JP2008187589A - Radio terminal apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remarkably reduce the deterioration of reception performance caused by electromagnetic noise even if a radio terminal apparatus employing an OFDM system is built in an electronic device. <P>SOLUTION: The radio terminal apparatus comprises: a frequency converting means 11 for converting a frequency of an OFDM radio signal sent from a transmitter 3 of a communicating party; a subchannel demodulating means 12 for generating a demodulation bit stream in compliance to a subcarrier modulation system by decomposing the OFDM radio signal into a modulation signal for each sub-channel; a decoding means 13 for decoding the demodulation bit stream into the original signal and outputting it by performing the error-correction processing of the bits while taking into account a tolerance that the bit of the demodulation bit stream has; an interfered subchannel specifying means 14 for determining a clock harmonic wave of a clock signal used in an electronic device 3 and specifying a subchannel that interferes with the clock harmonic wave; and a tolerance reducing means 15 for reducing the tolerance of the bit of the demodulation bit stream demodulated from the specified subchannel. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless terminal apparatus in a wireless communication system using an OFDM scheme.

  In recent years, with an increase in communication capacity, an OFDM (Orthogonal Frequency Division Multiplexing) method has attracted attention as one of communication methods capable of increasing the speed and capacity of data transmission. This OFDM system is a wireless communication system in which a plurality of low-speed data obtained by dividing high-speed data is transmitted in parallel by a plurality of subcarriers arranged at intervals of the reciprocal number of the symbol period, thereby improving the resistance to multipath interference. It is.

Wireless terminal devices in a wireless communication system using the OFDM system include, for example, wireless LAN (IEEE802.11a and IEEE802.11g) terminals, UWB (MB-OFDM UWB) terminals, and on-vehicle electronic devices such as car navigation systems. There are wireless LAN terminals and the like that are implemented (for example, see Non-Patent Document 1 below).
Y. Wang, J. Ge, B. Ai, P. Liu, and S. Yang, “A Soft Decision Decoding Scheme for Wireless COFDM with Application to DVB-T,” IEEE Transactions on Consumer Electronics, vol. CE-50, pp. 84-88, Feb. 2004.

  And in the wireless terminal device using these OFDM systems, interleaving and convolutional coding are often used in order to reduce the influence of interference waves.

  On the other hand, these wireless terminal devices are often used by being incorporated in an electronic device having a processor that operates at high speed, such as a personal computer, a peripheral device, or an OA device. In that case, electromagnetic noise from the electronic device itself, for example, CPU And is susceptible to interference from peripheral operation clock signals and their harmonics.

  However, when a wireless terminal device is built in an electronic device, even if the above interleaving and convolutional coding are used, it cannot be sufficiently reduced. At present, reception performance deteriorates due to the influence of electromagnetic noise from the electronic device. There is a problem that it is difficult to reduce.

  The present invention has been proposed in view of the above, and provides a wireless terminal device using the OFDM method that can greatly reduce the influence of electromagnetic noise from an electronic device even when incorporated in the electronic device. With the goal.

  In order to achieve the above object, according to the first aspect of the present invention, in a wireless terminal device in a wireless communication system using the OFDM scheme, an OFDM wireless signal transmitted from a transmission device of a communication partner is received and the frequency thereof is received. Frequency conversion means for converting the radio frequency to the intermediate frequency or baseband frequency, and the OFDM radio signal from the frequency conversion means is decomposed into modulation signals for each subchannel, and a demodulated bit string is generated in accordance with the subcarrier modulation method Sub-channel demodulating means, decoding means for performing error correction processing of the bits in consideration of the likelihood of each bit of the demodulated bit string, decoding the demodulated bit string into an original signal, and output, and the wireless terminal device The clock harmonics are obtained by frequency analysis of the clock signal used inside the mounted electronic device, and the clock harmonics are obtained. An interfered subchannel identifying means for identifying a subchannel that interferes with a harmonic, and each bit of the demodulated bit sequence demodulated from the subchannel identified by the interfered subchannel identifying means, provided in the decoding means And a likelihood reducing means for reducing the likelihood.

  In the invention described in claim 2, in the invention described in claim 1, the likelihood reducing means sets the likelihood of each bit of the demodulated bit string demodulated from the specified subchannel to “0”. ".

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the decoding by the decoding means is Viterbi decoding.

  In this invention, a clock harmonic is obtained by analyzing a frequency of a clock signal used inside an electronic device in which the wireless terminal device is mounted, a subchannel that interferes with the clock harmonic is identified, and the identified channel is identified. Each bit of the demodulated bit string demodulated from the subchannel is judged to be erroneous with a high probability and its likelihood is reduced to, for example, “0”. Therefore, only the demodulated bits with a low possibility of error in the decoding process Can be used to perform error correction processing, the error rate of the final decoded bit string can be improved, and interference with the radio terminal device due to clock harmonics can be greatly reduced.

  Further, the communication performance such as bit error rate, packet error rate, throughput, and minimum received signal level can be improved by greatly reducing interference.

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

  FIG. 1 is a block diagram showing a configuration of a wireless terminal device of the present invention. In FIG. 1, a wireless terminal device 1 of the present invention is a wireless terminal device in a wireless communication system using an OFDM system, such as a wireless LAN (IEEE802.11a and IEEE802.11g) terminal or a UWB (MB-OFDM UWB) terminal. The wireless LAN terminal is mounted on an on-vehicle electronic device such as a car navigation system, and includes a frequency conversion unit 11, a subchannel demodulation unit 12, a decoding unit 13, and an interfered subchannel specifying unit 14.

  The frequency conversion unit 11 receives the OFDM radio signal transmitted from the transmission apparatus 2 as a communication partner, and converts the frequency from a radio frequency to an intermediate frequency or a baseband frequency.

  The subchannel demodulating means 12 decomposes the OFDM radio signal from the frequency converting means 11 into modulated signals for each subchannel, and generates a demodulated bit string in accordance with the subcarrier modulation scheme. The subcarrier modulation method is predetermined according to the specification of the OFDM communication method, and for example, PSK (phase shift keying), QAM (quadrature amplitude modulation), or the like is used.

  The decoding unit 13 deinterleaves the demodulated bit string generated by the subchannel demodulating unit 12, and then performs error correction processing on the bit in consideration of the likelihood of each bit, and converts the demodulated bit string to the original signal. Decrypt and output.

  The interfered subchannel specifying unit 14 obtains a clock harmonic by analyzing the frequency of a clock signal used in the electronic device 3 in which the wireless terminal device 1 is mounted, and a subchannel that interferes with the clock harmonic. Is identified.

  The likelihood reducing means 15 is provided in the decoding means 13 and reduces the likelihood of each bit of the demodulated bit string demodulated from the subchannel specified by the interfered subchannel specifying means 14.

  As described above, in the embodiment of the present invention, the clock harmonic is obtained by analyzing the frequency of the clock signal used in the electronic device 3 in which the wireless terminal device 1 is mounted, and interferes with the clock harmonic. A subchannel is specified, and each bit of the demodulated bit string demodulated from the specified subchannel is determined to have a high probability of error, and its likelihood p is reduced, for example, “0” (that is, an error is possible) Therefore, in the decoding process, error correction processing can be performed using only demodulated bits with a low possibility of error, and the error rate of the final decoded bit string can be improved. Interference with the wireless terminal device 1 due to clock harmonics can be greatly reduced.

  Further, the communication performance such as bit error rate, packet error rate, throughput, and minimum received signal level can be improved by greatly reducing interference.

  FIG. 2 is a diagram showing a more specific configuration example of the wireless terminal device of the present invention. In FIG. 2, an OFDM radio signal transmitted from a transmitter (not shown) is received by an antenna of a radio terminal device (receiver) 10 and converted from a radio frequency to an intermediate frequency or a baseband frequency by a frequency converter 11a. The

  Subsequently, after the pilot signal and the guard interval are deleted, the OFDM radio signal is decomposed into modulated signals for each subchannel by an FFT (Fast Fourier Transform unit) 12a. The subchannel demodulator 12b obtains demodulated bits in accordance with the subcarrier modulation scheme. The deinterleaver 13a performs the reverse operation of the interleaving (rearrangement of the bit sequence transmission order) performed on the transmitter side to return the bit sequence to the original order in order to disperse the positions of error bits generated at the time of demodulation. The demodulated bit string that has been deinterleaved is input to the decoder 13b, and error bits are corrected using a Viterbi algorithm to obtain and output a final information bit string.

  However, in practice, receiver noise and noise from an electronic device (such as a PC) on which the receiver is mounted are input to the receiver 10. Much of the noise of electronic devices in the microwave band is due to leakage of harmonics of clock signals used inside the devices to operate the electronic devices. For this reason, an error is very likely to occur in the subchannel that matches the frequency of the clock signal harmonic (clock harmonic). If the percentage of error bits included in the demodulated bit string is large, the decoder cannot perform error correction, and as a result, a bit string containing errors is output.

  In order to prevent this, as shown in FIG. 2, a clock signal is supplied directly (by wire) from the clock generation circuit of the electronic device on which the receiver 10 is mounted, and the harmonic frequency is specified by the FFT 14a. Using this result, a subchannel that is subject to interference due to clock harmonics in the received OFDM radio signal is accurately identified. Further, if a subchannel that is subject to interference due to clock harmonics can be identified, it is possible to identify bits that are likely to have errors due to interference from the demodulated bit string input to the decoder 13b.

  Then, the likelihood of the bit string input to the Viterbi decoder 13b (corresponding to the reliability of the bits input to the error correction process) is reduced (for example, set to 0, ie, the error By ignoring bits with high possibility), the Viterbi decoder 13b can perform error correction processing using only demodulated bits with little possibility of error, so that the error rate of the final decoded bit string is improved. can do.

  FIG. 3 is a diagram for explaining likelihood reduction. In FIG. 3, the demodulated bit string shown in the upper stage is composed of bits a, b, c,..., N−1, n, n + 1,... (Demodulated bits) after being deinterleaved by the deinterleaver 13a. Each bit is given likelihood p. The likelihood p is given a value “1” here.

  Here, when it is specified that the demodulated bit demodulated from the subchannel that interferes with the clock harmonic is “n”, the present invention sets the likelihood p of the demodulated bit n as shown in the lower demodulated bit string. Reduce from “1” to a smaller value, eg, “0”.

  INDUSTRIAL APPLICABILITY The present invention is effective because it can determine a harmonic frequency with high accuracy even for harmonics of a frequency spread clock (a method of frequency modulating a clock signal) used in many electronic devices in recent years. high.

It is a block diagram which shows the structure of the radio | wireless terminal apparatus of this invention. It is a figure which shows the more specific structural example of the radio | wireless terminal apparatus of this invention. It is a figure for demonstrating likelihood reduction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radio | wireless terminal apparatus 11 Frequency conversion means 12 Subchannel demodulation means 13 Decoding means 14 Interfered subchannel identification means 15 Likelihood reduction means 2 Transmitter 3 Electronic equipment 10 Receiver 11a Frequency converter 12a FFT
12b Subchannel demodulator 13a Deinterleaver 13b Decoder

Claims (3)

In a wireless terminal device in a wireless communication system using OFDM,
A frequency conversion means for receiving an OFDM radio signal transmitted from a transmission apparatus of a communication partner and converting the frequency from a radio frequency to an intermediate frequency or a baseband frequency;
A subchannel demodulating means for decomposing the OFDM radio signal from the frequency converting means into a modulated signal for each subchannel and generating a demodulated bit string in accordance with a subcarrier modulation scheme;
Decoding means for performing error correction processing of the bit in consideration of the likelihood of each bit of the demodulated bit string, and decoding and outputting the demodulated bit string to the original signal;
A frequency harmonic of a clock signal used inside the electronic device in which the wireless terminal device is mounted is used to determine a clock harmonic, and an interfered subchannel identifying unit that identifies a subchannel that interferes with the clock harmonic;
A likelihood reducing means provided in the decoding means for reducing the likelihood of each bit of the demodulated bit string demodulated from the subchannel specified by the interfered subchannel specifying means;
A wireless terminal device comprising:   The radio terminal apparatus according to claim 1, wherein the likelihood reducing means sets the likelihood of each bit of the demodulated bit string demodulated from the specified subchannel to "0".   The wireless terminal apparatus according to claim 1 or 2, wherein decoding by said decoding means is Viterbi decoding.

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