QUALITY INDICATOR

FIELD OF THE INVENTION

The present invention relates to the wireless communication network, especially relates to a method and device for obtaining enhanced channel quality indicator.

BACKGROUND OF THE INVENTION

At present, CQI (Channel Quality Indicator) is based on CRS (Cell- specific

Reference Signal) in Rel.8 of 3GPP (third Generation Partnership Project). The CQI comprises three formats: wideband CQI, CQI of subband selected by UE (User Equipment) and CQI of subband configured by high layer. In a recent meeting, it is agreed that CQI calculation of Rel. lO is based on the assumption that BS (base station) utilizes a specific precoder.

SUMMARY OF THE INVENTION

For the channel quality indicator obtained by adopting CRS or based on CSI-RS (Channel State Information- Reference Signal), there are the following disadvantages:

1. scheduling prediction is not accurate:

the scheduling prediction information comprises channel preprocessing information, for example CoMP(Coordinated Multi-Points) cell, that is: which cells perform multi-cells coordination jointly so as to serve one or more UEs together; PMI (Precoding Matrix Index), that is, BS determines which code word of precoding is adopted to perform precoding for channel, and UE pairing, that is, for MU-MIMO (Multi-User Multi-Input Multi-Output) scenario, the combination of UEs that one or more BSs send a plurality of data streams with the same time frequency resources. However, since CRS or CSI-RS is reference signal without channel precoding, therefore, neither of CRS and CSI-RS comprises the aforesaid channel preprocessing information. Therefore, CQI obtained by UE based on CRS and CSI-RS is not accurate and can not reflect the actual channel condition.

2. sparse distribution in time domain and frequency domain:

CSI-RS distribution in RB (Resource Block) is very sparse and a RB for a cell only comprises a couple of CSI-RSs, so as to result in inaccurate CQI calculation.

3. delay:

Delay between CQI report and target transmission also influences performance of communication system. Therefore, the present invention proposes a method and device for obtaining enhanced CQI, and uses demodulated reference signal for CQI calculation.

In addition, besides performing MCS (Modulation and Coding Scheme) selection utilizing CQI, CQI may be desired to implement other functions. For example, CSI calibration being very important for CoMP transmission can be performed utilizing CQI or other implicit feedback, for example ACK (Acknowledge) and NACK (Not Acknowledge).

According to the first aspect of the present invention, there is provided a method, in a BS of the wireless communication network, for indicating a user equipment to feed back channel related information, the method comprises following steps: A. informing the user equipment of the related information of demodulated reference signal, wherein the user equipment will measure and feed back channel quality indicator utilizing the demodulated reference signal; B. performing channel preprocessing to the demodulated reference signal; D. sending the demodulated reference signal after channel preprocessing, to the user equipment.

According to the second aspect of the present invention, there is provided a method, in a user equipment of the wireless communication network, for feeding back channel quality information, the method comprises following steps: a. obtaining informing signaling from the BS dominating the user equipment, wherein the informing signaling is used for informing the user equipment of related information of demodulated reference signal for measurement; b. calculating channel quality indicator according to the informed demodulated reference signal; c. feeding back the channel quality indicator to the BS.

According to the third aspect of the present invention, there is provided a method, in a BS of the wireless communication network, for compensating reciprocal error between uplink and downlink, wherein the method comprises following steps:

I. explicitly or implicitly informing user equipment of information of reference signal, wherein the user equipment measures and feeds back channel quality indicator information utilizing the reference signal;

II. compensating the reference signal utilizing compensation parameters, to perform downlink channel information measurement, wherein the reference signal comprises cell specific reference signal and/or channel state information reference signal and/or demodulated reference signal;

III. sending the compensated reference signal to the user equipment;

IV. obtaining and saving channel quality information obtained according to the compensated reference signal and fed back by the user equipment;

after the step IV, the method further comprises:

V. repeating the steps II to IV with time interval of predetermined length or with predetermined times, wherein the step II repeated for each time adopts the same compensation parameter to obtain statistical average value of a plurality of channel quality information within the predetermined time interval or within the predetermined times;

after the step V, the method further comprises:

VI. repeating, in multi-turns, the steps II to V with sets of time interval of predetermined length or with sets of predetermined times to obtain statistical average values of a plurality of channel quality information respectively, wherein different compensation parameters are respectively adopted in each turn, and comparing the magnitude of the statistical average values of the plurality of channel quality information;

after the step VI, the method further comprises:

VII. using the compensation parameters for compensating channel, the compensation parameters being corresponding to the maximum statistical average value of channel quality information among statistical average values of the plurality of channel quality information.

According to the fourth aspect of the present invention, there is provided a method, in a BS of the wireless communication network, for compensating reciprocal error between uplink and downlink, wherein the method comprises following steps:

M. compensating a plurality of data to be sent utilizing compensation parameter;

N. obtaining and saving a set of response messages for the plurality of compensated data fed back by the user equipment within time interval of predetermined length, wherein the set of response messages comprises Acknowledge and Not Acknowledge;

O. calculating the ratio of the Acknowledge and Not Acknowledge within the time interval of predetermined length;

after the step O, the method further comprises:

- repeating the steps M to O with time interval of predetermined length or with predetermined times, wherein, the step M repeated for each time adopts the different compensation parameter, to obtain a plurality of sets of response messages corresponding to the predetermined time interval or within the predetermined times of each turn, and comparing the ratio in the plurality of sets;

- using the compensation parameters for compensating channel, the compensation parameters being corresponding to the set of response messages having the maximum ratio in the plurality of sets of response messages.

According to the fifth aspect of the present invention, there is provided a first device, in a BS of the wireless communication network, for indicating a user equipment to feed back channel related information, the first device comprises:

informing means, for informing the user equipment of the related information of demodulated reference signal, wherein the user equipment will measure and feed back channel quality indicator utilizing the demodulated reference signal;

preprocessing means, for performing channel preprocessing to the demodulated reference signal;

sending means, for sending the demodulated reference signal after channel preprocessing, to the user equipment.

According to the sixth aspect of the present invention, there is provided a second device, in a user equipment of the wireless communication network, for feeding back channel quality information, the second device comprises:

obtaining means, for obtaining informing signaling from the BS dominating the user equipment, wherein the informing signaling is used for informing the user equipment of related information of demodulated reference signal for measurement; calculating means, for calculating channel quality indicator according to the informed demodulated reference signal;

feeding back means, for feeding back the channel quality indicator to the BS.

For the system with spatial correlation, the solution of the present invention can obtain good performance only at the cost of less feedback overhead, and decrease the calculation complexity.

BRIEF DESCRIPTION OF THE DRAWINGS

By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects and advantages of the present invention will become apparent.

Fig. 1 shows a flowchart of a system method according to a detailed embodiment of the present invention;

Fig. 2 shows a sequence diagram according to a detailed embodiment of the present invention;

Fig. 3 shows a schematic diagram of CoMP transmission based on CRS according to a detailed embodiment of the present invention;

Fig. 4 shows a block diagram of device according to a detailed embodiment of the present invention.

In drawings, same or similar reference signs refer to the same or similar step feature or device/module.

DETAILED DESCRIPTION OF EMBODIMENTS

In the present invention, CoMP cell is taken as an example. Wherein BS 1 is the serving BS of UE 2. The skilled in the art may understand that the present invention is also suitable for single-cell wireless communication network.

Fig. 1 shows a flowchart of system method according to a detailed embodiment of the present invention. In step S10, BS 1 informs UE 2 of the related information of demodulated reference signal, wherein UE 2 measures and feeds back CQI utilizing the demodulated reference signal. The related information of the demodulated reference signal comprises sequence number of the DMRS, position of the DMRS or sequence adopted by the DMRS.

The demodulated reference signal comprises the demodulated reference signal not used for demodulating physical downlink shared channel (PDSCH) or demodulated reference signal for demodulating PDSCH. If the demodulated reference signal is used for demodulating PDSCH, the channel feature experienced by the demodulated reference signal is the same with the channel feature experienced by the PDSCH, therefore, the DMRS for demodulating PDSCH channel is suitable for smoothly changing channel, that is, when the channel feature of next time predicted by using DMRS keeps the same as that of the PDSCH channel currently for data transmission, the channel feedback information of the next time fed back by the DMRS based CQI is accurate; but if the demodulated reference signal is not used for demodulating PDSCH, since the DMRS does not need to be bound with PDSCH together, therefore, the DMRS has a high degree of freedom, the channel preprocessing to the DMRS needed for the next time can be performed flexibly according to scheduling strategy. For example, DMRS may be not experiencing channel precoding, and because DMRS has higher density than CSTRS, it can be taken as enhanced CSTRS; furthermore, DMRS can adopt different PMI from default PMI; or the DMRS may be based on CoMP cell combination based on next transmission and user pairing based on next transmission, so as to predict the channel performance of next transmission of next time accurately.

Furthermore, BS 1 may use UE specific DCI(Downlink Control Indicator) signaling to indicate which RE(Resource Element) or REs(Resource Elements) that the DMRS used by UE 1 for CQI measurement is located in, therefore UE 1 can perform CQI measurement according to the indicated DMRS, wherein the DMRS information comprises position of the DMRS, for example, in which RE in resource block the DMRS is located, that is , corresponding to which time domain symbol and frequency domain subcarrier, searched using the sequence number index in time domain and in frequency domain respectively.

Considering that adopting UE specific signaling to indicate DMRS information results in relative great signaling overhead, optionally, cell specific indicating signaling may be adopted for indicating DMRS for CQI measurement. For example, BS 1 may configure specific subframe for DMRS for CQI measurement, that is, BS 1 reserves certain DMRS ports for CQI measurement. Reserved DMRS for CQI measurement may be defined through high-layer signaling such as RRC (Radio Resource Control) signaling or through implicit manner such as combining with sequence number of SFN (Single Frequency Network). Then, UE is triggered to perform CQI measurement according to DMRS indicated by the signaling.

Then, in step SI 1, BS 1 performs channel preprocessing to DMRS. Preferably, channel preprocessing, experienced by the DMRS for CQI measurement of UE 2, is the same as the that experienced by the channel during next transmission.

Then, in step S13, BS 1 sends the demodulated reference signal after channel preprocessing, to UE 2.

Then, in step S14, UE 2 calculates CQI according to the informed demodulated reference signal.

Then, in step S15, UE 2 feeds back the calculated CQI to BS 1.

In aforesaid embodiment, in step S10, that BS 1 firstly sends to UE 2 the signaling comprising the DMRS indicating for CQI calculation considers that UE 2 needs to perform demodulation after receiving the signaling, so as to result in certain delay. For the purpose that UE2 can obtain these DMRS for CQI measurement in time, it is necessary to send these indicating signaling to UE2 in advance. Certainly, the skilled in the art may understand completely that aforesaid step S10 and step Sl l can also be parallel, or the sending of SI 1 is prior to S10.

Fig. 2 shows a sequence diagram according to a detailed embodiment of the present invention. Compared with traditional CQI, unused DMRS is adopted to perform CQI report so as to prolong the interval between the "predicted" transmission and "actual" transmission, as shown in Fig. 2. The skilled in the art may understand, the shorter the time interval between the two ones is, the more accurate the channel prediction information is.

In order to decrease the prolonged time interval, it is necessary to select suitable downlink transmission and uplink report mechanism with shortest delay. For TDD system, SRS (Sounding Reference Signal) based on aperiodicity can be adopted so that actual downlink transmission is not needed. For FDD system, downlink CRS or DMRS and long-term precoding matrix indicating symbol based on uplink are adopted, which can eliminate uplink report and shorten process delay.

In a varied embodiment, considering the RF mismatch among antennas of each BS of multiple cells, that is, there are great differences between the RF circuit of wireless transmitter and the RF circuit of wireless receiver, which thus results in the reciprocal error between uplink and downlink channel. Since the traditional self calibration can not thoroughly solve the RF mismatch among multiple cells. Therefore, the DMRS based CQI can be adopted to calibrate the RF mismatch error among multiple antennas. Taking two CoMP cells as an example as follows. Certainly, the skilled in the art may understand, the following described solution may also be extended to CoMP system with more than two BSs.

The H"' and H ^dl are both the IxM vectors respectively representing the

UL and DL channel parameters between the M transmitting antennas of the cell i and the single-antenna of CoMP UE. Therefore, the RF mismatch between antenna 1 and antenna 2 can be illustrated as:

Wherein J denotes power, that is, the amplitude offside, φ denotes the phase offset, ( Άπά φ are both compensation parameter acting on antennas, hf , hf denote the 1 ^th element of H ^ul and H ^dl respectively, mean denotes the average value of a plurality of measurements and calculation results.

For example, BS 1 and BS 3 serve UE 2 cooperatively, then, after BS 1 has performed channel preprocessing to DMRS in step S l l, and after BS 1 has sent the reference signal in step S 13, the method further comprises following adjustment step

S 12:

CoMP coordinated cells adjust the relative amplitude errors and relative phase errors between BS 1 and 3 according to ML (Maximum Likelihood)-alike method. Specifically, the adjustment step S 12 can be divided into:

Sub-step S 120: If the possible relative phase offset space between antenna of

BS 1 and antenna of BS 3 is , then the searching space could be π π

, where g denotes the search steps determined by the calibration 4 4

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accuracy requirement. For example, g =— , if the final calibration error should be

18

71

controlled within— , g denotes the phase increment in each loop relative to previous

18

loop. And, similar to phase adjustment, the adjustment space and step for amplitude can be defined as: σ = [-0.5dB : O. ldB : 0.5dB] , wherein O. ldB is the step of amplitude adjustment, in the following, O. ldB is denoted as s. For example, initially, BS 1 determines to take { σ, }={ -— , -0.5dB} as the first compensation parameter, to compensate antennas of BS 1 and BS 3. Calibration process for antennas in the following is also compensation for antennas.

Sub-step S 121: then, The BS 1 and BS 3 compensate their respective transmitting antennas in a MRT (Maximum Ratio Transmission) mode adopting the following formula respectively, that is, after the DMRS to be sent in step S 12 experiences base band channel preprocessing, the DMRS to be sent is further compensated adopting the following formulas in RF:

For antenna of BS 1, compensation formula:

For antenna of BS3, compensation formula:

Sub-step S 122: BS 1 and BS 3 send the compensated DMRS to UE 2.

Sub-step S 123: BS 1 obtains and saves the CQI obtained according to the compensated DMRS and fed back by UE 2.

Sub-step S 124: BS 1 repeats aforesaid sub-steps S 121 to S 123 with the same compensation parameters ⁽ d <p namely i ~~^ > -0.5dB}, till the predetermined condition is satisfied, the predetermined condition for example comprises:

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BS 1 repeats sending DMRS compensated by parameter { -— , -0.5dB} till time interval of predetermined length is reached, or the times for repeated sending reaches predetermined times. Then, BS 1 calculates statistic average value of these feedback CQIs according to CQI fed back for each time so as to finish antenna compensation for one turn.

Then, BS 1 performs antenna compensation for the next turn. For example,

BS 1 adjusts and #> according to values of g and s. The value of { σ, φ } is

{ -— +g, -0.5dB+s }, that is, { -—+—, -0.5dB+0.1dB} = {— - , -0.4dB}. BS 1 4 4 18 36

Ίπ

repeats aforesaid sub-steps S 121 to S 124 according to { , -0.4dB} again.

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Sub-steps S 121 to S 124 are repeated till aforesaid predetermined condition is satisfied, that is, after the repeated time length or the repeated times satisfies the predetermined time length or the predetermined times, the statistic average value of the CQI after compensation for this turn is calculated. Then, values of O and φ are again increased progressively, and ub-steps S 121 to S 124 are repeated till all of combinations within are traversed

so as to obtain statistic average values of a plurality of channel quality information corresponding to respective combination and compare the magnitude of statistic average value of the plurality of channel quality information.

Then, BS 1 selects the compensation parameters for compensating channel, the compensation parameters being corresponding to the maximum statistical average value of channel quality information among statistical average values of the plurality of channel quality information.

In one embodiment, based on simulation parameters set in table 1, table 2 shows simulation results of CQI average values corresponding to each compensation parameter pair { σ, } .

Table 1

Table 2

1 9.07 9.06 9.03 8.93 8.51 7.26

2 5.85 5.84 5.83 5.76 5.50 4.68

From table 2, it is easy to see that the DMRS based CQI calibration is very accurate. Furthermore, the calibration performance will be further improved if the preferable UE is selected to aid calibration, for example, according to certain regulation, for example, selecting UE with slow mobility or selecting UE without cells handover, or selecting the UE, being in the middle position of a plurality of BSs in CoMP cluster and being located at cell edge, to calibrate, or adopting longer statistic time for calibration.

In aforesaid simulation, assuming that calibration within cell is finished. Taking a BS with 4 antennas as an example, if calibration within a cell has already finished, it means that 4 antennas of a BS is calibrated.

Certainly, the present invention is also suitable for the scenario in which antennas within a cell are not calibrated. If antennas within a cell are not calibrated, firstly an antenna is fixed, other antennas in CoMP cluster are selected in turn, to be adjusted according to formula (1) and (2).

In each aforesaid embodiment, the solution of compensating according to

DMRS based CQI is described. It can be understood that CRS/CSI-RS based CQI may also be adopted for antenna calibration for multiple BSs besides DMRS based CQI.

Fig. 3 shows a schematic diagram of antennas according to the embodiment. Wherein 8 transmitting antennas and 8 receiving antennas are shown in Fig. 3. The solution of antenna compensation is similar to the aforesaid step S 12, thus it is not necessary to repeat again.

Influence that calibration process has on CRS CoMP

-influence on PDSCH:

There is no influence on cell edge users. For cell center users, as shown in

Fig. 3, since antennas originally serving the cell need to serve UEs of neighboring cells during CoMP coordination; therefore, there is averagely OdB interference on the inter-cell CRS position, which will probably decrease detection performance of PDSCH, but can be compensated by MCS (Modulation and Coding Scheme) selection.

-influence on PDCCH:

Similar to PDSCH, there is averagely OdB interference on PDCCH for those center UEs, which should be acceptable considering the robustness (non time-shifting property) on PDCCH. Furthermore, if necessary, interference can be eliminated via FDM (Frequency Division Multiplexing, comprising cross carrier scheduling for Rel.10) and TDM (Time Division Multiplexing, varied OFDM symbols for different cells), etc.

It should be taken into consideration that these influences occur only during calibration phase, which only occupies a small part of the whole communication time.

Since CRS indicates UE to measure according to corresponding information of CRS via operation such as predefined scrambling, etc, and needs not signaling indication, so it is called implicit informing manner.

Certainly, the skilled in the art may understand that how to perform CQI feedback is related to specific UE implementation. The skilled in the art may calculate CQI adopting more than one reference signals according the contents disclosed by the present invention, as long as the definition of CQI meets the norms.

In each aforesaid embodiment, the calibrations among antennas of multiple base stations are all performed utilizing CQI information. The calibrations among antennas of multiple base stations may be performed utilizing coarse feedback information such as ACK or NACK message besides CQI information.

For example, firstly, BS 1 utilizes compensation parameters to compensate a plurality of data to be sent, which BS 1 cooperates with BS 3 adopting CoMP manner. The compensation formulas are the same as formula (1) and formula (2).

Then, BS 1 obtains and saves a set of response messages for the plurality of compensated data fed back by UE 2 within time interval of predetermined length, wherein the set of response messages comprises ACK (Acknowledge) and NACK (Not Acknowledge).

Then, BS 1 calculates the ratio of the ACK and NACK within the time interval of predetermined length.

Then, BS 1 selects another pair of compensation parameters and continues to send a plurality of data compensated by such another pair of compensation parameters with time interval of predetermined length or with predetermined times, to obtain a set of response messages corresponding to such another pair of compensation parameters, and calculates the ratio of the ACK and NACK corresponding to such another pair of compensation parameters. BS 1 selects different compensation parameter pairs and repeats to perform aforesaid steps till BS 1 traverses all of possible combinations of compensation parameter pairs.

Then, BS 1 compares the ratios of the plurality of sets of obtained ACK and NACK and takes the compensation parameters corresponding to the set with maximum ratio as the compensation parameters of transmission channel.

Several embodiments of the present invention are described from the aspect of system method as above. The embodiments of the present invention will be generally described from the aspect of device as follows.

Fig. 4 shows a block diagram of device according to a detailed embodiment of the present invention. Wherein the first device 10 is located in BS 1, the second device 20 is located in UE 2. The first device 10 comprises informing means 100, preprocessing means 101 and sending means 102. The second device 20 comprises obtaining means 200, calculating means 201 and feeding back means 202.

Firstly, informing means 100 is used for informing the user equipment of the related information of demodulated reference signal, wherein the user equipment will measure and feed back channel quality indicator utilizing the demodulated reference signal.

Then, obtaining means 200 is used for obtaining informing signaling from the base station dominating the user equipment, wherein the informing signaling is used for informing the user equipment of the related information of demodulated reference signal for measurement;

Then, preprocessing means 101 is used for performing channel preprocessing to the demodulated reference signal;

Then, sending means 102 is used for sending the demodulated reference signal after channel preprocessing, to the user equipment.

Then, calculating means 201 is used for calculating channel quality indicator according to the informed demodulated reference signal;

Finally, feeding back means 202, is used for feeding back the channel quality indicator to the base station.

It should be noted that the above-mentioned embodiment is only illustrative rather than limitation to the present invention. Any technical solutions without departing from the spirit of the present invention should fall within the protection scope of the present invention, which comprises: the different technical features used in different embodiments may be combined with each other so as to obtain beneficial effect. In addition, any reference signs in the claims should not be regarded as limiting the related claims; the term "comprise" does not exclude the device or steps not listed in other claims or descriptions; the term "a/an" preceding an element does not exclude a plurality of such element exist; in a device comprising a plurality of means, the function of at least one of the plurality of means may be implemented by the same hardware or software module; the terms such as "first", "second", "third" are used to represent name rather than any specific order.