JP5408245B2 - Wireless base station apparatus, communication terminal, communication processing method and program - Google Patents

Description

  The present invention relates to a radio base station apparatus, a communication terminal, a communication processing method, and a program for causing a computer to execute the method.

  OFDM (Orthogonal Frequency Division Multiplexing) wireless communication is a multi-carrier scheme that transmits data for each user through serial-parallel conversion in a wide communication band. Since the respective signals are orthogonal to each other, the band can be narrowed compared to FDM communication. As described above, OFDM communication is capable of high-speed communication because of multi-carrier transmission. However, since the bit or symbol period is shortened, the influence of intersymbol interference becomes a problem.

  In OFDM communication, a guard interval is added to the head of data in order to avoid the influence of intersymbol interference. FIG. 1 is a diagram for explaining a guard interval.

  As shown in FIG. 1, a guard interval is added to each data symbol in a communication frame having a fixed period in order to avoid intersymbol interference due to a delayed wave. The guard interval is obtained by copying a certain interval after the data symbol to the head portion. Intersymbol interference can be avoided by adding a guard interval to the data.

  However, even if the capacity of the guard interval is small, it is a loss when viewed from the whole system. Therefore, if the guard interval is made longer than necessary, the transmission capacity is reduced. Therefore, various proposals have been made as methods for changing the length of the guard interval.

  An example of the proposal is disclosed in Japanese Patent Application Laid-Open No. 2006-352786 (hereinafter referred to as Patent Document 1). Patent Document 1 discloses that mobile stations are classified in consideration of the amount of delay spread of each mobile station, and a frequency is assigned to each mobile station for each classified mobile station within a specified time slot. Has been. The delay spread represents the temporal fluctuation (spread) of the propagation delay time between the mobile station and the base station. Patent Document 1 discloses that mobile stations having different reception delay spreads are allocated in time slots having an appropriate guard interval length in relation to the distribution of mobile stations in the area.

  In the method disclosed in Patent Document 1, a delay spread is determined for each mobile station, a symbol to which a guard interval for a relatively short delay spread is added, a symbol to which a guard interval for an average delay spread is added, and A communication frame is composed of a total of three types of symbols including a guard interval for a relatively long delay spread.

  FIG. 2 is a diagram for comparing communication processing methods of related technologies.

  FIG. 2 shows a frame when the GI length, which is the length of the guard interval (GI), is constant, and a frame according to the method disclosed in Patent Document 1. Referring to FIG. 2, comparing the case where the GI length is constant with the method disclosed in Patent Document 1, if the communication frame is configured with the same number of symbols, the method disclosed in Patent Document 1 is more GI. There is an advantage that the communication frame length can be shortened as compared with the case where the length is constant.

  Unlike mobile communications such as relay stations and TV broadcasts, mobile communications targeting mobiles such as automobiles, trains, and ships change the propagation environment from moment to moment. Problems arise.

  When the GI length is constant, in a propagation environment where there are many buildings with small cell radii and high numbers, the probability that a large delayed wave is generated is small, so the possibility of transmission capacity deterioration due to intersymbol interference is small. However, since the guard interval is basically a large loss in OFDM communication, if the guard interval is increased more than necessary in an environment where a large delay wave does not occur, the transmission capacity is reduced.

  On the other hand, in an open area where the cell radius is large and there are few buildings, and there is a reflection environment such as a mountain, there is a high probability that a large delayed wave with high power will be generated. The intersymbol interference occurs due to the influence of the delayed wave, causing a reduction in transmission capacity.

  Further, assuming an OFDM wireless communication system of a plurality of base stations and a plurality of mobile stations, the transmission capacity is further reduced.

  As described above, in mobile communication, since the propagation environment changes from moment to moment, delayed waves of various lengths are generated. Therefore, in OFDM wireless communication when the guard interval length is constant, the transmission capacity is reduced, leading to inefficiency of the communication system.

  In the method of Patent Document 1, in the FDD (Frequency Division Duplex) method in which the downlink and the uplink are different in frequency, the transmission rate can be increased as the communication frame length is shortened. However, there is a problem in the TDD (Time Division Duplex) system in which the downlink and uplink are the same.

  That is, when this method is realized by the TDD method, a guard period required when switching between the downlink and the uplink increases. A guard period is a section in which communication is not performed for a certain period of time, and is a loss from the viewpoint of the system. Therefore, when the TDD method is used, the frame length can be shortened by shortening the guard period, but there is a loss due to an increase in the guard period.

  Due to the above problems, in the method disclosed in Patent Document 1, in the communication method using the TDD method, the transmission rate cannot be increased even if the guard interval can be reduced.

  One of the objects of the present invention is to allow a computer to execute a radio base station apparatus, a communication terminal, a communication processing method, and a method for suppressing the influence of intersymbol interference and increasing the transmission capacity. Is to provide a program for

A radio base station apparatus according to an aspect of the present invention is based on a receiver that estimates a delay spread for each of a plurality of mobile stations based on signals received from each of a plurality of mobile stations, and a delay spread estimated by the receiver The length of the guard interval is determined for each mobile station, and the number of symbols, which is the number of data symbols that can be inserted in one frame, is calculated for each mobile station from the determined guard interval length and a predetermined length of data symbols. And a symbol corresponding to the mobile station calculated by the scheduling unit by adding a guard interval having a length determined for the mobile station by the scheduling unit to the head of the data symbol addressed to the mobile station. possess a guard interval adder for generating a frame including a number of data symbols addressed to the mobile station, a scheduling Parts are when calculating the number of symbols for each mobile station, it is configured to determine the number of symbols to be equal to or less than the length in which the predetermined "total length of a guard interval and a data symbol""number of symbols" ×.

A communication terminal according to an aspect of the present invention determines a delay interval based on a signal received from a radio base station, and a guard interval length based on the delay spread estimated by the receiver. A scheduling unit that calculates the number of data symbols that can be inserted in one frame from the length of the guard interval and a data symbol having a predetermined length, and a guard interval having a length determined by the scheduling unit. It was added at the beginning of the data symbols destined base station, possess a guard interval adder for generating a frame including the calculated number of data symbols symbol scheduling section addressed to the wireless base station, a scheduling unit, the symbol When calculating the number, "number of symbols" x "guard interval and data symbol The total length of the "is configured to determine the number of symbols to be equal to or less than the predetermined length.

The communication processing method according to one aspect of the present invention estimates a delay spread for each of a plurality of mobile stations based on signals received from each of the plurality of mobile stations, and sets a guard interval length for each mobile station based on the estimated delay spread. The number of symbols, which is the number of data symbols that can be inserted in one frame, is determined for each mobile station from the determined guard interval length and data symbols of a predetermined length. A guard interval of the determined length is added to the head of the data symbol addressed to the mobile station, a frame including the data symbol of the number of symbols corresponding to the mobile station is generated for the mobile station, and the number of symbols is calculated for the mobile station When calculating each number, the number of symbols so that “number of symbols” x “total length of guard interval and data symbols” is less than or equal to a predetermined length. It is those determined.

The program according to one aspect of the present invention estimates a delay spread for each of a plurality of mobile stations based on signals received from each of the plurality of mobile stations, and sets a guard interval length for each mobile station based on the estimated delay spread. The number of symbols, which is the number of data symbols that can be inserted in one frame, is determined for each mobile station from the determined guard interval length and data symbols of a predetermined length, and determined for each mobile station. adding the guard interval length to the beginning of the data symbol addressed to the mobile station, the frame including a number of symbols of the data symbol corresponding to the mobile station to execute the process of generating the addressed to the mobile station to the computer, the symbol When the number is calculated for each mobile station, the “number of symbols” x “total length of guard interval and data symbols” is a predetermined length. A shall to execute the process of determining the number of symbols to be less than the computer.

FIG. 1 is a diagram for explaining a guard interval. FIG. 2 is a diagram for comparing communication processing methods of related technologies. FIG. 3 is a block diagram illustrating a configuration example of the wireless device according to the present embodiment. FIG. 4 is a diagram for explaining an example when the wireless device shown in FIG. 3 is adapted to an actual environment. FIG. 5 is a schematic diagram of a frame showing a state when signals transmitted from each of the mobile stations shown in FIG. 4 are received by the base station. FIG. 6 is a flowchart showing an operation procedure of the wireless device of this embodiment. FIG. 7 is a schematic diagram showing a frame according to the communication processing method of the present embodiment and the frame shown in FIG. FIG. 8 is a block diagram illustrating a configuration example of the communication terminal according to the present embodiment.

  The configuration of the wireless device of this embodiment will be described. A case will be described where the radio apparatus of the present embodiment is a radio base station.

  FIG. 3 is a block diagram illustrating a configuration example of the wireless device according to the present embodiment. The configuration shown in FIG. 3 is an example when the IEEE 802.16e specification assumed to be used in mobile communication is used.

  As illustrated in FIG. 3, the wireless device 10 includes a wireless processing unit 108 that transmits and receives radio waves via an antenna 100, an OFDM reception unit 101, a scheduling unit 102, a control unit 103, a serial / parallel conversion unit 104, Subcarrier modulation section 105, IFFT (Inverse Fast Fourier Transform) section 106, and guard interval addition section 107 are provided.

  A signal received from each mobile station via the antenna 100 is sent to the OFDM receiver 101. The OFDM receiver 101 is a circuit that removes a guard interval from a received signal, performs FFT on the received signal, and demodulates a subcarrier. Further, the OFDM receiving unit 101 includes a circuit that estimates a delay spread based on signals from the respective mobile stations.

  The data signal demodulated by the OFDM receiving unit 101 is sent to the network (not shown) side, while the delay spread information is sent to the scheduling unit 102.

  The wireless device 10 is provided with a CPU (Central Processing Unit) (not shown) and a memory (not shown), and the scheduling unit 102 is virtually configured by the CPU executing a program. The scheduling unit 102 determines the guard interval length for each mobile station from the delay spread of each mobile station as follows. Scheduling section 102 obtains the difference between the desired wave and the delayed wave from the pilot symbol inserted in the frame. For example, the desired wave is a signal that arrives directly, and is a signal that arrives after being reflected on the wall or ground of a building. The desired wave is a signal received first among these received signals. The difference between these radio waves is proportional to the delay spread. Then, the scheduling unit 102 calculates the length of the guard interval corresponding to the difference. The scheduling unit 102 decreases the guard interval length as the difference is smaller, and increases the guard interval length as the difference is larger. That is, the scheduling unit 102 calculates a guard interval length proportional to the delay spread. Further, the scheduling unit 102 calculates the number of data symbols that can be packed in one frame from the obtained guard interval length and data symbol length. Hereinafter, the number of data symbols inserted in one frame is simply referred to as “symbol number”.

  When receiving information on the number of symbols from the scheduling unit 102, the control unit 103 is a circuit that controls the serial / parallel conversion unit 104 and the guard interval adding unit 107 in response to scheduling information including information on the number of symbols per frame. is there.

  The serial / parallel conversion unit 104 is a circuit that converts data input from the network from parallel data to serial data. The subcarrier modulation unit 105 is a circuit that is connected to the subsequent stage of the serial / parallel conversion unit 104 and modulates serial data. The IFFT unit 106 is a circuit that converts signals arranged on the frequency axis into a time axis.

  The guard interval adding unit 107 is a circuit that adds a signal having a guard interval length determined by the scheduling unit 102 to the head of the data symbol via the control unit 103. The frame including the data symbol to which the guard interval is added is transmitted from the antenna 100 via the radio processing unit 108 connected to the subsequent stage of the guard interval adding unit 107. A frame is allocated to each mobile station, and one frame is allocated to one user.

  Next, the operation of the wireless device 10 shown in FIG. 3 will be described. FIG. 4 is a diagram for explaining an example when the wireless device shown in FIG. 3 is adapted to an actual environment. The base station 301 shown in FIG. 4 is provided with the radio apparatus 10 shown in FIG.

  A base station 301 is provided in the center of the service area 3 shown in FIG. Service area 3 corresponds to a communication area in which base station 301 can wirelessly communicate with a mobile station. Then, as shown in FIG. 4, it is assumed that there are three mobile stations 302, 303, and 304 having different distances from the base station 301. Also, as shown in FIG. 4, it is assumed that buildings 402, 403, and 404 are scattered. In mobile communication, as shown in FIG. 4, a plurality of mobile stations 302, 303, and 304 communicate with one base station 301.

  When a signal is transmitted from each of the mobile stations 302, 303, and 304 to the base station 301, a delayed wave 32 u of the mobile station 302 is generated due to the effect of the building 402, and a delayed wave 33 u of the mobile station 303 is generated due to the effect of the building 403. And a delayed wave 34u of the mobile station 304 is generated due to the influence of the building 404. The delayed wave 32u of the mobile station 302 arrives at the antenna 100 of the base station 301 with a delay of time d1 with respect to the desired wave 32d. The delayed wave 33u of the mobile station 303 arrives at the antenna 100 of the base station 301 with a delay of time d2 with respect to the desired wave 33d. The delayed wave 34u of the mobile station 304 arrives at the antenna 100 of the base station 301 with a delay of time d3 with respect to the desired wave 34d.

  FIG. 5 is a schematic diagram of a frame showing a state when signals transmitted from each of the mobile stations shown in FIG. 4 are received by the base station. Each delay of the delay waves 32u, 33u, 34u is represented using a frame. From FIG. 5, it can be seen that there is a relationship of d1 <d2 <d3. The subchannel used by each mobile station is fixed.

  FIG. 6 is a flowchart showing an operation procedure of the wireless device of this embodiment.

  In FIG. 3, the signal of each mobile station received by the antenna 100 is demodulated by the OFDM receiving unit 101 via the radio processing unit 108, and the delay spread is estimated (step 101). The demodulated signal is sent to the network side, and information regarding the reception status of each mobile station, such as delay spread information of each mobile station and reception characteristics of subcarriers, is sent to the scheduling unit 102.

  The scheduling unit 102 determines each guard interval length from the reception status of each mobile station as follows. In the present embodiment, the scheduling unit 102 calculates the guard interval length corresponding to the delay spread for each mobile station as follows (step 102). The scheduling unit 102 decreases the guard interval length for a mobile station having a small delay spread, and increases the guard interval length for a mobile station having a large delay spread. The guard interval length is proportional to the delay spread of the mobile station, and differs according to the delay spread.

  A method for determining the guard interval length of the scheduling unit 102 will be specifically described with reference to FIG. When the delay time of the delay wave 32 u is small with respect to the desired wave 32 d as in the mobile station 302 shown in FIG. 5, the guard interval length is reduced, and the delay of the delay wave 34 u with respect to the desired wave 34 d as in the mobile station 304. If is large, increase the guard interval length.

  Subsequently, the scheduling unit 102 calculates a guard interval time that can be reduced per frame from the determined guard interval length. Then, the scheduling unit 102 calculates the number of symbols that can be added to one frame from the calculation result, and determines the number of symbols per frame. Then, the scheduling unit 102 sends the determined information on the guard interval length of the mobile station and the number of symbols per frame to the control unit 103.

  Serial parallel section 104 converts data sent from the network side from serial to parallel, and sends data from control section 103 to subcarrier modulation section 105 based on scheduling information including information on the number of symbols per frame. . The subcarrier modulation unit 105 performs modulation for each subcarrier, and the IFFT unit 106 converts data on the frequency axis into data on the time axis into time axis data. While the mobile station continues to communicate, one subcarrier is monopolized by that mobile station.

  The guard interval adding unit 107 determines the guard interval length determined for the mobile station by the scheduling unit 102 for each symbol based on the notification of the control unit 103 for the data symbol addressed to the mobile station. Is added (step 103). Subsequently, the guard interval adding unit 107 transmits a frame including data symbols of the number of symbols corresponding to the mobile station calculated by the scheduling unit 102 from the antenna 100 as an OFDM signal via the radio processing unit 108.

  Next, the frame by the communication processing method of this embodiment is compared with the frame shown in FIG.

  FIG. 7 is a schematic diagram showing a frame according to the communication processing method of the present embodiment and the frame shown in FIG. FIG. 7 shows a frame for each mobile station of user 1 to user 4.

  As shown in FIG. 7, in the case where the GI length is constant and in the case of Patent Document 1, when the number of symbols of the frames of user 1 to user 4 is summed, the total value is 16 in both cases. On the other hand, in this embodiment, when the number of symbols in the frames of the user 1 to the user 4 is totaled with the same frame length as the above two examples, the value is 18.

  In this embodiment, as shown in FIG. 7, the user 2 and the user 4 have a long guard interval length and the number of data symbols is 4, respectively, but the user 1 and the user 3 have a short guard interval length, Each has 5 data symbols. This is because in the signals of user 1 and user 3, data symbols can be added in the frame according to the time when the guard interval length is shortened. As can be seen from FIG. 7, in this embodiment, the transmission capacity can be improved as compared with the case where the GI length is constant and the case of Patent Document 1.

  In the present embodiment, the communication processing method from the uplink to the downlink by the radio base station device has been described. However, the communication processing method of the present embodiment is not a downlink by a communication terminal serving as a mobile station instead of the base station side. The communication may be performed from the upstream to the uplink. FIG. 8 is a block diagram illustrating a configuration example of the communication terminal according to the present embodiment. In FIG. 8, the same components as those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof is omitted. A communication terminal 300 illustrated in FIG. 8 includes an input unit 110 to which audio is input and an output unit 111 to output audio in addition to the configuration provided in the wireless device 10 illustrated in FIG. 3. In this case, each communication terminal 300 may determine the guard interval length in accordance with the delay spread of the signal received from the base station apparatus in the same manner as the operation of the radio apparatus 10, and detailed description thereof is omitted.

  In the present embodiment, a delay spread is calculated from delayed waves generated by various propagation environments, and the guard interval is dynamically changed from the determination value. The length of the guard interval is shortened for a mobile station that exists in a propagation environment with a small delay spread. On the other hand, the length of the guard interval is increased for a mobile station located in a propagation environment with a large delay spread. When the length of the guard interval in one frame can be finally shortened, the shortened time is assigned to the additional data symbol. As a result, the transmission capacity of the entire communication system can be increased.

  Further, since the difference between the desired wave and the delayed wave differs between mobile stations between the base station and each mobile station, a guard interval can be set for each mobile station. For mobile stations with a short difference, the transmission capacity can be improved by shortening the length of the guard interval and allocating the shortened time to the symbol data. On the other hand, it is possible to lengthen the guard interval for a mobile station having a large difference, thereby suppressing a reduction in transmission capacity due to intersymbol interference.

  In this embodiment, one frame is assigned to one user for communication. While the communication of a certain user continues, the user monopolizes the subcarrier, so that the subcarrier is not shared by a plurality of users on the time axis.

  In the present embodiment, the scheduling unit 102 calculates the length of the guard interval in proportion to the delay spread. Therefore, it is not necessary to prepare a plurality of guard interval length patterns in advance.

  In the present embodiment, since the length of the guard interval is determined by calculation for each frame (every short time on the order of milliseconds), communication processing can be performed in more real time.

  Furthermore, since the guard interval of OFDM wireless communication is set longer in consideration of intersymbol interference, comparing the case of a constant GI length and the case of this embodiment, the present embodiment is better for the entire communication system. Transmission capacity can be improved.

  In the present embodiment, the scheduling unit 102 has been described as being configured by the CPU executing a program. However, a dedicated circuit in accordance with the operation of the scheduling unit 102 may be provided in the wireless device.

  The present invention is not limited to the above embodiment. The present invention can also be applied to a wireless communication system that requires a guard interval, such as MC-CDMA (Multi-Carrier Code Division Multiple Access) communication.

  As an example of the effect of the present invention, the influence of intersymbol interference can be suppressed and the transmission capacity can be increased.

  While the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  Note that this application incorporates all the contents of Japanese Patent Application No. 2009-085550 filed on Mar. 31, 2009, and claims priority based on this Japanese application.

DESCRIPTION OF SYMBOLS 10 Radio | wireless apparatus 101 OFDM receiving part 102 Scheduling part 103 Control part 104 Serial parallel conversion part 105 Subcarrier modulation part 106 IFFT part 107 Guard interval addition part 108 Radio processing part

Claims (8)

A receiver that estimates a delay spread for each of the plurality of mobile stations based on signals received from each of the plurality of mobile stations;
The guard interval length is determined for each mobile station based on the delay spread estimated by the receiving unit, and can be inserted into one frame from the determined guard interval length and a data symbol of a predetermined length. A scheduling unit that calculates the number of symbols, which is the number of data symbols, for each mobile station;
The number of symbols corresponding to the mobile station calculated by the scheduling unit by adding a guard interval having a length determined by the scheduling unit corresponding to the mobile station to the head of the data symbol addressed to the mobile station A guard interval adding unit for generating a frame including the data symbol for the mobile station;
I have a,
When the scheduling unit calculates the number of symbols for each mobile station, the number of symbols is such that “the number of symbols” × “the total length of the guard interval and the data symbols” is equal to or less than a predetermined length. Determining a radio base station apparatus. The scheduling unit includes
The radio base station apparatus according to claim 1, wherein a length of the guard interval that is proportional to a size of the delay spread is calculated. A receiver for estimating a delay spread based on a signal received from a radio base station;
The length of the guard interval is determined based on the delay spread estimated by the receiving unit, and the number of the data symbols that can be inserted into one frame from the determined guard interval length and the data symbol of a predetermined length A scheduling unit for calculating a certain number of symbols;
A guard interval having a length determined by the scheduling unit is added to the head of the data symbol addressed to the radio base station, and a frame including the data symbols of the number of symbols calculated by the scheduling unit is addressed to the radio base station. A guard interval adding unit to be generated;
I have a,
The scheduling unit, when calculating the number of symbols, determines the number of symbols such that “the number of symbols” × “the total length of the guard interval and the data symbol” is equal to or less than a predetermined length. Communication terminal. The scheduling unit includes
The communication terminal according to claim 3, wherein a length of the guard interval that is proportional to a size of the delay spread is calculated. Estimating a delay spread for each of the plurality of mobile stations based on signals received from each of the plurality of mobile stations;
Determining the length of the guard interval for each mobile station based on the estimated delay spread;
Calculating the number of symbols, which is the number of data symbols that can be inserted in one frame, from the determined guard interval length and data symbols of a predetermined length for each mobile station;
A guard interval having a length determined corresponding to the mobile station is added to the head of the data symbol addressed to the mobile station, and a frame including the data symbols of the number of symbols corresponding to the mobile station is addressed to the mobile station. generated,
When calculating the number of symbols for each mobile station, the number of symbols is determined such that “the number of symbols” × “the total length of the guard interval and the data symbols” is equal to or less than a predetermined length. Processing method.   The communication processing method according to claim 5, wherein when determining the length of the guard interval, the length of the guard interval that is proportional to the size of the delay spread is calculated. Estimating a delay spread for each of the plurality of mobile stations based on signals received from each of the plurality of mobile stations;
Determining the length of the guard interval for each mobile station based on the estimated delay spread;
Calculating the number of symbols, which is the number of data symbols that can be inserted in one frame, from the determined guard interval length and data symbols of a predetermined length for each mobile station;
A guard interval having a length determined corresponding to the mobile station is added to the head of the data symbol addressed to the mobile station, and a frame including the data symbols of the number of symbols corresponding to the mobile station is addressed to the mobile station. Let the computer execute the process to generate ,
When calculating the number of symbols for each mobile station, a process of determining the number of symbols so that “the number of symbols” × “the total length of the guard interval and the data symbols” is equal to or less than a predetermined length. A program for causing the computer to execute . The program according to claim 7, wherein when determining the length of the guard interval, the program causes the computer to execute a process of calculating the length of the guard interval that is proportional to the size of the delay spread.

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