JP4627008B2 - Path searcher and path search method - Google Patents

Description

  The present invention relates to a technical field of wireless communication, and more particularly to a path searcher and a path search method for performing a path search based on a power delay profile.

  In general, a signal transmitted from a radio transmitter reaches the radio receiver as one or more reflected waves from a building or other obstacle or the ground in addition to or instead of reaching the radio receiver as a direct wave. To do. These direct waves or reflected waves form a series of incoming wave groups arranged on the time axis, and the series of incoming wave groups form a power delay profile in which a plurality of paths are arranged. In wireless communication, it is possible to restore the transmission signal satisfactorily by accurately determining the amplitude and timing of these paths. The detection of the path timing in the power delay profile is performed by a method called path search. In the conventional path search, a certain noise level is set, and the path is detected based on whether or not the power level of the path exceeds the noise level.

The conventional path search is described in Patent Document 1, for example.
JP 2001-217747 A

  However, path timing candidates appearing in the power delay profile may be due to path sidelobe components in addition to true path timing. For example, when a path with relatively high power passes through the roll-off filter, a side lobe component related to the path is generated, and the side lobe component may appear on the power delay profile. In conventional applications, such components may be relatively small and negligible, but in future high performance product applications, this may cause path search accuracy to degrade. It is difficult to sufficiently eliminate such extra paths by raising and lowering the threshold value set based on the noise level. Because if the threshold is too low, many extra paths will be adopted as true paths, while if the threshold is too high, not only the extra paths but also the true paths will be discarded. Because it becomes. In other words, there may be sidelobe components comparable to the power level of the true path.

  On the other hand, in a multi-input multi-output (MIMO) system that improves communication capacity, a plurality of transmission antennas and a plurality of reception antennas are used for a transceiver. Therefore, in the MIMO scheme, as shown in FIG. 1, multipath interference in a propagation path related to a certain reception antenna 208-x not only occurs between a certain transmission antenna 206-p but also separately. This also occurs between the transmission antennas 206-q. Therefore, in the MIMO scheme, the number of path candidates increases in accordance with the number of antennas, and high accuracy of the path search is particularly required, but there is a greater concern about the deterioration in the accuracy of the path search.

  The present invention has been made to address at least one of the above-mentioned problems, and its problem is to remove from the power delay profile the sidelobe component of the path generated by passing the received signal through the band-limiting filter. To provide a path searcher and a path search method for correctly detecting a path.

The path searcher according to one embodiment is
Generating means for generating a power delay profile for each combination of one transmission antenna and one reception antenna based on reception signals transmitted from a plurality of transmission antennas and received by a plurality of reception antennas ;
Means for combining a plurality of generated power delay profiles into one power delay profile;
Means for obtaining a side lobe component of a path in the synthesized one power delay profile by utilizing a response characteristic of a band limiting filter;
Sidelobe removal means for removing the sidelobe component from the one power delay profile and creating a modified power delay profile;
Based on the modified power delay profile, and means for detecting a timing of a path, a path searcher.

  According to the present invention, it is possible to correctly detect a path by removing, from the power delay profile, a side lobe component of a path generated when a received signal passes through a band limiting filter.

  In one aspect of the present invention, a power delay profile is created from the received signal, and a side lobe component of the path is calculated from the response characteristic of the band limiting filter. The sidelobe component is removed from the power delay profile and the path timing is detected based on the modified power delay profile. This makes it possible to effectively remove excess components that cannot be removed simply by raising or lowering the threshold set based on the noise level from the power delay profile.

  When signals from a plurality of transmission antennas are received by a plurality of reception antennas, the power delay profile is determined for each combination of one transmission antenna and one reception antenna (for each propagation path distinguished by the transmission and reception antennas). ) May be created.

  Multiple power delay profiles may be combined into one power delay profile. The synthesis may be performed by averaging, for example. The side lobe of the path may be calculated from the combined power delay profile. When sidelobe detection and removal is performed based on the averaged power delay profile, path timing and the like based on the averaged power delay profile are given to subsequent signal detection. Relatively little. On the other hand, from the viewpoint of achieving high accuracy in signal detection, it is desirable to individually correct the power delay profile created for each propagation path without performing such averaging.

  In the following, embodiments of the present invention will be described taking a MIMO wireless communication system adopting the DS-CDMA system as an example. May be used.

  FIG. 2 shows an overview of a MIMO communication system including a transmitter 202 and a receiver 204. As shown in the figure, the MIMO scheme used in this embodiment is a MIMO multiplexing scheme, and different signals are transmitted simultaneously from the plurality of transmission antennas 206-1 to 206-N at the same frequency. Note that the present invention may be applied to a MIMO diversity system in which signals having substantially the same contents are transmitted simultaneously from the respective transmission antennas. These transmission signals are received by a plurality of reception antennas 208-1 to 208 -N. For simplicity, the number of transmission antennas and the number of reception antennas are both N, but different numbers of antennas may be used.

FIG. 3 shows a conceptual diagram of the receiver 204. Reception signals y _{1 to} y _N received by the respective reception antennas are input to the signal detection unit 302. The received signals y _{1 to} y _N are also input to the path searcher 304. The path searcher 304 estimates a channel based on a received signal including a pilot signal known by both the transmitter and the receiver, creates a power delay profile, and transmits information on path timing, fading compensation, and the like to the signal detection unit 302. To give. The signal detection unit 302 detects and separates signals transmitted from each of the plurality of transmission antennas based on the received signal, the estimated path timing, and the like. As the signal separation method, for example, a method such as a least square error method (MMSE), a maximum likelihood determination method (MLD), or a QR decomposition method maximum likelihood determination method (QRM-MLD) may be used. The separated transmission signal is provided to a channel decoder for further demodulation processing.

  FIG. 4 shows a functional block diagram of a path searcher according to an embodiment of the present invention. The path searcher includes a power delay profile generation unit 402, a power delay profile averaging unit 404, a side lobe generation unit 406, a side lobe removal unit 407, and a path timing detection unit 408.

The power delay profile generation unit 402 generates a plurality of power delay profiles based on each of the reception signals y _{1 to} y _N received by the plurality of reception antennas and subjected to the band limitation process. More specifically, the power delay profile generation unit 402 performs channel estimation based on the received pilot signal for each combination of one transmission antenna and one reception antenna, and the power level of the path included in the reception signal And the timing is checked and information on the power delay profile is output. Therefore, the power delay profile generation unit 402 generates N _TX × N _RX power delay profiles. Here, N _TX represents the number of transmitting antennas, and N _RX represents the number of receiving antennas. In the MIMO scheme, a signal received by one receiving antenna includes signals from N _TX transmitting antennas. N _TX × N _RX combinations of the transmission antenna and the reception antenna can be distinguished by using, for example, a different pilot signal for each transmission antenna. These pilot signals are preferably selected to be orthogonal to each other.

  The power delay profile averaging unit 404 combines a plurality of power delay profiles corresponding to each of the plurality of receiving antennas into one while matching their respective timings. This combining is generally performed by averaging a plurality of power delay profiles. The averaging may be an arithmetic average or a weighted average.

FIG. 5 schematically shows a combined power delay profile. In the illustrated example, the nine paths with more power threshold E _th is set based on the noise level (indicated by the downward arrow), six 501-506 correspond to the true path However, three of 511 to 513 correspond to the side lobe components of the true path and may not exist in the actual channel. If such a sidelobe component is erroneously detected as a true path, the signal separation accuracy in the signal detection unit at the subsequent stage is degraded, and it may be difficult to restore the transmission signal satisfactorily. A path having relatively large power passes through a roll-off filter (band-limiting filter), so that such a sidelobe component is generated.

4 generates a side lobe component appearing in the power delay profile by using an impulse response characteristic of a roll-off filter (band limiting filter). The impulse response characteristic h _RC (t) is known at the receiver, has a characteristic as shown in FIG. 6, for example, and is expressed by the following equation (1):

ここで、Ｔｃはチップ周期を表し、αはロールオフファクタを表す（図６の例では、α＝０．２２である。）。一般に、正負１チップ周期の範囲内（｜ｔ｜≦Ｔｃ）はメインローブと呼ばれ、真のパスに関連し、それ以外の範囲（｜ｔ｜＞Ｔｃ）はサイドローブに関連する。

Here, Tc represents a chip period, and α represents a roll-off factor (α = 0.22 in the example of FIG. 6). In general, the range of a positive / negative 1 chip period (| t | ≦ Tc) is called a main lobe, which is related to a true path, and the other range (| t |> Tc) is related to a side lobe.

  For example, from the power level and timing of the head path 501 shown in FIG. 5, the power level and timing of the side lobes related to the head path 501 are obtained by the above equation (1). From the power level and timing of the next path 502, the side lobe for this path 502 is also determined. Similarly, a path with relatively large power is selected (for example, Y paths are selected), and a side lobe component related to the selected path is obtained. There are an infinite number of side lobe components in theory, but a required number of side lobe components (power level and timing) are required according to the application (for example, Z on the left and right of the main lobe). The path for which the sidelobe component is to be calculated may be determined by, for example, selecting paths (for example, Y) in descending order of power from among paths having power levels exceeding the threshold.

  The side lobe removal unit 407 in FIG. 4 removes the side lobe component obtained by the side lobe generation unit 406 from the power delay profile from the power delay profile averaging unit 404. Thereby, for example, unnecessary paths 511, 512, and 513 shown in FIG. 5 are removed, and six true paths 501,. . . , 506 only remains.

  The path timing detection unit 408 extracts the path timing based on the power delay profile corrected by the side lobe removal unit 407. In the illustrated example, six paths 501 to 506 are selected by comparing the power level of the path and the noise level. As described above, the path searcher according to the present embodiment performs a path search based on the power delay profile from which an extra path is eliminated, so that the path search can be performed accurately.

  FIG. 7 is a flowchart illustrating an operation example of the path searcher according to an embodiment of the present invention. This flow shows how the top Y paths are detected from the power delay profile. The flow begins at step 71 and proceeds to step 72. In step 72, the power delay profile generation unit 402 in FIG. 4 generates a power delay profile from the received signal. The power delay profile is created for each combination of one transmission antenna and one reception antenna. The plurality of power delay profiles are combined into one power delay profile by arithmetic average, weighted average, or some other method.

  In step 73, the Nth largest path is selected from the paths included in the power delay profile. It is assumed that parameter N is initially set to 1.

  In step 74, a predetermined number (Z) of side lobe components of the path are calculated from the timing and power of the selected path. The side lobe component is calculated by the side lobe generator 406 of FIG. 4 based on the response characteristic of the band limiting filter as shown in the above formula (1).

  In step 75, the calculated Z side lobe components are removed from the power delay profile by the side lobe removal unit 407. As a result, of the main lobe and side lobe of the Nth largest path, the side lobe component is removed from the power delay profile. The parameter N is incremented.

  In step 76, it is determined whether N is a predetermined value Y or less. If N is less than or equal to Y, the flow returns to step 73, the next highest power path is selected, and so on. On the other hand, if N exceeds the predetermined value Y, the flow proceeds to step 77. The power delay profile at this point includes the main lobe component of the upper Y paths, the main lobe and side lobe components of the smaller path, and does not include the side lobe components of the upper Y paths. Has been fixed.

  In step 77, based on the corrected power delay profile, the power and timing of the top Y and other paths are determined, and the flow proceeds to step 78 and ends.

FIG. 8 shows a simulation result comparing the technique according to the embodiment of the present invention and the conventional technique. The main conditions used in the simulation are as follows:
Modulation method: 8PSK
Turbo coding rate R: 3/4
The maximum Doppler frequency _f D: 20Hz
Pilot power ratio to data channel: 30%
Maximum number of fingers: 6
In the simulation, an exponential 2 dB attenuation 6-path signal model is adopted, and it is assumed that the power levels of 6 paths after the first path are attenuated by 2 dB each. In the figure, the horizontal axis represents the average of the signal power to noise power density ratio (Eb / N ₀ ) per bit of information per receiving antenna. The vertical axis represents the average block error rate (BLER). ● indicates the ideal estimation result by cheating and indicates the limit value of the estimation. The ◯, Δ, and □ marks that are close to the ideal curve indicate the estimation results according to the embodiment of the present invention. In the upper right of the figure, □, Δ, ×, and ▽ marks indicate estimation results by the conventional method.

The four types of conventional estimation results are obtained when the path search power threshold value (E _th ) is changed in four ways. _{A square} indicates a result when the power threshold is set equal to a certain average power value (P _A ) (E _th = P _A ). The Δ mark indicates the result when the power threshold is set to 3 times a certain average power value (P _A ) (E _th = 3P _A ). _A cross indicates a result when the power threshold is set to 5 times a certain average power value (P _A ) (E _th = 5P _A ). The ▽ mark indicates the result when the power threshold is set to 7 times the certain average power value (P _A ) (E _th = 7P _A ). Here, a certain average power value is the average power of the path after removing 24 paths from the power delay profile in descending order of power. The reason why the estimation result is bad when the power threshold is small is thought to be that a path other than the true path is included in the paths selected as paths exceeding the power threshold. On the other hand, even if the power threshold is large, the estimation result is bad because the true path to be selected is not selected below the power threshold.

The three types of estimation results according to the embodiment of the present invention are obtained when the number of sidelobe components to be removed (Y) is changed. The power threshold value for the path search is set to twice the certain average power value (E _th = 2P _A ). The Δ mark indicates the result when the left and right side lobe components of the true path are removed from the power profile (Y = 1). A square indicates the result when the left and right side lobes of the true path are removed from the power profile (Y = 2). The circles indicate the results when the left and right side lobes of the true path are removed from the power profile (Y = 3). In any case, it can be seen that the estimation result is very close to the ideal estimation result (● mark), which is greatly different from the estimation result by the conventional method.

FIG. 9 shows a functional block diagram of a path searcher according to an embodiment of the present invention. In addition to the power delay profile generation unit 402, the path searcher relates to a side lobe generation unit 406-n, a side lobe removal unit 407-n, and a path timing detection unit 408-n (n = 1,..., N _all ). It has N _all lines. However, N _all = N _TX × N _RX , where N _TX represents the number of transmission antennas and N _RX represents the number of reception antennas.

The power delay profile generation unit 402 performs channel estimation for each combination of one transmission antenna and one reception antenna, and generates N _TX × N _RX power delay profiles. N _TX × N _RX combinations of the transmission antenna and the reception antenna can be distinguished by using, for example, a different pilot signal for each transmission antenna. Information about each power delay profile is given to the side lobe generator and the side lobe remover in each system. Since the elements included in each of the N _all systems have the same configuration and function, the elements included in the first system will be described on behalf of them.

  The side lobe generation unit 406-1 generates a side lobe component appearing in the power delay profile using the impulse response characteristic of the roll-off filter (for example, expressed by the above formula (1)). A required number of side lobe components (power level and timing) are determined according to the application.

  The side lobe removal unit 407-1 removes the side lobe component obtained by the side lobe generation unit 406-1 from each power delay profile input thereto.

  The path timing detection unit 408-1 detects the path timing based on the power delay profile corrected by the side lobe removal unit 407-1.

In the present embodiment, N _all power delay profiles are not averaged, sidelobe component removal and path timing detection are performed for each power delay profile, and the detection result of FIG. Given. The signal detection unit 302 can perform signal separation with higher accuracy than in the case of the first embodiment, based on accurate path timing regarding individual propagation paths that are different for each transmission and reception antenna.

The conceptual diagram of a power delay profile is shown. 1 shows a conceptual diagram of a MIMO wireless communication system. The conceptual diagram of the receiver of a MIMO system is shown. 1 shows a functional block diagram of a path searcher according to one embodiment of the present invention. FIG. It is a figure which shows a power delay profile. It is a figure which shows the impulse response characteristic of a roll-off filter. It is a flowchart which shows the operation example of the path searcher by one Example of this invention. The simulation result which compares the method by the Example of this invention with the conventional method is shown. 1 shows a functional block diagram of a path searcher according to one embodiment of the present invention. FIG.

Explanation of symbols

202 transmitter; 204 receiver; 206-1 to N transmitting antenna; 208-1 to N receiving antenna;
302 signal detection unit; 304 path searcher;
402 power delay profile generation unit; 404 power delay profile averaging unit; 406 side lobe generation unit; 407 side lobe removal unit; 408 path timing detection unit;
501 to 506 True path; 511 to 513 Side lobe component of true path

Claims (2)

Based on the received signals received by a plurality of receiving antennas transmitted from a plurality of transmitting antennas, for each combination of one transmitting antenna and one receiving antenna, and generating means for generating a power delay profile,
The generated multiple power delay profile was, by using one response means and band-limiting filter for combining the power delay profile, determine the side lobe component of the path in the mix made the one power delay profile has been Means,
Sidelobe removal means for removing the sidelobe component from the one power delay profile and creating a modified power delay profile;
Based on the modified power delay profile, and means for detecting the timing of the path, the path searcher. Generating a power delay profile for each combination of one transmission antenna and one reception antenna based on reception signals transmitted from a plurality of transmission antennas and received by a plurality of reception antennas ;
Combining the plurality of generated power delay profiles into one power delay profile;
By utilizing the response characteristics of the band limiting filter, and determined Mel Step side lobe component of the path in the synthesis said one power delay profile has been,
Removing the sidelobe component from the one power delay profile to create a modified power delay profile;
Based on the modified power delay profile, and a step of detecting a timing of a path, the path search method.

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