JP2007282024A - Radio communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication apparatus using OFDMA (orthogonal frequency division multiple access) in which long-term frame disappearance does not occur in a data burst allocated to each subscriber even in a case where the frequency band of a certain sub-channel is being strongly interfered for a long time. <P>SOLUTION: The radio communication apparatus is characterized in comprising a scheduling means for performing control so as not to continuously allocate the same data burst to a quality deteriorated sub-channel if it is detected based on sub-channel line quality information that the quality of specific one or more sub-channels is deteriorated rather than prescribed quality continuously in time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio communication apparatus for BS (base station) that uses OFDMA (Orthogonal Frequency Division Multiplexing access) as a multiple access scheme and has scheduling means for assigning subchannels to data bursts.

  OFDM (Orthogonal Frequency Division Multiplexing) is the terrestrial digital TV broadcast in Japan and Europe, ADSL, IEEE802.11a of high-speed wireless LAN standard, and WiMAX, etc. Adopted in communication applications.

  OFDM achieves high frequency efficiency by using a plurality of subcarriers (subcarriers) having different center frequencies. This is a multiplex communication method in which data to be transmitted is divided finely and transmitted in parallel on a plurality of subcarriers. By dividing the data, the symbol transmission rate per subcarrier can be made slower than in the case of serial transfer, and a pilot signal used for phase correction or the like can be inserted. For this reason, it is possible to reduce the influence of fading (a phenomenon in which the signal strength and the like change greatly in time and space in wireless communication) as a whole. In addition, transmission is performed orthogonally to each other so that interference does not occur even if the bands of adjacent subcarriers are overlapped so as to overlap each other. In addition, OFDM uses a “guard interval” that sends data with some overlap in time. Even if a signal (ghost) that has a time shift due to diffuse reflection or the like arrives at the receiving point, it is multipath. A system that does not cause failures can be realized. This feature is one of the main reasons why OFDM is adopted in terrestrial digital TV broadcasting where multipath is likely to occur.

  OFDMA (Orthogonal Frequency Division Multiple Access) divides a carrier into a plurality of subcarriers like OFDM, but differs from OFDM in that the divided subcarriers are grouped. A subcarrier within a group is called a subchannel, and a single subscriber may occupy these subchannels, or a plurality of subscribers may share a subchannel.

  WiMAX will be described as a system that employs OFDMA. The WiMAX wireless access system is defined as a standard in Non-Patent Document 1.

  FIG. 1 is an explanatory diagram showing an example of a physical layer of a wireless communication device for WiMAX base station (BS) using OFDMA. In FIG. 1, functions not directly related to the present invention, such as synchronization processing, channel estimation, equalization processing, and power control, are omitted.

  First, transmission processing will be described.

  One of the transmission data al and the allocation information ql to the subscriber is selected by the switch 11 and input to the physical layer processing of the BS wireless communication apparatus. Here, the allocation information ql includes the following three pieces of information (details will be described later).

[1] FCH (Frame Control Header)
[2] DL-MAP (Downlink MAP)
[3] UL-MAP (Uplink MAP: Uplink allocation information)
Also, the transmission data al to the subscriber includes data for a plurality of subscribers who are communicating. Here, the transmission data al and the allocation information ql to the subscriber are both included in a PDU (Protocol Data Unit: protocol data unit) output from the MAC layer, and the PDU includes a MAC header, payload, CRC. (Cyclic Redundancy Check).

  The output bl of the switch 11 is input to the randomization processing unit 12. The purpose of randomization is as follows.

  (1) Reduce the number of unmodulated carriers so that transmission can be performed efficiently.

  (2) Ensure that enough bits are required for clock recovery.

  The randomized data cl is then input to the error correction coding processing unit 13 and subjected to error correction coding. As error correction, convolutional coding, which is random error correction coding, is used. Bit interleaving processing unit 14 performs bit interleaving on data dl that has been subjected to error correction coding in order to convert a burst error into a random error. Thereafter, the modulation mapping processing unit 15 maps the bit-interleaved data el to a signal point using a modulation scheme such as QPSK or 16QAM, and outputs a transmission symbol fl.

  The OFDMA multiplexing processing unit 16 performs processing for dividing the transmission symbol fl finely and carrying it in parallel on a plurality of subcarriers. In OFDMA, the divided subcarriers are grouped, the subcarriers in the group are called subchannels, and the subchannels are allocated to the subscribers so that the plurality of subscribers share the subchannels. The frame structure of OFDMA has a two-dimensional structure in which the horizontal axis is an OFDMA symbol number and the vertical axis is a subchannel number. Details of the frame structure will be described later. Subchannel allocation to data bursts on the OFDMA frame is adaptively performed in the time domain based on allocation information ql that is output from a scheduling processing unit 24 described later.

  Thereafter, the transmission signal gl multiplexed by OFDMA is processed by the transmission RF unit 17. The transmission RF unit 17 includes a transmission filter, an orthogonal modulation processing unit that up-converts the transmission carrier frequency, a power amplifier, and a transmission antenna.

  A transmission signal hl that is an output of the transmission RF unit 17 is transmitted to an SS (Subscriber Station).

  Next, processing of the receiving system will be described.

  A reception signal il transmitted from the SS and affected by fading, interference, and the like on the transmission path is input to the reception RF unit 18.

  The reception RF unit 18 includes a reception antenna, an LNA, an orthogonal demodulation processing unit that down-converts a reception signal to a baseband frequency, and a reception filter.

  An output signal jl from the reception RF unit 18 is divided into reception signals (reception symbol sequences) kl for each subscriber by the OFDMA division processing unit 19 based on allocation information ql which is an output from the scheduling processing unit 24 described later. . The subsequent processing is executed for each received signal for each subscriber.

  A reception symbol string kl that is a reception signal for each subscriber is converted into a reception bit string ll by the demodulation demapping processing unit 20. Thereafter, the received bit string 11 is bit deinterleaved by the bit deinterleave processing unit 21, and a bit string ml in which a burst error is converted into a random error is output. Next, the error correction decoding processing unit 22 performs error correction decoding on the bit string ml. Viterbi decoding is used as error correction decoding, and a bit string nl subjected to error correction decoding is output. The randomization restoration processing unit 23 performs a process reverse to the randomization on the bit string nl and outputs received data ol.

  Scheduling of the scheduling processing unit 24 is a function that adaptively assigns subchannels to data bursts in the time domain, but a specific scheduling method is defined in order to allow a vendor to be unique. It is assumed that it is performed in a layer higher than the MAC layer. The following three pieces of information are included as allocation information ql that is a scheduling result.

  [1] FCH (frame control header): Defines the profile of the subsequent downstream burst. Specifically, a DL-MAP profile (type of error correction code used in DL-MAP, DL-MAP message length, etc.) is shown.

  [2] DL-MAP (downlink allocation information): Data burst mapping information in downlink subframe (frame number, frame length, start OFDMA symbol number of each data burst, start subchannel logical number, and transmission of each data burst) The number of OFDMA symbols necessary for the transmission) and the physical layer profile (modulation scheme, error correction coding scheme, coding rate, etc.) of each data burst in the downlink subframe.

  [3] UL-MAP (uplink allocation information): data burst mapping information in uplink subframes (starting OFDMA symbol number of each data burst, starting subchannel logical number, OFDMA required for transmitting each data burst) And the physical layer profile (modulation method, error correction coding method, coding rate, etc.) of each data burst in the uplink subframe.

  FCH, DL-MAP, and UL-MAP are broadcast to all SSs (subscriber terminals).

  FIG. 6 is an explanatory diagram showing a frame structure of OFDMA. FIG. 6 shows an OFDMA frame structure of TDD (Time Division Duplexing) system. A frame n indicated by an index n includes a downlink (DL) subframe and an uplink (UL) subframe. The horizontal axis indicates the OFDMA symbol number (the index at the beginning of the frame is indicated as k), and the vertical axis indicates the subchannel logical number. Here, the subchannel logical number will be described. In OFDMA, after the divided subcarriers are grouped (the subcarriers in the group are called subchannels), for each subchannel, a carrier for data transmission, a pilot carrier used for phase adjustment, a guard band, etc. A null carrier to be used is assigned to each of the groups. A subchannel logical number is a group in which a number starting with an index s is assigned to only a subchannel assigned to a data transmission carrier for each group.

  TTG (Transmit / Receive Transition Gap) is a transmission / reception switching gap, and RTG (Receive / Transmit Transition Gap) is a reception / transmission switching gap.

  The assignment of each burst to the frame structure will be described below. The preamble used for frame synchronization, carrier recovery, clock recovery, etc. is arranged at the beginning of the frame, and then arranged in the order of FCH, DL-MAP, and UL-MAP. The arrangement rule starts from the OFDMA symbol number k and the subchannel logical number s, and is arranged in order so that the subchannel logical number increases by one. When s + 15 is reached, the process proceeds to the next OFDMA symbol number.

  The remaining part of the downlink subframe consists of data bursts for individual SSs. Each data burst is assigned an allocation area defined by DL-MAP and a modulation scheme, error correction coding scheme, and coding rate according to the burst profile. In FIG. 6, downlink bursts # 1 to # 14 are indicated for downlink data bursts. Each data burst assignment starts with the smallest OFDMA symbol number and smallest subchannel logical number that have not yet been assigned, and is assigned in increments of 2 symbols in the increasing direction of the OFDMA symbol number, reaching the last symbol in the data region. If so, it is assigned by folding back to the smallest OFDMA symbol number of the next subchannel logical number. In FIG. 6, for the sake of simplicity, each data burst is drawn to end with the last symbol in the data area. Further, although it is possible to assign a plurality of SSs to each downlink data burst, in the following description, it is assumed that one SS is assigned to one data burst for simplicity.

  After the downlink subframe, the uplink subframe starts with a TTG (gap for transmission / reception switching).

  The uplink subframe is composed of data bursts for individual SSs. Each data burst is assigned an allocation area defined by UL-MAP and a modulation scheme, error correction coding scheme, and coding rate according to the burst profile. In FIG. 6, uplink data bursts are indicated as uplink bursts # 1 to # 14. Each data burst assignment starts with the smallest OFDMA symbol number and smallest subchannel logical number that have not yet been assigned, and is assigned in increments of 3 symbols in the increasing direction of the OFDMA symbol number, reaching the last symbol in the data region. If so, it is assigned by folding back to the smallest OFDMA symbol number of the next subchannel logical number. In FIG. 6, for the sake of simplicity, each data burst is drawn to end with the last symbol in the data area. At the end of the uplink data burst, a ranging subchannel is assigned. The ranging subchannel is a channel for performing ranging in order to adjust the communication timing and transmission output between the BS and the SS. The SS uses the ranging subchannel specified by the BS to communicate with the BS. The transmission timing, output and frequency are adjusted while repeating the above.

  The subchannel line quality measurement unit 25 performs measurement for each burst for the purpose of selecting an uplink burst profile and performing uplink power control. Here, RSSI (Receive Signal Strength Indicator) and CINR (Carrier-to-Interference-and-Noise Ratio) for each burst from the received signal rl for each subchannel output from the OFDMA division processing unit 19. ) And the like are measured and input to the scheduling processing unit 24 as subchannel line quality information pl.

  Consider a case where voice communication is performed by the BS wireless communication apparatus, that is, voice encoded information is transmitted as transmission data. As a speech encoding method, for example, ITU-TG. Using 8 kbit / sCS-ACELP (conjugate structure-algebraic code-excited linear prediction), which is 729 standard (or TTC standard JT-G729), speech coding information (line spectrum pair) every 10 msec speech coding frame length. Information (synthesis filter parameters), adaptive codebook delay information, fixed codebook information, adaptive and fixed codebook gain information) are transmitted and received by the BS radio communication apparatus. Corresponding to this, the OFDMA frame length is 10 msec. In FIG. 6, subscribers # 1 to # 14 are assigned downlink bursts # 1 to # 14 on the downlink and uplink bursts # 1 to # 14 on the uplink. To do.

  When the loss of a coding parameter frame (equivalent to a 10 ms frame) is detected by CRC due to a poor channel environment or the like, ITU-TG. As defined in the H.729 standard (or TTC standard JT-G729), the following frame erasure compensation processing is performed in the speech decoder.

(1) Repetition of synthesis filter parameter-The synthesis filter in the lost frame uses the LP (Linear Prediction) parameter of the previous normal frame.

(2) Adaptation and attenuation of fixed codebook gain ・ The fixed codebook gain is obtained based on the attenuation of the past fixed codebook gain.

The adaptive codebook gain is obtained on the basis of the attenuated past adaptive codebook gain.
IEEE Std 802.16-2004, “Part 16: Air Interface for Fixed Broadband Wireless Access Systems”, 2004, [online] Internet <URL: http://standards.ieee.org/getieee802/802.16.html>

  The above frame loss compensation processing is effective when frame loss does not occur frequently. However, in FIG. 6, for example, if the frequency band of the sub-channel of the data burst assigned to a certain subscriber has been subjected to strong interference for a long time, frame loss will occur for a long period of time, and frame loss compensation Call quality is not improved by processing.

  In addition, since real-time characteristics are necessary in voice communication, it is not possible to use an ARQ (Automatic Repeat Request) function as in data communication.

  The present invention has been made in view of the above circumstances, and when it is detected that the quality of a specific one or more subchannels is continuously degraded in time from a predetermined quality, the same data burst is generated. It is an object of the present invention to provide a wireless communication apparatus using OFDMA (Orthogonal Frequency Division Multiple Access) that performs control so as not to be continuously assigned to the subchannel with degraded quality.

  In order to achieve the above object, the present invention uses OFDMA (Orthogonal Frequency Division Multiple Access) as a multiple access scheme, and is a two-dimensional frame configured with an OFDMA symbol number on one axis and a subchannel number on the other axis. In a wireless communication apparatus having a structure and adaptively assigning subchannels to data bursts in the time domain, subchannel line quality measuring means for measuring the channel quality of each subchannel, and the subchannel line quality measuring means If it is detected that the quality of one or more specific subchannels is continuously degraded in time from the predetermined quality based on the subchannel channel quality information that is output from the same data burst, And scheduling means for controlling such that the subchannel is not assigned to the degraded quality channel. It is an.

  For example, CINR (signal to interference noise ratio) or the like can be used as the subchannel line quality.

  By applying the radio communication apparatus of the present invention, even when a frequency band of a certain subchannel has been subjected to strong interference for a long time, a frame loss of a long period occurs in a data burst assigned to each subscriber. In other words, the frame erasure compensation process functions effectively in the voice decoder, and all subscribers can perform good voice communication.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The embodiment of the present invention uses OFDMA (Orthogonal Frequency Division Multiple Access) as a multiple access scheme, and has a two-dimensional OFDMA frame structure in which one axis is an OFDMA symbol number and the other axis is a subchannel number. The wireless communication apparatus shown in FIG. 1 is used as a wireless communication apparatus that adaptively assigns subchannels to data bursts in the time domain. In the embodiment of the present invention, the subchannel channel quality measurement unit 25 measures the channel quality of each subchannel, and the scheduling processing unit 24 that assigns the subchannel to the data burst outputs the output from the subchannel channel quality measurement unit 25. If it is detected that the quality of one or more specific subchannels is continuously degraded in time from a predetermined quality based on the subchannel channel quality information, the same data burst is continuously Control is performed so as not to be assigned to subchannels with degraded quality.

  1 measures the CINR (signal-to-interference noise ratio) for each subchannel from the received signal rl for each subchannel output from the OFDMA division processing unit 19 in the subchannel line quality measurement unit 25, The quality information pl is input to the scheduling processing unit 24.

  The scheduling processing unit 24 observes the CINR state in correspondence with the two-dimensional OFDMA frame structure, and detects a subchannel in which the CINR has deteriorated below a predetermined threshold over a long period of time. If a subchannel with degraded CINR is detected due to strong interference over a long period of time, scheduling is performed so that the same subscriber, that is, the same data burst is not continuously assigned to the degraded subchannel due to the interference. .

  An example of the scheduling method according to the embodiment of the present invention will be described with reference to FIGS.

  FIG. 2 focuses on the frame number n and shows the same OFDMA frame structure as FIG. 6, but is strong for a long time when the shaded subchannels (subchannel logical numbers s + 2 and s + 3) are detected. It represents a subchannel in which CINR deteriorates due to interference. First, in frame n, data bursts assigned to subchannels with subchannel logical numbers s + 2 and s + 3 are burst # 3 and burst # 4 in the downlink and uplink.

  In this state, in the next frame n + 1, the scheduling processing unit 24 assigns data bursts assigned to the subchannels of the subchannel logical numbers s + 2 and s + 3 to burst # 5 and burst # 6 in the downlink and uplink as shown in FIG. Replace. Further, in the next frame n + 2, as shown in FIG. 4, the data bursts assigned to the subchannels of the subchannel logical numbers s + 2 and s + 3 are replaced with burst # 7 and burst # 8 in the downlink and uplink. Further, in the next frame n + 3, as shown in FIG. 5, the data bursts assigned to the subchannels of the subchannel logical numbers s + 2 and s + 3 are replaced with the burst # 9 and the burst # 10 in the downlink and uplink. Similarly, for the subsequent frame, in frame n + 4, the data burst allocated to the subchannels of subchannel logical numbers s + 2 and s + 3 is replaced with burst # 11 and burst # 12 in the downlink and uplink, and in frame n + 5, the subchannel logic Data bursts assigned to subchannels numbered s + 2 and s + 3 are replaced with downlink burst # 14 for the downlink (downlink burst # 14 uses two subchannels), and uplink burst # 13 and uplink are assigned for the uplink. Replace with burst # 14. In the next frame n + 6, the data bursts assigned to the subchannels of the subchannel logical numbers s + 2 and s + 3 are replaced with the burst # 1 and the burst # 2 in the downlink and uplink. This data burst replacement is repeated until a change in the state of the subchannel line quality is detected.

  In the embodiment of the present invention, the TDD scheme is used as the duplex scheme, and the uplink / downlink is realized at the same frequency. Therefore, if the uplink subchannel channel quality is measured, the result is directly transmitted to the downlink. Applicable to lines.

  Further, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

1 is a configuration explanatory diagram illustrating an example of a physical layer of a wireless communication apparatus for WiMAX base station (BS) using OFDMA. FIG. It is an OFDMA frame structure explanatory drawing for demonstrating an example of the scheduling method which concerns on embodiment of this invention. It is an OFDMA frame structure explanatory drawing for demonstrating an example of the scheduling method which concerns on embodiment of this invention. It is an OFDMA frame structure explanatory drawing for demonstrating an example of the scheduling method which concerns on embodiment of this invention. It is an OFDMA frame structure explanatory drawing for demonstrating an example of the scheduling method which concerns on embodiment of this invention. It is explanatory drawing of an OFDMA frame structure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Switch, 12 ... Randomization process part, 13 ... Error correction encoding process part, 14 ... Bit interleave process part, 15 ... Modulation mapping process part, 16 ... OFDMA multiplexing process part, 17 ... Transmission RF part, 18 REFERENCE RF unit, 19 OFDMA division processing unit, 20 DEMODULATION demapping processing unit, 21 BIT DEINTERLETION processing unit, 22 ERROR CORRECTION decoding processing unit, 23 Randomization restoration processing unit, 24 SCANNING processing unit, 25. Subchannel line quality measurement unit.

Claims (1)

Uses OFDMA (Orthogonal Frequency Division Multiple Access) as a multiple access method, and has a two-dimensional frame structure in which one axis is an OFDMA symbol number and the other axis is a subchannel number. In a wireless communication device that performs allocation adaptively in the time domain,
Subchannel line quality measuring means for measuring the channel quality of each subchannel;
Based on the subchannel line quality information that is output from the subchannel line quality measuring means, it has been detected that the quality of one or more specific subchannels has deteriorated from a predetermined quality continuously in time. And a scheduling means for controlling so that the same data burst is not continuously assigned to the sub-channel having the degraded quality.

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