if the calculated block error rate is greater than the target block error rate, the correction value of the channel quality indicator is a negative adjustment step size of the channel quality indicator; if the calculated block error rate is less than or equal to the target block error rate, the correction value of the channel quality indicator is a positive adjustment step length of the channel quality indicator; adding the generated channel quality indication with a correction value of the channel quality indication to correct the channel quality indication.

8. An apparatus for correcting a channel quality indicator, comprising:

9. The correction device of claim 8, wherein the channel quality indication correction unit comprises:

a block error rate calculation unit for calculating a block error rate of the received data block;

a target block error rate storage unit for storing a target block error rate;

a channel quality indication adjustment step calculation unit for calculating a channel quality indication adjustment step according to a difference between the block error rate and a target block error rate;

a channel quality indication correction value calculation unit for calculating a channel quality indication correction value according to the block error rate and the channel quality indication adjustment step size;

a channel quality indication correction value adding unit for adding the channel quality indication and the channel quality indication correction value.

10. The apparatus according to claim 9, wherein the block error rate calculation unit counts cyclic redundancy check codes of all subframes of the downlink physical channel in one counting period, and calculates the block error rate of the received signal by a ratio of a number of subframes in which cyclic redundancy check codes are erroneous to the number of all subframes.

11. The apparatus according to claim 10, wherein the block error rate calculating unit dynamically determines the length of the statistic period according to a transport block size of data transmitted by the base station.

12. The correction apparatus according to claim 9, wherein the cqi adjustment step calculation unit is configured to determine the adjustment step of the cqi as an integer value of the difference divided by the target block error rate when the calculated block error rate is greater than the target block error rate; and when the calculated block error rate is less than or equal to the target block error rate, determining the adjustment step size of the channel quality indication as a preset value.

13. The correction apparatus according to claim 9, wherein if the calculated block error rate is greater than the target block error rate, the correction value of the channel quality indicator is a negative adjustment step size of the channel quality indicator; and if the calculated block error rate is less than or equal to the target block error rate, the correction value of the channel quality indicator is a positive adjustment step size of the channel quality indicator.

14. A user equipment, characterized in that it comprises a correction device of the channel quality indication according to any one of claims 8 to 13.