JP2009188497A - Radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system for eliminating defects in TDD radio communication which is inefficient in long distance communication, and preventing a coverage from being deteriorated due to propagation loss. <P>SOLUTION: This radio communication system is equipped with a mobile station, and a base station to perform TDD (Time Division Duplex) radio communication TS-1 - N at a first frequency and perform FDD (Frequency Division Duplex)radio communication TSU-1 - N at a second frequency different from the first frequency, between the base station and the mobile station. The FDD Radio communication TSU-1 - N, TSD-1 - N is performed in the guard time GT section of the TDD radio communication. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multiband wireless communication system that performs wireless communication in a plurality of frequency bands, and in particular, a hybrid duplex in which an FDD (Frequency Division Duplex) method and a TDD (Time Division Duplex) method are mixed. The present invention relates to a wireless communication system.

  A study is underway to standardize the so-called fourth generation mobile communication system (IMT-Advanced), which provides a data communication service much faster than the conventional third generation mobile communication system (IMT-2000) around 2010. Has been done. As described in Non-Patent Document 1, IMT-Advanced aims to achieve a communication speed of 100 Mbps in a mobile environment and 1 Gbps in a hot spot or quasi-static environment, and to achieve a frequency utilization rate of 10 bps / Hz. Yes.

  Duplex wireless communication used in a wireless communication system between a base station and a mobile station includes FDD wireless communication and TDD wireless communication. In FDD wireless communication, it is necessary to transmit uplink / downlink signals at different frequencies (pair bands). On the other hand, in TDD wireless communication, uplink / downlink signals are time-divided, and uplink / downlink signals are transmitted at the same frequency, so a pair band is unnecessary. In the latter TDD scheme, slot allocation according to each link can be flexibly realized by changing the allocation ratio of uplink and downlink transmission / reception slots.

  In order to achieve the communication speed of 1 Gbps required in the above communication system and the frequency utilization efficiency of 10 bps / Hz, the required frequency bandwidth needs to be 100 MHz. In addition, both real-time and non-real-time traffic data of the system are transmitted as packet signals, and the traffic is not necessarily symmetrical between the uplink and the downlink. For this reason, it is considered that the TDD scheme capable of flexibly realizing slot allocation is more appropriate than the FDD scheme for wireless communication in the next generation wireless communication system.

  Further, in order to accommodate the required frequency bandwidth described above, it is necessary to add an IMT-Advanced frequency separately from the IMT-2000 frequency. The frequency to be added is suitably a frequency in a frequency band of 5 to 6 GHz or less in consideration of mobile communication applications. In IMT-Advanced, the use of 3.4 to 4.2 GHz and 4.4 to 4.9 GHz is assumed.

  The next-generation mobile phone system is expected to support a wide range of locations (coverage, effective range) that can be connected to the network anytime and anywhere, and various services ranging from low speed to super high speed. In order to solve this problem, for example, a system described in Non-Patent Document 2 that links different wireless systems such as 3G / 4G and wireless LAN, or a multimode described in Patent Document 1 that selects an FDD method and a TDD method. Communication devices are being considered.

Y. Kim et.al., "Beyond 3G: Vision, Requirements, and Enabling Technologies", IEEE Commun. Mag., Vol. 41, pp. 120-124, Mar. 2003. H.Hrada, M.Kuroda, H.Morikawa, H.Wakana, F.Adachi, "The Overview of the New Generation Mobile Communication System and the Role of Software Defined Radio Technology", IEICE Trans.Commun., Vol.E86- B, No. 12, pp. 3374-3384, Dec. 2003. JP 2002-368725 A

  As described above, the TDD method is appropriate for the IMT-Advanced duplex method. In the TDD scheme in which uplink / downlink signals are time-divided and transmitted at the same frequency, it is necessary to insert a guard time between slots in order to prevent uplink / downlink interference caused by transmission delay between the base station and the mobile station. . However, since the length of the guard time depends on the cell radius, when the distance between the base station and the mobile station is large, the guard time becomes long and the TDD scheme becomes inefficient compared to the FDD scheme. There was a problem.

  Further, the propagation loss increases in proportion to approximately the 2.6th power of the frequency. For this reason, the propagation distance of IMT-Advanced that assumes the use of a microwave band of 3 GHz or more is shorter than the propagation distance of IMT-2000 that performs communication using the 800 Hz to 2 GHz band. As a result, IMT-Advanced has a problem in that the location rate is significantly deteriorated.

  The present invention has been made in order to solve the above-described problems. The present invention improves the shortcomings of TDD wireless communication, which is inefficient in long-distance communication, and can be used in a wide area even when performing ultrahigh-speed transmission. An object is to provide a wireless communication system capable of communicating at a rate.

  The wireless communication system according to the present invention performs TDD (Time Division Duplex) wireless communication at a first frequency between a mobile station and the mobile station, and a second frequency different from the first frequency. And a base station that performs FDD (Frequency Division Duplex) wireless communication. Then, the FDD wireless communication is performed in the guard time interval of the TDD wireless communication.

  According to the communication system of the present invention, since FDD wireless communication is performed in the TDD guard time interval, it is possible to improve the disadvantages of the TDD method, which is inefficient in long-distance communication.

<Embodiment 1>
FIG. 1 is a diagram showing a configuration of a wireless communication system according to the present embodiment. As shown in FIG. 1, the radio communication system according to the present embodiment includes mobile stations 1A and 1B and a base station 2.

FIG. 2 is a block diagram showing a configuration of base station 2 according to the present embodiment. As shown in FIG. 2, the base station 2 includes an antenna 10, a TDD transmission / reception unit 20, a TDD / FDD transmission / reception timing control unit 40, and an FDD transmission / reception unit 50. The base station 2 according to the present embodiment performs TDD wireless communication with the mobile stations 1A and 1B at the first frequency f _H using the TDD transmission / reception unit 20, and the FDD transmission / reception unit 50 performs first communication. FDD wireless communication is performed at second frequencies f _L1 and f _L2 that are different from the frequency f _H.

The TDD transmission / reception unit 20 according to the present embodiment includes an RF filter 21, changeover switches 22 and 26, an RF amplifier 23, a reception-side frequency converter 24, an A / D converter 25, and a local oscillator (LO). 27, a transmission side power amplifier 28, a transmission side frequency converter 29, a D / A converter 30, and a baseband unit 31. The TDD transmission / reception unit 20 selectively switches between RX (reception) and TX (transmission) modes using the changeover switches 22 and 26. Further, the TDD transceiver 20 uses the first frequency f _H of the local oscillator 27 in both the RX mode and the TX mode.

The TDD reception unit 20 performs the mobile station 1A, and 1B, via the antenna 10, the radio communication TDD mode at a first frequency f _H. The radio communication system according to the present embodiment assumes ultra-high-speed transmission by TDD radio communication. Therefore, in the present embodiment, it is assumed that the first frequency f _H used for TDD wireless communication belongs to a wide frequency band, and the frequency band includes a high frequency. In general, the higher the frequency used for wireless communication, the greater the degradation of the location rate. Therefore, as shown in FIG. 1, the base station 2 mainly performs TDD wireless communication with the mobile station 1A close to the base station 2. As described above, it is assumed that the first frequency f _H according to the present embodiment belongs to a frequency band sufficient to achieve ultrahigh-speed transmission, but the location rate is greatly deteriorated due to propagation loss.

The FDD transceiver 50 according to the present embodiment includes a reception-side RF filter 51, a reception-side RF amplifier 52, a reception-side frequency converter 53, a reception-side local oscillator (LO) 54, and an A / D converter 55. A transmission side RF filter 56, a transmission side power amplifier 57, a transmission side frequency converter 58, a transmission side local oscillator (LO) 59, a D / A converter 60, and a baseband unit 61. The FDD transceiver unit 50 performs both in parallel without switching between the RX and TX modes. Further, the FDD transceiver 50 uses the second frequency f _L1 of the reception-side local oscillator 54 in the RX mode, and uses the second frequency f _L2 (≠ f _L1 ) of the transmission-side local oscillator 59 in the TX mode. .

The FDD transceiver 50 performs FDD wireless communication with the mobile stations 1A and 1B via the antenna 10 at the second frequencies f _L1 and f _L2 . The second frequencies f _L1 and f _L2 used for the FDD wireless communication are different from the first frequencies f _H used for the TDD wireless communication. The second frequencies f _L1 and f _L2 used for FDD wireless communication belong to a narrow frequency band, and the frequency band is a low frequency. In the present embodiment, the second frequencies f _L1 and f _L2 used for the FDD wireless communication are lower than the first frequency f _H used for the TDD wireless communication, and the degradation of the location rate is small. Shall. In this way, as shown in FIG. 1, the base station 2 can perform FDD wireless communication with the mobile station 1 </ b> B far from the base station 2.

  The TDD / FDD transmission / reception timing control unit 40 performs timing control between transmission / reception of the TDD transmission / reception unit 20 and transmission / reception with the FDD transmission / reception unit 50. In the present embodiment, the TDD / FDD transmission / reception timing control unit 40 controls time slots of the TDD scheme and the FDD scheme. The base station 2 performs hybrid duplex wireless communication under the control of the TDD / FDD transmission / reception timing control unit 40. FIG. 3 is a diagram for explaining the control of the TDD / FDD transmission / reception timing control unit 40. In this figure, a group of N time slots is defined as a frame.

  In conventional TDD wireless communication, in order to prevent uplink / downlink interference caused by a transmission delay between the mobile stations 1A, 1B and the base station 2, between adjacent slots TS-1 to N of the TDD scheme. The guard time GT for stopping the TDD wireless communication is inserted. However, the length of the guard time GT depends on the cell radius, and when the distance between the mobile stations 1A and 1B and the base station 2 is large, the guard time GT becomes long, and the TDD scheme is compared with the FDD scheme. There was a problem of inefficiency.

  On the other hand, in the radio communication system according to the present embodiment, FDD reception slots TSU-1 to N and FDD transmission slots TSD-1 to N are inserted in each guard time GT interval. Thus, in the radio communication system according to the present embodiment, FDD radio communication is performed in the TDD radio communication guard time GT section under the control of the TDD / FDD transmission / reception timing control unit 40.

As described above, according to the radio communication system according to the present embodiment, in the guard time GT section of TDD radio communication (TS-1 to N), FDD radio communication (TSU-1 to N, TSD). -1 to N). As described above, by effectively using the guard time GT section, it is possible to improve the disadvantage of the TDD scheme that is inefficient in long-distance communication. Since the first frequency f _H is different from the second frequencies f _L1 and f _L2 , they do not interfere with each other.

Further, in the present embodiment, the second frequencies f _L1 and f _L2 used for FDD wireless communication are less degraded in the location rate than the first frequency f _H used for TDD wireless communication. Therefore, the wireless communication system according to the present embodiment performs ultra-high-speed transmission by TDD wireless communication, and performs FDD wireless communication having a wide space ratio even when the space ratio decreases. You can communicate with.

<Embodiment 2>
FIG. 4 is a block diagram showing a configuration of base station 2 according to the present embodiment. Hereinafter, in the configuration of the radio communication system according to the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the components not newly described are the same as those in the first embodiment. It shall be.

As shown in FIG. 4, the base station 2 according to the present embodiment is similar to the first embodiment in that the antenna 10, the TDD transmission / reception unit 20, the TDD / FDD transmission / reception timing control unit 40, and the FDD transmission / reception unit 50 Is provided. The configurations of TDD transmission / reception unit 20 and FDD transmission / reception unit 50 according to the present embodiment are the same as those of the first embodiment. Thus, the base station 2 performs radio communication TDD mode at a first frequency f _H, performs wireless communication FDD scheme at a first frequency f _H is different from the second frequency f _L1, f _L2. Base station 2 according to the present embodiment further includes radio resource control unit 70 and quality estimation unit 71 in addition to the above configuration.

  The wireless communication system according to the present embodiment transmits / receives data to / from mobile stations 1A and 1B by the above-described TDD wireless communication. The data according to the present embodiment is assumed to be packet data. The TDD transmission / reception unit 20 performs data transmission (best effort transmission) from low speed to ultra high speed. The wireless communication system according to the present embodiment transmits important information for maintaining wireless communication between the mobile stations 1A and 1B and the base station 2 to the mobile stations 1A and 1B by the above-described FDD wireless communication. Send and receive. Here, for example, control channel information corresponds to important information for maintaining wireless communication between the mobile stations 1A and 1B and the base station 2.

  Since the FDD transmission / reception unit 50 has a wide coverage characteristic, the FDD transmission / reception unit 50 shares the quality estimation of the mobile stations 1A and 1B. The quality estimation unit 71 receives the signal from the FDD transmission / reception unit 50, estimates the quality, and inputs the estimation result to the radio resource control unit 70. The quality here refers to, for example, SNR (Signal to Noise Ratio) / PER (Packet Error Rate) / movement speed. The radio resource control unit 70 according to the present embodiment distributes packet data to be transmitted to the TDD transmission / reception unit 20 or the FDD transmission / reception unit 50 according to the estimation result of the quality estimation unit 71. The radio resource control unit 70 normally distributes the packet data to the TDD transmission / reception unit 20, but distributes the packet data to the FDD transmission / reception unit 50 only when the signal quality from the mobile stations 1A and 1B deteriorates. Then, the FDD transmitting / receiving unit 50 transmits the distributed packet data to the mobile stations 1A and 1B while reducing the packet data to the lowest data transmission rate allowed by itself.

FIG. 5 is a diagram illustrating an operation of the radio communication system according to the present embodiment. The base station 2 mainly transmits information for maintaining the above-described wireless communication to the mobile stations 1A and 1B using the second frequencies f _L1 and f _L2 having wide coverage characteristics of FDD wireless communication. Then, the base station 2 optionally guarantees a guarantee-type low-speed packet data transmission, that is, a minimum data transmission rate for the mobile station 1B, when the quality of wireless communication with the mobile station 1B deteriorates, for example. Transmission. As described above, the wireless communication system according to the present embodiment uses the FDD wireless communication in accordance with the quality of the wireless communication with the mobile stations 1A and 1B, in addition to the above information, a part of the above data. Send and receive.

  According to the radio communication system according to the present embodiment as described above, in addition to the effects of the first embodiment, it is possible to perform best effort type ultra-high speed data transmission and guarantee type low speed data transmission. .

1 is a diagram showing a configuration of a radio communication system according to Embodiment 1. FIG. 2 is a block diagram showing a configuration of a base station of the wireless communication system according to Embodiment 1. FIG. 6 is a diagram for explaining time slot control of the wireless communication system according to Embodiment 1. FIG. 6 is a block diagram showing a configuration of a base station of a radio communication system according to Embodiment 2. FIG. 6 is a diagram illustrating a configuration of a wireless communication system according to a second embodiment. FIG.

Explanation of symbols

  1A, 1B mobile station, 2 base station, 10 antenna, 20 TDD transceiver, 21 RF filter, 22, 26 changeover switch, 23 RF amplifier, 24, 53 reception side frequency converter, 25, 55 A / D converter, 27 Local oscillator, 28 Transmission side power amplifier, 29, 58 Transmission side frequency converter, 30, 60 D / A converter, 31, 61 Baseband unit, 40 TDD / FDD transmission / reception timing control unit, 50 FDD transmission / reception unit, 51 Reception side RF filter, 52 Reception side RF amplifier, 54 Reception side local oscillator, 56 Transmission side RF filter, 57 Transmission side power amplifier, 59 Transmission side local oscillator, 70 Radio resource control part, 71 Quality estimation part, GT guard time.

Claims (5)

A mobile station,
TDD (Time Division Duplex) wireless communication is performed with the mobile station at a first frequency, and FDD (Frequency Division Duplex) wireless communication is performed at a second frequency different from the first frequency. With a base station,
In the guard time interval of the TDD wireless communication, the FDD wireless communication is performed.
Wireless communication system. The second frequency used for the FDD wireless communication has a smaller degradation of the location rate (coverage) than the first frequency used for the TDD wireless communication.
The wireless communication system according to claim 1. Sending and receiving data to and from the mobile station by the TDD wireless communication,
Transmitting and receiving information for maintaining wireless communication between the mobile station and the base station to and from the mobile station by the FDD wireless communication;
The radio | wireless communications system of Claim 1 or Claim 2. Depending on the quality of wireless communication with the mobile station, the FDD wireless communication transmits and receives part of the data in addition to the information.
The wireless communication system according to claim 3. The data includes packet data;
The radio | wireless communications system of Claim 3 or Claim 4.

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