The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.
In operation S401, at least one ranging symbol is received from each of a plurality of antennas. The ranging symbol received in operation S401 is expressed as a time domain signal. As described above, in the antenna selection method according to an embodiment of the present invention, the time domain signal of the ranging symbol is used. When applying the antenna selection method using a time domain calculation, a method and a configuration of an apparatus for selecting an antenna become simplified, thereby efficiently using system resources and enabling scalability.
In operation S402, a reliability value of an antenna from the plurality of antennas is calculated by correlating the time domain signal of the received ranging symbol.
In operation S501, a first sample signal and a second sample signal are sampled from the ranging symbol of the ranging signal received in a time domain from the antenna. According to an embodiment of the present invention, lengths of the first sample signal and the second sample signal sampled in operation S501 may be determined based on a length of a cyclic prefix of the received ranging symbol. The first sample signal may include a cyclic prefix interval of the ranging symbol, and the second sample signal may include a guard interval of the ranging symbol. The described configuration is caused by a repetition property in a time domain of an OFDM/OFDMA symbol.
Accordingly, signals of the cyclic prefix interval 601 and the guard interval 603 may have exactly matching patterns when interference, delay spread, or distortion of the signal is not considered. Also, even when considering a certain effect caused by noise, the signals of the two intervals may be estimated to maintain a similar pattern. In the present embodiment, performance of the antenna is determined by comparing signal patterns of the cyclic prefix interval 601 and the guard interval 603 with each other. To compare the signals of the two intervals, in the antenna selection method according to the present embodiment, the first sample signal and the second sample signal are sampled from the received ranging symbol in a time domain.
According to an embodiment of the present invention, the first sample signal may be sampled from the cyclic prefix interval 601 of the ranging symbol and the second sample signal may be sampled from the guard interval 603.
As described above, the lengths of the first sample signal and the second sample signal may be determined based on a length of the cyclic prefix interval (601) of the time domain ranging symbol signal. Hereinafter, the content of the present invention will be described in a case in which the lengths of the first sample signal and the second sample signal are identical with the length of the cyclic prefix interval. However, the technical scope of the present invention is not limited by the embodiments to be described. For example, it is well known to those skilled in the art that the lengths of the two sample signals may be determined to be shorter than the length of the cyclic prefix interval or to be longer than the length of the cyclic prefix interval with respect to a certain ranging symbol.
As described above, the ranging symbol that becomes an object of sampling of the first sample signal and the second sample signal, may be transmitted a number of times. For reference, in IEEE802.16d/e standards, a case of transmitting twice and a case of transmitting four times are specified.
In an OFDM/OFDMA communication system, a cyclic prefix interval has a problem that a signal may be distorted due to a multi-path fading channel occurring between symbols. Particularly, in the case of an initially received ranging symbol, it is difficult to measure an effect caused by a multi-path fading channel. In addition, since a signal is distorted due to another symbol disposed just prior to the ranging symbol, it may be difficult to use an entire cyclic prefix interval.
On the other hand, in the case of a ranging symbol received after an initially received ranging symbol, when a delay spread interval of a multi-path fading channel is smaller than a designated cyclic prefix interval, a repetition feature of the second ranging symbol is guaranteed. Therefore, to increase precision of a reliability value calculation, the reliability value may be calculated by sampling the first sample signal and the second sample signal from a time domain signal of the ranging symbol received after an initially received ranging symbol.
In addition, the initially received ranging symbol may be applied to the present invention.
A starting position of an OFDM/OFDMA symbol including a ranging symbol is identified based on frame timing.
In addition, the initially received ranging symbol may be applied to the present invention in spite of this problem.
On the other hand, in operation S502 of
Also, in operation S503, a deviation value of the first sample signal and the second sample signal is calculated in the correlation interval. Operations S502 and S503 may be sequentially or simultaneously performed.
Calculating the correlation value and the deviation value performed in operations S502 and S503 may be according to following methods. According to one method, the correlation value is calculated by cumulatively adding a complex conjugate of each sample of the first sample signal multiplied by a corresponding sample of the second sample signal, or a cumulative addition of a complex conjugate of each sample of the second sample signal multiplied by a sample of the first sample signal may be employed.
The deviation value calculated by the operation S503 may include various type of values indicating a difference level of the first sample signal and the second sample signal, such as a standard deviation value or a variance value. As an example, the deviation value may be calculated by cumulatively adding a square of an absolute value of a difference between samples of the first sample signal and the second sample signal. The cumulative addition for the correlation value and the deviation value calculation is performed during the correlation interval of the predetermined length. The predetermined length may be identical or associated with the lengths of the first sample signal and the second sample signal. Namely, the length of the correlation interval may also be determined based on a length of the cyclic prefix interval of the time domain signal of the received ranging symbol.
The calculated correlation value and the deviation value between the first sample signal and the second sample signal are used for calculating the reliability value of the antenna in operation S504. In detail, the reliability value is calculated by a ratio of the correlation value and the deviation value. As the pattern of the first sample signal is similar to the pattern of the second sample signal, the correlation value is increased and the deviation value is decreased. Since the reliability value of the antenna receiving the ranging symbol is determined to be large when the time domain received ranging symbol signal is less distorted, the reliability value may be defined to be in proportion to the correlation value and in inverse proportion to the deviation value.
The described method of calculating the reliability value may be shown as Equation 2.
Reliabilityant k indicates a reliability value with respect to a k-th antenna, L indicates a length of a correlation, r1(i) indicates a first sample signal, and r2(i) indicates a second sample signal. For reference, a numerator of Equation 2 is corresponding to the correlation value between the first sample signal and the second sample signal, and a denominator of Equation 2 is corresponding to the deviation value between the first sample signal and the second sample signal. As described above, the reliability value of the antenna is obtained by a ratio of the correlation value and the deviation value between the first sample signal and the second sample signal.
For reference, a division of the correlation length L common in both the numerator and the denominator of Equation 2 is shown only for easily understanding the correlation value and the deviation value but may not be used in an actual embodiment. As is well-known, to embody a division operation, more software and/or hardware resources are required than for other operations, and much time is consumed for the operation. Accordingly, excluding a particular case, for example, there is a great restriction on a range of numerical values that are calculated by a cumulative adder used for embodying the method of calculating the reliability value, therefore, the division operation may be not included in the operation of calculating the correlation value and the deviation value.
Hitherto, operation S402 of calculating the reliability value by using the time domain ranging symbol signal has been described. Referring to
According to an aspect of the present invention, since whether to select an antenna is determined based on a new reference such as the reliability value calculated by using a time domain signal pattern of a ranging symbol, an antenna may be optimally selected in a multi-path fading channel environment in which interference and delay of a signal and a distortion of the signal caused by the interference and delay occur in various patterns.
As shown in
In operation S1002, the reliability value is calculated by using the time domain signal of the received ranging symbol, and the reliability value calculation method described with reference to
In the case of a plurality of antennas, in operation S1003, operations S1001 and S1002 are repeatedly performed with respect to each of the plurality of antennas.
For reference, in operation S1003, calculating the reliability values with respect to each of the plurality of antennas may be sequentially performed or may be simultaneously performed by a plurality of apparatuses.
In operation S1004, a maximum reliability value of the reliability values calculated with respect to each of the plurality of antennas is selected, and an antenna corresponding to the maximum reliability value is selected as an optimal antenna.
The reliability value calculated with respect to the each of the plurality of antennas may be used for antenna selection using a calculated maximum reliability value as in the described embodiment, or may be selected by determining whether to select the antenna based on a predetermined threshold value. In the latter case, at least one antenna may be selected, and a plurality of the selected antennas is used for a preliminary purpose, or for an intermediate antenna selection result when layering the antenna selection process because a total number of antennas is huge.
According to another embodiment of the present invention, strength of the time domain signal of the ranging symbol may be further referred to in addition to using the reliability value calculated as described above, for selecting the antenna. As described above, the accuracy of the antenna selection may be improved when using a complex reference based on various pieces of information. For reference, “strength” of a signal, mentioned in the present specification, indicates an index for amplitude of a wireless signal propagated via a wireless channel, an electrical power or energy of the signal, where a quality index of a wireless signal is not considered. A unit for the strength includes a milliwatt (mW), a decibel milliwatt (dBm), a received signal strength indication (RSSI), and other various units used for indicating power or energy of a signal.
The strength of the received ranging symbol additionally used in determining whether to select the antenna may include an SINR value used in a conventional antenna selection method.
The described antenna selection method is for selecting an antenna performing ranging detection. Accordingly, the technical scope of the present invention is applied to a ranging detection method of an OFDM/OFDMA system, as it is. A ranging detection method according to an embodiment of the present invention includes the operations of calculating a reliability value with respect to each of a plurality of antennas by correlating a respective ranging symbol received from the plurality of antennas, selecting an antenna based on the calculated reliability value, and detecting the ranging based on a calculation in a time domain, with respect to a ranging symbol received from the selected antenna.
In the operation of detecting the ranging, performed by the selected antenna, a ranging signal may be detected based on the calculation in the time domain. Therefore, when performing the ranging detection operation in the time domain, an advantage of the present invention is clearly shown. Namely, in this case, in the present invention, waste of hardware and software resources for conversion into a frequency domain signal may be prevented, for detection of the ranging signal by using the antenna selected in the frequency domain.
As described above, the ranging detection method according to the present embodiment increases scalability of an entire system including an antenna selection apparatus and a ranging detection apparatus, by selecting an antenna based on a calculation in a time domain.
The antenna selection method according to the present invention may be embodied as a program instruction capable of being executed via various computer units and may be recorded in a computer-readable recording medium. The computer-readable medium may include a program instruction, a data file, and a data structure, separately or cooperatively. The program instructions and the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those skilled in the art of computer software arts. Examples of the computer-readable media include magnetic media (e.g., hard disks, floppy disks, and magnetic tapes), optical media (e;g., CD-ROMs or DVD), magneto-optical media (e.g., floptical disks), and hardware devices (e.g., ROMs, RAMs, or flash memories, etc.) that are specially configured to store and perform program instructions. The media may also be transmission media such as optical or metallic lines, wave guides, etc. including a carrier wave transmitting signals specifying the program instructions, data structures, etc. Examples of the program instructions include both machine code, such as that produced by a compiler, and files containing high-level language codes that may be executed by the computer using an interpreter. The hardware elements above may be configured to act as one or more software modules for implementing the operations of this invention.
The ranging symbol storage unit 1101 stores a time domain signal of a respective ranging symbol received from a plurality of antennas. For example, the ranging symbol storage unit 1101 forming the antenna selection apparatus may receive at least one ranging symbol with respect to each of the plurality of antennas and may store a time domain signal of the respective received ranging symbol. Also, a first sample signal 1112 and a second sample signal 1113 may be sampled from a stored ranging symbol 1111 received and stored after an initially received ranging symbol.
The first sampling unit 1102 and the second sampling unit 1103 sample the first sample signal 1112 and the second sample signal 1113 from a stored ranging symbol 1111, respectively. A number of samples of the first sample signal 1112 and the second sample signal 1113 is determined based on a length of a cyclic prefix interval included in the stored ranging symbol 1111. For example, the first sample signal 1112 and the second sample signal 1113 may include the cyclic prefix interval and a guard interval of the stored ranging symbol 1111, respectively. The first sample signal 1112 and the second sample signal 1113 may be sequentially or simultaneously sampled.
The correlation value calculation unit 1104 and the deviation value calculation unit 1105, shown in
Referring to
The deviation value calculation unit 1105 may include a subtracter calculating a difference between the first sample signal 1112 and the second sample signal 1113 for each sample, an absolute value square operator 1204 calculating a square of an absolute value of a subtraction result, and a deviation value calculator 1205 cumulatively adding the square of the absolute value of the calculated difference between samples with respect to the predetermined correlation interval.
As shown in
As described above, the lengths of the first sample signal 1112 and the second sample signal 1113 and a length of the correlation interval in which the calculation result for each sample is cumulatively added by the correlation value calculator 1203 and the deviation value calculator 1205 may be determined based on the length of the cyclic prefix interval of the used ranging symbol, respectively.
The antenna selection unit 1107 selects an antenna corresponding to a maximum reliability value from a plurality of calculated reliability values 1116. As described above, according to another embodiment of the present invention, the antenna selection process may be performed by comparing the reliability value with a predetermined threshold value instead of the calculated maximum reliability value.
The antenna selection apparatus of
The present invention is applied to antenna selection and ranging detection embodied by a base station system. As described above, a base station generally includes a plurality of antennas and transmits and receives a signal by using the plurality of antennas.
When receiving a ranging request from the plurality of antennas having a different channel delay spread, the base station has to first select an antenna to perform ranging detection of a relevant terminal.
Accordingly, the base station system according to the present invention may include a plurality of antennas for receiving a ranging symbol from a mobile communication terminal, an antenna selection apparatus selecting at least one antenna from the plurality of antennas based on correlation of a time domain signal of the respective ranging symbol received from the plurality of antennas, and a ranging detection apparatus detecting up-link ranging between the mobile communication terminal and the base station system by using the selected antenna.
The base station system according to the present invention may improve resource efficiency of an entire system when the ranging detection apparatus performing ranging detection using the antenna selected by the antenna selection apparatus uses a time domain calculation or a frequency domain calculation.
Namely, since the antenna selection apparatus included in the base station system according to the present invention performs a reliability value calculation by using the time domain signal, an additional hardware or software apparatus for an FFT and an inverse FFT is not used when the ranging detection apparatus using a result of the reliability value calculation is based on the time domain calculation.
Also, when the ranging detection apparatus is based on frequency domain calculation, since an FFT operator is not included with respect to the plurality of antennas and is only included with respect to the selected antenna, efficient use of hardware and software resources is improved.
Hitherto, since the antenna selection apparatus and the mobile communication base station system according to exemplary embodiments of the present invention have been described and the contents described with reference to the embodiments of
According to an aspect of the present invention, there is provided a method of accurately selecting an optimal antenna in a multi-path fading channel environment based on a reliability value of an antenna obtained by a predetermined calculation method.
According to an aspect of the present invention, there is also provided an antenna selection method in which a reliability value is calculated by using a time domain signal of a received ranging symbol, thereby providing a simple and scalable antenna selection method.
According to an aspect of the present invention, there is also provided an antenna selection method in which a pilot symbol is not used in calculating a reliability value in a process compatible with IEEE802.16d/e and OFDM/OFDMA standards.
According to an aspect of the present invention, there is also provided an antenna selection method in which a cyclic prefix interval and a guard interval including a signal having the same pattern from a received ranging symbol are referred to, to accurately select an optimal antenna by sufficiently reflecting a channel feature.
According to an aspect of the present invention, there is also provided an antenna selection method in which a cyclic prefix interval and a guard interval of a ranging symbol received after an initially received ranging symbol from a plurality of received ranging symbols is sampled to prevent being affected by a distortion of the ranging signal due to multi-path fading, thereby accurately selecting the optimal antenna.
According to an aspect of the present invention, there is also provided an antenna selection apparatus in which it is not required to use FFT units for each of a plurality of antennas, thereby simplifying a configuration of the apparatus, reducing a manufacturing cost of the apparatus, and improving antenna selection speed.
According to an aspect of the present invention, there is also provided a base station system in which an optimal antenna for ranging detection is quickly and efficiently selected in response to a ranging request received from a plurality of mobile communication terminals, thereby providing the ranging detection with respect to the plurality of mobile communication terminals by using a small amount of time and cost.
Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.