JP2013146098A - Radio communication system and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to use a frequency in a TDD system like the IEEE 802.22 even if the frequency is such that only a unidirectional link can be used due to mainly reception quality of a downlink signal becoming to a low SIR by limitation of downlink transmission power of a base station and interference from a primary utilization system in white space.SOLUTION: In a radio communication system 1 performing radio communication by utilizing white space, a receiving station 200 includes: interference suppression processing unit 202 for performing processing to reduce interference inflicted on a signal transmitted by a transmission station 100 at a frequency of white space; a reception quality estimation unit 203 for estimating communication quality of communication using the frequency of white space on the basis of the signal processed by the interference suppression processing unit 202; and a reception quality notification unit 204 for transmitting communication quality information estimated by the reception quality estimation unit 203 to the transmission station 100.

Description

  The present invention relates to a wireless communication system using a white space, and more particularly to a frequency allocation technique to be used.

  The progress of the information society in recent years has been remarkably remarkable, and as a communication method in many information communication devices and services, wireless communication is often used in addition to wired communication. Along with this, the demand for radio frequency, which is a finite resource, is constantly increasing, and the depletion of allocatable frequencies has become a major problem in countries around the world. In general, a frequency is license managed by the country, and only those who are assigned a license can use the frequency under strict control at a specific location and time. However, in order to meet the frequency demand that will continue to increase in the future, there is a need for a new frequency utilization method that is not limited to the conventional utilization method.

  Therefore, in recent years, as a new frequency utilization method to solve the frequency depletion problem, a method that uses a frequency band (white space) that has not been used spatially and temporally even though it has already been allocated has been studied. Has been. For example, a licensed user (hereinafter referred to as “primary user”) sufficiently avoids the influence on the frequency usage of the existing system, while the unlicensed user (hereinafter referred to as “secondary user”). ") Is being researched and developed for cognitive radio communication systems that flexibly use white space radio waves (for example, Non-Patent Document 1).

For example, in a wireless regional area network (WRAN) system using white space, which is standardized by IEEE802.22, each wireless station accesses its own database by accessing a database on the IP network. The transmittable frequency list and the maximum transmittable power based on the position information are acquired. The transmittable frequency list is a base station (BS: Base) connected to a terminal (CPE: Customer Premises Equipment) such as a slave station or a mobile phone installed by each door.
A spectrum manager (SM) in the station) is collectively managed while being updated as needed. And BS determines the frequency which can be utilized for communication bidirectionally between BS and CPE as a use frequency based on this transmittable frequency list.

  Each wireless station (BS and CPE, hereinafter the same) has a spectrum sensing function. When each wireless station detects that the determined use frequency is being used by the existing system (primary user's system) by this spectrum sensing, it notifies the SM of the information. Then, the SM excludes this frequency from the transmittable frequency list. The wireless communication system using white space avoids the influence on the frequency use of the primary user by performing dynamic spectrum access based on the information updated every moment in this way, and at the same time, the secondary user. Communication is also realized.

  By the way, IEEE802.22 specifies only time division duplex (TDD) as a duplex system. The BS and CPE use the same frequency during data transmission by TDD, but realize bidirectional communication by performing communication at different transmission timings. However, the duplex method using only TDD uses the same frequency for bidirectional communication. Therefore, TDD is not necessarily an efficient communication method for a wireless communication system using a white space where the frequency that can be transmitted is different for each wireless station or the maximum transmission power that can be transmitted may be different. I want. For example, when one radio station can transmit with high power at a certain frequency, but the other radio station can only transmit with low power at that frequency, the bidirectional communication quality becomes asymmetric. Therefore, if such a frequency is allocated, communication cannot be performed efficiently.

  In addition, although one radio station can transmit data at a certain frequency, even when the other radio station cannot receive at that frequency, transmission and reception in the reverse direction may be possible. In this case, the link becomes a one-way link that can perform only one-way transmission / reception, but such a frequency cannot naturally be used in IEEE802.22 TDD.

Koji Fujii, “Cognitive Radio: Eliminating Use of Radio Waves, Core Technology for Utilizing White Space”, [online], Rick Telecom, [Search June 9, 2011], Internet "IEEE Std 802.22-2011 Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Policies and Procedures for Operation in the TV Bands", (USA), IEEE Standardization Association, July 27, 2011

  As described above, since IEEE802.22 defines only TDD as a duplex method, communication in a one-way link is outside the scope of IEEE802.22. However, from the viewpoint of effective use of frequency resources, there are cases where it is better to use a frequency that is a one-way link.

  Here, in general, an antenna is often installed at a high position such as a steel tower or a roof of a building in the BS, but an antenna is often installed at a low position in the ground such as a low-rise building. In addition, CPE often installs a directional antenna toward the BS, but the BS antenna often employs an omni antenna. Therefore, when the BS and the CPE transmit signals with the same transmission power, the BS transmits to the primary user located in a geographically distant location even if the uplink signal transmitted by the CPE does not cause interference. Since it is assumed that the downlink signal to be overreached causes interference to the primary user, the BS may have a stricter transmission power limit.

  In addition to this, for example, when considering terrestrial digital TV broadcasting, which is a primary usage system assumed in IEEE802.22, the required electric field strength is high because a high-order modulation method is used in such TV broadcasting. Since there are many cases where the radius of the TV broadcast area is wider than the service area radius of the IEEE802.22WRAN system, the signal-to-interference power ratio (SIR :) of the WRAN system is even outside the TV broadcast area. There is a high possibility that a TV broadcast signal having a sufficient strength to degrade the Signal to Interference power Ratio is present in the WRAN service area.

  Therefore, in view of the above problems, the present invention provides a wireless communication system that uses white space, and the reception quality of the downlink signal is mainly low due to the above situation, that is, the limitation of the downlink transmission power of the BS and the signal of the primary usage system. Even if the frequency is such that only a one-way link can be used, the IEEE802.22TDD system can be used as it is by using this frequency as a two-way link, enabling efficient frequency allocation. For the purpose.

  In IEEE802.22, when determining the frequency to be used, it is possible to use an index that affects the communication quality such as the frequency occupation pattern and interference power of the primary user's existing system. However, what index is used and how it is out of the range of IEEE802.22.

  In order to solve the above problems, (1) an aspect of the present invention is a wireless communication system configured to include a transmitting station and a receiving station that perform wireless communication with each other and perform the wireless communication using a white space. Then, the receiving station receives a signal transmitted by the transmitting station at the first frequency of the white space, and interference suppression for performing processing to reduce interference received by the signal received by the signal receiving unit. A communication quality estimation unit that estimates communication quality of communication using the first frequency based on a signal processed by the interference suppression unit, and communication quality information estimated by the communication quality estimation unit A communication quality information transmitting unit for transmitting to the communication station, wherein the transmitting station receives the communication quality information from the receiving station, and the communication quality received by the communication quality information receiving unit. Based on the information, a frequency allocation processing unit that allocates the first frequency as a frequency at the time of transmission of a control signal to the receiving station, and an allocation result transmission that transmits an allocation result in the frequency allocation processing unit to the receiving station A wireless communication system characterized by comprising:

  (2) In one aspect of the present invention, the communication quality estimation unit performs the reduction processing by the interference suppression unit on the signal received at the first frequency and the reduction processing by the interference suppression unit. Communication quality is estimated for each of the cases where it is not applied, the communication quality of the quality of the estimated communication quality is finally obtained, the frequency allocation processing unit received from the receiving station A frequency at which data transmission is possible is determined based on the communication quality information, and the determined frequency is assigned as a frequency at the time of data transmission to the receiving station.

  (3) In an aspect of the present invention, the transmitting station performs the wireless communication with one or a plurality of the receiving stations according to an OFDMA (Orthogonal Frequency-Division Multiple Access) scheme, and the control information includes the transmitting station The frequency allocation processing unit modulates the communication quality information received from the receiving station with interference at the first frequency by using a modulation scheme having a lower required SINR than data transmission from the receiving station to the receiving station. When the control signal is received and it is determined that only the control signal can be received, the frequency at the time of transmission of the control signal to the receiving station is assigned to the first frequency, and the data transmission Is assigned to a second frequency different from the first frequency.

  (4) In one aspect of the present invention, the transmitting station performs the wireless communication with a plurality of receiving stations by OFDMA, and the transmitting station transmits the control signal and the data by the frequency allocation processing unit. A signal transmission unit configured to transmit simultaneously at a plurality of allocated frequencies, and the frequency allocation processing unit applies a modulation scheme having a higher communication quality indicated by the communication quality information to each of the plurality of receiving stations. If it is determined that the quality is enough to withstand data communication, the first frequency is determined to be a frequency at which data transmission is possible from the transmitting station, and the communication quality indicated by the communication quality information uses a high-order modulation scheme. If it is determined that the quality is unbearable for performing data communication, the second frequency other than the first frequency is determined as a frequency at which data transmission is possible, and the transmitting station transmits the control signal, the data, Simultaneously transmitting at the first frequency and the second frequency allocated by the frequency allocation unit.

  (5) In one aspect of the present invention, in a wireless communication system that performs wireless communication using a white space, the receiving device of a receiving station that performs wireless communication with a transmitting station, the first frequency of the white space Based on the signal receiving unit that receives the signal transmitted by the transmitting station, the interference suppressing unit that performs processing to reduce interference received by the signal received by the signal receiving unit, and the signal processed by the interference suppressing unit A communication quality estimation unit that estimates communication quality of communication using the first frequency, and a communication quality information transmission unit that transmits the communication quality information estimated by the communication quality estimation unit to the transmission station, Based on the communication quality information from the receiving station, the transmitting station assigns the first frequency as a frequency when transmitting a control signal to the receiving station, and performs wireless communication with the transmitting station. The It can provide a receiving apparatus according to symptoms.

According to the invention of the aspect of (1), since the interference signal can be reduced and the reception quality can be improved when the white space is used, the downlink signal becomes a low SIR environment at the first frequency of the white space. Even in this case, it is possible to receive the downlink control signal at the first frequency. Thereby, in the invention of the aspect of (1), it is possible to use the uplink at the first frequency while maintaining the TDD system, and it is possible to realize the effective use of the frequency of the entire system.
According to the invention of the aspect of (2), it becomes possible to assign a frequency at the time of data transmission based on communication quality information for appropriately evaluating the quality at the time of data communication.

According to the invention of the aspect of (3), the modulation method in which the transmitting station performs radio communication with one or a plurality of receiving stations by the OFDMA method, and the control information is lower in the required SINR than the data transmission from the transmitting station to the receiving station. In the wireless communication system that is modulated in (1), the first frequency of the white space for transmitting the control signal or the other second frequency can be allocated as the frequency for data transmission.
According to the invention of the aspect of (4), the transmitting station performs radio communication with a plurality of receiving stations by the OFDMA method, and the transmitting station transmits a control signal and data simultaneously at a plurality of frequencies assigned by the frequency assignment processing unit. The present invention can be applied to a wireless communication system having a signal transmission unit, and data communication can be performed using a white space for communication performed using a high-order modulation method such as TV broadcasting.

  According to the invention of the aspect of (5), it is possible to suppress the signal that interferes when using the white space and improve the reception quality, so that the downstream signal is in a low SIR environment at the first frequency of the white space. Even in this case, it is possible to receive the downlink control signal at the first frequency. Thereby, in the invention of the aspect of (5), it is possible to use the uplink at the first frequency while maintaining the TDD system, and it is possible to realize the effective use of the frequency of the entire system.

It is a figure which shows an example of the whole structure of the radio | wireless communications system which concerns on this embodiment. It is a figure used for the description which compared service area radius R2 of the existing system, and service area radius R1 of a radio | wireless communications system. It is a figure which shows the example of the allocation pattern of a TDD frame. It is a block diagram which shows the structural example of the transmitting station of the radio | wireless communications system which concerns on this embodiment, and a receiving station. It is a figure which shows the more specific structural example of BS. It is a figure which shows the more specific structural example of CPE.

  Embodiments of the present invention will be described with reference to the drawings.

[Outline of wireless communication system]
FIG. 1 is a diagram illustrating an example of the overall configuration of a wireless communication system according to the present embodiment. The wireless communication system 1 according to the present embodiment is a wireless communication system (white space use system, secondary use system) that uses a white space.

  As shown in FIG. 1, a wireless communication system 1 is connected to CPE 21 and CPE 22 which are wireless communication terminals (subscriber station devices) such as slave stations and mobile phones installed by each door, and these wireless communication terminals. The base station 10 includes a BS 10, a backhaul line 30 of the BS 10, and the Internet 40.

  The communication system 2 shown in FIG. 1 is a broadcast or communication system (primary use system, hereinafter referred to as “existing system”) of a primary user who is licensed to use a frequency from the country. The existing system 2 includes a transmitting station 50 and a receiving station 60. The primary user of the existing system 2 has a license for the frequency f1 from the country. In the following description, in the wireless communication system 1, a secondary user who has not received a license for using the frequency f1 from the country uses the frequency f1 as a white space.

  Here, as shown in FIG. 1, the wireless communication system 1 is located geographically close to the existing system 2. However, in the wireless communication system 1, the service area of the wireless communication system 1 is arranged with a sufficient separation distance from the service area of the existing system 2, and the transmission power of the wireless stations constituting the wireless communication system 1 is sufficiently reduced. For example, even if transmission is performed using the frequency f1, communication can be performed without causing interference to the existing system 2.

  However, at this time, the antenna of the BS 10 is an omni antenna installed at a high position, and the antenna of the CPE 22 is a directional antenna installed at a low position. In the geographical arrangement as shown in FIG. If the transmission power is not reduced, interference with the existing system 2 occurs. Therefore, it is assumed that the CPE can transmit with medium power and the BS can transmit with low power.

At this time, as illustrated in FIG. 2, when the service area radius R2 of the existing system 2 is sufficiently wider than the service area radius R1 of the wireless communication system 1, the separation distance between the two service areas is D [m]. From the relationship shown in the following example, the signal of the existing system 2 exists in the service area of the wireless communication system 1 with high strength.
[ Example ]
R ₂ = 5 × R ₁
D = R ₁
Then, the shortest distance D ₂₁ between the CPE existing at the area end of the wireless communication system 1 and the transmitting station of the existing system 2 is
D ₂₁ = R ₂ + D = 5 × R ₁ + R ₁ = 6 × R ₁ = 1.2 × R ₂
It is 1.2 times the distance R2 from the transmitting station at the area end of the existing system 2.
Meanwhile, the shortest distance _{D 12} between the receiving station and the wireless communication system 1 of the base station existing in the area edge existing systems _{2 D 12 = R 1 + D} = R 1 + R 1 = 2 × R 1
It is twice the distance R ₁ from the BS at the area end of the wireless communication system 1.

  In general, radio wave propagation loss in wireless communication is often modeled as being proportional to the Nth power of the distance between the transmitting antenna and the receiving antenna (N is an integer or real number) (Nth power law of distance, free space) N = 2) for propagation. That is, even if a sufficient separation distance is provided between the areas of both systems so that the signals of the wireless communication system 1 do not interfere with the existing system 2, the signals of the existing system 2 having a wider service area than the wireless communication system 1 Thus, the wireless communication system 1 reaches the service area with high strength.

As for the frequency f2, since there is no existing system that uses the frequency f2 around the radio communication system 1, all radio stations in the radio communication system 1 can transmit with high power.
In the present embodiment, the wireless communication system 1 using the white space is a frequency resource that can be used geographically even if the signal of the existing system 2 may reach the service area with high strength. Can be used effectively.

[ Example of TDD frame allocation pattern ]
Here, the concept of TDD frame allocation in the BS 10 of this example will be described with reference to FIG. The wireless communication system 1 of this example conforms to IEEE802.22 and uses OFDMA (Orthogonal) as an access method.
Frequency-Division Multiple Access) is used. The TDD frame includes a downlink subframe and an uplink subframe with a variable TDD ratio. A data signal to each CPE in the downlink subframe and a data signal from each CPE in the uplink frame are arranged in a two-dimensional area of frequency and time in units called bursts. Control information (Control) including MAP information and the like for instructing each CPE from the BS 10 to arrange the burst (data burst) is arranged near the head of the downlink subframe. Actually, the control information is composed of a plurality of control bursts, and they are modulated by a modulation scheme (for example, QPSK control information for a 16QAM data burst) having a lower required SINR than a data burst.

FIG. 3A shows an example of a conventional basic pattern, and FIG. 3B shows an example of an improvement pattern according to the present embodiment. 3 also assumes a situation in which downlink interference is strong at the frequency f1 as described in FIG. In FIG. 3A, the frequency f1 is not used because the downstream signal to the CPE 21 becomes a low SIR at the frequency f1 and becomes a one-way link.
On the other hand, in FIG. 3B, only control information is arranged in the downlink subframe of frequency f1. The CPE 21 and CPE 22 can receive (decode) a control signal by an interference canceller or the like even at the frequency f1, and can transmit while suppressing the interference of the existing system by a directional antenna or the like. The frequency f2 can be basically used in the same manner as in FIG. In particular, by using the frequency f1 and the frequency f2 for upstream burst transmission, the number of bursts packed in the upstream subframe of the frequency f2 can be reduced, and the overhead of control information transmitted in the downstream subframe of the frequency f2 can be reduced. It is expected that there will be more choices in the arrangement of and optimization of the overall throughput.

FIG. 4 is a block diagram illustrating a configuration example of the transmitting station 100 and the receiving station 200 of the wireless communication system 1 according to the present embodiment.
As illustrated in FIG. 4, the wireless communication system 1 includes a transmitting station 100 that transmits data by wireless communication, and a receiving station 200 that receives data transmitted from the transmitting station 100. In the present embodiment, the transmitting station 100 corresponds to the BS 10 in FIG. 1, and the receiving station 200 corresponds to the CPE 21 and CPE 22 in FIG. The number of receiving stations 200 may be one, or a plurality of receiving stations 200 may exist as shown in FIG. Further, it is assumed that the frequencies that can be used as the white space include at least two frequencies (channels) f1 and f2.
Hereinafter, the configuration of the transmitting station 100 and the receiving station 200 will be described with reference to FIG.

[Configuration of receiving station 200]
The receiving station (receiving device or receiving device of the receiving station) 200 includes a signal receiving unit 201, an interference suppression processing unit 202, a reception quality estimation unit 203, and a reception quality notification unit 204.

  The signal receiving unit 201 receives a signal transmitted by the transmitting station 100 at a specific frequency f1 (and f2). In the present embodiment, the signal received by the signal receiving unit 201 is a downlink signal transmitted from the BS 10 to the CPE 21 and CPE 22. The signal received by the signal reception unit 201 is passed to the interference suppression processing unit 202 and the reception quality estimation unit 203. Here, the specific frequency f1 is (one of) frequencies transmitted by the transmitting station 200, which is found in the process of initial operation (establishment of synchronization) of the receiving station 200 and spectrum sensing.

  The interference suppression processing unit 202 performs processing to suppress (reduce) a signal that interferes with the signal received by the signal receiving unit 201 to improve SIR. Then, the signal whose SIR is improved by the interference suppression processing unit 202 is passed to the reception quality estimation unit 203. At this time, the SIR improvement method of the interference suppression processing unit 202 may be an interference suppression method based on signal processing such as cumulative addition of repeatedly transmitted signals such as a preamble, and spatial interference suppression by multi-antenna signal processing. It may be a method.

  Reception quality estimation section 203 detects whether or not data can be received at a specific frequency f1, using signals passed from signal reception section 201 and interference suppression processing section 202. Further, in the present embodiment, the reception quality estimation unit 203 estimates the reception quality for each of the cases where interference suppression is applied when data is received at a specific frequency f1 and when the data is not applied. Choose the good side.

  Specifically, the reception quality estimation unit 203 determines the reception quality as follows. That is, the received signal may be demodulated and decoded, and reception quality may be received when no error is detected by an error detection code such as a CRC (Cyclic Redundancy Check) code, such as a pilot signal included in each signal. The SINR is estimated using a known signal, and the received quality may be received when the SINR is equal to or greater than a threshold value. In addition, the SINR estimation result and the bit error rate history may be retained for a certain period, and the average value may be used to determine whether reception is possible. Furthermore, a plurality of threshold values may be provided, and an index of communication quality may be provided for each threshold value. A maximum transmission rate at which communication is possible is derived by referring to a table stored in advance, and this may be used as communication quality.

  In general, the signal from the BS first received by the CPE is a broadcast control signal such as a preamble or a control burst, but is not limited to the reception quality estimation performed based on these signals. In other words, it may be estimation based on reception of a dedicated test signal for estimation of reception quality, reception quality estimation based on reception of a control signal such as a beacon or a broadcast data signal, or unicast to other stations. The reception quality may be estimated by intercepting the data signal.

  If it is determined that the control signal transmitted from the transmitting station 100 can be received by the above procedure, the receiving station 200 sequentially starts network entry to the transmitting station 100 (ie, BS), and f1 is transmitted to the transmitting station 100. The communication channel is established with the same frequency.

  The reception quality notification unit 204 notifies the transmission station 100 of reception quality information through the communication channel. At this time, if it is determined on the transmitting station 100 side that the downlink quality is good (the receiving station 200 can receive data), not only uplink data communication but also downlink data communication is performed at the frequency of f1. If it is determined on the transmitting station 100 side that it is moderate (the receiving station 200 can only receive the control signal (although it is subject to interference)), the upstream data communication is performed at the frequency of f1, and the downstream data Communication is performed at a different frequency (for example, f2). Here, the reception quality information can be notified as a CBP (Coexistence Beacon Protocol) burst as an example.

[Configuration of Transmitting Station 100]
As shown in FIG. 4, the transmitting station (transmitting device or communication device of the transmitting station) 100 includes a signal transmitting unit 101, a reception quality information receiving unit 102, a communication quality information holding unit 103, and a frequency allocation processing unit 104. And an allocation result notifying unit 105.

  The reception quality receiving unit 102 receives the reception quality information transmitted from the receiving station 200. As described above, in this embodiment, the reception quality information is communication quality when the receiving station 200 receives a downlink signal. Note that the uplink quality is usually held by the transmission station 100 as the reception quality when the transmission station 100 receives the reception quality information.

  The communication quality information holding unit 103 receives and holds reception quality information transmitted from the receiving station 200. Specifically, the communication quality information holding unit 103, for example, associates an identifier (Device ID) for identifying each of a plurality of receiving stations 200 with the received quality information in the form of a database or the like in its own hard disk. Stored in a storage device. Further, the reception quality information may be held in association with information on the frequency for which the communication quality is determined.

The frequency allocation processing unit 104 refers to the reception quality information held in the communication quality information holding unit 103, determines frequencies at which downlink control signals can be transmitted and data transmission, and controls these to the receiving station 200. The frequency is assigned for signal transmission and data transmission. For example, when the frequency allocation processing unit 104 refers to the reception quality information and determines that the reception station 200 can receive the control signal, the reception quality of the reception station 200 at the frequency of f1 is a high-order modulation scheme (required SINR). If it is determined that the quality can withstand data communication using a high modulation method), downlink data transmission is also performed at f1, and if it is determined that the data communication using a high-order modulation method cannot be performed, the reception is performed. For the station 200, only the downlink control signal is transmitted at f1, and the downlink data transmission is performed at another frequency (for example, f2) with better quality. If a frequency other than f1 is used well at that time, that frequency can be set to f2, and if not used, it is selected from candidate frequencies and backup frequencies (channels). These determinations and assignments are made for each of the plurality of receiving stations 200. That is, the downlink data to some of the receiving stations 200 may be arranged in the downlink subframe of f1, and the downlink data to the remaining receiving stations 200 may be arranged in the downlink subframe of f2. As a result, the data communication is preferentially assigned to the higher frequency of the uplink quality and the downlink quality for each of the uplink direction and the downlink direction.
The allocation result notification unit 105 transmits the allocation result in the frequency allocation processing unit 104 to the receiving station 200 through the signal transmission unit 101. As an example, the allocation result is transmitted by control information, a super frame control header (SCH), or the like. If there is a receiving station that has responded to reception quality information indicating downlink quality that is worse than the quality that cannot withstand data communication using a higher-order modulation method at frequency f1, or a receiving station that does not respond to reception quality information. If the majority of the receiving stations are not good in uplink quality and downlink quality, it is highly likely that f1 is receiving or giving interference from an existing system or the like, or it is difficult to use f1 effectively. It is desirable to cancel.

[ Specific configuration of BS 10 (transmitting station 100) ]
Next, a more specific configuration of the BS 10 will be described with reference to FIG. In the present embodiment, the BS 10 corresponds to the transmission station 100 described above .
As shown in FIG. 5, the BS 10 has an antenna 151 that transmits and receives radio waves, a data transmission unit 152 that transmits and receives radio signals (including data, control information, and the like), and a main controller that controls the entire local station. The control unit 153, the spectrum manager (SM) 154 that manages the usable frequencies of the CPE 21 and the CPE 22, the interface unit 155 serving as an interface with the backhaul line 30 and an external device, and the backhaul line 30 and the external device are connected. Terminal 156.

The SM 154 includes the communication quality information holding unit 103 and the frequency allocation processing unit 104 described above. That is, the SM 154 holds communication quality information for each receiving station 200, and performs frequency assignment processing when a frequency assignment request is received from the receiving station 200.
The data transmission unit 152 includes an RF unit 161, a baseband (BB) signal processing unit 162, and a MAC processing unit 163.
The RF unit 161 performs frequency conversion from the baseband to the radio frequency band, frequency conversion from the radio frequency band to the baseband, signal amplification, and the like.
The BB signal processing unit 162 performs error correction coding, decoding processing, modulation / demodulation processing, and the like. The data transmission unit 152 has an FFT size variable configuration or a multi radio configuration so that OFDM signals can be simultaneously transmitted and received at a plurality of frequencies (channels).

  The MAC processing unit 163 performs processing such as control of the frequency channel and data transmission / reception timing used by the local station, addition of the local station identifier to the packet, and recognition of the wireless device that is the data transmission source.

  The functions of the signal transmission unit 101, the reception quality information reception unit 102, and the allocation result notification unit 105 described above are such that the antenna 151 and the data transmission unit 152 receive reception quality information under the control of the main control unit 153. This is realized by transmitting the allocation result.

  The main control unit 153 can be configured by, for example, a processor, a data storage area defined on the memory, and software. The processing in the BB signal processing unit 162, the MAC processing unit 163, and the SM 154 is performed, for example, by the processor of the main control unit 153 reading a program stored in a data storage device such as a hard disk on the memory and executing it. It is possible to realize.

[ Specific configuration of CPE21 and CPE22 (receiving station 200) ]
Next, a more specific configuration of the CPE 21 and CPE 22 will be described with reference to FIG. In the present embodiment, CPE 21 and CPE 22 correspond to the receiving station 200 described above.

As shown in FIG. 6, the CPE 21 and the CPE 22 include an antenna 251 that transmits and receives radio waves, a data transmission unit 252 that transmits and receives data, a main control unit 253 that controls the entire local station, and a BS 10. A reception quality estimation unit 203 that estimates communication quality when a signal is received, an interface unit 255 serving as an interface with an external line or an external device, and a terminal 256 for connecting to the external line or the external device are provided.
The data transmission unit 252 includes an RF unit 261, a baseband (BB) signal processing unit 262, and a MAC processing unit 263.
The RF unit 261 performs processing such as frequency conversion from the baseband to the radio frequency band, frequency conversion from the radio frequency band to the baseband, and signal amplification.
The BB signal processing unit 262 performs error correction coding, decoding processing, modulation / demodulation processing, and the like.

  The MAC processing unit 263 performs processing such as control of the frequency channel and data transmission / reception timing used by the local station, addition of the local station identifier to the packet, and recognition of the wireless device that is the data transmission source.

  Further, the functions of the signal receiving unit 201, the interference suppression processing unit 202, the reception quality estimation unit 203, and the reception quality notification unit 204 described above are controlled by the main control unit 253 so that the antenna 251 and the data transmission unit 252 can perform various signals. This is realized by performing processing and data transmission / reception.

  Note that the main control unit 253 can be configured by, for example, a processor, a data storage area defined on the memory, and software. The processing in the BB signal processing unit 262, the MAC processing unit 263, and the reception quality estimation unit 203 is performed, for example, by the processor of the main control unit 253 reading a program stored in a data storage device such as a flash memory onto the memory. It can be realized by executing.

[ Effect in this embodiment ]
As described above, according to this embodiment, in the wireless communication system 1 using the white space, it is possible SIR of the downlink signal is received by signal a Ri control signal under Te low environmental odor, to apply the TDD system .

  Furthermore, reception quality information (downlink quality) for each receiving station at each frequency is collected, and efficient frequency allocation can be performed for each bidirectional communication. Specifically, in the data communication, the uplink quality and the downlink direction are preferentially assigned to the higher frequency of the uplink quality and the downlink quality, and even if the frequency is not good, the downlink quality is low. If it is possible to secure a moderate level (a level that can receive a control signal), it is used together. This improves the frequency utilization efficiency of the entire system in an environment where the quality is asymmetric between downlink and uplink.

  Note that, as in this embodiment, various types of multi-channel schemes in which the BS 10 transmits at a plurality of frequencies can be used, such as channel bonding and channel aggregation for the physical layer, and multi-channel MAC extension for the MAC. known.

[Modification of this embodiment]
In the description of the present embodiment, it is assumed that the operation frequency is changed to f2 after detecting the interference at the first use (operation) frequency f1, but f2 can be selected from the transmittable frequency list from the beginning. Thereafter, the present invention can be applied to a situation in which the frequency f1 (not in the list) is also used in response to a bandwidth request from the CPE. In that case, the BS 10 outbands transmission at the frequency f1.
Broadcasting or the like is performed, and each CPE receives this, and the reception quality estimation unit 203 estimates the degree of interference from the existing system or the like. The reception quality information can be notified at a frequency other than f1 if a communication channel has been established with the BS 10.

Further, although the interference frequency f1 has been described as the same as the frequency used by the neighboring existing system, since unnecessary radiation from the adjacent frequency can also be an interference source, an application that refrains from using the adjacent frequency is also assumed. Even in that case, the BS 10 can allocate the above-mentioned frequency f1 to the adjacent frequency and obtain a response of the reception quality information from each CPE.
Moreover, although it demonstrated as what communicates between BS and CPE, it is applicable also to the chain connection of BS. In that case, BS 10 is assumed to be a master BS, and at least one of CPE 21 or 22 is read as a slave BS.

The interfered frequency f1 can also be applied to direct communication between terminals, communication with different systems, and the like. In the direct communication between terminals, each CPE transmits and receives in the uplink subframe according to the burst arrangement specified in the downlink subframe of the frequencies f1 and f2. The communication with different systems is for sharing information such as transmittable frequencies and facilitating discovery of hidden existing systems, and has applications such as out-of-band broadcasting and rendezvous channels.
Also, the control information transmitted by the BS 10 at the interfered frequency f1 can be repeatedly arranged in the downlink subframe, and the SINR can be improved by adding them on the CPE side.

  The wireless communication system 1 according to the present embodiment is particularly suitable for a wireless communication system defined by IEEE802.22, but is not limited thereto. When applied to a system in which one base station can transmit data to a terminal only on one frequency (channel), the BS 10 of this embodiment is a base station for each frequency (that is, corresponding to each of f1 and f2). What is necessary is just to behave as several base stations installed in the same place which has ID.

  1 wireless communication system, 2 existing system, 10 BS, 21 and 22 CPE, 30 backhaul line, 40 Internet, 100 transmitting station, 101 signal transmitting unit, 102 received quality information receiving unit, 103 communication quality information holding unit, 104 frequency Allocation processing unit, 105 Allocation result notification unit, 151 antenna, 152 data transmission unit, 153 main control unit, 154 spectrum manager, 155 interface unit, 156 terminal, 161 RF unit, 162 baseband signal processing unit, 163 MAC processing unit, 200 reception station, 201 signal reception unit, 202 interference suppression processing unit, 203 reception quality estimation unit, 204 reception quality notification unit, 251 antenna, 252 data transmission unit, 253 main control unit, 255 interface unit, 256 terminal, 261 RF unit , 26 2 Baseband signal processor, 263 MAC processor

Claims (4)

  A wireless communication method in which a base station and a plurality of slave stations perform communication by alternately transmitting at a predetermined cycle using a white space frequency,
  A first step in which the plurality of slave stations receive signals transmitted by the base station at the first frequency and the second frequency of the white space;
  A second step in which the plurality of slave stations estimate downlink communication quality using at least the first frequency based on the signal processed in the first step;
  A third step in which the plurality of slave stations transmit the downlink communication quality information estimated in the second step to the transmitting station;
  A fourth step in which the base station respectively receives the downlink communication quality information from the plurality of slave stations;
  Based on the downlink communication quality information received in the fourth step, the base station allocates control information and downlink data transmission to the slave station to the first frequency or the second frequency, A fifth step for each slave station;
  A sixth step in which the base station estimates uplink communication quality using at least one of the first frequency and the second frequency based on signals received from the plurality of slave stations, and
  Seventh step for determining whether the base station allocates transmission of uplink data from the slave station to the first frequency or the second frequency based on the uplink communication quality information received in the sixth step When,
  And an eighth step in which the base station transmits the allocation results in the fifth step and the seventh step to the receiving station by at least one of the first frequency and the second frequency for each period. And
  In the fifth step, when the downlink communication quality information at the first frequency satisfies the first quality for each of the plurality of slave stations, the base station determines both the control information and the downlink data. When transmission is assigned to the first frequency and the downlink communication quality information at the first frequency satisfies a second quality that is worse than the first quality, transmission of the control information is performed at the first frequency. And transmission of downlink data is assigned to the second frequency,
  In the eighth step, the base station allocates uplink data to the first frequency based on the uplink communication quality information even when downlink data to any of the slave stations is not allocated to the first frequency. A wireless communication method.   The base station and the plurality of slave stations communicate by the TDD method,
  The control information transmitted in the eighth step includes information indicating the allocation result of uplink data and downlink data at a frequency at which the control information is transmitted, and is a modulation scheme having a lower required SINR than transmission of the downlink data. The radio communication method according to claim 1, wherein the radio communication method is modulated or repeatedly arranged and transmitted a plurality of times in a downlink subframe.   The base station and the plurality of slave stations are connected with OFDMA (Orthogonal
Frequency-Division Multiple Access) and the TDD method with a variable TDD ratio,
  The information indicating the allocation result included in the control information is MAP information indicating an arrangement of each burst of downlink data and uplink data in a downlink subframe and an uplink subframe in a two-dimensional region of frequency and time. The wireless communication method according to claim 2, wherein:   The allocation of each of the fifth step and the seventh step is performed with priority given to the frequency having the better uplink quality and downlink quality, for each of the uplink data and downlink data, for each of the plurality of slave stations. The wireless communication method according to claim 1.

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