JP4509872B2 - Base station, mobile station and method - Google Patents

Description

  The present invention relates to a base station, a mobile station and a method used in a wireless communication system.

  In a conventional mobile communication system, a circuit switching type communication method is adopted, and a dedicated channel is assigned to a user. Such a method is suitable for a system in which interactive services such as voice and moving images are mainly used. However, in a future mobile communication system, traffic is transmitted in bursts as IP packets as the core network becomes IP (Internet Protocol). Therefore, signal transmission by a packet switching method is desirable even in a wireless section. Further, with packetization in the wireless section, it is necessary to minimize delay in the wireless section, reduce required transmission power, increase link capacity, and the like. Furthermore, it must be considered to reduce the influence of errors in the radio section and perform highly reliable packet transmission.

Even in such a packet-type mobile communication system, it is necessary to sufficiently suppress interference between cells. In Patent Document 1, the frequency band is divided into a plurality of subcarrier blocks, and frequency hopping is performed on each user signal within the block, and an attempt is made to reduce other cell interference in the uplink.
Japanese Patent Laid-Open No. 2004-312291

  However, since the multi-carrier method is used in Patent Document 1, the ratio (peak-to-average power ratio) (PAPR) between the peak power and the average power of the transmission signal may become very large. For this reason, distortion components are mixed in the output of the power amplifier, and there are concerns about adverse effects such as signal quality degradation and increased out-of-band radiation.

  An object of the present invention is to provide a base station, a mobile station, and a method for preventing an excessive increase in peak-to-average power ratio (PAPR) and improving uplink information transmission efficiency.

The base station used in one embodiment is
A memory for storing a channel mapping pattern of the uplink channel;
Means for notifying two or more mobile stations in a cell of channel mapping patterns orthogonal to each other in the frequency direction stored in the memory;
Chip repetition means for receiving an uplink channel signal generated by a predetermined access method and performing decoding and time non-compression, and the uplink channel according to the channel mapping pattern has a frequency spectrum arranged in a comb shape. An uplink channel from one mobile station is generated by sequentially using at least first and second channel mapping patterns orthogonal to each other,
A base station from which an uplink channel according to the second channel mapping pattern is derived by shifting the frequency spectrum of the uplink channel according to the first channel mapping pattern by a predetermined frequency .

The mobile station used in one embodiment is
Means for encoding, time compression and duplication of a signal transmitted by a predetermined access method;
Means for generating and transmitting an uplink channel by using at least the first and second channel mapping patterns orthogonal to each other notified from the base station in order, and the uplink channel according to the channel mapping pattern includes: An uplink channel having a frequency spectrum arranged in a comb shape and shifting the frequency spectrum of the uplink channel according to the first channel mapping pattern by a predetermined frequency to thereby follow the second channel mapping pattern Is the mobile station from which is derived.

  According to the present invention, it is possible to improve uplink information transmission efficiency without excessively increasing the peak-to-average power ratio.

  According to an aspect of the present invention, the spectrum of a transmission signal is corrected in a comb shape by the VSCRF-CDMA system, and the transmission signal of each user is transmitted to the base station with a channel mapping pattern that is different for each cell. The channel mapping pattern is a pattern in which the uplink channels of two or more mobile stations are orthogonal to each other in the frequency direction, the time direction, or the frequency and time directions. The channel mapping pattern indicates how the symbol arrangement in the assigned frequency band is rearranged. The frequency at which each uplink signal is transmitted is switched at regular intervals according to a different pattern for each cell in which a plurality of uplink signals are orthogonalized in a cell, so that only a specific uplink signal has a significant influence on other cell interference. It can suppress effectively receiving.

  FIG. 1 shows an outline of a mobile communication system. In the illustrated example, the base station BS1 and users (Users) A and B are communicating in the left cell, and the base station BS2 and users C and D are communicating in the adjacent cells. In each cell, transmission power control is performed on the uplink, and the transmission power of each mobile station is controlled so that the same reception quality can be obtained at the base station regardless of the position of the user in the cell. For example, the user C far from the base station BS2 transmits a signal with a larger transmission power than the user D close to the base station BS2, or the transmission power is adjusted so that the transmission power of the user D is weaker than the transmission power of the user C. Is done.

On the other hand, the signals transmitted from the users C and D reach the base station BS1 of the adjacent cell as an interference signal. In the illustrated positional relationship, the user C is located at the cell edge, and the user D is located far from the cell edge. Therefore, the signal transmitted from the user C becomes a large interference signal with respect to the base station BS1, but the signal transmitted from the user D does not become a very large interference signal with respect to the base station BS1. FIG. 2 shows a schematic spectrum of an interference signal observed at the base station BS1. It is assumed that user C uses band B ₁ and user D uses band B ₂ to transmit signals. In this case, if the user A transmits a signal in the band B ₁ and the user B transmits a signal in the band B ₂ , the uplink signal of the user A may receive a large interference due to the signal from the user C. is expected. User B's uplink signal is not expected to experience so much interference.

  Thus, the uplink signal of a user (mobile station or terminal) that uses the same band in adjacent cells may be greatly affected by interference from other cells. The apparatus and method according to the embodiments described below are intended to suppress such other cell interference as much as possible, and to promote an increase in information transmission efficiency and system capacity.

  FIG. 3 shows a portion of a transmitter according to one embodiment of the present invention. This transmitter is typically provided in a mobile station as in this embodiment. In FIG. 3, a channel encoding unit 31, a data modulation unit 32, a hopping pattern storage unit 33, a frequency control unit 34, a frequency adjustment unit 35, and a band pass filter unit 36 are depicted.

  The channel encoder 31 performs channel encoding on the data to be transmitted according to some encoding algorithm. For example, convolutional coding or turbo coding may be used as the coding.

  The data modulation unit 32 performs multi-level modulation of data to be transmitted. As a modulation scheme, various modulation multi-level schemes such as BPSK, QPSK, 16QAM, and 64QAM may be used.

  The hopping pattern storage unit 33 stores a hopping pattern for performing frequency hopping, and outputs the content of the hopping pattern according to downlink control information. The hopping pattern is a pattern specific to the cell. It is desirable that the hopping pattern is notified to the mobile station through the broadcast channel before starting communication.

  The frequency control unit 34 outputs a control signal for adjusting the frequency according to the hopping pattern.

  The frequency adjustment unit 35 appropriately shifts the frequency band of the signal to be transmitted according to the control signal from the frequency control unit 34. The frequency adjustment unit 35 may be constituted by a frequency mixer, for example.

  The bandpass filter unit 36 removes frequency components outside the band and outputs a transmission signal to a radio unit (not shown).

  When a frequency band used in the system is divided into a plurality of frequency blocks, and units such as resource allocation and information transmission are managed by the frequency block, information on the frequency block is also notified to the frequency control unit 34. . A frequency block is also called a frequency chunk or chunk, and one frequency block includes one or more carriers. For example, identification information for distinguishing frequency blocks that can be used by the mobile station may be notified to the frequency control unit 34. For example, a plurality of hopping patterns may be distinguished by a pattern number corresponding to each hopping pattern. The hopping pattern may be different between a plurality of frequency blocks, or the same hopping pattern may be used in two or more frequency blocks. When the hopping pattern is different for each frequency block, identification information for distinguishing the hopping pattern may be included in the downlink control information and notified to the hopping pattern storage unit 33. When the system band is divided into a plurality of frequency blocks, the control signal output from the frequency control unit 34 indicates a frequency obtained by adding a frequency shift amount due to frequency hopping to the center frequency of the frequency block used for communication. .

  Although not used in the present embodiment, when the transmission signal is code-spread, a spreading unit 325 is provided between the data modulation unit 32 and the frequency adjustment unit 35, and the transmission signal is spread there.

  FIG. 4 shows part of a receiver according to an embodiment of the invention. This receiver is typically provided in a base station as in this embodiment. The base station processes the received signal for each subordinate user. Since the processing related to each user is the same, the processing of the received signal related to user 1 will be described as a representative. FIG. 4 shows a hopping pattern storage unit 41, a frequency control unit 42, a frequency adjustment unit 43, a bandpass filter unit 44, a data demodulation unit 45, and a channel decoding unit 46.

  The hopping pattern storage unit 41 stores a hopping pattern for frequency hopping and outputs the contents of the hopping pattern as necessary. When the frequency band used in the system is divided into a plurality of frequency blocks and the hopping pattern is different for each frequency block, identification information for distinguishing the hopping pattern and the frequency block is notified to the hopping pattern storage unit 41. Good.

  The frequency control unit 42 outputs a control signal for adjusting the frequency according to the hopping pattern. When the system band is divided into a plurality of frequency blocks, the control signal indicates a frequency obtained by adding a frequency shift amount due to frequency hopping to the center frequency of the frequency block used for communication.

The frequency adjustment unit 43 appropriately shifts the frequency band of the signal to be transmitted according to the control signal from the frequency control unit 42. The frequency adjustment unit 43 may be configured by, for example, a frequency mixer. The bandpass filter unit 44 removes out-of-band frequency components.

  The data demodulator 45 performs demodulation corresponding to the multilevel modulation performed on the transmission side.

  The channel decoding unit 46 performs decoding corresponding to the channel encoding performed on the transmission side.

  Although not used in this embodiment, when the transmission signal is code-spread, a despreading unit 445 is provided between the bandpass filter unit 44 and the data demodulation unit 45, and the received signal is despread there.

  FIG. 5 shows a flowchart of an operation example according to an embodiment of the present invention. In step 1, a cell-specific hopping pattern is notified by a downlink signal from the base station to the mobile station. When a band used in the system is divided into a plurality of frequency blocks and one frequency block is multiplexed and used by one or more users, hopping patterns for the number of users are notified (for example, by hopping numbers). . This downlink signal can be transmitted using a common control channel or a broadcast channel for transmitting information to all users in the cell.

  In step 2, the mobile station requests the base station to schedule communication.

  In step 3, the base station notifies the mobile station of the frequency and hopping pattern that the mobile station may use in response to a scheduling request from the mobile station. When a plurality of frequency blocks are prepared in the system, information that can specify usable frequency blocks and hopping patterns is notified to the mobile station.

  In step 4, data is transmitted from the mobile station at the specified frequency or frequency block and hopping pattern.

FIG. 6 shows an example of an uplink signal scheduled with an appropriate hopping pattern. Similar to the case shown in FIG. 2, the upper diagram in FIG. 6 shows the interference signal observed at the base station BS1. For the cell of the base station BS1, signals from users C and D in adjacent cells become interference signals. In the illustrated example, the uplink signal from the user A in the cell of the base station BS1 is transmitted using alternating frequency band B ₁ or B ₂ every predetermined period. The hopping pattern of user B's uplink signal is the reverse of the hopping pattern of user A's uplink signal. In other words, the signal of user A is a period of time is transmitted in a frequency band B _1, the signal of user B is transmitted at a frequency band B _2. Signal of the user A reversed in the next period is transmitted at a frequency band B _2, the signal of user B is transmitted at a frequency band B _1. Thereafter, this transmission procedure is repeated. By switching the band used by each user for uplink signal transmission according to the hopping pattern in this way, it is possible to avoid that only the uplink signal of a specific user is affected by large interference. In other words, the influence of inter-cell interference can be distributed to one or more users in the cell.

  7 and 8 show hopping examples when the frequency band used in the system is divided into a plurality of frequency blocks (chunks). FIG. 7 is a diagram illustrating a state before frequency hopping is performed in the frequency block. One frequency block is shared by a plurality of users. In the illustrated example, a 20 MHz band is used in the entire system, and the band is divided into four frequency blocks each having a width of 5 MHz, and one frequency block is shared by a maximum of four users. Therefore, instantaneously, one user uses a band of 1.25 MHz. In the example shown in FIG. 7, one frequency block in the cell 1 is shared by users 1, 2, 3, and 4. In addition, one frequency block in the cell 2 is shared by the users 5, 6, 7, and 8. For simplicity of illustration, symbols relating to the users 3, 4, 7, and 8 are omitted. The illustrated frequency blocks used in cells 1 and 2 have the same center frequency. Therefore, if the base station schedules uplink signals as in this symbol mapping example, the user 1 and the user 5 always have a relationship of causing interference. The user 2 and the user 6 are always in a relationship of causing interference. Other users also have a relationship that interferes with one of the users.

FIG. 8 is a diagram illustrating a state after frequency hopping is performed in the frequency block. In the illustrated frequency hopping example, each user is scheduled to transmit an uplink signal using the frequency bands B ₁ , B ₂ , B ₃ , and B ₄ cyclically at regular intervals. User 1 in order from the frequency band _{B 1,} the user 2 is cyclically using four bands of 1.25MHz from the frequency band _{B 2} in order. The uplink signals of users 5 and 6 in the cell 2 are scheduled with a hopping pattern different from such a hopping pattern.

  As mentioned in the description of FIGS. 3 and 4, the transmission signal may be code spread and then transmitted from the transmitter, and the reception signal may be code despread at the receiver. Furthermore, the code spreading and code despreading may be a code division multiple access (VSCRF-CDMA: Variable Spreading Factors-Code Division Multiple Access) method using a variable spreading factor chip repetition factor. In this case, the diffusing section provided at a location referred to by reference numeral 325 in FIG. 3 may be as shown in FIG. Further, the despreading unit provided at a location referred to by reference numeral 445 in FIG. 4 may be as shown in FIG. Since the VSCRF-CDMA system can be used with a single carrier, the peak-to-average power ratio (PAPR) does not need to be excessively increased unlike the multicarrier system.

  FIG. 9 is a block diagram of a spreading unit used in a VSCRF-CDMA transmitter. The spreading unit includes a code multiplying unit 1602, an iterative combining unit 1604, and a phase shifting unit 1606.

  The code multiplier 1602 multiplies the transmission signal by a spreading code. In FIG. 9, the multiplier 1612 multiplies the transmission signal by a channelization code determined under a given code spreading factor SF. Furthermore, the multiplier 1614 multiplies the transmission signal by the scramble code. The code spreading factor SF is appropriately set according to the communication environment. More specifically, the code spreading factor SF may be set based on one or more of (1) propagation path state, (2) cell configuration, (3) traffic volume, and (4) radio parameter. The code spreading factor SF may be set by the base station or the mobile station. However, when information managed on the base station side such as traffic volume is used, it is preferable to determine the code spreading factor at the base station.

  The iterative combining section 1604 compresses the spread transmission signal in terms of time and repeats it a predetermined number of times (CRF times). The configuration and operation when the number of repetitions CRF is equal to 1 are equal to those of the direct sequence CDMA (DS-CDMA) system (however, when CRF = 1, no phase shift is required in the phase shift unit). ).

  The phase shifter 1606 shifts (shifts) the phase of the transmission signal by a predetermined frequency. The phase amount to be shifted is set uniquely for each mobile station.

  FIG. 10 is a block diagram of a despreading unit used in a VSCRC-CDMA receiver. The despreading unit includes a phase shift unit 1702, an iterative combining unit 1704, and a code despreading unit 1706.

  Phase shift section 1702 multiplies the received signal by the phase amount set for each mobile station, and separates the received signal into a signal for each mobile station.

  The iterative combining unit 1704 expands the repeated data in time (uncompresses) and restores the uncompressed data.

  The code despreading section 1706 performs despreading by multiplying the received signal by the spreading code for each mobile station.

FIG. 11 is a diagram for explaining main operations in the VSCRF-CDMA system. For convenience of explanation, one data group having a signal sequence after code spreading is represented by d ₁ , d ₂ ,. . . , D _Q and the period of each data d _i (i = 1,..., Q) is T _S. One piece of data d _i may correspond to one symbol, or any other appropriate information unit. This group of signal sequences has a period corresponding to T _S × Q as a whole. This signal series 1802 corresponds to an input signal to the iterative combining unit 1604. This signal sequence is temporally compressed to 1 / CRF and converted so that the compressed signal is repeated over a period of T _S × Q. The converted signal sequence is represented by 1804 in FIG. FIG. 11 also shows the period of the guard interval. Temporal compression can be performed using, for example, a frequency that is CRF times higher than the clock frequency used for the input signal. Thereby, the period of the individual data d _i is compressed to T _S / CRF (however, it is repeated CRF times). The compressed and repeated signal sequence 1804 is output from the iterative combining unit 1604, input to the phase shifting unit 1606, shifted by a predetermined phase amount, and output. The phase amount is set for each mobile station, and is set so that uplink signals for each mobile station are orthogonal to each other on the frequency axis.

  The frequency spectrum of the uplink signal generally looks as shown at 1806 in FIG. In the figure, the band shown as the spreading bandwidth indicates a band that will be occupied if the signal sequence 1802 after spreading (the spectrum of the input signal of the repetitive combining unit 1604) is transmitted as it is. The spectrum at the stage where time compression and repetition (the spectrum of the output signal of the repetition combiner 1604) is localized in a plurality of narrow bands, but such a spectrum is common to all mobile stations. By shifting the spectrum by a phase amount specific to the mobile station, these bands can be prevented from overlapping each other. By performing time compression, repetition, and phase shift, the frequency band for each mobile station can be narrowed, and the frequency spectrum for each mobile station can be arranged in a comb shape. Furthermore, by shifting the phase of the signal for each mobile station, orthogonalization on the frequency axis can be realized among a plurality of users in the cell.

  The operation on the receiving side is the reverse of that on the transmitting side. That is, in accordance with the phase amount for each mobile station, the phase is added to the received signal by the phase shifter 1702 in FIG. The input signal is uncompressed in time, converted into a spread signal sequence, and output from the iterative combining unit 1704. Despreading is performed by multiplying this signal by a predetermined spreading code in the despreading section 1706.

  Inter-cell interference can be effectively suppressed by appropriately setting the hopping pattern in the frequency and / or time direction even between cells of a system in which such VSCRF-CDMA communication is performed. For example, it is assumed that VSCRF-CDMA communication is performed in cells 1 and 2 of the system as shown in FIG. In this case, the base station BS1 of the cell 1 observes a comb-like spectrum as shown on the upper side of FIG. 12 due to the interference signals from the users C and D. It is assumed that user C is located at the cell edge and user D is not located at the cell edge. In the example of FIG. 12, one frequency block is shared between users A and B. As shown in the lower side of FIG. 12, the uplink signals of users A and B are scheduled to be transmitted by alternately using two types of bands indicated by the comb-like spectrum.

  The choice of band to hop is determined by the maximum number of users that are multiplexed in the entire expected band (one chunk band if chunks are used). 7 and 8, the maximum multiplexing number is 4. In the VSCRF-CDMA system, the maximum number that can be multiplexed within a given band is the number of chip repetitions (CRF) (the signals of CRF users can be made orthogonal to each other). Since hopping band options can be prepared for the number of chip repetitions, more hopping patterns can be flexibly derived, and the ability to suppress inter-cell interference can be enhanced.

1 is a schematic diagram of a mobile communication system. It is a figure which shows an example of a frequency spectrum. 1 shows a block diagram of a transmitter according to one embodiment of the present invention. FIG. 1 shows a block diagram of a receiver according to one embodiment of the present invention. FIG. 5 is a flowchart of an operation example according to an embodiment of the present invention. It is a figure which shows an example of the uplink signal scheduled with the appropriate hopping pattern. It is a figure which shows a mode before frequency hopping is performed within a frequency block. It is a figure which shows the mode after frequency hopping is performed within the frequency block. It is a block diagram of the spreading | diffusion part used for the transmitter of a VSCRF-CDMA system. It is a block diagram of the de-spreading part used for the receiver of a VSCRF-CDMA system. It is explanatory drawing of the principle of operation of a VSCRF-CDMA system. It is a figure which shows an example of the uplink signal scheduled with the appropriate hopping pattern.

Explanation of symbols

31 Channel Encoding Unit 32 Data Modulating Unit 33 Hopping Pattern Storage Unit 34 Frequency Control Unit 35 Frequency Adjustment Unit 36 Band Pass Filter Unit 41 Hopping Pattern Storage Unit 42 Frequency Control Unit 43 Frequency Adjustment Unit 44 Band Pass Filter Unit 45 Data Demodulation Unit 46 Channel decoding unit 1602 Code multiplying unit 1604 Iterative combining unit 1606 Phase shifting unit 1702 Phase shifting unit 1704 Iterative combining unit 1706 Despreading unit

Claims (8)

A memory for storing a channel mapping pattern of the uplink channel;
Means for notifying two or more mobile stations in a cell of channel mapping patterns orthogonal to each other in the frequency direction stored in the memory;
Chip repetition means for receiving an uplink channel signal generated by a predetermined access method and performing decoding and time non-compression, and the uplink channel according to the channel mapping pattern has a frequency spectrum arranged in a comb shape. An uplink channel from one mobile station is generated by sequentially using at least first and second channel mapping patterns orthogonal to each other,
A base station that derives an uplink channel according to the second channel mapping pattern by shifting the frequency spectrum of the uplink channel according to the first channel mapping pattern by a predetermined frequency .   The base station according to claim 1, wherein the predetermined access scheme is a code division multiple access (VSCRF-CDMA) scheme using a variable spreading factor chip repetition factor. Means for encoding, time compression and duplication of a signal transmitted by a predetermined access method;
Means for generating and transmitting an uplink channel by using at least the first and second channel mapping patterns orthogonal to each other notified from the base station in order, and the uplink channel according to the channel mapping pattern includes: The uplink channel according to the second channel mapping pattern has frequency spectrums arranged in a comb shape, and the frequency channel of the uplink channel according to the first channel mapping pattern is shifted by a predetermined frequency. Derived mobile station.   The mobile station according to claim 3, wherein the predetermined access scheme is a code division multiple access (VSCRF-CDMA) scheme using a variable spreading factor chip repetition factor. Notifying two or more mobile stations in a cell of channel mapping patterns orthogonal to each other in the frequency direction;
Receiving an uplink channel signal generated by a predetermined access method and performing decoding and time non-compression, and the uplink channel according to the channel mapping pattern has a frequency spectrum arranged in a comb shape. An uplink channel from one mobile station is generated by sequentially using at least first and second channel mapping patterns that are orthogonal to each other;
The uplink channel according to the second channel mapping pattern is derived by shifting the frequency spectrum of the uplink channel according to the first channel mapping pattern by a predetermined frequency. Method used in.   6. The method according to claim 5, wherein the predetermined access scheme is a code division multiple access (VSCRF-CDMA) scheme using a variable spreading factor chip repetition factor. Performing encoding, time compression and duplication of a signal transmitted by a predetermined access method;
An uplink channel is generated by using at least the first and second channel mapping patterns orthogonal to each other notified from the base station in order, and the uplink channel according to the channel mapping pattern includes: And an uplink channel according to the second channel mapping pattern by shifting the frequency spectrum of the uplink channel according to the first channel mapping pattern by a predetermined frequency. A method used in a mobile station, characterized in that a channel is derived.   8. The method of claim 7, wherein the predetermined access scheme is a code division multiple access (VSCRF-CDMA) scheme using a variable spreading factor chip repetition factor.

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