JP3616956B2 - Diversity receiver - Google Patents

Description

この式（１）の示す意味は、３つの独立した値をデータ・ビットに対して持つことができることである。３つの値とは、事前確率情報Ｌ（ｕ_ｋ），チャネル情報Ｌ_ｃ・ｙ，誤り訂正復号器から得られる値Ｌ_ｅ（ｕ_ｋ）である。
誤り訂正復号器で、軟出力を取り出すことができるものとしては、例えば、畳み込み符号化に対するビタビ誤り訂正復号器が知られている。これらの複数のコンポーネント受信機３１０，３２０は独立して受信して復号を行っている。
図２において、受信機が２つの例を用いて説明する。受信された信号は、まず、それぞれのコンポーネント受信機３１０，３２０において復調されて、誤り訂正復号器３１６，３２６で、誤り訂正復号され、軟出力を得る。この場合、式（１）で、事前確率情報がないので、事前確率情報Ｌ（ｕ_ｋ）＝０であり、第１および第２の受信機からの出力は、
【数２】

と表すことができる。
次に、コンポーネント受信機３１０，３２０からの軟出力を、選択／合成器３４０において選択し、他のコンポーネント受信機の誤り訂正復号器に対して、事前確率情報として与える。それぞれのコンポーネント受信機の誤り訂正復号器３１６，３２６では、入力された事前確率情報と復調信号とを用いて、再度、同じ情報に対して誤り訂正復号が行われる。
【数３】

このような、復号化の処理の繰り返しを何度か行い、最後に、それぞれの誤り訂正復号器の軟出力を選択／合成器３４０において合成し、その値を判定することで、受信データｙが得られる。
【数４】

これにより、ダイバーシチ受信の利得の向上を得ることができる。
【０００８】
上述は、２つの受信機の場合を例に説明したが、３つ以上の受信機を用いて、その出力を選択／合成器３４０で選択して、他の受信機の誤り訂正復号器に入力することで、同様に行うことができる。このとき、いくつかのコンポーネント受信機からの合成出力を選択／合成器３４０において生成し、他のコンポーネント受信機への入力として与えても良い。
【０００９】
【実施例】
上述のダイバーシチ受信と誤り訂正復号を統合的に行うことを、図１に示した、４位相変位変調（ＱＰＳＫ）−直交周波数分割多重（ＯＦＤＭ）方式の受信機に適用した例で、本発明の効果を具体的に説明する。この例の受信機構成を図３に示す。
図３において、ダイバーシチ受信機４００は、２つのコンポーネント受信機４１０，４２０、合成器４３０、データ判定回路４４０から構成される。それぞれのコンポーネント受信機４１０，４２０はアンテナ４１１，４２１、フーリエ変換器４１２，４２２、復調器４１４，４２４、並直列変換器４１６，４２６そして軟出力を供給できる軟判定の第１ビタビ誤り訂正復号器４１８，４２８および第２ビタビ誤り訂正復号器４１９，４２９からなる。
【００１０】
この構成では、第１ビタビ誤り訂正復号器４１８，４２８の出力は、それぞれ、他のコンポーネント受信機の第２ビタビ誤り訂正復号器４１９，４２９の事前確率情報として入力している。それぞれの第２ビタビ誤り訂正復号器４１９，４２９の出力を合成器４３０で合成し、判定器４４０に入力してデータ出力を得ている。このように、各コンポーネント受信機内に２つの誤り訂正復号器を用いることにより、１回繰り返しの誤り訂正復号処理に対して、パイプライン処理を用いることができる。
誤り訂正符号として、符号化率１／２、拘束長７の畳み込み符号を用いている。信号変調は、キャリヤ数１４０５本のＱＰＳＫ−ＯＦＤＭ方式を用いている。なお、この方式は、ディジタルＴＶ放送の暫定方式と同様のものである。
この構成においてシミュレーションで、従来の構成による受信との比較を行う。このシミュレーションの通信路としては、電力スペクトル密度Ｎ_０の白色ガウス雑音通信路を考え、また評価は、ビット誤り率で行っている。
【００１１】
図４に、従来方式と比較したビット誤り率特性のグラフを示す。まず、図１に示した従来方式であるが、復調器でのダイバーシチ受信の効果により、ダイバーシチを用いない場合に比べ、３．０ｄＢの利得が稼げている（図４の（従来）参照）。
これに対し、図３に示した本発明の実施例の構成（１回繰り返し）では、ダイバーシチによる利得を誤り訂正復号まで拡張した構成になっているため、従来のダイバーシチ受信機より、さらに０．５ｄＢの利得の増加がある（図４の（１回繰り返し）参照）。
さらに反復復号の回数を増加して（即ち、各コンポーネント受信機内の復号器を増加して）復号化を行うと、さらに利得があがる。例えば、構成は図示していないが、６回の繰り返し処理による誤り訂正処理（即ち、誤り訂正復号器７台を用いて行うパイプライン処理での繰り返し処理）では、従来の受信と比較すると１．０ｄＢ程度の利得の増加が得られている（図４の（６回繰り返し）参照）。
【００１２】
【発明の効果】
本発明の構成により、独立に扱われていたダイバーシチ受信と誤り訂正復号を統合的に行うことで、大きな利得を得ることができる。
【図面の簡単な説明】
【図１】従来の位相変位変調（ＱＰＳＫ）−直交周波数分割多重（ＯＦＤＭ）方式の送信・受信の構成を示す図である。
【図２】本発明のダイバーシチ受信の構成を示す図である。
【図３】本発明の構成を位相変位変調（ＱＰＳＫ）−直交周波数分割多重（ＯＦＤＭ）の受信機に適用した構成を示す図である。
【図４】従来の構成と本発明の構成による誤り率特性の比較を示す図である。
【符号の説明】
１００ 送信機
１１０ 誤り訂正符号化器
１２０ 直並列変換器
１４０ 逆フーリエ変換器
２００ 受信機
２１０ フーリエ変換器
２１２ 復調器
２３０ 合成器
２４０ 直並列変換器
２５０ 誤り訂正復号器
３００ ダイバーシチ受信機
３１０，３２０ コンポーネント受信機
３１２，３２２ アンテナ
３１４，３２４ 復調器
３１６，３２６ 誤り訂正復号器
３４０ 選択／合成器
４００ ダイバーシチ受信機
４１０，４２０ コンポーネント受信機
４１１，４２１ アンテナ
４１２，４２２ フーリエ変換器
４１４，４２４ 復調器
４１６，４２６ 並直列変換器
４１８，４２８ 第１誤り訂正復号器
４１９，４２９ 第２誤り訂正復号器
４３０ 合成器
４４０ データ判定回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diversity receiver.
[0002]
[Technical background]
In the conventional diversity receiver, even if error correction coding is performed on the transmission side, it is not used at the time of diversity reception, and diversity reception and error correction decoding are treated as independent from each other.
FIG. 1 shows the configuration of a conventional transmitter and receiver. FIG. 1 shows a case where an error correction code is transmitted and received by quadrature phase shift keying (QPSK) -orthogonal frequency division multiplexing (OFDM). FIG. 1A shows a configuration on the transmission side. The input data is subjected to error correction coding by convolutional coding at the error correction encoder 110 and is subjected to serial / parallel conversion by the serial / parallel converter 120. The parallelized data is assigned to each carrier on the frequency and subjected to four-phase displacement modulation. The data on this frequency is inverse Fourier transformed by the inverse Fourier transformer 140 to obtain a transmission waveform on the time axis and transmitted.
[0003]
FIG. 1B shows the configuration of diversity reception on the receiving side. In FIG. 1B, using two receivers, the transmission waveform on the time axis is returned to the frequency domain by the Fourier transformers 210 and 220, demodulated by the demodulators 212 and 222, and then the diversity reception is combined. Do. Thereafter, a serial signal is obtained by the serial-parallel converter 240, and after error correction is performed by the error correction decoder 250, it is output as data.
As shown in FIG. 1B, in the conventional diversity receiver 200, the synthesis of a plurality of signals is performed only at the stages of the demodulators 212 and 222. For this reason, even when a signal subjected to error correction coding is received on the transmission side, it is performed completely independently of the error correction decoder 250 in the subsequent stage, and the improvement in characteristics due to diversity reception is reflected in the error correction code. Was not.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to perform diversity reception and error correction decoding, which are conventionally handled independently, and obtain a large gain.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a diversity receiver for receiving a transmission signal that has been subjected to error correction coding, and comprises at least a plurality of error correction decoders that perform an antenna, a demodulator, and a soft output. And a selector / combiner that selects / combines the soft outputs of the decoding results of the data individually received by the respective receivers, and outputs the error correction decoder to the error correction decoder of another receiver. The diversity receiving apparatus is characterized in that the data is decoded by repeating the error correction decoding process, finally combining the outputs, and improving the data decoding reliability.
With this configuration, diversity reception and error correction decoding can be integrated and a large gain can be obtained.
A plurality of error correction decoders can be provided in each receiver, and repeated error correction decoding processing can be performed by pipeline processing. Thereby, the delay regarding a process can be minimized.
The selector / synthesizer may combine the soft outputs of the decoding results from a plurality of receivers, and then input the result to a selector / synthesizer of another receiver.
As this error correction, error correction using a convolutional code can be performed.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings.
The configuration of a diversity receiver 300 according to the present invention is shown in FIG. As shown in FIG. 2, the receiver 300 of the present invention includes a plurality of component receivers 310 and 320. Each of the component receivers 310 and 320 includes antennas 312 and 322, demodulators 314 and 324, and error correction decoders 316 and 326. The input / output of the used error correction decoders 316 and 326 is a soft input-soft output, which is output as a likelihood for error correction.
[0007]
Here, the function of the soft input / soft output error correction decoder used will be described.
Soft-input / soft-output error correction decoders are designed to perform soft decision decoding in the log-likelihood region. This type of decoder allows prior probability information L (u _k ) along with channel information L _c · y for all information bits u _k . The decoder provides a soft output represented by the following equation for each decoded bit u _k . Here, the soft output is broken down into three terms.
[Expression 1]

The meaning of equation (1) is that it can have three independent values for the data bits. The three values are the prior probability information L (u _k ), the channel information L _c · y, and the value L _e (u _k ) obtained from the error correction decoder.
For example, a Viterbi error correction decoder for convolutional coding is known as an error correction decoder that can extract a soft output. The plurality of component receivers 310 and 320 independently receive and perform decoding.
In FIG. 2, the receiver will be described using two examples. The received signals are first demodulated in the respective component receivers 310 and 320 and error-corrected and decoded by error-correcting decoders 316 and 326 to obtain a soft output. In this case, since there is no prior probability information in equation (1), prior probability information L (u _k ) = 0, and the outputs from the first and second receivers are:
[Expression 2]

It can be expressed as.
Next, the soft outputs from the component receivers 310 and 320 are selected by the selector / synthesizer 340 and given as prior probability information to the error correction decoders of the other component receivers. The error correction decoders 316 and 326 of the respective component receivers perform error correction decoding on the same information again using the input prior probability information and the demodulated signal.
[Equation 3]

The decoding process is repeated several times. Finally, the soft outputs of the respective error correction decoders are combined in the selector / synthesizer 340, and the value is determined to determine the received data y. can get.
[Expression 4]

Thereby, the gain of diversity reception can be improved.
[0008]
In the above description, the case of two receivers has been described as an example, but the output is selected by a selector / synthesizer 340 using three or more receivers and input to an error correction decoder of another receiver. This can be done in the same way. At this time, a combined output from several component receivers may be generated in the selector / synthesizer 340 and given as an input to another component receiver.
[0009]
【Example】
An example in which the above-described diversity reception and error correction decoding are performed in an integrated manner is applied to the four-phase displacement modulation (QPSK) -orthogonal frequency division multiplexing (OFDM) receiver shown in FIG. The effect will be specifically described. The receiver configuration of this example is shown in FIG.
In FIG. 3, the diversity receiver 400 includes two component receivers 410 and 420, a combiner 430, and a data determination circuit 440. Each component receiver 410, 420 includes antennas 411, 421, Fourier transformers 412, 422, demodulators 414, 424, parallel-serial converters 416, 426, and a soft decision first Viterbi error correction decoder capable of supplying a soft output. 418, 428 and second Viterbi error correction decoders 419, 429.
[0010]
In this configuration, the outputs of the first Viterbi error correction decoders 418 and 428 are input as prior probability information of the second Viterbi error correction decoders 419 and 429 of the other component receivers, respectively. The outputs of the second Viterbi error correction decoders 419 and 429 are combined by a combiner 430 and input to a determiner 440 to obtain a data output. In this way, by using two error correction decoders in each component receiver, pipeline processing can be used for one-time error correction decoding processing.
As an error correction code, a convolutional code having a coding rate of 1/2 and a constraint length of 7 is used. Signal modulation uses a QPSK-OFDM system with 1405 carriers. This system is the same as the provisional system for digital TV broadcasting.
In this configuration, the simulation is compared with reception by the conventional configuration. As a communication channel for this simulation, a white Gaussian noise communication channel having a power spectral density N ₀ is considered, and evaluation is performed with a bit error rate.
[0011]
FIG. 4 shows a graph of bit error rate characteristics compared with the conventional method. First, in the conventional system shown in FIG. 1, a gain of 3.0 dB is gained by the effect of diversity reception at the demodulator as compared to the case where no diversity is used (see (conventional) in FIG. 4).
On the other hand, in the configuration of the embodiment of the present invention shown in FIG. 3 (repeated once), the gain by diversity is extended to error correction decoding. There is a 5 dB gain increase (see (repeated once) in FIG. 4).
Further, when decoding is performed by increasing the number of iterations (that is, by increasing the number of decoders in each component receiver), the gain is further increased. For example, although the configuration is not shown, in error correction processing by six iterations (that is, iterative processing in pipeline processing using seven error correction decoders), compared to conventional reception, 1. An increase in gain of about 0 dB is obtained (see (repeated 6 times) in FIG. 4).
[0012]
【The invention's effect】
With the configuration of the present invention, a large gain can be obtained by performing diversity reception and error correction decoding, which have been handled independently.
[Brief description of the drawings]
FIG. 1 is a diagram showing a conventional transmission / reception configuration of phase shift keying (QPSK) -orthogonal frequency division multiplexing (OFDM).
FIG. 2 is a diagram showing a configuration of diversity reception according to the present invention.
FIG. 3 is a diagram showing a configuration in which the configuration of the present invention is applied to a phase shift keying (QPSK) -orthogonal frequency division multiplexing (OFDM) receiver.
FIG. 4 is a diagram showing a comparison of error rate characteristics between the conventional configuration and the configuration of the present invention.
[Explanation of symbols]
100 Transmitter 110 Error Correction Encoder 120 Serial-Parallel Converter 140 Inverse Fourier Transformer 200 Receiver 210 Fourier Transformer 212 Demodulator 230 Synthesizer 240 Series-Parallel Converter 250 Error Correction Decoder 300 Diversity Receiver 310, 320 Component Receivers 312 and 322 Antennas 314 and 324 Demodulators 316 and 326 Error correction decoder 340 Selector / combiner 400 Diversity receiver 410 and 420 Component receivers 411 and 421 Antennas 412 and 422 Fourier transformers 414 and 424 Demodulator 416 426 Parallel-serial converters 418 and 428 First error correction decoders 419 and 429 Second error correction decoder 430 Synthesizer 440 Data determination circuit

Claims (4)

A diversity receiver that receives a transmission signal that has been subjected to error correction coding,
A plurality of receivers each including at least an antenna, a demodulator, and an error correction decoder performing soft output;
A selector / synthesizer that selects / synthesizes the soft output of the decoding result of the data received individually by each receiving device;
The output of the error correction decoder is input to the error correction decoder of another receiver, the error correction decoding process is repeatedly performed, and finally the outputs are combined to improve the reliability of data decoding and decode the data. A diversity receiver characterized in that: 2. The diversity receiving apparatus according to claim 1, wherein a plurality of error correction decoders are provided in each receiver, and repeated error correction decoding processing is performed by pipeline processing. 3. The diversity receiver according to claim 1, wherein the selector / synthesizer combines the soft outputs of the decoding results from a plurality of receivers, and then inputs them to the selector / synthesizer of another receiver. A diversity receiver characterized by the above. The diversity receiver according to claim 1, wherein the error correction decoder performs error correction using a convolutional code.

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