JP4139706B2 - Receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a communication device on a receiving side (hereinafter referred to as a receiving device) in a wireless communication field such as a car phone, a mobile phone, and a wireless LAN, and more particularly, a circuit for calculating a soft decision value for each bit. It is related with the receiver provided with.
[0002]
[Prior art]
For example, as a conventional receiving apparatus that receives a multi-level modulated signal and calculates a soft decision value for each bit, there is a receiving apparatus described in Non-Patent Document 1, and here, particularly when multi-level modulation is applied. The likelihood (log-likelihood ratio) input to the decoder of the above has been studied. According to this document, when calculating the soft decision value for each bit, that is, when calculating the log likelihood ratio, it is necessary to multiply the demodulated signal by the minimum signal point distance. It is disclosed.
[0003]
[Non-Patent Document 1]
Hanaoka et al., “Likelihood Calculation Method Suitable for Multilevel Modulation” (2002 IEICE Communication Society B-5-85)
[0004]
[Problems to be solved by the invention]
However, the conventional receiving apparatus has a problem that the circuit scale increases because it is necessary to multiply the demodulated signal by the minimum signal point distance when calculating the soft decision value for each bit. . Further, when the conventional receiving apparatus moves at a high speed, the signal level during reception also fluctuates at a high speed, so that the minimum signal point distance also fluctuates at the same time. Therefore, in the conventional receiver, the soft decision value fluctuates in proportion to the square of the received signal, and the number of effective bits of the soft decision value needs to be determined in consideration of the amount of fluctuation. There is a problem that not only the circuit for calculating the soft decision value for each but also the scale of the error correction processing circuit in the subsequent stage increases.
[0005]
The present invention has been made in view of the above, and an object of the present invention is to obtain a receiving apparatus capable of reducing the overall circuit scale by reducing the circuit scale for calculating a soft decision value for each bit. To do.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, the receiving apparatus according to the present invention performs soft decision for each bit with respect to a signal obtained by demodulating a modulation signal by a multilevel QAM (Quadrature Amplitude Modulation) method. A receiving apparatus including a soft decision processing unit for calculating a value, wherein the soft decision processing unit has a received signal point (demodulated symbol) within a predetermined threshold range obtained based on a demodulated signal Then, a soft decision value of the MSB (most significant bit) is calculated using the amplitude value of the demodulated symbol as a reliability, and when the demodulated symbol is outside the predetermined threshold range, the demodulated symbol amplitude value is calculated. The first soft decision means for calculating the MSB soft decision value using the value obtained by subtracting the minimum signal point distance from twice as much as the reliability, and the distance between the demodulated symbol and the predetermined threshold value as the reliability LSB ( The least significant bit) Second soft decision means for calculating a constant value, and alternately outputting the MSB soft decision value and the LSB soft decision value.
[0007]
According to the present invention, the circuit scale for calculating the soft decision value for each bit is reduced by calculating the soft decision value for each bit without requiring the conventionally used multiplication processing.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a receiving apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.
[0009]
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a receiving apparatus according to the present invention. Here, the operation of the receiving apparatus according to the present invention will be briefly described.
[0010]
First, the analog reception processing unit 2 that receives a high-frequency reception signal via the antenna 1 performs processing such as down-conversion to a baseband signal and gain control. Next, the analog / digital converter (A / D) 3 converts the received signal from an analog signal to a digital signal.
[0011]
Next, the demodulation processing unit 4 performs demodulation processing by processing such as synchronous detection and RAKE combining, and outputs the demodulated signal to the soft decision processing unit 5 as a result. For example, when receiving a signal of a code division multiple access (CDMA) system, Nagayasu et al., “Frequency offset correction method in DS-CDMA receiver” (1999 Annual Conference of the Institute of Electronics, Information and Communication Engineers B) -5-123) and the structure described in Okawa et al., “2 Mbps Multicode Transmission Characteristics in DS-CDMA” (1998 Society of Electronics, Information and Communication Engineers Communication Society Conference B-345).
[0012]
Next, the soft decision processing unit 5 calculates a soft decision value for each bit from the demodulated signal. Finally, the error correction processing unit 6 receives a soft decision value for each bit, and performs deinterleaving, HARQ (Hybrid Automatic Repeat reQuest) packet combining processing, decoding processing, and the like.
[0013]
Next, the operation of the soft decision processing unit 5 that is a feature of the present embodiment will be described in detail. FIG. 2 is a diagram illustrating a configuration example of the soft decision processing unit 5 according to the first embodiment. The soft decision processing unit 5 includes a parallel / serial conversion unit (P / S) 11, an amplitude calculation unit 12, The delay processing unit 13, the MSB soft decision unit 14, the LSB soft decision unit 15, and a parallel / serial conversion unit (P / S) 16 are included. On the transmission side, a 16QAM (Quadrature Amplitude Modulation) signal shown in FIG. 3 is transmitted. Further, each symbol in 16QAM indicates the MSB of the I-axis component, the MSB of the Q-axis component, the LSB of the I-axis component, and the LSB of the Q-axis component. However, MSB represents the most significant bit, and LSB represents the least significant bit.
[0014]
In P / S11, the I-axis component and Q-axis component of the demodulated signal are input, and each component is output alternately. The amplitude calculator 12 calculates the absolute value of the demodulated signal output from the P / S 11 and outputs ½ of the average value as the amplitude value. For example, for each N symbols (I-axis component N / 2 symbols, Q-axis component N / 2 symbols), the amplitude value of the demodulated signal is calculated by the following equation (1).
A (n) = 0.5 × Σ (ABS (x (i + N × n))) (1)
Note that Σ calculates the sum for i = 0, 1,..., N−1. ABS (a) represents the absolute value of the real number a. A (n) represents the estimated value of the amplitude of the demodulated signal output for each 128-symbol block, and x (i + N × n) represents the i-th demodulated symbol of the n-th block. The amplitude calculator 12 can also calculate an amplitude value based on other information such as a known pilot symbol.
[0015]
In the delay processing unit 13, the amplitude calculation unit 12 delays the demodulated symbol by the time for calculating the amplitude value.
[0016]
The MSB soft decision unit 14 calculates the soft decision value using the size of the demodulated symbol after the delay addition processing or the size obtained by subtracting the minimum signal point distance from the double value as the reliability. Specifically, the soft decision value of the MSB is calculated by the following equations (2) and (3).
ym (i + N * n) = x (i + N * n)
(ABS (x (i + N × n)) <2 × A (n)) (2)
ym (i + N * n) = (2 * ABS (x (i + N * n))-2 * A (n)) * SIGN (x (i + N * n))
(ABS (x (i + N × n))) ≧ 2 × A (n)) (3)
SIGN (a) indicates +1 when the sign of the real number a is positive, and indicates -1 when the sign of the real number a is negative. Moreover, ym (i + N × n) is a soft decision value for the MSB of x (i + N × n).
[0017]
The LSB soft decision unit 15 calculates the soft decision value using the distance between the demodulated symbol after the delay addition process and a predetermined threshold value (boundary between adjacent signal points) as the reliability. Specifically, the soft decision value of LSB is calculated by the following equation (4).
yl (i + N * n) = ABS (x (i + N * n) -2 * A (n)) (4)
Note that yl (i + N × n) is a soft decision value for the LSB of x (i + N × n).
[0018]
In P / S16, the MSB soft decision value ym (i + N × n) and the LSB soft decision value yl (i + N × n) are input, and the respective soft decision values are alternately output.
[0019]
4, 5, 6, and 7 are diagrams illustrating signal points (black circles a to d) and reception signal points (white circles) when focusing on the I-axis component. The Q-axis component can be similarly explained. The distance from the Q axis to the signal point a is A (n), and the distance from the Q axis to the threshold value (here, the boundary between the signal points 00 and 01 and the boundary between the signal points 10 and 11) is 2 × A (n), and the distance from the Q axis to the signal point d is 3 × A (n).
[0020]
In the present embodiment, as shown in FIG. 4, when the received signal point (demodulated symbol) is within the threshold ± 2 × A (n), the distance from the Q axis to the received signal point is the MSB reliability. Represents size. That is, the reliability is the amplitude value of the demodulated symbol, the sign of the soft decision value is “+” when the demodulated symbol is a positive number, and the sign of the soft decision value is “−” when the demodulated symbol is a negative number. And
[0021]
FIG. 5 shows the magnitude of the MSB reliability when the demodulated symbol is outside the threshold value ± 2 × A (n). Here, the reliability is set to twice the distance between the demodulated symbol and the internal signal point b, the sign of the soft decision value is “+” when the demodulated symbol is a positive number, and the demodulated symbol is a negative number. The sign of the soft decision value is “−”.
[0022]
6 and 7 show the LSB reliability when the demodulated symbols are inside and outside the threshold value ± 2 × A (n). Here, the reliability is the distance between the demodulated symbol and the threshold value, and when the demodulated symbol is inside the threshold value (close to the Q axis), the sign of the soft decision value is “+”, and the demodulated symbol is the threshold value. If it is outside, the sign of the soft decision value is “−”.
[0023]
Thus, in this embodiment, the soft decision value for each bit is calculated without requiring multiplication processing. Thereby, the circuit scale for calculating the soft decision value for each bit can be reduced, and as a result, the circuit scale of the entire apparatus can be reduced. In addition, the amplitude value used for calculating the soft decision value is directly calculated from the demodulated signal. Thereby, even when the level of the received signal changes at a relatively high speed, the soft decision value can be estimated with high accuracy.
[0024]
Embodiment 2. FIG.
FIG. 8 is a diagram illustrating a configuration example of the soft decision processing unit 5 according to the second embodiment. This soft decision processing unit 5 replaces the MSB soft decision unit 14 and P / S 16 described above with an MSB soft decision unit. It includes a determination unit 21 and an output switching unit 22, receives a reception modulation scheme signal from the outside, and switches between 16QAM and QPSK (Quadrature Phase Shift Keying) for reception. In addition, about the structure similar to the above-mentioned Embodiment 1, the same code | symbol is attached | subjected and the description is abbreviate | omitted. Here, only operations different from those of the first embodiment will be described.
[0025]
Here, the operation of the soft decision processing unit 5 of the present embodiment will be described. For example, when calculating a soft decision value of a 16QAM signal, the MSB soft decision unit 21 performs the same processing as the MSB soft decision unit 14 shown in FIG. 2 and outputs a soft decision value for each bit. On the other hand, when the MSB soft decision unit 21 calculates the soft decision value of the QPSK signal, the MSB soft decision value calculated by the equation (2) described above is used as the soft decision value for each bit of QPSK. .
[0026]
When outputting the soft decision value of the 16QAM signal, the output switching unit 22 outputs both the LSB soft decision value and the MSB soft decision value. On the other hand, when outputting the QPSK signal soft decision value, the MSB soft decision value is output as the QPSK signal soft decision value.
[0027]
As described above, in this embodiment, the reception modulation scheme signal is received from the outside, and the soft decision value for each bit is output by switching between 16QAM and QPSK. As a result, it is possible to realize a receiving apparatus capable of processing soft decision values for each bit corresponding to a plurality of modulation schemes with a relatively small circuit scale.
[0028]
Embodiment 3 FIG.
FIG. 9 is a diagram illustrating a configuration example of the soft decision processing unit 5 according to the third embodiment. The soft decision processing unit 5 further includes a correction amount calculation in addition to the configuration of the first embodiment described above. A unit 31, normalization processing units 32 and 33, a storage unit 34, and a correction unit 35 are included. In addition, about the structure similar to the above-mentioned Embodiment 1, the same code | symbol is attached | subjected and the description is abbreviate | omitted. Here, only operations different from those of the first embodiment will be described.
[0029]
The correction amount calculation unit 31 receives the amplitude value output from the amplitude calculation unit 12 and calculates a correction amount S for use in normalization processing. For example, a correction amount S that satisfies the following equation (5) is calculated.
2 ^K ≦ A (n) / 2 ^S <2 ^{K + 1} (5)
Here, K is a constant that determines the magnitude of the amplitude value after correction, and S is the correction amount used for normalization processing.
[0030]
In the normalization processing unit 32, the amplitude value A (n) output from the amplitude calculation unit 12 is normalized by the following equation (6) with the correction amount S output from the correction amount calculation unit 31, and the normalized amplitude value B (N) is output to the MSB soft decision unit 14 and the LSB soft decision unit 15.
B (n) = A (n) >> S (6)
Here, >> represents a right bit shift.
[0031]
Further, the normalization processing unit 33 normalizes the demodulated symbol x (i + 128 × n) output from the delay processing unit 13 by the correction amount S output from the correction amount calculation unit 31 according to the following equation (7), and after normalization The demodulated symbol z (i + N × n) is output to the MSB soft decision unit 14 and the LSB soft decision unit 15.
z (i + N × n) = x (i + N × n) >> S (7)
[0032]
Thereafter, after the soft decision value is output at P / S 16 in the same process as in the first embodiment, the storage unit 34 outputs the soft decision value ym (i + N × n) of the MSB output from P / S 16 and the soft decision value of LSB. The value yl (i + N × n) is received, and the soft decision value is stored until the subsequent error correction processing unit 6 can process the value.
[0033]
The correction unit 35 reads the soft decision values from the storage unit 34 when the error correction processing unit 6 becomes processable, and corrects the magnitudes of the soft decision values by the following equation (8).
wm (i + N × n) = ym (i + N × n) << S (8)
wl (i + N × n) = yl (i + N × n) << S (9)
<< represents a left bit shift. Further, wm (i + N × n) represents the soft decision value after correction of the MSB soft decision value ym (i + N × n), and wl (i + N × n) represents the LSB soft decision value yl (i + N × n). Represents the soft decision value after correction.
[0034]
As described above, in the present embodiment, the demodulation symbol is normalized based on the amplitude value. As a result, the bit width after the normalization process can be reduced without degrading the performance. Further, by reducing the bit width after the normalization process, the circuit scale of the soft decision processing unit can be reduced as a result. In addition, since the bit width of the soft decision value can be reduced, the size of the storage unit can also be reduced. As a result, a small and low power consumption receiver can be realized.
[0035]
Note that the soft decision processing unit 5 of the third embodiment is not limited to FIG. 9, and for example, the storage unit 34 and the correction unit 35 may be deleted. In this case, for example, storage and correction processing are performed inside the error correction processing unit 6 at the subsequent stage. Also, the soft decision processing unit 5 of the third embodiment may be configured to receive both 16QAM and QPSK, as shown in FIG.
[0036]
【The invention's effect】
As described above, according to the present invention, a soft decision value for each bit can be calculated without requiring a multiplication process as in the prior art. As a result, the circuit scale for calculating the soft decision value for each bit can be reduced, and as a result, the circuit scale of the entire apparatus can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a receiving apparatus according to the present invention.
FIG. 2 is a diagram illustrating a configuration of a soft decision processing unit according to the first embodiment;
FIG. 3 is a diagram illustrating a signal point arrangement of a 16QAM signal.
FIG. 4 is a diagram illustrating signal points and reception signal points when attention is paid to an I-axis component.
FIG. 5 is a diagram showing signal points and reception signal points when attention is paid to an I-axis component.
FIG. 6 is a diagram illustrating signal points and reception signal points when attention is paid to an I-axis component.
FIG. 7 is a diagram illustrating signal points and reception signal points when attention is paid to an I-axis component.
FIG. 8 is a diagram illustrating a configuration of a soft decision processing unit according to the second embodiment.
9 is a diagram illustrating a configuration of a soft decision processing unit according to Embodiment 3. FIG.
[Explanation of symbols]
1 antenna, 2 analog reception processing unit, 3 analog / digital converter (A / D), 4 demodulation processing unit, 5 soft decision processing unit, 6 error correction processing unit, 11 parallel / serial conversion unit (P / S), 12 amplitude calculation unit, 13 delay processing unit, 14 MSB soft decision unit, 15 LSB soft decision unit, 16 parallel / serial conversion unit (P / S), 21 MSB soft decision unit, 22 output switching unit, 31 correction amount calculation unit 32, 33 Normalization processing unit, 34 storage unit, 35 correction unit.

Claims (6)

In a receiving apparatus including a soft decision processing unit that calculates a soft decision value for each bit with respect to a signal obtained by demodulating a modulation signal by a multilevel QAM (Quadrature Amplitude Modulation) method,
The soft decision processing unit
When the received signal point (demodulated symbol) is within a predetermined threshold range determined based on the demodulated signal, the soft decision value of the MSB (most significant bit) is calculated with the amplitude value of the demodulated symbol as the reliability. On the other hand, when the demodulated symbol is outside the predetermined threshold range, the soft decision value of the MSB is calculated with the reliability obtained by subtracting the minimum signal point distance from twice the amplitude value of the demodulated symbol. First soft decision means;
Second soft decision means for calculating a soft decision value of LSB (least significant bit) using a distance between a demodulated symbol and the predetermined threshold as a reliability;
With
A receiving apparatus that outputs the soft decision value of the MSB and the soft decision value of the LSB. The receiving apparatus according to claim 1, wherein the predetermined threshold value is twice the amplitude value of a demodulated signal calculated in units of a plurality of symbols. The receiving apparatus according to claim 2, wherein an amplitude value of the demodulated signal is ½ of an average value of absolute values of the demodulated signal. Further, a correction amount calculating means for calculating a correction amount for use in normalization processing based on the amplitude value of the demodulated signal,
First normalizing means for normalizing the amplitude value of the demodulated signal using the correction amount;
Second normalizing means for normalizing the demodulated symbol using the correction amount;
With
The first and second soft decision means calculate a soft decision value based on the amplitude value of the demodulated signal after normalization and the demodulated symbol after normalization. Receiver device. Further, each soft decision value is stored until subsequent error correction processing becomes possible, and when the error correction processing becomes possible, the stored soft decision value is corrected using the correction amount. Correction means,
The receiving apparatus according to claim 4, further comprising: When transmitting a modulated signal by QPSK (Quadrature Phase Shift Keying) method on the transmission side,
The first soft decision means calculates a soft decision value using the amplitude value of the demodulated symbol as a reliability,
The receiving apparatus according to claim 1, wherein the soft decision processing unit outputs only the soft decision value.

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