Abstract:
This patent discloses a method and a system of radio resource allocation for a mobile MIMO-OFDMA system, the method comprising the steps of: generating a diagonal matrix according to a channel matrix; determining a sum capacity function associated with the diagonal matrix, a plurality of transmission powers, and a plurality of subcarrier fractions; performing a first subcarrier fraction allocation by maximizing the sum capacity function according to a predetermined user capacity condition; performing a first transmission power allocation according to the first subcarrier allocation; and performing a second subcarrier fraction allocation by maximizing the sum capacity function according to the first transmission power allocation and the predetermined user capacity condition.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to radio resource allocation, and more particularly to radio resource allocation on transmission power and subcarrier fraction for downlink mobile MIMO-OFDMA, in which the crucial mobile channel conditions are handled and the computation complexity is much reduced. 
     2. Description of the Related Art 
     In the next generation of wireless communication, due to the tremendous demand of various applications, the capability of supporting gigabit or higher data rate for nomadic users and hundreds of megabit data rate for users with high mobility is becoming a must, wherein said capacity demand of wireless communication can be met with the help of a properly allocation of the radio resource shared among the rated number of users of the MIMO-OFDMA communication system. 
     Orthogonal Frequency Division Multiple Access (OFDMA) is widely considered as the multiple access technology for state-of-the-art and future wireless communication due to its high-spectral efficiency and superior flexibility in radio resource allocation. Multiple Input Multiple Output (MIMO) technology can significantly improve the physical capacity of the wireless communication due to its multiple antennas structure. Therefore, the MIMO-OFDMA is becoming one of the key technologies for broadband mobile communication systems. 
     To fully utilize the capacity of the MIMO-OFDMA communication system, proper radio resource allocation is needed. Among the known arts, the OFDM-based round robin TDMA strategy is the typical one to the increase of the capacity of the MIMO-OFDMA communication system. However, if the computation complexity is taken into account, there is still some room for improvement on capacity versus computation complexity of the known technology mentioned above. We need a technology able to offer superior capacity with much less computation effort. 
     SUMMARY OF THE INVENTION 
     In view of the description above, an objective of the present invention is to provide an effective and robust method of radio resource allocation on transmission power and subcarrier fraction for downlink mobile MIMO-OFDMA communication, and still another objective of the present invention is to further provide a system capable of efficiently allocating the radio resource among the users for mobile MIMO-OFDMA communication in a reasonable amount of computations. 
     The present novel method and system of radio resource allocation, with a proposed channel equalization scheme and a resource allocation algorithm having linear complexity, can be utilized to greatly increase the capacity of the mobile MIMO-OFDMA communication. 
     A method of radio resource allocation is proposed accordingly for determining the transmission powers and subcarrier fractions for mobile stations in the downlink mobile MIMO-OFDMA system with a known channel matrix, a predetermined user capacity condition, and a plurality of default transmission powers, the method comprising the steps of: performing a matrix operation on the known channel matrix to generate a diagonal matrix; performing a first subcarrier fraction allocation by maximizing a sum capacity function according to the default transmission powers and the predetermined user capacity condition to allocate a plurality of first subcarrier fractions of the mobile stations; performing a first transmission power allocation according to the first subcarrier fractions of the mobile stations to allocate a plurality of first transmission powers of the mobile stations; and performing a second subcarrier fraction allocation by maximizing the sum capacity function according to the first transmission powers and the predetermined user capacity condition to allocate a plurality of second subcarrier fractions of the mobile stations, wherein the sum capacity function is associated with the diagonal matrix, the transmission powers, and the subcarrier fractions. 
     The proposed method of radio resource allocation on transmission power and subcarrier fraction for downlink mobile MIMO-OFDMA with known channel matrix of each of the mobile stations, capable of determining the transmission power and subcarrier fraction for each of the mobile stations to maximize the sum capacity of the mobile MIMO-OFDMA according to a diagonal matrix derived from the known channel matrix, and to an algorithm including a modified water-filling optimal power allocation scheme and a constraint linear programming of maximizing a sum capacity function, which represents the total capacity allocated to the mobile stations and is related to the subcarrier fraction, transmission power and the diagonal terms of the diagonal matrix, includes the steps of: performing an operation on the known channel matrix to generate a diagonal matrix; determining the transmission power according to a default allocation; determining a first subcarrier fraction allocation according to a constraint linear programming of maximizing the sum capacity function with the transmission power in the default allocation; determining a first power allocation according to the modified water-filling optimal power allocation scheme with the subcarriers allocated according to the first subcarrier fraction allocation; and determining a second subcarrier fraction allocation according to a constraint linear programming of maximizing the sum capacity function with the transmission power allocated according to the first power allocation. 
     Based on the method, the present invention further provides a novel system capable of efficiently and robustly allocating the radio resource of transmission power and subcarrier fraction for MIMO-OFDMA communication, which comprises: a matrix transformer for performing a matrix operation on the known channel matrix to generate a diagonal matrix; a first subcarrier fraction allocation unit for allocating a plurality of first subcarrier fractions of the mobile stations by maximizing a sum capacity function according to a set of predetermined transmission powers and a predetermined user capacity condition; a first transmission power allocation unit for allocating a plurality of first transmission powers of the mobile stations according to the first subcarrier fractions of the mobile stations; and a second subcarrier fraction allocation unit for allocating a plurality of second subcarrier fractions of the mobile stations by maximizing the sum capacity function according to the first transmission powers and the predetermined user capacity condition; wherein the sum capacity function is associated with the diagonal matrix, the transmission powers, and the subcarrier fractions. 
     The proposed system of the present invention of radio resource allocation on transmission power and subcarrier fraction for downlink mobile MIMO-OFDMA with known channel matrix of each of the mobile stations, capable of determining the transmission power and subcarrier fraction for each of the mobile stations to maximize the sum capacity of the mobile MIMO-OFDMA according to a diagonal matrix derived from the known channel matrix, and to an algorithm including a modified water-filling optimal power allocation scheme and a constraint linear programming of maximizing a sum capacity function, which represents the total capacity allocated to the mobile stations and is related to the subcarrier fraction, transmission power and the diagonal terms of the diagonal matrix, includes: a matrix transformer for performing an operation on the known channel matrix to generate a diagonal matrix; a first subcarrier fraction allocation unit for determining a first subcarrier fraction allocation according to a constraint linear programming of maximizing the sum capacity function with the transmission power in a default allocation; a first transmission power allocation unit for determining a first power allocation according to the modified water-filling optimal power allocation scheme with the subcarriers allocated according to the first subcarrier fraction allocation; and a second subcarrier fraction allocation unit for determining a second subcarrier fraction allocation according to a constraint linear programming of maximizing the sum capacity function with the transmission power allocated according to the first power allocation. 
     To make it easier to understand the objective of the invention, its structure, innovative features, and performance, we use a preferred embodiment together with the attached drawings for the detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is the flow chart of a preferred method of the present invention. 
         FIG. 2  is a block diagram of a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in more detail hereinafter with reference to the accompanying drawings that show the preferred embodiment of the invention. 
     Throughout the description, we assume the number of antenna as N, the number of mobile stations as U, the number of symbols included in an OFDMA frame as T, and the number of subcarriers in each symbol as K. 
     Before describing the specific steps of the method of the present invention, the signal model of the system should be addressed first. In the invention, the time domain transmitted signal vector can be represented as x=Ψ H X, the received signal vector of mobile station u can be represented as r u =D u Ψ H X+W u , and the demodulated signal vector can be represented as 
     Y u =ΨD u Ψ H X+Ψw u =Ω u X+W u , Ω u =ΨD u Ψ H , where D u  is the channel matrix, Ψ H  is related to MIMO-OFDMA transmission scheme, Ω u  is called as equivalent channel matrix, and Ψ, D u , Ψ H  are all known factors. According to Ω u , on which some matrix operations can be performed, we can extract the information relating to signal to noise ratio for radio resource allocations thereafter. 
     Please refer to  FIG. 1 , which shows the flow chart of the present resource allocation method. As shown in the  FIG. 1 , the method of a radio resource allocation on transmission power and subcarrier fraction for downlink mobile MIMO-OFDMA includes the steps of: generating a diagonal matrix (step a); determining a sum capacity function (step b); performing a first subcarrier fraction allocation (step c); performing a first transmission power allocation (step d); and performing a second subcarrier fraction allocation (step e). 
     In step a, a diagonal matrix is generated according to a matrix decomposition, for example but not limited to QR decomposition on the known channel matrix Ω u , which is used in the formulation of the demodulated signal vector as Y u =Ω u X+W u , where Y u  is the demodulated signal vector, X is the transmitted signal vector, and W u  is the additive noise vector, such that, Ω u =Q u R u  where Q u  is an unitary matrix, R u  is an upper triangular matrix and the diagonal terms of R u  are equal to the diagonal terms of the diagonal matrix. 
     In step b, a sum capacity function C t (ω u,α,t,k ,P αt,k ) is determined as, C t =Σ u C u , u=0 to U−1, C u =Σ α Σ t Σ k ω u,α,t,k  log(1+SNR u,α,t,k ), α=0 to N−1, t=0 to T−1, k=0 to K−1 and SNR u,α,t,k =|r u,α,t,k P α,t,k | 2 /(BN O /K), where C t  is the sum capacity, C u  is the capacity allocated to mobile station u, ω u,α,t,k  is the fraction of subcarrier k in symbol t on transmit antenna α assigned for mobile station u, SNR u,α,t,k  is the signal to noise ratio of subcarrier k in symbol t on transmit antenna α for mobile station u, r u,α,t,k  are the diagonal terms of the diagonal matrix, and P α,t,k  is the power allocated to subcarrier k in symbol t on antenna α. 
     In step c, a first subcarrier fraction allocation is determined, according to a maximization of the sum capacity function with the default transmission power allocation, C t =MAX P     α,t,k     ω     u,αt,k   Σ u C u , u=0 to U−1, C u =Σ α Σ t Σ k ω u,α,t,k  log(1+SNR u,α,t,k ), α=0 to N−1, t=0 to T−1, k=0 to K−1, and SNR u,α,t,k =|r u,α,t,k P α,t,k | 2 /(BN O /K), where C t  is the sum capacity, C u  is the capacity allocated to mobile station u, ω u,α,t,k  is the first subcarrier fraction of subcarrier k in symbol t on transmit antenna α assigned for mobile station u, SNR u,α,t,k  is the signal to noise ratio of subcarrier k in symbol t on transmit antenna α for mobile station u, r u,α,t,k  are the diagonal terms of the diagonal matrix, and P α,t,k  is the default transmission power allocated to subcarrier k in symbol t on antenna α. The solution concerned in this maximization can be but not limited to a constraint linear programming with a total power constraint 
     Σ α Σ t Σ k P α,t,k ≦P T , α=0 to N−1, t=0 to T−1, k=0 to K−1, where P T  is the total transmission power, a fraction constraint Σ u ω u,α,t,k ≦1, u=0 to U−1, for all α, t, k, where ω u,α,t,k  is the fraction of subcarrier k in symbol t on transmit antenna α assigned for mobile station u, and a fairness constraint C u /C t =γ u , wherein C u  is the capacity allocated to mobile station u and γ u  is a corresponding fairness parameter configured by the designers. 
     In step d, a first transmission power allocation is determined according to a modified water-filling optimal power allocation scheme with the first subcarrier fraction allocation but without the fairness constraint 
     P α,t,k =[P T /NTK+(1/NTK)Σ α Σ t Σ k BN O /K|r u     Λ       α,t,s,     α,α,t,k | 2 −BN O /K|r u     α,t,k,     α,α,t,k | 2 ], α=0 to N−1, t=0 to T−1, k=0 to K−1, where P α,t,k  is the first transmission power allocated to subcarrier k in symbol t on antenna α, P T  is the total transmission power, r u,α,t,k  are the diagonal terms of the diagonal matrix, and  u     Λ       α,t,s   =MAX u ω u,α,t,s  for each subcarrier (α,t,k). 
     In step e, a second subcarrier fraction allocation is determined according to a maximization of the sum capacity function with the transmission power arranged in the first allocation, C t =MAX P     α,t,k     ω     u,α,t,k   Σ u C u , u=0 to U−1, 
     C u =Σ α Σ t Σ k ω u,α,t,k  log(1+SNR u,α,t,k ), α=0 to N−1, t=0 to T−1, k=0 to K−1, and SNR u,α,t,k =|r u,α,t,k P α,t,k | 2 /(BN O /K), where C t  is the sum capacity, C u  is the capacity allocated to mobile station u, ω u,α,t,k  is the second subcarrier fraction of subcarrier k in symbol t on transmit antenna α assigned for mobile station u, SNR u,α,t,k  is the signal to noise ratio of subcarrier k in symbol t on transmit antenna α for mobile station u, r u,α,t,k  are the diagonal terms of the diagonal matrix, and P α,t,k  is the first transmission power allocated to subcarrier k in symbol t on antenna α. The solution concerned in this maximization can be but not limited to a constraint linear programming with a total power constraint 
     Σ α Σ t Σ k P α,t,k ≦P T , α=0 to N−1, t=0 to T−1, k=0 to K−1, where P T  is the total transmission power, a fraction constraint Σ u ω u,α,t,k ≦1, u=0 to U−1, for all α, t, k, where ω u,α,t,k  is the fraction of subcarrier k in symbol t on transmit antenna α assigned for mobile station u, and a fairness constraint C u /C t =γ u , wherein C u  is the capacity allocated to mobile station u and γ u  are the fairness parameters configured by the designers. 
     Please refer to  FIG. 2 , which shows a block diagram of a system implementing the algorithm shown in  FIG. 1 . As shown in the  FIG. 2 , the system of a radio resource allocation on transmission power and subcarrier fraction for downlink mobile MIMO-OFDMA comprises: a matrix transformer  200 , capable of generating a diagonal matrix  202  by performing an operation on the known channel matrix  201 ; a first subcarrier fractions allocation unit  210 , capable of generating a first subcarrier fraction allocation  212  according to the diagonal matrix  202 ; a first transmission powers allocation unit  220 , capable of generating a first transmission power allocation  222  according to the first subcarrier fraction allocation  212  and the diagonal matrix  202 ; and a second subcarrier fractions allocation unit  230 , capable of generating a second subcarrier fraction allocation  232  according to the diagonal matrix  202  and the first transmission power allocation  222 . 
     In the matrix transformer  200 , a diagonal matrix  202  can be generated according to a QR decomposition, and the inter-antenna interference and inter-carrier interference can be eliminated through this operation. 
     In the first subcarrier fractions allocation unit  210 , a first subcarrier fraction allocation  212  is generated according to a maximization of the sum capacity function with the default transmission power allocation 
     C t =MAX P     α,t,k     ω     u,α,t,k   Σ u C u , u=0 to U−1, 
     C u =Σ α Σ t Σ k ω u,α,t,k  log(1+SNR u,α,t,k ), α=0 to N−1, t=0 to T−1, k=0 to K−1, and SNR u,α,t,k =|r u,α,t,k P α,t,k | 2 /(BN O /K), where C t  is the sum capacity, C u  is the capacity allocated to mobile station u, ω u,α,t,k  is the first subcarrier fraction  212  of subcarrier k in symbol t on transmit antenna a assigned for mobile station u, SNR u,α,t,k  is the signal to noise ratio of subcarrier k in symbol t on transmit antenna α for mobile station u, r u,α,t,k  are the diagonal terms of the diagonal matrix  202 , and P α,t,k  is the default transmission power allocated to subcarrier k in symbol t on antenna α. The solution concerned in this maximization can be but not limited to a constraint linear programming with a total power constraint Σ α Σ t Σ k P α,t,k ≦P T , α=0 to N−1, t=0 to T−1, k=0 to K−1, where P T  is the total transmission power, a fraction constraint Σ u ω u,α,t,k ≦1, u=0 to U−1, for all α, t, k, where ω u,α,t,k  is the fraction of subcarrier k in symbol t on transmit antenna α assigned for mobile station u, and a fairness constraint C u /C t =γ u , wherein C u  is the capacity allocated to mobile station u and γ u  are the fairness parameters configured by the designers. 
     In the first transmission powers allocation unit  220 , a first transmission power allocation  222  is generated according to a modified water-filling optimal power allocation scheme with the first subcarrier fraction allocation  212  but without the fairness constraint 
     P α,t,k =[P T /NTK+(1/NTK)Σ α Σ t Σ k BN O /K|r u     Λ       n,t,s,     α,α,t,k | 2 −BN O /K|r u     α,t,k,     α,α,t,k | 2 ], α=0 to N−1, t=0 to T−1, k=0 to K−1, where P α,t,k  is the first transmission power  222  allocated to subcarrier k in symbol t on antenna α, P T  is the total transmission power, r u,α,t,k  are the diagonal terms of the diagonal matrix  202 , and  u     Λ     α,t,s =MAX u ω u,α,t,s  for each subcarrier (α, t, k). 
     In the second subcarrier fractions allocation unit  230 , a second subcarrier fraction allocation  232  is generated according to a maximization of the sum capacity function with the first transmission power allocation  222   
     C t =MAX P     α,t,k     ω     u,α,t,k   Σ u C u , u=0 to U−1, 
     C u =Σ α Σ t Σ k ω u,α,t,k  log(1+SNR u,α,t,k ), α=0 to N−1, t=0 to T−1, k=0 to K−1, and SNR u,α,t,k =|r u,α,t,k P α,t,k | 2 /(BN O /K), where C t  is the sum capacity, C u  is the capacity allocated to mobile station u, ω u,α,t,k  is the second subcarrier fraction  232  of subcarrier k in symbol t on transmit antenna a assigned for mobile station u, SNR u,α,t,k  is the signal to noise ratio of subcarrier k in symbol t on transmit antenna α for mobile station u, r u,α,t,k  are the diagonal terms of the diagonal matrix  202 , and P α,t,k  is the first transmission power  222  allocated to subcarrier k in symbol t on antenna α. The solution concerned in this maximization can be but not limited to a constraint linear programming with a total power constraint Σ α Σ t Σ k P α,t,k ≦P T , α=0 to N−1, t=0 to T−1, k=0 to K−1, where P T  is the total transmission power, a fraction constraint Σ u ω u,α,t,k ≦1, u=0 to U−1, for all α, t, k, where ω u,α,t,k  is the fraction of subcarrier k in symbol t on transmit antenna α assigned for mobile station u, and a fairness constraint C u /C t =γ u , wherein C u  is the capacity allocated to mobile station u and γ u  are the fairness parameters configured by the designers. 
     While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures. 
     In summation of the above description, the present invention herein enhances the performance than the conventional structure and further complies with the patent application requirements and is submitted to the Patent and Trademark Office for review and granting of the commensurate patent rights.