JP2008017521A - Radio base station used in cdma communication, and transmission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve proper balance of speeding up of a data rate and suppression of transmission power in a CDMA communication system. <P>SOLUTION: When a plurality of spreading codes can be secured, a decision section 101 notifies a user data separation section 103 and spreading sections 105-1 to 105-n that code multiplexing is performed. The user data separation section 103 separates user data and delivers them to the spreading sections 105-1 to 105-n. The spreading sections 105-1 to 105-n use spreading codes that are different from one another to spread the user data. A code multiplexing section 106 multiplexes and transmits the user data spread by the spreading sections 105-1 to 105-n. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication apparatus used in a mobile communication system using CDMA, and more particularly to a radio base station used in a mobile communication system using CDMA.

In recent years, CDMA (Code Division Multiple Access) technology, particularly DS-CDMA (Direct Spread −
Development of digital cellular radio communication systems using CDMA technology is underway.

  In a CDMA communication system, a code is generally assigned to each channel or each user, and each channel or each user is identified from each other by that code. Therefore, in the CDMA communication system, a plurality of communications are realized simultaneously using the same frequency.

  However, when a plurality of communications are performed simultaneously, the signals of the respective channels interfere with each other. As a result, the number of channels (channel capacity) that can be communicated simultaneously is limited. Here, the interference between signals depends on the transmission power of each signal. Therefore, when the communication quality of the transmission path is good, the interference between signals is reduced by reducing the transmission power, and the channel capacity is increased. This technique is often called transmission power control (TPC), and has an effect of suppressing power consumption of the mobile device.

  In recent years, a technique for preparing a plurality of modulation schemes in advance and adaptively selecting a modulation scheme to be actually used between a base station and a mobile device according to a communication environment has been studied. Hereinafter, this adaptive modulation system will be described.

  In adaptive modulation in a CDMA communication system, the modulation scheme is usually adaptively changed based on the communication quality (for example, signal-to-interference power ratio, error rate, etc.) of the transmission path between the base station and the mobile station. As a modulation method, for example, QPSK shown in FIG. 1A, 16QAM shown in FIG. 1B, and 64QAM shown in FIG. 1C are prepared. Here, in QPSK, four signal points are defined on the phase plane, and 2-bit data is transmitted for each symbol. In 16QAM, 16 signal points are defined on the phase plane, and 4-bit data is transmitted for each symbol. Further, in 64QAM, 64 signal points are defined on the phase plane, and 6-bit data is transmitted for each symbol. For example, when the communication environment is not good, data is transmitted using QPSK, and when the communication environment is good, data is transmitted using 16QAM or 64QAM. Thereby, efficient data transmission is realized.

  FIG. 2 is a block diagram of an existing transmitter that can perform adaptive modulation. Here, it is assumed that the transmission device multiplexes user data and control data and transmits the multiplexed data. This transmission apparatus is a base station apparatus provided in the mobile communication system.

  The data flow rate monitoring unit 1 monitors the data rate of user data to be transmitted. The encoding unit (CHCOD) 2 encodes user data to be transmitted according to a predetermined encoding method. The variable rate control unit 3 temporarily holds the user data and outputs the user data at a predetermined rate while referring to the monitoring result by the data flow rate monitoring unit 1. The adaptive modulation unit 4 determines the modulation method based on the line quality information. The channel quality information represents the state of the channel between the base station and the mobile device, and for example, a signal-to-interference power ratio is used.

  The spreading unit 10 modulates user data according to the modulation scheme determined by the adaptive modulation unit 4 and spreads the modulated data. Specifically, the mapping unit 11 arranges user data at corresponding signal points according to the modulation scheme determined by the adaptive modulation unit 4. The spreading code generator 12 generates a spreading code assigned to user data to be transmitted (or a mobile device that receives the user data). Then, the spreader 13 multiplies the output of the mapping unit 11 by the spreading code generated by the spreading code generator 12.

  The spreading unit 20 spreads the control data. The configuration of the diffusion unit 20 is basically the same as that of the diffusion unit 10. However, the spreading unit 20 generates a predetermined spreading code for the control data, and the control data is spread by the spreading code. Further, the control data is basically not adaptively modulated.

  The code multiplexing unit 21 multiplexes and transmits the output of the spreading unit 10 and the output of the spreading unit 20. A receiving device (here, a mobile device) that receives a signal transmitted from the transmitting device reproduces user data using the same code as the spreading code used in the transmitting device.

  An example of adaptive modulation operation in the transmission apparatus will be briefly described. Here, it is assumed that user data is currently modulated by QPSK and transmitted. It is also assumed that the line quality is good.

In this case, the transmission apparatus can selectively execute the following three operations.
(1) The transmission power is reduced without changing the modulation method.
(2) The symbol rate is reduced to ½, and the modulation method is changed from QPSK to 16QAM. In this case, since the number of bits per symbol is doubled, the data rate does not change. On the other hand, since the symbol rate is halved, as a result, increase in transmission power can be suppressed to some extent.
(3) The modulation scheme is changed from QPSK to 16QAM without changing the symbol rate. In this case, since the number of bits per symbol is doubled, the data rate is doubled. However, the transmission power increases.

  In general, mobile communication systems are required to increase the channel capacity, to suppress the transmission power of the communication device (especially to reduce the power consumption of the mobile device), and to increase the data rate of user data. The These requests are realized by appropriately selecting the above (1) to (3).

  However, the existing technology cannot satisfy these requirements at the same time. That is, in order to maintain the data transmission error rate at a constant value, the distance between signal points arranged on the phase plane shown in FIGS. 1A to 1C needs to be a constant value. On the other hand, as is well known, the transmission power is proportional to the square of the distance from the origin to the corresponding signal point in the phase plane coordinates. Therefore, if the number of signal points to be used increases, the transmission power inevitably increases. For example, assuming that the distance between signal points is the same, 16QAM transmission power is about 6 dB larger than QPSK transmission power, and 64 QAM transmission power is about 12 dB larger than QPSK transmission power.

  As described above, in the existing adaptive modulation technique, when the data rate is increased, transmission power or power consumption is increased. Alternatively, when trying to ensure a certain quality under a predetermined transmission power, the data rate may not be increased.

  An object of the present invention is to achieve a high balance of data rate increase and transmission power suppression in a CDMA communication system.

  The radio base station of the present invention is used in a CDMA communication system, and increases the number of code multiplexes applied when transmitting data to one mobile station maintaining a certain modulation scheme when increasing the data rate. Is provided with a determination unit that gives priority to a change to another modulation system in which the number of types of signal points arranged on the phase plane is larger than that of the modulation system.

According to the above configuration, the number of code multiplexing is increased in preference to the change of the modulation scheme, which can contribute to the suppression of power consumption.
Note that the determination unit may increase the number of code multiplexes based on a notification of reception quality from the mobile station. The increase in the number of code multiplexes is performed, for example, in a range where code multiplex is possible.

  According to the present invention, in a CDMA communication system, an increase in data rate and a reduction in transmission power can be realized in a balanced manner.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 3 is a diagram showing a mobile communication system according to the embodiment of the present invention. In FIG. 3, the base station 30 has a function of transmitting and receiving radio signals to and from a mobile station (MS) 40 in a communication area. On the other hand, each mobile device 40 has a function of transmitting and receiving radio signals to and from the base station 30. The mobile device 40 transmits and receives data via the base station 30 when communicating with other terminal devices.

  The communication system is a CDMA communication system. Here, in the CDMA communication system, a code (spreading code) is generally assigned to each channel or each user, and each channel or each user is identified from each other by the spreading code. However, in the system of the embodiment, a plurality of spreading codes may be adaptively assigned to one user according to the communication environment. Also, a modulation scheme for signals transmitted between the base station 30 and the mobile device 40 is adaptively selected according to the communication environment.

  The base station 30 includes a spreading code management unit 31 and manages a predetermined number of spreading codes used in the communication area. That is, the spreading code management unit 31 manages the spreading code to be assigned to the mobile device 40 for communication within the communication area. Therefore, the spreading code managing unit 31 grasps the number of unused spreading codes among a predetermined number of spreading codes prepared in advance.

  In addition, the base station 30 includes a quality estimation unit 32, and detects or estimates the quality of the line between the base station 30 and each mobile device 40. That is, the quality estimation unit 32 receives a signal transmitted from each mobile device 40 and detects or estimates a signal-to-interference power ratio (SIR), an error rate, received power, and the like for each mobile device. A method for detecting or estimating a signal-to-interference power ratio (SIR), an error rate, received power, and the like is a known technique.

On the other hand, each mobile device 40 includes a quality estimation unit 41 in order to estimate the quality of the line with the base station 30. The quality estimation unit 41 receives a signal transmitted from the base station 30 and detects or estimates a signal-to-interference power ratio (SIR), an error rate, received power, and the like. The channel quality information detected or estimated by the quality estimation unit 41 is notified to the base station 30.

  Next, the transmission apparatus according to the embodiment will be described. In the following, a case where data is transmitted from the base station 30 to the corresponding mobile device 40 in the system shown in FIG. 3 will be described. That is, the transmission apparatus of the embodiment is assumed to be the base station 30 shown in FIG. However, the present invention is not limited to this, and can also be applied to the case where data is transmitted from the mobile device 40 to the base station 30.

FIG. 4 is a block diagram showing functions of the base station 30. As shown in FIG. In FIG. 4, only functions directly related to the present invention are shown.
The base station 30 includes a transmission unit (MOD) 100 and a reception unit (DEM) 200. Here, the transmitting unit 100 has a function of modulating and spreading control data and user data to be transmitted to the corresponding mobile device 40, and multiplexing and transmitting these data. The receiving unit 200 has a function of demodulating a signal received from the mobile device 40 and reproducing data.

  The data flow rate monitoring unit 1 monitors the data rate of user data to be transmitted to the corresponding mobile device 40. The encoding unit (CHCOD) 2 encodes user data to be transmitted according to a predetermined encoding method. The determination unit 101 determines whether code multiplexing should be performed based on the data rate information, the number of users information, and the line quality information. The data rate information is detected by the data flow rate monitoring unit 1. The number-of-users information is information representing the number of users communicating in the communication cell, or information representing the number of unused spreading codes not assigned to any mobile device 40. 3 is provided from the spreading code management unit 31 shown in FIG. Further, the channel quality information is detected or estimated by the quality estimation unit 41 of the corresponding mobile device 40 and is received via the reception unit 200.

  The variable rate control unit 102 temporarily holds the user data and outputs the user data at a predetermined rate in accordance with an instruction from the determination unit 101. The user data separation unit 103 distributes the user data output from the variable rate control unit 102 to one or a plurality of spreading units (105-1 to 105-n) according to an instruction from the determination unit 101. Adaptive modulation section 104 determines a modulation scheme based on an instruction from determination section 101, data rate information, and channel quality information. The data rate information and the line quality information are as described above.

  Spreading sections 105-1 to 105-n each include mapping section 11, spreading code generator 12, and spreader 13, and modulate and spread given user data. That is, the mapping unit 11 arranges user data at corresponding signal points according to the modulation scheme determined by the adaptive modulation unit 104. The spreading code generator 12 generates a spreading code assigned to the corresponding channel or user. Then, the spreader 13 multiplies the output of the mapping unit 11 by the spreading code generated by the spreading code generator 12. Note that the spreading units 105-1 to 105-n spread user data using different spreading codes.

  As described with reference to FIG. 2, the spreading unit 20 spreads the control data using a predetermined spreading code. Then, code multiplexing section 106 multiplexes and transmits the outputs of spreading sections 105-1 to 105-n and the output of spreading section 20. The mobile device 40 reproduces user data and control data using the same code as the spreading code used in the base station 30.

  The receiving unit 200 includes a demodulating unit 201 and an extracting unit 202. Here, the demodulator 201 demodulates the signal transmitted from the mobile device 40 and reproduces the data. Further, the extraction unit 202 extracts line quality information obtained in the mobile device 40 from the data reproduced by the demodulation unit 202. Then, this line quality information is passed to determination section 101 and adaptive modulation section 104.

  FIG. 5 is a diagram schematically showing a format of data transmitted from the base station 30 shown in FIG. Here, the user data is shown as being separated into three data strings by the user data separation unit 103.

  The control data includes pilot signals used for channel estimation and the like, and control bits for various controls such as transmission power control. The control data is modulated and spread by the spreader 20. Here, the modulation method is QPSK. In addition, the spreading unit 20 uses “spreading code 0” fixed in advance to spread the control data.

  On the other hand, user data (three data strings output from the user data separation unit 103) is modulated and spread by arbitrary three spreading units in the spreading units 105-1 to 105-n, respectively. At this time, each user data is modulated by a modulation scheme (QPSK, 8PSK, 16QAM, 64QAM, etc.) designated by the adaptive modulation section 104. Each user data is spread using spreading codes (spreading codes 1 to 3 in this example) that are dynamically assigned.

These data are transmitted to the corresponding mobile device 40 via the control channel and user channels 1 to 3 identified by the spreading code.
Next, the code multiplexing operation in the base station 30 will be described with reference to FIG. 6 and FIG. Here, FIG. 6 shows a data flow when code multiplexing is not performed, and FIG. 7 shows a data flow when code multiplexing is performed. FIG. 7 illustrates a case where code multiplexing is performed using three spreading codes.

  When code multiplexing is not performed, the user data is sent to the spreading unit 105-1 as it is without being separated, as shown in FIG. The user data is modulated by the mapping unit 11 and spread by the spreader 13 using the spread code 1. Here, assuming that the modulation method is QPSK, user data is arranged at corresponding signal points by 2 bits. That is, 2-bit data is transmitted for each symbol.

  On the other hand, when code multiplexing is performed, the user data is separated into three data strings by the user data separation unit 103 and sent to the spreading units 105-1 to 105-3 as shown in FIG. Each data string is modulated by the corresponding mapping unit 11 and spread by the corresponding spreader 13. At this time, “spreading code 1” is used in the spreading unit 105-1, “spreading code 2” is used in the spreading unit 105-2, and “spreading code 3” is used in the spreading unit 105-3. Therefore, assuming that the modulation method is QPSK, each spreading section 105-1 to 105-3 transmits 2-bit data for each symbol. That is, when code multiplexing is performed using three spreading codes, a total of 6-bit data is transmitted in one symbol time. In other words, assuming that the modulation scheme and the spreading factor (the number of chips per symbol) are the same, when code multiplexing is performed using n spreading codes, the user is compared with the case where code multiplexing is not performed. The data rate for transmitting data becomes n times.

Thus, when code multiplexing is performed, the data rate for transmitting user data can be increased.
Next, the point that transmission power can be suppressed by performing code multiplexing will be described. Here, a case where code multiplexing is performed and a case where code multiplexing is not performed are compared under the condition that the data rate is the same. As an example, a case is assumed in which 6-bit data is transmitted in one symbol time.
(1) When not performing code multiplexing In order to transmit 6-bit data for each symbol without performing code multiplexing, for example, 64QAM is considered to be common. In 64QAM, as shown in FIG. 1C, 64 signal points on the phase plane are used. Here, assuming that 64 signal points are arranged around the origin, and the minimum distance between the signal points is “2”, each signal point is represented by (+1, +1) (−1, +1). ) (-1, -1) (+1, -1) ... (+7, +7) (-7, +7) (-7, -7) (+7, -7). When a signal is transmitted using a certain signal point, the transmission power corresponds to the square of the distance from the origin to the signal point. Therefore, the average transmission power of 64QAM is calculated as follows.
Average power = {4 × (1 ² +2 ² ) + 8 × (1 ² +3 ² ) + 8 × (1 ² +5 ² ) + 8 × (1 ² +7 ² ) +8 (3 ² +5 ² ) + 8 × (3 ² +7 ² ) + 8 × (5 ² +7 ² ) + 4 × (3 ² +3 ² ) + 4 × (5 ² +5 ² ) + 4 × (7 ² +7 ² )} / 64
= 42
In this case, the average amplitude is 6.48.
(2) Code multiplexing Here, it is assumed that 6-bit data is transmitted in one symbol time by the method shown in FIG. That is, it is assumed that user data is modulated by QPSK by 2 bits each in spreading sections 105-1 to 105-3 and multiplexed in code multiplexing section 106.

In QPSK, assuming that signal points are arranged around the origin and the minimum distance between the signal points is “2”, the signal points are (+1, +1) (−) as shown in FIG. 1A. 1, +1) (-1, -1) (+1, -1). In addition, when the three QPSK signals modulated in the spreading sections 105-1 to 105-3 are multiplexed, the I component and Q component of the multiplexed signal are the I component and Q component of the three QPSK signals, respectively. It is obtained by adding. For example, when the I and Q components of the three QPSK signals generated by the spreading sections 105-1 to 105-3 are all (+1, +1), the signal point of the multiplexed signal is (+3, +3). become. Further, when the I component and Q component of the three QPSK signals are all (-1, -1), the signal point of the multiplexed signal is (-3, -3). Alternatively, if the I and Q components of the three QPSK signals are (−1, −1), (+1, −1), and (+1, +1), respectively, the signal point of the multiplexed signal is (+1, +1). -1). In this way, the added value is calculated for all the combinations. The multiplexed signal is (+1, +1) (-1, +1) (-1, -1) (+1, -1). +3, +3) (−3, +3) (−3, −3) (+3, −3) are arranged at 16 signal points. That is, the same signal point arrangement as 16QAM shown in FIG. 1B is obtained. Therefore, the average power of this multiplexed signal is calculated as follows.
Average power = {4 × (1 ² +2 ² ) + 8 × (1 ² +3 ² ) + 4 × (3 ² +3 ² )} / 16 = 10
In this case, the average amplitude is 3.16.

  According to the above (1) and (2), assuming that the data rate is the same, transmission of data using code multiplexing significantly reduces transmission power compared to the case where code multiplexing is not used. I understand that. In other words, power consumption can be reduced by using code multiplexing. In the above example, if 3 multi-code transmission is performed, an equivalent error rate can be obtained even if the transmission power is reduced by 6 dB compared to 64 QAM.

  In this way, by performing code multiplexing, it is possible to realize a high data rate and / or a reduction in power consumption. For example, in a conventional transmission apparatus that does not perform code multiplexing, it is assumed that there is a request for high-speed transmission that cannot be transmitted unless 64QAM is used. In this case, if the electric field strength satisfying the required Eb / No cannot be obtained with 64QAM, data transmission is performed at a data rate lower than that requested by the user or data transmission is not performed. It was. On the other hand, since the transmission apparatus of the embodiment performs code multiplexing using a plurality of spreading codes, the error rate is improved by about 3 dB even with the same transmission power as that of the conventional transmission apparatus. Eb / No of can be satisfied. That is, it is possible to satisfy the demand for high-speed transmission.

  In code multiplexing, as a matter of course, a plurality of spreading codes are simultaneously used for one user data. That is, when code multiplexing is performed, it is necessary that a plurality of spreading codes remain without being used in the communication area. Therefore, the base station of the embodiment adaptively or dynamically determines whether or not to perform code multiplexing based on the remaining number of unused spreading codes. Hereinafter, data transmission processing including processing for determining whether or not to perform code multiplexing will be described with reference to flowcharts.

  FIG. 8 is a flowchart showing the operation of the base station shown in FIG. Note that this flowchart shows only processing related to data transmission. Further, the following processing is mainly executed by the determination unit 101 and the adaptive modulation unit 104.

  In step S1, a transmission parameter is calculated based on the data rate of user data (or a requested transmission rate from the user) detected by the data flow rate monitoring unit 1. Here, as transmission parameters, parameters relating to code multiplexing and parameters relating to modulation schemes are calculated.

  As parameters related to code multiplexing, the number of multicodes and a symbol rate are calculated. The “multi-code number” is the number of spreading codes to be used simultaneously. On the other hand, the “symbol rate” represents the number of symbols to be transmitted per unit time for each spreading code. Here, this symbol rate is uniquely determined with respect to the spreading factor (SF), assuming that the chip rate is constant. Therefore, the number of multicodes and the spreading factor may be calculated as parameters related to code multiplexing.

Parameters related to code multiplexing are determined so as to satisfy the data rate requested by the user. Specifically, parameters that satisfy the following conditions are selected.
Required data rate ≤ (Number of bits per symbol) x (Symbol rate) x (Number of multicodes)
Here, if QPSK is used in spreading sections 105-1 to 105-n when code multiplexing is performed, “the number of bits per symbol = 2”. If the maximum value of the spreading code that can be assigned to each user is “n (n: natural number)”, “1” to “n” can be selected as the “multi-code number”. . However, “the number of multicodes = 1” means that code multiplexing is not performed. Further, as the “symbol rate”, a value corresponding to a certain spreading factor appropriately selected from a plurality of predetermined spreading factors is used.

  A combination of “symbol rate” and “number of multi-codes” satisfying the above conditions is selected as a candidate parameter. When there are a plurality of candidate parameters, the higher the “number of multi-codes”, the higher the priority.

  On the other hand, multi-value numbers and symbol rates are calculated as parameters related to the modulation method. Note that “multi-level number” generally means the number of signal points arranged on the phase plane, but here it means “number of bits per symbol”. That is, for example, QPSK is “2”, 8PSK is “3”, 16QAM is “4”, and 64QAM is “6”.

As a parameter related to the modulation method, a parameter satisfying the following condition is selected.
Required data rate ≤ (Multi-valued number) x (Symbol rate)
Then, a combination of “multi-value number” and “symbol rate” satisfying the above conditions is selected as a candidate parameter. When there are a plurality of candidate parameters, the higher the “multi-value number”, the higher the priority.

As described above, in step S1, transmission parameter candidates related to code multiplexing and transmission parameter candidates related to a modulation scheme are selected.
In step S2, an unused spreading code is searched with reference to the spreading code management unit 31 shown in FIG. As shown in FIG. 9A, the spreading code management unit 31 manages the use states (used / unused) of a predetermined number of spreading codes prepared in advance. The spreading code is represented by a tree structure (or hierarchical structure) as shown in FIG. 9B. In this example, 256 spreading codes are prepared.

  In steps S3 to S6, it is checked whether code multiplexing can be performed. Specifically, the “number of multi-codes” obtained in step S1 is compared with the “number of usable spreading codes” detected in step S2. At this time, if the “number of usable spreading codes” is equal to or greater than the “multi-code number”, it is considered that the corresponding code multiplexing can be performed, and the process proceeds to step S21. In step S21, a corresponding user channel is assigned. When a plurality of candidates are selected in step S1, the largest “multi-code number” is selected within a range not exceeding “the number of usable spreading codes”.

  If it is determined that code multiplexing cannot be performed (for example, when a higher-order code is used in a system using a layered orthogonal code), the optimum modulation scheme is determined in steps S11 to S16. It is determined. At this time, the quality of the line between the base station 30 and the corresponding mobile device 40 is examined, and a modulation scheme that can be used in such a communication environment is determined. If there are a plurality of available modulation schemes, the modulation scheme with the highest priority is selected. In this embodiment, information representing the line quality is received from the quality estimation unit 41 of the corresponding mobile device 40 in step S12.

  If it is determined that there is no modulation scheme that can be used in the detected communication environment, it is assumed that a user channel for transmitting the received user data cannot be allocated, and that is notified to the user in step S22. Notice.

In the channel assignment in step S21, the following processing is performed.
(1) When performing code multiplexing The determination unit 101 notifies the user data separation unit 103 of the “number of multicodes”. At this time, for example, if “the number of multicodes = 3”, the user data separation unit 103 separates the received user data into three data strings as shown in FIG. Then, the three data strings are passed to the diffusion units 105-1 to 105-3.

  Further, adaptive modulation section 104 notifies "modulation scheme: QPSK" to spreading sections 105-1 to 105-n. Thereby, spreading sections 105-1 to 105-n modulate user data with QPSK, respectively.

  Furthermore, the determination unit 101 notifies different spreading codes to the spreading units 105-1 to 105-n that process user data. Here, these spreading codes are assigned by the spreading code management unit 31, for example. Then, spreading sections 105-1 to 105-n to which spreading codes are assigned spread the user data using the codes.

In this way, user data is QPSK modulated in each of the plurality of spreading sections 105-1 to 105-n, further spread using different spreading codes, and then multiplexed.
(2) When Code Multiplexing is Not Performed The determining unit 101 notifies the user data separating unit 103 of “multicode number = 1”. In this case, the user data separation unit 103 passes the received user data as it is to the spreading unit 105-1.

  The adaptive modulation section 104 notifies the spreading section 105-1 of the modulation scheme (QPSK, 8PSK, 16QAM, 64QAM, etc.) adaptively determined according to the line quality. Then, spreading section 105-1 modulates user data using the notified modulation scheme.

  In this way, in the data transmission of the flowchart shown in FIG. 8, whether or not code multiplexing can be performed according to the usage status of the spreading code (or the number of users communicating in the communication area). The modulation scheme is determined according to the quality of the line. As a result, user data is transmitted by an appropriate method according to the communication environment, so that the data rate can be increased and / or the power consumption can be reduced. However, the present invention is not limited to this, and it may be determined whether or not to perform code multiplexing based on both the use status of the spreading code and the quality of the line.

FIG. 10 is a flowchart of processing for determining whether or not to perform code multiplexing based on the data rate, the usage status of the spreading code, and the channel quality.
In step S31, the data rate of user data is detected. In step S32, the usage status of the spreading code is detected. In step S33, the line status is detected. In step S34, it is determined whether or not to perform code multiplexing. Specifically, for example, first, “the number of multi-codes” and “symbol rate (or spreading factor)” that satisfy the data rate requested by the user are calculated. Subsequently, an unused spreading code is searched to check whether or not the calculated number of spreading codes can be assigned. In addition, considering the state of the line, it is checked whether or not a predetermined quality can be ensured when data transmission is performed at the calculated “number of multicodes” and “symbol rate”. As a result, if it is determined that a necessary number of assignable spreading codes remain and a predetermined quality can be ensured, settings for performing code multiplexing are performed in step S35.

On the other hand, when code multiplexing is not performed, a modulation scheme is determined in step S36, and a corresponding notification is performed in step S37.
In the above embodiment, when code multiplexing is performed, user data is modulated by QPSK in spreading sections 105-1 to 105-n. However, the present invention is not limited to this. Absent. That is, even when code multiplexing is performed, user data may be modulated by a method other than QPSK in spreading sections 105-1 to 105-n.

As described above, the base station 30 adaptively changes the data transmission method according to the communication environment or the like. At this time, the change of the data transmission method is notified to the corresponding mobile device 40 as shown in FIG. That is, when the base station 30 determines the transmission method, the base station 30 notifies the mobile device 40 of parameters (multicode number, spreading code, modulation method, etc.) corresponding thereto. Mobile machine 40
Determines whether or not a signal transmitted by the transmission method notified from the base station 30 can be received, and responds to the result to the base station 30. When the mobile device 40 can receive data, the base station 30 changes the transmission method. On the other hand, the base station 40 changes the reception method.

As described above, the change of the data transmission method is advanced by negotiation between the base station 30 and the mobile device 40.
FIG. 12 is a block diagram of a mobile device that receives a signal transmitted from the base station shown in FIG. Here, only the main part of the function directly related to data reception is shown.

  A signal transmitted from the base station 30 is received via the antenna and passed to the despreading sections 501-1501-n and 502. Here, despreading sections 501-1 to 501-n despread and demodulate the received signal. On the other hand, the despreading section 502 reproduces control data by despreading and demodulating the received signal.

  The configurations of the despreading units 501-1 to 501-n and 502 are basically the same. That is, the spreading code generator 511 generates a predetermined spreading code or a spreading code assigned by the base station 30. The spreader 512 multiplies the received signal by the spread code generated by the spread code generator 511. The demodulator 513 demodulates the despread signal. Further, the combiner 503 combines the demodulated signals from the despreading units 501-1 to 501-n. The composite unit 504 combines the outputs of the combiner 503 and outputs the combined user data. On the other hand, the demodulated data by the despreading unit 502 is output as control data.

  In the mobile device, the demodulation method in the demodulator 513 follows the instruction from the base station 30. When code multiplexing is performed using k spreading codes, the combiner 503 combines the demodulated signals from the despreading units 501-1 to 501-k to reproduce user data.

Next, other embodiments (second to sixth embodiments) of the present invention will be described.
FIG. 13 is a configuration diagram of a base station according to the second embodiment of this invention. In the base station according to the second embodiment, the quality of the line with the mobile device 40 is detected or estimated at the base station. In other words, the receiving unit (DEM) 200 of this base station includes a channel quality estimating unit 203 that detects or estimates the quality of the channel with the mobile device 40. Here, the channel quality estimation unit 203 receives a signal transmitted from the corresponding mobile device 40, and detects or estimates a signal-to-interference power ratio (SIR), an error rate, received power, and the like. A method for detecting or estimating a signal-to-interference power ratio (SIR), an error rate, received power, and the like is a known technique.

  The operation of the transmission unit (MOD) 100 is basically as described with reference to FIG. That is, determination section 101 determines whether or not to perform code multiplexing based on the channel quality detected or estimated by channel quality estimation section 203, and adaptive modulation section 104 determines a modulation scheme based on the channel quality. To do.

  FIG. 14 is a flowchart illustrating the operation of the base station according to the second embodiment. The operation of the base station of the second embodiment is realized by replacing step S12 shown in FIG. 8 with step S41. That is, in the flowchart shown in FIG. 8, the channel quality information is received from the corresponding mobile device 40, but in the second embodiment, the channel quality information is detected or estimated by the base station.

FIG. 15 is a configuration diagram of a base station according to the third embodiment of the present invention. In the base station according to the third embodiment, the quality of the line with the mobile device 40 is estimated in consideration of both the value detected by the mobile device 40 and the value detected by the base station. . That is, the receiving unit (DEM) 200 of the base station includes both the extracting unit 202 and the channel quality estimating unit 203 described above. Then, the average value of these values, or the worse one of these values, is sent to determination section 101 and adaptive modulation section 104 as channel quality information passing.

  Note that the quality of the downlink for transmitting a signal from the base station 30 to the mobile station 40 and the quality of the uplink for transmitting a signal from the mobile station 40 to the base station 30 are generally the same. However, when the uplink and downlink carrier frequencies are significantly different from each other, usually the uplink quality and the downlink quality are different from each other. According to the base station of the third embodiment, even when the uplink quality and the downlink quality are different from each other, an optimum data transmission method can be selected in consideration of both of them.

  FIG. 16 is a flowchart illustrating the operation of the base station according to the third embodiment. The operation of the base station of the third embodiment is realized by inserting steps S41 and S42 after step S12 shown in FIG. That is, in step S42, the average quality or the worst quality is obtained from the channel quality detected by the mobile device 40 and the channel quality detected by the base station. In step S13, it is determined whether the modulation scheme to be executed is appropriate based on the quality obtained in step S42.

  FIG. 17 is a configuration diagram of a base station according to the fourth embodiment of the present invention. The base station according to the fourth embodiment includes a beamformer 111 and an adaptive array antenna 112 in addition to the configuration shown in FIG. 4, and can perform user separation within a communication area. That is, this base station can transmit a radio signal using a beam having directivity as shown in FIG. At this time, if the beams do not overlap each other or if there is little overlap between the beams, the users in the communication cell are separated from each other for each beam. That is, even when the same spreading code is assigned to a plurality of users, the base station 30 can identify the users from each other if they are located in different beams. However, the same spreading code cannot be assigned to a plurality of users within one beam.

  Therefore, the base station according to the fourth embodiment manages the use status of the spreading code or the number of users for each beam, and determines whether or not code multiplexing can be performed based on the management status. For this reason, as shown in FIG. 19, the spreading code management unit 31 manages the spreading code allocation status for each beam. It is assumed that the correspondence between each mobile device and the beam is managed by a known technique.

  Further, in the base station of the fourth embodiment, the determination unit 101 refers to the spreading code management unit 31 when determining whether or not to perform code multiplexing in data transmission to a certain mobile device 40, The number of spreading codes that can be used in the beam corresponding to the position of the mobile device 40 is examined. When the number of spreading codes necessary for code multiplexing can be secured, the determination unit 101 sets parameters for code multiplexing to the user data separation unit 103, the adaptive modulation unit 104, and the spreading unit 105-1. -105-n. Thereby, multi-code transmission is realized.

  FIG. 20 is a configuration diagram of a base station according to the fifth embodiment of the present invention. The base station of the fifth embodiment is a combination of the fourth embodiment and the second embodiment. That is, the base station according to the fifth embodiment has a function of detecting the quality of a channel with the mobile device 40 (channel quality estimation unit 203) and a function of separating users by an adaptive array (beamformer 111, adaptive array). An antenna 112) is provided.

FIG. 21 is a configuration diagram of a base station according to the sixth embodiment of the present invention. The base station of the sixth embodiment is a combination of the fourth embodiment and the third embodiment. That is, the base station according to the fifth embodiment has a function of detecting the quality of a channel to and from the mobile device 40 (extraction unit 202, channel quality estimation unit 203) and a function of separating users by an adaptive array (beamformer). 111, adaptive array antenna 112).

  The spreading code is a finite communication resource and needs to be used efficiently and fairly. Therefore, when the number of users requesting communication in the communication area is large, code multiplexing may be limited. For example, in the situation where there is no spreading code available, when a new user requests to start communication, the base station changes data transmission by code multiplexing to data transmission using one spreading code. You may make it do. In this case, the usable spreading code can be assigned to the new user.

  Moreover, although the above-mentioned Example demonstrated the data transmission from a base station to a mobile device, this invention is not limited to this. That is, the present invention can also be applied to data transmission from a mobile device to a base station. However, in this case, it is necessary to notify the mobile station of information relating to the usage status of the spreading code from the base station.

  Furthermore, in the above-described embodiment, a plurality of spreading sections 105-1 to 105-n are provided to perform code multiplexing, but the present invention is not limited to this. That is, an operation equivalent to the diffusion operation by the plurality of diffusion units 105-1 to 105-n is realized by repeating the diffusion process for user data while one diffusion unit cyclically changes a predetermined number of diffusion codes. You may do it.

1A, 1B, and 1C are diagrams illustrating the arrangement of signal points of QPSK, 16QAM, and 64QAM, respectively. It is a block diagram of the existing transmitter which can perform adaptive modulation. It is a figure which shows the mobile communication system concerning embodiment of this invention. It is a block diagram which shows the function of a base station. It is a figure which shows typically the format of the data transmitted from the base station shown in FIG. It is FIG. (1) explaining the code | symbol multiplexing in embodiment. It is FIG. (2) explaining the code | symbol multiplexing in embodiment. 5 is a flowchart showing an operation of the base station shown in FIG. It is an Example of a spreading code management part. It is an example of a structure of a spreading code. It is a flowchart of the process which judges whether code multiplexing is performed based on a data rate, the use condition of a spreading code, and channel quality. It is a figure explaining the negotiation between a base station and a mobile device. It is a block diagram of the mobile apparatus which receives the signal transmitted from the base station shown in FIG. It is a block diagram of the base station of the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the base station of 2nd Embodiment. It is a block diagram of the base station of the 3rd Embodiment of this invention. It is a flowchart which shows operation | movement of the base station of 3rd Embodiment. It is a block diagram of the base station of the 4th Embodiment of this invention. It is a figure which shows the directional beam by an adaptive array. It is an Example of the spreading code management part which manages a spreading code for every beam. It is a block diagram of the base station of the 5th Embodiment of this invention. It is a block diagram of the base station of the 6th Embodiment of this invention.

Claims (7)

In a radio base station used in a CDMA communication system,
When the data rate is increased, the increase in the number of code multiplexes applied when transmitting data to one mobile station that maintains one modulation scheme is determined by the type of signal points arranged on the phase plane. Judgment means that has priority over changes to other modulation schemes more than modulation schemes,
A radio base station comprising: The determination means increases the number of code multiplexes based on a notification of reception quality from the mobile station.
The radio base station according to claim 1. The determination means performs the increase in the number of code multiplexing within a range where code multiplexing is possible.
The radio base station according to claim 1. The one modulation scheme is a QPSK modulation scheme, and the other modulation scheme is a QAM modulation scheme.
The radio base station according to claim 1. In a transmission control method in a radio base station used in a CDMA communication system,
An increase in the number of code multiplexes applied when transmitting data to a certain mobile station is given priority over a change to a modulation scheme with more types of signal points arranged on the phase plane.
A transmission control method in a radio base station. In a wireless transmission device used in a CDMA communication system capable of changing and controlling a modulation scheme to be applied,
By applying a plurality of code multiplexing numbers, when transmitting data that can be transmitted without changing the QPSK modulation scheme to a certain radio receiving apparatus, the number of code multiplexing applied is increased to the plurality and the QPSK modulation applied. A determination unit that prioritizes control for changing to a QAM modulation system in which the number of signal points arranged on the phase plane is larger than that of the QPSK modulation system by not changing the system;
A wireless transmission device comprising: In a transmission control method in a wireless transmission device used in a CDMA communication system capable of changing and controlling a modulation scheme to be applied,
By applying a plurality of code multiplexing numbers, when transmitting data that can be transmitted without changing the QPSK modulation scheme to a certain radio receiving apparatus, the number of code multiplexing applied is increased to the plurality and the QPSK modulation applied. A wireless system characterized by preferentially increasing the number of code multiplexes by not changing the system over the control for changing to a QAM modulation system in which the number of signal points arranged on the phase plane is larger than the QPSK modulation system. A transmission control method in a transmission apparatus.

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