Patent Application
20080009302
The above and other objects, features and advantages of certain exemplary embodiments of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures.
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of the exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
An exemplary embodiment of the present invention provides an apparatus and method for adaptively grouping channels according to their statuses and for feeding back the CQI of a total frequency band based on the channel grouping. While an exemplary embodiment of the present invention is described in the context of an Orthogonal Frequency Division Multiple Access (OFDMA) communication system, it is also applicable to communication systems using other multiple access schemes.
Referring to
The RF processor 301 downconverts an RF signal received through an antenna to a baseband signal.
The FFT processor 303 converts the time signal received from the RF processor 301 to a frequency signal by FFT.
The channel estimator 305 estimates downlink channels by using a pilot signal included in the frequency signal.
The CQI generator 307 groups channels in similar statuses among the total frequency channels by using downlink channel estimates received from the channel estimator 305. The CQI generator 307 determines a representative value for each channel group and generates feedback information with the group indexes of the channels and the representative values of the groups.
The CQI generator 307 can be configured as illustrated in
Referring to
The grouper 401 orders the total frequency channels according to the channel estimates received from the channel estimator 305 and groups them so as to minimize Mean Squared Error (MSE). For example, the grouper 401 divides the total frequency channels into groups each having the same number of channels. Then the grouper 401 selects two groups, starting from a group in the poorest channel status and adjusts a separation point between every pair of two adjacent groups. The representative value of each group is assumed to be the average of the channel estimates of channels included in the group. The grouper 401 calculates the MSE by
where Ni denotes the number of channels in an ith group, xj denotes the CQI of a jth channel, mi denotes the representative value (i.e. average) of the ith group, and L denotes the number of the total groups.
The grouper 401 groups the total frequency channels by Equation (1) as illustrated in
Referring to
The grouper 401 determines a separation point between group 1 and group 2 in the poorest channel status so as to minimize the MSEs of the two groups. That is, the grouper 401 calculates an MSE variation that can occur when a channel in one group moves to the other group, for each channel in group 1 and group 2 and then determines a separation point that minimizes the MSEs of the two groups. When a channel xN
where Ni denotes the number of the channels in the ith group, mi denotes the representative value of the ith group, and xn
When a channel xN
where Ni denotes the number of the channels in the ith group, mi denotes the representative value of the ith group, and xn
The grouper 401 compares the MSE variations calculated by Equation (2) and Equation (3). If a smaller MSE variation is less than 0, the separation point between the two groups is in a position corresponding to the smaller MSE variation. The grouper 401 continues to change the separation point until the MSE variations computed by Equation (2) and Equation (3) become larger than 0.
After determining a separation point that minimizes the MSEs of group 1 and group 2, the grouper 401 selects the next better-status groups, i.e. group 2 and group 3 and repeats the above operation to determine a separation point between group 2 and group 3. The grouper 401 may group the channels according to their statuses for every CQI feedback period.
If four channel groups are produced, the grouper 401 determines a separation point between group 1 and group 2, a separation point between group 2 and group 3, and a separation point between group 3 and group 4 so that the MSEs of the groups are minimized, as illustrated in
The CQI decider 403 determines a group index for each channel according to the grouping of the grouper 401. For instance, the CQI decider 403 determines group indexes for the respective channels as illustrated in
Referring to
Subsequently, the CQI decider 403 generates feedback information including the group index of each channel and the representative value of each group and transmits the feedback information to the BS.
Referring to
In step 505, the grouper 401 selects two groups, starting from a group in the poorest channel status and determines a separation point between every pair of adjacent groups so that the MSEs of the two groups are minimized. For example, the grouper 401 calculates MSE variations that may occur when a channel moves from one group to the other group according to Equation (2) and Equation (3) and determines a separation point that minimizes the MSEs of the two groups.
Then, the grouper 401 ends the algorithm of an exemplary embodiment of the present invention.
The MS generates feedback information based on group information created in the procedure of
Referring to
In step 605, the MS feeds back the group indexes of the channels and the representative values of the groups to the BS. Then the MS ends the algorithm.
In accordance with an exemplary embodiment of the present invention, the MS groups total frequency channels and then feeds back the group indexes of the channels and the representative values of the groups.
In another exemplary implementation of the present invention, the group index of each channel is transmitted in time division as illustrated in
Referring to
Now a description will be made of performance variations in the case of feedback by an AGFS in the wireless communication system. To evaluate AGFS performance variations, a simulation was performed under the conditions of a bandwidth of 10 MHz, 16 subbands, 8 users, and a carrier of 2 GHz.
Specifically,
Referring to
Referring to
As noted from the graph, the AGFS performs almost the same as the perfect feedback scheme and outperforms the CCFS by about 100 bits/symbol or above in throughput. Thus it can be concluded that the AGFS offers higher throughput than the CCFS because the AGFS provides an accurate CQI of entire channels.
As described above, the AGFS of an exemplary embodiment of the present invention performs well, compared to the CCFS or the best-M scheme. For example, the AGFS uses a similar amount of feedback information to that of the CCFS or the best-M scheme, as illustrated in Table 1 below.
Table 1 illustrates the amounts of feedback information per unit time when information about L groups is fed back in C unit times in the AGFS, CCFS, and best-M scheme, respectively. For example, for 16 subbands or channels (N=16), five groups (L=5), and four unit times (C=4), assuming that every CQI is 5 bits in length, the AGFS, the CCFS, and the best-M scheme require similar feedback amounts, i.e., 13 bits, 10 bits, and 15 bits respectively.
In accordance with exemplary embodiments of the present invention as described above, total channels are adaptively grouped according to their statuses so as to narrow the difference between an original CQI and a recovered CQI and then the group index of each channel and the representative value of each group are fed back in a wireless communication system. The accurate feedback of the CQI of a total frequency band from a receiver to a transmitter increases higher throughput and minimizes necessary information. Therefore, the frequency efficiency of the system is maximized.
While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-0063303 | Jul 2006 | KR | national |
