Abstract:
A method that provides quality of service in a multiuser orthogonal frequency division multiplex system. The method assures quality of service at application level, which directly affects user&#39;s satisfaction with the service for interactive applications, such as web browsing, and real-time applications. The method uses advanced dynamic resource allocation to achieve a common subjective user state and/or dynamic resource allocation to optimize the throughput of the system while increasing the quality of service at application level. The method takes advantages of the information of the instantaneous channel gain and information of the objective technical parameters of the system and applications. With the incorporation of the technical parameters of the system and applications into the subcarrier allocation, the method may provide quality of service at application level, allow explicit control of system resources, ensure fairness in resource allocation and achieve the optimal throughput of the multiuser orthogonal frequency division multiplex system.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method that provides quality of service (QoS) at application level in a multiuser orthogonal frequency division multiplex (OFDM) system, wherein quality of service is provided with advanced dynamic resource allocation. 
         [0003]    2. Description of the Related Art 
         [0004]    Nowadays users expect high data rates, high availability and appropriate quality of service in wireless and mobile communication systems under adverse conditions such as hostile mobile environments, intersymbol interference, limited available spectrum and radio propagation anomalies. Recent known systems provide quality of service at the network level, which does not include the entire end-to-end communication chain or take into account users&#39; satisfaction with the service, perception of quality and previous experience with the system. Assuring quality of service at application level is therefore important factor because it directly affects users&#39; satisfaction with the service. 
         [0005]    Recently, research has been carried out on algorithms for subcarrier and power allocation in multiuser OFDM systems. Said algorithms can be categorized into two general types: static and dynamic resource allocation. The systems using dynamic resource allocation consider information of instantaneous channel gain on communication channel with associated algorithms solving complex systems of equations with the nonlinear optimization problem. Some recent algorithms also provide fairness to the process of resource allocation. Fairness is typically incorporated into the system by using different utility functions, adaptive subcarrier allocation with proportional constraints or by assigning different priorities to individual users. Providing said priorities and achieving relevant quality of service at application level are still unresolved issues. 
       BRIEF SUMMARY 
       [0006]    In one aspect, the method may provide an optimal quality of service at application level and optimal throughput of the wireless and mobile multiuser OFDM systems by using advanced dynamic resource allocation on the transmit unit of the system. 
         [0007]    This effect may be achieved with the characteristics disclosed in the first claim. The method provides an appropriate QoS at application level for all users of the wireless environment while optimizing the throughput of the OFDM system by using advanced dynamic subcarrier allocation. QoS at application level is provided for interactive and real-time applications. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0008]    These and other features are described in more detail in the following description, given by the way of example and with the accompanying drawings, where 
           [0009]      FIG. 1  shows a block diagram of the multiuser OFDM system with dynamic subcarrier and power allocation, 
           [0010]      FIG. 2  shows a flow diagram of the method, which determines the user&#39;s required capacities to achieve individual subjective states, 
           [0011]      FIG. 3  shows a flow diagram of the method that uses dynamic subcarrier allocation to achieve a common subjective user state, and 
           [0012]      FIG. 4  is a flow diagram of the method that uses dynamic subcarrier allocation to optimize the throughput of the OFDM system while increasing the QoS at application level. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The method described herein relates to wireless networks, such as a local wireless network and mobile networks, using multiuser OFDM system. As used hereinafter, the term “transmit unit” includes but is not limited to a base station or other similar devices capable of transmitting signals in wireless environment. The term “receive unit” includes but is not limited to a mobile station, user equipment or other similar devices capable of receiving signals in wireless environment. In addition, the term “base station” includes but is not limited to an eNode B in LTE technology, access points or other interfacing devices capable of transmitting signals. The term “user” includes user equipment capable of receiving signals in wireless environment. The present disclosure assumes that the information of instantaneous channel gain on each subcarrier is available to the transmit unit, and therefore the transmit unit can utilize the information to determine the assignment of subcarriers to users. Furthermore, the disclosure also assumes that the transmit unit has available information of the technical parameters of the system and applications, such as the web page size, round trip time, packet loss, etc., and information of previous subjective users&#39; states (i.e. previous users&#39; satisfaction with the service), such as previous MOS (Mean opinion score) states. The MOS methodology provides a connection between the objective technical parameters of the system and applications, such as delay, throughput, jitter, packets loss, web page size in case of web browsing, and subjective user states which represent user satisfaction with the service or QoS at application level. Typically, the five point MOS scale (states 1, 2, 3, 4 and 5) is used, which is also proposed in the present invention, although the invention is not limited to only five point MOS scale, but also allows using other subjective scales that represent user satisfaction or QoS at application level. 
         [0014]      FIG. 1  shows a block diagram of the multiuser OFDM system. The system  100  generally includes a transmit unit  101 , incorporated in a base station, and a receive unit  102  (not described in details). Transmit unit  101  consists of a dynamic subcarrier and a power allocation module  103 , a modulation module  104 , an inverse fast Fourier transform (IFFT) module  105 , a guard period insertion module  106 , a module  107  for signal transmission and filtering, and a transmit antenna  108 . 
         [0015]    The module  103  requires for providing QoS at application level the relevant information of the system and users&#39; application parameters, the information of instantaneous channel gain on each subcarrier and information of previous users&#39; MOS states. In case of interactive applications, the web page size, delay and round trip time are appropriate technical parameters, while packet loss, delay and jitter are relevant parameters in case of audio and video applications. The modulation module  104  applies the corresponding modulation schemes (e.g. BPSK, QPSK, QAM) on the symbols. Further, the IFFT module  105  transforms the output complex symbols of the modulation module  104  into the time domain samples by using IFFT. The guard period insertion module  106  inserts a guard period to the end of each OFDM time domain symbol. 
         [0016]    This disclosure assumes the multiuser OFDM system with K users and N subcarriers. The disclosure also assumes that the bandwidth of each subcarrier is sufficiently smaller than the coherence bandwidth of the channel. Based on those assumptions, the method provides appropriate QoS at application level and optimizes the throughput of the OFDM system. 
         [0017]    According to the module  103 , the method  300  ( FIG. 3 ) dynamically allocates subcarriers to users of the multiuser OFDM system to achieve a common subjective user state (e.g. state MOS=3). 
         [0018]    The method  300  dynamically allocates subcarriers to users to achieve a common subjective user state com_MOS. In case of using five point MOS scale, it may be preferable to use state MOS=3 for the common subjective user state, although any MOS value can be used. One embodiment may be illustrated with the MOS function for web browsing which maps the objective technical parameters and the subjective user states. The presented MOS function serves as an example for web browsing, although other more complex MOS functions can be used, which include characteristics of video and audio applications and connect subjective user states with the objective technical parameters: 
         [0000]      MOS=4.109 *e   −0.1522*d(r) +1.05 
         [0000]    where function d(r) represents delay. The delay is defined as latency between the time a request for a web page was sent (i.e. HTTP request message) and the time of reception of the entire web page contents. Function d(r) can be described with the following equation: 
         [0000]    
       
         
           
             
               d 
                
               
                 ( 
                 r 
                 ) 
               
             
             = 
             
               
                 4 
                  
                 RTT 
               
               + 
               
                 FS 
                 r 
               
               + 
               
                 C 
                  
                 
                   MTU 
                   r 
                 
               
               - 
               
                 
                   2 
                    
                   
                     MTU 
                      
                     
                       ( 
                       
                         
                           2 
                           L 
                         
                         - 
                         1 
                       
                       ) 
                     
                   
                 
                 r 
               
             
           
         
       
     
         [0000]    where variable r [bit/s] represents bit rate, RTT [s] the round trip time, FS [bit] the web page size, C the constant and MTU [bit] the maximum transmit unit. In case of web browsing, the transmit unit can acquire the information of the web page size through the web proxy server which is usually placed in the operator&#39;s environment. The web page size can be obtained from the “HTTP response” message send by the web server, or calculated by using various prediction methods. It is important to note that the value of the delay function depends on the network level parameters such as bit rate, round trip time and application level parameters like the web page size. This means that the value of the delay function adapts to the individual user based on user&#39;s application requirements. The method  300  ( FIG. 3 ) allocates subcarriers by selecting user kεU, where U={1, 2, . . . , K), with the minimum previous user MOS state prev_MOS k  and assigns to the selected user k the subcarrier nεA, where A={1, 2, . . . , N}, on which user k has the best channel gain until user k achieves the common MOS state com_MOS. The method  300  provides explicit control of system resources, incorporates fairness into the system and assures appropriate QoS at application level for each user. In case of connecting a new user to the system, a random initial MOS value can be determined as the previous user MOS state. The proposed initial value for a new user in case of using five point MOS scale is MOS=3. 
         [0019]    The method  300  starts with the step  301 , which calculates the required capacities r k,1 ,r k,2 ,r k,3 , . . . , r k,max(MOS) . These values represent user&#39;s required capacities to achieve different MOS states. Step  301  is presented in more detail in  FIG. 2  as the method  200 . The method  200  in step  201  initializes for each user specific variables that represent user&#39;s required capacities to obtain specific MOS states according to user&#39;s application parameters. In case of defining the common MOS state as com_MOS=3, the method needs to calculate the user&#39;s required capacity r k,com     —     MOS  to achieve the common MOS state and capacities r k,com     —     MOS+1 , . . . , r k,max(MOS)  for all higher MOS states (step  203 ). The required capacities can be calculated from the MOS function, which maps the subjective user states and the objective technical parameters of the system and applications. The advantage of using the MOS function in case of web browsing application is dependence of the MOS function on the system and application parameters, such as delay. Furthermore, the delay depends on the web page size, bit rate and round trip time. Calculating the user&#39;s required capacity to achieve a certain delay and consequently specific MOS state allows explicit control of system resources in the OFDM system according to user&#39;s application requirements. 
         [0020]    The method  300  continues with the initialization of variable C k  and new_MOS k  (step  302 ). The variable C k  represents allocated capacity to user k, while the variable new_MOS k  represents the new user MOS state. After the initialization, the method  300  finds user kεU with the lowest previous user MOS state min[prev_MOS k ] (step  303 ). Step  304  assigns to selected user k the subcarrier nεA on which user k has the best channel gain. Step  304  solves the following system of equations: 
         [0000]      | H   k,n   |≧|H   k,j | for ∀ jεA  
 
         [0000]    where H k,n  represents channel gain of user k on subcarrier n. Step  305  updates variable C k  for user k (variable p k,n  in  FIG. 3  represents assigned power of user k on subcarrier n, where power can be equally distributed among users) and removes the assigned subcarrier n from the pool of available subcarriers A. Step  305  also changes the initial value of the variable prev_MOS k , which represents the previous user MOS states, as follows. For the selected user k, the variable prev_MOS k  increases for the maximum MOS value of the system. Changing the value of the variable prev_MOS k  for user k allows choosing in the next iteration of the method  300  a new user that has equal or higher previous user MOS state than the current selected user k. Increasing the previous user MOS state and consequently choosing a new user in each iteration of the method ensures fairness into the resource allocation. Step  306  verifies if the assigned capacity is higher than the required capacity r k,com     —     MOS  of user k to achieve common MOS state. If the condition is not met, the method  300  continues with the step  308 . If the condition is met, the step  307  is performed, which eliminates selected user k from additional subcarrier allocation for user state com_MOS. Step  308  verifies if all users of the system achieve common MOS state. If the condition is met, the method  300  ends and the method  400  is performed ( FIG. 4 ). 
         [0021]    The method  400  as shown in  FIG. 4  optimizes the throughput of the OFDM system and increases QoS at application level by using advanced dynamic subcarrier allocation. 
         [0022]    The method  300  ( FIG. 3 ) can continue with the method  400  if all users achieve in method  300  the defined common MOS state corn MOS. The essence of the method  400  is optimizing the throughput of the OFDM system while increasing user&#39;s QoS; that is achieving higher user&#39;s MOS state than the defined common MOS state. The throughput of the system is optimized in step  402  which finds user kεU with the best channel gain on selected available subcarrier n EA. Step  402  solves the following system of equations: 
         [0000]      | H   k,n   |≧|H   j,n | for ∀ jεU  
 
         [0023]    Step  403  updates the capacity C k  for user k and removes the assigned subcarrier n from the pool of available subcarriers A. Step  404  verifies if the capacity C k  of user k is higher than the user&#39;s required capacity r k,com     —     MOS+1  for MOS state com_MOS+1, which represents one higher MOS state than the defined common MOS state. If the condition in step  404  is met, the step  405  is performed, which eliminates user k from the further subcarrier allocation for MOS state com_MOS+1. Step  406  verifies if all users achieve MOS state com_MOS+1. If the condition is met, the method  400  repeats from the beginning. Step  408  changes the value of the defined common MOS state com_MOS. The variable is increased in one higher MOS state than the current common MOS state. If the condition in step  406  is not met, the method  400  repeats with the allocation of the next available subcarrier. The method  400  ends when all users achieve the maximum MOS state (step  409 ), or when A=0. The variable new_MOS k  represents the new user MOS state and is used as the previous user MOS state in the next iteration of the method  300  or method  400 . 
         [0024]    While the foregoing written description enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific exemplary embodiments and methods herein. The invention should therefore not be limited by the above described embodiments and methods, but by all embodiments and methods within the scope and spirit of the invention as claimed.