Mobile communication system receiver, path tracking method, and control program thereof

To prevent disabling of the path tracking function.A path allocation unit allocates a signal power peak of a delay profile crated by a delay profile creation unit as a path to a finger reception unit. When tracking a path which has been allocated by the path allocation unit, it is judged whether a path tracking region set for each path is overlapped with a mask region. The path is tracked by performing a process not to cause a loss of a path tracking function due to overlap. Demodulation of the path which has been allocated is performed by a finger reception unit. Each of the demodulated signals outputted from the finger reception unit are rake combined to reproduce the transmitted information signal.

TECHNICAL FIELD

The present invention relates to a mobile communication system receiver, a path tracking method, and a control program thereof. More specifically, the present invention relates to a receiver in a mobile communication system having a fine multipath tracking function, and to a path tracking method as well as a control program thereof.

BACKGROUND ART

When trying to transmit an information bit string (data object) to a receiver side in a DS-CDMA mode (Direct Sequence Code Division Multiple Access) used in mobile communication, the information bit string is modulated into spread spectrum signals by spreading the string with spread codes, and the modulated signals in a form of radio signals are transmitted to the receiver side for achieving communication.

Chip rate of the spread codes used in the DS-CDMA mode is a sufficiently high rate for a signal rate of the information bit string, and it is selected as a sufficiently high rate for propagation delay time between a mobile terminal device and a base station.

Therefore, it becomes possible to separate the radio signals reached via a specific propagation path based on the propagation delay time from the multipath signals that reach a mobile terminal device (receiver) via different propagation paths generated due to indirect reflected waves, diffracted waves, or the like, i.e., via different propagation path lengths. Each of the separated DS-CDMA signals having different propagation delay time is referred to as a multipath signal. It is well-known that a path diversity effect can be obtained and receiver gain can be improved through performing demodulation by allocating respective finger receiver units to the separated multipath signals and performing rake combining of each demodulated signal.

Separation of the multipath signals described above is performed based on a delay profile that shows received signal power distribution for the propagation delay time (reaching time to the receiver). The delay profile can normally be obtained through calculating the code correlations with respect to the spread codes of receiving waves by using a matched filter or a sliding correlator by each chip rate or by each over-sampling rate that is an integral multiple of the chip rate.FIG. 10shows an example where there are three paths in the delay profile. The horizontal axis inFIG. 10represents relative propagation delay time, and the longitudinal axis represents signal powers. Reference numeral301inFIG. 10indicates a noise level, and it is assumed that there exists an effective path when the signal power is at a peak position302for the noise level301.

For such paths present in the delay profile, the aforementioned finger receiver is allocated and demodulation is performed. When the allocation is done once, there is taken a measure to prevent allocation of other finger receivers to the vicinity of the allocated path, i.e., there is taken a measure to set a mask region to the vicinity of the path to which the finger receiver is allocated so as to prevent allocation of other finger receivers to the path to which the mask region is set.

Reasons for taking the above-described preventing measure are as follows. That is, paths in the vicinity of the significant path in many cases are side lobes of that path, i.e., paths that are not independent of the allocated path. Thus, even if finger receivers are allocated to such paths and rake combine is performed thereon, the path diversity effect cannot be obtained. In addition, noise and interference components are superimposed on the demodulated signals, which may possibly result in deteriorating the reception qualities. Furthermore, limited resources of finger receivers are to be used wastefully.

In addition to setting the aforementioned mask regions, state of the propagation paths is constantly fluctuated in the mobile telecommunications, i.e., there is a fluctuation occurred in the delay profile constantly. In order to maintain a fine reception quality, the delay profile is updated periodically. If it becomes necessary as a result thereof, there is performed tracking processing for the path whose propagation delay is fluctuated, or there is performed update processing of the allocation of the finger receivers for emerging paths and fading paths. For that, as shown inFIG. 11, employed is a method which performs the path tracking processing and the update processing of path allocation to the finger receivers through setting a path tracking region303for searching fluctuation of signal power peak positions, and mask regions304for preventing allocation of other finger receivers to the vicinity of the path that has been allocated to a finger receiver on the delay profile.

Patent document 1 discloses a synchronous tracking method in a spread spectrum communication system having a path search function. A delay profile measuring device, an extracting device for extracting path timing signals from the delay profile, and a path identifying device for identifying a subordinate path group and an independent path are used for the path tracking operation. The path identifying device contains a threshold value setting device that is capable of setting a threshold value, and identifies each path with the path timing signal that has a value equals to or higher than the threshold value (e.g., each path with the path timing signals within ±1-chip time length) as a subordinate path group.Patent Document 1: Japanese Unexamined Patent Publication 2001-313590

There are also following issues even if the aforementioned known method is employed. That is, in a case of the delay profile shown inFIG. 12, i.e., a delay profile where three paths305,306, and307are close to each other (a delay profile especially with a small difference in the propagation delay time), the side lobes in the vicinity of the signal power peaks of the three paths305,306, and307overlap with each other, and there are the mutually overlapped signal power peaks of the three paths305,306, and307present in the delay profile.

When the aforementioned path tracking regions and mask regions are set for the paths305,306, and307in the delay profile shown inFIG. 12, a part of the path tracking region set for a single path comes to lose the function as the path tracking region because of the mask region set for its neighboring path as shown inFIG. 12, since the path tracking regions and the mask regions set for each of the aforementioned three paths305,306, and307overlap with each other.

Therefore, path tracking operations cannot be done in the right direction for the path305, in both directions for the path306, and in the left direction for the path307. When such incapability of path tracking operations occurs continuously in fluctuation of the delay profile, in particular, the reception quality becomes deteriorated. At last, it may result in disconnection of calls.

In Patent Document 1, for identifying whether the paths in the delay profile are subordinate path group or independent path, it is judged whether the paths are the subordinate group or not only depending on the presence of the path timing signals but no other factors are considered for grouping the paths. That is, it is not designed to perform grouping of the paths other than the aforementioned manner.

DISCLOSURE OF THE INVENTION

The present invention is designed in view of the foregoing circumstances, and it is an object of the present invention to provide a path tracking method and a receiver, which are used in spread spectrum communications for improving the path tracking performance for a plurality of multipaths.

In order to overcome the foregoing issues, a receiving mechanism in a mobile communication system according to the present invention includes: a path tracking processing function of detecting signal power peaks from a delay profile of multipath multiplexed signals received via a plurality of propagation paths, separating/extracting each path contained in the multipaths based on propagation delay of the detected signal power peaks, allocating finger receivers to the signals of each of the separated/extracted paths for performing demodulation as well as rake combine of each demodulated signal, updating the delay profile every prescribed time interval for tracking chronological changes of the propagation paths, when a signal power peak position within a path tracking region set in advance for each path is fluctuated, estimating that the path is fluctuated, and performing tracking of the fluctuated path; and a mask region setting function of setting mask regions for preventing other finger receivers than the reception finger receivers to the path from being allocated to the vicinity of the path when performing the path tracking processing, wherein, when the finger receivers are allocated to each of the paths of the multipaths in which each of the paths is close to each other in terms of time, each of the constituent paths is put into a group, priority orders are set for each of the constituent paths within the group for performing path tracking operations, and path tracking processing is performed according to the priority orders.

For the path tracking processing performed according to the priority orders, it is desirable to set the path tracking region and the mask regions for each path.

For the path tracking processing performed according to the priority orders, the path tracking region may be set for each path to perform a tracking operation of the path, and the mask regions may be set for the path after completing the tracking operation.

It is desirable for the grouping processing to be performed every time the tracking operation of a single path is performed. The grouping processing may also be performed when the tracking operations of all the assumed multipaths are completed.

Further, the grouping processing may also be performed to put each of the adjacent paths when “Td<2(Tt+Tm)” applies, provided that a propagation delay time difference of the adjacent paths is “Td”, a half of time length of the path tracking region is “Tt”, and time length of the mask region is “Tm”.

Furthermore, the grouping processing may also be performed to put each of the adjacent paths into a group, when the propagation delay time difference of the adjacent paths is within prescribed time that is set in advance.

Further, the priority orders may be so set that the path having the maximum signal power within the group is given the highest priority, or may be set in order from the path having the higher signal power to the path having the lower signal power. The priority orders may be set in order of time at which separation/extraction of the paths is executed, or may be set in order of executing separation/extraction of the paths from the latest to the oldest.

After the path tracking operation is performed by setting the path tracking region and the mask regions for the most preferential allocated path among the paths under the priority order, the path tracking operations for the remaining paths may be executed by setting the path tracking regions and the mask regions for the paths uniformly. After performing the tracking operation of the path under the priority order by setting the path tracking region and the mask regions for the path according to the priority order and resetting the path tracking region and the mask regions to the path to which the tracking operation has been done, the path tracking regions and the mask regions may be set for the remaining paths to perform the path tracking operations.

A path tracking method of a mobile communication system according to the present invention, which: detects signal power peaks from a delay profile of multipath multiplexed signals received via a plurality of propagation paths; separates/extracts each path contained in the multipaths based on propagation delay of the detected signal power peaks; allocates finger receivers to the signals of each of the separated/extracted paths for performing demodulation as well as rake combine of each demodulated signal; updates the delay profile every prescribed time interval for tracking chronological changes of the propagation paths; when a signal power peak position within a path tracking region set in advance for each path is fluctuated, assumes that the path is fluctuated; and sets a path tracking region to the fluctuated path and sets mask regions for preventing other finger receivers than the finger receivers allocated to the path from being allocated to the vicinity of the path, wherein, when the finger receivers are allocated to each of the paths of the multipaths in which each of the paths is close to each other in terms of time, each of the constituent paths is put into a group, priority orders are set for each of the constituent paths within the group for performing path tracking operations, and path tracking processing is performed according to the priority orders.

The path tracking processing performed according to the priority orders may be executed by setting the path tracking region and the mask regions for each path. Alternatively, the path tracking region may be set for each path to perform the tracking operation of the path, and the mask regions may be set for the path after completing the tracking operation.

The path tracking processing may be executed after completing the tracking operations of all the assumed multipaths.

Further, the grouping processing may also be performed to put each of the adjacent paths when “Td<2(Tt+Tm)” applies, provided that a propagation delay time difference of the adjacent paths is “Td”, a half of time length of the path tracking region is “Tt”, and time length of the mask region is “Tm”. The grouping processing may also be performed to put each of the adjacent paths into a group, when the propagation delay time difference of the adjacent paths is within prescribed time that is set in advance.

Further, the priority orders are so set that the path having the maximum signal power within the group is given the highest priority. The priority orders may be set in order from the path having the higher signal power to the path having the lower signal power. The priority orders may be set in order of time at which separation/extraction of the paths is executed, or may be set in order of executing separation/extraction of the paths from the latest to the oldest.

After the path tracking operation is performed by setting the path tracking region and the mask regions for the most preferential allocated path among the paths under the priority order, the path tracking operation for the remaining paths may be executed by setting the path tracking regions and the mask regions for the paths uniformly. After performing the tracking operation of the path under the priority order by setting the path tracking region and the mask regions for the path according to the priority order and resetting the path tracking region and the mask regions to the path to which the tracking operation has been done, the path tracking regions and the mask regions may be set for the remaining paths to perform the path tracking operations.

With the present invention, for performing the tracking operations of the paths fluctuated in accordance with chronological changes of the propagation paths at the time of receiving multipath multiplexed signals, when finger receivers are allocated to each of the paths of the multipaths close to each other in terms of time, the paths are put into a group, priority orders for performing the tracking operations are given to each path within the group, and path tracking processing is performed according to the priority orders. Therefore, the path tracking operations can be prevented from becoming incapable because of the mask regions, so that the reception qualities can be improved.

BEST MODES FOE CARRYING OUT THE INVENTION

Exemplary embodiments of the invention will be described hereinafter by referring to the accompanying drawings.

As a basic structure, a mobile communication system receiver according to the exemplary embodiment is a receiver which, based on a delay profile of multipath multiplexed signals to be received, separates/extracts each path contained in multipaths, demodulates received signals by each of the separated paths, and performs rake combine on the demodulated signals. The receiver separates/extracts each path contained in the multipaths and allocates demodulation finger receivers to the separated/extracted paths, and sets priority orders for paths in an adjacent path group having small propagation delay time separated/extracted from the multipaths to eliminate interference generated between adjacent paths according to the priority orders, and performs path tracking processing. Next, the exemplary embodiments will be described in details by using a specific example.

A case of applying the receiver of the mobile communication system according to the exemplary embodiments to a DS-CDMA mode receiver will be described as a first exemplary embodiment. As described above, a CDMA receiver1according to the first exemplary embodiment puts the paths of multipath multiplexed signals received via a plurality of propagation paths into a group when path tracking regions and mask regions set for those paths overlap with each other, gives priority orders to each path within the groups, and performs tracking operations of each path according to the priority orders. As shown inFIG. 1, the CDMA receiver1has a delay profile creation unit12, a path allocation unit14, a plurality of numbers of finger reception units16, and a rake combine unit18. Although not shown, the CDMA receiver has a radio reception unit and an A/D conversion unit. Base band digital signals that are digital signals converted from analog signals in the A/D conversion unit are inputted to the delay profile creation unit12.

The radio reception unit down-converts received signals from a radio frequency and also converts those to base band analog (I/Q) signals by phase demodulation. The A/D conversion unit converts the base band analog signals to base band digital signals, and outputs the base band digital signals to the delay profile creation unit12. The delay profile creation unit12creates a delay profile (for example, the delay profile shown inFIG. 4) based on the base band digital signals. The delay profile creation unit12updates the delay profile every time the base band digital signal is inputted from the A-D conversion unit.

The path allocation unit14separates/extracts paths contained in the multipaths based on the delay profile outputted from the delay profile creation unit12, and allocates the separated/extracted paths to the finger reception units16. The path allocation unit14sets the priority orders for the paths of an adjacent path group having small propagation time difference separated from the multipaths to eliminate interference between the adjacent paths according to the priority orders, and performs path tracking operations. Further, the path allocation unit14assumes each peak of the signal power values in the delay profile as the paths and, among the paths, allocates the path that is assumed to be effective (equal to or more than the threshold value) to each finger reception unit16. The path allocation unit14performs the path tracking operation based on the updated delay profile every time the delay profile creation unit12updates the delay profile. That is, the path allocation unit14detects whether the peak of signal power value of each path assumed before update is fluctuated or not, and updates allocation of the finger reception unit for the path based on the detection result.

Specifically, the path allocation unit14is configured with a grouping unit22, a judging unit24, and a path tracking processing unit26, as shown inFIG. 2.

The grouping unit22puts the paths into an independent path and paths of an adjacent path group when separating/extracting each path from the multipaths based on the delay profile, and allocates the finger reception unit16to each of the grouped paths. That is, when allocating the finger reception units16, the grouping unit22puts the paths into the independent path and the paths of the adjacent path group by judging whether the propagation time difference of the adjacent paths is within set time or not.

This will be described in a concretive manner. It is assumed here that the created delay profile is the one shown inFIG. 4. The grouping unit22calculates propagation delay time difference “Td” between a first path201and a succeeding path202shown inFIG. 4, and acknowledges the paths with the propagation time difference within the set time (Td<2(Tt+Tm)) as the paths within the adjacent path group, based on the fact that a condition “Td<2(Tt+Tm)” applies or not. The condition “Td<2(Tt+Tm)” will be described. For a path such as the path201inFIG. 5, a path tracking region PC is set as a region for tracking a position to be the peak of the signal power value, and mask regions MS are set in side lobes of the path tracking region PC. “2Tt” indicates time length of the path tracking region PC, and “2Tm” indicates time length of the mask regions MS. The grouping unit22assumes the position where the signal power value in the delay profile becomes the peak as the position of the path, and performs aforementioned grouping processing based on the assumed result.

In the delay profile shown inFIG. 4, “2(Tt+Tm)<Td” applies for the path202with respect to the succeeding path201. Thus, the grouping unit22acknowledges the path201as an independent path (single path).

In the delay profile shown inFIG. 4, the paths202,203, and204have extremely small propagation delay time difference, and are propagated closely. “2(Tt+Tm)>Td” applies for the paths202,203, and204, so that the grouping unit22acknowledges the paths202,203, and204as the paths of the adjacent path group.

The grouping unit22separates the paths202,203, and204contained in the adjacent path group into the individual paths based on the information acknowledged for the paths202,203, and204in the delay profile shown inFIG. 4.

As a way of example, a following case will be described. In the delay profile shown inFIG. 4, when the grouping unit22separates the paths202,203, and204contained in the adjacent path group into the individual paths, the grouping unit22sets the priority orders based on the signal power values of the paths, eliminates the interference between the adjacent paths according to the priority orders, and separates the paths into individual paths.

In the delay profile shown inFIG. 4, among the paths202,203, and204contained in the adjacent path group, the second path203received with propagation delay time with respect to the path202has the highest signal power value. The path having the second highest signal power value following the signal power value of the path203is the path204, and the path having the lowest signal power value is the path202. Thus, the grouping unit202separates the paths202,203, and204contained in the adjacent path group into the individual paths based on the signal power values of the paths (signal power value of the path203>signal power value of the path204>signal power value of the path202).

Through the above-described processing, the grouping unit22allocates the path201as the independent path and the paths202,203,204contained in the adjacent path group to the finger reception units16. When the signal power values of the path201as the independent path and the paths202,203,204contained in the adjacent path group are equal to or less than the threshold value, the grouping unit22stops allocations of the paths201,202,203,204to the finger reception units16.

The judging unit24receives information from the grouping unit22, and judges each of the paths201,202,203, and204allocated by the grouping unit22to find out whether the path201is the single path or not, and whether the paths202,203,203are the paths of the adjacent path group or not. The judging unit24outputs the judgment result to the path tracking processing unit26.

The path tracking processing unit26performs path tracking processing for the path201as the single and the paths202,203,204contained in the adjacent path group based on the information outputted from the judging unit24. It is to be understood that the path201is the single path and the paths202,203,204are the paths contained in the adjacent path group in the information outputted from the judging unit24.

As shown inFIG. 5, the path tracking processing unit26sets the path tracking region PC for the path201, sets the mask regions MS in the side lobes thereof, and performs path tracking processing for the path201. Specifically, the path tracking processing unit26performs processing to judge whether or not there is time shift generated in the peak position of the signal power value of the path201before and after updating, based on the information with which the grouping unit22assumes the peak position in the delay profile as the path201and the information with which the grouping unit22assumes the peak position in the updated delay profile as the path201. InFIG. 5, the regions with dotted lines in the path201are the mask regions MS.

Next, described is a case where the path tracking processing unit26performs the path tracking processing for the paths202,203, and204other than the path201. As shown inFIG. 5-FIG.9, the path tracking processing unit26sets the priority orders to the paths202,203,204that are contained in the adjacent path group, sets the path tracking regions PC and the mask regions MS to each of the paths202,203,204according to the priority orders, and performs the path tracking processing for each of the paths202,203, and204. Specifically, the path tracking processing unit26performs the processing to judge whether or not there is time shift generated in the peak positions of the signal power value of the paths202,203, and204before and after updating, based on the information with which the grouping unit22assumes the peak positions in the delay profile as the paths202,203,204, and the information with which the grouping unit22assumes the peak positions in the updated delay profile as the paths202,203,204, by a path unit according to the priority orders.

In the delay profile shown inFIG. 4, the path tracking processing unit26sets the priority orders in order of the path203, the path204, and the path202, and performs the path tracking processing for the path203first, then performs the path tracking processing for the path204, and performs the path tracking processing for the path202at last.

The finger reception unit16performs CDMA code demodulation (despread) of the receiving signals for each path according to an instruction from the path allocation unit14. The rake combine unit18performs rake combine of the demodulated signals for each path from each of the finger reception units16, and outputs the CDMA demodulation signal.

In the explanations above, the CDMA receiver according to the first exemplary embodiment is built as hardware. However, it is not limited only to such case. It may be built as software for allowing a CPU of a computer configuring the CDMA receiver to execute each of the above-described functions of the delay profile unit12, the path allocation unit14, the finger reception unit16, and the rake combine unit18based on a control program.

Next, actions of the receiver of a mobile communication system according to the exemplary embodiment will be described by referring toFIG. 3.

For the sake of explanations, it is to be understood that the delay profile creation unit12creates the delay profile shown inFIG. 4based on the inputted base band digital signals, and that the path allocation unit14assumes, based on the delay profile shown inFIG. 4, the four points201,202,203, and204on the delay profile as the paths having the significant signal powers, and allocates the finger reception units16to the assumed paths201,202,203,204, respectively.

Now, described is a case where, under the above-described state, the delay profile creation unit12updates the previous delay profile, extracts each path contained in the multipaths based on the updated delay profile, performs path tracking processing for the extracted paths, and updates the allocation of the finger reception units16for the paths to which the path processing is performed.

InFIG. 4, the paths201,202,203, and204are assumed as the paths at the positions of the signal power value peaks in the updated delay profile. InFIGS. 4,201a,202a,203a, and204aare the points assumed as the paths at the positions of the signal power value peaks in the delay profile before being updated. As shown inFIG. 4, unit sampling time Tt for specifying the path tracking region for the path is set on the left and right sides with respect to the peak position of the path signal power value, and the path tracking region is set as sampling time 2Tt. Unit sampling time Tm for specifying the mask region is set on the outer sides of the path tracking region, respectively, and the mask regions are set as sampling time 2Tm. WhileFIG. 4shows a case where the path tracking region PC (2Tt) and the mask regions MS (2Tm) are set for the path201, the paths tracking region (2Tt) and the mask regions MS (2Tm) are also set in the same manner for the paths202,203, and204. InFIG. 4, the propagation delay time difference of the path202with respect to the path201is propagation delay time Td. The propagation delay time difference Td also exists between the path202and the path203as well as between the path203and the path204, although the lengths thereof vary.

First, the grouping unit22calculates the propagation delay time difference Td between the first path201and the succeeding path202shown inFIG. 4(step S1ofFIG. 3).

The grouping unit22judges whether or not the condition “Td<2(Tt+Tm)” applies, based on the calculated propagation delay time difference Td (step S2ofFIG. 3).

In the delay profile shown inFIG. 4, “2(Tt+Tm)>Td” applies for the path202with respect to the succeeding path201. The grouping unit22acknowledges the path201as an independent path (step S2ofFIG. 3; N).

In the delay profile shown inFIG. 4, the path202, the path203, and the path204have very small propagation delay time differences and are propagated closely, so that “2(Tt+Tm)>Td” does not apply for the paths202,203, and204. Therefore, the grouping unit22acknowledges the paths202,203, and204as the paths of the adjacent path group (step S2ofFIG. 3; Y).

When the above-described processing is not performed for all the adjacent paths (step S5ofFIG. 3; N), the grouping unit22shifts the processing to step S1. In the meantime, when the above-described processing is performed for all the adjacent paths (step S5ofFIG. 3; Y), the grouping unit22assumes the position of the signal power peak in the updated delay profile as the path201based on the information with which it acknowledges the paths202,203, and204in the updated delay profile shown inFIG. 4. Similarly, the grouping unit22assumes the positions of the signal power peaks in the updated delay profile as the paths202,203,204, and puts the adjacent paths202,203,204into a group as the paths of the adjacent path group.

The grouping unit22considers the second path203received with propagation delay time with respect to the path202as the path having the highest signal power value, considers the path204as the path having the second highest signal power value following the signal power value of the path203, and considers the path202as the path having the lowest signal power value. Based on the signal power values of the paths, the grouping unit22separates the paths202,203, and204contained in the adjacent path group into the individual paths.

Through the above-described processing, the grouping unit22allocates the finger reception units16to the path201as the independent path and the paths202,203,204contained in the adjacent path group.

Next, the judging unit24receives the information from the grouping unit22, and judges whether the path201is the independent path or not and whether the paths202,203,204are the paths of the adjacent path group or not regarding the paths201,202,203, and204allocated by the grouping unit22(step S6ofFIG. 3). The judging unit24outputs the judgment result to the path tracking processing unit26.

The path tracking processing unit26performs the path tracking processing described below separately for a case where the path is the single path (independent path) and for a case where the paths are the paths of the adjacent path group based on the information outputted from the judging unit24.

When the path201is the single path (step S6ofFIG. 3; Y), the path tracking processing unit26sets the path tracking region PC for the path201and sets the mask regions MS in the side lobes as inFIG. 5, and performs the path tracking processing for the path201, i.e., performs processing for searching the highest point of the signal power value in the path201. That is, the path tracking processing unit26assumes that the path is fluctuated when there is fluctuation in the peak201aof the signal power value within the path tracking region PC, and have the path track the peak position of the signal power value (step S7ofFIG. 3). In the case ofFIG. 5, the peak of the path201is consistent with the peak position of the signal power value. Thus, the path tracking processing unit26ends the path tracking processing for the path201(step S7ofFIG. 3).

Next, the path tracking processing unit26performs the path tracking processing in a manner described below for the paths202,203, and204that are contained in the adjacent path group, since the adjacent paths202,203, and204are the paths of the adjacent path group (step S6ofFIG. 3; N).

As shown inFIG. 5-FIG.9, the path tracking processing unit26sets the priority orders of the paths202,203,204contained in the adjacent path group, sets the path tracking regions PC and the mask regions MS for each of the paths202,203,204according to the priority orders, and performs the path tracking processing for each of the paths202,203,204, i.e., performs the processing for searching the highest point of the signal power values in each of the paths202,203,204.

That is, as shown inFIG. 4, the path tracking processing unit26selects the path203that has the highest signal power value (step S8ofFIG. 3). Then, as shown inFIG. 6, the path tracking processing unit26sets the path tracking region PC to the path203, sets the mask regions MS to the side lobes, and performs the path tracking processing for the path203. As shown inFIG. 6, the peak position of the signal power value within the path tracking region PC is shifted to the right side from the peak203a. Thus, the path tracking processing unit26assumes that the path203is fluctuated, and makes the peak of the path203follow the peak203ato the right side thereof as shown inFIG. 7(step S9ofFIG. 3).

Then, the path tracking processing unit26performs the path tracking processing for the remaining paths of the above-described adjacent path group such as each of the paths203and204shown inFIG. 4(step S10ofFIG. 3). That is, as shown inFIG. 8, the path tracking processing unit26performs the path tracking processing for the path204by setting the path tracking region PC and the mask regions MS to the path204. InFIG. 8, among the waveform of the path204, the area shown with a solid line is the path tracking region PC, and the areas shown with dotted lines are the mask regions MS. As can be seen fromFIG. 8, the peak position of the signal power value within the path tracking region PC is shifted to the right side from the peak204a. Thus, the path tracking processing unit26assumes that the path204is fluctuated, and makes the peak of the path204follow the peak204ato the right side thereof as shown inFIG. 8(step S10ofFIG. 3). In this case, the path tracking region PC and the mask regions MS for the path203that is adjacent to the path204are not set. Thus, the mask regions in the side lobes of the path203and the path204do not overlap with each other, i.e., there is no interference occurred.

As shown inFIG. 8, there is time shift in the peak position of the signal power value of the path204. Thus, the path tracking processing unit26performs the path tracking processing as inFIG. 9(step S10ofFIG. 3).

The path tracking processing unit26performs the same processing as that of the path204for the path202as well (step S10ofFIG. 3).

The path tracking processing unit26judges whether or not the processing from step S6to step S10is completed for all the allocated paths (step S11ofFIG. 3). When not completed (N in step S11ofFIG. 3), the path tracking processing unit26repeatedly executes the processing from step S6to step S10. Inversely, when the path tracking processing has been completed for all the allocated paths (Y in step S11ofFIG. 3), as shown inFIG. 9, the path tracking processing unit26ends a series of processing for the current updating operation of the paths (step S12ofFIG. 3).

After the series of processing (after a prescribed time period), an updating operation of the next path allocation, i.e., searching of new paths and canceling of allocation to the fading paths, is also performed as in the conventional case. The updating operation of the path allocation is not the substance of this exemplary embodiment, so that explanations thereof are omitted.

In the first exemplary embodiment, it is judged to find out whether or not the path tracking regions and the mask regions set for each of the allocated paths overlap with each other before setting the paths tracking regions and the mask regions for the allocated paths. Further, the path tracking region and the mask regions are set preferentially for the path that has the highest signal power among the paths in the overlapping regions, and the path tracking processing is performed. Therefore, it is possible to avoid having a part of the path tracking region of that path to be set within the mask regions that are set for another allocated path. In other words, it is not to be killed by the mask region set for another allocated path. Therefore, it is possible to prevent the path tracking ability to become incapable. This makes it possible to continuously maintain the reception quality.

In the first exemplary embodiment, the priority orders when performing the path tracking operations for the paths of the adjacent path group are set based on the signal power values. However, it is not limited only to such case. The priority orders may be set based on the time orders at which the paths of the adjacent path group are separated/extracted. The same effects as those of the first exemplary embodiment can be obtained also with this structure. Further, for grouping the paths, it is possible to put the paths into a group every time the path tracking processing is performed for a single path or at the point where the path tracking processing for all the assumed multipaths is completed.

In this exemplary embodiment, the priority orders when performing the path tracking operations for the paths set as the adjacent path group may be set based on the orders of allocating the finger reception units to the paths. The same effects as those of the first exemplary embodiment can be obtained also with this structure.

In this exemplary embodiment, after the path tracking operation is performed by setting the path tracking region and the mask regions for the most preferential allocated path among the adjacent path group allocated by the path allocation unit, if the mask regions set for the remaining paths do not interfere with each other, the path tracking operations for the allocated paths within the adjacent path group may be executed by setting the path tracking regions and the mask regions for the remaining paths uniformly. With this structure, the path tracking processing for the remaining paths can be executed in parallel, which is advantageous in respect that the path tracking processing can be performed promptly.

In this exemplary embodiment, every time the path tracking processing for a single allocated path is completed, it is judged whether or not the allocated paths overlap with each other, and the path tracking processing may be performed based on the judgment result. This structure is advantageous in respect that it is possible to surely prevent interference of the mask regions of the paths that are contained in the adjacent path group.

In this exemplary embodiment, the path tracking processing according to the priority orders may be performed as follows. That is, the path tracking region may be set for the highest priority path for performing the path tracking operation, the mask regions may be set for the highest priority path when the tracking operation is completed, and the path tracking operation may be performed for the paths after the highest priority path by setting the path tracking region and the mask regions successively.

Industrial Applicability

The present invention can be applied not only to the CDMA receiver but also to receivers of other forms which receive multipath multiplexed signals other than spread spectrum signals received via a plurality of propagation paths in a spread spectrum mode.

This applications is based upon and claims the benefit of priority from Japanese patent applications No.2006-053582, filed on Feb. 28, 2006, the disclosure of which is incorporated herein in its entirety by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1is a block diagram showing an electrical structure of a CDMA receiver according to a first exemplary embodiment of the invention;

FIG. 2is a block diagram showing a specific structure of a path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention;

FIG. 3is a flowchart for describing actions of the path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention;

FIG. 4is an illustration showing an example of paths allocated by the path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention;

FIG. 5is an illustration showing a setting example of path tracking regions and mask regions set by the path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention;

FIG. 6is an illustration showing a setting example of path tracking regions and mask regions set by the path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention for an allocated path that has the maximum signal power;

FIG. 7is an illustration showing an example of a state after completing a path tracking operation performed by the path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention;

FIG. 8is an illustration showing an example of mask regions set by the path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention;

FIG. 9is an illustration showing another example of the state after completing the path tracking operation performed by the path allocation unit of the CDMA receiver according to the first exemplary embodiment of the invention;

FIG. 10is an illustration showing an example of a delay profile created by a conventional CDMA-mode receiver;

FIG. 11is an illustration showing a path tracking regions and mask regions set for the paths in a delay profile with a conventional technique; and

FIG. 12is an illustration for describing a technical problem that occurs when setting path tracking regions and mask regions for each of a plurality of multipaths in the delay profile with the conventional technique.

REFERENCE NUMERALS

12Delay profile creation unit

14Path allocation unit

26Path tracking processing unit