JP2005236364A - Multicarrier signal transmitter-receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Gaussian type multicarrier signal transmission system employing an adaptive equalizer. <P>SOLUTION: An interference canceller is attached to a receiver. The receiver includes: a received signal input section 30; a synchronization detection unit 31 configured to include a synchronization detector 31a; and a turbo equalization unit 34 configured to include an interference replica generator 34a; an LLR-modulation signal expected value converter 34b; a MAP detector 34c; and an interference elimination adder 34d. Further, the receiver also includes: a synchronization detection unit use channel estimate unit 32a using a pilot symbol; a turbo equalization unit use channel estimate unit 32b; and an FFT 33. The receiver also includes a synchronization detection / turbo equalization changeover switch 35; a CRC decoder 36; an interleaver 37a; a de-interleaver 37b; an adder 38 for a coded bit logarithmic likelihood ratio and a de-interleave output; a MAP decoder 39; a discrimination unit 40; and a bit information output section 41. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a signal transmitter / receiver used in a multicarrier communication system, and in particular, in communication using a plurality of carrier waves, a signal transmitted from a transmitter is narrowed and transmitted. The present invention relates to a multi-carrier communication system that performs equalization processing and reproduces an original signal. In particular, a system using a signal transceiver according to the present invention is intended to reduce interference with systems of different communication systems in a power line communication system, a digital subscriber line system, a wireless communication system, and the like.

  In order to realize ubiquitous communication, various digital communication systems based on the Internet have been studied. Power line communications (PLC) makes effective use of already installed indoor wiring and facilitates high-speed transmission to each room. There is a possibility that a very flexible and highly reliable ad hoc network system can be constructed by coexistence of a plurality of systems with a wireless LAN (Local Area Network) or the like. However, it has been pointed out that it is necessary to overcome problems related to EMC such as interference radio wave emission from the PLC to other communication systems and devices, and disturbance from other systems to the PLC, since the power line has a property as an antenna.

  As countermeasures against radiation suppression for a specific spectrum, conventionally, a notch filter is introduced in CDMA (Code Division Multiple Access), and a carrier hole is introduced in OFDM (Orthogonal Frequency Division Multiplex). However, the spectral suppression is only about 30 dB. This is because, in the former case, if a large dip is introduced, a large delay occurs in the transmission pulse and the transmission characteristics are greatly degraded.In the latter case, the spectrum side lobe of the orthogonal subcarrier is not sufficiently suppressed. It can be cited as a reason.

On the other hand, the multi-carrier scheme using Gaussian pulses that minimizes the product of time and frequency domain dispersion is known to be efficient (Non-Patent Documents 1 and 2), but it is practical including an equalizer It has not been studied as a secure transmission system.
IEEE Global Telecommuni. Conf., Vol. 1, pp. 310-314, Nov. 1997. IEEE Trans. On Communi., Vol. 51, no. 7, pp. 1111-1122, July 2003.

  The conventional communication system using the multi-carrier system has a problem in that interference radio wave radiation is generated in communication systems with different systems, and interference from communication systems with different systems is received.

  The present invention has been made in view of such problems, and an object thereof is to provide a multicarrier signal transceiver capable of realizing a Gaussian multicarrier transmission system using an adaptive equalizer.

  A multicarrier signal transceiver according to the present invention includes an encoder that encodes an input data sequence, an interleaver that interleaves the encoded bit sequence, and an S / P (serial / serial) that distributes the interleaved bit sequence to subcarriers. A parallel) converter, a multi-carrier modulator that generates a multi-carrier signal using Gaussian pulses by forming modulation symbols from bits allocated to each sub-carrier, and a control signal from the receiving side. A transmitter having a transmission side modulation controller for controlling modulation parameters, a detector for detecting subcarrier components from the received signal to generate bit information, and a channel for generating a reference carrier necessary for detection From the estimator, the decoder that performs deinterleaving and decoding on bit information, and further interleaving, and the decoder An interference component replica signal is generated from the interleaved output, and based on this and the received signal, an interference processing detector that performs detection processing again, and the reliability of the decoded bit sequence from the decoder are checked, A receiver having a demodulation controller that outputs the decoded bit sequence; and a receiver that monitors the signal status of the receiver and instructs the transmitter modulation controller to change the modulation parameter in accordance with the status And a modulation controller.

  Furthermore, the multicarrier modulator may arrange the Gaussian pulses in a square arrangement or in a honeycomb arrangement.

  Further, the S / P converter may be configured not to distribute data to subcarriers corresponding to carrier holes.

  In addition, as a transmission side modulation controller, coding scheme, interleave format, symbol rate, multi-level number of subcarrier modulation, modulation scheme of subcarrier modulation, Gaussian pulse width, Gaussian pulse arrangement method, subcarrier At least one of the interval and the subcarrier position and width of the carrier hole may be varied as a modulation parameter.

  Alternatively, a soft decision decoder may be used as a decoder, and a bit sequence encoded with the same code as that of the transmission side may be generated from the decoded bit sequence as an output of bit information.

  Further, a MAP (Maximum A-Posteriori) decoder is used as a decoder, and an interference component replica signal is used as an interference processing detector from a log likelihood ratio (LLR) which is bit information of the MAP decoder output. It is good also as using the expected value obtained.

  Further, the channel estimator may use a least square method using the replica signal of the received signal generated using the bit information of the decoder and the received signal as input data.

  A Gaussian pulse can easily realize a steep spectral attenuation characteristic of 50 dB or more, and can realize a carrier hole having a deep dip. Further, unlike OFDM having a guard interval, the multicarrier scheme using Gaussian pulses is inherent in the modulated signal with intersymbol interference (ISI) and intersubcarrier interference (ICI). However, removing these interferences is relatively easy with the MAP equalization technique.

  According to the multicarrier signal transmitter / receiver according to the present invention, the Gaussian multicarrier transmission system using the adaptive equalizer is realized, so that interference with systems of different communication systems can be reduced, for example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of a transmitter 1 in a multicarrier signal transceiver according to an embodiment of the present invention. The transmitter 1 includes a data input unit 10, an error correction coding and interleaving unit 11, a delay element 13 (13a to 13b), a Gaussian pulse generation unit 14 (14a to 14d), and a subcarrier generation unit 15 (15a to 15d). ), A subcarrier synthesis unit 16, a signal transmission unit 17, a transmission side modulation control unit 18, and a transmission control signal input unit 19.

The transmission data sequence input from the data input unit 10 is encoded and interleaved by the error correction encoding and interleaving unit 11 and input to the multicarrier modulator. A transmission symbol is formed in each subcarrier. Next, a Gaussian pulse is generated for each transmission symbol in the Gaussian pulse generation unit 14 for the data series subjected to serial-parallel conversion by the delay circuit 12, and a baseband subcarrier modulation signal is generated. The The subcarrier modulation signal is frequency-converted to each subcarrier signal by the subcarrier generation unit 15, and a signal s (t) that is synthesized and modulated by the subcarrier synthesis unit 16 is generated and output from the signal transmission unit 17. . In the figure, a delay circuit 12 is inserted every other subcarrier. This is to insert a delay of T _S / 2 into the Gaussian pulse in the case of 1 according to δ = 0 or1. A control signal from the receiving side is input from the transmission control signal input unit 19 to the transmission side modulation control unit 18 to control the modulation parameter.

The arrangement of the generated Gaussian pulse train in the frequency / time domain is shown in FIGS. FIG. 2A shows a square arrangement, and FIG. 2B shows a honeycomb arrangement. In the square arrangement, δ = 0 and no delay is inserted. On the other hand, when obtaining a honeycomb arrangement, δ = 1 and every other pulse is shifted by T _S / 2, as described above. In the case of the honeycomb arrangement, since ICI is relaxed, f _S can be lowered. In the following, the honeycomb structure is selected for further study.

  FIG. 3 shows a basic configuration of receiver 2 in the multicarrier signal transceiver according to the present embodiment. The receiver 2 includes a reception signal input unit 20, a frequency conversion unit 21, a low-pass filter 22, a detection processing unit 23, a decoding processing unit 24, and a reception data sequence output unit 25.

  In order to extract the target subcarrier complex amplitude from the received signal, the received signal input from the received signal input unit 20 is frequency-converted by the frequency converting unit 21, and a low-pass filter ( LPF (low pass filter) processing is performed. The low-pass filter uses an impulse response filter having the same waveform as the transmission pulse in order to perform matched filter reception. Detection processing is performed in the detection processing unit 23 based on the output from the low-pass filter. Further, the decoding processing unit 24 performs decoding processing corresponding to interleaving and encoding on the transmission side, and the reception data sequence output unit 25 outputs the reception data.

  Since Gaussian pulses arranged on the frequency axis and the time axis are not orthogonal to each other, interference occurs. Therefore, an interference canceller is added to the receiver 2 described above. The interference canceller reconstructs the transmission signal based on the decoded data and removes the interference component from the received signal. The demodulation process and the decoding process are performed again from the signal from which the interference is removed, and the decoding result is output. For the decoding process, hard decision, soft decision or the like can be used. The application of turbo equalization can be considered as the one that can expect the highest performance. This is to obtain high performance by integrating interference cancellation and decoding and repeating the processing.

  A configuration including a turbo equalizer on the receiving side is shown in FIG. This receiver includes a received signal input unit 30, a synchronous detection unit 31 including a synchronous detector 31a, an interference replica generator 34a, a log likelihood ratio (LLR) -modulated signal expected value converter 34b, A turbo equalization unit 34 including a MAP (Maximum A-Posteriori) detector 34c and an interference removal adder 34d. This receiver also has a channel estimator 32a for synchronous detection units using pilot symbols, a channel estimator 32b for turbo equalization units using pilot symbols, and an FFT 33. The receiver further includes a synchronous detection / turbo equalization changeover switch 35, a CRC (cyclic redundancy code) decoder 36, an interleaver 37a, a deinterleaver 37b, a logarithmic likelihood ratio of encoded bits and a deinterleaver output. Adder 38, MAP decoder 39, determiner 40, and bit information output unit 41.

  In the synchronous detection mode, the synchronous detection unit 31 and the decoder 39 are operated, and in the turbo equalization mode, the turbo equalization unit 34 and the decoder 39 are operated. In the initial operation, the receiver operates in the synchronous detection mode. When no error is detected by the CRC 36 error detection, the decoding data is output and the operation is terminated. When an error is detected, the mode shifts to the turbo equalization mode, and the expected value of the modulation signal is obtained based on the log likelihood ratio (LLR) of the encoded bits that is the output of the MAP decoder 39. Further, the turbo equalization unit 34 generates an interference replica signal by using the expected value of the modulation signal, and removes the interference by subtracting from the received signal. The signal from which the interference is removed is converted into an LLR by the MAP detector 34C, and is input to the MAP decoder 39 after deinterleaving. In the turbo equalization mode, interference cancellation and MAP decoding are repeated until no signal determination error is detected by the CRC 36 or until the maximum number of repetitions.

Next, signal transmission / reception operations in the multicarrier signal transceiver according to the present embodiment will be described. For the transmission signal, the carrier frequency of the modulated multicarrier signal s _t (t) is f _c , the complex envelope is s (t), the number of subcarriers (odd number) is N, the subcarrier frequency interval is f _s , when the carrier frequency f _n and _{f n = nf s, s (} t) is expressed by the following equation.

However, a _n (t) is a modulation signal of the n-th subcarrier, b _n is transmission subcarrier data, T _s is a symbol interval, and g (t) is a Gaussian impulse response. The energy of g (t) is normalized to 1, and δ _{n in} equation (4) is 1 only when n is an odd number in the honeycomb arrangement, and is 0 in the case of an even number in the honeycomb arrangement and in the square arrangement. It is.

  Next, regarding the received signal, the relationship of the received signal will be discussed with a complex envelope. The received signal r (t) is as follows.

Here, n (t) is white Gaussian noise (AWGN), and <n (t) n * (t + τ)> = N ₀ / 2δ (τ). Where δ (τ) is a Dirac delta. The filter output y _n (i) of the equivalent baseband signal of the nth subcarrier of the received signal r (t) is as follows.

Here, the symbol with “˜” attached to n is n′−n, and the symbol with “x” inside ○ is a convolution symbol. The reception signal when t = iT _S is established as follows.

  A symbol in which “˜” is added on i is i-i ′. The first term on the right side of the above equation is the filtered desired data output, the second term is interference of other data, and the third term is noise.

  In the output signal of Expression (12), the interference of the second term on the right side can be classified as follows.

  The first term on the right side of the above formula represents ISI, the second term represents ICI, and the third term represents ISCI.

[Example 1]
Computer simulation was performed to confirm the performance of the Gauss multicarrier system. Table 1 shows the simulation conditions. Since the basic performance is mainly confirmed, the modulation is BPSK. The number of subcarriers was adjusted to the wireless LAN 802.11a specification. The Gaussian pulse was set to σ / T _s = 0.275. With this selection, intersymbol interference between the same subcarriers is suppressed to about 0.2. As an error correction method, a convolutional code having a constraint length of 7 and an encoding rate of 0.5 was used. Block interleaving has a size of 6 × 8 and is a process closed by one symbol subcarrier.

  A Gaussian pulse waveform is shown in FIGS. 5A shows a pulse waveform in the time domain, and FIG. 5B shows a power spectrum in the frequency domain.

Transmission spectrum characteristics are shown in FIGS. 6A shows a square arrangement, and FIG. 6B shows a honeycomb arrangement. The spectrum does not depend on the configuration if the values of f _s T _s are the same. In the figure, f _s T _s is 1.0 in FIG. 6A and 0.5 in FIG. 6B. In order to observe the frequency characteristics of the spectrum hole, the output of 3 subcarriers in FIG. 6A and 6 subcarriers in FIG. It can be observed. Thus, it can be seen that the spectrum falls rapidly and is effective in suppressing specific subcarriers.

In subcarrier transmission using a Gaussian pulse, interference occurs because adjacent subcarriers are not orthogonal. The interference is generated not only from adjacent but also from adjacent data of the same subcarrier. These interferences affect transmission characteristics. FIG. 7 shows the relationship between the normalized pulse width σ / T _s of the Gaussian pulse and the amount of interference. When f _s T _s = 1.0, which is the same frequency interval as OFDM, it can be seen that mutual interference is suppressed in the region of 0.25 ≦ σ / T _s ≦ 0.8. It can be seen that there is considerable interference when f _s T _s = 0.5, and detection processing cannot be performed without an interference canceller.
[Example 2]
The processing shown in Table 2 was examined as a receiving system that takes into account interference associated with modulation between Gaussian pulses. Here, “with IC” first performs provisional demodulation without performing interference cancellation processing, and forms and cancels a replica, assuming that the transmission path estimation is complete based on the decoding result. Re-demodulate and decode. Interleaving is used together in encoding. For comparison, the case where there is no error correction is included.

A comparison of demodulation characteristics at f _s T _s = 1 is shown as a bit error rate (BER) in FIG. However, the turbo equalization method will be described later. It is shown that the characteristics can be in the order of SD, HD, and no encoding. It can also be seen that the effect of interference cancellation is great.

Next, the influence of f _s T _s is shown in FIG. The previous figure shows the characteristics for “SD with IC”, which has the highest performance. An interference canceller is essential because the amount of interference increases when f _s T _s is reduced. From this figure, it can be seen that practical characteristics can be obtained up to about f _s T _s = 0.6.

Furthermore, FIG. 10 shows a highly effective turbo equalization characteristic. In turbo equalization, characteristics are improved by iterative processing. In this figure, it can be seen that about twice is sufficient. It can be seen that practical characteristics can be obtained up to about f _s T _s = 0.5 by applying turbo equalization. This is approximately twice the spectral efficiency of OFDM.

  As described above, in this embodiment, a multicarrier scheme using Gaussian pulses has been proposed as a modulation / demodulation scheme suitable for power line communication. Since the spectral convergence of the Gaussian pulse is very good, it is suitable for the formation of spectral holes. However, when the pulse density in the time / frequency domain is increased in order to increase the modulation efficiency, intra-modulation interference due to ISI and ICI occurs. In order to eliminate this, a demodulation method including an interference canceller was cited, and its performance was confirmed by computer simulation. As a result of examining the soft decision decoding, the hard decision decoding added with an interference canceller, and the one using turbo equalization, it was confirmed that the turbo equalization characteristics are extremely excellent.

It is a block diagram which shows the structure of the transmitter in the multicarrier signal transmitter-receiver which concerns on one embodiment of this invention. It is a figure which shows the arrangement | positioning method of a gauss pulse, (A) shows square arrangement, (B) shows honeycomb arrangement. It is a block diagram which shows the basic composition of the receiver in the multicarrier signal transmitter-receiver which concerns on one embodiment of this invention. It is a block diagram which shows the structure of the receiver which has a turbo equalizer. It is a figure which shows a Gaussian pulse waveform, (A) is a time domain display, (B) shows the waveform in a frequency domain display. It is a figure which shows a transmission spectrum, (A) shows a square arrangement | positioning, (B) shows the characteristic in a honeycomb arrangement | positioning. It is a figure which shows an interference amount characteristic. It is a figure which shows an error rate characteristic when the normalization subcarrier space | interval is set to 1. It is a figure which shows the dependence (SD with IC) with respect to the frequency interval of an error rate characteristic. It is a figure which shows the error rate characteristic at the time of using turbo equalization.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transmitter, 2 ... Receiver, 18 ... Transmission side modulation control part, 31 ... Synchronous detection unit, 34 ... Turbo equalization unit.

Claims (2)

An encoder for encoding an input data sequence;
An interleaver for interleaving the encoded bit sequence;
An S / P converter for allocating the interleaved bit sequence to the subcarriers;
A multicarrier modulator that forms a modulation symbol from the bits allocated to each subcarrier and generates a multicarrier signal using a Gaussian pulse;
A transmitter having a transmission-side modulation controller that processes a control signal from the reception side and controls modulation parameters;
A detector that detects subcarrier components from the received signal and generates bit information;
A channel estimator that generates the reference carrier needed for detection;
A decoder that deinterleaves and decodes the bit information, and further interleaves;
An interference processing detector that generates a replica signal of an interference component from the interleaved output from the decoder, and performs detection processing again based on this and the received signal;
A receiver having a demodulation controller that checks the reliability of the decoded bit sequence from the decoder and outputs the decoded bit sequence;
A multi-carrier signal transceiver comprising: a reception-side modulation controller that monitors a signal state of the receiver and instructs the transmission-side modulation controller to change a modulation parameter in accordance with the situation. . As the transmission-side modulation controller, coding scheme, interleave format, symbol rate, multi-level number of subcarrier modulation, modulation scheme of subcarrier modulation, Gaussian pulse width, Gaussian pulse arrangement method, subcarrier spacing The multicarrier signal transmitter / receiver according to claim 1, wherein at least one of the carrier hole subcarrier position and width is variable as a modulation parameter.

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