JP3670445B2 - Wireless communication system - Google Patents

Wireless communication system Download PDF

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Publication number
JP3670445B2
JP3670445B2 JP17466397A JP17466397A JP3670445B2 JP 3670445 B2 JP3670445 B2 JP 3670445B2 JP 17466397 A JP17466397 A JP 17466397A JP 17466397 A JP17466397 A JP 17466397A JP 3670445 B2 JP3670445 B2 JP 3670445B2
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Japan
Prior art keywords
signal
base station
subcarrier
wireless terminal
wireless
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Expired - Fee Related
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JP17466397A
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JPH1127231A (en
Inventor
一美 佐藤
稔 行方
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株式会社東芝
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Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless communication system that transmits signals using an orthogonal frequency division multiplexing (OFDM) scheme.
[0002]
[Prior art]
In recent years, there is a need for high-speed wireless data communication systems indoors or outdoors, but multipath interference in which transmitted signals are received through various paths due to reflection or shadowing by buildings or the like becomes a major problem. . When multipath interference occurs, the signal may be strengthened or weakened depending on the phase relationship of signals received through a plurality of propagation paths. Even in the same multipath propagation environment, there are cases where they are combined in phase and in phase depending on the frequency, and distortion called frequency selective fading occurs in the frequency spectrum of the received wave. In particular, when the bit rate is increased, the occupied bandwidth of the signal is greatly widened. Therefore, severe distortion such as a plurality of notches is generated in the band due to frequency selective fading. When frequency selective fading occurs, signal processing of a receiver in a high-speed wireless communication system becomes very difficult.
[0003]
In view of this, a multi-carrier transmission scheme has been proposed in which the influence of frequency selective fading is small and signal processing speed can be reduced.
[0004]
In the multicarrier transmission method, a transmission data sequence is divided into a plurality of signals, and signals are transmitted using subcarriers of different frequencies. At this time, the signal of each subcarrier can be slowed down, and the signal processing speed can be slowed down.
[0005]
In multicarrier transmission, since each subcarrier signal is a narrow band, even if frequency selective fading occurs, it seems that each subcarrier is subjected to flat fading. Therefore, the reception characteristics are improved by not transmitting a signal on a notched subcarrier or by performing frequency hopping.
[0006]
One of the multi-carrier transmission schemes is an orthogonal frequency division multiplexing (OFDM) scheme. This OFDM system is a system in which subcarriers are set up at a minimum interval orthogonal to each other. Theoretically, several thousand subcarriers can be set up in a transmission band of several ΜHz, which increases the number of users. Yes. Also, by setting a large number of subcarriers, the transmission rate of each subcarrier can be greatly reduced, and at the time of modulation / demodulation, digital signal processing of a similar algorithm such as fast inverse Fourier transform or fast Fourier transform is performed. Since the plurality of subcarrier signals are modulated and demodulated at once, these digital signal processing units can be integrated. Therefore, it can be said that this “FD” method is a transmission method suitable for high-speed data communication used in a mobile body moving at high speed.
[0007]
[Problems to be solved by the invention]
However, this “FD” method has the following problems.
[0008]
First, when an integrated digital signal processing circuit that modulates and demodulates thousands of subcarriers at the same time is mounted on the portable wireless terminal side, the circuit scale is large, although not as much as a multicarrier transmission system other than OFDM. As a result, there is a problem that the entire apparatus becomes large and portability is impaired.
[0009]
Second, if a notch in the frequency axis direction caused by frequency selective fading enters, the reception characteristics of the subcarrier signal in that portion are extremely deteriorated, and reception of a radio terminal using the subcarrier signal is received. There is a problem that the characteristics are extremely deteriorated.
[0010]
The present invention has been made to solve such problems, and a first object is to suppress the digital signal processing circuit of the wireless terminal to a small scale.
[0011]
A second object of the present invention is to provide a wireless communication system capable of improving communication efficiency and reception characteristics.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a wireless communication system according to the first aspect of the present invention provides:In a wireless communication system in which a base station and a plurality of wireless terminals perform wireless communication using an orthogonal frequency division multiplexing system, the base station includes a measuring unit that measures a propagation environment of wireless communication, and a wireless terminal based on a measurement result of the measuring unit. A first setting control means for determining an operating environment for the communication, a notification means for notifying the wireless terminal of the operating environment determined by the first setting control means, and an operation determined by the first setting control means Subcarrier variable assigning means for assigning a subcarrier signal to a wireless terminal from among a plurality of subcarrier signals that can be assigned for communication with the wireless terminal based on the environment, and the wireless terminal has an operating environment notified from the notifying means Is set as its own operating environment, and the sampling frequency when the wireless terminal converts the received signal from the base station into a subcarrier signal is provided. And that is set lower than the sampling frequency when the base station is collectively converted to a time signal subcarrier signalsIt is characterized by.
[0014]
  The wireless communication system of the invention according to claim 2In a wireless communication system in which a base station and a plurality of wireless terminals perform wireless communication using an orthogonal frequency division multiplexing system, the base station includes a measuring unit that measures a propagation environment of wireless communication, and a wireless terminal based on a measurement result of the measuring unit. A first setting control means for determining an operating environment for the communication, a notification means for notifying the wireless terminal of the operating environment determined by the first setting control means, and an operation determined by the first setting control means Subcarrier variable assigning means for assigning a subcarrier signal to a wireless terminal from among a plurality of subcarrier signals that can be assigned for communication with the wireless terminal based on the environment, and the wireless terminal has an operating environment notified from the notifying means And a second setting control means for setting the self-operating environment as a self-operating environment. Station is characterized in that it is set lower than the sampling frequency when converting the received signal from the wireless terminal to the sub-carrier signal.
[0016]
According to a third aspect of the present invention, there is provided a wireless communication system in which a base station and a plurality of wireless terminals perform wireless communication using an orthogonal frequency division multiplexing method, and the base station receives an access request from any one of the wireless terminals. Then, based on at least one of the number of the wireless terminals that are accessing the base station or the propagation environment at that time, a transmission band used for wireless communication with the wireless terminal that has made the access request, an occupied bandwidth, and Setting control means for determining a control condition for controlling at least one of the modulation methods, and means for returning the control condition determined by the setting control means to the wireless terminal that has made the access request, The wireless terminal includes setting control means for setting the internal items according to the control conditions returned from the base station.
[0017]
In the case of the invention according to claim 3, the base station uses at least one of the number of wireless terminals that have requested access to the base station and at least one of the propagation environments, a transmission band used in wireless communication, an occupied bandwidth, and a modulation scheme. One item is determined as condition control, and the wireless terminal sets its own environment according to the control condition determined by the base station.
[0018]
In other words, since the band of the signal allocated to the wireless terminal is set according to the propagation environment and the number of connected wireless terminals, the influence of frequency selective fading can be reduced, and the propagation environment and the condition of the transmission path can be reduced. It is possible to perform wireless communication with the corresponding transmission method and transmission band. As a result, the reception characteristics of the wireless terminal can be improved.
[0019]
A radio communication system according to a fourth aspect of the present invention is the radio communication system according to the second aspect, wherein the base station determines a sampling frequency when the radio terminal converts a received signal from the base station into a subcarrier signal. It is characterized in that it is set lower than the sampling frequency when batch conversion of subcarrier signals into time signals.
[0020]
In the case of the invention described in claim 4, the sampling frequency at which the wireless terminal converts the received signal from the base station into the subcarrier signal is set to be higher than the sampling frequency at which the base station converts the subcarrier signal into the time signal at once. Since it is set low, the scale of the digital signal processing circuit on the wireless terminal side can be reduced to a small scale.
[0021]
A radio communication system according to a fifth aspect of the present invention is the radio communication system according to the second aspect, wherein the base station determines a sampling frequency when the radio terminal collectively converts a subcarrier signal into a time signal from the radio terminal. The received signal is set to be lower than the sampling frequency when converting the received signal into a subcarrier signal.
[0022]
In the case of the invention according to claim 5, the sampling frequency at which the radio terminal collectively converts the subcarrier signal into the time signal is set to be higher than the sampling frequency at which the base station converts the received signal from the radio terminal into the subcarrier signal. Since it is set low, the scale of the digital signal processing circuit on the wireless terminal side can be reduced to a small scale.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0028]
FIG. 1 is a diagram showing a configuration of a wireless communication system according to a first embodiment of the present invention. In the figure, CS is a base station, and PS1 to ΡS3 are wireless terminals. Bidirectional communication is performed between these wireless terminals PS1 to ΡS3 and the base station CS using ΟFDM signals of different bands.
[0029]
As shown in FIG. 2, the base station CS includes a subcarrier allocation unit 1, an OFDM transmission / reception unit 2, an antenna 3, a propagation environment measurement unit 4, a setting control unit 5, a setting notification unit 6, and the like. When there is an access request from any one of the plurality of radio terminals PS1 to ΡS3, for example, the radio terminal PS1 or the like, the subcarrier allocation unit 1 is a plurality of subcarriers that can be allocated to each radio terminal PS1 to ΡS3. Of the signals, subcarrier signals are allocated to the radio terminal PS1 by the number corresponding to the amount of information communicated by the radio terminal PS1. For example, a plurality of subcarrier signals are allocated when the amount of information to be communicated is large, and only one is allocated when the amount of information to be communicated is small. The OFDM transmission / reception unit 2 transmits / receives the OFDM signals transmitted from the wireless terminals PS1 to ΡS3 via the antenna 3. The propagation environment measuring unit 4 measures the propagation environment when a known information symbol is received or when an access request is made. The setting control unit 5 uses a transmission band used for wireless communication with the wireless terminal that has made an access request based on the number of wireless terminals that are already accessing the access request or at least one of the propagation environments at that time. The control condition for controlling at least one of the occupied bandwidth and the modulation method is determined. The setting notification unit 6 returns (notifies) the control conditions determined by the setting control unit 5 to the wireless terminal that has made the access request.
[0030]
As shown in FIG. 3, the wireless terminal includes an OFD transmission / reception unit 7, a setting control unit 8, an antenna 9, and the like. The OFD soot transceiver 7 transmits and receives the soot FDM signal transmitted from the base station CS via the antenna 3. That is, the OFD / transmission / reception unit converts a signal to be transmitted into a time signal and transmits it from the antenna 9 and converts a signal received by the antenna 9 into a data series.
[0031]
The OFDM transmitter / receiver 2 of the base station CS and the ΟFDM transmitter / receiver 7 of the wireless terminals PS1 to ΡS3 are composed of a receiver 10 and a transmitter 11 as shown in FIG. The receiving unit 10 includes a reception processing unit 15, a fast Fourier transform unit (FFT) 16, and a demodulation unit 17. The reception processing unit 15 performs reception processing such as frequency conversion, A / D conversion, establishment of synchronization, and guard time removal on the signal input to the reception unit 10. A fast Fourier transform unit (FFT) 16 converts the time signal obtained by the reception process into subcarrier signals at once. The demodulator 17 converts only the desired signal out of each subcarrier signal into a digital data series and outputs it. The transmission unit 11 includes a modulation unit 12, a fast inverse Fourier transform unit (IFFT) 13, and a transmission processing unit 14. The modulation unit 12 modulates an input signal to the transmission unit 11 and generates a subcarrier signal. The fast inverse Fourier transform unit 13 converts the subcarrier signal into a time signal. The transmission processing unit 14 adds a guard time, performs transmission processing such as D / Α conversion and frequency conversion, and outputs the result. The configuration of the base transceiver station FDM transceiver unit 2 and the wireless terminal OFDM transceiver unit 7 are the same, but the configuration of each part of the OFDM transceiver unit 7 may be different. For example, a transmission bandwidth capable of batch processing of transmission / reception signals.
[0032]
The operation of the wireless communication system according to the first embodiment will be described below with reference to FIGS. FIG. 5 is a diagram illustrating a band (subcarrier) allocated by the base station CS, and FIG. 6 is a generation process of a FDM signal transmitted from the base station CS to any one of the radio terminals, for example, the radio terminal PS1, that is, the base station CS. FIG. 7 is a diagram showing how the radio terminal PS1 obtains a reception subcarrier signal after the transmission subcarrier signal is generated, and FIG. 7 is a generation process of an FDM signal transmitted from the radio terminal PS1 to the base station CS, that is, the radio terminal It is a figure which shows a mode after the transmission subcarrier signal is produced | generated by PS1 until base station CS obtains a reception subcarrier signal.
[0033]
In the case of the wireless communication system of the first embodiment, the received signal received by the antenna 3 is converted into a subcarrier signal by the FDM transmitting / receiving unit 2. The subcarrier allocation unit 1 distributes the subcarrier signal obtained by the FDM transmitting / receiving unit 2 to a signal corresponding to each wireless terminal. Here, when the received signal is an access request from the radio terminal PS1, for example, in the base station CS, the propagation environment measuring unit 4 measures the propagation environment from the received signal and outputs the measurement result to the setting control unit 5. Further, the subcarrier allocation unit 1 outputs the number of wireless terminals that perform communication to the setting control unit 5. The setting control unit 5 determines (sets) a band, a subcarrier modulation method, and the like used for communication with each of the radio terminals PS1 to PS3 based on the propagation environment, the number of radio terminals, and the like. The allocator 1 is controlled.
[0034]
As shown in FIG. 5, the subcarrier allocating unit 1 selects the band 52 of the wireless terminal PS2 in communication or the wireless terminal PS3 according to the state of the free channel and the amount of information from all the bands 50 that can be allocated by itself. A band 51 different from the band 53 is allocated. That is, a necessary number of subcarrier signals different from the radio terminals PS2 and 3 are allocated. The radio terminal PS1 and the other radio terminals PS2 and ΡS3 may have different subcarrier modulation schemes, signal transmission bandwidths, and the like. Between the signal transmission bands used for communication between the base station CS and each of the radio terminals PS1 to ΡS3, there is a guard section that does not send signals, and the guard section prevents the signals of each user from interfering with each other. Yes.
[0035]
The setting notification unit 6 converts the content set by the setting control unit 5 into a setting notification signal for the wireless terminal PS1 that communicates with the base station CS. The setting notification signal output from the setting notification unit 6 is input to the subcarrier allocation unit 1, and the subcarrier allocation unit 1 and the signal allocated to each subcarrier in the band of the base station CS as shown in FIG. The signals are collectively converted into a time signal and transmitted from the antenna 3 using a part of the FDM signal. This setting notification signal is transmitted, for example, on a dedicated channel for the setting notification signal. Before the subcarrier for data transmission is allocated to the radio terminal PS1, the subcarrier for data transmission set by the base station CS from the base station CS to the radio terminal PS1 using the dedicated channel for setting notification signal, A setting notification signal for notifying the wireless terminal PS1 of the modulation method and the like is transmitted. After the subcarrier for data transmission is set and data transmission is started, for example, the base station CS uses one of the subcarriers allocated for data transmission to use other data in the OFDM signal. The setting notification signal may be transmitted together with the signal, or the ΟFDM symbol for the setting notification signal may be transmitted periodically using the assigned subcarrier. Here, a generation operation of a signal transmitted from the base station CS to the radio terminal PS1 will be described in detail.
[0036]
In the base station CS, as shown in FIG. 6A, signals are transmitted using M subcarriers with a carrier interval Δf. The M subcarriers also include a guard interval for preventing interference. Among these, the number of subcarriers that can be used for signal transmission to the radio terminal PS1 is m including a guard interval in which no signal is transmitted. The M subcarriers including the m subcarriers addressed to the radio terminal PS1 are converted into signals in the time direction as shown in FIG. 6B by fast inverse Fourier transform, and ΟFDM effective symbols are generated. The generated effective symbols are M sample values with a time interval of 1 / MΔf, and are converted into ΟFDM symbols by D / Α conversion of the transmission processing unit with a guard time added. FIG. 6C shows an OFDM symbol after D / A conversion. The OFDM symbol is converted to a radio frequency and transmitted.
[0037]
When the wireless terminal PS1 receives the ΟFDM symbol, the base station CS converts it to a baseband signal having the center frequency of the m subcarriers transmitted to the wireless terminal PS1, and the reception processing unit 15 performs で / D conversion. After the received signal sample points are obtained, the guard time is removed. At this time, the sampling interval of the received analog signal is 1 / mΔf, which is M / m times longer than the sampling value interval obtained after the fast inverse Fourier transform of the base station CS as shown in FIG. That is, the sampling rate of the wireless terminal ΡS1 is slower than the sampling rate of the fast inverse Fourier transform unit of the base station CS. The fast Fourier transform unit of the wireless terminal ΡS1 performs fast Fourier transform using m sample points after removing the guard time, and assigns it to the wireless terminal ΡS1 at the base station CS as shown in FIG. 6 (e). M subcarrier signals can be obtained. ΡS1 demodulates the digital data sequence by demodulating each subcarrier.
[0038]
In the radio terminal PS1, when the OFDM transmission / reception unit 7 receives the setting notification signal transmitted from the base station CS through the antenna 9, the OFDM transmission / reception unit 7 receives the reception signal input to the reception unit 10 in the reception processing unit 15. Reception processing such as frequency conversion, A / D conversion, synchronization establishment, and guard time removal is performed, and a time signal is output to the fast Fourier transform unit 16. The fast Fourier transform unit 16 collectively converts the input time signal into a subcarrier signal, and the demodulator 17 converts the time signal into a digital data series, that is, a setting notification signal, and then outputs the digital data series to the setting control unit 8.
[0039]
The setting control unit 8 sets the operating environment of the wireless terminal PS1 itself, that is, items such as the band and the subcarrier modulation scheme, based on the input setting notification signal, and thereafter communicates in the operating environment.
[0040]
When a communication signal, such as voice, is input to the transmitter 11 of the OFDM transmitter / receiver 7, the input signal is modulated by the modulator 12, and a subcarrier signal is generated. The subcarrier signal is converted into a time signal by the fast inverse Fourier transform unit 13 and is output after transmission processing such as guard time addition, D / Α conversion, and frequency conversion is performed by the transmission processing unit 14.
[0041]
Here, a generation operation of a signal transmitted from the radio terminal PS1 to the base station CS will be described.
[0042]
In S1, as shown in FIG. 7A, a signal is transmitted using m ′ subcarriers with a carrier interval Δf ′. The m ′ subcarrier also includes a guard interval for preventing interference. Here, as the subcarrier transmitted from the radio terminal PS1 to the base station CS, the same subcarrier transmitted from the base station CS to ΡS1 may be used in a time-sharing manner, so Δf ′ = Δf may be used. . When exactly the same subcarrier is used for transmission and reception, m ′ = m.
[0043]
FIG. 7A shows a subcarrier signal generated by the radio terminal PS1. Each subcarrier interval is Δf ′, and there are m ′ subcarriers including a guard interval. The subcarrier signal is subjected to fast inverse Fourier transform by the fast inverse Fourier transform unit (IFFT) 13 having the number of points m ′, and converted to a discrete signal in the time direction represented by m ′ sample values as shown in FIG. 7B. Is done. At this time, the sample interval is 1 / m′Δf ′. The signal in FIG. 7B is D / A converted, added with a guard time, and converted into an OFDM transmission symbol as shown in FIG. In each wireless terminal, FDM symbols having the same symbol length are generated. The FDM symbols generated by the radio terminals PS1 to PS3 are frequency-converted to different radio frequencies and transmitted to the base station CS.
[0044]
Since the base station CS simultaneously receives the OFDM symbols transmitted from the wireless terminals PS1 to PS3, the reception baseband signal obtained by frequency conversion at the base station CS is transmitted from all the wireless terminals PS1 to PS3. ΟFDM symbols are added by shifting the frequency, as shown in FIG. The base station CS A / D converts the received symbol to obtain the waveform of FIG. The sampling rate of A / D conversion is 1 / M′Δf ′, and when a plurality of wireless terminals PS1 to PS3 communicate with the base station CS using different frequencies, M ′> m ′. That is, the base station CS performs sampling at an interval shorter than the sampling interval of the wireless terminals PS1 to PS3. In other words, each of the wireless terminals PS1 to PS3 performs sampling at an interval wider than the sampling interval of the base station CS.
[0045]
Thus, by making the sampling rate of each of the radio terminals PS1 to PS3 slower than the sampling rate of the base station CS, the digital signal processing circuit (fast inverse Fourier transform unit (IFFT) 13 and high speed) of each of the radio terminals PS1 to PS3. The scale of the Fourier transform unit (FFT) 16 or the like) can be made smaller than the scale of the base station CS.
[0046]
The M ′ sample values obtained in this manner are converted into “sub-carrier signals” by a fast Fourier transform unit (FFT) 16 of “Μ points”. The converted subcarrier signals include m ′ subcarrier signals transmitted from the radio terminal PS1, as shown in FIG. 7 (f). Therefore, the subcarrier allocation unit 1 of the base station CS in FIG. 2 can extract the subcarrier signal transmitted from the radio terminal PS1.
[0047]
As described above, according to the radio communication system of the first embodiment, when there is an access request from the radio terminal PS1 to the base station CS, the base station CS itself assigns all subcarriers that can be allocated to the radio terminals PS1 to PS3. Of the signals, the number of subcarriers corresponding to the amount of information of the radio terminal PS1 is allocated to the radio terminal PS1, and the allocated subcarrier signals are collectively converted into time signals, multiplexed, and transmitted, so that each radio terminal PS1 The subcarriers can be efficiently allocated according to the availability of the channel of PS3 and the amount of information.
[0048]
Also, since the sampling frequency when the radio terminal PS1 converts the received signal from the base station CS into the subcarrier signal is set lower than the sampling frequency when the base station CS converts the subcarrier signal into the time signal at once. The scale of digital signal processing circuits such as the fast inverse Fourier transform unit (IFFT) 13 and the fast Fourier transform unit (FFT) 16 of the radio terminal PS1 can be reduced to a small scale.
[0049]
Further, the sampling frequency when the radio terminal PS1 converts the subcarrier signal into a time signal at a time is set lower than the sampling frequency when the base station CS converts the received signal from the radio terminal PS1 into a subcarrier signal. Therefore, the scale of digital signal processing circuits such as the fast inverse Fourier transform unit (IFFT) 13 and the fast Fourier transform unit (FFT) 16 of the wireless terminal PS1 can be reduced to a small scale.
[0050]
Next, a radio communication system according to a second embodiment of the present invention will be described with reference to FIG. The configuration of the radio communication system of the second embodiment is almost the same as that of the first embodiment, and the subcarrier band is divided according to the type of information (for radio communication or broadcast) on the base station CS side. The only difference is that FIG. 8 is a diagram illustrating the operation of the radio communication system according to the second embodiment, and in particular, the allocation of subcarriers when the base station CS converts broadcast subcarriers and communication subcarriers into time signals at once. This is an example.
In this case, the base station CS is a first band for performing general two-way radio communication with the radio terminals PS1 to PS4 out of all bands 80 that can be allocated to the radio terminals PS1 to PS4. In addition to performing wireless communication using different subcarrier signals in 81, broadcasting using subcarrier signals in the second band 82 different from the first band 81, that is, downlink to a plurality of wireless terminals. Broadcast information provided only in the direction is also converted into a time signal, multiplexed, and transmitted. In addition, OFDM signals having different frequencies may be transmitted from a plurality of base stations.
[0051]
On the other hand, the wireless terminals PS1 to PS4 can receive information using subcarrier signals assigned to themselves for wireless communication even when wireless communication has already been performed.
[0052]
Further, the radio terminals PS1 to PS4 can receive a broadcast by partially receiving only a desired signal from subcarrier signals assigned for broadcasting. As described above, according to the radio communication system of the second embodiment, the base station CS assigns the radio terminals PS1 to PS4 in addition to the subcarriers assigned for communication performed with the individual radio terminals PS1 to PS4. The subcarrier signal allocated to transmit the broadcast information addressed is also collectively converted into a time signal, multiplexed and transmitted, and on the wireless terminals PS1 to PS4 side, the bandwidth of the signal transmitted from the base station CS Among them, a part of them is selectively demodulated and a desired signal is received, so that each wireless terminal PS1 to PS4 can receive a desired signal even in a system in which broadcasting and communication are combined. For example, the wireless terminal PS1 can receive content such as broadcasting, and the other wireless terminals PS2 to PS4 can receive normal wireless signals.
[0053]
【The invention's effect】
As explained aboveBookAccording to the invention,The base station determines, as condition control, at least one of a transmission band, an occupied bandwidth, and a modulation method used in wireless communication from at least one of the number of wireless terminals that have made an access request to itself and a propagation environment. Since the wireless terminal sets its own environment according to the control conditions determined by the base station, it is possible to perform wireless communication using a transmission method and transmission band according to the propagation environment and the condition of the transmission path.
[0056]
Also bookAccording to the invention, the sampling frequency when the wireless terminal converts the received signal from the base station into the subcarrier signal is set lower than the sampling frequency when the base station converts the subcarrier signal into the time signal at once. The scale of the digital signal processing circuit on the wireless terminal side can be reduced to a small scale.
[0057]
In addition, bookAccording to the invention, the sampling frequency used when the base station converts the subcarrier signal into the time signal at a time is set lower than the sampling frequency used when the base station converts the received signal from the radio terminal into the subcarrier signal. The scale of the digital signal processing circuit on the wireless terminal side can be reduced to a small scale.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an OFDΜ wireless communication system according to an embodiment of the present invention.
2 is a block diagram showing a configuration of a base station in the OFDΜ wireless communication system of FIG. 1;
3 is a block diagram showing a configuration of a wireless terminal in the OFDΜ wireless communication system of FIG. 1;
4 is a block diagram showing an internal configuration of an OFD transmission / reception unit of the base station of FIG. 2 and the wireless terminal of FIG. 3;
FIG. 5 is a diagram showing an example of a total bandwidth of a base station and a bandwidth allocated to each wireless terminal.
FIG. 6 is a diagram showing a state of change in an OFDM signal transmitted from a base station to a wireless terminal.
FIG. 7 is a diagram showing a state of change in an OFDM signal transmitted from a wireless terminal to a base station.
FIG. 8 is a diagram showing a subcarrier signal of a base station including a communication band and a broadcast band.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Subcarrier allocation part, 2 ... OFDM transmission / reception part, 3, 9 ... Antenna, 4 ... Propagation environment measurement part, 5 ... Setting control part, 6 ... Setting notification part, 7 ... OFDM transmission / reception part, 8 ... Setting control part, DESCRIPTION OF SYMBOLS 10 ... Reception part, 11 ... Transmission part, 12 ... Modulation part, 13 ... IFFT, 14 ... Transmission processing part, 15 ... Reception processing part, 16 ... FFT, 17 ... Demodulation part, CS ... Base station, PS1-ΡS4 ... Wireless Terminal.

Claims (2)

  1. In a wireless communication system in which a base station and a plurality of wireless terminals perform wireless communication by orthogonal frequency division multiplexing,
    The base station
    Measuring means for measuring a propagation environment of the wireless communication;
    First setting control means for determining an operating environment for communication with the wireless terminal based on a measurement result of the measuring means;
    Notification means for notifying the wireless terminal of the operating environment determined by the first setting control means;
    Subcarrier variable assigning means for assigning a subcarrier signal to the wireless terminal from among a plurality of subcarrier signals assignable for communication with the wireless terminal based on the operating environment determined by the first setting control means. ,
    The wireless terminal includes second setting control means for setting the operating environment notified from the notification means as its own operating environment,
    The sampling frequency when the radio terminal converts the received signal from the base station into a subcarrier signal is set lower than the sampling frequency when the base station converts the subcarrier signal into a time signal at once. A wireless communication system.
  2. In a wireless communication system in which a base station and a plurality of wireless terminals perform wireless communication by orthogonal frequency division multiplexing,
    The base station
    Measuring means for measuring a propagation environment of the wireless communication;
    First setting control means for determining an operating environment for communication with the wireless terminal based on a measurement result of the measuring means;
    Notification means for notifying the wireless terminal of the operating environment determined by the first setting control means;
    Subcarrier variable assigning means for assigning a subcarrier signal to the wireless terminal from among a plurality of subcarrier signals assignable for communication with the wireless terminal based on the operating environment determined by the first setting control means. ,
    The wireless terminal includes second setting control means for setting the operating environment notified from the notification means as its own operating environment,
    The sampling frequency when the wireless terminal converts subcarrier signals into time signals at once is set lower than the sampling frequency when the base station converts received signals from the wireless terminals into subcarrier signals. A wireless communication system.
JP17466397A 1997-06-30 1997-06-30 Wireless communication system Expired - Fee Related JP3670445B2 (en)

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