JP2007013285A - Base station of multi-beam wireless communication system and inter-beam resource distribution method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base station capable of sharing resources to each beam by taking into account an information quantity and signal quality by each beam in a multi-beam wireless communication system and to provide an inter-beam resource distribution method. <P>SOLUTION: The base station in the multi-beam wireless communication system includes: a traffic measuring section for measuring the information quantity of each beam for communication with a terminal; a signal quality measuring section for measuring the signal quality for the communication with the terminal and detecting a beam wherein the signal quality is at the outside of its permissible range; a resource sharing section for distributing the wireless resources so that the ratio of the information quantity of the concerned beam with respect to the information quantity of all the beams is coincident with a ratio of a transmission rate of the beam with respect to the transmission rate of all the beams, and the resource distributing section shares again the wireless resource so that the transmission rate of the beam whose signal quality is at the outside of its permissible range is a multiple of X (X is a real number greater than 1) of the pre-assigned transmission rate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a base station and an inter-beam resource allocation method for a multi-beam wireless communication system.

In a wireless communication system, there are limits to radio resources (hereinafter referred to as “resources”) such as frequency bands and transmission power that can be used in the entire system. A typical example is a multi-beam wireless communication system in which resources are allocated to a plurality of beams constituting a service area and the total of the resources is controlled so as not to exceed an upper limit. In a multi-beam wireless communication system, the following resource allocation method is effective for increasing the transmission rate and improving the signal quality.
・ Share frequency bands between beams.
・ Distribute a lot of resources to beams with a lot of information.

  FIG. 1 is a beam characteristic diagram showing a beam gain that interferes with a peripheral beam.

  According to FIG. 1, it can be understood that the beam gain of the high traffic beam leaks into the peripheral beam. According to such characteristics, beams sharing a frequency band can be interference sources. Moreover, if a large amount of transmission power is distributed to a beam in which a large amount of information is generated, it becomes a large interference source with respect to surrounding beams. In a beam subjected to such interference, the transmission speed is lowered and the signal quality is also lowered. Accordingly, the following techniques are known as conventional techniques for reducing interference and improving signal quality.

  As a first conventional technique, there is a technique that distributes transmission power to a beam according to the amount of information generated, although the frequency band is fixed to each beam.

  FIG. 2 is a cluster configuration diagram using three adjacent beams in the first prior art.

  According to FIG. 2, a cluster is constituted by three adjacent beams, and the system frequency band is repeatedly used for each cluster. Adjacent beams have the greatest influence of interference, so that the frequency bands are not overlapped in the cluster. In addition, the system frequency band is divided into three equal parts and fixedly allocated to each beam. Then, the beam in an area where terminals are crowded has a large amount of information, the beam in an area where terminals are sparse has a small amount of information, and the amount of information for each beam becomes non-uniform.

  According to the first prior art, transmission power is distributed to the beam according to the amount of information generated. However, when a large amount of transmission power is allocated to a beam with a large amount of information, a large interference is exerted on the surrounding beams, and the transmission speed of the entire system is reduced.

  As a second conventional technique, there is a technique for variably allocating a frequency band and transmission power according to the amount of information for each beam (for example, see Non-Patent Document 1).

  FIG. 3 is a system configuration diagram in the second prior art.

  According to FIG. 3, the base station 1 can communicate with the terminal 2 via the satellite 3. The traffic measurement unit 101 of the base station 1 measures the information amount of each beam. The resource allocation unit 102 allocates the frequency band and the transmission power so that the ratio of the beam information amount to the total beam information amount matches the transmission rate of the beam with respect to the transmission rate of all beams.

  According to the second conventional technique, a large amount of frequency band and transmission power are allocated to a beam having a large amount of information. However, the second prior art has a smaller transmission power than the first prior art because of the wide frequency band. Therefore, interference with the peripheral beam is reduced, and the transmission rate of the entire system is increased. Although it is necessary to increase the transmission speed in order to improve the signal quality, setting the transmission speed to each beam in consideration of the signal quality is effective.

  For example, “delay time” is assumed as the signal quality. Real-time traffic (such as voice and video) has more severe restrictions on delay time than non-real-time traffic (such as FTP). Therefore, in order to improve signal quality (reduction in delay time), it is desirable to set a large transmission rate for a beam in which real-time traffic is concentrated. However, according to the second prior art, the resources are allocated without considering the signal quality, so that the effect of improving the signal quality is small.

  As a third conventional technique, there is a technique for allocating resources to each beam according to the signal quality for each beam (see, for example, Non-Patent Document 2).

  FIG. 4 is a system configuration diagram in the third prior art.

  According to FIG. 4, the signal quality measuring unit 103 of the base station measures the signal quality of each beam. If a signal that deteriorates in signal quality and falls outside the allowable range is generated, communication with the terminal in the peripheral beam is stopped for a certain period. As a result, the amount of interference from the peripheral beams is reduced, and the signal quality of the beam whose signal quality is deteriorated is improved to continue communication. According to the third prior art, although the signal quality of the beam whose signal quality is deteriorated is improved, the communication of the peripheral beam is stopped for a certain period, so that the signal quality is lowered as a whole system.

Satoshi KONISHI, Yoji KISHI and Shinichi NOMOTO, `` Optimum Radio Channel Allocation Taking Account of Both Frequency and Power Constraints for Wide-Area Wireless Access Systems '', IEICE Trans.Commun., VOL.E87-B, No.12 DECEMBER 2004. Chen Arashi, Hidetoshi Kayama, Narumi Umeda, “Coordination Control Method for Inter-Base Station Resources Considering Wireless QoS”, IEICE Technical, RCS2002-25, CQ2002-25 (2002-04)

  According to the prior art 1, a beam with high transmission power greatly interferes with a peripheral beam, and signal quality deteriorates. According to the prior art 2, since resources are not allocated according to the signal quality, the effect of improving the signal quality is small. According to the prior art 3, although the signal quality is improved with respect to some beams, the signal quality of the entire system is lowered.

  Accordingly, the present invention provides a base station and an inter-beam resource allocation method capable of allocating resources to each beam in consideration of the information amount and signal quality for each beam in a multi-beam wireless communication system. Objective.

According to the present invention, in a base station of a multi-beam wireless communication system,
Traffic measurement means for measuring the amount of information for each beam in communication with the terminal;
A signal quality measuring means for measuring a signal quality in communication with a terminal and detecting a beam whose signal quality is outside an allowable range;
Resource allocation means for allocating radio resources so that the ratio of the information amount of the beam to the information amount of all beams matches the ratio of the transmission rate of the beam to the transmission rate of all beams;
The resource distribution means redistributes radio resources so that the transmission rate of the beam whose signal quality is out of the allowable range is X times the transmission rate assigned previously (X is a real number greater than 1). It is characterized by.

  According to another embodiment of the base station of the present invention, X times the transmission rate is the maximum value at which the signal quality of the beam whose signal quality is within the allowable range remains within the allowable range by the next signal quality measurement time. It is also preferable to further include an addition rate calculating means for determining so that

  Further, according to another embodiment of the base station of the present invention, the next signal quality measurement time is determined to be a time when the signal quality of a beam whose signal quality is outside the allowable range changes within the allowable range. It is also preferable to further include a signal quality measurement timer.

  Furthermore, according to another embodiment of the base station of the present invention, it is preferable to further include resource optimization means for allocating radio resources so that the sum of transmission rates of all beams is maximized.

  Furthermore, according to another embodiment of the base station of the present invention, it is also preferable to communicate with the terminal via a multi-beam satellite.

  Furthermore, according to another embodiment of the base station of the present invention, it is preferable that the traffic measurement means sets the information amount for each beam as an average value within a predetermined period.

  Furthermore, according to another embodiment of the base station of the present invention, it is preferable that the traffic measurement means measures the number of users for each beam instead of the information amount for each beam.

  Furthermore, according to another embodiment of the base station of the present invention, the signal quality measuring means measures the average of the signal quality between all the terminals in the beam instead of the signal quality in the communication with the terminal. Is also preferable.

  Furthermore, according to another embodiment of the base station of the present invention, the signal quality is preferably a delay time, a throughput, a combination of the delay time and the throughput, or a value that can be derived from the delay time and / or the throughput.

  Furthermore, according to another embodiment of the base station of the present invention, the radio resource is preferably a frequency band, transmission power, time slot, or a combination of two or more thereof.

According to the present invention, in the inter-beam resource allocation method of the base station in the multi-beam wireless communication system,
The amount of information for each beam in communication with the terminal is measured, and radio resources are allocated so that the ratio of the information amount of the beam to the amount of information of all beams matches the ratio of the transmission rate of the beam to the transmission rate of all beams. A first step of allocating;
The signal quality in communication with the terminal is measured, and the transmission speed of the beam whose signal quality is outside the allowable range is X times the transmission speed determined in the first step (X is a real number greater than 1). It is characterized by redistributing radio resources so that.

  According to the present invention, in a multi-beam wireless communication system, signal quality can be improved because resources are allocated to each beam according to signal quality and information amount.

  FIG. 5 is a configuration diagram of a radio communication system according to the present invention.

  In the system of FIG. 5, a base station 1 communicates with a plurality of terminals 2 via a multi-beam satellite 3. The service area is covered by a plurality of beams of the satellite 3. The terminal 2 exists in an arbitrary area covered by the beam. Depending on the area, there are an area where the terminals 2 are crowded and an area where the terminals 2 are sparse. Therefore, the information amount of each beam becomes non-uniform.

  In the wireless communication system via the multi-beam type satellite 3, the frequency band or transmission power that can be used in the entire system is further limited as compared with other communication systems, so that the resource allocation according to the present invention improves signal quality. The effect is great.

  The base station 1 includes a plurality of modems 100, a traffic measurement unit 101, a resource distribution unit 102, a signal quality measurement unit 103, a resource optimization unit 104, an addition rate calculation unit 105, a signal quality measurement timer 106, Have

  The modem 100 forms a beam for the terminal 2 through the satellite 3.

  The traffic measurement unit 101 measures the amount of information for each beam in communication with the terminal from each modem 100. The traffic measurement unit 101 notifies the resource allocation unit 102 of the measured information amount for each beam.

  The signal quality measuring unit 103 measures the signal quality in communication with the terminal and detects a beam whose signal quality is outside the allowable range. The signal quality measurement unit 103 holds information on the allowable range of signal quality in advance, and notifies the resource allocation unit 102 of the beam whose signal quality has deteriorated and is out of the allowable range.

  For real-time traffic, “delay time” is signal quality, and for non-real-time traffic, “throughput” is signal quality. In order to apply to a network in which these two types of traffic are mixed, the signal quality measurement unit 103 measures “delay time” and “throughput” as signal quality.

  When the “delay time” is severely demanded, even if the amount of information is the same, there is a high possibility that the signal quality is deteriorated in a beam having a lot of real time traffic. On the other hand, when the demand for “throughput” is severe, even if the amount of information is the same, there is a high possibility that the signal quality is deteriorated in the beam having a large amount of non-real-time traffic.

  Of course, the signal quality may be other than “delay time” or “throughput” depending on communication contents. For example, in real-time traffic, the upper limit value of the delay time is determined in advance, and the information is discarded when the upper limit value is exceeded. Therefore, the “information discard rate” can be used as the signal quality.

  Further, the signal quality may be a combination of delay time and throughput, or a value that can be derived from the delay time and / or throughput.

  The resource allocation unit 102 determines resources to be allocated to each beam.

  FIG. 6 is an explanatory diagram of resource allocation by the resource allocation unit 102 according to the present invention.

In the first step, the resource allocation unit 102 allocates resources so that the ratio of the beam information amount to the total beam information amount matches the ratio of the beam transmission rate to the total beam transmission rate.
Ratio of information amount of the beam = Information amount of the beam / Information amount of all beams Ratio of the transmission speed of the beam = Transmission speed of the beam / Transmission speed of all beams

  In this case, the same transmission rate is assigned to beams having the same information amount. As is clear from step 1 in FIG. 6, the frequency band and the transmission power, which are resources, are allocated so that the information amount ratio and the transmission rate ratio match. Since each beam is assigned a transmission rate according to the amount of information of the beam, the signal quality is improved.

  Furthermore, in the second step, the resource allocation unit 102 sets the transmission rate of the beam whose signal quality is out of the allowable range to X times the transmission rate assigned previously (X is a real number greater than 1). To reallocate resources.

  As is clear from step 2 in FIG. 6, when the signal quality is out of the allowable range in the central beam, the transmission speed of the beam is doubled, for example. At this time, other beams are affected as a decrease in transmission speed. However, at this time, resources are allocated to all the beams so that the signal quality does not fall outside the allowable range. In particular, more resources are allocated to a beam having a large amount of information and a low signal quality, and the signal quality is improved.

  The addition rate calculation unit 105 determines X times the transmission rate so that the signal quality of the beam whose signal quality is within the allowable range reaches the maximum value within the allowable range until the next signal quality measurement time. Here, the signal quality of the beam whose signal quality is within the allowable range is the maximum that remains within the allowable range in the period from the current information amount and the increase rate of the past information amount to the next signal quality measurement time. Calculate the value.

  The larger the addition rate, the higher the transmission speed of the beam whose signal quality is out of the allowable range, and the signal quality is improved. On the other hand, the transmission capacity of a beam whose signal quality is within an allowable range is reduced, and the signal quality is lowered. Therefore, the probability that the signal quality of the entire beam is within the allowable range can be maximized.

  The signal quality measurement timer 106 determines that the next signal quality measurement time is a time when the signal quality of the beam whose signal quality is outside the allowable range changes within the allowable range. Here, the next signal quality measurement time is set to the time when the signal quality of the beam whose signal quality is outside the allowable range changes within the allowable range, and the addition rate is set only for the minimum period.

  The longer the period for setting the addition rate, the lower the signal quality of the beam whose signal quality is within the allowable range. Therefore, the signal quality measurement timer 106 keeps the signal quality of the beam whose signal quality is out of the allowable range within the allowable range, and minimizes the deterioration of the signal quality of the beam whose signal quality is within the allowable range, thereby reducing the entire beam. The signal quality can be kept optimal.

  The resource optimizing unit 104 calculates an optimal resource allocation (hereinafter referred to as “optimal allocation”) from which the maximum transmission capacity is obtained in the entire system from the beam traffic distribution.

  For beams sharing a frequency band, the interference with the surrounding beams increases as the transmission power increases. On the other hand, it is conceivable to reduce the amount of interference by reducing the transmission power. However, in order to obtain a certain transmission capacity, the frequency band becomes large. As a result, the frequency band for the peripheral beam is reduced, and as a result, a large transmission power is required, so that the amount of interference from the peripheral beam increases. Therefore, optimal distribution is required. There are the following methods for optimal allocation.

  According to the first optimal allocation method, a frequency band is freely allocated to each beam, and one distribution having the maximum transmission capacity is selected from all the distributions. According to this method, it is possible to reliably calculate the distribution that maximizes the transmission capacity. However, in general, it takes time because a huge amount of calculation processing is required.

  According to the second optimal allocation method, the optimal allocation for obtaining the maximum capacity is determined using a predetermined optimization method. According to this method, the calculation time is shortened because the optimization method is used. However, there may be extreme solutions that fail to maximize.

  According to the third optimal allocation method, the constraint condition for optimal allocation is found by the first optimal allocation method, and the optimal allocation is determined by applying the constraint condition to the second optimal allocation method. According to this method, the calculation time can be shortened as in the second optimal allocation method, and at the same time, the probability of falling into an extreme solution can be reduced. Therefore, it can be said to be the most effective optimal allocation method.

  By using the third optimal allocation method, the resource optimization unit 104 can maximize the transmission capacity of the entire beam and improve the signal quality with a small amount of calculation processing and calculation time.

In a multi-beam wireless communication system, inter-beam interference between beams sharing a frequency has the greatest influence on the reduction in transmission capacity. Therefore, in order to reduce the inter-beam interference as a whole system, the following constraint conditions can be considered.
(Condition 1) The sum of the frequency bands allocated to the plurality of beams constituting the frequency cluster must be the upper limit frequency band of the system.
(Condition 2) The frequency band of the frequency sharing beam is made equal among all clusters.

As the second optimal allocation method, it is conceivable to apply a general optimization method targeting a nonlinear model such as sequential quadratic programming. In other words, the amount of resources for each beam is solved by sequential quadratic programming with constrained conditions so that the transmission capacity between the beams corresponds to the ratio of the information amount of each beam and the inter-beam interference is minimized in the entire system. As a result, resource optimization can be performed. Using such a method, there is a difference in system capacity, for example, as follows, with and without resource optimization processing.

  The amount of beam information tends to increase as the number of terminals in the beam increases. Therefore, the same effect can be obtained when the traffic measuring unit 101 measures the number of users for each beam instead of the amount of beam information.

  The amount of information for each beam changes from moment to moment. When the amount of information at a certain moment is a special case and is very large or very small with respect to the average value, it is difficult to perform effective resource allocation. Therefore, the traffic measurement unit 101 increases the signal quality improvement effect by setting the information amount for each beam to an average value within a predetermined period.

  Each terminal in the beam has a different signal quality. Even though the signal quality of the majority of terminals is within the allowable range, if the signal quality of some terminals is outside the allowable range, many resources are allocated to the beam, and effective resource allocation is difficult to be performed. Therefore, the signal quality measuring unit 103 increases the signal quality improvement effect by measuring the average of the signal quality with all the terminals in the beam instead of the signal quality in the communication with the terminal.

  FIG. 7 is a graph showing received power / interference power with respect to transmission capacity / frequency band.

  The transmission rate is derived from the frequency band, modulation scheme, coding scheme, coding rate, interference power, and received power (product of transmission power and beam gain). As modulation schemes, BPSK (Binary Phase Shift Keying), QPSK (Quadri-Phase Shift Keying), 8PSK (8 Phase Shift Keying) and 16QAM (16 Quadrature Amplitude Modulation) ) Is shown. The resource means a frequency band, a modulation scheme, a coding scheme, a coding rate, and transmission power. Since the modulation scheme, coding scheme, and coding rate are uniquely determined, the resources to be allocated are the frequency band and transmission power. Further, an upper limit value of resources (frequency and power) that can be used in the entire system is determined. The base station allocates resources to each beam so that the upper limit value of resources is not exceeded.

  In the above-described embodiment, the resource to be allocated has been described as the frequency band and the transmission power. However, for example, when using time division multiple access, a “time slot” can be set as the resource to be allocated. Further, the radio resource may be a combination of two or more of a frequency band, transmission power, and time slot.

  FIG. 8 is a graph comparing the signal quality of the present invention and the signal quality of the prior art in simulation.

  According to FIG. 8, the delay time and the throughput for the traffic are shown by comparing the present invention with the prior art. In the present invention, the delay time is reduced to 1/3 of the prior art 2. As for throughput, the present invention is 1.2 times faster than the prior art 1.

  As described above, according to the present invention, in a multi-beam wireless communication system, signal quality can be improved because resources are allocated to each beam according to signal quality and information amount.

It is a beam characteristic figure showing the beam gain which interferes with a peripheral beam. It is a cluster block diagram by 3 adjacent beams in the 1st prior art. It is a system configuration figure in the 2nd conventional technology. It is a system block diagram in the 3rd prior art. It is a block diagram of the radio | wireless communications system in this invention. It is explanatory drawing of the resource allocation in this invention. It is a graph showing the reception power / interference power with respect to transmission capacity / frequency band. It is the graph which compared the signal quality of this invention and the signal quality of a prior art in simulation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base station 100 Modem 101 Traffic measurement part 102 Resource distribution part 103 Signal quality measurement part 104 Resource optimization part 105 Addition rate calculation part 106 Signal quality measurement timer 2 Terminal 3 Satellite

Claims (11)

In a base station of a multi-beam wireless communication system,
Traffic measurement means for measuring the amount of information for each beam in communication with the terminal;
Signal quality measuring means for measuring signal quality in communication with a terminal and detecting a beam whose signal quality is outside an allowable range;
Resource allocation means for allocating radio resources so that the ratio of the information amount of the beam to the information amount of all beams matches the ratio of the transmission rate of the beam to the transmission rate of all beams;
The resource allocation means reallocates radio resources so that a transmission rate of a beam whose signal quality is out of an allowable range is X times a transmission rate allocated previously (X is a real number greater than 1). A base station characterized by:   There is further provided an addition rate calculating means for determining that X times the transmission rate is a maximum value in which the signal quality of the beam within the allowable range remains within the allowable range by the next signal quality measurement time. The base station according to claim 1.   3. The signal quality measurement timer according to claim 2, further comprising a signal quality measurement timer for determining the next signal quality measurement time to be a time when the signal quality of the beam whose signal quality is outside the allowable range changes within the allowable range. Base station described in.   The base station according to any one of claims 1 to 3, further comprising resource optimization means for allocating radio resources so that a sum of transmission rates of all beams is maximized.   The base station according to any one of claims 1 to 4, wherein the base station communicates with a terminal via a multi-beam type satellite.   The base station according to any one of claims 1 to 5, wherein the traffic measurement unit sets the information amount for each beam as an average value within a predetermined period.   The base station according to claim 1, wherein the traffic measurement unit measures the number of users for each beam instead of the information amount for each beam.   8. The signal quality measuring unit according to any one of claims 1 to 7, wherein the signal quality measuring unit measures an average of signal quality with all terminals in the beam instead of signal quality in communication with the terminal. Base station described in.   9. The base according to claim 1, wherein the signal quality is a delay time, a throughput, a combination of the delay time and the throughput, or a value derivable from the delay time and / or the throughput. Bureau.   The base station according to any one of claims 1 to 9, wherein the radio resource is a frequency band, transmission power, time slot, or a combination of two or more thereof. In a method for allocating resources between beams of a base station in a multi-beam wireless communication system,
The amount of information for each beam in communication with the terminal is measured, and radio resources are allocated so that the ratio of the information amount of the beam to the amount of information of all beams matches the ratio of the transmission rate of the beam to the transmission rate of all beams. A first step of allocating;
The signal quality in the communication with the terminal is measured, and the transmission speed of the beam whose signal quality is outside the allowable range is X times the transmission speed determined in the first step (X is a real number larger than 1). A base station inter-beam resource allocation method characterized by reallocating radio resources so that

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