KR101005720B1 - Downlink Scheduling Algorithm based on Incumbent User Occurrence for Cognitive Radio Communication System - Google Patents

Abstract

The present invention efficiently uses idle frequency resources that are not used by a user in downlink transmission in a wireless cognitive communication system. Therefore, the present invention is inherent in applying the proportional fairness scheduling typically used in a conventional wireless communication system. Considering that the problem of resource allocation deterioration is caused by not considering the appearance of the user first, efficient scheduling of idle resources is performed by considering the frequency of user appearance for each radio channel accumulated up to the current scheduling period. It relates to a scheduling method for assigning.

Cognitive Radio, User Frequency, Downlink Scheduling, Resource Allocation, CR Node

Description

Downlink Scheduling Algorithm Based on Incident Frequency in Wireless Cognitive Communication System

The present invention provides scheduling for efficiently allocating idle frequency resources to CR nodes that are not used by a first user (IU) in downlink transmission in a centralized Cognitive Radio (CR) communication system. (Scheduling) method.

Recently, various types of wireless communication technologies that are rapidly developing are being used more closely not only in daily life but also throughout the industry. Among them, the rapid development of wireless communication technologies such as Wideband Code Division Multiple Access (WCDMA), IMT-2000, WiBro, etc. has provided an opportunity to easily access a lot of information anywhere. However, the emergence of various radio technologies has consumed resources of all frequency bands, and especially low frequency bands have no extra frequency band. Such frequency resources are recognized as intangible property of the state, and while the resources are limited, the demand for them is rapidly increasing. In particular, since band allocation in a specific band is primarily user-oriented, idle frequencies may occur in time, space, and region, but they are allocated to a specific wireless communication system and cannot be reused for other purposes. To solve this problem, CR technology is being studied to reuse idle frequencies and increase the efficiency of radio frequency resources.

Proportional Fairness (PF) scheduling method, a widely used scheduling method for allocating resources to users in a mobile communication system, improves the overall throughput and improves fairness according to channel quality between mobile stations (MSs). Scheduling scheme that provides fairness. In the base station using the proportional fairness scheduling scheme for downlink scheduling, the wireless channel state and the average transmission amount of each user are transmitted through channel quality information (CQI) fed back from each mobile station at every scheduling period. After that, we allocate the radio resource to the user using it. A detailed method of determining a user to allocate a resource is shown in Equation 1.

[ Equation  One]

I is an index representing a user, and R _i (t) represents the current transmission amount of the user i. In addition, T _i (t) means the average transmission amount of the user i and is updated by Equation 2 in every scheduling period.

[ Equation  2]

Where t _c is a weight used to calculate the average transmission amount. Through Equations 1 and 2, a user having the largest R _i (t) / T _i (t) value is allocated a radio resource of a corresponding scheduling period.

In the radio-cognitive communication system considered in the present invention, when a user first appears, resources are first assigned to the first user. Therefore, if the existing proportional fairness scheduling is applied to the radio-cognitive communication system, it considers only the quality of the channel for each CR node and does not consider the appearance of the priority user of the channel. First of all, due to the appearance of the user, there is a problem that can not be transmitted. Due to this problem, resource allocation is made different from the intention of proportional fairness scheduling, and the original performance is not shown.

In order to solve this problem, the present invention additionally considers the frequency of priority user appearance in each radio channel as well as the radio channel state between the base station and each CR node. In this way, a proportional fairness-based downlink scheduling method can be used to more efficiently use idle frequency resources by allocating a radio channel having a high channel state and a low priority user appearance first to a CR node, thereby reducing transmission failure due to the appearance of a priority user. To provide.

According to the present invention, in order to solve the problem that the performance of proportional fairness scheduling is deteriorated due to transmission failure of a CR node that occurs as a user first appears in a radio cognitive communication system, the frequency of appearance of a user is added to the existing proportional fairness scheduling method. Scheduling takes place in consideration.

To this end, first, the first step of obtaining the maximum amount of transmission possible for each channel of the CR nodes through the channel quality information fed back from the CR nodes, and by using the first user appearance frequency information for each radio channel accumulated up to the current scheduling period A second step of giving a high weight to a radio channel having a low priority user appearance by multiplying it by the current transmission rate; a third step of allocating a resource block to a CR node in consideration of the two steps and the average transmission amount of each CR node; In the radio-cognitive communication system including a fourth step of updating the average amount of transmission to be used for the next scheduling after scheduling, the downlink scheduling method considering the frequency of user appearance first.

 In the present invention, in applying the proportional fairness scheduling method, which is typically used for downlink transmission of a conventional wireless communication system, to downlink transmission of a radio-cognitive communication system, channel quality is high and priority user appearance frequency is first considered in consideration of user appearance frequency. By assigning weights to lower channels, radio resources are allocated to each CR node. As a result, despite the fact that the CR node is allocated resources through scheduling, the idle frequency resources of a very limited radio cognitive communication system can be effectively reduced by reducing the performance degradation of proportional fairness scheduling caused by transmission failure due to the appearance of users. Provides a method that can be used.

Summary of the Invention In accordance with an aspect of the present invention, in the efficient transmission of idle frequency resources not used by a user in downlink transmission in a radio-cognitive communication system, proportional fairness scheduling typically used in a conventional wireless communication system may be applied as it is. Since the problem that the original resource allocation performance is deteriorated is caused by not considering the appearance of the user first, the scheduling is performed considering the user appearance frequency information for each radio channel accumulated up to the current scheduling period. Thereby minimizing these problems.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a structural diagram conceptually illustrating a downlink scheduler existing in a base station of a wireless cognitive communication system according to the present invention, and allocates data of a scheduler 100 and a CR node existing in a base station of a wireless cognitive communication system. The resource block 200, n CR node queues 300, channel quality information 110, and first user frequency information 120 are included.

Downlink transmission scheduling in a radio-cognitive communication system is largely performed through the following process. First, the base station can know the maximum amount of transmission per channel between the base station and the CR node through the channel quality information received from the CR nodes, respectively. In addition, priority user appearance frequency information 120 for each radio channel accumulated up to the current scheduling period is collected. The scheduling algorithm using the above two information selects a CR node to be transmitted in the current transmission period and a resource block to which resources are allocated. At this time, the resource block used is targeted to the idle resource block, not the resource block used by the user. In this manner, downlink scheduling of one transmission time interval (TTI) is performed by allocating packets of CR nodes to all idle resource blocks through repetition of the scheduling of the idle resource blocks. Finally, the average transmission amount for each CR node to be used for the next scheduling is updated. By repeating this process, communication is performed between the base station and the CR node using idle resources through scheduling in every transmission period.

The scheduling algorithm provided by the present invention is a scheduling algorithm additionally considering a frequency of appearance of a user based on a proportional fairness scheduling algorithm, which is determined by Equation 3.

[ Equation  3]

In Equation 3, I ^* (t) denotes a group of users who are allocated resources to each resource block 200 through scheduling, and I denotes a CR node in which downlink data exists in the CR node queue 300 at time t . Means a group.

In the current time period, the CR node i maximizing the value of the priority function Pr (i, j, t) and the resource block j to which the packet is to be transmitted are determined, and the group I ^* ( Determine t). At this time, the priority function Pr (i, j, t) is expressed by Equation 4 below.

[ Equation  4]

In Equation 4, R _i (t) represents the amount of data that can be transmitted according to the channel state when the CR node i allocates a resource to the resource block j in a transmission time interval t , which is determined according to a modulation technique and a coding technique. do.

F _j (t) represents the frequency of appearance of the preferred user of resource block j . In addition, T is _i (t) refers to the average transmission rate per scheduling period to the CR transmission node i to the present time.

By multiplying 1- F _j (t) by R _ij (t) as shown in Equation 4, the lower the user appearance frequency is, the higher the weight is, so that the resource block with higher channel quality and lower user appearance frequency is preferentially selected. do. Therefore, by reducing the frequency of the CR node allocated resources through scheduling due to the appearance of the user, it is possible to minimize the performance degradation problem of proportional fairness scheduling. F _j (t) used at this time can be obtained through Equation 5.

[ Equation  5]

In Equation 5, A _j (t) indicates whether a user first appears for the resource block j in the transmission time interval t , and has a value of 0 or 1 (A _j (t) ∈ {0, 1}). That is, through the sum of A _j (t), the number of appearances of the preferred user up to the current TTI can be known. N_TTI is the total number of TTIs operated so far. Therefore, as shown in Equation 5, the frequency of priority user appearance of resource block j can be calculated by dividing the number of TTIs operated so far by the number of user appearances.

Meanwhile, the average transmission amount T _i (t) is updated every transmission time interval for scheduling of the next transmission period and can be expressed as Equation 6.

[ Equation  6]

   Equation 6 is in the form of an Exponential Weighted Moving Average (EWMA), wherein the upper formula represents a method of updating the average amount of transmission of the CR node allocated to the resource in the transmission period t, and the lower formula represents a resource. It shows a method of updating the average amount of transmission of unassigned CR nodes. This is because the CR node that has not allocated a resource does not have a corresponding transmission period, so the current transmission amount of the exponentially weighted moving average becomes 0, and the average transmission rate is updated using only the past average value.

2 is a flowchart schematically illustrating a scheduling process of a base station in a wireless cognitive communication system according to the present invention.

For scheduling (S101), first, a resource block S102 that is available due to unused use of a user is detected. The resource block information is collected using the channel quality information 110 fed back from the CR nodes and the appearance frequency information 120 of the user first (S103). Obtain the maximum amount of transmissions per channel of the CR nodes through the two information, and allocate resources by selecting the CR node and the resource block with the maximum Pr (i, j, t) value in consideration of the average transmission amount of each CR node. (S104). Next, after updating, the average transmission amount T _i (t) to be used for the next scheduling is updated, and it is determined whether the CR node is scheduled in the corresponding resource block for each CR node (S105).

When the CR node i is allocated to the corresponding resource block j in the transmission time period t as a result of the determination, the average transmission amount for scheduling in the next resource block is calculated and updated according to Equation 6 (a) (S106).

On the other hand, if the CR node i is not allocated to the corresponding resource block j in the transmission time period t , the average transmission amount for scheduling in the next resource block is updated according to Equation 6 (b) (S107).

This process is performed for all resource blocks in the system (S108), and then scheduling is terminated (S109).

1 is a structural diagram conceptually illustrating a downlink scheduler existing in a base station of a wireless cognitive communication system considered in the present invention;

2 is a flowchart schematically illustrating a scheduling process of a base station in a wireless cognitive communication system according to the present invention.

Claims (7)

delete delete delete The scheduler 100 existing in the base station, a resource block 200 to allocate the data of the CR node, n CR node queue 300, the radio quality including the channel quality information 110, first user frequency information 120 In a downlink scheduling method considering the frequency of user appearance in a cognitive communication system, A first step (S1) of obtaining a maximum amount of transmission per channel between the base station and the CR node based on the channel quality information fed back from the CR nodes; A second step (S2) of collecting priority user appearance frequency information for each radio channel accumulated up to a current scheduling period; A third step (S3) of selecting a CR node to be transmitted in a current transmission period and an idle resource block to which resources are allocated through a scheduling algorithm using the maximum amount of transmission available for each channel and priority user appearance frequency information; And a fourth step (S4) of updating the average amount of transmission for each CR node to be used for the next scheduling after the scheduling. The method of claim 4, wherein The scheduling algorithm of the third step (S3)

In this case, I ^* (t) refers to a group of users who are allocated resources to each resource block 200 through scheduling, and I indicates that downlink data exists in the CR node queue 300 at time t . Determining the CR node group, the CR node i maximizing the value of the priority function Pr (i, j, t) and the resource block j to transmit the packet in the current time interval is determined, and by repeating A downlink scheduling method in which a user appearance frequency is first considered in a radio-cognitive communication system for determining a group I ^* (t) of a CR node to be transmitted. The method of claim 5, The priority function Pr (i, j, t) is

Where R _ij (t) represents the amount of data that can be transmitted according to the channel state when CR node i allocates a resource to resource block j in a transmission time interval t , and F _j (t) represents a resource. In the wireless cognitive communication system, downlink considering the frequency of priority user appearance in a radio communication system, characterized in that it represents the frequency of appearance of the preferred user of block j , T _i (t) means the average amount of transmission per scheduling period transmitted to the CR node i to the present time. Link Scheduling Method. The method of claim 4, wherein The average transmission amount T _i (t) of the fourth step S4 is for scheduling the next transmission period.

Is updated at every transmission time interval, and the equation is in the form of an exponential weighted moving average (EWMA), where (a) represents a method of updating an average transmission amount of a CR node allocated with a resource in transmission period t. , (b) shows how to update the average transmission amount of CR nodes that have not been allocated resources. In the case of CR nodes that have not been allocated resources, the current transmission volume of the exponentially weighted moving average becomes zero because there is no transmission in the corresponding transmission period. In the cognitive communication system, the average transmission rate is updated only by the average value of the downlink scheduling method considering the frequency of user appearance first.

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