US 20100027698 A1 Abstract A channel estimation apparatus of the present invention includes a preamble channel operation unit for carrying out an operation on pilot channel estimation values of pilots, which are transmitted from a transmitting antenna that transmits a preamble, as an improved pilot channel estimation value by employing a preamble channel estimation value based on a preamble included in received signals respectively received by a plurality of receiving antennas, a first channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing the improved pilot channel estimation value, and a second channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas.
Claims(55) 1. A channel estimation apparatus in a Multiple Input Multiple Output (MIMO) wireless communication system supporting OFDM or OFDMA, the channel estimation apparatus comprising:
a first channel operation unit for carrying out an operation on pilot channel estimation values of pilots, which are transmitted from a transmitting antenna that transmits a preamble, as an improved pilot channel estimation value with respect to each of a plurality of receiving antennas by employing a preamble channel estimation value based on the preamble included in received signals received by the plurality of receiving antennas, respectively; a first channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing the improved pilot channel estimation value; and a second channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. 2. The channel estimation apparatus according to 3. The channel estimation apparatus according to H(a,s)=W1(a,s)ืH_pre(a, s)+W2(a, s)ืH_pil(a,s) [Equation](H indicates the improved pilot channel estimation value, W 1 indicates a preamble weight value, H_pre indicates the preamble channel estimation value, W2 indicates a pilot weight value, H_pil indicates the pilot channel estimation values of the pilots transmitted from the transmitting antenna, a indicates a subcarrier index, and s indicates a symbol index).4. The channel estimation apparatus according to W2=1−W1(symbol offset is symbol offset based on a preamble) 5. The channel estimation apparatus according to a first symbol index channel estimation unit for estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the improved pilot channel estimation value with respect to each of the receiving antennas; and a first frequency axis channel estimation unit for estimating a channel of the frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing a channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. 6.-8. (canceled)9. The channel estimation apparatus according to a second symbol index channel estimation unit for estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the pilot channel estimation values of the pilots transmitted from the same transmitting antenna; and a second frequency axis channel estimation unit for estimating a channel of the frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing a channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. 10.-11. (canceled)12. The channel estimation apparatus according to 13.-14. (canceled)15. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA, the channel estimation apparatus comprising:
a first channel estimation unit for estimating a channel for each of a plurality of receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from a transmitting antenna, which transmits a preamble included in received signals received by the respective receiving antennas; a first channel operation unit for estimating an improved channel with respect to each of the receiving antennas through operation of the estimated channel estimation value and a preamble channel estimation value of the preamble; and a second channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. 16. The channel estimation apparatus according to a first symbol index channel estimation unit for estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the pilot channel estimation values of the pilots; and a first frequency axis channel estimation unit for estimating a channel of the frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing channel estimation values estimated along the symbol axis with respect to each of the receiving antennas. 17.-19. (canceled)20. The channel estimation apparatus according to a second symbol index channel estimation unit for estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the pilot channel estimation values of the pilots transmitted from the same transmitting antenna; and a second frequency axis channel estimation unit for estimating a channel of the frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing a channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. 21.-22. (canceled)23. The channel estimation apparatus according to 24. The channel estimation apparatus according to H1(a, s)=W3(a, s)ืH_pre(a, s)+W4(a, s)ืH_pil1(a, s) [Equation](H 1 indicates the improved channel estimation value, W3 indicates a preamble weight value, H_pre indicates the preamble channel estimation value, W4 indicates the estimated channel weight value, H_pil indicates the estimated channel estimation value, a indicates a subcarrier index, and s indicates the symbol index).25. The channel estimation apparatus according to W4=1−W3(symbol offset is symbol offset on the basis of a preamble). 26.-28. (canceled)29. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA, the channel estimation apparatus comprising:
a first channel operation unit for carrying out an operation on pilot channel estimation values of pilots as improved pilot channel estimation values by employing a preamble channel estimation value of a preamble, of the preamble and the pilots included in a first received signal received from a first transmitting antenna through a first receiving antenna; a first channel estimation unit for estimating a channel with respect to the first received signal through interpolation of a symbol axis and a frequency axis employing the improved pilot channel estimation value; and a second channel estimation unit for estimating a channel with respect to a second received signal, received from a second transmitting antenna through the first receiving antenna, through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values based on pilots included in the second received signal. 30. The channel estimation apparatus according to a third channel operation unit for carrying out an operation on a pilot channel estimation value based on pilots included in a third received signal, received from the first transmitting antenna through a second receiving antenna, as an improved pilot channel estimation value by employing a preamble channel estimation value based on a preamble included in the third received signal, of the preamble and the pilots included in the third received signal; a third channel estimation unit for estimating a channel with respect to the third received signal through interpolation of a symbol axis and a frequency axis by employing the improved pilot channel estimation value of the pilots include in the third received signal; and a fourth channel estimation unit for estimating a channel with respect to a fourth received signal, received from the second transmitting antenna through the second receiving antenna, through interpolation of a symbol axis and a frequency axis by employing a pilot channel estimation value based on pilots included in a fourth received signal. 31. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA, the channel estimation apparatus comprising:
a first channel estimation unit for estimating a channel with respect to a first received signal, taken from a first transmitting antenna through a first receiving antenna, through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots, of a preamble and the pilots included in the first received signal; a first channel operation unit for estimating an improved channel with respect to the first received signal through operation of the estimated channel estimation value and a preamble channel estimation value of the preamble; and a second channel estimation unit for estimating a channel with respect to a second received signal, received from a second transmitting antenna through the first receiving antenna, through interpolation of a symbol axis and a frequency axis employing a pilot channel estimation value based on pilots included in the second received signal. 32. The channel estimation apparatus according to a third channel estimation unit for estimating a channel with respect to a third received signal received from the first transmitting antenna from a second receiving antenna through interpolation of a symbol axis and a frequency axis employing a pilot channel estimation value based on pilots included in the third received signal, of a preamble and the pilots included in the third received signal; a third channel operation unit for estimating an improved channel with respect to the third received signal through operation of the channel estimation value estimated with respect to the third received signal and a preamble channel estimation value based on the preamble included in the third received signal; and a forth channel estimation unit for estimating a channel with respect to a forth received signal, received from a second transmitting antenna through the second receiving antenna, through interpolation of a symbol axis and a frequency axis employing a pilot channel estimation value based on pilots included in the forth received signal. 33.-34. (canceled)35. A channel estimation apparatus in a wireless communication system supporting OFDM or OFDMA, the channel estimation apparatus comprising:
a TO estimation unit for estimating time offset using a received signal; a TO compensation unit for compensating for phase error using the estimated time offset; a weight value storage unit configured to store predetermined calculated weight values; and at least one channel estimation unit for estimating a channel of the received signal by employing the product of pilot channel estimation values, with respect to the received signal whose time offset has been compensated for, and the weight values. 36. (canceled)37. The channel estimation apparatus according to 38. The channel estimation apparatus according to 39. The channel estimation apparatus according to 40. The channel estimation apparatus according to 41.-44. (canceled)45. A channel estimation method in a MIMO wireless communication system supporting OFDM or OFDMA, the method comprising the steps of:
carrying out an operation on pilot channel estimation values of pilots, which are transmitted from a transmitting antenna that transmits a preamble, as an improved pilot channel estimation value with respect to each of a plurality of receiving antennas by employing a preamble channel estimation value based on the preamble included in received signals received by the plurality of receiving antennas, respectively; estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing the improved pilot channel estimation value; and estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. 46. The channel estimation method according to 47. The channel estimation method according to H(a,s)=W1(a,s)ืH_pre(a, s)+W2(a, s)ืH_pil(a,s) [Equation](H indicates the improved pilot channel estimation value, W
1 indicates a preamble weight, H_pre indicates the preamble channel estimation value, W2 indicates a pilot weight value, H_pil indicates the pilot channel estimation values of the pilots transmitted from the transmitting antenna, a indicates a subcarrier index, and s indicates a symbol index).48. The channel estimation method according to W2=1−W1(symbol offset is symbol offset based on a preamble) 49. The channel estimation method according to estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the improved pilot channel estimation value with respect to each of the receiving antennas; and estimating a channel of the frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing a channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. 50.-52. (canceled)53. The channel estimation method according to estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the pilot channel estimation values of the pilots transmitted from the same transmitting antenna; and estimating a channel of the frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing a channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. 54.-55. (canceled)56. The channel estimation method according to 57.-58. (canceled)59. A channel estimation method in a MIMO wireless communication system supporting OFDM or OFDMA, the method comprising the steps of:
estimating a channel for each of a plurality of receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from a transmitting antenna, which transmits a preamble included in received signals received by each of the receiving antennas; estimating an improved channel with respect to each of the receiving antennas through operation of the estimated channel estimation value and a preamble channel estimation value of the preamble; and estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. 60. The channel estimation method according to estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the pilot channel estimation values of the pilots; and estimating a channel of the frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing a channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. 61.-63. (canceled)64. The channel estimation method according to estimating a channel of the symbol axis with respect to each of the receiving antennas through interpolation of the symbol axis employing the pilot channel estimation values of the pilots transmitted from the same transmitting antenna; and 65.-67. (canceled)68. The channel estimation method according to H1(a, s)=W3(a, s)ืH_pre(a, s)+W4(a, s)ืH_pil1(a, s) [Equation](H
1 indicates the improved channel estimation value, W3 indicates a preamble weight value, H_pre indicates the preamble channel estimation value, W4 indicates the estimated channel weight value, H_pil indicates the estimated channel estimation value, a indicates a subcarrier index, and s indicates the symbol index).69. The channel estimation method according to W4=1−W3(symbol offset is symbol offset on the basis of a preamble). 70. A channel estimation method in a MIMO wireless communication system supporting OFDM or OFDMA, the channel estimation method comprising the steps of:
estimating a channel of a symbol axis with respect to each of a plurality of receiving antennas through interpolation of a symbol axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a plurality of transmitting antennas; and estimating a channel of a frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing the channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. 71. The channel estimation method according to 72. The channel estimation method according to 73.-83. (canceled)84. A channel estimation method in a wireless communication system supporting OFDM or OFDMA, the method comprising the steps of:
(a) finding a pilot channel estimation value with respect to a pilot obtained in a subcarrier frequency allocation unit; and (b) estimating a channel by employing weight values, which are predetermined based on at least one of interpolation on a time axis, interpolation on a frequency axis and an moving average, and the pilot channel estimation value. 85. The channel estimation method according to 86. The channel estimation method according to Description The present invention relates to an apparatus and method for estimating a channel in a wireless communication system and, more particularly, to an apparatus and method for estimating a channel in a Multiple Input Multiple Output (MIMO) wireless communication system in which IEEE 802.16d/e, WiBro, and WiMAX standard specifications are used and Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiplexing Access (OFDMA) is supported. Mobile wireless channel environment includes a multi-path characteristic between a base station and a mobile station due to radio wave obstacles, which are distributed all around and have various sizes and materials, and also has a time-variable characteristic of a received signal since the mobile station or radio wave obstacles are moved. A multi-path between the base station and the mobile station has paths of different lengths, and has a delay spread characteristic in which a received signal is lengthily extended. A wireless packet channel has time selective fading where a channel is varied according to time due to this characteristic and frequency selective fading having frequency components of different sizes and phases due to delay reception through multiple paths having a variety of lengths, resulting in the distortion of a transmission signal. These channel characteristics have different sizes and phases according to time and path. In order to obtain an original transmission signal from a received signal, channel state information of the transmission signal, which is related to the signal distortion, needs to be known. As well known to those having ordinary skill in the art, a training symbol that is previously defined between a transmitter and a receiver is necessary in order to estimate a channel in a mobile station. In particular, training symbols that can be used in the downlink of systems to which the IEEE 802.16e standard is applied, or a Wibro system of the systems include a preamble and a pilot. The preamble is transmitted through a first OFDMA symbol of the entire downlink frame, and the pilot is transmitted through the entire OFDMA symbols of a downlink frame except for the preamble. Therefore, in a communication mobile station, a channel has to be estimated by employing the preamble and/or the pilot, and an original transmission signal has to be acquired from a received signal by employing the estimated channel. Accordingly, the present invention has been made to fulfill the above needs, and an object of the present invention is to provide an apparatus and method for estimating a channel in a MIMO wireless communication system supporting OFDM or OFDMA. Another object of the present invention is to provide an apparatus and method for estimating a channel by employing a pilot channel estimation value of a downlink Partial Usage of Sub-Channels (PUSC) mode included in received signals received by a plurality of receiving antennas. A further object of the present invention is to provide an apparatus and method for estimating a channel by employing a preamble channel estimation value and pilot channel estimation values of pilots transmitted from a plurality of transmitting antennas. Yet another object of the present invention is to provide an apparatus and method for estimating a channel through interpolation of a preamble channel estimation value and a pilot channel estimation value. Still another object of the present invention is to provide an apparatus and method for estimating a channel by carrying out an operation on a channel, which is estimated through interpolation of pilot channel estimation values, and a preamble channel estimation value and then employing the operation result. Still another object of the present invention is to provide an apparatus and method for estimating a channel by employing the pattern of pilots in a wireless communication system supporting OFDM or OFDMA. Still another object of the present invention is to provide a channel estimation apparatus and method, wherein a weight value according to the pattern of pilots is previously determined off-line in a MIMO wireless communication system supporting OFDM or OFDMA, thus reducing complexity when a receiving system estimate a channel. For the above objects, a channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes a first channel operation unit for carrying out an operation on pilot channel estimation values of pilots, which are transmitted from a transmitting antenna that transmits a preamble, as an improved pilot channel estimation value with respect to each of a plurality of receiving antennas by employing a preamble channel estimation value based on the preamble included in received signals received by the plurality of receiving antennas, respectively; a first channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing the improved pilot channel estimation value; and a second channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes a first channel estimation unit for estimating a channel for each of a plurality of receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from a transmitting antenna, which transmits a preamble included in received signals received by the respective receiving antennas; a first channel operation unit for estimating an improved channel with respect to each of the receiving antennas through operation of the estimated channel estimation value and a preamble channel estimation value of the preamble; and a second channel estimation unit for estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes a symbol index channel estimation unit for estimating a channel of a symbol axis with respect to each of a plurality of receiving antennas through interpolation of a symbol axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a plurality of transmitting antennas; and a frequency axis channel estimation unit for estimating a channel of a frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing the channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes a first channel operation unit for carrying out an operation on pilot channel estimation values of pilots as improved pilot channel estimation values by employing a preamble channel estimation value of a preamble, of the preamble and the pilots included in a first received signal received from a first transmitting antenna through a first receiving antenna; a first channel estimation unit for estimating a channel with respect to the first received signal through interpolation of a symbol axis and a frequency axis employing the improved pilot channel estimation value; and a second channel estimation unit for estimating a channel with respect to a second received signal, received from a second transmitting antenna through the first receiving antenna, through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values based on pilots included in the second received signal. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes a first channel estimation unit for estimating a channel with respect to a first received signal, received from a first transmitting antenna through a first receiving antenna, through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots, of a preamble and the pilots included in the first received signal; a first channel operation unit for estimating an improved channel with respect to the first received signal through operation of the estimated channel estimation value and a preamble channel estimation value of the preamble; and a second channel estimation unit for estimating a channel with respect to a second received signal, received from a second transmitting antenna through the first receiving antenna, through interpolation of a symbol axis and a frequency axis employing a pilot channel estimation value based on pilots included in the second received signal. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes first and second symbol axis channel estimation units for estimating channels of a symbol axis with respect to first and second received signals, respectively, which are received through a first receiving antenna, through interpolation of the symbol axis employing a pilot channel estimation value based on pilots included in the first and second received signals; and first and second frequency axis channel estimation units for estimating channels of a frequency axis with respect to the first and second received signals through interpolation of the frequency axis employing the channel estimation values of the symbol axis of the first and second received signals. A channel estimation apparatus in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes a TO estimation unit for estimating time offset using a received signal; a TO compensation unit for compensating for phase error using the estimated time offset; a weight value storage unit configured to store predetermined calculated weight values; and at least one channel estimation unit for estimating a channel of the received signal by employing the product of pilot channel estimation values, with respect to the received signal whose time offset has been compensated for, and the weight values. A channel estimation method in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes the steps of carrying out an operation on pilot channel estimation values of pilots, which are transmitted from a transmitting antenna that transmits a preamble, as an improved pilot channel estimation value with respect to each of a plurality of receiving antennas by employing a preamble channel estimation value based on the preamble included in received signals received by the plurality of receiving antennas, respectively; estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing the improved pilot channel estimation value; and estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. A channel estimation method in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes the steps of estimating a channel for each of a plurality of receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from a transmitting antenna, which transmits a preamble included in received signals received by the respective receiving antennas; estimating an improved channel with respect to each of the receiving antennas through operation of the estimated channel estimation value and a preamble channel estimation value of the preamble; and estimating a channel for each of the receiving antennas through interpolation of a symbol axis and a frequency axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a transmitting antenna that does not transmit the preamble, of a plurality of transmitting antennas. A channel estimation method in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes the steps of estimating a channel of a symbol axis with respect to each of a plurality of receiving antennas through interpolation of a symbol axis employing pilot channel estimation values of pilots transmitted from the same transmitting antenna, of pilots transmitted from a plurality of transmitting antennas; and estimating a channel of a frequency axis with respect to each of the receiving antennas through interpolation of the frequency axis employing the channel estimation value estimated as the symbol axis with respect to each of the receiving antennas. A channel estimation method in a MIMO wireless communication system supporting OFDM or OFDMA according to an aspect of the present invention includes the steps of (a) compensating for error according to time offset and/or carrier frequency offset by extracting pilots from a received signal; and (b) estimating a channel with respect to the received signal by employing the product of channel estimation values of the pilots whose error has been compensated for and predetermined weight values. Accordingly, the present invention has an advantage in that it can increase the accuracy of channel estimation by employing a preamble channel estimation value of a preamble and pilot channel estimation values of pilots transmitted from a plurality of transmitting antennas in a MIMO communication system. Furthermore, the present invention can estimate a channel by employing a pilot channel estimation value of a downlink PUSC channel mode included in received signals received by a plurality of receiving antennas. Further, the present invention accuracy of channel estimation by estimating a channel through interpolation of a preamble channel estimation value and a pilot channel estimation value. Furthermore, the present invention accuracy of channel estimation by carrying out an operation on a channel estimated through interpolation between a pilot channel estimation value and a preamble channel estimation value. Further, the present invention channel estimation by estimating a channel by setting weight values differently according to pilot patterns. The present invention will now be described in detail in connection with preferred embodiments with reference to the accompanying drawings. For reference, in the following description, detailed description on the known functions and constructions, which may make the gist of the present invention unnecessarily vague, will be omitted. Before detailed description, the term communication mobile station used in this specification refers to a communication mobile station that supports an OFDM scheme or an OFDMA scheme, preferably, a communication mobile station that supports PUSC, Full Usage of Sub-Channels (FUSC), and Band Adaptation Modulation Coding (AMC) channel modes in a wireless communication system that uses IEEE 802.16d/e, WiBro, and WiMAX standard specifications. Further, only the PUSC channel mode is described in the detailed description of the present invention. However, the present invention may also be applied to the FUSC and Band Adaptive Modulation Coding (AMC) channel modes. Further, the term wireless communication system used in this specification may refer to a system based on one of IEEE 802.16d/e standard, WiBro, and WiMAX. Further, the term symbol used in this specification refers to an OFDMA or OFDM symbol. Referring to In particular, in relation to the present invention, if it is sought to employ 1024 Fast Fourier Transform (FFT) of a subcarrier allocation method relating to the downlink PUSC mode, allocation can be performed as in the following table 1.
Referring to Table 1 and The downlink PUSC mode is defined over 2 symbol periods that are consecutive on the time axis, and includes a Frame Control Header (FCH) for transmitting frame configuration information. Furthermore, the downlink PUSC zone comprises subcarriers distributed on the frequency axis, and one downlink PUSC subchannel includes 4 pilot subcarriers and 48 data subcarriers. Further, the basic configuration unit of the downlink PUSC subchannel is a cluster. In the cluster, all subcarriers other than the null subcarriers and the DC subcarriers are blocked into 14 neighboring subcarriers. Meanwhile, the present invention is applied to a MIMO system for carrying out MIMO transmission using a plurality of transmitting antennas and a plurality of receiving antennas. The MIMO system is described below with reference to As illustrated in Unlike the above configuration, the MIMO system is configured to perform MIMO transmission through a plurality of channels, which are formed between a plurality of transmitting antennas and a plurality of receiving antennas. A method of transmitting the signal of the 2ื2 MIMO system is described in detail below with reference to In the downlink period, a base station (or a radio access station) transmits signals through the two transmitting antennas TxAnt For reference, Further, preamble subcarriers are positioned at predetermined intervals ( Meanwhile, Referring to In this case, the pilots and data pattern received by each receiving antenna are illustrated in Referring to An apparatus and method for estimating a channel in accordance with a variety of embodiments of the present invention are described below with reference to Referring to The first and second FFT units The transformed received signal includes a preamble signal, a pilot signal, a data signal, and so on. The channel estimation apparatus in accordance with the present invention is configured to estimate a channel by employing a preamble and a pilot related to the downlink PUSC mode, included in the received signal. The pilots, which are included in the received signals and received from the two transmitting antennas, have different pilot patterns. The first channel operation unit The improved pilot channel estimation value can be represented by the following Equation 2. where H indicates the improved pilot channel estimation value, W The preamble weight value and the pilot weight value can be represented by the following Equation 3.
where symbol offset indicates symbol offset on the basis of a preamble. The third channel operation unit The first channel estimation unit The first channel estimation unit The first symbol index channel estimation unit In the case of a channel not located between the improved pilot channel estimation values on the symbol axis, a pilot channel estimation value located at the nearest symbol index, of the improved pilot channel estimation values, can be copied to the channel not located between the improved pilot channel estimation values. At this time, in the case of a channel located between an improved pilot channel estimation value having the smallest symbol index, of the improved pilot channel estimation values, on the symbol axis and the preamble channel estimation value, the channel can be estimated through interpolation of the improved pilot channel estimation value having the smallest symbol index and the preamble channel estimation value. The first frequency axis channel estimation unit At this time, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated along the symbol axis can be copied to the channel not located between the estimated channels. The second channel estimation unit The second channel estimation unit The second symbol index channel estimation unit At this time, in the case of a channel not located between the pilot channel estimation values of the pilots transmitted from the second transmitting antenna in the symbol axis, a pilot channel estimation value located at the nearest symbol index, of the pilot channel estimation values of the pilots transmitted from the second transmitting antenna, can be copied to the channel not located between the pilot channel estimation values of the pilots transmitted from the second transmitting antenna. The second frequency axis channel estimation unit At this time, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol axis can be copied to the channel not located between the estimated channels. Referring back to The fourth channel estimation unit In other words, in the channel estimation apparatus in accordance with the present invention as illustrated in The operation of Referring to For example, a preamble channel estimation value P so the pilot channel estimation value p On the other hand, since the pilot channel estimation value p Thus, the pilot channel estimation values p If the operation on the pilot channel estimation values of the pilots transmitted from the first transmitting antenna is finished through the above process, the first symbol index channel estimation unit estimates a channel of the symbol axis by interpolating the pilot channel estimation value, which has been improved by the first channel operation unit, or the pilot channel estimation value that has not been improved as the symbol axis. At this time, the nearest improved pilot channel estimation value or the nearest unimproved pilot channel estimation value can be copied to a channel not located between the improved pilot channel estimation values or the unimproved pilot channel estimation values. For example, in the first subcarrier, channels d In this case, a channel located between the preamble channel estimation value and the pilot channel estimation value, of channels not located between the improved pilot channel estimation values, can be interpolated by employing a preamble channel estimation value and an improved pilot channel estimation value. For example, in the first subcarrier, the channels d As described above, a channel of a symbol axis can be estimated through interpolation of the symbol axis where the pilot channel estimation values of the pilots p If the channel of the symbol axis is estimated in the first symbol index channel estimation unit, a channel of a frequency axis is estimated through interpolation of the estimated channel of the symbol axis in the first frequency axis channel estimation unit. At this time, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol axis can be copied to the channel not located between the estimated channels. For example, in the pilot pattern illustrated in The channel H Meanwhile, the channel H Referring back to At this time, the nearest pilot channel estimation value can be copied to a channel not located between the pilot channel estimation values. For example, in the first subcarrier, the channels d If the channel of the symbol axis is estimated in the second symbol index channel estimation unit, the second frequency axis channel estimation unit estimates a channel of a frequency axis by interpolating the estimated channel of the symbol axis as the frequency axis. At this time, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol axis can be copied to the channel not located between the estimated channels. This operation is the same as the operation of the first frequency axis channel estimation unit and, therefore, detailed description thereof will be omitted. Referring to When comparing the first channel estimation unit The first and second FFT units Further, the first channel estimation unit The first channel estimation unit The first channel estimation unit may be constructed as illustrated in Referring to The first symbol index channel estimation unit At this time, in the case of a channel not located between the pilot channel estimation values of the pilots transmitted from the first transmitting antenna in the symbol axis, a pilot channel estimation value located at the nearest symbol index, of the pilot channel estimation values of the pilots transmitted from the first transmitting antenna, can be copied to the channel not located between the pilot channel estimation values. At this time, in the case of a channel located between a pilot channel estimation value having the smallest symbol index in the symbol axis, of the pilot channel estimation values of the pilots transmitted from the first transmitting antenna, and a preamble channel estimation value, the channel can be estimated through interpolation of the pilot channel estimation value having the smallest symbol index and the preamble channel estimation value. The first frequency axis channel estimation unit At this time, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol axis can be copied to the channel not located between the estimated channels. As can be seen from Referring back to In the operation of the estimated channel estimation value and the preamble channel estimation value, the estimated channel estimation value is converted into the improved channel estimation value only when the preamble channel estimation value and the estimated channel estimation value are located at the same frequency. At this time, a channel estimation value, which is estimated through interpolation of the pilot channel estimation values of the pilots transmitted from the first transmitting antenna and the preamble channel estimation value, of the estimated channel estimation values, is not operated along with the preamble channel estimation value. In other words, the estimated channel estimation value becomes an improved channel estimation value. The improved channel estimation value can be represented by the following Equation 4. where H The preamble weight value and the estimated channel weight value can be represented by the following Equation 5.
where the symbol offset indicates symbol offset on the basis of the preamble. The first channel operation unit The first channel operation unit In this case, in the event that a channel estimation value located between the preamble channel estimation value P On the other hand, in the event that a channel estimation value located between the preamble channel estimation value P Referring to A channel is estimated by employing a preamble channel estimation value and a pilot channel estimation value in the above embodiments, whereas in the third embodiment of the present invention illustrated in The first and second FFT units The first, second, third, and fourth channel estimation units In other words, the first channel estimation unit The second channel estimation unit The third channel estimation unit The fourth channel estimation unit As evident from the above, the entire channel estimation units The first channel estimation unit Referring to The first symbol index channel estimation unit In other words, the first symbol index channel estimation unit At this time, in the case of a channel not located between the pilot channel estimation values of the pilots transmitted from the first transmitting antenna in the symbol axis, a pilot channel estimation value located at the nearest symbol index, of the pilot channel estimation values of the pilots transmitted from the first transmitting antenna, can be copied to the channel not located between the pilot channel estimation values of the pilots transmitted from the first transmitting antenna. The first frequency axis channel estimation unit At this time, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol index can be copied to the channel not located between the estimated channels. As described above, the channel estimation apparatus according to the third embodiment of the present invention can estimate a channel by employing pilot channel estimation values of pilots transmitted from a transmitting antenna or can estimate a channel by employing a preamble channel estimation value and pilot channel estimation values. As illustrated in The FFT unit The offset estimation unit The offset compensation unit Meanwhile, the weight value storage unit The channel estimation unit On the other hand, although not illustrated in The construction of the channel estimation apparatus constructed above according to the fourth embodiment of the present invention is described in more detail. As illustrated in The first phase difference operator The first phase difference accumulator The first liner phase operator The TO operator
A detailed example of the method of estimating TO is described below with reference to Referring to
The linear phase Φ The embodiment according to the present invention may also employ a method of carrying out an operation on the phase difference according to the TO by employing a pilot pair having the same symbol index, a method of carrying out an operation on the phase difference according to the TO by employing two pairs of pilots having the same symbol index difference, and so on as well as the above TO estimation method. On the other hand, referring back to indicate pilot and data with compensated TO, of the downlink PUSC mode, and l(l=0, 1, . . . , 23) indicates an OFDMA symbol index. At this time, an exponential function for the linear phase kΦ As illustrated in The second phase difference operator The second phase difference accumulator The second liner phase operator The CFO operator
The parameter converter indicates an updated coefficient. A detailed example of the method of estimating CFO is described below. First, a pilot extraction unit (not shown) extracts pilots with compensated TO in the same form as that of the Equation 1. The pilot extraction unit differs from the above pilot extraction unit in that pilots with compensated TO are extracted. Further, the second phase difference operator
The liner phase operator The linear phase Φ For reference, the fourth embodiment may employ a method of calculating a phase difference according to CFO by using a preamble and pilots transmitted from the same transmitting antenna, a method of calculating a phase difference according to CFO by using two pairs of pilots having the same subcarrier index difference, and so forth other than the above-mentioned CFO estimation method. A linear phase according to CFO can also be found out by employing another combination of a preamble and pilots other than the above-described methods. The method of calculating weight values previously stored in the weight value storage unit is described in detail below with reference to First, in relation to pilots comprised of the pattern as shown in the Equation 1 in the downlink PUSC mode, each of two symbols that are consecutive on the time axis and four subcarriers that are consecutive on the frequency axis is divided into subclusters, as illustrated in A channel response in relation to the divided subclusters is calculated and represented as channel response with respect to one or more adjacent subclusters or pilots having the same channel distance (S Thereafter, the channel response of the at least one adjacent subcluster or pilot is represented by around pilots on the basis of the subclusters and a combination of a relative symbol distance ratio between the around pilots (S Thereafter, the channel response of the subcluster is represented as a combination of around pilots on the basis of the subcluster and a relative symbol distance ratio of the around pilots (S Finally, the relative symbol distance ratio for each around pilot is calculated and a coefficient for each pilot is stored in the weight value storage unit (S In the present embodiment, the six pilots are used to represent the channel response H of one subcluster. It is, however, evident that a plurality of pilots may be used to represent the channel response H of one subcluster in the same manner. For example, four adjacent pilots may be used to represent the channel response H of one subcluster as follows. That is, if it is sought to represent the channel response H of the subcluster illustrated in As an alternative embodiment, in the same manner as the above method, each cluster can be divided into subcluster units, a weight value can be calculated with respect to the pilots of the subcluster on the basis of at least one of interpolation on the time axis, interpolation on the frequency axis, and a moving average, and then stored in the weight value storage unit If it is summarized using the method described so far, weight values for the entire channels can be found out as listed in the following Tables 2 to 8. The following Tables 2 and 3 are the results of summarizing channel weights for respective pilots in the symbols located at the ends of the right and left sides. In more detail, in Tables 2 and 3, respective subcluster-based weight values are summarized with respect to the ends on the left and right sides of the frame (l In Table 2, in relation to a channel estimation value P(y, x) for a pilot, y(y=0, 1) indicates a pilot index and x(x=0, 1, . . . , 11) indicates a slot symbol (since a channel is estimated in two symbol units in the downlink PUSC mode, the two symbol units are referred to as the slot symbol). In this case, the pilot index is set to 0 when a corresponding pilot is placed at a 6 or higher and is set to 1 when a corresponding pilot is placed at a 6 or lower on the basis of a total of 14 subcarriers on the frequency axis.
Meanwhile, in the following Table 3, mod(l−l
On the other hand, the following Table 4 illustrates the arrangement of each subcluster-based weight value in a frame, received through the second channel H
The following Tables 5 to 7 illustrates the arrangement of each subcluster-based weight value, which is found from the frame received through the first channel H
Referring back to For example, in the case of the subcluster
For example, when the pilot P Meanwhile, although only the first channel estimation unit Referring to Pilot channel estimation values of pilots, which are transmitted from the transmitting antenna that transmits a preamble using a preamble channel estimation value based on a preamble included in each Fourier-transformed and received signal, are calculated as improved pilot channel estimation values with respect to each of the receiving antennas (S In this case, only when a frequency where a subcarrier of the preamble channel estimation value is located is identical to a frequency where the pilot channel estimation values are located, operation between the preamble channel estimation value and the pilot channel estimation values is carried out. If the pilot channel estimation values of the pilots transmitted from the first transmitting antenna are calculated in the respective receiving antennas based on the preamble channel estimation value, the pilot channel estimation value is transformed into the improved pilot channel estimation values. The pilot channel estimation value improved by the preamble channel estimation value can be represented by the above Equations 2 and 3. If the operation process of the pilot channel estimation values employing the preamble channel estimation value is performed, the channels H An estimation step S In this case, the channel can be estimated through interpolation of the symbol axis and the frequency axis employing the pilot channel estimation values of the pilots transmitted from the same transmitting antenna. It has been illustrated that in Referring to In this case, in the symbol axis, in the case of a channel not located between the improved pilot channel estimation values, a pilot channel estimation value of the improved pilot channel estimation values, which is located at the nearest symbol index, can be copied to a channel not located between the improved pilot channel estimation values. In this case, in the symbol axis, in the case of a channel located between a pilot channel estimation value having the smallest symbol index, of the improved pilot channel estimation values, and a preamble channel estimation value, the channel located between the pilot channel estimation value having the smallest symbol index and the preamble channel estimation value can be estimated through interpolation of the improved pilot channel estimation value having the smallest symbol index and the preamble channel estimation value. If the channel of the symbol axis is estimated, the channel of the frequency axis with respect to each of the receiving antennas is estimated by interpolating the channel estimated as the symbol axis as the frequency axis (S In this case, in the case of a channel not located between channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol axis can be copied to the channel not located between the estimated channels. Referring to In this case, in the symbol axis, in the case of a channel not located between the pilot channel estimation values of the pilots transmitted from the same transmitting antenna, a pilot channel estimation value located at the nearest symbol index, of the pilot channel estimation values transmitted through the channel, can be copied to the channel not located between the pilot channel estimation values transmitted through the channel. If the channel of the symbol axis is estimated, a channel of a frequency axis with respect to each of the receiving antennas is estimated by interpolating the channel, estimated as the symbol axis, as the frequency axis (S In this case, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol axis can be copied to the channel not located between the estimated channels. Referring to A channel with respect to each of the receiving antennas is estimated by employing pilot channel estimation values of pilots transmitted from a transmitting antenna that transmits a preamble, of pilots included in the received signals transformed into the frequency band (S In this case, the channel can be estimated by interpolating the pilot channel estimation values of the pilots transmitted from the transmitting antenna that transmits the preamble, along a symbol axis and a frequency axis. A channel estimation value estimated with respect to each of the receiving antennas is calculated by employing a preamble channel estimation value, and an improved channel with respect to each of the receiving antennas is estimated through the operation (S In this case, such transform of the estimated channel estimation value into the improved channel estimation value can be performed according to the above-mentioned Equations 4 and 5. In this case, such operation of the estimated channel estimation value and the preamble channel estimation value is performed only when the preamble channel estimation value and the estimated channel estimation value are located at the subcarrier of the same frequency, so the estimated channel estimation value is transformed into the improved channel estimation value. In the case of a channel estimation value estimated through interpolation of the pilot channel estimation value and the preamble channel estimation value, of the estimated channel estimation values, operation with the preamble channel estimation value is not performed. In other words, the estimated channel estimation value becomes an improved channel estimation value. Step S In this case, the channel can be estimated through interpolation of the symbol axis and the frequency axis employing the pilot channel estimation values of the pilots transmitted from the same transmitting antenna, and an operation thereof is the same as that of It has been described in Referring to In this case, in the case of a channel not located between the pilot channel estimation values of the pilots transmitted from the transmitting antenna that transmits the preamble in the symbol axis, a pilot channel estimation value located the nearest symbol index, of the pilot channel estimation values, can be copied to the channel not located between the pilot channel estimation values. In this case, in the case of a channel located between a pilot channel estimation value having the smallest symbol index, of the pilot channel estimation values of the pilots transmitted from the transmitting antenna that transmits the preamble, and a preamble channel estimation value in the symbol axis, the channel can be estimated through interpolation of the pilot channel estimation value having the smallest symbol index and the preamble channel estimation value. If the channel of the symbol axis is estimated, a channel of a frequency axis with respect to each of the receiving antennas is estimated by interpolating the channel, estimated as the symbol axis, as the frequency axis (S In this case, in the case of a channel not located between channels estimated as the symbol axis, the nearest channel estimation value of the channel estimation values estimated as the symbol axis can be copied to the channel not located between the estimated channel estimation values. Referring to The received signals of a time domain with the baseband are transformed into signals of a frequency band by Fourier-transforming the received signals respectively received by the plurality of receiving antennas through FFT (S Channels of a symbol axis for the respective receiving antennas are estimated by interpolating pilot channel estimation values of pilots transmitted from the same transmitting antenna, of the pilots respectively included in the received signals of the receiving antennas, along a symbol axis (S In this case, in the symbol axis, in the case of a channel not located between pilot channel estimation values of pilots transmitted through a corresponding channel, a pilot channel estimation value located at the nearest symbol index, of the pilot channel estimation values of the pilots transmitted through the corresponding channel, can be copied to the channel not located between the pilot channel estimation values of the pilots transmitted through the corresponding channel. If the channel of the symbol axis is estimated, a channel of a frequency axis with respect to each of the receiving antennas is estimated by interpolating the channel estimated as the symbol axis as the frequency axis (S In this case, in the case of a channel not located between the channels estimated as the symbol axis, the nearest channel of the channels estimated as the symbol axis can be copied to the channel not located between the estimated channels. Lastly, A pilot is extracted in the same manner as that of the Equation 1 described in step S Meanwhile, functions used in an apparatus and a method disclosed in the present specification can be embodied in storage media that a computer can read as codes that the computer can read. The storage media that the computer can read, include all sorts of record devices in which data that can be read by a computer system is stored. Examples of the storage media that the computer can read, include ROMs, RAMs, CDROMs, magnetic tape, floppy discs, optic data storage devices, etc., and also, include things embodied in the form of carrier wave (e.g., transmission through the internet). Furthermore, the storage media that the computer can read is distributed in a computer system connected with networks. Then, the codes that the computer can read, are stored in the distributed storage media in a distribution scheme, and the codes can be executed in the distribution scheme. 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. Therefore, the spirit and scope of the present invention must be defined not by described embodiments thereof but by the appended claims and equivalents of the appended claims. Patent Citations
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