CN107359923B

CN107359923B - Maximum likelihood detector and method, and wireless signal receiver

Info

Publication number: CN107359923B
Application number: CN201610302537.2A
Authority: CN
Inventors: 张仲尧; 黄伟杰; 杨易洵
Original assignee: Realtek Semiconductor Corp
Current assignee: Realtek Semiconductor Corp
Priority date: 2016-05-09
Filing date: 2016-05-09
Publication date: 2023-01-13
Anticipated expiration: 2036-05-09
Also published as: CN107359923A

Abstract

The invention discloses a maximum likelihood detector and a method thereof and a wireless signal receiver, wherein, the maximum likelihood detector comprises a searching value selection circuit and a maximum likelihood detection circuit. The search value selection circuit is used for selecting a search value according to one of the following modes: selecting the search value according to a communication index and a modulation method; and determining the search value according to a default value. The communication index is a communication index of a received signal or a derivative signal thereof; the search value corresponds to a search range, and the number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation mode. The maximum likelihood detection circuit is configured to perform a maximum likelihood operation according to one of the received signal and the derived signal thereof and the search value to calculate a log-likelihood ratio associated with each candidate signal value within the search range.

Description

Maximum likelihood detector and method, and wireless signal receiver

Technical Field

The present invention relates to wireless signal reception, and more particularly, to wireless signal reception with maximum likelihood detection.

Background

In wireless communication applications, the user's demand for high data transmission rate is rising, and how to effectively increase the bandwidth utilization efficiency and further increase the system Throughput (TP) in the limited system bandwidth is always an issue to be researched by those in various industries. In the market trend, spatial Multiplexing (Spatial Multiplexing) transmission scheme under MIMO (Multiple-Input Multiple-Output) technology can greatly increase system throughput without increasing bandwidth, and thus the transmission scheme has attracted considerable attention in recent years.

The transmission method of spatial multiplexing mainly utilizes a plurality of antennas at the transmitting end to transmit mutually independent signals on the same frequency band at the same time, and the receiving end also adopts a plurality of antennas to receive and detect the signals. In order to achieve better demodulation performance, the receiving end may use Maximum Likelihood (ML) method. The maximum likelihood method can be understood as an optimization-pursuing algorithm that estimates the best solution of the transmitted signal among all possible solutions from the received signal in the form of an Exhaustive Search (explicit Search). However, exhaustive search is not an efficient search method, since it takes long Computation time delay (Processing Latency), complexity (Complexity) and Computation Power (Computation Power) to compute all possible solutions.

More prior art can be found in the following documents: chinese patent application publication No. CN101582748 a; and IEEE, massimiliano Siti, michael P.Fitz, "A Novel Soft-Output Layered ordered software Detector for Multiple Antenna Communications," IEEE International Conference on Communications (ICC), 2006.

Disclosure of Invention

In view of the deficiencies of the prior art, it is an object of the present invention to provide a maximum likelihood detector and a detection method thereof, and a wireless signal receiver using the maximum likelihood detector, so as to improve the prior art.

An embodiment of the invention includes a search value selection circuit and a maximum likelihood detection circuit. The search value selection circuit is used for selecting a search value according to one of the following modes: selecting the search value according to a communication index and a modulation method, wherein the communication index is a communication index of a received signal or a derivative signal thereof; and determining the search value according to a default value. The maximum likelihood detection circuit is configured to perform a maximum likelihood operation according to one of the received signal and the derived signal and according to the search value to calculate a log-likelihood ratio associated with each candidate signal value within a search range. The number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation mode.

The invention also discloses a maximum possibility detection method, one embodiment of which comprises the following steps: selecting a search value according to a communication index and a modulation method or determining the search value according to a default value, wherein the communication index is the communication index of a received signal or a derivative signal thereof, the search value corresponds to a search range, and the number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation method; and performing a maximum likelihood operation according to one of the received signal and the derived signal and according to the search value.

The invention also discloses a wireless signal receiver adopting maximum possibility detection, and one embodiment of the wireless signal receiver comprises: a discrete Fourier transform circuit for transforming a time domain signal into a frequency domain signal; a reference signal extracting circuit for generating an extracted reference signal according to the frequency domain signal; a channel estimation circuit for generating an estimation signal according to the extracted reference signal; a data signal extraction circuit for generating an extracted data signal according to the frequency domain signal; a signal detection circuit for generating a detection signal according to the estimation signal and the extracted data signal; and a decoding circuit for generating a decoding signal according to the detection signal. An embodiment of the signal detection circuit comprises a maximum likelihood detector for selecting a search value according to a communication index and a modulation scheme, or determining the search value according to a default value, and performing a maximum likelihood operation according to one of the frequency domain signal and its derivative signal and the search value to generate the detection signal, wherein the search value corresponds to a search range, and the number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation scheme.

The features, embodiments and effects of the present invention will be described in detail with reference to the drawings.

Drawings

FIG. 1 is a diagram of a wireless signal receiver employing maximum likelihood detection according to an embodiment of the present invention;

FIG. 2 is a tree diagram for an exhaustive search;

FIG. 3 is a tree diagram of the structure of a hierarchical orthogonal lattice detector;

FIG. 4a is a diagram of an embodiment of the maximum likelihood detector of the present invention;

[ FIG. 4b ] is a diagram illustrating the implementation details of FIG. 4 a;

FIG. 5 is a constellation diagram for an implementation of the maximum likelihood detector of FIG. 4 a;

FIG. 6 is a tree diagram corresponding to FIG. 5; and

FIG. 7 is a diagram illustrating an embodiment of a maximum likelihood detection method according to the present invention.

Detailed Description

The following description is made with reference to terms commonly used in the art, and some terms are defined or explained in the specification, and the explanation of the terms in the specification is based on the description or the definition in the specification.

The disclosure of the present invention includes a maximum Likelihood detector and a detection method, and a wireless signal receiver using the maximum Likelihood detection, which output a corresponding Log Likelihood Ratio (LLR) as an input value of a decoding circuit in a Soft Decision (Soft Decision) manner in units of bits to perform error correction. Some of the components of these detectors and receivers, taken alone, may be known components, and the details of the individual known components will be omitted from the following description without departing from the full disclosure and applicability of the invention; in addition, the method can be in the form of software and/or firmware, and can be implemented by hardware devices of the present invention or equivalent circuits. The invention is suitable for receiving signals of multi-Dimension (Multiple-Dimension) or multi-Layer (Multiple-Layer), such as receiving signals of a Multiple-Input Multiple-Output (MIMO) communication system. The communication technology using MIMO, such as Long-Term Evolution (LTE) technology, wireless Local-Area Network (WLAN) technology, worldwide Interoperability for Microwave Access (WiMax), etc. For convenience of understanding, the following description will be given by taking the application of the LTE communication system as an example, but the application of the present invention is not limited thereto.

Please refer to fig. 1, which is a diagram illustrating a wireless signal receiver employing maximum likelihood detection according to an embodiment of the present invention. As shown in fig. 1, the wireless signal receiver 100 includes: a Discrete Fourier Transform (DFT) circuit 110 for converting a time domain signal into a frequency domain signal; a reference signal Extraction (Extraction) circuit 120 for generating an extracted reference signal according to the frequency domain signal; a Channel Estimation (Channel Estimation) circuit 130 for generating an Estimation signal according to the extracted reference signal; a data signal extracting circuit 140 for generating an extracted data signal according to the frequency domain signal; a signal detection circuit 150 for generating a detection signal according to the estimated signal and the extracted data signal; and a decoding circuit 160 for generating a decoding signal according to the detection signal. The signal detection circuit 150 includes: a Maximum Likelihood (ML) detector 152 for selecting a search value according to a communication index and a modulation scheme, or determining the search value according to a default value, and performing a Maximum Likelihood operation according to the frequency domain signal or its derivative and the search value to generate the detection signal, wherein the search value corresponds to a search range, and the number of candidate signal values in the search range is not greater than the number of all candidate signal values in the modulation scheme. One embodiment of the decoding circuit 160 comprises a Descrambler (Descrambler) for generating a descrambled signal according to the detection signal and a Turbo Decoder (Turbo Decoder) for generating the decoded signal according to the descrambled signal. Any of the discrete fourier transform circuit 110, the reference signal extraction circuit 120, the channel estimation circuit 130, the data signal extraction circuit 140, and the decoding circuit 160, taken alone, is a conventional or self-developed circuit.

As mentioned above, the time domain signal is discrete Fourier transformed and then is the signal Y of the nth subcarrier in the frequency domain _n Can be expressed as an N _R The vector of x1, as follows:

Y _n ＝H _n X _n +W _n (formula one)

Wherein H _n N viewed for the nth sub-carrier _R ×N _T Of the channel matrix, X _n For N on the nth sub-carrier _T X1 transmission signal, W _n Noise of the nth sub-carrier, N _R Is the number of receiving antennas, and N _T Is the number of transmit antennas. In the present embodiment, a signal of one subcarrier is taken as a processing unit, and for convenience of representation, in the following description, the subscript n is omitted; in addition, the present embodiment is applied to the two-input two-output spatial multiplexing transmission, that is, the number of independent spatial streams (spatial streams) at the transmitting end and the number of independent spatial streams at the receiving end are both 2 (in this case, N) _R And N _T Each of at least 2), so equation one can be simplified to:

y = HX + W (formula two)

In the LTE system, since the Reference Signal (RS) and the Data Signal (Data Signal) are carried on different subcarriers, the channel estimation circuit 130 can calculate the channel response matrix of the required Data Signal by interpolation or extrapolation according to the channel estimation performed by the Reference Signal

The signal detection circuit 150 then aligns the matrices

Performing QR decomposition or its equivalent is as follows:

where Q is a Unitary Matrix (Unitary Matrix) and R is an Upper Triangular Matrix (Upper Triangular Matrix). After QR decomposition or equivalent operation, the signal detection circuit 150 multiplies the reception signal Y (i.e., the extracted data signal) by Q ^H (Hermitian matrix of matrix Q) or performing an equivalent operation to obtain signal Z as follows:

Z≡Q ^H Y＝Q ^H (HX+W)＝Q ^H (QRX+W)＝RX+w' (formula four)

Wherein W' ≡ Q ^H W is added. Next, the maximum Likelihood detector 152 calculates a Log approximate Ratio (LLR) in bits from the signal Z obtained by equation four in the following manner:

wherein b is _i For the (i) th bit, the bit,

is equal to the set of 0 in the ith bit for all transmitted signals,

the set of bits equal to 1 for all transmitted signals,

representing candidate signal values during operation, the symbol "" is used to distinguish from the real signal X.

Equation five can be regarded as an optimization pursuit equation, and can be solved by means of Exhaustive Search (explicit Search) as described in the prior art. If the Modulation technique of the transmitted signal belongs to M-QAM (Quadrature Amplitude Modulation) in which the size of the signal set (or the number of Constellation points on the Constellation Diagram (Constellation Diagram) corresponding to the Modulation technique) is M, and the probability of the solution (or candidate signal value) of the formula five is M in total for two-input two-output two-layer independent data streams ² The seed can be represented by a tree diagram, as shown in fig. 2.

Further, since R is an upper triangular matrix, the search is performed

The operation of (2) can be simplified. Firstly, the method

Can be disassembled such asThe following:

since the square of the absolute value is not necessarily less than zero, it is chosen

In the case of (a) in (b),

must occur when

The following relationships are satisfied:

<xnotran> Γ [ </xnotran>]Is a Quantizer (Quantizer). In other words, in the selection

After the step (2) is performed,

is the only solution that can be obtained by equation seven. The structures represented by the six and seven are called hierarchical Orthogonal lattice detectors (LORD), and the tree diagram searched under the structures can be greatly simplified as shown in fig. 3. In the LORD architecture corresponding to FIG. 3, the first layer is expanded

All the possibilities (M), the second layer is directly obtained by the formula seven

Does not need to be expanded again as shown in FIG. 2

All possibilities of (a), therefore, the overall computational complexity is to manipulate the expansion at the first level

The number of (2).

The LORD structure corresponding to fig. 3 is used to solve the formula five, so as to obtain the log-likelihood ratio of each bit, and then the obtained log-likelihood ratio is transmitted to the decoder, so as to perform error correction to complete the reception. However, for M-QAM as an example, there are still M possible solutions under the LORD architecture (or the first layer expansion in FIG. 3)

M) where some of the possible solutions are less likely to be correct solutions, should be excluded to further simplify the operation. Therefore, the maximum likelihood detector 152 of fig. 1 does not directly calculate the log-likelihood ratios for M possibilities, but first selects a search value according to the frequency domain signal or its derivative (e.g., the extracted data signal) and performs a maximum likelihood operation according to the search value to generate the detection signal including the log-likelihood ratios, wherein the number of candidate signal values within the search range corresponding to the search value (or the constellation points corresponding to the search range in the constellation corresponding to the modulation mode) is not greater than the number of all candidate signal values of the modulation mode (or all constellation points in the constellation corresponding to the modulation mode). In other words, the maximum likelihood detector 152 of FIG. 1 is spread out on the first layer

(or

) Only K possible solutions (where K ≦ M) are expanded, thereby achieving lower computational complexity and power consumption without substantial performance penalty. It is noted that the maximum likelihood detector 152 may be deployed first

Re-spread (in the first layer)

(at the second level), as desired.

In particular, one embodiment of the maximum likelihood detector 152 is shown in FIG. 4a, and includes a search value selection circuit 410 and a maximum likelihood detection circuit 420. The search value selection circuit 410 is used to select a search value according to one of the following ways: selecting the search value according to a communication index and a modulation method, wherein the communication index is a communication index of a received signal (e.g., the frequency domain signal) or a communication index of a derivative signal of the received signal (e.g., the extracted reference signal); and determining the search value according to a default value. The search value corresponds to a search range, and the number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation mode. The maximum likelihood detection circuit 420 is configured to perform a maximum likelihood operation according to the received signal (e.g., the frequency domain signal) or a derivative signal thereof (e.g., the extracted data signal) and the search value to calculate a log-likelihood ratio associated with each candidate signal value within the search range, wherein the maximum likelihood operation includes an operation corresponding to the formula five, an operation corresponding to the formula seven, an operation corresponding to the formula eight, and a table lookup operation or an equivalent thereof.

The signal detection circuit 150 of fig. 4a is shown in detail in fig. 4b, and comprises: a QR decomposition unit 430 for decomposing the estimated signal (corresponding to the channel response matrix) according to the above

) Executing the operation of the third formula or the equivalent thereof; a signal generating unit 440 for performing the operation of formula four or the equivalent thereof according to the extracted data signal (corresponding to the signal Y); the search value selection circuit 410; and the maximum likelihood arithmetic circuit 420. In fig. 4b, the maximum likelihood calculation circuit 420 includes: a candidate signal value determining unit 422 for executing the formula eight according to the extracted data signalGenerating an operation result by performing the operation or the equivalent operation, and generating an operation result by performing the table look-up operation or the equivalent operation according to the operation result and the search value; a corresponding value calculating unit 424, for performing the operation of formula seven or the equivalent operation thereof according to the operation result to generate a calculation result; and a logarithmic approximation ratio calculation unit 426 for performing the operation of formula five or its equivalent according to the calculation result. Either of the QR decomposition unit 430 and the signal generation unit 440, taken alone, are conventional or self-developed units.

The way in which the maximum likelihood detection circuit 420 selects the search range corresponding to the search value is determined by the landing point of the received signal on the constellation corresponding to the modulation. Based on equation six, the maximum likelihood detection circuit 420 may include a Zero-Forcing (ZF) Equalizer (Equalizer) (included in the candidate signal value decision unit 422) to perform a Zero-Forcing operation to obtain

The drop points on the constellation are as follows:

using the characteristics of the constellation diagram, each constellation point and the drop point

The distance relationship of (a) can be known in advance.

Take 64-QAM of LTE as an example, according to the drop point

Position of (i.e. drop point)

Corresponding reference value) and constellation points, 14 intervals can be defined as shown in table one, and in each interval, the left-to-right sequence in table 1 represents the constellation point and the drop point

From near to far; by means of the constellation diagram of figure 5,

drop points on the constellation diagram

It is more clearly shown that the symbol "x" in the numerical value notation "1 x1x1 x", "x 0x1x 1", etc., may be 0 or 1. In the example of figure 5, it is shown,

the Real Part (Real-Part) of the constellation point falls in an interval 2 ≦ S ≦ 3, the Real parts of the constellation points from near to far are 3, 1, 5, -1, 7, -3, -5, -7 in sequence, and the total possibility is 8; in the same way, the method for preparing the composite material,

the Imaginary Part (Imaginary-Part) of (a) falls in an interval of-3 ≦ S ≦ 2, and the Imaginary parts of the near-to-far constellation points are sequentially-3, -1, -5, 1, -7, 3, 5, and 7, which is 8 possibilities. Assume that the search value determined by search value selection circuit 410 is 25 (i.e., maximum likelihood detection circuit 420 is spread out at the first level)

(or

) Only 25 possible solutions are expanded), the maximum likelihood detection circuit 420 sequentially extracts the departure points

The nearest real part and imaginary part are 5 in each case to match up 5 × 5=25 possibilities (or 25 candidate signal values), and the physical meaning represented by these is that the real part and the imaginary part are dotted in fig. 5

Framed by the centreSearch area (e.g., rectangular or other shaped area) where the constellation points fall is the most likely detection circuit 420 to spread out in the first layer

Time-computed constellation points (e.g. drop points)

Nearest constellation points), the rest of the constellation points are not considered in the region, so that the present embodiment can achieve the purpose of reducing the computation complexity, as shown in the tree diagram of fig. 6. It is noted that the embodiment may query the pre-established contents (e.g., the contents of table 1) by a table lookup operation to obtain the combination of the real part and the imaginary part, thereby allowing the maximum likelihood detection circuit 420 to calculate the log-likelihood ratio according to the formula five more efficiently.

TABLE 1

As can be seen from fig. 5, the size of the search area determines the complexity of the operation, and when the area is large enough to include all constellation points (e.g., 64 constellation points in fig. 5), the complexity of the operation of the embodiment is comparable to that of the aforementioned lor architecture. Of course, the size of the search area may be predetermined or adjusted according to the communication condition. When the size of the area is predetermined, the search value is determined by the search value selection circuit 410 according to the default value (e.g., the search value is equal to the default value). When the size of the region is determined according to the communication condition, the indicator of the communication condition (i.e. the aforementioned communication indicator) can be the signal-to-noise ratio, the energy intensity of the received signal of the subcarrier, the energy intensity of the channel, the channel energy intensityAt least one of correlation, channel estimation accuracy, interference energy intensity, etc. When the modulation is M-QAM, a non-limiting example of the search value is an integer greater than M/4, or another non-limiting example of the search value is an integer and 4 ≦ search value ≦ M-1 ² 。

As mentioned above, when the size of the search area is determined according to the communication condition, the size of the search area is determined by the maximum likelihood detection circuit 420 performing a zero forcing operation to obtain the zero forcing result

Point of contact on constellation diagram

The Signal-to-Noise Ratio (SNR) of time, which can be defined as γ, can be expressed as follows:

wherein

For noise energy, the estimation method is well known in the art, and R ₁₁ Is one of the elements of the upper triangular matrix R. The greater γ, the more reliable the result of the zero forcing operation of the maximum likelihood detection circuit 420, so that the smaller search value (or smaller search area) can be selected by the search value selection circuit 410; conversely, as γ is smaller, the search value selection circuit 410 may select a larger search value (or larger search area). According to the above concept, the present embodiment can define several thresholds T _g (G =1,2, …, G), where T _g <T _g+1 When the value of gamma exceeds a certain threshold value T _g The search value selection circuit 410 may use a smaller search value as shown in Table two, where K is _G+1 <K _G <…<K ₂ <K ₁ 。

TABLE 2

In addition to using the snr (s/n ratio) as the communication indicator, as described above, the search value selection circuit 410 can select the search value (or the size of the search area) according to other communication indicators. For example, search value selection circuitry 410 may select a search value based on a channel correlation p, where p may be expressed as:

in the formula ten, h ₁ Is a channel response matrix

First row of (Column), h ₂ Is that

The second row of (2). The maximum likelihood detection circuit 420 is configured to detect when ρ is larger (i.e., 1/ρ is smaller)

The less reliable the result of the zero forcing operation, so that the search value selection circuit 410 selects the larger search value (or larger search area); conversely, as ρ is smaller (i.e., 1/ρ is larger), the search value selection circuit 410 selects a smaller search value (or smaller search area). To sum up, the search value is a first search value when the communication indicator (which may be γ, 1/ρ or other indicators) is higher than a first threshold, the search value is a second search value when the communication indicator is lower than the first threshold, the first search value is smaller than the second search value, and the communication status represented by the communication indicator higher than the first threshold is better than the communication status represented by the communication indicator lower than the first threshold.

In addition to the above circuits, the present invention also discloses a maximum likelihood detection method as shown in fig. 7, which can be executed by the maximum likelihood detection circuit 152 or its equivalent circuit, and includes the following steps:

step S710: selecting a search value according to a communication index of a received signal or a derived signal thereof and a modulation method, or selecting the search value according to a default value, wherein the search value corresponds to a search range, and the number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation method of the received signal.

Step S720: a maximum likelihood calculation is performed according to the received signal or a derivative thereof and the search value to calculate a log-likelihood ratio associated with each candidate signal value within the search range.

Since one skilled in the art can deduce the details and variations of the embodiments of the present method by using the disclosure of the circuit embodiments, more specifically, the technical features of the circuit embodiments can be reasonably applied to the embodiments of the present method, and therefore, the repeated and redundant descriptions are omitted herein without affecting the disclosure requirements and the feasibility of the embodiments of the present method.

In summary, the maximum likelihood detector and the detecting method of the present invention and the wireless signal receiver using the maximum likelihood detection can achieve low computation delay, low computation complexity and low computation power consumption, and achieve a low error rate similar to the prior art.

Although the embodiments of the present invention have been described above, these embodiments are not intended to limit the present invention, and those skilled in the art can make variations on the technical features of the present invention according to the explicit or implicit contents of the present invention, and all such variations may fall within the scope of the patent protection sought by the present invention.

Description of the symbols

100. Wireless signal receiver

110. Discrete Fourier transform

120. Reference signal extraction

130. Channel estimation

140. Data signal extraction circuit

150. Signal detection circuit

152. Maximum likelihood detector

160. Decoding circuit

410. Search value selection circuit

420. Maximum likelihood detection circuit

422. Candidate signal value determining unit

424. Corresponding value calculating unit

426. Logarithm approximate ratio calculating unit

430 QR decomposition unit

440. Signal generating unit

Point of impact on constellation diagram

S710 to S720

Claims

1. A maximum likelihood detector, comprising:

a searching value selecting circuit, which selects the searching value according to a communication index and a modulation mode, or determines the searching value according to a default value, wherein the communication index is the communication index of a received signal or a derivative signal thereof; and

a maximum likelihood detection circuit, for performing a maximum likelihood operation according to the search value and one of the received signal and its derived signal to calculate a log-likelihood ratio associated with each candidate signal value within a search range, the maximum likelihood operation comprising a calculation according to the following equation:

wherein L is the log approximate ratio, b _i Is the ith oneThe bits, Y, are the received signal,

is equal to the set of 0 in the ith bit for all transmitted signals,

the set of bits equal to 1 for all transmitted signals,

representing candidate signal values during the calculation, R being an upper triangular matrix, Z being the derivative signal,

wherein, the passing formula

Calculating the candidate signal value, wherein gamma]In order to be a quantizer, the method comprises the steps of,

wherein, the first and the second end of the pipe are connected with each other,

is of the through type

Derived, and the structure represented by the two formulas is called a hierarchical orthogonal lattice detector,

wherein the search range corresponds to the search value, and the number of the candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation scheme.

2. The maximum likelihood detector of claim 1, wherein the maximum likelihood detector circuit performs a zero forcing operation according to the received signal or a derivative thereof to obtain a reference value, and determines the search range according to the reference value and the search value, so as to perform the maximum likelihood operation according to the search range.

3. The maximum likelihood detector of claim 2, wherein the candidate signal values in the search range are K candidate signal values closest to the reference value among all candidate signal values of the modulation scheme, wherein K is equal to the search value.

4. The apparatus of claim 2 wherein the maximum likelihood detection circuit performs a lookup operation according to the reference value and the search value to determine candidate signal values within the search range, thereby performing the maximum likelihood operation according to the candidate signal values within the search range.

5. The maximum likelihood detector of claim 1 wherein the communication metric is at least one of a signal-to-noise ratio, a subcarrier energy level, a channel correlation, a channel estimation accuracy and an interference energy level.

6. The maximum likelihood detector of claim 1 wherein the number of candidate signal values in the search range is greater than one quarter of the number of all candidate signal values for the modulation scheme.

7. The maximum likelihood detector of claim 1, wherein when the modulation is quadrature amplitude modulation and the size of the quadrature amplitude modulated signal set is M, the number of candidate signal values in the search range is not less than 4 and not more than (M-1) ² 。

8. The maximum likelihood detector of claim 1, wherein the search value is a first search value when the communication indicator is above a first threshold, the search value is a second search value when the communication indicator is below the first threshold, the first search value is less than the second search value, and the communication status represented by the communication indicator above the first threshold is better than the communication status represented by the communication indicator below the first threshold.

9. A maximum likelihood detection method, comprising:

selecting a search value according to a communication index and a modulation method or determining the search value according to a default value, wherein the communication index is a communication index of a received signal or a derivative signal thereof, the search value corresponds to a search range, and the number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation method; and

calculating a log-likelihood ratio associated with each candidate signal value within a search range by performing a maximum likelihood operation based on the received signal and one of its derivatives and on the search value, the maximum likelihood operation comprising a calculation according to the following equation:

wherein L is the log approximate ratio, b _i Is the ith bit, Y is the received signal,

is equal to the set of 0 in the ith bit for all transmitted signals,

the set of bits equal to 1 for all transmitted signals,

wherein, the passing formula

Calculating the candidate signal value, wherein Γ [ ]]In order to be a quantizer, the method comprises the steps of,

wherein the content of the first and second substances,

is a through type

Derived and the architecture represented by these two equations is called a hierarchical orthorhombic lattice detector.

10. A wireless signal receiver employing maximum likelihood detection, comprising:

a discrete Fourier transform circuit for transforming a time domain signal into a frequency domain signal;

a reference signal extracting circuit for generating an extracted reference signal according to the frequency domain signal;

a channel estimation circuit for generating an estimation signal according to the extracted reference signal;

a data signal extraction circuit for generating an extracted data signal according to the frequency domain signal;

a signal detection circuit for generating a detection signal according to one of the frequency domain signal and its derivative signal; and

a decoding circuit for generating a decoding signal according to the detection signal;

wherein, this signal detection circuit contains: a maximum likelihood detector for selecting a search value according to a communication index and a modulation method, or determining the search value according to a default value, and for performing a maximum likelihood operation according to one of the frequency domain signal and its derivative signals and the search value to generate the detection signal, wherein the communication index is the communication index of the frequency domain signal or its derivative signals, and the maximum likelihood operation includes calculation according to the following equation:

where L is the log-likelihood ratio associated with each candidate signal value in a search range, b _i Is the ith bit, Y is the frequency domain signal,

is equal to the set of 0 in the ith bit for all transmitted signals,

the set of bits equal to 1 for all transmitted signals,

wherein, the passing formula

Calculating the candidate signal value, wherein gamma]A quantizer, wherein the search value corresponds to a search range, the number of candidate signal values in the search range is not greater than the number of all candidate signal values of the modulation scheme,

wherein the content of the first and second substances,

is a through type