Wireless communication system, wireless communication terminal, base station and wireless communication method

The present invention relates to wireless communication systems, wireless communication terminals and base stations, and wireless communication methods.

In recent years, in mobile communication, there has been a demand for a communication method capable of assigning channels in a wide band and changing the channel band at high speed in response to a demand for communication speed and a demand for securing the number of users. As a method to realize this, WiMAX (Worldwide Interoperability for Microwave Access: IEEE802.16 series), which adopts the OFDMA (Orthogonal Frequency Division Multiple Access) method as a multiple access technology, is attracting attention as a next-generation broadband mobile communication system. There is.

In this WiMAX, one wide frequency band can be referred to by multiple terminals, and a specific part (frequency and timing) of the referenceable band can be assigned to each terminal as an information providing part (MAP). It is supposed to be. In such WiMAX, when a plurality of cells are arranged to cover a wide service area, the frequency and timing of the MAP are determined for each cell so that the MAPs do not interfere with each other. In this case, since there is an upper limit to the number of frequency combinations that the MAP can take, it is necessary to design the cells so that the cells having the same frequency in the MAP do not overlap in radio waves.<nplcit num="1"><text>"Second Generation Cordless Telephone System Standard RCR STD-28" Association of Radio Industries and Businesses (ARIB)</text></nplcit><nplcit num="2"><text>"WiMAX Standard 802.16_2004" WiMAX FORUM</text></nplcit>

<p> However, in order for the cell design as described above to be effective, the error range (including the one over time) of the actual area with respect to the area assumed by the cell needs to be sufficiently small. Therefore, in an environment such as an urban area where the error range of the area is likely to expand, the area must be sufficiently large in consideration of the error. Such expansion of the area causes an increase in transmission power and communication delay, and there is a problem that the influence of interference is likely to occur as the number of users increases.</p><p> On the other hand, in order to avoid the above-mentioned problems related to cell design, there is also a method of not performing cell design. That is, like the conventional PHS (Personal Handyphone System), autonomous distributed control is performed between base stations using a shared control channel (CCH) that can be used at a predetermined cycle for each base station, thereby performing MAP, etc. There is a method of communicating by making the communication timing of control information (that is, the timing of using a shared control channel) different for each cell. However, according to this method, the communication timing of the control information must be prepared for the maximum number of cells in which interference between cells can occur. Therefore, one base station can use the communication timing, that is, shared control. The cycle in which the channel can be used becomes long (about 100 ms cycle). As a result, the cycle in which the communication band can be changed for one terminal becomes long, and there arises a problem that the utilization efficiency of wireless resources decreases.</p><p> The present invention has been made in view of the above-mentioned circumstances, and does not require cell design (transmission power and area are small), is capable of high-speed band variable, and is capable of wideband, band variable, and multi-user movement. The purpose is to realize physical communication.</p>

<p> In order to achieve the above object, in the present invention, as a first solution relating to a wireless communication system, a base station and a wireless communication terminal communicate with each other by the OFDMA method, and each base station is used at a predetermined cycle. A wireless communication system that communicates using a possible shared control channel and a plurality of traffic channels that can be adaptively assigned to each wireless communication terminal, wherein the wireless communication terminal is via the shared control channel. The base station includes a channel requesting means for requesting the base station to allocate an individual control channel, and a communication control means for wirelessly connecting the individual control channel assigned from the base station to communicate control information. When a request for allocation of the individual control channel is received from the wireless communication terminal via the shared control channel, any one of the traffic channels is used as an individual control channel dedicated to the wireless communication terminal.<u style="single">Adaptively</u>A channel allocating means for allocating is provided, and the channel allocating means allocates a traffic channel for data communication, and allocates information of the traffic channel for data communication via the individual control channel.<u style="single">Every frame</u>The communication control means has a function of transmitting to a wireless communication terminal, and the communication control means wirelessly connects a traffic channel for data communication indicated by the traffic channel allocation information obtained via the individual control channel to the base station. It is characterized by performing data communication.</p><p> Further, in the present invention, the first aspect relating to a wireless communication system<u style="single">2</u>As the first solution, the wireless communication terminal includes a first determination means for determining the channel quality of a traffic channel for data communication assigned by the base station, and the communication control means. Is to transmit information for rejecting the traffic channel for data communication assigned from the base station to the base station via the individual control channel based on the determination result by the first determination means. It is a feature.</p><p> Further, in the present invention, the first aspect relating to a wireless communication system<u style="single">3</u>As a solution to<u style="single">Or the second</u>In any of the above-mentioned solutions, the base station includes a second determination means for determining the channel quality of the uplink of each wireless communication terminal, and the channel allocation means is based on the determination result by the second determination means. Based on this, the individual control channel to be assigned to the wireless communication terminal and the traffic channel for data communication are determined.</p><p> Further, in the present invention, as a first solution relating to a wireless communication terminal, a shared control channel that communicates with a base station by an OFDMA method and can be used at a predetermined cycle for each base station is adapted from the base station. A wireless communication terminal that communicates with a traffic channel assigned to the base station, and provides control information including traffic channel allocation information for data communication to the base station via the shared control channel. From the channel requesting means for requesting the allocation of individual control channels to be communicated and the base station.<u style="single">Adaptively</u>Wirelessly connect the assigned individual control channels to communicate the control information.<u style="single">Every frame</u>It is characterized by comprising a communication control means for performing the communication.</p><p> Further, in the present invention, the first aspect relating to a wireless communication terminal.<u style="single">2</u>In the first solution, the first determination means for determining the channel quality of the traffic channel for data communication assigned by the base station is provided, and the communication control means is the first. Based on the determination result by the determination means, information for rejecting the traffic channel for data communication assigned from the base station is transmitted to the base station via the individual control channel.</p><p> Further, in the present invention, as the first solution relating to the base station, the above-mentioned first solution is used.<u style="single">Or the second</u>When a request for allocation of the individual control channel is received from a wireless communication terminal having the solution of the above via the shared control channel, any of the traffic channels is assigned as an individual control channel dedicated to the wireless communication terminal. It is characterized by providing means.</p><p> Further, in the present invention, as a second solution for a base station, in the first solution, the channel allocation means allocates a traffic channel for data communication, and the individual control channel is used. It is characterized by having a function of transmitting traffic channel allocation information for data communication to a wireless communication terminal.</p><p> Further, in the present invention, as the third solution means for the base station, the first or second solution means the second determination means for determining the channel quality of the uplink channel of each wireless communication terminal. The channel allocation means is characterized in that an individual control channel and a traffic channel for data communication to be assigned to the wireless communication terminal are determined based on the determination result by the second determination unit.</p><p> Further, in the present invention, as a first solution relating to a wireless communication method, a shared control channel that communicates between a base station and a wireless communication terminal by an OFDMA method and can be used at a predetermined cycle for each base station is provided. , A wireless communication method in which communication is performed using a plurality of traffic channels that can be adaptively assigned to each wireless communication terminal, wherein the wireless communication terminal communicates with the base station via the shared control channel. The first step of requesting the allocation of an individual control channel for communicating control information including the traffic channel allocation information for data communication, and the base station of the individual control channel from the wireless communication terminal via the shared control channel. When an allocation request is received, one of the traffic channels is used as an individual control channel dedicated to the wireless communication terminal.<u style="single">Adaptively</u>The second step of allocating and the wireless communication terminal wirelessly connect the traffic channel for data communication indicated by the traffic channel allocation information obtained through the individual control channel assigned from the base station to the base station. Perform data communication with<u style="single">Do it every frame</u>It is characterized by having a third step.</p>

<p> According to the present invention, in a wireless communication system that communicates using a shared control channel that can be used in a predetermined cycle for each base station and a plurality of traffic channels that can be adaptively assigned to each wireless communication terminal. , One of the traffic channels is assigned as an individual control channel dedicated to the wireless communication terminal, and control information is communicated with the base station in units of 1 frame (5 ms) via the individual control channel, so wireless resources are extremely fast. (Band) allocation control can be performed. Therefore, it is possible to realize mobile communication corresponding to a wide band, a variable band, and a large number of users, which does not require a cell design (transmission power and area are small) and can change a band at high speed.</p>

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a main configuration of a wireless communication system, a base station, and a wireless communication terminal according to the present embodiment. As shown in FIG. 1, the wireless communication system in this embodiment includes a base station CS and a wireless communication terminal T.

Although a plurality of base station CSs are provided at regular distance intervals, for example, only one base station CS is shown in FIG. 1 for simplification of illustration, and the base station CSs are a plurality of wireless communications. Although wireless communication is performed with the terminal T, one wireless communication terminal T is illustrated in FIG. Further, in the following description, the wireless communication system in the present embodiment uses the orthogonal frequency division multiple access method (OFDMA) as the multiple access technology in addition to the time division multiple access method (TDMA) and the time division duplex system (TDD). It shall be adopted. In the following, the wireless communication terminal T will be referred to as a terminal T.

As shown in FIG. 1, the base station CS includes a control unit 1, a wireless communication unit 2, and a storage unit 3, and the control unit 1 has a channel quality determination unit 1a (second determination means) as its functional element. , QoS control unit 1b and scheduler 1c (channel allocation means) are provided. Further, this base station CS is connected to the public network N, and can communicate with other base stations, servers, etc. connected to the public network N via the public network N.

In the base station CS, the control unit 1 is based on the base station control program stored in the storage unit 3, the received signal acquired via the wireless communication unit 2, and the external signal acquired via the public network N. Controls the overall operation of this base station CS. In this control unit 1, the channel quality determination unit 1a determines the quality of the uplink channel of each terminal T based on the quality element of the channel acquired via the wireless communication unit 2, and outputs the determination result to the scheduler 1c. To do. As the quality factor for determining the quality of the uplink, when determining the quality of a channel that has already communicated and has a desired wave, SINR (SINR) indicating the channel quality based on the strength of the interfering wave with respect to the desired wave. Signal-to-Interference. And Noise Power Ratio: Signal-to-Noise Ratio (SNR), CINR (Carrier-to-Interference.). And Noise Power Ratio), CNR (Carrier to Noise Ratio), communication rate after demodulation, etc. are used. When determining the quality of a channel that has not yet been used when allocating a channel, RSSI (Received Signal Strength Indicator) indicates the strength of the signal received (carrier sense) on that channel, that is, the strength of the signal that becomes an interfering wave. Etc. are used.

The QoS control unit 1b assigns a service class to the terminal T based on the user priority of the application operating in the upper layer and the terminal T to be connected to the communication, allocates the radio resource according to the service class, and determines the communication timing. Request scheduler 1c to make an allocation. Although details will be described later, the radio resources are allocated in units of OFDMA subchannels (hereinafter simply referred to as subchannels), and communication timing is allocated in units of TDMA slots (hereinafter simply referred to as slots).

The scheduler 1c uses the service class assigned to the terminal T to be communicated, the state of the packet queue between the base station CS and the terminal T, and the determination result of the channel quality determination unit 1a (that is, the channel quality of the uplink channel). Based on the above, scheduling regarding the allocation of subchannels and slots to the terminal T is performed. In addition, this scheduler 1c allocates a packet coding rate and a modulation method according to the channel quality of the uplink channel. As the slots, both the down channel slot and the up channel slot are scheduled.

Here, the scheduling of the sub-channel, the downlink channel slot, and the uplink channel slot in the scheduler 1c will be described in detail. As described above, in the OFDMA system, a plurality of subcarriers having an orthogonal relationship are shared by a plurality of terminals T, and an arbitrary plurality of subcarriers are used at an arbitrary communication timing (since TDMA is adopted in this embodiment, this communication timing is a slot. This is a technology that realizes multiple access by adaptively allocating to each terminal T and positioning it as a subchannel. Figure 2 shows the relationship between such subchannels and TDMA slots. In FIG. 2, the vertical axis represents frequency and the horizontal axis represents time.

As shown in FIG. 2, one subchannel in one frequency channel is used as a shared control channel (CCH) that can be used in a predetermined period (about 100 ms) for each base station, and the remaining frequency channels are traffic channels. Used as (TCH). And, like the conventional PHS (PHS that does not use OFDMA), there are 4 TDMA slots per frame for both the downlink channel and the uplink channel, and since TDD is adopted, the downlink channel and the uplink channel are used. Subchannels are used symmetrically for both purposes.

In the present embodiment, one of the above TCHs is assigned as an individual control channel dedicated to the terminal T (hereinafter referred to as an anchor subchannel: ASCH). Further, in the present embodiment, the TCH assigned for data communication is referred to as an extra subchannel (ESCH). That is, the CCH in the present embodiment is shared among all base stations and all terminals as in the conventional PHS, and the period of timing at which one base station CS can use the CCH is very long (about 100 ms). However, since the ASCH in this embodiment is assigned from the TCH, it can be used every 1 frame period (5 ms). In the following, the schedule information of the subchannel as shown in Fig. 2 is referred to as MAP.

The CCH is used for communication of LCH allocation request and response, incoming call request to terminal T, system notification information, etc., as in the conventional PHS, while the ASCH is used for communication of ESCH allocation information. Will be done.

The control unit 1 transmits ASCH and ESCH, modulation method, and code rate allocation information to the terminal T via the wireless communication unit 2 based on the scheduling by the scheduler 1c as described above, and also by the scheduling described above. The wireless communication unit 2 is controlled so as to perform modulation and error correction coding at the determined modulation method and coding rate.

Under the control of the control unit 1, the wireless communication unit 2 performs error correction coding, modulation, and multiplexing by OFDMA of the control signal or data signal output from the control unit 1, and RFs the multiplexed signal (OFDMA signal). After frequency conversion to the frequency band, it is transmitted to the terminal T as a transmission signal.

More specifically, as shown in FIG. 3, the transmitter side of the wireless communication unit 2 has an error correction coding unit 2a, an interleaver 2b, a serial-parallel transform unit 2c, a digital modulation unit 2d, and an IFFT (Inverse Fast Fourier). It has a Transform) section 2e, a GI (Guard Interval) addition section 2f, and a transmitter section 2g.

The error correction coding unit 2a is, for example, a FEC (Forward Error Correction) encoder, and has redundant information in a bit string of a control signal or a data signal input from the control unit 1 based on the coding rate assigned by the scheduler 1c. The error correction code is added and output to interleaver 2b. The interleaver 2b performs interleaving processing on the bit string to which the error correction code is added by the error correction coding unit 2a. The serial-parallel conversion unit 2c divides the bit string after the interleaving process into bit units for each subcarrier included in the ASCH or ESCH assigned by the scheduler 1c and outputs the bit string to the digital modulation unit 2d.

The same number of digital modulation units 2d as the subcarriers are provided, and the bit data divided for each subcarrier is digitally modulated using the subcarrier corresponding to the bit data, and the modulated signal is output to the IFFT unit 2e. To do. Each digital modulation unit 2d is digitally modulated using the modulation method assigned by the scheduler 1c, for example, BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM, etc. I do.

The IFFT unit 2e generates an OFDMA signal by performing inverse Fourier transform on the modulation signal input from each digital modulation unit 2d and orthogonally multiplexes the modulation signal, and outputs the OFDMA signal to the GI addition unit 2f. The GI addition unit 2f adds a guard interval (GI) to the OFDMA signal input from the IFFT unit 2e and outputs it to the transmission unit 2g. The transmission unit 2g frequency-converts the OFDMA signal input from the GI addition unit 2f into an RF frequency band and transmits it to the terminal T as a transmission signal.

On the other hand, although not shown, the receiver side of the wireless communication unit 2 includes a component that performs an operation opposite to that of the transmitter side. That is, the receiver side of the wireless communication unit 2 frequency-converts the received signal received from the terminal T into the IF frequency band, extracts the received OFDM signal, removes the guard interval from the received OFDM signal, performs FFT processing, and digitally. The bit string is reconstructed by demodulation, parallel-serial conversion processing, deinterleaver processing, and error correction / decoding processing, and output to the control unit 1.

Returning to FIG. 1, the storage unit 3 stores the base station control program and other various data used in the control unit 1, and also serves as a buffer used for flow control, retransmission control, etc. in the control unit 1. Has the function of.

Next, the configuration of the terminal T will be described. As shown in FIG. 1, the terminal T includes a communication control unit 10 (communication control means), a wireless communication unit 11, an operation unit 12, a display unit 13, and a storage unit 14. Further, the communication control unit 10 includes a channel request unit (channel request means) 10a as its functional element.

In the terminal T, the communication control unit 10 bases the terminal T based on the terminal control program stored in the storage unit 13, the reception signal acquired via the wireless communication unit 11, and the operation signal input from the operation unit 12. Controls the overall operation of. In this communication control unit 10, when the channel request unit 10a receives a communication request from the upper control means of the own terminal (for example, an upper layer application operating in the control unit 10) or the base station CS, the channel request unit 10a sends the ASCH to the base station CS. An ASCH allocation request signal for requesting allocation is generated, and the ASCH allocation request signal is transmitted to the base station CS via the radio communication unit 11. The above CCH is used for transmitting this ASCH allocation request signal. Further, the communication control unit 10 wirelessly connects the ASCH assigned from the base station CS to communicate control information, and data indicated by the ESCH allocation information obtained from the base station CS via the ASCH. Wirelessly connect ESCH for communication to perform data communication with base station CS.

Under the control of the communication control unit 10, the wireless communication unit 11 performs error correction coding, digital modulation, and multiplexing by OFDMA of the control signal or data signal output from the communication control unit 10, and performs multiplexing signals (OFDMA signals). ) Is frequency-converted to the RF frequency band, and then transmitted to the base station CS as a transmission signal. The sub-channel, modulation method, and coding rate used by the wireless communication unit 11 are assigned by the base station CS (specifically, the scheduler 1c). Since the configurations of the transmitter side and the receiver side of the wireless communication unit 11 are the same as those of the wireless communication unit 2 in the base station CS, the description thereof will be omitted.

The operation unit 12 is composed of operation keys such as a power key, various function keys, and a numeric keypad, and outputs an operation signal based on the operation input by these operation keys to the communication control unit 10. The display unit 13 is, for example, a liquid crystal monitor or an organic EL monitor, and displays a predetermined image based on a display signal input from the communication control unit 10. The storage unit 14 stores the terminal control program and various data used by the communication control unit 10, and also has a function as a buffer used for retransmission control and the like.

Next, the communication operation between the base station CS and the terminal T in the wireless communication system configured as described above will be described with reference to the flowchart of FIG.

First, the communication control unit 10 of the terminal T monitors the incoming call response request included in the downlink channel CCH transmitted from the base station CS via the wireless communication unit 11 in the idle state (standby state), and at the same time, It monitors the outgoing call request from the higher-level application of the own terminal and decides whether to make an incoming call or an outgoing call. Here, when there is an incoming call answering request or an outgoing call request, the communication control unit 10 transmits / receives a control signal related to synchronization with the base station CS and exchanges various parameters (negotiation) via the wireless communication unit 11. And establish a connection with the base station CS (step S1). Communication related to establishing a connection between the terminal T and the base station CS is performed using CCH.

When the connection with the base station CS is established as described above, the communication control unit 10 transmits the LCH allocation request signal to the base station CS via the wireless communication unit 11 using the CCH of the uplink channel (step S2). ..

On the other hand, when the control unit 1 of the base station CS receives the LCH allocation request signal via the wireless communication unit 2, it instructs the scheduler 1c to allocate ASCH to the terminal T. Here, the channel quality determination unit 1a controls the wireless communication unit 2 to perform carrier sense of the uplink channel (step S3), and based on the acquired quality element of each uplink channel, of the uplink channel of each terminal T. The quality is judged, and the judgment result is output to the scheduler 1c. As the quality element, RSSI obtained by carrier sensing the channel, that is, the strength of a signal that becomes an interfering wave is used. Based on the judgment result of the channel quality judgment unit 1a, the scheduler 1c allocates a traffic channel that can be regarded as a free channel (good channel quality) as an ASCH to the terminal T, and then uses the downlink CCH to use the wireless communication unit. The above ASCH allocation information is transmitted to the terminal T via 2 (step S4).

Then, when the communication control unit 10 of the terminal T receives the ASCH allocation information via the wireless communication unit 11, it captures the ASCH allocated from the base station CS by the carrier sense of the downlink channel (step S5). If the acquisition is possible, the wireless communication unit 11 is controlled to make an ASCH wireless connection (step S6).

Subsequently, the channel quality determination unit 1a of the base station CS controls the wireless communication unit 2 to perform carrier sense of the uplink channel (step S7), and based on the RSSI of the received signal of each uplink channel acquired, each The channel quality of the upstream channel of the terminal T is judged, and the judgment result is output to the scheduler 1c. The scheduler 1c allocates a traffic channel that can be regarded as a free channel (good channel quality) as an ESCH to the terminal T based on the judgment result of the channel quality judgment unit 1a, and then uses the downlink channel ASCH to use the wireless communication unit. The above ESCH allocation information (MAP) is transmitted to the terminal T via 2 (step S8).

Then, when the communication control unit 10 of the terminal T receives the above-mentioned ESCH allocation information via the wireless communication unit 11, it controls the wireless communication unit 11 to make a wireless connection of the ESCH, and uses the ESCH to make a base. Perform data communication with station CS (step S9).

As described above, according to the present embodiment, one of the traffic channels is assigned as an individual control channel (ASCH) dedicated to the terminal T, and a control signal (5 ms) with the base station CS is transmitted via the ASCH. In other words, by communicating ESCH allocation information), it is possible to perform radio resource (bandwidth) allocation control at a very high speed compared to the case of using a long-period (about 100 ms) CCH as in the past. it can. As a result, the utilization efficiency of wireless resources can be improved.

In this way, by adopting OFDMA for the TDMA / TDD method adopted for PHS etc., the transmission power and area can be reduced without the need for cell design, and high speed is achieved by using the individual control channel (ASCH). Bandwidth variable is possible, and mobile communication that supports wideband, band variable, and multiple users can be realized.

In the above embodiment, the ESCH allocation information is transmitted / received using the individual control channel (ASCH), but the present invention is not limited to this, and other control information may be transmitted / received using the above ASCH.

Further, the terminal T is provided with a determination unit (first determination means) for determining the channel quality of the ESCH (traffic channel for data communication) assigned by the base station CS, and the communication control unit 10 is based on the above determination unit. Based on the determination result, a configuration may be adopted in which the information (RMAP) for rejecting the ESCH assigned from the base station CS is transmitted to the base station CS via the individual control channel (ASCH). In mobile communication, the channel quality of ESCH changes from moment to moment, so by adopting such a configuration, if the channel quality of the assigned ESCH deteriorates, RMAP is transmitted to the base station CS. Demand new channel quality ESCH allocation.

Further, in the above embodiment, next-generation broadband movement that employs orthogonal frequency division multiple access (OFDMA) as a multiple connection technology in addition to time division multiple access (TDMA) and time division duplex (TDD) as a wireless communication system. Although the body communication system has been described as an example, the wireless communication system is not limited to this, and can be adaptively assigned to each wireless communication terminal and a shared control channel that can be used in a predetermined cycle for each base station. It is applicable to any wireless communication system that communicates with multiple traffic channels.

<figref num="1">It is a block diagram of the structure of the wireless communication system which includes the base station CS and the wireless communication terminal (terminal) T in one Embodiment of this invention.</figref><figref num="2">It is a schematic diagram which shows the scheduling of the subchannel and the slot of the wireless communication system in one Embodiment of this invention.</figref><figref num="3">It is a detailed explanatory drawing of the wireless communication part 2 in one Embodiment of this invention.</figref><figref num="4">It is a flowchart which shows the operation of the wireless communication system in one Embodiment of this invention.</figref>

Code description

CS ... base station, T ... wireless communication terminal (terminal), 1 ... control unit, 10 ... communication control unit, 2, 11 ... wireless communication unit, 3, 14 ... memory Unit, 1a ... channel quality judgment unit, 1b ... QoS control unit, 1c ... scheduler, 12 ... operation unit, 13 ... display unit, 10a ... channel request unit, N .. .Public network