JP2005012366A - Wireless communication system and wireless communication method - Google Patents

Abstract

An object of the present invention is to prevent interference between communication lines and improve communication quality per radio resource in a radio communication system using both a CDMA system and a multiple access system other than the CDMA system.
A downlink carrier frequency band ΔFd is set wider than an uplink carrier frequency band ΔFu. Therefore, the number n of carrier frequency parameters corresponding to the parameters of the second multiple access scheme for the downlink increases. Since this corresponds to an increase in selectable carrier frequencies, the probability that the communication lines are opened on the same frequency band is reduced, and the communication lines are less likely to interfere with each other.
[Selection] Figure 2

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio communication system and a radio communication method adopting a code division multiple access scheme.
[0002]
[Prior art]
In recent years, wireless communication systems for cellular mobile phones employing spread spectrum communication systems have been commercialized. A typical standard for this commercial cellular system is the IMT-2000 CDMA-DS (Code Division Multiple Access-Direct Sequence) system.
[0003]
A feature of the spread spectrum communication system is that a code division multiple access (CDMA) system is adopted as a communication multiple access system, thereby enabling communication of a plurality of lines in the same frequency band and the same time band. In this CDMA system, since the gain difference of the spread code is small compared to the gain difference due to the carrier frequency, communication degradation is generally likely to occur due to mutual interference between communication lines. Therefore, transmission power control is performed to observe the communication quality of each line and increase or decrease the transmission power of the transmission signal so that the communication quality is constant.
[0004]
However, in spread spectrum communication, even if transmission power control is performed, communication degradation is likely to occur due to mutual interference between communications. Therefore, a multiple access method other than the CDMA method (hereinafter referred to as a second multiple access method). There has been proposed a communication system using a CDMA system together with the CDMA system.
[0005]
In the IMT-2000 CDMA-DS standard, the frequency band is divided into an uplink and a downlink, and each line is further divided into 12 frequency bands and communication channels are allocated. This is a multiple access system called a CDMA-FDD system that uses both a code division multiple access (CDMA) system and a frequency division multiple access (FDMA) system. By separating the downlink and uplink frequency bands, an uplink transmission signal of a certain mobile station 1 is prevented from interfering with another mobile station 2 existing in the vicinity of the mobile station 1.
[0006]
In addition, there is an invention that uses multiple access other than code multiple access to prevent the reception quality of a mobile station from deteriorating due to interference of downlink signals (see, for example, Patent Document 1). In general, it can be said that the downlink transmission power for the mobile station 1 far from the base station is larger than the downlink transmission power for the mobile station 2 in the vicinity. Assign different parameters for the second multiple access method. Thereby, it is possible to reduce the influence of the downlink transmission signal for the mobile station 1 on the downlink signal for the mobile station 2.
[0007]
[Patent Document 1]
JP 2001-36950 A
[Problems to be solved by the invention]
However, as described in the above-mentioned patent document, the conventional wireless communication system is free from radio resources (communication system resources) without considering the characteristic that the downlink is more susceptible to interference than the uplink. Frequency band widths are equally allocated to the uplink and downlink. For example, in the IMT-2000 CDMA-DS standard, the width of the uplink frequency band is 60 MHz (1920 to 1980 MHz), and the width of the downlink frequency band is 60 MHz (2110 to 2170 MHz). Therefore, there is a problem that radio resources are not effectively used.
[0009]
The present invention has been made in view of the above points, and an object of the present invention is to provide a radio communication system and a radio communication method capable of preventing interference between communication lines and improving communication quality per radio resource. To do.
[0010]
[Means for Solving the Problems]
The wireless communication system of the present invention uses a code division multiple access scheme and a multiple access scheme other than the code division multiple access scheme in combination, and performs communication per unit transmission rate used in a multiple access scheme other than the code division multiple access scheme. A configuration is adopted in which more system resources are allocated to the downlink than to the uplink, and communication of a plurality of lines is performed.
[0011]
The radio communication system of the present invention adopts a configuration in which, in the above configuration, a multiple access scheme other than the code division multiple access scheme is a frequency division multiple access scheme and a wider frequency band is allocated to the downlink than the uplink.
[0012]
The radio communication system of the present invention adopts a configuration in which, in the above configuration, a multiple access scheme other than the code division multiple access scheme is a time division multiple access scheme, and a longer communication time is allocated to the downlink than to the uplink.
[0013]
In the wireless communication system of the present invention, in the above configuration, a communication line in which communication quality is deteriorated due to interference or a communication line in which communication quality is expected to be deteriorated due to interference is specified, and the code is assigned to a plurality of communication lines. A configuration is adopted in which different parameters of the multiple access method other than the divided multiple access method are assigned.
[0014]
The wireless communication system of the present invention has the above configuration, wherein communication lines are grouped into a plurality of groups based on the attenuation amount of transmission power in communication, and the code division multiple access is used for communication with communication terminals of different groups. A configuration is adopted in which one different parameter in a multiple access scheme other than the scheme is assigned.
[0015]
A wireless communication apparatus according to the present invention includes a first communication unit that performs wireless communication with a plurality of communication terminals using a code division multiple access method, and the plurality of communication terminals using a multiple access method other than the code division multiple access method. A second communication means for performing wireless communication with the communication means, and in the second communication means, communication system resources per unit transmission rate used for the downlink are compared with communication system resources per unit transmission rate used for the uplink And a control means for controlling the second communication means so as to be distributed as much as possible.
[0016]
A base station apparatus according to the present invention employs a configuration including the above-described wireless communication apparatus.
[0017]
The wireless communication method of the present invention uses a code division multiple access method and a multiple access method other than the code division multiple access method in combination, and performs communication per unit transmission rate used in a multiple access method other than the code division multiple access method. More system resources are allocated to the downlink than to the uplink, and multiple line communication is performed.
[0018]
The wireless communication program of the present invention includes a first communication step for performing wireless communication with a plurality of communication terminals using a code division multiple access method, and the plurality of communication terminals using a multiple access method other than the code division multiple access method. A second communication step for performing wireless communication with a communication system resource per unit transmission rate used for the downlink in the second communication step, and a unit transmission rate used for the uplink in the second communication step The distribution step of allocating more than the per-communication system resource is executed by the computer.
[0019]
According to these configurations, in downlink communication in which deterioration of communication quality due to interference occurs more than in uplink communication, more than multiple access methods (second multiple access method) other than code division multiple access methods. Since radio resources per unit transmission rate can be allocated, more parameters of the second multiple access method can be taken. Therefore, different second multiples are used for communication with a mobile station (communication terminal) in which communication quality is deteriorated due to interference or communication with a mobile station in which communication quality is expected to be deteriorated due to interference. More connection method parameters can be allocated compared to uplink communication.
[0020]
Further, more second multiple access parameters necessary to prevent interference of a downlink signal with strong transmission power from the base station to the mobile station 1 far away from the received signal of the mobile station 2 near the base station are obtained. Can do.
[0021]
Therefore, interference between communication lines can be prevented and communication quality per radio resource can be improved.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The essence of the present invention is that the code division multiple access method and a multiple access method other than the code division multiple access method are used in combination, and communication system resources per unit transmission rate used in the multiple access method other than the code division multiple access method are In this case, more communication is allocated to the downlink than to the uplink and communication is performed on a plurality of lines.
[0023]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments of the invention describe a system in which uplink and downlink transmission rates are the same.
[0024]
(Embodiment 1)
FIG. 1A and FIG. 1B are diagrams showing the strength (power density) of signals communicated between a base station and a mobile station in a cellular mobile phone system employing a spread spectrum communication system. The communication system according to the present embodiment employs spread spectrum communication using both the CDMA method and the FDMA method, and transmission power control is also performed. Hereinafter, the influence (interference) of the uplink and downlink of this communication system on the base station and each mobile station will be considered using these figures.
[0025]
Specifically, (1) interference caused by a transmission signal (uplink) of the mobile station 151 to the base station 100 to a signal (downlink) transmitted from the base station 100 to the mobile station 152, (2) to the base station 100 Interference I2 that the transmission signal S2 (uplink) from the mobile station 151 gives to the signal (uplink) transmitted from the mobile station 152 to the base station 100, (3) Signal S3 (from the base station 100 to the mobile station 151) The interference in the three cases of interference I3, which is given to the signal (downlink) transmitted from the base station 100 to the mobile station 152 by the downlink) is compared, and which interference has the greatest influence is considered. Here, the interference (1) is not shown. The solid and dotted arrows indicate the desired wave and the interference wave to be communicated, respectively, and the thickness of the arrow indicates the magnitude of the power density of the signal.
[0026]
First, the interference (1) is eliminated by separating the carrier frequency bands of the uplink and downlink. On the other hand, when the interference I2 in (2) and the interference I3 in (3) are compared, the interference I3 in (3) has a greater influence for the following reason.
[0027]
That is, with respect to the interference I2 in (2), as shown in FIG. 1A, in the cellular cellular phone system for normal spectrum communication, transmission power control is performed so that each communication has almost the same communication quality. Therefore, the power density (P11 ′, P21 ′) of the received signal of the base station 100 of the signal from the mobile station 151 and the signal from the mobile station 152 is the distance between the remote mobile station 151 and the base station 100 and the vicinity thereof. The order is almost the same regardless of the distance between the mobile station 152 and the base station 100.
[0028]
Similarly, as shown in FIG. 1B, the power density P13 when the signal (power density P11) transmitted from the base station 100 to the mobile station 151 reaches the mobile station 151 and the mobile station 151 move from the base station 100. The power density P22 when the signal (power density P21) transmitted to the station 152 reaches the mobile station 152 is such that the transmission power is controlled by the base station 100 so that the received power at the mobile station is substantially constant. The order is almost the same regardless of the distance between the mobile station 151 and the base station 100 and the distance between the mobile station 152 and the base station 100.
[0029]
At this time, with respect to the interference I3 in (3) above, the transmission signal S3 of the base station 100 to the mobile station 151 existing far from the base station 100 is transmitted to the mobile station 152 existing in the vicinity of the base station 100 as an interference signal I3 ( When received as power density P12), the power density is much higher than the received power density (power density P22) of the desired wave of the original mobile station 152. This is because the transmission power control is performed so that the power density P13 when the transmission signal S3 attenuates and reaches the distant mobile station 151 is substantially the same as the received power density P22 of the desired wave of the mobile station 152. It is because it has been. Therefore, the power density P12 of the transmission signal S3 when reaching the same distance as the mobile station 152 is much larger than the received power density P22 of the desired wave of the mobile station 152.
[0030]
From the above examination, the influence (interference) exerted on each other's communication signal is larger in the interference I3 in (3) than in the interference I2 in (2), so that (3) It can be seen that it is necessary to prioritize measures against the interference I3.
[0031]
Therefore, in the present embodiment, different frequency carriers are assigned to a plurality of communication lines in which interference has occurred or a plurality of communication lines in which interference is expected to occur. Specifically, the communication channels are grouped into a plurality of groups based on the transmission power attenuation amount in the communication line, and the same frequency carrier is assigned to the communication channels in the same group. That is, different frequency carriers are assigned to different groups of communication channels. As a result, mobile stations in different groups with large differences in attenuation are assigned multiple access parameters in different groups so that the amount of interference is small. However, the amount of interference can be reduced with respect to other mobile stations. Therefore, it is possible to improve the communication quality per radio resource. Moreover, since the amount of radio resources can be reduced when realizing the same communication quality, the number of mobile stations accommodated in the communication system can be increased.
[0032]
Furthermore, in order to make the above-described interference countermeasures more effective, the downlink carrier frequency band ΔFd is set wider than the uplink carrier frequency band ΔFu as shown in FIG. 2 (see Equation 1). Assuming that the frequency band of one carrier signal is Δf, the number of lines (number of carrier frequency parameters) n that can be opened at different carrier frequencies in a downlink having a carrier frequency band of ΔFd is n = ΔFd / Δf. (See Equation 2). Therefore, the carrier frequencies of the carrier signal are f1, f2,. Similarly, the number m of lines that can be opened at different carrier frequencies in an uplink having a carrier frequency band of ΔFu is m = ΔFu / Δf.
[0033]
Thus, by setting the downlink carrier frequency band ΔFd wider than the uplink carrier frequency band ΔFu, the number n of carrier frequency parameters corresponding to the parameters of the second downlink multiple access scheme increases. Since the selectable carrier frequency increases, the probability that the communication lines are opened on the same frequency band is reduced, and the communication lines are less likely to interfere with each other.
[0034]
As shown in FIG. 3, in the conventional radio communication system, the uplink carrier frequency band ΔFu and the downlink carrier frequency band ΔFd are allocated equally (see Equation 3). Therefore, the number n of carrier frequency parameters for uplink and downlink are equal (see Equation 4).
[0035]
Conventionally, it has been common to distribute uplink and downlink communication system resources asymmetrically. For example, in an ADSL (Asymmetric Digital Subscriber Line) system, which has recently become widespread rapidly, different transmission rates are set for the uplink and the downlink, so if the communication system resource allocation per unit transmission rate is the same, the transmission is performed. Many communication system resources are allocated to a line with a high rate. On the other hand, in the case of the present invention, communication system resources per unit transmission rate are distributed asymmetrically in order to reduce interference between transmission signals.
[0036]
Heretofore, in order to simplify the description, the case where there are two mobile stations 151 and 152 has been described as an example. However, as a matter of course, this embodiment can also be applied to a case where a plurality of mobile stations 153-1 to 153-n exist as shown in FIG. That is, the interference I4 that the transmission signal S4 for the mobile station 153-n existing far from the base station 100 gives to the mobile station 153-1 near the base station 100 can be reduced by the above method.
[0037]
Next, an example in which the above-described wireless communication method for assigning different carrier frequency bands for uplink and downlink is realized in a single wireless communication apparatus will be described. FIG. 5 is a block diagram showing the main configuration of the base station apparatus according to the present embodiment. Here, a base station apparatus is taken as an example of the above-described wireless communication apparatus.
[0038]
The base station apparatus includes a CDMA transmission unit 101, an FDMA transmission unit 102, a transmission / reception sharing unit 103, an antenna 104, a CDMA reception unit 105, an FDMA reception unit 106, and a system resource control unit 107.
[0039]
The transmission data is subjected to CDMA and FDMA wireless transmission processing in the CDMA transmission unit 101 and the FDMA transmission unit 102, respectively, and transmitted to the mobile station via the transmission / reception sharing unit 103 and the antenna 104. The signal transmitted from the mobile station is received by the antenna 104, and subjected to CDMA and FDMA wireless reception processing in the CDMA receiving unit 105 and the FDMA receiving unit 106 via the transmission / reception sharing unit 103, respectively. Is taken out.
[0040]
The system resource control unit 107 controls the FDMA transmission unit 102 and the FDMA reception unit 106 so that the carrier frequency band is allocated. Thereby, the above-described wireless communication method is realized.
[0041]
The carrier frequency allocation method described above may be programmed and stored in a storage medium. The base station executes the allocation of the carrier frequency of the communication line according to this program, thereby realizing a communication system that exerts the same effect as described above.
[0042]
As described above, according to the present embodiment, in downlink communication in which degradation of communication quality due to interference occurs, more per unit transmission rate than a multiple access scheme (second multiple access scheme) other than the CDMA scheme. Therefore, the parameter selection range of the second multiple access method becomes large. Therefore, the parameters of the second multiple access method are used for communication with a mobile station (communication terminal) whose communication quality is deteriorated due to interference or communication with a mobile station whose communication quality is expected to be deteriorated due to interference. Can be allocated more. Therefore, it is possible to reduce interference that a downlink signal having strong transmission power to a mobile station located far from the base station gives to a received signal of the mobile station located near the base station. That is, interference between communication lines can be prevented and communication quality per radio resource can be improved.
[0043]
(Embodiment 2)
A feature of this embodiment is that the present invention is applied to a communication system using both a CDMA system and a TDMA (time division multiple access) system. That is, communication terminals are grouped into a plurality of groups based on transmission power attenuation in communication between a base station and a mobile station (communication terminal), and the same time slot is used for communication with communication terminals in the same group. assign. That is, different time slots are assigned to different groups.
[0044]
At this time, as shown in FIG. 6, the downlink communication time ΔTd is set longer than the uplink communication time ΔTu (see Equation 5). This increases the number of selectable time slots n (see Equation 6) corresponding to the parameters of the second multiple access method. Therefore, the probability of overlapping communication in the same time zone (time slot) is reduced, and the communication lines are less likely to interfere with each other. In the conventional radio communication system, the uplink communication time ΔTu per unit transmission rate and the downlink communication time ΔTd per unit transmission rate are allocated equally, so that the uplink and downlink can be selected. The number of time slots n was equal (see Equation 7).
[0045]
As described above, according to the present embodiment, as in the first embodiment, in downlink communication in which degradation of communication quality occurs due to interference, the multiple access scheme (second multiple access scheme) other than the CDMA scheme is used. Since more radio resources are allocated per unit transmission rate, the parameter selection range of the second multiple access method is increased. Therefore, the parameters of the second multiple access method are used for communication with a mobile station (communication terminal) whose communication quality is deteriorated due to interference or communication with a mobile station whose communication quality is expected to be deteriorated due to interference. Can be allocated more. Therefore, it is possible to reduce interference that a downlink signal having strong transmission power to a mobile station located far from the base station gives to a received signal of the mobile station located near the base station. That is, interference between communication lines can be prevented and communication quality per radio resource can be improved.
[0046]
In the first embodiment, the communication system using both the CDMA system and the FDMA system is described in connection with the communication system using the CDMA system and the TDMA system in the second embodiment. However, the present invention is not limited to the CDMA system and the CDMA system. It can be applied to all communication systems using multiple access methods other than the above.
[0047]
In addition to the interference countermeasure methods described in the first embodiment and the second embodiment, communication quality degradation due to interference has occurred, or a plurality of communication lines that are expected to be degraded are connected to the second multiple access scheme. By assigning parameters of different multiple access schemes, it is possible to prevent deterioration of communication quality due to interference.
[0048]
The radio communication apparatus according to the present invention can be mounted on a base station apparatus that uses both a CDMA scheme and a multiple access scheme other than the CDMA scheme, thereby providing a base station apparatus having the same effects as described above. can do.
[0049]
Here, although the case where the present invention is configured by hardware has been described as an example, it can also be realized by software.
[0050]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent interference between communication lines and improve communication quality per radio resource.
[Brief description of the drawings]
FIG. 1A is a diagram showing the strength of an uplink signal communicated between a base station and a mobile station in a cellular mobile phone system that employs a spread spectrum communication system. FIG. 1B employs a spread spectrum communication system. FIG. 2 is a diagram illustrating the strength of signals communicated between a downlink base station and a mobile station in a cellular mobile phone system. FIG. 2 is a diagram illustrating a radio communication method according to Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating a radio communication method of a conventional communication system. FIG. 4 is a diagram illustrating a case where there are a plurality of mobile stations. FIG. 5 is a block diagram illustrating a main configuration of the radio communication device according to the first embodiment of the present invention. FIG. 6 is a diagram explaining a radio communication method according to Embodiment 2 of the present invention.
DESCRIPTION OF SYMBOLS 100 Base station 101 CDMA transmission part 102 FDMA transmission part 103 Transmission / reception sharing part 104 Antenna 105 CDMA reception part 106 FDMA reception part 107 System resource control part 151,152,153 Mobile station

Claims (9)

The code division multiple access method and a multiple access method other than the code division multiple access method are used together, and communication system resources per unit transmission rate used in the multiple access method other than the code division multiple access method are downlinked from the uplink. Distribute more on the line and communicate on multiple lines,
A wireless communication system. A multiple access method other than the code division multiple access method is a frequency division multiple access method, and a wider frequency band is allocated to the downlink than the uplink,
The wireless communication system according to claim 1. A multiple access method other than the code division multiple access method is a time division multiple access method, and a longer communication time is allocated to the downlink than the uplink,
The wireless communication system according to claim 1. The wireless communication system according to claim 1, wherein
A communication line in which communication quality is deteriorated due to interference or a communication line in which communication quality is expected to be deteriorated due to interference is specified, and different parameters of multiple access methods other than the code division multiple access method are assigned to a plurality of communication lines. assign,
A wireless communication system. Based on the attenuation of transmission power in communication, communication lines are grouped into a plurality of groups, and one different parameter in a multiple access method other than the code division multiple access method is assigned to communication with a communication terminal in a different group. ,
The wireless communication system according to claim 4. First communication means for performing wireless communication with a plurality of communication terminals using a code division multiple access method;
Second communication means for performing wireless communication with the plurality of communication terminals using a multiple access method other than a code division multiple access method;
In the second communication means, the second communication means allocates more communication system resources per unit transmission rate used for the downlink than communication system resources per unit transmission rate used for the uplink. Control means for controlling the communication means;
A wireless communication apparatus comprising: A base station apparatus comprising the wireless communication apparatus according to claim 6. The code division multiple access method and a multiple access method other than the code division multiple access method are used together, and communication system resources per unit transmission rate used in the multiple access method other than the code division multiple access method are downlinked from the uplink. Distribute more on the line and communicate on multiple lines,
A wireless communication method. A first communication step of performing wireless communication with a plurality of communication terminals using a code division multiple access method;
A second communication step of performing wireless communication with the plurality of communication terminals using a multiple access method other than a code division multiple access method;
Distributing step of allocating more communication system resources per unit transmission rate used for the downlink in the second communication step than communication system resources per unit transmission rate used for the uplink in the second communication step When,
A wireless communication program that causes a computer to execute the above.

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