Patent Application
20090303948
The present invention relates to an OFDMA communication system, base station, and communication method.
As a wireless access scheme of a digital portable telephone system, a PHS system, etc., a TDMA (Time Division Multiple Access) and TDD (Time Division Duplex) scheme in which TDMA and TDD are combined has been adopted. Additionally, an OFDMA (Orthogonal Frequency Division Multiplexing Access) scheme using OFDMA has been proposed.
The OFDM is a scheme for dividing a carrier to modulate data into a plurality of “subcarriers” (subdivided carriers) orthogonal to each other and distributing and transmitting a data signal in each subcarrier.
Hereinafter, the overview of the OFDM scheme will be described.
The parallel data is allocated to each subcarrier configuring OFDM and mapped in a frequency domain. Here, each subcarrier is modulated by BPSK, QPSK, 16QAM, 64QAM, etc. The mapping data is transformed from frequency-domain transmission data to time-domain transmission data by performing an IFFT operation. Thereby, multicarrier modulation signals into which a plurality of subcarriers orthogonal to each other are modulated independently are generated. An output of the IFFT unit 202 is supplied to a guard interval adding unit 203.
As shown in
The orthogonal modulation unit 204 orthogonally modulates a base-band OFDM signal supplied from the guard interval adding unit 203 using a carrier signal supplied from a local oscillator 105 of the OFDM modulation device, and performs frequency conversion into an intermediate frequency (IF) signal or a radio frequency (RF) signal. That is, after frequency-converting the base-band signal into a desired transmission frequency band, the orthogonal modulation unit outputs it to a transmission path.
An OFDM reception signal input to the OFDM demodulation device is supplied to an orthogonal demodulation unit 211. The orthogonal demodulation unit 211 orthogonally demodulates the OFDM reception signal using a carrier signal supplied from a local oscillator 212 of the OFDM demodulation device, performs frequency conversion from an RF signal or an IF signal to a base-band signal, and obtains a base-band OFDM signal. The OFDM signal is supplied to a guard interval removing unit 213.
The guard interval removing unit 213 removes a signal added by the guard interval adding unit 203 of the OFDM modulation device according to a timing signal supplied from a symbol timing synchronizing unit (not shown). A signal obtained by the guard interval removing unit 213 is supplied to a fast Fourier transform (FFT) unit 214.
The FFT unit 214 performs transformation to frequency-domain reception data by performing an FFT operation on input time-domain reception data. De-mapping is performed in the frequency domain and parallel data is generated for each subcarrier. Here, the demodulation to the modulation of BPSK, QPSK, 16QAM, 64QAM, etc. performed for each subcarrier is performed. Parallel data obtained by the FFT unit 214 is supplied to a parallel/serial conversion unit 215 and output as reception data.
Above-described, the OFDM is a scheme for dividing a carrier into a plurality of subcarriers. The OFDMA is a scheme for collecting and grouping a plurality of subcarriers among subcarriers in the above-described OFDM and performing multiplex communication by allocating one or more groups to each user. Each group described above is called a subchannel. That is, each user performs communication using one or more subchannels allocated. According to a communication data amount, a propagation environment, etc., subchannels are adaptively increased/decreased and allocated.
Patent Document 1 discloses a method for adaptively varying and allocating pilot carriers according to a channel environment of each subchannel. This allocation method allocates a small number of pilot carriers when the channel environment is good and allocates a large number of pilot carriers when the channel environment is bad. Thereby, the number of subchannels capable of being allocated to one user is varied.
Patent Document 1: JP-A-2005-520432
In the above-described art, a base station releases an unnecessary subchannel for another user terminal when transmission data is temporarily decreased while communication of a user terminal is in progress.
When a transmission data amount of the user terminal has increased again, it must wait for a subchannel allocated for another user terminal to be released so as to re-use the released-subchannel. At this time, since the number of avaliable subchannels has decreased even when a communication data amount of the user terminal has increased again, there is a problem in that the communication throughput of the user terminal is not increased and a time is required until data transmission is completed.
When the subchannel is allocated, carrier sensing is required to pre-check whether or not the subchannel is available. Since carrier sensing is performed for all subchannels when a data amount is increased and a subchannel is newly allocated, its process is time-consuming. Consequently, since the subchannel allocation is time-consuming, the communication throughput of the user terminal is lowered.
In the above-described case, the communication throughput corresponding to QoS cannot be provided to a user terminal.
The present invention has been made to solve the above-described problem, and an object of the invention is to obtain an OFDMA communication system, base station, and communication method that can continue communication without lowering the throughput of communication in a user terminal even when transmission data is decreased temporarily and then increased again while communication of the user terminal is in progress and can provide the throughput corresponding to QoS to the user terminal.
To solve the above-described problem, a communication system according to the present invention is an OFDMA communication system for performing communication using one or more subchannels between a base station and a plurality of terminals, characterized by including: a communication data amount acquisition unit that acquires a communication data amount; and a channel allocation unit that allocates the subchannels according to the communication data amount, wherein when the communication data amount has decreased, the channel allocation unit maintains the subchannel allocation based on a pre-given priority about corresponding communication (claim 1).
It is characterized in that the channel allocation unit determines the number of subchannels to be maintained among the allocated subchannels on the basis of the priority (claim 2).
It is characterized in that the channel allocation unit determines a time for maintaining an allocated subchannel on the basis of the priority (claim 3).
It is characterized in that the priority is a QoS class (claim 4).
A base station according to the present invention is an OFDMA base station for communicating with a plurality of terminals using one or more subchannels, characterized by including: a communication data amount acquisition unit that acquires a communication data amount for a terminal in which communication has been established; and a channel allocation unit that allocates the subchannels to the terminal in which the communication has been established according to the communication data amount, wherein when a communication data amount for the terminal in which the communication has been established has decreased, the channel allocation unit maintains the subchannel allocation based on a pre-given priority about corresponding communication (claim 5).
It is characterized in that the channel allocation unit determines the number of subchannels to be maintained among the allocated subchannels on the basis of the priority (claim 6).
It is characterized in that the channel allocation unit determines a time for maintaining an allocated subchannel on the basis of the priority (claim 7).
A communication method according to the present invention is an OFDMA communication method for performing communication using one or more subchannels between a base station and a plurality of terminals, characterized by including: a communication data amount acquisition step of acquiring a communication data amount; and a channel allocation step of allocating the subchannels according to the communication data amount, wherein when the communication data amount has decreased, the channel allocation step maintains the subchannel allocation based on a pre-given priority about corresponding communication (claim 8).
According to the present invention, when an amount of communication data between a base station and a terminal in which communication has been established has decreased, allocation is maintained without releasing at least one of a plurality of data-free subchannels and allocation to another terminal is not performed. When the terminal communication has increased again, the throughput corresponding to QoS can be provided to a user terminal without lowering the communication throughput.
15-4: QoS CLASS ACQUISITION UNIT
Hereinafter, an exemplary embodiment of a communication system according to the present invention will be described in detail with reference to the drawings.
This communication system is an OFDMA communication system for performing communication by a frame configured by a plurality of subchannels for each frequency band between a base station (CS: cell station) and a plurality of terminals (PS: personal station).
For example, the frame configuration. of
In
The above-described first frequency band can be the highest frequency band or the lowest frequency band. The control subchannel indicates which subchannel of each time slot is used in each frequency band.
The example of
In the remaining 27 frequency bands, traffic subchannels T1 to T108 for transmitting and receiving data are configured and a total of 108 subchannels are configured since 27 subchannels are configured in the frequency direction and 4 subchannels are configured in the time-axis direction.
The traffic subchannels are configured by anchor subchannels and extra subchannels.
The anchor subchannel is a subchannel used to provide each terminal with a notification indicating which user uses which subchannel or used for the base station and the terminal to negotiate whether data has been accurately exchanged in retransmission control.
The extra subchannel is a subchannel for transmitting data to be used actually, and an arbitrary plurality of extra subchannels can be allocated to one terminal. In this case, as the number of allocated extra subchannels increases, high-speed communication is possible since a band extends.
Next, a configuration of a base station to be used in this communication system will be described.
As shown in
The control unit 15 acquires a communication data amount (a communication data amount acquisition unit) and allocates subchannels according to the communication data amount (a channel allocation unit). When the communication data amount has decreased, control is performed to maintain at least one of the allocated subchannels.
Thus, the control unit 15 has an ESCH (extra subchannel) setting unit 15-1 for setting allocation for each terminal of an extra subchannel (ESCH) to be used by communication, an ESCH allocation maintaining control unit 15-2 for commanding the ESCH (extra subchannel) setting unit 15-1 to release an extra subchannel and commanding an invalid signal (disapproval-indicating signal) generation unit 15-3 to maintain extra subchannel allocation, by determining whether or not to start allocation maintaining of an extra subchannel without transmission data, the invalid signal (disapproval-indicating signal) generation unit 15-3 for generating an invalid signal (disapproval-indicating signal) in a V field of a PHY frame of an extra subchannel, and a QoS class acquisition unit 15-4 for acquiring information about a QoS class of the user from the storage unit 16.
In the communication system according to the exemplary embodiment of the present invention, a determination as to whether or not to continue a subchannel connection is performed by a difference in the degree of occupancy of the extra subchannel (ESCH) on the basis of QoS information of the terminal.
Thereby, the throughput corresponding to the QoS information can be provided to the user.
QoS (Quality of Service) is a function for reserving a specific communication band and guaranteeing the quality of seamless data transmission.
A QoS class included in the QoS information is a class divided according to a communication priority, and, for example, can be classified into three types of streaming, file transmission, and best effort. The streaming is a class in which the delay or stop of communication such as a real-time distribution of voice or video, a video-phone call, etc. is not allowed, and is set to class 1 whose priority is highest.
The file transmission is a class that is good when a degree of band for an electronic file is secured and is set to class 2 whose priority is lower than that of the streaming.
The best effort is a class in which QoS is not guaranteed and is set to class 3 whose priority is lowest.
An extra subchannel allocation maintaining flow in the base station of the OFDMA communication system according to the exemplary embodiment of the present invention will be described.
The allocation maintaining flow is started.
The QoS class acquisition unit 15-4 of the base station 1 acquires information about a QoS class of a user from the storage unit 16 (step S1).
The control unit 15 sets a communication band according to the acquired QoS class (step S2). For example, when it is classified into three types of classes (classes 1 to 3), a communication band to be allocated to class 1 with the highest priority is set to the broadest band. A communication band to be allocated to class 2 with the second highest priority is set to an intermediate level band. A communication band to be allocated to class 3 with the lowest priority is set to the narrowest band.
The ESCH setting unit 15-1 establishes communication by setting allocation for every terminal of an extra subchannel (ESCH) to be used by the communication (step S3).
The ESCH allocation maintaining control unit 15-2 determines whether or not transmission data is present within each extra subchannel which is being used by communication between the base station and the terminal (step S4), and data transmission is continued directly (step S5) in the case of the extra subchannel determined to have transmission data (Y of step S4).
In the case of the extra subchannel without transmission data (N of step S4), the ESCH allocation maintaining control unit 15-2 determines whether or not to start the allocation maintaining of the extra subchannel (step S6), and commands the ESCH setting unit 15-1 to release the extra subchannel when it is determined that the allocation maintaining is not started (step S8), and terminates the allocation maintaining flow.
When it is determined that the allocation maintaining is started (Y of step S6), a command is sent to the invalid signal (disapproval-indicating signal) generation unit 15-3 and an invalid signal (disapproval-indicating signal) is contained and transmitted in a V field of a PHY frame, so that a data-free extra subchannel is transmitted continuously (the allocation is maintained). The control unit 15 determines whether a predetermined allocation maintaining time has elapsed (step S7) and returns to the process of step S4 when the allocation maintaining time has elapsed (Y of step S7).
Whether to release an extra subchannel without transmission data or maintain its allocation determines the number of extra subchannels to be released and the number of extra subchannels for maintaining the allocation according to the QoS class. For example, when it is classified into the above-described three types of classes (classes 1 to 3), class 1 releases no extra subchannel, class 2 releases a half of extra subchannels, and class 3 releases a quarter of extra subchannels.
When the extra subchannel allocation is maintained, an allocation maintaining time is changed according to the QoS class. For example, when it is classified into the three types of classes (classes 1 to 3), a predetermined allocation maintaining time is allocated so that t1>t2>t3, where the allocation maintaining time of class 1 is t1, the allocation maintaining time of class 2 is t2, and the allocation maintaining time of class 3 is t3.
Preferably, a released subchannel is allocated to an extra subchannel without being allocated to an anchor subchannel of another terminal. This is because the anchor subchannel is not released until a communication connection is terminated, for example, even though a transmission data amount has decreased when it is allocated to the anchor subchannel of the other terminal, but there is a possibility that it may be released again in the case of the extra subchannel.
A communication method according to the exemplary embodiment of the present invention will be described in detail using the sequence of a communication procedure between a terminal and a base station shown in
Types of subchannels (a control channel (CCH) and an anchor subchannel (ASCH) and an extra subchannel (ESCH) configuring a traffic channel (TCH)) to be communicated in a terminal (PS) and a base station (CS) are divided and shown.
This communication method continuously sends a signal from the base station to the terminal for a given time even when user data decreases temporarily and prevents the base station from allocating the extra subchannel (ESCH) to another terminal. As shown in
In
(1-1) Connection Procedure
At a connection time, a connection is made in the same sequence as that of an existing PHS system.
A link channel (LCH) establishment (decision) signal is transmitted by the control channel (CCH) from the terminal to the base station.
Carrier sensing is performed in the base station.
A link channel (LCH) assignment (allocation) signal is transmitted by the control channel (CCH) from the base station to the terminal.
Carrier sensing is performed in the terminal.
As described above, before an anchor subchannel (ASCH) connection, the carrier sensing is surely performed in both the base station and the terminal. Thereby, the control of a stable band can be used.
(1-2) Extra Subchannel Allocation and Communication Establishment
When an unused subchannel as the extra subchannel (ESCH) is allocated to the terminal, carrier sensing is performed.
A ranging request (band setting request) is transmitted by the anchor subchannel (ASCH) from the terminal to the base station in an RCH field.
The extra subchannel (ESCH) request/allocation signal is transmitted through the anchor subchannel (ASCH).
Carrier sensing is performed in the base station.
A ranging response (band setting) is transmitted by the anchor subchannel (ASCH) in a MAP field from the base station to the terminal.
User data transmission/reception between the base station and the terminal is started.
A ranging request (band setting request) is transmitted by the anchor subchannel (ASCH) in an RCH field from the terminal to the base station.
Carrier sensing is performed in the base station.
Since an unused subchannel as the extra subchannel (ESCH) is allocated to the terminal when the extra subchannel (ESCH) is added, carrier sensing is performed.
(1-3) Extra Subchannel (ESCH) Allocation Maintaining
A ranging response (band setting) is transmitted by the anchor subchannel (ASCH) in a MAP field from the base station to the terminal.
User data is transmitted/received between the base station and the terminal.
In the case where communication data has decreased when the user data is transmitted/received, “Invalid” which is a disapproval-indicating signal is contained in a V field of the anchor subchannel and continuously transmitted from the terminal to the base station (communication continuation). At this time, allocation is continuously maintained without releasing the extra subchannel (ESCH).
At this time, the number of extra subchannels to be released and the number of extra subchannels for maintaining the allocation are determined according to the QoS class. When the extra subchannel allocation is maintained, the allocation maintaining time is changed according to the QoS class.
When data has increased again, user data is transmitted using the above-described extra subchannel (ESCH) whose allocation is continuously maintained without being released.
(1-4) Communication Termination
A communication channel (TCH) release request is performed by the control channel (CCH) from the base station to the terminal.
Communication is terminated by a call disconnection.
Next, a sequence of an OFDMA communication method when QoS is not considered will be described as a comparative example.
(2-1) Connection Procedure
At a connection time, a connection is made in the same sequence as that of an existing PHS system.
A link channel (LCH) establishment (decision) signal is transmitted by the control channel (CCH) from the terminal to the base station.
Carrier sensing is performed in the base station.
A link channel (LCH) assignment (allocation) signal is transmitted by the control channel (CCH) from the base station to the terminal.
Carrier sensing is performed in the terminal.
As described above, before an anchor subchannel (ASCH) connection, the carrier sensing is surely performed in both the base station and the terminal. Thereby, the control of a stable band can be used.
(2-2) Extra Subchannel Allocation and Communication Establishment
A ranging request (band setting request) is transmitted by the anchor subchannel (ASCH) in an RCH field from the terminal to the base station.
A band setting signal, that is, an extra subchannel (ESCH) request/allocation signal, is transmitted through the anchor subchannel (ASCH).
Carrier sensing of the anchor subchannel (ASCH) of the base station is performed.
A ranging response (band setting) is transmitted by the anchor subchannel (ASCH) in a MAP field from the base station to the terminal.
User data is transmitted/received between the base station and the terminal.
A ranging request (band setting request) is transmitted by the anchor subchannel (ASCH) in an RCH field from the terminal to the base station.
Carrier sensing of the anchor subchannel (ASCH) of the base station is performed.
A ranging response (band setting) is transmitted by the anchor subchannel (ASCH) in a MAP field from the base station to the terminal.
User data is transmitted/received between the base station and the terminal.
(2-3) Extra Subchannel (ESCH) Release
The terminal is notified that the extra subchannel (ESCH) has been released using the MAP of the anchor subchannel (ASCH) from the base station to the terminal. At this time, the terminal does not continue the downlink transmission (from the base station to the terminal) on the released extra subchannel (ESCH).
User data is transmitted/received between the base station and the terminal.
A ranging request (band setting request) is transmitted by the anchor subchannel (ASCH) in an RCH field from the terminal to the base station.
Since the base station allocates an unused subchannel as the extra subchannel even when the released extra subchannel (ESCH) is allocated on the basis of a band addition request, carrier sensing of the anchor subchannel (ASCH) of the base station is performed.
When communication is performed without considering QoS, carrier sensing is needed upon addition of the extra subchannel (ESCH).
A ranging response (band setting) is transmitted by the anchor subchannel (ASCH) in a MAP field from the base station to the terminal.
User data is transmitted/received between the base station and the terminal.
(2-4) Communication Termination
A communication channel (TCH) release request is performed by the control channel (CCH) from the base station to the terminal.
Communication is terminated by a call disconnection.
According to the present invention as described above, when an amount of communication data between a base station and a terminal in which communication has been established has decreased, allocation is maintained without releasing at least one of a plurality of subchannels and allocation to another terminal is not performed. When the terminal communication has increased again, the communication throughput is not lowered. A QoS service can be provided to a user terminal by changing the number of subchannels for maintaining the allocation or a maintaining time according to a QoS class.
Priority is claimed on Japanese Patent Application No. 2006-254386, filed Sep. 20, 2006 and Japanese Patent Application No. 2006-347754, filed Dec. 25, 2006, the contents of which are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-254386 | Sep 2006 | JP | national |
| 2006-347754 | Dec 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/068211 | 9/19/2007 | WO | 00 | 7/16/2009 |
