This application claims the priority benefit of Taiwan application serial no. 97129102, filed on Jul. 31, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification.
1. Field of the Invention
The present invention relates to a multiple-input multiple-output detector. More particularly, the present invention relates to a multiple-input multiple-output detector and a detection method using the same.
2. Description of Related Art
In a field of high-speed wireless transmission, a transmission system with a limited bandwidth requires a plenty of wireless channels to achieve the high-speed transmission. Therefore, the transmission system has to apply a plurality of transmission and receiving antennas for providing a function of multiple-input and multiple-output, so as to implement a high data rate transmission in fading channels having multi paths. Compared to a single-antenna system, the multiple-input multiple-output (MIMO) system can increase a transmission throughput without increasing of bandwidth and power.
In the MIMO system, execution results of different MIMO detectors in a wireless communication channel are different. Generally, performance of a maximum-likelihood (ML) detector is better than that of a linear detector. In case of abnormal conditions, for example, a low signal-to-noise ratio (SNR) or rank deficiency of transmission channel matrix, signals of the MIMO system cannot be normally transmitted. Therefore, the MIMO detectors have to be applied to confront losses of the signals due to being transmitted within a channel having adverse conditions, and provide diversity gains.
As described above, the MIMO system can increase the transmission throughput without increasing of the bandwidth and the power. In a spatial multiplexing technique field, the MIMO system can provide a high data rate transmission. In a downlink, a transceiver can implement data stream transmission via two or more antennas, and can receive data stream via a plurality of receiving antennas.
As to a transmitter, information and data are encoded via an encoding mechanism. For example, a viterbi algorithm or turbo codes, and the data can be transformed into a symbol via processing methods such as interpolating, interlacing or mapping, etc. Next, the transmitter multiplexedly transmits the symbol to the air via the transmission antennas. As to a receiver, after the receiver receives the data stream, the MIMO detector is applied for detecting the data.
Generally, the MIMO detector has a plurality of types, for example, the MIMO detector can be a zero-forcing (ZF) detector, a minimum mean squared error (MMSE) detector, a vertical Bell-Lab layered space-time (V-BLAST) detector, a sphere decoder (SD) or a maximum-likelihood (ML) detector.
The V-BLAST is a vertical space multiplexing detector based on linear interference suppression. In a layer selected via a high SNR, the received data is first detected. Next, the detected bit is taken as an obstacle by other data, and is removed from the remained data. Now, in the remained data, an obstacle is disappeared. Next, such processing method is repeated until all of the signals are detected.
Moreover, the ZF detector and the MMSE detector are all simple and linear detectors. To achieve a better performance, the MIMO system generally utilizes a second best detector, for example, a sphere detector. In the MIMO system, the sphere detector is a detector applying a hardware detection method, which has a performance close to that of the ML detector.
The present invention provides a MIMO detector for detecting a data symbol to output a candidate result. The MIMO detector includes a plurality of detectors and a selection device. The detectors mutually different, and each of the detectors detects the data symbol according to a channel frequency response estimation value for outputting a corresponding candidate result. The selection device is coupled to the detectors for selecting one of the candidate results output from the detectors to serve as a detected result according to a channel condition and a selection criterion.
The present invention provides a detection method for a MIMO detector including a plurality of detectors and a selection device, wherein the detectors are mutually different. The detection method includes following steps. First, a plurality of candidate results is provided. Next, a channel condition and a selection criterion are provided. Finally, one of the candidate results is selected to serve as a detected result according to the channel condition and the selection criterion.
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
To fully convey the concept of the present invention to those skilled in the art, before embodiments of the present invention are described, basic concepts of the exemplary invention are described with reference of transmission simulation results of a plurality of MIMO detectors.
For example, in a low SNR region, a BER performance of the V-BLAST detector is better than that of the MMSE detector. Conversely, in a high SNR region, the BER performance of the MMSE detector is better than that of the V-BLAST detector. As long as the line sections having better performances are combined, namely, in the low SNR region, the V-BLAST detector is utilized, and in the high SNR region, the MMSE detector is utilized, performance of such detector combination must be better than that of the MMSE detector or the V-BLAST detector.
On the other hand, solution spaces can be utilized to explain the concept of the present invention.
As shown in
Further, a selection mechanism of the selection device 201 is implemented according to a selection criterion having a weight value, for example, a ML selection criterion, a minimum singular value selection criterion, a MSE selection criterion or a capacity selection criterion. Moreover, the weight value can be different under a different channel condition.
ed
i
=∥y−H{circumflex over (x)}
i
∥i=1, . . . , n (1)
i
opt=arg min{w1*ed1, w2* ed2, . . . , 2n*edn} (2)
{circumflex over (x)}out={circumflex over (x)}i
Referring to
Meanwhile, a Euclid calculation unit 211 calculates distances edi of the MIMO detectors 201_1-202—n according to the equation (1). Next, a combination calculation unit 210 multiplies the distances edi of the MIMO detectors 201_1-202—n respectively with the weight values Wi thereof for transmitting the multiplications to the selection unit 201a. Moreover, the selection unit 201a selects an optimal multiplication according to the equation (2), and performs an operation (for example an anti-function operation) to the optimal multiplication to obtain the exponent iopt, wherein the optimal multiplication is for example the minimum multiplication. Finally, a multiplexer 201b outputs the detected result {circumflex over (x)}out according to the equation (3). Namely, the multiplexer 201b selects one of the candidate results {circumflex over (x)}1-{circumflex over (x)}n as the detected result {circumflex over (x)}out according to the exponent iopt.
Two embodiments are introduced hereafter, and execution results thereof are simulated for demonstrating effects of the provided MIMO detectors.
The MIMO detectors of the aforementioned embodiments are all implemented via a simple method. In the following description, simulations are performed to the detectors of the aforementioned embodiments and a conventional detector, so as to demonstrate operation performances of the MIMO detectors and the conventional detector.
As to hardware of the simulation, a platform of simulating the 802.16e environment includes a viterbi encoder/decoder, an interleaver, a replacer/de replacer, fast Fourier transformer/inverse fast Fourier transformer, and modulator/demodulator, etc. In a 1024-ary orthogonal frequency division multiplexing (OFDM) symbol, 120-ary thereof is selected for testing. Moreover, length of a forward error correction (FEC) block is set to 288 bits. A code rate of the viterbi encoder/decoder is ½. A range of the SNR of the simulation environment is 0 dB to 40 dB, though for simplicity's sake, only a part of the range is illustrated.
First, as to a transmitter (not shown), an information block is encoded via an external error correcting coding (ECC) encoder having the ½ code rate. The encoder may apply any of ECC encoder mechanisms, for example, a viterbi algorithm, a turbo code, or a low-density parity check (LDPC) encoding, etc. An encoded stream is strengthened via replacing of the interleaver, so as to confront burst errors. An output stream of the interleaver maps to complex vectors generated based on a linear modulation mechanism. For example, the modulation mechanism includes a quadrature phase shift keying (QPSK), a 16-ary quadrature amplitude modulation (16QAM) and other modulations, wherein in the QPSK, two bits map to a complex signal, and in the 16QAM, four bits map to a complex signal. Signals are output from the modulator via a plurality of narrowband antennas. Then, through a multi-path channel in the air, the signals are received by a plurality of receiving antennas. Moreover, functions of a receiver correspond to that of the transmitter.
In the MIMO detectors referred in the aforementioned embodiments, the V-BLAST detector has an optimal performance. Therefore, the execution performance of the V-BLAST detector is taken as a comparison standard for demonstrating the simulation results.
Referring to
Referring to
Referring to
Moreover, the modulation mechanism can also be the 16QAM. Referring to
In summary, according to the MIMO detectors and the detection method of the present invention, the performance of the second best MIMO detector can be achieved by combining the MIMO detectors and selecting the suitable weight values. Accordingly, a whole performance of the MIMO detector can be improved without increasing of the complexity thereof. Moreover, the aforementioned embodiments can be applied to the MIMO detectors applying the IEEE 802.16e standard.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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97129102 | Jul 2008 | TW | national |