JPH11261457A - Waveform equalizing processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveform equalizing processing method of little operation processing amount without deteriorating equalizing performance. SOLUTION: In a tap selection part, a mutual correlation value at each tap position between a reception signal and a known training system is calculated 101, the normalized number of taps are extracted 102 from a tap of a big mutual correlation value, and a waveform equalization part is instructed 103. The waveform equalization part reduces the amount of processing in the waveform equalizing processing by eliminating taps other than the taps specified by the tap selection part from waveform equalization processing objects.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a waveform equalization processing method in a wireless communication system.

[0002]

2. Description of the Related Art An adaptive equalizer is known as a technique for removing intersymbol interference caused by multipath fading in a wireless communication system. This is due to the fact that the radio signal transmitted from the transmitter passes through a plurality of paths having different path lengths directly or by reflection, etc., so that a difference in the arrival time of each radio signal occurs at the receiver antenna. Is equalized.

FIG. 2 shows a configuration of a decision feedback equalizer (hereinafter, referred to as a DFE) which is a kind of adaptive equalizer. The DFE includes an equalizing filter unit 21, a data determining unit 22, an error estimating unit 23, and a tap gain updating unit 24. The equalization filter unit 21 includes a feedforward (FF) tap unit 2 including j taps.
The feedback (FB) tap section 26 is composed of 5 and k taps.
The tap 25 is set at the symbol time or 1/2 symbol time, and the FB tap 26 is set at the symbol time.

Next, before starting the description of the operation of the waveform equalizing section, FIG. 3 shows a configuration example 300 of a slot transmitted in a radio section. The slot is a known training sequence 301
And a data series 302. Therefore, the receiving side estimates the propagation state of the wireless section using the received known training sequence.

[0005] The waveform equalizing operation for this slot will be described again with reference to FIG. The reception signal Y1 is sequentially captured by the FF tap 25 (X1). First, a known signal sequence in the sequentially captured reception signal X1 and a known signal sequence 27 (training sequence) stored on the receiving side. After making the tap gain coefficient W converge (switch 1: training mode) with the difference between the received signal X1 and the determination value as the estimation error e, the difference between the received signal X1 and its determination value is set as e. Of the tap gain coefficient W (switch 2: tracking mode). Here, the training sequence is input to the FB tap 26 in the training mode, and the determined value X0 after equalization is input in the tracking mode.

Update of the tap gain coefficient in the training / tracking mode is performed by LMS (Least Mean Square).
e) Algorithms and RLS (Recursive Least Squares)
) Use an algorithm. In this manner, the DFE can remove the distortion of the received signal Y1 and obtain the signal d after the waveform equalization. This DFE is described in IEICE Transactions B-II, Vol. J72-B-II
No. 10 (1989), pages 515-523.

In the DFE, particularly, the processing amount of the above algorithm is large. Therefore, it is a problem to reduce the calculation amount without deteriorating the equalization performance as much as possible.

[0008]

In the conventional waveform equalizer, when the delay spread under the assumed propagation environment is large, a large number of taps are required to include the delayed wave. In particular, when performing high-speed transmission, the symbol interval with respect to the delay amount becomes relatively small, and more taps are required. This increase in the number of taps leads to an increase in the processing amount in the waveform equalization processing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an equalization processing method which minimizes deterioration of reception performance and requires a small amount of arithmetic processing.

[0010]

In order to achieve the above object, a waveform equalization processing method according to the present invention employs a tap gain coefficient obtained by using a training sequence of a slot to be subjected to waveform processing, and particularly includes a waveform and the like. Extract the effective taps for the conversion process,
Only the tap is used for the waveform equalization processing.

[0011]

FIG. 6 shows a configuration example of the present invention, and FIG. 1 shows a processing flow. The present invention is roughly divided into two parts, one is a tap selection unit 603 and the other is a waveform equalization unit 602. The received signal 601 is output from the tap selection unit 6
03, and the tap selection unit 603 calculates 101 a cross-correlation value with a known signal inserted in the transmission signal on the transmission side. Received signal 601 is an I / Q signal 400 at baseband as shown in FIG. I401 corresponds to a real part in a complex plane, and Q402 corresponds to an imaginary part. A cross-correlation value between the received I / Q signal 400 and the known training sequence signal 500 shown in FIG. 5 is calculated. The cross-correlation value calculation formula (Equation 1) is shown below.

[0012]

(Equation 1)

FIG. 7 shows an example of the result of the cross-correlation calculation. FIG. 7 shows a reception signal 700 and a path 1 signal 701 and a path 2 signal 702 having different arrival routes from the transmitter to the receiver constituting the reception signal. The path 1 signal 701 and the path 2 signal 702 are added and combined at the receiver antenna end to generate a received signal 700. The received signal 700 is input to the above-described tap selection unit 603, and calculates a cross-correlation value 705 with a known training sequence signal. Pass 1
Known training sequence signal part 7 in signal 701
The cross-correlation value at the corresponding position of the known training sequence signal portion 704 in the 03 and path 2 signals 702 is large as a result of the cross-correlation calculation 705 with the known training sequence signal.

In FIG. 7, the number of taps prepared by the waveform equalizer 602 is 7, and a total of two taps are selected from taps having a large cross-correlation value at tap positions. The position of the tap having a large cross-correlation value corresponds to the time position of the direct wave and the delayed wave. Accordingly, in the waveform equalization processing, tap information of the position of the direct wave and the position of the delayed wave, which is information necessary for equalizing the waveform of a symbol at a certain time, is obtained.

The result of the tap selection is instructed to the waveform equalizer 103, and the gain coefficient of the tap not selected is calculated /
By removing the taps from the update target, the seven taps prepared by the waveform equalization unit are reduced to the waveform equalization processing 104 using the selected two taps.

It should be noted that the present invention has no problem even when used in combination with reception diversity. For example, as shown in FIG. 8, even in the case of a two-branch transversal combining DFE using two FF taps, the processing amount can be reduced by reducing the number of processing target taps as described above. in this case,
The selection tap may be determined for each branch. Alternatively, the tap at the common position of each branch may be selected from the result of adding the cross-correlation value of each branch to the tap at the same position.

FIG. 9 shows a simulation result in the present invention. As a simulation condition, the modulation method is Q
PSK, a maximum Doppler frequency of 16 Hz, and a maximum delay amount are a 6-tap model of about 7 symbols. The number of taps prepared in the waveform equalizer is 2 × 14.2 for each of FF and FB, and the number of taps is doubled because of the diversity of two branches. In this simulation, the maximum delay wave is at a position of about 7 symbols from the top. Therefore, in a normal DFE, 14 taps are required for FF taps at a half symbol interval. From this simulation result, it can be seen that, even when the number of taps to be processed is reduced to 8 according to the present invention, reception performance degradation of about 1 dB can be achieved at BER = 1E-3, when 14 FF taps are prepared / used. It can be seen that not all taps are required.

According to the document "Waveform equalization technology for digital mobile communication", Trikeps Co., Ltd. (1994), in the case of the RLS algorithm, the operation amount of the waveform equalization algorithm is proportional to the square of the number of taps. . Therefore, when the number of taps prepared by the waveform equalizer is A and the number of taps to be selected is B, (B / A) 2 is obtained according to the present invention. For example, if A = 30 and B = 18, the processing amount is 0.1.
36, which is about a third reduction. This reduction in processing amount is based on software processing such as a DSP and a CPU. However, when a logic circuit is used, the number of operating logics can be reduced, and the effect of reducing power consumption can be expected.

In a wireless system requiring frame synchronization such as TDMA, an erroneous acquisition of a frame synchronization unit leads to a deterioration in reception performance. This is because if the frame synchronization unit mistakenly captures a delayed wave in a multipath fading environment where multiple delayed waves exist,
This is because a received signal is not input to the waveform equalizer at a predetermined timing, so that a reception sequence required for waveform equalization is not input to the waveform equalizer, and a sufficient waveform equalization effect cannot be expected. . In order to remedy this frame synchronization capture error, the number of taps of the waveform equalizer may be prepared by twice the expected delay time. However, this leads to an increase in the processing amount of the waveform equalization processing unit as described above. In the present invention, even if the number of taps twice as long as the expected delay time is prepared in consideration of frame synchronization error in the waveform equalizing unit, the number of taps to be processed is reduced to the specified number by the tap selecting unit. Therefore, even if erroneous acquisition of frame synchronization is taken into account, the amount of processing does not increase, and the effect of complementing frame synchronization can be expected.

Note that the modulation method in the present invention is QPS
K or π / 4 shift QPSK or 16QA
M may be used. Further, modulation methods other than these may be used. In any case, the equalization processing method of the present invention can perform high-speed equalization processing with a small amount of arithmetic processing.

Further, in the waveform equalization processing method according to the present invention, it is not always necessary to reduce the number of taps to a specified number. It may be a variable type.

[0022]

According to the waveform equalization processing method of the present invention, taps particularly effective for waveform equalization processing are extracted from tap gain coefficients obtained using a known training sequence in a slot for performing waveform equalization. By using only those taps for the waveform equalization process, the number of taps to be processed can be reduced, and the amount of processing in the waveform equalizer can be reduced.

Also, in a wireless system requiring frame synchronization such as TDMA, even if the frame synchronization detection unit erroneously captures a delay wave, the tap of the waveform equalization unit is twice as long as the expected delay wave. If the degree is prepared, it is possible to absorb the reception performance deterioration due to the erroneous acquisition of the frame synchronization without increasing the processing amount.

[Brief description of the drawings]

FIG. 1 is a processing flowchart of an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a conventional waveform equalizer.

FIG. 3 is an explanatory diagram showing a configuration example of a slot transmitted in a wireless section.

FIG. 4 is a waveform chart showing an example of a reception baseband signal.

FIG. 5 is a waveform chart showing a known signal example.

FIG. 6 is a block diagram showing a configuration example of an apparatus for performing a waveform equalization process according to the present invention.

FIG. 7 is an explanatory diagram showing a cross-correlation between a received signal obtained from signals from two paths and a known training sequence signal.

FIG. 8 is a block diagram showing a waveform equalizer using two-branch diversity.

FIG. 9 is a characteristic diagram showing a simulation result of the equalization processing according to the present invention.

[Explanation of symbols]

21: Equalization filter unit, 22: Data determination unit, 23: Error estimation unit, 24: Tap gain update unit, 25, 85, 88
... Feed forward tap part, 26 ... Feedback tap part, 27 ... Reference signal for training.

Claims (6)

[Claims] 1. A plurality of complex taps provided for performing a waveform equalization process, wherein a part of the plurality of complex taps provided in advance is selected and used for the waveform equalization process. Waveform equalization processing method. 2. The waveform equalization processing according to claim 1, wherein the selection of the complex tap is performed based on a result of a cross-correlation between the received signal and a known training sequence stored in a memory in the receiving-side radio. Method. 3. A waveform according to claim 1, wherein a predetermined number is selected from taps having a large cross-correlation value between the received signal and a known training sequence stored in advance in a memory in the reception-side radio. Equalization processing method. 4. A tap according to claim 1, wherein a tap having a cross-correlation value between a received signal and a known training sequence stored in a memory in a receiving-side radio device larger than a prescribed value is selected. Waveform equalization processing method. 5. The waveform equalization processing method according to claim 1, wherein a waveform equalization device and reception diversity are combined. 6. A method for calculating a cross-correlation value with a known training sequence for each branch, adding cross-correlation values at the same position of each branch, and selecting a specified number from taps having a large value of the addition result. 6. The waveform equalization processing method according to claim 5, wherein: