JP2006333405A - Frequency band allocation apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frequency band allocation apparatus which attain multi-rating while effectively utilizing frequency resources in a communication system utilizing SCPC and FDMA systems. <P>SOLUTION: The frequency allocation apparatus is used for a radio communication system wherein one or more mobile stations each capable of changing a frequency band for communicating a signal of a single carrier are connected with a base station in a frequency division multiple access (FDMA) system. This apparatus includes: a database for managing, for each mobile station, a band to be allocated to a mobile station and a restriction condition determining the relation of correspondence to an allocation standard parameter to be commonly used for all the mobile stations; a means for deriving a value of the allocation standard parameter so that the total of bands to be allocated to all the mobile stations becomes a desired value in the radio communication system; and a means for calculating a band to be allocated to each of the mobile station, respectively based on the derived allocation standard parameter, so that idle bands become minimum. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention generally relates to the technical field of radio communication, and more particularly, to a frequency allocation apparatus and method in a radio communication system in which a plurality of mobile stations communicate with a base station using a frequency division multiple access (FDMA) scheme.

  In the FDMA method, which is one of multiple access methods between a plurality of mobile stations and one base station, a frequency bandwidth is allocated to each mobile station, and the mobile station can occupy the bandwidth. Therefore, according to the FDMA scheme, the configuration and function of the transmitter mounted on the mobile station can be designed easily. For this reason, the FDMA scheme is suitable for applications such as a satellite communication system via a geostationary satellite with severe power restrictions and a mobile communication system with a limited terminal size.

As an example, there is a satellite communication system as described in Non-Patent Document 1. In this system, communication is performed using a single carrier having a frequency bandwidth (non-multirate system) in which a base station and a mobile station are fixed. Such a method is called an SCPC (Single Carrier Per Channel) method. SCPC can effectively use the capacity of an amplifier mounted on a mobile station, as compared with MCPC of a multicarrier system. Conventionally assumed applications are mainly only for voice communication, so that the required transmission rate is almost constant, and a desired quality of service (QoS) can be efficiently realized. Furthermore, since the frequency band per carrier is fixed, the frequency is allocated fairly regardless of the order in which communication requests are generated until the number of mobile stations (number of simultaneous connections) simultaneously communicating reaches the maximum value. Can do.
“Domestic mobile satellite communication system using S band”, ARIB STD-T49 version 3.0, Radio Industry, p. 5, p. 10

  In such a conventional system, the amount of communication performed in the entire system is proportional to the number of simultaneous connections. Therefore, in a situation where the number of simultaneous connections is small, resources (frequency, satellite repeater power, etc.) prepared in the system are not fully utilized, which is not a desirable situation. If the frequency bandwidth allocated to the mobile station is increased, the resource utilization efficiency in a situation where the number of simultaneous connections is small may be somewhat improved. However, doing so reduces the maximum number of simultaneous connections, which is undesirable from the standpoint of accommodating a larger number of users.

  On the other hand, traffic transmitted on the Internet includes a large number of applications, and the speed required by each application is not the same. Since it is difficult to efficiently accommodate such traffic in a non-multirate conventional system, a future communication system is required to be multirate (provided with a function for changing the communication speed). If the communication speed can be changed, the frequency bandwidth allocated to the mobile station can be changed. Furthermore, it is also desired to satisfy various application requirements, to realize flexible QoS control, to maintain fairness between mobile stations, and the like.

  The present invention has been made to address at least one of the above-described problems, and its problem is to achieve multi-rate while effectively using frequency resources in a communication system using SCPC and FDMA systems. A frequency band allocation apparatus and method are provided.

  In the present invention, a frequency allocation apparatus used in a radio communication system connected to a plurality of mobile station base stations capable of changing a frequency band for communicating a single carrier signal by a frequency division multiple access (FDMA) system Is used. The apparatus includes a database for managing a constraint condition for defining a correspondence relationship between a bandwidth allocated to a mobile station and an allocation level parameter commonly used for all mobile stations, and all mobile stations. Means for deriving the value of the allocation level parameter such that the total bandwidth allocated to the mobile communication system becomes a desired value in the wireless communication system, and each mobile station based on the derived allocation level parameter so that the available bandwidth is minimized Means for calculating each of the bandwidths to be allocated to each.

  ADVANTAGE OF THE INVENTION According to this invention, when allocating a frequency band with the communication system using a SCPC and FDMA system, it can respond to multi-rate, utilizing frequency resources effectively.

  In the frequency band allocating device according to one aspect of the present invention, when a new frequency allocation request is generated from a mobile station, or when a release request is generated from a mobile station that has already been allocated a frequency band, frequency band allocation is performed. The contents are changed. The allocation content is calculated so that the sum of the frequency bandwidths allocated to each mobile station matches the total frequency bandwidth available in the system. The total frequency bandwidth that can be used in the system is a constant value that does not depend on the number of mobile stations that request allocation. As a result, frequency resources can be effectively utilized regardless of the number of simultaneous connections. In other words, frequency resources can be utilized so that the vacant bandwidth is always the minimum regardless of the increase or decrease in the total number of mobile stations that request allocation. In particular, even when the number of simultaneous connections is small, the communication capacity of the entire system can be increased, and the communication speed per mobile station can be increased. Such a frequency band allocating device is typically provided in a base station, but may be provided in a place other than the base station.

The allocation content may be derived using a solution x = α that satisfies Σf _m (x) = W _all . Here, f _m (x) represents a band allocated to the m-th mobile station, and x represents an allocation level parameter. W _all is the total frequency bandwidth available in the system. Thereby, it is possible to quickly derive an appropriate frequency band to be assigned to each mobile station.

  The database includes a first lower limit value and an upper limit value of a band determined from a hardware condition of the mobile station, and a second lower limit value and an upper limit value of a band determined from a request for service provided to the mobile station. May be managed. The minimum value of the band allocated to the mobile station may be set to the larger one of the first and second lower limit values. The maximum value of the band allocated to the mobile station may be set to the smaller of the first and second upper limit values.

  The band allocated to each mobile station may be notified so that a plurality of mobile stations change the frequency band in synchronization. As a result, it is possible to avoid inappropriate frequency band allocation.

  FIG. 1 shows an example of a system using the present invention. In FIG. 1, a base station 11, a satellite repeater 12, and a service area 13 are depicted. There are a plurality of mobile stations 14 in the service area 13. The service area is formed by a single beam or multiple beams. The multi-beam may be a beam that does not perform frequency repetition, or a beam that performs frequency repetition but can ignore interference from other beams. The base station 11 is connected to a higher-level device (not shown) and supports communication of the subordinate mobile station 14.

  Each of the plurality of mobile stations 14 in the service area can change the frequency bandwidth and can communicate a single carrier signal. The base station communicates simultaneously with many mobile stations connected by the FDMA method. Between the base station 11 and the mobile station 14, the control signal is transmitted through the (radio) control channel and the data signal is transmitted through the communication channel via the satellite repeater 12. Through this control channel, the base station 11 can control the frequency band of the transmission signal of the mobile station 14. Note that the control channel and the communication channel indicate logical divisions and do not necessarily exist on physically independent lines.

  In the present invention, the satellite repeater 12 is not essential, but the present invention is particularly advantageous when frequency resources are allocated in the satellite communication system as shown.

  FIG. 2 shows a schematic functional block diagram regarding the base station 11 and the mobile station 14. In FIG. 2, the functions of the base station and the mobile station that are particularly relevant to the description of the present invention are illustrated, and other normally provided elements are omitted. In the figure, a communication request control unit 21 and a transmitter 27 are depicted on the mobile station 14 side. In the figure, on the base station 11 side, a communication request management unit 22, a mobile station management database 23, an allocated frequency bandwidth control unit 24, a receiver 25, and a mobile station transmission capability estimation unit 26 are depicted.

  The communication request control unit 21 in the mobile station 14 requests a new frequency allocation at the start of communication, requests a release of a frequency band that has already been allocated, or updates the contents of constraint information described later. When the allocation contents of other frequency bands are to be changed, a request signal indicating that is generated. The request signal is notified to the base station via the satellite channel through the control channel.

  The transmitter 27 transmits a signal in the frequency band notified from the base station 11.

  The communication request management unit 22 in the base station 11 receives a request signal from the mobile station 14. The request signal includes information indicating mobile station identification information, new allocation request, release request, and the like.

  The mobile station management database 23 stores information (hereinafter referred to as “constraint information”) such as maximum and minimum values of frequency bands that can be allocated to mobile stations, priority among mobile stations in frequency allocation (hereinafter referred to as “constraint information”). to manage. The maximum value, the minimum value, and the priority determine the correspondence (function) between the frequency band allocated to the mobile station and the allocation level parameter commonly used for all mobile stations.

  The range of frequency bands that can be set for each mobile station depends on physical conditions such as transmission capability and communication environment of the mobile station. For example, the frequency bandwidth allocated to the mobile station is the frequency bandwidth when the received CNR measured on the receiving side (base station) matches the required CNR when the mobile station transmits a signal with the maximum transmission power. Limited to This is because even if a larger bandwidth is allocated to the mobile station, the required CNR cannot be realized at the base station. Note that not only the CNR but also other signal quality quantities such as SIR may be measured. On the other hand, the range of frequency bands that can be set for a mobile station depends on conditions required by an application in addition to the physical conditions of the mobile station. Therefore, the maximum value of the frequency band that can be allocated to the mobile station is preferably set to the smaller one of the value restricted by physical conditions and the value restricted by the application. Further, it is desirable that the minimum value of the frequency band that can be allocated to the mobile station is set to the larger one of the value restricted by physical conditions and the value restricted by the application. Furthermore, in addition to physical conditions and application conditions, restrictions by legal regulations such as the Radio Law can be taken into account.

The allocated frequency bandwidth control unit 24 calculates a frequency band to be allocated to each mobile station according to the constraint information set for each mobile station. constraint information regarding the m-th (m is a natural number equal to or less than mobile stations the total number M) mobile station, its m-th are assigned to the mobile station the frequency band f _m, allocation level parameters used in common to all mobile stations Define the correspondence with x. Therefore, to be precise,
f _m = f _m (x; h _m , l _m , a _m )
For simplicity, it is abbreviated as f _m = f _m (x). As an example, f _m (x) can be determined as follows.

図３は、ｙ＝ｆ_ｍ（ｘ）のグラフの概形を示す。簡明化のため、ａ_ｍ＝１としている。図４は、ｌ_ｍ＝ｈ_ｍ＝Ａ（一定値）の場合のグラフを示す。これは、パラメータｘの値によらずｙの値は一定となり、固定された周波数帯域しか割り当てらないようなＱｏＳを実現する場合に相当する。図５は、ｌ_ｍ＝Ｂ（一定値），ｈ_ｍ＝∞の場合のグラフを示す。これは、例えば音声通信用の通信速度を最低限確保しながら、割り当てる周波数帯域幅がパラメータｘに比例するようなＱｏＳを実現する場合に相当する。図６は、ｌ_ｍ＝０及びｈ_ｍ＝∞の場合のグラフを示す図である。これは、割り当てる周波数帯域幅が完全にパラメータｘに比例するようなＱｏＳを実現する場合に相当する。

FIG. 3 shows an outline of the graph of y = f _m (x). For simplicity, a _m = 1. FIG. 4 shows a graph in the case of l _m = h _m = A (constant value). This corresponds to a case in which the value of y is constant regardless of the value of the parameter x, and QoS is realized in which only a fixed frequency band is allocated. FIG. 5 shows a graph in the case of l _m = B (constant value) and h _m = ∞. This corresponds to, for example, a case where QoS is realized such that the allocated frequency bandwidth is proportional to the parameter x while ensuring a minimum communication speed for voice communication. FIG. 6 is a diagram showing a graph in the case of l _m = 0 and h _m = ∞. This corresponds to a case where QoS is realized such that the allocated frequency bandwidth is completely proportional to the parameter x.

Although the constraint information such as the maximum value h _m , the minimum value l _m, and the priority a _m may be different for each mobile station, the allocation level parameter x does not depend on the value of m, but all mobile stations Note that it is used in common. Accordingly, the frequency band assigned to the first mobile station is represented by f ₁ (x), the frequency band assigned to the second mobile station is represented by f ₂ (x), and so on. The frequency band assigned to is represented by f _M (x).

The allocation frequency band control unit 24 of FIG. 2 assigns the allocation level parameter x such that the sum of the frequency bands used by all the mobile stations becomes a desired value W _all based on the constraint information of each mobile station. to derive the value of _{x 1.} That is,
Σf _m (x) = f ₁ (x) + f ₂ (x) +... + F _M (x) = W _all (P)
A solution x = α that satisfies the above is derived. The desired value W _all is the total frequency bandwidth available for the entire system. By substituting the derived solution x = α into each of f _m (x), the frequency bands f ₁ (α), f ₂ (α),. . . , F _M (α) is derived. These calculation results are notified to each mobile station 14.

  The receiver 25 receives a signal from the mobile station 14 via the satellite repeater 12.

  The transmission capability estimation unit 26 determines the transmission capability of the mobile station in the communication environment based on the received signal quality (for example, reception CNR) of the signal from the mobile station, the frequency bandwidth set for the mobile station, and the like. presume. The estimation result is notified to the mobile station management database 23, and the constraint information related to the mobile station (for example, the maximum value of the assignable frequency band) is updated as necessary.

  On the other hand, when an adaptive modulation and channel coding (AMC) method is used in a wireless communication system, the modulation multi-level number and the coding rate are adaptively set according to the received signal quality. The If the transmission power is constant, the reception CNR tends to increase as the frequency bandwidth decreases. Therefore, instead of increasing the modulation multi-level number and the coding rate, the communication speed can be improved while maintaining the transmission power and the signal quality by setting the frequency bandwidth narrower. Thereby, the power resource of the mobile station can be further effectively utilized.

  FIG. 7 shows a flow for calculating the frequency band of the mobile station performed in the base station. In step 72, constraint information for each mobile station is prepared. The constraint information is managed in the mobile station management database 23 of FIG.

In step 74, calculation for solving the equation (P) is performed. As described above, the constraint information is managed for each mobile station, restriction information defines the correspondence between f _{m (x)} between the frequency band f _m and allocation levels parameter x. FIG. 8 schematically shows the relationship of f _m (x) of various functional forms, their sum, and the solution x = α of the equation.

In step 76, using the obtained solution x = α, a frequency band f _m (α) (m = 1,..., M) to be allocated to each mobile station is calculated and notified to each mobile station. In response to this notification, each mobile station can change the frequency bandwidth to be used.

These series of steps are performed every time there is a request to change the frequency band allocation content. Such a request is made when there is a new frequency band allocation request, a release request, a constraint information update request, or the like. When calculating the sum (Σf _m (x)) of the frequency bands of each mobile station in step 74, for a new allocation request, the function f _k (x) for that mobile station is added to the sum before the change. In the case of a release request, the calculation efficiency can be increased by subtracting it.

FIG. 9 shows an example of the relationship between the number of mobile stations that are simultaneously communicating and the frequency assigned to the mobile station. In this example, the function form of f _m (x) shown in FIG. 6 is used (f _m (x) = x). While all the frequency bandwidths that can be used in the system are always used, the frequency bandwidth allocated to each mobile station is changed fairly as the number of simultaneous connections changes. In this example, the frequency bandwidth allocated to each mobile station is equal to the value obtained by dividing the frequency bandwidth W _all available in the system by the number of simultaneous connections.

  By the way, the process of switching the frequency bandwidth should be performed in cooperation by all mobile stations. Otherwise, there is a possibility that the transmission signals of the mobile stations interfere with each other and the desired communication quality cannot be ensured. For this reason, it is desirable to establish time synchronization between mobile stations and switch the assigned frequency band periodically or irregularly. In this case, in order to aggregate communication requests and release requests generated within a certain period and reflect them in the restriction information and the frequency band at the same time, it is better to switch frequently (if it is done periodically) , Shorter cycle is desirable). It is not essential that the time synchronization in this case is accurate as performed in a time division multiple access (TDMA) system, and time synchronization is appropriately performed according to the frequency at which the communication request of each mobile station changes. It is only necessary to set the period. Since the change in environment is small and the frequency of switching frequency bands is low, the time synchronization cycle can be lengthened. Therefore, even devices with relatively low accuracy time synchronization capability can be realized. Can do. Further, when there is a difference in propagation delay time due to a difference in position of the mobile station, a guard time is required to avoid signal collision at the time of switching. If the time synchronization period is set longer than the guard time, it is possible to suppress a decrease in transmission efficiency due to the guard time.

According to the present embodiment, it is possible to realize allocation of frequency bands that satisfy the QoS of each mobile station while using up all the frequency bandwidths that can be used in the system. Since in this embodiment is fixed to 1 the priority a _m for all mobile stations, the mobile station is equal to each other, it is allocated fairly resource. However, if the sum of the maximum values is smaller than the frequency band available in the system, that is,
Σh _m <W _all
In this case, it is not possible to use up all the frequency bands that can be used in the system.

In the above embodiment, although the priority a _m between the mobile station has been set to all 1, it may be set other values. In the example shown in FIG. 10, the priority a ₁ of the mobile station 1 is set to 1, but the priority a ₂ of the mobile station ₂ is set to 1.5, and the priority a ₃ of the mobile station ₃ is 0. .5 is set. The maximum value and the minimum value are set as h _m = ∞ and l _m = 0. If the priority is set in this way, the mobile station 2 can receive an allocation of 1.5 times more frequency band than the mobile station 1. Only half of the frequency band of the mobile station 1 is allocated to the mobile station 3. In general, when based on the m th mobile station, the n-th mobile station is assigned a _{n /} a _m times the frequency bands. By setting the priority for each mobile station in this way, QoS can be controlled relatively between mobile stations. If all priorities are set to the same value as in the first embodiment, each mobile station can be handled uniformly.

  FIG. 11 shows simulation results showing changes in system capacity with respect to the number of simultaneous transmission stations. The system capacity is a communication speed achieved in the entire mobile station in communication. In the figure, of the four curved lines, two are related to the prior art and two are according to the present invention. One of the two lines related to the prior art is related to the case where the adaptive modulation and coding scheme is adopted and the other is not adopted. The two lines related to the present invention are also related to the case where one employs an adaptive modulation and coding scheme and the other does not. As shown, the system according to the present invention can achieve a larger system capacity than the prior art. It can also be seen that a larger system capacity can be realized by performing the adaptive modulation and coding than without performing the adaptive modulation and coding.

In the prior art, since the frequency band allocated to one mobile station is fixed, it can be seen that the system capacity increases linearly as the number of simultaneous connections increases. In the simulation, it is assumed that a limit to the transmission capability of the mobile station _{(0 <h m <∞)} . Therefore, according to the present invention, when the number of simultaneous connections is small, the entire usable frequency band cannot be used up, and thus the system capacity is small. I understand. If there is no limit to the transmission capability of the mobile station (h _m = ∞), the maximum system capacity (in this example, about 42 Mbps) can always be maintained regardless of the number of simultaneous connections.

  FIG. 12 shows a simulation result regarding the communication speed for one mobile station. As shown in the figure, it can be seen that the method according to the present invention can achieve a higher bit rate than the prior art. It can also be seen that a larger bit rate can be realized by performing the adaptive modulation and coding than not. In the prior art, since the frequency band assigned to one mobile station is fixed, a constant bit rate is maintained regardless of the number of simultaneous connections. As shown in the figure, when the number of simultaneous connections is small, the mobile station can be allocated a frequency band that can realize a very large bit rate as long as the transmission capability permits.

It is a figure which shows an example of a communication system. 1 shows a schematic block diagram of a base station and a mobile station. shows a graph of y _{= f} m (x). shows a graph of _{y = f m (x) (} l m = h m = A). shows a graph of _{y = f m (x) (} l m = B, h m = ∞) is. shows a graph of y _{= f} m (x) is a _{(l m = 0, h m} = ∞). 3 shows a flowchart for calculating the frequency band of each mobile station. It is a diagram showing how to calculate the _{Σf m (x) = W all} . It is a figure which shows an example of the number of simultaneous connections and the allocated frequency band. It is a diagram showing an example of different priorities _{a m} function _f m (x). It is a figure which shows the simulation result regarding a system capacity | capacitance. It is a figure which shows the simulation result regarding a communication speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Base station 12 Satellite repeater 13 Service area 14 Mobile station 21 Communication request control part 22 Communication request management part 23 Mobile station management database 24 Control part of allocated frequency bandwidth 25 Receiver 26 Transmission capability estimation part 27 Transmitter

Claims (6)

A frequency allocation apparatus used in a radio communication system in which a plurality of mobile stations capable of changing a frequency band for communicating a single carrier signal is connected to a base station by a frequency division multiple access (FDMA) system. ,
A database for managing, for each mobile station, a constraint condition that defines a correspondence relationship between a bandwidth allocated to the mobile station and an allocation level parameter commonly used for all mobile stations;
Means for deriving a value of an allocation level parameter such that a sum of bands allocated to all mobile stations is a desired value in a wireless communication system;
Means for calculating each band allocated to each mobile station based on the derived allocation level parameter so that the available band is minimized;
A frequency allocation device comprising: The correspondence is expressed by the following equation:

Here, f m _(x) represents the bandwidth allocated to the m th mobile station, x is expressed allocation level parameter, l _m represents the minimum bandwidth allocated to the m th mobile station, h _m is m th represents the maximum value of the allocated band to the mobile station, a _m is the frequency assignment system according to claim 1, wherein a representative of the relative priority between the mobile stations. The database includes a first lower limit value and an upper limit value of a band determined from a hardware condition of the mobile station, and a second lower limit value and an upper limit value of a band determined from a request for a service provided to the mobile station. Manage
The minimum value of the band allocated to the mobile station is set to the larger one of the first and second lower limit values,
The frequency allocation apparatus according to claim 1, wherein a maximum value of a band allocated to the mobile station is set to a smaller one of the first and second upper limit values. The frequency allocation apparatus according to claim 1, wherein a band allocated to each mobile station is notified so that a plurality of mobile stations change the frequency band in synchronization. The frequency allocation apparatus according to claim 1, wherein the frequency allocation apparatus is used in a radio communication system using an adaptive modulation and coding (AMC) system. A frequency allocation method used in a radio communication system in which a plurality of mobile stations capable of changing a frequency band for communicating a single carrier signal is connected to a base station by a frequency division multiple access (FDMA) system. ,
Set a constraint for each mobile station that defines the correspondence between the bandwidth allocated to the mobile station and the allocation level parameter commonly used for all mobile stations,
Deriving the value of the allocation level parameter such that the total bandwidth allocated to all mobile stations is a desired value in the wireless communication system;
A frequency allocation method, characterized in that, based on the derived allocation level parameter, a bandwidth allocated to each mobile station is calculated so that a free bandwidth is minimized.

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