Abstract:
There is disclosed a finger for effectively processing signals received via multi-path in a receiver of a mobile communication system and a RAKE receiver having the finger. In processing signals received by a plurality of antennas in the present invention, a single finger batch-processes the signals received by the plurality of antennas using the property that the time delays of the received signals are almost same and a time division method. At this time, a single apparatus batch-processes a portion necessary for a common calculation and a plurality apparatus separately process portions necessary for separate calculations. Thus, the present invention can provide a high-performance finger and a RAKE receiver having the finger wherein a single finger can process each of signals received by a plurality of antennas.

Description:
TECHNICAL FIELD 
   The invention relates generally to a receiver of a mobile communication system. More particularly, the present invention relates to a finger using a time division method by which signals received by a plurality of antennas in a receiver of a mobile communication system are effectively processed and a RAKE receiver having the finger. 
   BACKGROUND OF THE INVENTION 
     FIG. 1  shows a construction of a conventional RAKE receiver. As shown, assuming that signals received from various paths and antennas are entered through independent paths, each finger controls each of the signals. 
   Radio frequency analog signals received by the M′-number of antennas  100  are converted into baseband digital signals at a RF analog to baseband digital converter  110 . Then, the converted signals are inputted into a signal searcher  120  and a signal controller  130 , respectively. The signal searcher  120  searches the intensity of the received signals and then informs the result to the signal controller  130  and fingers  140 , respectively. Meanwhile, the signal controller  130  sends the signals received by the M′-number of antennas  100  to the fingers  140 , one by one, according to information from the signal searcher  120 . 
   In the above-mentioned conventional RAKE receiver, the complexity of the fingers becomes increased linearly depending on the number of the signal paths to be combined since one finger processes a single signal. Thereby, if the number of the signal paths is increased in order to increase the performance of the receiver, there arises a problem that the complexity of the receiver is further severe. 
   As one option to solve these problems, there has been proposed a thesis “A RECEIVER OF SIMPLE STRUCTURE FOR ANTENNA ARRAY CDMA SYSTEMS” by J. Choi, IEEE Trans. Vehic. Techn, Vol 48, No. 5, pp 1332-1340, 1999, which discloses that signals from various antennas and signals received via various paths are processed by only one finger. In the proposed receiver, when the signals are processed, they are processed at a time using time-space two-dimensional filtering scheme. However, there is a problem that the amount of calculation is increased since the coefficients of the filters must be calculated every symbols. 
   SUMMARY OF THE INVENTION 
   The present invention is contrived to solve the above-mentioned problems and the purpose of the present invention is to provide a finger of a simplified structure including a single apparatus for batch-processing a common calculation within a finger and a plurality of apparatuses for performing separate calculations. In the present invention, also, a single finger effectively processes signals, received by a plurality of antennas and having almost the same time delays, by using time-division method. Thus, it can provide a high-performance finger and a RAKE receiver having the finger. 
   In order to accomplish the above object, in a finger using a time division method according to the present invention and a RAKE receiver using the finger, the finger comprises an antenna signal combiner for combining signals, received by a plurality of antennas and having the almost same time delays, with an adequate delay to produce multiplexed signals; a tracking apparatus for receiving the multiplexed signals to estimate time delay information on the multiplexed signals; a de-spreading apparatus for de-spreading the multiplexed signals with the estimated time delay information, each of which are received from the antenna signal combiner and the tracking apparatus, respectively; and a demodulating apparatus of demodulating the de-spread signals received from the de-spreading apparatus, to estimate original signals received by the plurality of antennas. 
   Also, a finger according to the present invention comprises an antenna signal combiner for combining signals, received by a plurality of antennas and having the almost same time delays, with an adequate delay to produce multiplexed signals; a tracking apparatus for receiving the multiplexed signals to estimate time delay information on the multiplexed signals; a de-spreading apparatus for de-spreading the multiplexed signals with the estimated time delay information, each of which are received from the antenna signal combiner and the tracking apparatus, respectively; and a non-coherent demodulating apparatus of demodulating only the de-spread signals from the de-spread apparatus to estimate original signals received by the plurality of antennas. 
   Preferably, a RAKE receiver according to the present invention comprises a RF analog to baseband digital converter for converting RF analog signals received by a plurality of antennas having the almost same time delays into baseband digital signals; a signal searcher for receiving the output signals from the RF analog to baseband digital converter to generate information on the intensity of the baseband digital signals; a signal controller for receiving information on the intensity of the signals for the signal searcher and the output signals from the RF analog to baseband digital converter to send the M number of the signals among the output signals from the RF analog to baseband digital converter using the information on the intensity of the signal; fingers for receiving the M number of signals from the signal controller to estimate a common time delay information in the received M number of signals and for estimating original signals received per the plurality of antennas using the estimated time delay information and a time division method; and a combiner for receiving the estimated original signals from the fingers and for combining the original signals, to thus estimate original signals received by the plurality of antennas. 
   According to one aspect of the present invention, a method of estimating signals of a finger comprises a first step of combining signals, received by a plurality of antennas and having the almost same time delays, with an adequate delay to produce multiplexed signals; a second step of estimating a common time delay information on the multiplexed signals; a third step of de-spreading the multiplexed signals using the estimated time delay information to produce de-spread signals; a fourth step of estimating channel information on the de-spread signals; and a fifth step of demodulating the de-spread signals on signals of each of the antennas basis using the estimated channel information to estimate signals received by the plurality of antennas. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned aspects and other features of the present invention will be explained in the following description, taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  shows a construction of a conventional RAKE receiver; 
       FIG. 2  is an overall structure of a RAKE receiver according to one embodiment of the present invention; 
       FIG. 3  is an overall structure using time division method according to one embodiment of the present invention; and 
       FIG. 4  is a detailed construction of a finger using time division method according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will be described in detail by way of a preferred embodiment with reference to accompanying drawings. 
     FIG. 2  is an overall structure of a RAKE receiver according to one embodiment of the present invention. It should be noted that the present invention employs a principle that the time delays of signals received via a plurality of antennas are the same if the distance between the antennas is not greater, compared to the wavelength of carrier waves, because the bandwidths of the signals received by the antennas are much smaller than the carrier wave. 
   The RAKE receiver according to the present invention includes a RF analog to baseband digital converter  210  for converting RF analog signals received by the M′-number of antennas  200  into baseband digital signals, a signal searcher  220  for generating information on the intensity of the signals received from the RF analog to baseband digital converter  210 , a signal controller  230  for sending M number of the signals from the RF analog to baseband digital converter  210  to every one of fingers  240 , according to the information from the signal searcher  220 , fingers  240  for estimating original signals received by the plurality of antennas using the signals from the signal controller  230  and the signal searcher  220 , and a combiner  250  for combining the original signals estimated at respective fingers to estimate original signals from the plurality of antennas. 
   The operation of the RAKE receiver having this structure will now be explained in detail. First, the RF analog signals received by the M′ number of antennas  200  are converted into baseband digital signals at the RF analog to baseband digital converter  210 . The converted signals are then inputted to the signal searcher  220  and the signal controller  230 . The signal searcher  220  searches the intensity of the received signals and then informs the result to the signal controller  230  and fingers  240 , respectively. Meanwhile, the signal controller  230  sends every M (≦M′) number of the signals received from the RF analog baseband digital converter  210  to every one of the fingers  240 , according to information from the signal searcher  220 . The fingers  240  estimate an original signal each of the M number of the signals received via individual paths and then forward the results to the combiner  250 . The combiner  250  combines the original signals estimated at respective fingers  240  to estimate original signals received by the plurality of antennas  200 . Also, the fingers  240  may send respective original signals for the M number of the estimated signals to the combiner after combining them. 
   Referring now to  FIG. 3 , there is shown an overall structure of a finger  300  in the RAKE receiver using time division method according to the present invention. The finger includes a tracking apparatus for detecting time delay of the signals transmitted from the signal controller  310 , a de-spreading apparatus  330  for reverting the spread signals into before-spreading signals using the detected time delay, a demodulating apparatus  340  for demodulating the transmitted signals using the de-spread signals from the de-spreading apparatus  330  and channel estimates from a channel estimating apparatus  350 , and a channel estimating apparatus  350  for estimating the states of the channels in the demodulating apparatus  340  to which the signals are inputted and then informs the results to the receiver. At this time, if the demodulating apparatus  340  does not need information on its channels and the state of the channels presently used are monitored outside the finger  300 , the finger  300  may not include the channel estimating apparatus  350 . 
   The operation of the finger  300  having this structure will now explained in detail. The tracking apparatus  320  receives the signals having almost the same time delays received by the plurality of antennas through the signal controller  310  within the RAKE receiver. The received signals are processed through three steps. First, the tracking apparatus  320  detects any of the received signals having the time delay falling under a predetermined range error and then sending it to the de-spreading apparatus  330 . Then, the de-spreading apparatus  330  uses the received information on the time delay to revert the spread signals into before-spreading signals. Here, if the de-spreading apparatus  330  does not know a spreading factor of the spread signal, it de-spreads the spread signal using a minimum spreading factor and then sends the de-spreaded signal to the demodulating apparatus  340 . (After a spreading factor is obtained, the de-spread signals by the minimum spreading factor are then combined by the amount corresponding to the spreading factor, thus completing a de-spreading procedure.) Finally, the demodulating apparatus  340  detects the signals and then sends the detected signal to the combiner  360 . 
   Referring to  FIG. 4 , there is shown a detailed construction of a finger  400  using a time division method according to one embodiment of the present invention. The structure of respective constituent elements constituting the finger  400  and their operation will be explained in detail. 
   The finger  400  includes a tracking apparatus  420  consisting of a time delay information estimator  421 , a demultiplexer  422 , a storage means  423  and a combiner  424 ; a de-spreading apparatus  430  consisted of a de-spreading information extractor  431 , a demultiplexer  432  and a storage means  433 ; a channel estimating apparatus  460  consisted of a channel state estimator  461 , a demultiplexer  462  and a storage means  463 ; a demodulating apparatus  450  consisting of a transmitting signal estimator  451  and a combiner  452 ; and a combining apparatus  470 . The finger  400  further includes an antenna signal combiner  410  for combining received signals with an adequate delay and a multiplexer  440  for extending the distance between the received signals. 
   The operation of the finger  400  having this structure will be now explained. First, selected N 1  (≦M) signals S 1 , . . . S N1  among the signals from the signal controller  401  are inputted to the antenna signal combiner  410  within the finger  400 . Then, the antenna signal combiner  410  adequately delays and combines the received N 1  number of signals so that a single apparatus can easily process a plurality of signals received from various antennas. 
   At this time, if the sampling rate of the signals received by the respective antennas is f c =1/T c , a combining method is employed by which an N 1  number of antennas are selected according to a pre-determined basis, signals received by a k-th (k=1 . . . N 1 ) antenna are combined with a (k−1) T c /N 1  delay and the signals having the sampling rate off c =N 1 /T c  are produced. 
   The multiplexed signal  411  generated by these procedures is inputted to the tracking apparatus  420  for detecting time delays of the signals received by the plurality antennas. The inputted multiplexed signals  411  are then inputted to the time delay information estimator  421  in the tracking apparatus  420 . At this time, in order to process the N 1  number of multiplexed signals, a time division method is employed, by which a time period of T c  (=1/f c ) is processed by dividing it into the N 1  number of periods. Thus, a single signal can be processed every single period. The processed signals are inputted to the demultiplexer  422  for demultiplexing, which are then transmitted to the storage means  423  consisted of N1 storages. The signal processing procedure from the time delay information estimator  421  to the storage means  423  is repeated during a predetermined time or by a predetermined number of times. As a result, the signals are selectively combined at the combiner  424 , thus producing time delay information on the N 1  number of multiplexed signals. 
   The estimated time delay information from the tracking apparatus  420  and the N 1  number of the multiplexed signals from the antenna signal combiner  410  are inputted to the de-spreading apparatus  430 . A single de-spreading apparatus  430  processes the inputted N 1  number of the multiplexed signals and the estimated time delay information using a time division method. Thus, the signals inputted to the de-spreading information extractor  431  in the de-spreading apparatus  430  are processed one by one during every single period. The processed signals are then inputted to the demultiplexer  432  for demultiplexing. Thereafter, the demultiplexed signals are inputted to the storage means  433 . At this time, the inputted signals are differently stored into the N 1  number of the storage means. The signal processing procedure from the dispreading information extractor  431  to the storage means  433  is repeated during a predetermined time or by a predetermined number of times, as in the process by the tracking apparatus  420 , so that the inputted signals can be de-spread. The output signals of the de-spreading signal, that is, from the dispreading apparatus  430  in which the N 1  number of signals are bundled by T c /N 1  distance, are produced a symbol period or every symbol period depending on a minimum spreading factor. The produced signals are then inputted to the demodulating apparatus  450  and the channel estimating apparatus  460 , respectively. 
   On the other hand, before the output signals from the dispreading apparatus  430  are inputted to the demodulating apparatus  450  and the channel estimating apparatus  460 , the multiplexer  440  can extend the distance between the N 1  number of the signals being the output signals of the dispreading apparatus  430  so that the demodulating apparatus  450  and the channel estimating apparatus  460  can be smoothly operated. The de-spread signals  441  transformed through these procedures are then inputted to the channel estimating apparatus  460  and the demodulating apparatus  450 , respectively, thus smoothly operating the channel estimating apparatus  460  and the demodulating apparatus  450 . 
   The de-spread signals or the transformed de-spread signals  441  are then inputted to the channel state estimator  461  in the channel estimating apparatus  460 . The channel state estimator  461  processes respective signals by dividing the time period of T c  into the N 1  number of periods Thus, a single signal every respective period can be processed, that is, channels of respective signals can be estimated. The channel information on the respective estimated signals are inputted to the demultiplexer  462  and the demultiplexed information are then stored at the storage means  463 . Thus, channels of the signals received by the respective antennas can be estimated. 
   Meanwhile, the output signal or the transformed dispreading signals  441  of the de-spread apparatus  430  and the estimated channel information from the channel estimating apparatus  460  are inputted to the transmitting signal estimator  451  in the demodulating apparatus  450 . The transmitting signal estimator  451  performs a demodulating process on a signal basis of respective antennas by dividing the time period of T c  into the N 1  number of periods, thus estimating original signals of the respective signals per antenna. 
   In case that a non-coherent demodulating apparatus is employed, the demodulating apparatus divides the time period of T c  being a given time period into the N 1  number of periods without any output signal from the channel estimating apparatus and the transmitting signal estimator performs a non-coherent demodulating process on a signal basis of respective antennas. 
   Each of the original signals estimated at the transmitting signal estimator  451  is inputted to the combiner  452 . The combiner  452  selectively combines each of the inputted original signals to estimate the original signals received by the plurality of antennas. The output signals of the demodulating apparatus  450 , being the estimated original signals, are inputted to the combining apparatus  470  so that they can be combined by a predetermined method, or are separately inputted to the combining apparatus  470  so that they can be combined by a predetermined method along with the outputs from different fingers. 
   The present invention has been described with reference to a particular embodiment in connection with a particular application. Those having ordinary skill in the art and access to the teachings of the present invention will recognize additional modifications and applications within the scope thereof. 
   It is therefore intended by the appended claims to cover any and all such applications, modifications, and embodiments within the scope of the present invention. 
   As mentioned above, the present invention can implement a high-performance finger capable of combining a log of signals, in which a single finger can effectively process signals having the same time delays and received by a plurality of antennas using a time division method. Also, the present invention has an effect that it can implement a finger of a simplified structure and a RAKE receiver having the same since it includes a single apparatus for batch-processing a common calculation within the finger and a plurality of apparatuses for performing separate calculations.