JP2007335973A - Mobile communication system and receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile communication system capable of improving the degradation of the utilizing efficiency of a frequency caused by arranging a guard interval and adopting an orthogonal frequency division multiplex modulation system, and to provide a receiver. <P>SOLUTION: When receiving a wireless signal not including the guard interval, the receiver applies FFT processing to a range including a symbol interval of a processing object and its multipath component, applies frequency equivalent and inverse FFT processing to the signal after being subjected to the FFT processing, and executes the FFT processing for the signal after being subjected to the inverse FFT processing for a range of the symbol interval to demodulate the signal. When receiving a multicast notice signal for informing that data to be transmitted are for multicast transmission, the receiver furthermore extends the object range of the FFT processing. In the case of the multicast transmission, a transmission apparatus transmits a wireless signal with a guard interval of a length predicating unicast transmission inserted thereto, and the receiver extends the object range of the FFT processing so as to space-compose the same signals transmitted from the transmission apparatuses and to capture the composite signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a mobile communication system and a receiving apparatus using an orthogonal frequency division multiplexing modulation system.

  In a mobile communication system, radio waves radiated from a transmitting antenna are reflected by surrounding terrain and the like, and arrive at a receiver as a group of waves. Therefore, it is a phenomenon called multipath fading resulting from these results that always becomes an obstacle to realizing high-quality wireless communication. One radio communication scheme that suppresses the degradation of communication quality due to multipath fading is an orthogonal frequency division multiplex modulation scheme (hereinafter referred to as an Orthogonal Frequency Division Multiplex: OFDM scheme).

  The OFDM system is excellent in frequency utilization efficiency and exhibits excellent communication characteristics even in a multipath fading environment, so that it is actively studied for application to the next generation mobile communication system.

  One reason why the OFDM scheme exhibits excellent characteristics in a multipath fading environment is to provide a guard interval. The guard interval is provided in order to prevent the influence from adjacent symbols, and there is a process called a cycle prefix as a typical process for providing this guard interval.

  In the cycle prefix, since the entire symbol is subjected to FFT (Fast Fourier Transform) processing at the time of demodulation, in order to extend the entire symbol to a time longer than the delay time caused by multipath, for example, the second half of the symbol is The process of copying and pasting at the beginning of a symbol. By such processing, the FFT operation becomes unitary similarity transformation for the cyclic matrix, and becomes a diagonal matrix with eigenvalues, and an orthogonal state without intersymbol interference or intercarrier interference can be created.

  A conventional OFDM system using a cycle prefix will be described with reference to FIG.

  As shown in FIG. 8, in the conventional OFDM system, the last part of a symbol to be FFT processed is copied by a cycle prefix, and a guard interval is added to the head of the symbol. This signal can be regarded as a signal having a long time interval while maintaining periodicity.

  The receiving apparatus receives a signal that has been spatially synthesized by adding a signal whose time interval has been increased by this processing as a delayed signal due to multipath. Since the receiving apparatus cuts out the FFT processing target symbol section and performs the FFT processing, the cyclic matrix is multiplied by the FFT matrix.

  In the OFDM system, since inverse FFT (IFFT) processing is performed in the transmission apparatus, these processing becomes a diagonal matrix having eigenvalues as elements by unitary similarity transformation on the cyclic matrix. That is, an orthogonal state without intersymbol interference or intercarrier interference can be created.

  The guard interval is preferably set to be longer so that it can cope with a large delay wave caused by multipath, so that the communication performance is improved. However, since the guard section is basically a section that is not used for information transmission, there is a drawback in that the frequency utilization efficiency is lowered.

  Thus, several methods have been proposed for realizing the OFDM scheme without using the guard interval, which is a factor that reduces the frequency utilization efficiency. One of them is a technique called IOTA (Isotropic Orthogonal Transform Algorithm). IOTA is described in detail in Non-Patent Document 1, for example.

  In IOTA, two-dimensional orthogonal OFDM formed by time and frequency can be realized, and inter-symbol interference and inter-carrier interference can be prevented without using a guard interval. Hereinafter, IOTA will be briefly described.

IOTA is configured based on OQAM (Offset Quadrature Amplitude Modulation), and realizes orthogonality in the time axis direction and the frequency axis direction as shown in the following equation. For example, the subcarrier number is m, the half symbol number is k, the transmission symbol is A _{m, k} (real value), and the IOTA modulation signal x (t) is

とすると、

Then,

の直交条件を満足するパルスシェーピングにより

By pulse shaping that satisfies the orthogonal condition of

となり、時間軸方向に直交する。

And is orthogonal to the time axis direction.

  Where

に対して直交条件

Orthogonal condition for

を追加すると、

If you add

となり、周波数軸方向にも直交する二次元直交変換となる。

Thus, the two-dimensional orthogonal transform is also orthogonal to the frequency axis direction.

As another method for realizing the OFDM scheme without using the guard interval, a method for removing intersymbol interference or intercarrier interference caused by lack of guard interval using subcarriers is disclosed in Non-Patent Document 2, for example. Are listed.
Bernard Le Floch, Michel Alard and Claude Berrou, "Coded Orthogonal Frequency Division Multiplex", Proceedings of the IEEE, Volume 83, Number 6, June 1995, pp. 982-996 Steffen Trautmann, Tanja Karp and Norbert J. Fliege, "Frequency Domain Equalization of DMT / OFDM Systems with Insufficient Guard Interval", IEEE International Conference on Communication Volume 3, pp. 1646-1650

  However, among the methods for realizing the OFDM scheme without using the guard interval described above, in the method using IOTA, the ideal orthogonal relationship is established based on the imaginary number j. Time / frequency orthogonal relationship cannot be maintained. Further, as a practical problem, the pilot signal used for axis estimation is also in the same state as the symbol, and therefore there is a problem that it cannot be converted into a highly accurate two-dimensional orthogonal state.

  On the other hand, the method of removing intersymbol interference and intercarrier interference caused by lack of guard intervals using subcarriers does not use guard intervals, but uses subcarriers instead. Since the medium for transmission is lost, there is an inevitable problem that the use efficiency of the radio frequency is reduced.

  By the way, in recent years, a multicast service has attracted attention as one of the main services of the next generation mobile communication system.

  Multicast is a service that efficiently distributes information to a large number of users, and highly efficient transmission is required. An example of a mobile communication system having a multicast transmission function is shown in FIG. FIG. 9 shows an example in which information is distributed over a wide area using the site diversity effect in order to reliably distribute information to a large number of users. However, FIG. 9 shows a state in which information is distributed to a single user (mobile station).

  When the OFDM system is applied to a mobile communication system that realizes such a multicast service, the same distribution data transmitted from each base station to the mobile station is received by each mobile station due to the unique property of OFDM called spatial synthesis. A site diversity gain can be obtained at the end.

  However, when the conventional OFDM method using a guard interval is applied to a mobile communication system that performs a multicast service, it is necessary to fit the time difference of the same signal transmitted from each base station within the guard interval. Usually, since the base stations are arranged apart from each other, this time difference becomes larger than the time difference of multipath components in the unicast service.

  Therefore, in order to eliminate the influence of the time difference between the signals transmitted from the respective base stations, it is necessary to set the guard interval longer, and there is a problem that the use efficiency of the radio frequency is lowered.

  In the multicast service, a method of providing two types of guard sections for multicast transmission and unicast transmission is being studied in order to improve a decrease in radio frequency utilization efficiency due to provision of guard sections. However, such a method has a problem that a control method and a data format become complicated.

  The present invention has been made in order to solve the above-described problems of the prior art, and applies an orthogonal frequency division multiplexing modulation system that can improve a decrease in frequency utilization efficiency caused by providing a guard section. An object of the present invention is to provide a mobile communication system and a receiving apparatus thereof.

In order to achieve the above object, the mobile communication system of the present invention transmits a radio signal by orthogonal frequency division multiplexing modulation without inserting a guard interval for suppressing intersymbol interference and intercarrier interference due to multipath components. Equipment,
The FFT processing is performed on the received symbol section to be processed and the range including the multipath component, the frequency equivalent processing is performed on the signal after the FFT processing, the inverse FFT processing is performed, and the inverse FFT processing is performed. A receiving apparatus that performs FFT processing on a subsequent signal in a symbol interval and demodulates the signal after the FFT processing;
Have

  In the mobile communication system as described above, a transmitter transmits a radio signal without inserting a guard interval, and a receiver performs FFT processing on a range including a symbol interval to be processed and its multipath component. Then, frequency equalization processing is performed on the signal after FFT processing, then inverse FFT processing is performed, FFT processing is performed on the signal after inverse FFT processing with a symbol interval as a range, and the signal after FFT processing is Since demodulation is performed, it is possible to provide a mobile communication system that is excellent in frequency utilization efficiency and has multipath fading resistance.

In addition, another mobile communication system of the present invention is a mobile communication system that performs unicast transmission and multicast transmission by an orthogonal frequency division multiplexing modulation system,
A transmission device that transmits a multicast notification signal for informing beforehand that data to be transmitted is a wireless signal for multicast transmission;
FFT processing is performed on a range including a symbol section to be processed and a multipath component received from at least one transmission device, frequency equalization processing is performed on the signal after the FFT processing, and then inverse FFT processing is performed. Performing an FFT process on the signal after the inverse FFT process to demodulate the signal after the FFT process, and receiving the multicast notification signal, the FFT process, the frequency equivalent process, and A receiving device that further expands the target range of the inverse FFT processing;
Have

  In the mobile communication system as described above, the receiving device that has received the multicast notification signal expands the target range of the FFT processing by reducing the processing speed and changing the configuration to time-sharing processing to cover the expansion of the processing range, for example. By absorbing the spread of long multipath components during multicasting, information can be distributed over a wide area with high efficiency and reliability.

Furthermore, another mobile communication system of the present invention is a mobile communication system that performs unicast transmission and multicast transmission by an orthogonal frequency division multiplexing modulation system,
A transmitter that transmits a radio signal in which a guard interval for suppressing inter-symbol interference and inter-carrier interference due to a multipath component is inserted at the time of the multicast transmission on the premise of the unicast transmission;
FFT processing is performed on a range including a symbol section to be processed and a multipath component received from at least one transmission device, frequency equalization processing is performed on the signal after the FFT processing, and then inverse FFT processing is performed. A receiver that performs FFT processing with a symbol interval as a range on the signal after the inverse FFT processing and demodulates the signal after the FFT processing;
Have

  In the mobile communication system as described above, at the time of multicast transmission, a radio signal inserted with a guard interval having a length assuming unicast transmission is transmitted from the transmission device. Even if a multicast service is started after that, multicast transmission can also be supported in the guard section of the same length used in unicast transmission.

On the other hand, the receiving device of the present invention is a receiving device that receives a radio signal transmitted by an orthogonal frequency division multiplexing modulation system,
A first FFT processing unit that performs FFT processing on a range including a symbol section to be processed and a multipath component received from at least one transmission device;
A frequency equivalent unit for performing frequency equivalent to the signal after the FFT processing;
An inverse FFT processing unit for performing an inverse FFT process on the output signal of the frequency equivalent unit;
A second FFT processing unit for performing FFT processing with a symbol interval as a range on the signal after the inverse FFT processing;
A demodulator that demodulates the output signal of the second FFT processor;
Have

  In the receiving apparatus as described above, a deconvolution process that removes the influence of aliasing in the frequency domain is performed even if there is no guard interval, so that it is possible to provide a receiving apparatus with multipath fading resistance that is excellent in frequency utilization efficiency.

  According to the present invention, it is possible to provide a system using an orthogonal frequency division multiplex modulation scheme that is resistant to multipath fading and that is capable of improving a decrease in frequency utilization efficiency caused by providing a guard interval.

Next, the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing a configuration of a transmission apparatus used in the first embodiment of the mobile communication system of the present invention, and FIG. 2 shows a reception apparatus used in the first embodiment of the mobile communication system of the present invention. It is a block diagram which shows a structure.

  The mobile communication system according to the first embodiment is an example in which no guard interval is added by a transmission device that transmits a radio signal.

  In FIG. 1, transmission data is modulated by the modulation unit 101, and data corresponding to sample points of FFT operation target symbols for parallel processing is sent from the serial-parallel conversion unit 102 to the IFFT unit 103 in a lump. The IFFT-processed signal is sent without adding a guard section to multiplexing section 104 for multiplexing with the pilot signal.

  The pilot signal is generated by the pilot signal generation unit 105, parallelized by the serial / parallel conversion unit 106, and sent to the IFFT unit 107. At this time, only the pilot signal subjected to IFFT processing is added with a guard interval by the guard interval insertion unit 108 and transmitted to the multiplexing unit 104. That is, in this embodiment, a guard interval is not used for transmission data other than the pilot signal. FIG. 2 shows a configuration example of a receiving apparatus that receives a wireless signal generated in this way.

  In FIG. 2, the received signal is input to the FFT unit 201, and a normal OFDM reception process is performed on the pilot signal by the guard interval removing unit 207 to delete the guard interval. Thereafter, the FFT processing unit 208 performs FFT processing on the pilot symbols, and converts the pilot symbols into signals on the frequency axis, which are then sent to the channel estimation unit 209.

  On the other hand, as shown in the lower right of FIG. 2, the data other than the pilot symbol is subjected to FFT processing by the FFT processing unit 201 on the range including the symbol section subject to the FFT operation and its multipath component, and the frequency It is converted into an on-axis signal and input to the frequency equalizer 202.

  FIG. 3 shows these signals in detail. Note that FIG. 3 shows an example in which the FFT process is extended and implemented only behind the FFT operation target symbol to simplify the explanation, but as shown in FIG. The FFT processing may be performed by extending each of the front and rear. FIG. 3 shows a state in which an impulse response at the sample point K described above in FIG. 3 is assumed as a multipath transmission line.

  As shown in FIG. 3, the received signal is input as an FFT operation target symbol without a guard interval, but a symbol is input to the FFT processing unit 201 each time with a length expanded backward by the sample point K. That is, the FFT processing unit 201 executes the FFT process by extending the length of the impulse response of the multipath transmission path.

  The number of sample points expanded is N, the discrete Fourier transform value of the impulse response of the multipath transmission line is H (n), the discrete Fourier transform value for the transmission signal of the FFT target symbol is X (n), and the expanded range If the discrete Fourier transform value for the received signal is Y (n),

の関係が成り立つ。

The relationship holds.

  However, for the sake of brevity, the noise component in the transmission line is ignored here. Also, it is assumed that the sample points on the time axis of each signal are unified to the length N by zero insertion.

Channel estimation section 209 estimates H (n) from the pilot signal with the cycle prefix added. Here, the pilot pattern set to p in vector notation, the channel matrix became cyclic matrix by cycle prefix and H _C, when the noise vector is n, the received signal vector y _p for the pilot signals,

となる。但し、

It becomes. However,

とする。

And

FFT processor 208, implement the FFT processing of multiplying the FFT matrix F with respect to the received vector y _p,

を出力する。

Is output.

  Here, if the discrete Fourier transform value for the pilot signal is P (n),

となり、また、

And again

であるから、上記（９）式は以下のようになる。

Therefore, the above equation (9) is as follows.

この関係から、チャネル推定部２０９はチャネル推定

From this relationship, the channel estimation unit 209 performs channel estimation.

を以下のよう計算する。

Is calculated as follows.

こうして得られたチャネル情報を基に、周波数等価器２０２は上記（６）式より以下の（１４）式により送信信号に対する離散フーリエ変換値Ｘ（ｎ）を計算する。

Based on the channel information thus obtained, the frequency equalizer 202 calculates a discrete Fourier transform value X (n) for the transmission signal from the above equation (6) according to the following equation (14).

なお、特性改善のため、ＭＭＳＥ（minimum mean square error:最小平均二乗誤差）規範に基づき、

In order to improve the characteristics, based on the MMSE (minimum mean square error) standard,

に代わって

on behalf

を用いてもよい。

May be used.

  The transmission signal including the FFT operation target symbol on the frequency axis thus calculated is input to the IFFT processing unit 203 and output as a signal on the time axis. The bottom of FIG. 3 represents the output signal. In this example, since the FFT process is extended behind the target symbol, the last part in the signal is discarded before being input to the FFT processing unit 204 as shown in FIG.

  The processing after the FFT processing unit 204 is the same as the OFDM demodulation processing in the conventional symbol interval. That is, the FFT-processed signal is demodulated by the demodulator 205, converted to serial data by the parallel-serial converter 206, and output.

According to the mobile communication system of the present embodiment, a transmitter transmits a radio signal without inserting a guard interval, and a receiver performs FFT processing on a range including a symbol interval to be processed and its multipath component. After performing the frequency equivalent processing on the signal after the FFT processing, performing the inverse FFT processing, performing the FFT processing with the symbol interval as the range on the signal after the inverse FFT processing, Since the signal is demodulated, it is possible to provide a mobile communication system that has excellent frequency utilization efficiency and multipath fading resistance.
(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 9, in the multicast transmission using the OFDM scheme, the same radio signal is transmitted from a plurality of base stations, so that the mobile station can easily perform so-called spatial synthesis in which soft combining is performed with an RF signal. it can.

  In this case, as shown in FIG. 4, if a mobile station receives signals transmitted from a plurality of base stations as multipath signals having different delay times and can capture them without any problem, it can provide a high-speed data service. This is a great merit.

  In view of the mobile communication system employing the OFDM scheme using the guard section shown in FIG. 4, the received power that contributes to the improvement of the received signal-to-noise ratio (SNR) is large, but a multicast signal from a distant base station is received. In order to do so, it is necessary to set the guard interval longer than that in unicast transmission.

  However, such a method is not used in the mobile communication system of this embodiment. Instead, first, a multicast notification signal including channel information and timing information for starting multicast transmission is transmitted from the base station (transmitting device) to the mobile station (receiving device) through the downlink.

  The mobile station further expands the target range of processing by the FFT processing unit 201, the frequency equalizer 202, and the IFFT processing unit 203 shown in FIG. 2 based on the information included in the multicast notification signal. At this time, in order to cover the expansion of the processing range, the processing speed may be reduced and processing may be performed in a time-sharing manner. Therefore, the spread of multipath components at the time of multicast transmission can be dealt with by expanding the range of aliasing, and information can be distributed accurately and reliably to a wide area by such deconvolution processing.

  Alternatively, when the OFDM system using the guard section is already equipped with a unicast service function and a multicast service is newly started, a guard section considering unicast transmission has already been added. As shown, there is a possibility that the delayed wave due to multicast transmission cannot be sufficiently absorbed. Therefore, the receiving apparatus shown in FIG. 2 is used in this embodiment.

  In that case, the configuration shown in FIG. That is, a short unicast guard section is added and transmitted to the FFT processing target symbol used for information transmission using the unicast guard section insertion unit 710. Other configurations are the same as those of the transmission apparatus illustrated in FIG. 1, the modulation unit 701 corresponds to 101, the serial-parallel conversion unit 702 corresponds to 102, the IFFT unit 703 corresponds to 103, and the multiplexing unit 704 Corresponds to 104, pilot signal generation section 705 corresponds to 105, serial / parallel conversion section 706 corresponds to 106, IFFT section 707 corresponds to 107, and guard interval insertion section 708 corresponds to 108.

  The guard section added to the pilot signal by the guard section insertion unit 708 is set to a long section in consideration of multicast transmission, but may be set to a short length assuming unicast transmission. . In that case, a method of extending the above-described FFT processing target range may be adopted, and the method of canceling interference shown in the third embodiment is also applicable.

According to the mobile communication system of the present embodiment, at the time of multicast transmission, a radio signal with a guard interval having a length assuming unicast transmission is transmitted from the transmission device. Even when the system is constructed and then the multicast service is started, the multicast transmission can be handled in the guard section of the same length used in the unicast transmission. Therefore, even when multicast transmission is added to a unicast transmission main system, there is little influence on the system.
(Third embodiment)
The third embodiment shows an example of processing related to a pilot signal.

  In the above-described equation (7) of the received signal of the pilot signal, the transmission line matrix is treated as a cyclic matrix by using a cycle prefix that can absorb all delayed waves. In the third embodiment, a case is considered where there is interference in which the delayed wave does not fit in the cycle prefix.

  The received signal vector of the pilot signal that does not use the cycle prefix is expressed by the following equation.

ここで、

here,

・・・（１７）
である。

... (17)
It is.

  Therefore, if the pilot signal is repeatedly used from the same pilot pattern,

の関係が成り立ち、（１６）式は、

And the equation (16) is

となって巡回行列を伝送路行列とする上述の（７）式〜（１３）式で説明した方法によりチャネル推定を行うことができる。

Thus, channel estimation can be performed by the method described in the above equations (7) to (13) using a cyclic matrix as a transmission line matrix.

  Further, when a pilot signal of a short length U guard section added for unicast transmission is used for multicast transmission that requires a long section, the received signal of the pilot is expressed by the following equation.

ここで、

here,

・・・（２１）
である。

(21)
It is.

  So to make a circular matrix,

の関係が成り立てばよい。（２１）式より、Ｈ_BUはＨ_SUの列ベクトルを右にＵだけシフトさせたものである。したがって、ｐ（ｎ−１）のパイロットパターンを上にＵだけ巡回シフトさせたパターンでｐ（ｎ）を構成すれば、（２２）式の条件が成り立ち、

The relationship should be established. From equation (21), H _BU is obtained by shifting the column vector of H _SU to the right by U. Therefore, if p (n) is configured with a pattern in which the pilot pattern of p (n-1) is cyclically shifted upward by U, the condition of equation (22) is satisfied,

となり、巡回行列を伝送路行列とする上述の（７）式〜（１３）式で説明した方法によりチャネル推定を行うことができる。

Thus, channel estimation can be performed by the method described in the above equations (7) to (13) using a cyclic matrix as a transmission line matrix.

  By the way, since the cyclic shift corresponds to phase rotation on the frequency axis, it is only necessary to give phase rotation to the signal before IFFT processing on the transmission side.

  FIG. 6 is a block diagram showing a configuration of a transmitting apparatus to which the idea is applied, and is an example in which a multicast transmission function is added to a mobile communication system designed with an optimal guard interval length of unicast transmission.

  In FIG. 6, the pilot signal generated by the pilot signal generation unit 805 is subjected to phase rotation by the phase rotation unit 820, parallelized by the serial / parallel conversion unit 806, and then converted to a time axis signal by the IFFT unit 807. Is sent to the guard section insertion unit 808. The guard section inserted by the guard section insertion unit 808 is a short section for unicast transmission, but interference can be removed by phase rotation.

  The output signal of the guard interval insertion unit is transmitted as a radio signal via the multiplexing unit 804. At this time, a pilot signal to which phase rotation is applied in advance or a pilot signal to which IFFT processing or a guard interval is added in advance is prepared, and the amount of calculation may be reduced by appropriately selecting and using the pilot signal. Other configurations are the same as those of the transmission apparatus illustrated in FIG. 5, the modulation unit 801 corresponds to 701, the series-parallel conversion unit 802 corresponds to 702, the IFFT unit 803 corresponds to 703, and the unicast guard section The insertion part 810 corresponds to 710.

  In addition, the adoption of non-strict software inter-base station synchronization has advantages in system construction cost and inter-base station synchronization operation cost. In this case, the same signal transmitted from a plurality of base stations shown in FIG. The time difference becomes even greater. For this reason, in the conventional OFDM system using the cycle prefix, it is necessary to set a larger guard interval, which deteriorates frequency use efficiency.

  Therefore, if the present invention is used, the card section can be covered by a short unicast card, which is a great advantage in reducing CAPEX (capital expenditure) and OPEX (operational expenditure).

  FIG. 7 is a block diagram for detecting the pilot signal given the phase rotation in this way.

  As shown in FIG. 7, the configuration is the same as that of pilot detection using a normal cycle prefix. This is because the interference component is removed by the phase rotation, and only the term of the transmission line matrix due to the cyclic matrix remains behind. However, since the pilot signal thus detected is accompanied by phase rotation, it is necessary to remove the phase rotation component. The phase reverse rotation unit 904 shown in FIG. Other configurations are the same as those of the receiving apparatus shown in FIG. 2, the guard interval removing unit 907 corresponds to 207, the FFT processing unit 908 corresponds to 208, the channel estimation unit 909 corresponds to 209, and the data portion The processing unit 901 corresponds to the upper process in FIG. The parallel-serial converter 903 is only used for serial processing.

  According to the mobile communication system of the present embodiment, FFT processing is performed on a pilot signal given phase rotation, and demodulation is performed based on the signal after FFT processing, so that the pilot signal given phase rotation is on the time axis. In this case, since it is a cyclic shift and acts to cancel interference, accurate frequency equivalence and synchronous detection can be performed by inverse matrix calculation. For this reason, inter-symbol and inter-carrier interference due to multipath components can also be suppressed for pilot signals used for channel estimation necessary for demodulation, so that it is possible to provide a foundation for highly accurate frequency equivalence and synchronous detection.

It is a block diagram which shows the structure of the transmitter used in 1st Embodiment of the mobile communication system of this invention. It is a block diagram which shows the structure of the receiver used in 1st Embodiment of the mobile communication system of this invention. FIG. 3 is a schematic diagram illustrating a relationship between processing timings of multipath delay times and FFT processing symbols when the OFDM signal is demodulated by the receiving apparatus illustrated in FIG. 2. It is a schematic diagram which shows the mode at the time of the multicast transmission in the mobile communication system using the guard area for conventional unicast. It is a block diagram which shows the structure of the transmitter used in 2nd Embodiment of the mobile communication system of this invention. It is a block diagram which shows the structure of the transmitter used in 3rd Embodiment of the mobile communication system of this invention. It is a block diagram which shows the structure of the receiver used in 3rd Embodiment of the mobile communication system of this invention. It is a schematic diagram which shows the process by the OFDM system using the conventional cycle prefix. It is a schematic diagram which shows an example of the mobile communication system which performs multicast transmission.

Explanation of symbols

101, 701, 801 Modulator 102, 106, 702, 706, 802, 806 Series-parallel converter 103, 107, 703, 707, 803, 807 IFFT unit 104, 704, 804 Multiplexer 105, 705, 805 Pilot signal Generation unit 108, 708, 808 Guard interval insertion unit 201, 204, 208, 908 FFT processing unit 202 Frequency equalizer 203, 903 IFFT processing unit 205 Demodulation unit 206 Parallel serial conversion unit 207, 907 Guard interval removal unit 209, 909 channel Estimating unit 710, 810 Unicast guard interval inserting unit 820 Phase rotating unit 901 Data part processing unit 904 Phase counter rotating unit

Claims (8)

A transmitter that transmits a radio signal in an orthogonal frequency division multiplex modulation system without inserting a guard interval for suppressing intersymbol interference and intercarrier interference due to multipath components;
The FFT processing is performed on the received symbol section to be processed and the range including the multipath component, the frequency equivalent processing is performed on the signal after the FFT processing, the inverse FFT processing is performed, and the inverse FFT processing is performed. A receiving apparatus that performs FFT processing on a subsequent signal in a symbol interval and demodulates the signal after the FFT processing;
A mobile communication system. A mobile communication system that performs unicast transmission and multicast transmission using orthogonal frequency division multiplexing modulation,
A transmission device that transmits a multicast notification signal for informing beforehand that data to be transmitted is a wireless signal for multicast transmission;
FFT processing is performed on a range including a symbol section to be processed and a multipath component received from at least one transmission device, frequency equalization processing is performed on the signal after the FFT processing, and then inverse FFT processing is performed. Performing an FFT process on the signal after the inverse FFT process to demodulate the signal after the FFT process, and receiving the multicast notification signal, the FFT process, the frequency equivalent process, and A receiving device that further expands the target range of the inverse FFT processing;
A mobile communication system. A mobile communication system that performs unicast transmission and multicast transmission using orthogonal frequency division multiplexing modulation,
A transmitter that transmits a radio signal in which a guard interval for suppressing inter-symbol interference and inter-carrier interference due to a multipath component is inserted at the time of the multicast transmission on the premise of the unicast transmission;
FFT processing is performed on a range including a symbol section to be processed and a multipath component received from at least one transmission device, frequency equalization processing is performed on the signal after the FFT processing, and then inverse FFT processing is performed. A receiver that performs FFT processing with a symbol interval as a range on the signal after the inverse FFT processing and demodulates the signal after the FFT processing;
A mobile communication system. The transmitter is
Add a phase rotation to the generated pilot signal, and transmit a radio signal with a guard interval of a length premised on the unicast transmission,
The receiving device is:
The mobile communication system according to claim 3, wherein the phase rotation component is removed from the received pilot signal with the phase rotation. The transmitter is
Add the guard interval of a length assuming unicast transmission to the pilot signal,
The mobile communication system according to claim 3, wherein the same guard interval is used when performing the multicast transmission. A receiving device for receiving a radio signal transmitted by an orthogonal frequency division multiplexing modulation system,
A first FFT processing unit that performs FFT processing on a range including a symbol section to be processed and a multipath component received from at least one transmission device;
A frequency equivalent unit for performing frequency equivalent to the signal after the FFT processing;
An inverse FFT processing unit for performing an inverse FFT process on the output signal of the frequency equivalent unit;
A second FFT processing unit for performing FFT processing with a symbol interval as a range on the signal after the inverse FFT processing;
A demodulator that demodulates the output signal of the second FFT processor;
A receiving apparatus. The first FFT processing unit, the frequency equivalent unit, and the inverse FFT processing unit are:
The receiving apparatus according to claim 6, wherein when a multicast notification signal that notifies that transmission data is a multicast radio signal is detected in advance, the processing target range is further expanded.   The receiving apparatus according to claim 6, further comprising a phase reverse rotation unit that removes the phase rotation component from the pilot signal when the pilot signal to which the phase rotation is added is received.

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