Abstract:
An apparatus and a method for joint power control in a wireless communication system are provided, in which customer premise equipments to be serviced are selected by scheduling, upon receipt of service requests from the customer premise equipments, the interference level of each of the selected customer premise equipments that affects an incumbent system is calculated, a total interference level affecting the incumbent system is calculated by summing the interference levels of the selected customer premise equipments, and a transmit power of the each customer premise equipment is reduced, if the total interference level is larger than a threshold.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of a Korean Patent Application filed in the Korean Intellectual Property Office on Jan. 12, 2007 and assigned Serial No. 2007-0004003, the entire disclosure of which is hereby incorporated by reference. 
       TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to a wireless communication system. More particularly, the present invention relates to an apparatus and a method for performing joint power control in a Cognitive Radio (CR) wireless communication system. 
       BACKGROUND OF THE INVENTION 
       [0003]    A variety of ever-evolving wireless communication technologies have become necessities to daily living. The wireless communication technologies have evolved from 2nd Generation (2G) Code Division Multiple Access (CDMA) to 3rd Generation (3G) International Mobile Telecommunication-2000 (IMT-2000) in which data as well as voice is fast transmitted. Wireless Broadband (WiBro) or future-generation wireless communication systems are under development for faster data service than IMT-2000. 
         [0004]    To co-exist with incumbent systems, the new wireless communication systems require different frequencies. However, since all available frequencies are occupied, a new frequency assignment within a few gigaherts is difficult and limited free frequency bands cause frequency interference between heterogeneous devices deploying a new wireless communication system. Yet, there are unused spectrums at or above 2 GHz and partially unused TV spectrums at or below 1 GHz. Hence, the Federal Communications Commission (FCC) has conducted a study on real spectrum use of these unused or under-utilized frequencies and sought comments on unlicensed access to unused frequencies through the Notice of Proposed Rule Making (NRPM) in order to increase frequency use efficiency. 
         [0005]    In this context, J. Mitola introduced CR technology that senses an unused frequency or channel among allocated frequencies and efficiently shares the unused frequency. Although the CR technology is effective in solving the problem of limited frequencies, it is required that CR users do not cause harmful interference to authorized user, namely primary users by the frequency sharing. 
         [0006]    Conventionally, a CR wireless communication system allocates explicit time-frequency resources as well as transmit power to Mobile Stations (MSs) by use of a scheduler, upon their service request. From the viewpoint of primary users that are charged for use of frequency bands, they may experience performance degradation due to inference from multiple users as well as a single user. 
         [0007]    Accordingly, there exists a need for an apparatus and method for preventing multiple MSs from causing interference to primary users in a CR wireless communication system, when they transmit data simultaneously. 
       SUMMARY OF THE INVENTION 
       [0008]    To address the above-discussed deficiencies of the prior art, it is a primary aspect of exemplary embodiments of the present invention to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide an apparatus and method for allocating radio resources in a wireless communication system. 
         [0009]    Another aspect of exemplary embodiments of the present invention is to provide an apparatus and method for performing joint power control in a CR wireless communication system. 
         [0010]    A further aspect of exemplary embodiments of the present invention is to provide an apparatus and method for preventing an MS from interfering with a primary user in a CR wireless communication system, when the MS attempts to receive a service in the same frequency band as the primary user or a frequency band adjacent to the frequency band of the primary user. 
         [0011]    In accordance with an aspect of exemplary embodiments of the present invention, there is provided a method for controlling power in a CR wireless communication system, in which customer premise equipments (CPEs) to be serviced are selected by scheduling, upon receipt of service requests from the CPEs, the interference level of each of the selected CPEs that affects an incumbent system is calculated, and a total interference level affecting the incumbent system is calculated by summing the interference levels of the selected CPEs. 
         [0012]    In accordance with another aspect of exemplary embodiments of the present invention, there is provided an apparatus for controlling power in a CR wireless communication system, in which a scheduler selects CPEs to be serviced by scheduling, upon receipt of service requests from CPEs, a path loss calculator calculates the interference level of each of the selected CPEs that affects an incumbent system and calculates a total interference level that reaches a protected contour of the incumbent system using the interference levels, and a power controller reduces the transmit power of the each CPE, if the total interference level is larger than a threshold. 
         [0013]    In accordance with a further aspect of exemplary embodiments of the present invention, there is provided a method for controlling power in a CR wireless-communication system, in which the interference level of each of BSs that affects an incumbent system is calculated, a total interference level affecting the incumbent system is calculated by summing the interference levels of the BSs, and the transmit power of the each BS is reduced, if the total interference level is larger than a threshold. 
         [0014]    Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0016]      FIG. 1  illustrates the configuration of a CR wireless communication system according to an exemplary embodiment of the present invention; 
           [0017]      FIG. 2  is a flowchart of a joint power control operation in the CR wireless communication system according to an exemplary embodiment of the present invention; and 
           [0018]      FIG. 3  is a block diagram for a joint power control apparatus in the CR wireless communication system according to an exemplary embodiment of the present invention. 
       
    
    
       [0019]    Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features and structures. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIGS. 1 through 3 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged wireless communication system. 
         [0021]    Exemplary embodiments of the present invention provide a joint power control apparatus and method for mitigating interference caused by frequency sharing among MSs in a CR wireless communication system. The CR wireless communication system is referred to as a CR system. The CR system can collect geo-location information from the Global Positioning System (GPS) and form geo-location information by collecting information from the GPS. The geo-location information includes information about the protected contour of an incumbent system. 
         [0022]      FIG. 1  illustrates the configuration of a CR wireless communication system according to an exemplary embodiment of the present invention. 
         [0023]    Referring to  FIG. 1 , an incumbent system includes a Relay Station (RS)  150  and Incumbent Users (IUs)  152  to  164 . The incumbent system is a system that uses a licensed frequency band in the CR technology. An IU is a receiving terminal, for example, a TV receiver. The RS  150  receives a TV broadcasting signal from a broadcasting station and broadcasts the TV broadcasting signal to the IUs  152  to  164 . The IUs  152  to  164  receive a broadcasting service within the protected contour  166  of the incumbent system by the TV broadcasting signal. 
         [0024]    A CR system includes Base Stations (BSs)  100  and  130  and Customer Premise Equipments (CPEs)  102  to  112  and  132  to  138 . 
         [0025]    The BSs  100  and  130  schedule services for the MSs  102  and  112  and the MSs  132  to  138  within their service areas, upon request of service access from them, and perform joint power control using geo-location information to avoid interference to the incumbent system. The geo-location information includes information about the distance between each CPE and the protected contour  166  of the incumbent system and the locations of the CPE. 
         [0026]    The joint power control is carried out so that signals from the CPEs  104 ,  106  and  108  do not cross the protected contour  166  of the incumbent system. If the signals cross the protected contour  166  of the incumbent system, they interfere with the IUs  154 ,  158  and  160  during TV reception. Thus, the BSs  100  and  130  transmit data to the CPEs  102  to  112  and  132  to  138  with transmit power that does not go beyond the protected contour  166  of the incumbent system. 
         [0027]    Under the joint power control of the BSs  100  and  130 , the CPEs  102  to  112  and  132  to  138  transmit signal to the BSs  100  and  130  with transmit power that do not interfere with the IUs  150  to  164  of the incumbent system. 
         [0028]    The CR system and the incumbent system can share the same frequency band in two methods. One is that the CR system uses unallocated and unused channels of the incumbent system. The other method is that when transmitters of the incumbent system are remote enough from the CR system, the CR system uses the whole or part of channels allocated to the incumbent system. Thus, the CR system minimized interference to the incumbent system. Herein, the following description is made in the context of the environment of the second method. 
         [0029]    In summary, the CR system can detect an unused frequency without causing interference to the IUs  150  to  164  of the incumbent system and has knowledge of the distances between each CPE and the protected contour of the incumbent system. 
         [0030]      FIG. 2  is a flowchart of a joint power control operation of a BS in the CR wireless communication system according to an exemplary embodiment of the present invention. 
         [0031]    Referring to  FIG. 2 , the BS receives information from CPEs in step  200 . The information is service access requests from the CPEs, for example. 
         [0032]    In step  202 , the BS schedules the CPEs and controls the transmit power of the CPEs. For example, the BS selects CPEs to be serviced from among the CPEs and allocates transmit power to the selected CPEs. 
         [0033]    For each selected CPE, the BS determines whether a specific channel or its adjacent channels are in use in the incumbent system in step  203 . If the channel or the adjacent channels are in use, the BS determines whether there is at least one CPE using the same channel among the scheduled CPEs in step  204 . 
         [0034]    If at least one CPE using the same channel exists, the BS-calculates the total interference levels of the CPEs using the same channel, for joint power control in step  206 . The total interference level includes interference from the CPEs using the same channel and interference from the adjacent channels. The interference levels of CPEs using the allocated channel can be calculated by a conventional interference measuring technique. For example, the interference level of each CPE can be measured using path loss that is based on the distance from the CPE to the protected contour  166  of the incumbent system as follows: 
         [0000]        I ( P   CPE,k   d   k,n )≦ T   max,n   −M′   [Eqn. 1] 
         [0000]    In Equation 1, if channel N has m adjacent channels at each of both sides, n denotes one of channels N−m to N+m that may cause interference, k denotes the index of the CPE, d k,n  denotes the distance between CPE k and the protected contour  166  of the incumbent system, I(P CPE,k , d k,n ) denotes the interference level induced by the transmission of CPE k on channel n, T max,n  denotes a maximum tolerable interference threshold level at the protected contour  166  for channel n, and M′ denotes a predetermined margin for protecting the incumbent system for individual CPE power control. Therefore, Equation  1  describes that the interference from neighbor channels and the interference from the CPE (the interference from a channel used for the CPE) to the protected contour should be equal to or less than the maximum tolerable interference threshold level minus the margin. 
         [0035]    If the incumbent system is not using the specific channel or the adjacent channels in step  203 , the BS starts a service in step  210 . 
         [0036]    If more than one CPE are scheduled, the BS starts the service in step  210 . 
         [0037]    If the total interference level satisfies equation (2) in step  208 , the BS starts the service for the scheduled CPEs in step  210 . The total interference level is interference received at the protected contour  166  of the incumbent system. If the total interference level satisfies Equation 2, this means that signals from the CPEs  102  to  140  do not affect the IUs  152  to  164  of the incumbent system. 
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         [0038]    In Equation 2, d k,n  denotes the distance between CPE k and the protected contour  166  of the incumbent system, I(P CPE,k  d k,n ) denotes the interference level induced by the transmission of CPE k on channel n, T max,n  denotes a maximum tolerable interference threshold level at the protected contour  166  of primary users using channel n, and M denotes a predetermined margin for protecting the incumbent system for individual CPE power control. Therefore, Equation 2 describes that the sum of interferences from the CPEs to the protected contour should be equal to or less than the maximum tolerable interference threshold level minu the margin. 
         [0039]    If the total interference level does not satisfy Equation 2, the BS reduces the power of the scheduled CPEs in step  212 . Because primary users are interfered by the transmit power of the CPEs, the BS reduces the power of the CPEs so that the transmit power of the CPEs do not exceed an allowed power level. The transmit power of the CPEs can be reduced at an equal percentage or by an equal value. The percentage-based power reduction is expressed as: 
         [0000]        P   CPE,K   new   =P   CPE,k ( I−Δ   k %)   [Eqn. 3] 
         [0000]    In Equation 3, Δ k  denotes a predetermined positive percentage constant for each CPE (Δ k &gt;0), P CPE,k  denotes the power of CPE k before joint power control, and P CPE,k   new  denotes the power of CPE k after the joint power control. 
         [0040]    The BS returns to step  206  and calculates the total interference level of the CPEs. The BS then compares the total interference level with an interference level threshold in step  208 . 
         [0041]    Then, the BS ends the joint power control. 
         [0042]      FIG. 3  is a block diagram for a joint power control apparatus of the BS in the CR wireless communication system according to an exemplary embodiment of the present invention. 
         [0043]    Referring to  FIG. 3 , the joint power control apparatus includes a Radio Frequency (RF) processor  300 , an Analog-to-Digital Converter (ADC)  302 , an Orthogonal Frequency Division Multiplexing (OFDM) demodulator  304 , a decoder  306 , a controller  308 , a scheduler  310 , a path loss calculator  312 , a power controller  314 , an encoder  316 , an OFDM modulator  318 , a Digital-to-Analog Converter (DAC)  320 , and an RF processor  322 . 
         [0044]    The RF processor  300  downconverts an RF signal received through an antenna. The ADC  302  converts the analog signal received form the RF processor  300  to sample data. The OFDM demodulator  304  converts the sample data to frequency data by Fast Fourier Transform (FFT). 
         [0045]    The decoder  306  selects data on desired subcarriers from the frequency data and demodulates and decodes the selected data at a predetermined Modulation and Coding Scheme (MCS) level. 
         [0046]    The controller  308  analyzes a control message received from the decoder  308  and operates in accordance with the analysis. In accordance with the present invention, the controller  308  performs joint power control by controlling the scheduler  310 , the path loss calculator  312 , and the power controller  314 . 
         [0047]    The scheduler  310  receives information about CPEs that request a service from the controller  308  and selects CPEs to be serviced by scheduling. 
         [0048]    The path loss calculator  312  calculates the interference levels of scheduled CPEs using the same channel and the interference level of adjacent channels based on information about the CPEs, geo-location information, and information about interference from the channels neighboring to the used channel by Equations 1 and 2. The geo-location information is received from the GPS or if the CPEs are fixed, manually input coordinates can be received from the CPEs. 
         [0049]    The power controller  314  determines whether to perform a joint power control by comparing a total interference level calculated by the path loss calculator  312  with an interference level threshold and notifies the controller  308  of the decision. The interference level threshold is set taking into account the interference levels of the adjacent channels and the interference levels of the CPEs using the same channel. 
         [0050]    During the joint power control, the transmit power of each CPE is reduced at a percentage or by a value. 
         [0051]    The controller  308  generates a control message including information about transmit power determined through the joint power control. 
         [0052]    The encoder  316  encodes and modulates the control message at a predetermined MCS level. The OFDM modulator  318  converts the modulated data to sample data (i.e., an OFDM symbol) by Inverse Fast Fourier Transform (IFFT). The DAC  320  converts the same data to an analog signal. The RF processor  322  upconverts the analog signal to an RF signal and transmits the RF signal through an antenna. 
         [0053]    The joint power control apparatus and method described above with reference to  FIGS. 2 and 3  are for uplink joint power control. The joint power control can be performed at a CPE by receiving geo-location information from the BS. Also, an upper-layer network entity above the BS can carry out a joint power control for the downlink from the BS to the CPE. 
         [0054]    As is apparent from the above description, the present invention advantageously enables frequency sharing without causing interference to an incumbent system by joint power control in a CR wireless communication system. 
         [0055]    Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.