JP2005123926A - Transmitter and transmitting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To finely adjust transmission signal timing with a time resolving power smaller than sampling interval when ranging is carried out. <P>SOLUTION: At the time of OFDM modulation, phase of a transmission symbol on the frequency axis is revolved along the frequency axis and then subjected to multicarrier modulation. When phase modulation is carried out, a phase value is determined based on the subcarrier number, a required delay, and transmission symbol phase data and then subtracted on a sine table thus obtaining a symbol imparted with a revolution depending on a required delay along the frequency axis. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a transmission apparatus and a transmission method for performing transmission processing of a multicarrier signal, and in particular, performs amplitude and phase modulation for each carrier and performs inverse FFT on the plurality of carriers, thereby orthogonalizing each carrier on the frequency axis. The present invention relates to a transmission apparatus and a transmission method for performing transmission processing on an OFDM (Orthogonal Frequency Division Multiplexing) signal that is converted into a time-axis signal and transmitted while maintaining the characteristics.

  More specifically, the present invention relates to a transmission apparatus and a transmission method that perform distance measurement / positioning between reception apparatuses based on the time from packet transmission to reception using time resolution in the UWB communication system. The present invention relates to a transmission apparatus and a transmission method for finely adjusting a transmission signal timing with a time resolution smaller than a sampling interval when performing a distance.

  As a system for releasing a user from a wired LAN connection, a wireless LAN has attracted attention. According to the wireless LAN, most of the wired cables can be omitted in a work space such as an office, so that a communication terminal such as a personal computer (PC) can be moved relatively easily. In recent years, the demand for wireless LAN systems has increased remarkably with the increase in speed and cost. In particular, recently, in order to establish a small-scale wireless network between a plurality of electronic devices existing around a person and perform information communication, introduction of a personal area network (PAN) has been studied. For example, different radio communication systems and radio communication apparatuses are defined using frequency bands that do not require a license from a supervisory agency, such as 2.4 GHz band and 5 GHz band.

  For example, in recent years, a method called “ultra-wide band (UWB) communication” for performing wireless communication by placing information on a very weak impulse train has attracted attention as a wireless communication system that realizes short-range ultrahigh-speed transmission, and its practical use. Is expected. Currently, in IEEE802.15.3, etc., a data transmission system having a packet structure including a preamble has been devised as an access control system for ultra-wideband communication.

  By the way, when a wireless network is constructed in a working environment where many devices are mixed in a room, it is assumed that a plurality of networks are constructed in an overlapping manner. In a wireless network using a single channel, there is no room for repairing a situation even if another system interrupts during communication or communication quality deteriorates due to interference or the like. For this reason, a multi-channel communication scheme is considered in which a plurality of frequency channels are prepared and operated by frequency hopping. For example, when communication quality deteriorates due to interference or the like during communication, network operation can be maintained by frequency hopping, and coexistence with other networks can be realized.

  Further, when a wireless network is constructed indoors, a multipath environment is formed in which the receiving device receives a superposition of a direct wave and a plurality of reflected waves / delayed waves. Multipath causes delay distortion (or frequency selective fading), and causes an error in communication. Intersymbol interference resulting from delay distortion occurs.

  As a main countermeasure against delay distortion, a multicarrier transmission system can be cited. In the multi-carrier transmission method, transmission data is distributed and transmitted to a plurality of carriers having different frequencies, so that the band of each carrier becomes narrow and is not easily affected by frequency selective fading.

  For example, in OFDM (Orthogonal Frequency Division Multiplexing), which is one of the multicarrier transmission schemes, the frequency of each carrier is set so that the carriers are orthogonal to each other within a symbol interval. At the time of information transmission, serial / parallel conversion is performed for each symbol period slower than the information transmission rate, and a plurality of data output is assigned to each carrier, and amplitude and phase are modulated for each carrier. By performing inverse FFT on the plurality of carriers, it is converted into a time-axis signal and transmitted while maintaining the orthogonality of each carrier on the frequency axis. At the time of reception, the reverse operation, that is, FFT is performed to convert the time-axis signal into the frequency-axis signal and perform demodulation corresponding to each modulation method for each carrier, and parallel / serial conversion to the original Play back the information sent in the serial signal.

  The OFDM modulation scheme is adopted as a standard for wireless LAN in IEEE 802.11a / g, for example. Also in IEEE802.15.3, information is obtained using a DS-UWB system in which the spreading speed of a DS (direct spreading) information signal is extremely high, and an impulse signal sequence having a very short period of about several hundred picoseconds. In addition to the impulse-UWB system in which signals are transmitted and received, standardization is being advanced for the UWB communication system employing the OFDM modulation system. In the case of the OFDM_UWB communication system, three subbands each having a frequency of 3.1 to 4.8 GHz are frequency hopped (FH) each having a width of 528 MHz, and OFDM modulation using IFFT / FFT in which each frequency band is composed of 128 points. (For example, see Non-Patent Document 1).

  On the other hand, UWB communication has a high time resolution by using ultra-fine pulses, and it is possible to perform “ranging” for performing radar and positioning using this property. In particular, recent UWB communication can have both high-speed data transmission exceeding 100 Mbps and the original ranging function (see, for example, Patent Document 1).

  In the future, WPAN (Wireless Personal Access Network) of near field communication represented by UWB is expected to be installed in all home appliances and CE (Consumer Electronics) devices. Therefore, it is conceivable that, apart from high-speed data transmission, the use of position information by ranging, such as navigation and near field communication (NFC), may produce added value of radio, and distance measurement function together with high-speed data transmission. It is also considered desirable to implement.

  For example, as part of the standardization of UWB communication in IEEE 802.15.3, UWB ranging technology is incorporated in addition to the OFDM modulation scheme (see, for example, Non-Patent Document 1).

  Here, the distance is generally measured from the time from packet transmission to reception. However, there is a problem in that it is inconvenient in a system in which processing contents vary depending on the length and type of a packet to set the time from when a wireless device receives a packet to when it is returned. Also, adding special information to the packet for distance measurement is not preferable from the viewpoint of effective use of bandwidth.

JP 2002-51001 A IEEE 802.15.3a TI Document <URL: http: // grouper. iee. org / groups / 802/15 / pub / 2003 / May03 File name: 03142r2P802-15_TI-CFP-Document. doc>

  An object of the present invention is to suitably perform transmission processing of a multi-carrier signal that is converted into a time-axis signal by performing amplitude and phase modulation for each carrier on the frequency axis and performing inverse FFT on the plurality of carriers. Another object of the present invention is to provide an excellent transmission apparatus and transmission method that can be used.

  A further object of the present invention is to provide an excellent transmission device and transmission method capable of performing ranging and positioning between reception devices based on the time from packet transmission to reception using time resolution in the UWB communication system. It is to provide.

  A further object of the present invention is to provide an excellent transmission apparatus and transmission method capable of finely adjusting the transmission signal timing with a time resolution smaller than the sampling interval when ranging.

The present invention has been made in consideration of the above-described problems, and is a transmission device that transmits a multicarrier signal, and at the time of multicarrier modulation,
Swiveling means for swirling the phase of the transmission symbol on the frequency axis along the frequency axis;
Modulation means for multi-carrier modulating the swung symbol;
It is a transmitter characterized by comprising.

  Here, the turning means turns the transmission symbol on the frequency axis by a phase corresponding to a desired delay amount of the transmission timing.

  When performing phase modulation, a phase value is obtained based on the subcarrier number, the required delay amount, and transmission symbol phase data, and is obtained along the frequency axis by subtracting the obtained phase value from the sine table. It is possible to obtain a symbol given a turn corresponding to a delay amount.

  According to such an apparatus configuration, transmission timing adjustment can be performed with a time section brain that is smaller than the sampling interval T. Further, since the sign table is used before IFFT in this way, it is not necessary to increase the processing so much.

  According to the present invention, a multi-carrier signal transmitted by converting each carrier into a time-axis signal by performing amplitude and phase modulation for each carrier on the frequency axis and performing inverse FFT on the plurality of carriers is suitably used. An excellent transmission device and transmission method capable of performing transmission processing can be provided.

  Furthermore, according to the present invention, an excellent transmission apparatus and transmission method that can perform distance measurement and positioning between reception apparatuses based on the time from packet transmission to reception using time resolution in the UWB communication system. Is to provide.

  Further, according to the present invention, it is possible to provide an excellent transmission apparatus and transmission method capable of finely adjusting the transmission signal timing with a time resolution smaller than the sampling interval when ranging.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

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

  The present invention relates to a communication system that employs an OFDM scheme that is expected as a technique for realizing high-speed and high-quality wireless transmission. The OFDM scheme is a type of multi-carrier transmission scheme, and the frequency of each carrier is set so that the carriers are orthogonal to each other within a symbol interval. As a result of transmitting a high-speed signal by dividing it into a large number of subcarriers, the transmission speed of the subcarrier alone becomes low, and it is strong against delay wave interference.

  FIG. 1 schematically shows a functional configuration of an OFDM transmission apparatus used for implementing the present invention. As shown in the figure, the OFDM transmitter includes an encoder 11, a modulator 12, a serial / parallel converter 13, an IFFT 14, a parallel / serial converter 15, and a guard interval insertion unit 16. ing.

  The encoder 11 encodes transmission data with an error correction code. When receiving transmission data, the modulation unit 12 performs modulation, for example, according to the QPSK method according to the modulation information and timing supplied from the transmission control unit 109. Here, QPSK (Quadrature Phase Shift Keying) is one of the phase modulation methods as a digital modulation method, and (0, 0) for 0 phase, (0, 1) for π / 2 phase, ( (1, 0) and 3 / π phases are transmitted in correspondence with (1, 1).

  When the transmission data is modulated, a known data sequence may be inserted as a pilot symbol into the modulation symbol sequence according to the pilot symbol insertion pattern and timing. A pilot signal having a known pattern is inserted for each subcarrier or at intervals of several subcarriers.

  The serial-to-parallel converter 13 converts the modulated serial signal into parallel data corresponding to the number of parallel carriers according to the number of parallel carriers and the timing.

  The IFFT 14 and the parallel-serial converter 15 perform inverse Fourier transform for the FFT size according to a predetermined FFT size and timing, and convert the signal into a time-axis signal while maintaining orthogonality of each carrier on the frequency axis.

  The guard interval inserting unit 16 inserts a guard interval made up of, for example, a repetitive signal after a signal for one OFDM symbol is transmitted. The digital transmission signal with the guard signal inserted is subjected to quadrature modulation and A / D conversion, up-converted to an RF signal, and transmitted from a transmission antenna (not shown).

  The wireless communication system according to the present invention employs the UWB transmission method in which information is carried on a weak impulse train and performs wireless communication. Configured to perform.

  Here, it is common to measure the distance from the time from packet transmission to reception, but the time from when the wireless device receives the packet until it returns is fixed, depending on the length and type of the packet. There is a problem that it is inconvenient in a system in which the processing content changes. Also, adding special information to the packet for distance measurement is not preferable from the viewpoint of effective use of bandwidth.

  Therefore, as one embodiment of the present invention, a packet is transmitted from a transmission source wireless device, and the packet is transmitted after a time corresponding to an integral multiple of a predetermined unit time has elapsed since the packet was received at the transmission destination wireless device. Returning, and then, at the source radio, removing an integral multiple of a predetermined unit time from the required time from sending the packet until receiving the return packet, obtaining the round-trip transmission time of the packet, the round-trip transmission Consider a ranging / positioning system that measures the distance between the source and destination radios based on time.

  When a transmission source wireless device transmits a packet to a transmission destination wireless device, the transmission destination always transmits the packet after receiving the packet and after an elapse of an integral multiple of the unit time from the time of packet detection.

  Then, the transmitter radio performs the packet detection process only in the vicinity of the timing at which the packet is returned from the transmission destination after it transmits, and the time from when the packet is transmitted until the packet of the radio is detected Is measured with a counter to determine the time from detection of a destination packet to transmission. Ranging can be performed by converting the time determined here and the time obtained by subtracting the processing time of the transmission source radio itself from the measurement time into the propagation distance to the communication counterpart radio.

  According to such a ranging / positioning system, the time between the wireless device receiving the packet and returning it is not fixed, and no special information is added to the packet for distance measurement. Ranging and positioning can be suitably performed between two wireless communication devices that transmit and receive. Such distance measurement / positioning system is described in, for example, Japanese Patent Application No. 2003-52274 already assigned to the present applicant.

  On the other hand, in such a ranging / positioning system, when performing ranging, the transmitter side must finely adjust the transmission signal timing. For example, in order to obtain a spatial resolution of about 10 cm at a sampling interval of 500 MHz, that is, 2 microseconds in UWB ranging, it is necessary to adjust the transmission signal timing by about 300 picoseconds.

  For example, in order to adjust the transmission time of the transmission signal, the transmission signal on the frequency axis can be converted into a time axis signal by inverse FFT, and then the sampling at the time of DA conversion can be shifted. In this case, the timing control can be performed only with the time resolution of the sampling interval T.

  Therefore, the present inventors, in a communication system using a multicarrier modulation scheme such as OFDM, when finely adjusting the transmission signal timing for ranging or other purposes, the transmission symbol on the frequency axis is used as the frequency axis. We propose a method of giving a certain turn along the way.

  Here, the OFDM signal x (t) on the time axis to be transmitted is represented by the following equation.

Here, X _k is a transmission symbol on the frequency axis of the kth subcarrier, and f _sc is a subcarrier width. The function rot (x) is defined as rot (x) = exp (j2πx).

  According to the above equation, a signal whose transmission timing is shifted by a delay time τ smaller than the sampling interval T is expressed as the following equation.

  Since τ is a value smaller than the small sampling interval T, the influence of the transmission window is small (if 128 points, it is smaller than the time window 128T). Therefore, the above equation x (t) can be approximated as the following x ′ (t).

Then, it is possible to shift the transmission timing by the delay amount τ by OFDM-modulating X ′ _k that is equivalently given a fixed turn along the frequency axis of the transmission symbol X _k .

In particular, when a phase modulation scheme such as QPSK (Quadrature Phase Shift Keying) is applied to the transmission symbol X _k , assuming that the number of phases is M (M = 4 in the case of QPSK), the transmission symbol Xk is as follows: Expressed.

Therefore, the symbol X ′ _{k obtained} by giving the transmission symbol X _k a certain turn along the frequency axis is _represented by the following equation.

  Here, U sine tables (SinTable) are prepared in advance, in which one round of the circumference is quantized with a sufficient phase resolution U. The sine table can be subtracted by inputting the phase value i as an argument.

Therefore, by subtracting the phase value (kf _sc τ + d _k / M) obtained based on the subcarrier number k of the transmission symbol, the necessary delay amount τ of the transmission timing, and the data d _k from the sign table as an index i. Thus, the symbol X ′ _{k obtained} by turning the transmission symbol X _k along the frequency axis corresponding to the delay amount τ can be acquired at high speed.

FIG. 2 schematically shows an apparatus configuration for obtaining a symbol X ′ _{k in} which the original symbol Xk to be transmitted is given a certain turn along the frequency axis.

The table index calculation unit 101 uses the phase value (kf _sc + d _k / M) as the table index i based on the subcarrier number k of the transmission symbol, the delay amount τ required for transmission timing, and the data d _k. Ask.

Next, by subtracting the table index i from the sine table 102, a symbol X ′ _k is obtained by giving the transmission symbol X _k a turn corresponding to the delay amount τ along the frequency axis. Further, since the sign table is used before IFFT in this way, it is not necessary to increase the processing so much.

The IFFT unit 103 performs inverse Fourier transform on the symbol symbol X ′ _k on the frequency axis to convert it into a signal on the time axis while maintaining the orthogonality of each carrier.

  Then, the transmission window processing unit 104 performs predetermined window processing and sends a transmission signal x ′ (t) on the time axis to the transmission line.

  According to such an apparatus configuration, transmission timing adjustment can be performed with a time section brain that is smaller than the sampling interval T. Further, since the sign table is used before IFFT in this way, it is not necessary to increase the processing so much.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention.

  In this specification, as an application example of the technique according to the present invention in which transmission signal timing control is performed on the transmitter side, a case where distance measurement is performed in a UWB communication system has been described as an example. It is not limited to. It goes without saying that the present invention can be similarly realized in general when the timing of transmission signals is adjusted in a multicarrier signal transmission apparatus.

  In short, the present invention has been disclosed in the form of exemplification, and the description of the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims section described at the beginning should be considered.

FIG. 1 is a diagram schematically showing a functional configuration of an OFDM transmission apparatus provided for implementing the present invention. FIG. 2 is a diagram schematically showing an apparatus configuration for obtaining a symbol X ′ _{k in} which the original symbol Xk to be transmitted is given a certain turn along the frequency axis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Encoder 12 ... Modulator 13 ... Serial / parallel converter 14 ... IFFT
DESCRIPTION OF SYMBOLS 15 ... Parallel / serial converter 16 ... Guard interval insertion part 21 ... Synchronization detection part 22 ... Serial / parallel converter 101 ... Table index calculation part 102 ... Sign table 103 ... IFFT part 104 ... Transmission window process part

Claims (6)

A transmission device that transmits a multicarrier signal, and at the time of multicarrier modulation,
Turning means for turning the phase of the transmission symbol on the frequency axis along the frequency axis;
Modulation means for multi-carrier modulating the swung symbol;
A transmission device comprising: The turning means turns a transmission symbol on the frequency axis by a phase corresponding to a desired delay amount of transmission timing.
The transmission apparatus according to claim 1, wherein: Phase value calculating means for obtaining a phase value based on a subcarrier number, a required delay amount and transmission symbol phase data when performing phase modulation;
A sine table describing the correspondence between phase values and sine values;
Further comprising
By subtracting the phase value obtained by the phase value calculating means with the sine table, a symbol is given that has been turned according to the required delay along the frequency axis.
The transmission apparatus according to claim 1, wherein: A transmission method for transmitting a multicarrier signal, and at the time of multicarrier modulation,
A swivel step that swivels the phase of the transmitted symbol on the frequency axis along the frequency axis;
A modulation step of multi-carrier modulating the swung symbol;
A transmission method comprising: In the turning step, the transmission symbol on the frequency axis is turned by a phase corresponding to a desired delay amount of the transmission timing.
The transmission method according to claim 4. When performing phase modulation, obtaining a phase value based on a subcarrier number, a required delay amount, and transmission symbol phase data;
Subtracting the obtained phase value with a sine table to obtain a symbol given a turn according to the required delay along the frequency axis;
The transmission method according to claim 4, further comprising:

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