WO2014075398A1

WO2014075398A1 - Utility-based radio resource allocation method in ofdma system

Info

Publication number: WO2014075398A1
Application number: PCT/CN2013/070391
Authority: WO
Inventors: 李锋; 刘莹; 朱世华; 耿莉娜
Original assignee: 西安交通大学
Priority date: 2012-11-13
Filing date: 2013-01-11
Publication date: 2014-05-22
Also published as: CN103067328B; LU92347B1; CN103067328A

Abstract

Disclosed is a utility-based radio resource allocation method in an OFDMA system, including: providing a utility function for all users in the system, the utility function comprehensively taking into account channel state information (CSI), time delay, service QoS coefficient, data queue state information (QSI) and the number of data packets transmitted by the user; then in the case that the total power of a base station and the power distributed to each sub-carrier are limited, using the sum of the utility function of each user as a target for resource allocation; and finally, according to the designed utility function, allocating resources to the user to reach the objective of resource allocation. By comprehensively taking into account the influence of multiple factors of CSI, time delay, service QoS coefficient, QSI and the number of data packets transmitted by a user, compared with a conventional resource allocation method, the present invention can realize better balance among system throughput, time delay and user fairness.

Description

Say 3⁄4 book

Utility-based radio resource allocation method in 0FDMA system

The invention belongs to the technical field of radio resource allocation, and relates to a utility-based radio resource allocation method in an 0FDMA system.

Background technique

OFDMA (Orthogonal Frequency Division Multiple Access) is developed based on OFDM technology. Its basic idea is to spread high-speed data streams over multiple subcarriers. These subcarriers are mutually Orthogonal. Therefore, the symbol rate on the subcarrier is greatly reduced, and the duration of the symbol is lengthened, so that the delay spread can be resisted, and the intersymbol interference is greatly reduced. In OFDM modulation, each subcarrier is relatively independent, and each subcarrier can have its own specific modulation mode and transmission power level. OFDMA is similar to conventional frequency division multiplexing FDMA, but FDMA needs to have a guard band, and OFDMA No protection band is needed, and waste of band resources is avoided.

In wireless networks, wireless spectrum resources are scarce, and wireless resources are shared by more and more users. The allocation and scheduling methods of wireless resources are important topics in wireless network research. As the demand for multimedia services continues to grow, such as: international protocol television, online gaming and telemedicine, the required transmission bandwidth will also increase. The increase in bandwidth leads to a drop in system performance, due to intersymbol interference caused by frequency selective fading. Orthogonal Frequency Division Multiple Access (OFDMA) physical layer (PHY) and medium access control (MAC) techniques avoid frequency selectivity. In addition, OFDMA allocates a set of available subcarrier sets to each user without the need for the entire bandwidth. Range transmission, therefore, can save transmission power. Moreover, while the subcarrier gain varies with time, OFDMA can update its subcarrier allocation with multi-user characteristics to obtain multi-user diversity gain. Adaptive resource allocation for multi-user OFDMA systems, by utilizing multi-user diversity, can achieve higher spectral efficiency without increasing network facilities.

In the standardization process of 3GPP LTE, OFDMA has become the mainstream multiple access of the downlink Say 3⁄4 book

At the same time, OFDM technology is also a popular technology for uplink. The modulation scheme of the WiMAX Forum also selects OFDMA. OFDMA has also become the core physical layer technology in IEEE802.16. The IEEE802.16d standard and the 802.16e standard respectively propose fixed-band wireless access and mobile bandwidth wireless access standards.

Because bandwidth and power resources are limited, base stations need to allocate them most efficiently. Traditional research on OFDMA resource allocation mostly focuses on the physical layer. However, layer-based network structure is not conducive to the effective use of resources. When only physical layer optimization is considered, the packet is usually assumed to be infinitely long. In actual systems, the arrival of data packets is random, which results in waste of resources, reduced spectrum resource utilization, and user QoS levels.

Summary of the invention

The problem to be solved by the present invention is to provide a utility-based radio resource allocation method in an OFDMA system, which can better combine physical layer and MAC layer features, thereby more effectively allocating resources.

The invention is achieved by the following technical solutions:

A utility-based wireless resource allocation method in an OFDMA system, comprising the following steps:

1) In a single-cell multi-user downlink OFDMA system, M users are served by the same base station, and there are a variety of alternative modulation modes. The system is divided into N mutually orthogonal subcarriers, and all users' packets arrive in the process of obeying Loose distribution, each time slot has a new data packet arrival, the user's data queue length L is equal to the sum of the newly arrived data packet of the current time slot and the amount of remaining data packets in the queue; the utility function of the user on the subcarrier is /^ = f(L, N _t , r, r, a), the value of _Mnmk means that the subcarrier "e {l,..., N} is assigned to any user me {l, ..., M } and The benefits that can be obtained by using the modulation method ^ {1, ..., ^};

Not only the impact of the reachable rate ^ delay ^ and user QoS coefficient, but also the information of the user's data queue length L and the number of sent packets ^; the utility function / is a monotonically increasing function of r ^ and L , is a monotonically decreasing function of ^;

2) Resource allocation is performed on each subcarrier, and the subcarrier allocation matrix is found at the time of allocation Ι _ΧΛ ^ Say 3⁄4 book

The total utility of the OFDMA system is maximized. The matrix indicates which user is allocated to each subcarrier and its modulation mode and which subcarriers each user is assigned to;

/„ _mt is any element in the subcarrier allocation indication matrix I _WxMxJf , indicating whether the subcarrier “has been assigned to the user whose modulation mode is A, and its value is 0 or 1, 7„ _m , _e {0, l} ;

When /^ =1, it indicates that the subcarrier "has been assigned to the user m with the modulation mode _; when /„ _mt =0, the subcarrier is not allocated to the user whose modulation mode is _;

Optimized by Lagrangian multiplication, the optimization goal is

-l _Pnmk) ), where A„, M = 1,...,N, subcarrier “corresponding non-negative Lagrangian multiplier, is the power allocated to subcarrier w; constraints include ∑∑ „ _Μ υ ^ and ∑f n n = ., N, where is the total power of the base station, and P _sub is the maximum limited power allocated to each subcarrier. Specifically, the following operations are included:

Initialization: All subcarriers are allocated at the beginning of each time slot. Each subcarrier does not belong to any user before being allocated. Initialize the subcarrier allocation matrix ι^ _χΜχ = ο and all Lagrangian multipliers 1 „ =0,ra = l,...,N;

Subcarrier pre-allocation: Sub-carrier pre-allocation is performed according to step 2), sub-carrier is allocated to the user and modulation mode on which the maximum utility is transmitted, and the sub-carrier is obtained according to the modulation mode and the signal-to-noise ratio of the user on the subcarrier. The power required by the carrier, the power being no greater than the maximum limited power that can be allocated to the subcarrier;

Under the condition that the subcarrier power limitation is satisfied, if a user has more than two modulation modes selectable on a certain subcarrier, the subcarrier selects a modulation mode with the largest utility value;

After all the subcarriers are pre-allocated, the sum of the powers of the subcarriers is calculated, and compared with the total power of the base station, if the total power of the base station is exceeded, subcarrier reassignment is performed, otherwise, the subcarriers are allocated. Say 3⁄4 book

Match result

Redistribution: When the sum of the powers of the subcarriers exceeds the total power of the base station, first find the subcarriers allocated to the most power among all the subcarriers, the user currently belonging, and the selected modulation mode k', at this time, the subcarrier allocation The element of the corresponding subcarrier in the matrix = 1;

Reassign the user and power to the subcarrier M, re-find the new user m and the modulation method ^, when satisfied (^'^argminC^^, - μ _η . -Λ _η (Ρ _η '-Ρ , , , , , ) ), subcarrier "find new m, k ^nmk

The user m and the new modulation mode _; then reassign the power of the subcarrier w, updating the elements of the corresponding subcarrier in the subcarrier allocation matrix: I _n =0, /„ _mY =1 and the corresponding Lagrangian multiplier: λ η, =λ η, +μ ' n,m ,k , - 'μ n,mk -λ η,(ρ ^χ n ,m ,k , -ρ

n *m *ν ).

k; then calculate the sum of the powers on all subcarriers and compare them with the total power of the base station until the total power limit of the base station is met. All users have their utility value _Ami on any subcarrier. The priority of the user to obtain the subcarrier depends on its utility value. The larger the utility value, the higher the priority.

The one user can divide a plurality of subcarriers, and each subcarrier can be allocated to at most one user. According to the characteristic properties of Α^=/^Λ^,Γ,Γ,α) functions, different forms of utility functions are designed according to the exponential criterion and the proportional criterion.

The = / (L, N, , r, Γ, α) is one of the following utility functions:

L

f(L,N,,r,T,a) = ~ *are ^T , or / (L,W,,r,r,a)=^^,

N ₍ ,

', Say 3⁄4 book

Where is the length of the user data queue, L. Is the average data queue length of all users, b is a constant greater than 0, and the QoS coefficient is determined by the user's service type.

There are four modulation methods, namely: BPSK, QPSK, 16QAM and 64QAM. Compared with the prior art, the present invention has the following beneficial technical effects:

The utility-based radio resource allocation method in the OFDMA system disclosed in the present invention is a cross-layer resource allocation scheme applicable to the uplink and downlink of an OFDMA system, and the utility function adopts the user's data queue length L and the transmitted data. The impact of the number of packets N, the reachability rate r, the delay r and the user QoS coefficient, while ensuring the latency requirements of real-time services, also improves the fairness between users.

Some methods guarantee system throughput, but cannot guarantee fairness between users; some methods are the opposite. However, in the OFDMA system of the present invention, the utility-based radio resource allocation method, in order to achieve a balance between the two, increases the user's data queue length and the number of sent packets in the utility function, so one The user cannot always communicate. If the user continues to communicate, the number of sent packets increases, so that the user utility value decreases and cannot be allocated to resources; if the channel conditions are poor, especially for users at the edge of the cell, for a long time Without the transmission resources, the queue length will increase sharply, and the number of bursts will also decrease at the same time, so that the utility value will increase and the priority assigned to the resource will rise.

In the OFDMA system of the present invention, the utility-based radio resource allocation method performs sub-carrier, power, and bit allocation according to the utility function of the system, and different systems can follow / OL^ r according to their own conditions and target performance to be achieved. , ^) the characteristic nature, design a utility function that meets its requirements, to better serve the user.

DRAWINGS Say 3⁄4 book

Figure 1 shows the downlink resource allocation model of the OFDMA system;

Figure 2 shows the uplink resource allocation model of the OFDMA system;

Figure 3 shows the cross-layer resource allocation structure between the physical layer and the MAC layer;

Figure 4 shows the total throughput of the average time-slot system in systems System 1, System 2 and System 3;

Figure 5 shows the delay performance of the three systems;

Figure 6 shows the case where System 1 receives and transmits data packets per user when the packet arrival rate is 8 in 50 time slots.

Figure 7 shows the case where System 2 receives and transmits data packets per user when the packet arrival rate is 8 in 50 time slots.

Figure 8 shows the case where System 3 receives and transmits data packets per user when the packet arrival rate is 8 in 50 time slots.

Detailed ways

The invention will be further described in detail with reference to the specific embodiments, which are to be construed as illustrative and not limiting.

Figure 1 shows the downlink resource allocation model of the OFDMA system. The transmitting base station allocates data of different users to the most suitable subcarrier according to the channel state information fed back by the user and the data queue state information of each user, and selects a modulation and coding scheme and allocates power for the subcarrier, and the channel state information is The user uses the dedicated channel feedback to the base station, and the resource allocation result information is also transmitted to the user by using a dedicated channel. After the resource allocation is completed, all data is subjected to inverse fast Fourier transform (IFFT) and parallel-to-serial conversion; a cyclic prefix is inserted in front of each OFDM symbol. After the above processing, the OFDM symbol reaches the receiving end through the frequency selective channel, and the receiving end performs the opposite signal processing, that is, the cyclic prefix before the OFDM symbol is removed first, then the serial-to-parallel conversion and the fast Fourier transform (FFT) are performed, and the user according to the base station The transmitted resource allocation information extracts user data from the corresponding subcarriers.

Analogous downlink resource allocation, uplink resource allocation model is shown in Figure 2. Not allocated with downlink resources Description

The same is true: the uplink resource allocation is performed by the base station, the channel state information is not required by the user, but is estimated by the base station itself; the resource allocation result is sent to the user through the downlink channel, and the user can know the allocated resource according to the information. And use the resources allocated to transfer their own data.

Referring to FIG. 3, a utility-based radio resource allocation method in an OFDMA system according to the present invention is a cross-layer resource allocation scheme suitable for uplink and downlink of an OFDMA system, and the utility function adopts a comprehensive consideration of a user data queue length L. The impact of the number of sent packets N _; , the reachable rate r, the delay τ and the user QoS coefficient, while ensuring the real-time service delay requirement, also improves the fairness between users.

Considering a single-cell multi-user downlink OFDMA system, the total number of users is M, and there are a variety of alternative modulation modes. All users are served by the same base station, and the total system bandwidth is divided into N mutually orthogonal subcarriers, each subcarrier. Through flat fading, real-time and non-real-time services, all users' data is encapsulated into packets of fixed size.

Performing radio resource allocation in the above-mentioned single-cell multi-user downlink OFDMA system. First, providing a utility function for all users in the system, the utility function will be channel state information (CSI), delay, service QoS coefficient, data queue state information ( QSI) and the number of packets sent by the user are comprehensively considered; secondly, in the case where the total power of the base station and the power allocated to each subcarrier are limited, the sum of the utility functions of each user is used as the target of resource allocation; According to the utility function, the user is allocated resources to achieve the goal of resource allocation.

The utility function is given as:

The duration of each time slot is r _s seconds, and the user _me {l,...,M} whose modulation mode is A _e { 1, ... , is on the subcarrier /^ {1,... } Channel state information (CSI), ie signal-to-noise ratio (SNR)

Α^ (0 is known at the base station and remains unchanged in one time slot. The user can reach the transmission rate r s _mA on the subcarrier "0 and the required power; ^ _λ (0 with modulation scheme Related to the choice, the relationship between them is

Rnmk ( = !O ₂ (! +

( P _nmk (0) ( Say 3⁄4 book

This is called the signal-to-noise ratio error, which is usually used to compensate for the difference between the actual value and the theoretical value. It is a function related to the bit error rate and is expressed as β ^ - ^ (2)

- \n(5BER) At the beginning of each time slot, all users have new packets arriving. Therefore, the user's data queue length is equal to the sum of the newly arrived packets in the current time slot and the amount of data remaining in the queue. In a multi-user environment, channel characteristics of different users are assumed to be independent of each other. Therefore, users may experience deep fading on some subcarriers but not on other subcarriers. Similarly, each subcarrier pair is The channel conditions are good for the user and not ideal for other users.

Resource allocation is performed on each subcarrier. One user can divide more subcarriers, but each subcarrier can only be assigned to at most one user. All users have their own utility value on any subcarrier. The priority of the user to obtain the subcarrier depends on its utility value. The larger the value, the higher the priority, and vice versa.

Definition 1 P _BS , ^ respectively represent the subcarrier allocation indication matrix, the total power of the base station and the maximum limited power on each subcarrier. In systems that support real-time and non-real-time services, the goal of optimization problems is

Max U (3) where t/ is the utility sum of all users.

There are two power limiting conditions, one is the total power limit of the base station, as in formula (4)

N M K

The other is the power limit assigned to each subcarrier, as in equation (5)

M K

P nmk I nmk - ^ub 1,..., N (5) m=l k=l

Where I„ _mk is an element in the subcarrier allocation indication matrix Ι^ _Μ ^, indicating whether the subcarrier η has been divided Say 3⁄4 book

For users with modulation mode of , the value is 0 or 1, that is

^ ^{0,1} (6)

When / _{nmt =} l, the subcarrier „ has been assigned to the user _{m with} modulation mode _; when / _BmA =0, it is not assigned to the user m. At the same time, each subcarrier can only be assigned to one user when it is allocated. So there is

M K

∑∑^ =1 n = l,...,N (7)

m=l k=l

The goal of the above resource allocation optimization problem is to find a suitable subcarrier allocation matrix I _WxMxjC to maximize the total utility of the system, which matrix indicates which user is allocated to each subcarrier and its modulation mode and which subcarriers each user is assigned. The value of the utility function represents the benefit that can be obtained by assigning the subcarrier η to any user m and using the modulation scheme. μ _ηιΛ not only considers the influence of the reach rate r, the delay τ and the user QoS coefficient, but also takes into account the information of the user's data queue length L and the number of sent packets N, ie

n _mk =f(L,N _t ,r,r,a) (8)

This combines the physical layer and the MAC to design the utility function as a function of the reach rate r, the delay r, the service QoS coefficient, the data queue length L, and the number of packets sent by the user. The effect of the physical layer is represented by the reachable rate r, and r is a function related to the channel state information. The better the channel, the greater the reachable rate, and vice versa; the influence of the MAC layer is reflected by the length of the data queue, the length of the data queue It can be the length of the data queue per user, or the sum of the average data queue length of all users and the length of all user data queues; r and "is a parameter related to the service; consideration of N _t is to better achieve the inter-user Fairness.

The larger the value of the user on the subcarrier, the better the channel condition is, so the subcarrier "assigned to the user m will get a larger throughput; if the user has not received the resource transmission data for a long time, the delay τ and the data queue The length L will continue to increase. If the user is a real-time user, the delay will not be Description

Will satisfy; therefore, the utility function /„ _mt is a monotonically increasing function of r, τ and L.

In a multi-user system, considering the fairness, a user cannot always communicate. If the user continues to communicate, the number of sent packets is increased by N, so the utility function /^ is a monotonic decreasing function. In this way, when the continuation increases, the user utility value is reduced until it can no longer be allocated to the resource; if the channel condition is poor, especially the user at the edge of the cell, the transmission resource is not available for a long time, and L will continuously increase. It is also decreasing, so that the utility value increases and the priority assigned to the resource rises.

At the beginning of each time slot, the corresponding utility value is recalculated, and the allocation of the subcarriers is performed based on the utility value. Here, a heuristic algorithm based on Lagrangian number multiplication is taken as an example to illustrate the process of resource allocation. Lagrangian number multiplication transforms constrained optimization problems into unconstrained optimization problems,

N M K

k ( _nmk - P )) (9)

n=l m=l k=l

Where 4, w = l,..., N, 4 subcarriers correspond to the non-negative Lagrangian multipliers. So the utility function given for all users in the system is:

In a single-cell multi-user downlink OFDMA system, M users are served by the same base station, and there are a variety of alternative modulation modes. The system is divided into N mutually orthogonal subcarriers, and all users' packet arrival processes obey the Poisson distribution. Each time slot has a new data packet arrival, and the user's data queue length L is equal to the sum of the newly arrived data packet amount in the current time slot and the remaining data packet amount in the queue; the utility function of the user on the subcarrier is /^ =f(L, N _t , r, r, a), the value of _Mnmk means that the subcarrier "e{l,...,N} is assigned to any user me{l,...,M} and modulation is employed The benefit of the method ^{1,...,^};

Not only the impact of the reachable rate ^ delay r and user QoS coefficient, but also the information of the user's data queue length L and the number of sent packets ^; the utility function /^ _A is r, τ and Book

The monotonically increasing function of L is a monotonically decreasing function of ^;

2) Resource allocation is performed on each subcarrier, and the subcarrier allocation matrix is found at the time of allocation to maximize the total utility of the OFDMA system. The matrix indicates which user is allocated to each subcarrier and its modulation mode and which sub-users are assigned to each sub-carrier. Carrier wave

/ ^ is any element in the subcarrier allocation indication matrix I^ _MxJf , indicating whether the subcarrier "has been assigned to the user m whose modulation mode is, and its value is 0 or 1, /„„, e{0,l} ;

When a = l, w denotes a subcarrier has been allocated to user m is the modulation _scheme; when / "user" _A = 0, then no subcarriers "the modulation scheme is assigned to the

Optimized by Lagrangian multiplication, the optimization goal is m _aX ( /^d , where 4, w = l,...,N, subcarrier "corresponding non-negative Lagrangian multiplier, Ρ ^ For the power assigned to the subcarriers; the constraints include n = l,...,N, where

For the total power of the base station, _Psub is the maximum limited power allocated to each subcarrier. The following operations are included in the resource allocation:

Initialization: All subcarriers are allocated at the beginning of each time slot. Each subcarrier does not belong to any user before being allocated. Initialize the subcarrier allocation matrix i^ _xM> ^=o and all Lagrangian multipliers. „ =0,ra = l,...,N;

Subcarrier pre-allocation: Sub-carrier pre-allocation is performed according to step 2), sub-carriers are allocated to the user and modulation mode on which the maximum utility is transmitted, and sub-carriers are obtained according to the modulation mode and the signal-to-noise ratio of the user on the subcarrier. The required power, the power is not greater than the maximum limited power that can be allocated to the subcarrier;

Under the condition that the subcarrier power limitation is satisfied, if one user has more than two modulation modes selectable on a certain subcarrier, the subcarrier selects a modulation mode with the largest utility value; storytelling

After all the subcarriers are pre-allocated, the sum of the powers of the subcarriers is calculated, and compared with the total power of the base station, if the total power of the base station is exceeded, subcarrier reassignment is performed; otherwise, the allocation result is obtained;

Redistribution: When the sum of the powers of the subcarriers exceeds the total power of the base station, first find the subcarriers allocated to the most power among all the subcarriers, the user to which n belongs, and the selected modulation mode k', at this time, the subcarriers The element of the corresponding subcarrier in the allocation matrix is =1;

Redistributing the user and power to the subcarrier M, re-finding the new user m and the modulation method ^, when (^' argminC^^-μ _η . -Λ _η (Ρ _η '-Ρ,,,,, ) ) is satisfied , subcarrier "find new user m and new modulation mode _; then redistribute the power of subcarrier w, update the elements of the corresponding subcarrier in subcarrier allocation matrix i _WxMxjr ": i _n = o, i _nmY =1 and corresponding Lagrangian multiplier: λ , = λ, +μ, V - · , . -λ

η η ' nm ' nm k n,(ρ n,m .k . - ' " " );

The sum of the powers on all subcarriers is then calculated and compared to the total power of the base station until the total power limit of the base station is met.

According to the characteristic properties of ^^=/( ^^,«) function, different forms of utility function are designed according to the exponential criterion and the proportional criterion:

^ = /(L, N _t , r, Γ, is one of the following utility functions:

L

f(L,N,,r,T,a) = ~ *are ^T , aLrr

Or f(L,N _t ,r,T,a) f{L,N _t ,rj,a, : arre ^Nt

Or f(L, N _t , r, τ, a) = raL(b + e ^N <),

Where is the length of the user data queue, L. Is the average data queue length for all users, b is large Book

1, non-real-time service at 0 constant, QoS coefficient "determined by the user's business type, such as

ί + τ, real-time business, specifically using one of the above specific forms of utility function

1, non-real time business

, called the utility function 3, and its effect with the traditional only considers the reachable rate r Ι + τ, the real-time service delay r and the user QoS coefficient, and has a similar form to ^ ^^* ^^ ^

The L _a ^N _t functions ^ _λ = ^ and ^^ are called utility function 1 and utility function 2, respectively, for performance comparison, including system throughput, real-time user delay, and fairness between users.

And the system parameters are set as follows:

There are four modulation methods: BPSK, QPSK, 16QAM and 64QAM;

User distribution is evenly distributed;

The number of users is 10;

The number of subcarriers is 8;

The total power of the base station is 5W;

Subcarrier power does not exceed 1W;

The number of time slots is 50;

The user data packet length is 4096 bits.

The comparison results are shown in Figure 4 to Figure 8:

Figure 4 shows the total throughput of the average per-slot system in System 1, System 2 and System 3. The three systems use utility functions 1, 2 and 3, respectively. The horizontal axis represents the packet arrival rate (package number). /timeslot/user), the value range is 5:20, the vertical axis represents the average number of packets arriving per time slot system / the average throughput per time slot system, where the top "*" line indicates every hour The average number of packets arriving in the slot system, and the remaining three lines represent the total throughput of the system per time slot in the three systems. From the results of Figure 4, we can see the swallow that can be achieved by the system 1 using the utility function 1. Book

The throughput is the largest, because the utility function 1 does not consider the fairness between users, and assigns most subcarriers to users with good channel conditions on them; due to the full consideration of the delay performance of real-time users, the system The throughput of 2 is minimal; the utility function 3 used by System 3 compromises between throughput, latency, and user fairness, and the throughput achieved is slightly smaller than System 1, but larger than System 2.

Figure 5 shows the average delay performance of real-time users in three systems. The horizontal axis represents the packet arrival rate (packets/time slots/users), the value range is 5:20, and the vertical axis represents the average of real-time users. Delay (leap seconds). From the results in Figure 5, it can be seen that the real-time user in System 3 has the best delay performance, the system is second, and the system 1 is the worst. This is because the delay of the real-time user in System 1 has little effect on the utility value; System 2 increases the impact of real-time user delay on the utility value, but when there is a real-time user with extremely poor channel conditions, the delay is effective. The effect of the value is not very large; the utility function used by System 3 considers the user data queue length and the number of packets sent by each user more than the utility function of System 2, when there is a real-time user with extremely poor channel conditions, the data The queue length and the number of sent packets have a large impact on the utility value, so real-time users have the best average latency performance.

Figure 6 shows the case where each user receives and transmits a data packet when the packet arrival rate is 8 in 50 time slots. The horizontal axis in the figure represents the number of all users, and the value is 1:10. Integers, where 1-5 are non-real-time users, 6-10 are real-time users, dark bars indicate the amount of packets each user arrives, and light bars indicate the amount of packets sent. As can be seen from the results in Fig. 6, in system 1, whether it is a real-time user or a non-real-time user, the more likely the user with good channel conditions to obtain data to transmit data, the more data will be transmitted.

Figure 7 shows the case where System 2 receives and transmits data packets for each user in the 50 time slots when the packet arrival rate is 8, in which the horizontal axis represents the number of all users, and the value is 1:10. Integers, where 1-5 are non-real-time users, 6-10 are real-time users, dark bars indicate the amount of packets each user arrives, and light bars indicate the amount of packets sent. In the system 2, since the real-time user's utility value is increased more considering the delay performance of the real-time user, the resource is almost allocated to the real-time user. storytelling

Figure 8 shows the case where each user of System 3 receives and transmits a data packet when the packet arrival rate is 8 in 50 time slots. The horizontal axis in the figure represents the number of all users, and the value is 1:10. Integers, where 1-5 are non-real-time users, 6-10 are real-time users, dark bars indicate the amount of packets each user arrives, and light bars indicate the amount of packets sent. Most of the resources of system 3 are allocated to real-time users, but some sub-carriers are allocated to non-real-time users. Compared with system 2, the real-time user delay requirement is ensured, and the amount of data transmitted by non-real-time users is increased. .

Claims

Claim

A utility-based radio resource allocation method in an 0FDMA system, comprising the steps of:

1) In a single-cell multi-user downlink OFDMA system, M users are served by the same base station, and there are a variety of alternative modulation modes. The system is divided into N mutually orthogonal subcarriers, and all users' packets arrive in the process of obeying Loose distribution, each time slot has a new data packet arrival, the user's data queue length L is equal to the sum of the newly arrived data packet of the current time slot and the amount of remaining data packets in the queue; the utility function of the user on the subcarrier is =f{L,N _t ,r,z,a), the value of μ indicates that the subcarrier "e{l,...,N} is assigned to any user me{l,...,M} and modulation is used the way

The income that can be obtained;

Not only the influence of the reachable rate ^ delay r and user QoS coefficient, but also the information of the user's data queue length L and the number of sent packets N, the utility function /^ _λ is r, τ and L Monotonically increasing function, is a monotonically decreasing function;

/ ^ is any element in the subcarrier allocation indication matrix I _WxMxJf , indicating whether the subcarrier "has been assigned to the user m with modulation mode, its value is 0 or 1, l _nmk s {0, l};

When /^ =1, it indicates that the subcarrier „ has been assigned to the user whose modulation mode is _; when /^ =0, the subcarrier is not allocated to the user whose modulation mode is _;

Optimized by Lagrangian multiplication,

Where 4, M = 1,...,N, is the non-negative Lagrangian multiplier for the subcarrier, _P „ _mA is the power allocated to the subcarrier; constraints include ∑∑1 ^/^ ≤ and ∑| „ _m U n = l,...,N, where P _BS is the total power of the base station, and P _uh is the maximum limited power allocated to each subcarrier. Right ^ request

2. The utility-based radio resource allocation method in an OFDMA system according to claim 1, comprising the following operations:

Initialization: All subcarriers are allocated at the beginning of each time slot. Each subcarrier does not belong to any user before being allocated. Initialize the subcarrier allocation matrix i^ _xMx = o and all Lagrangian multipliers = 0 , M = 1"."N;

Under the condition that the subcarrier power limitation is satisfied, if there are more than two modulation modes selectable on a certain subcarrier, the subcarrier selects a modulation mode with the largest utility value;

Redistribution: When the sum of the powers of the subcarriers exceeds the total power of the base station, first find the subcarriers ^, M currently belonging to the user ^, and the selected modulation mode k', among all the subcarriers, The element of the corresponding subcarrier M in the subcarrier allocation matrix /, =1;

For subcarriers "Reassign user and power, re-find new user m and modulation method ^, when (m", ) = argmin( _w ^, - - - ρ , , . )), subcarrier "find new The user and the new modulation scheme then redistribute the power of the subcarrier w, updating the elements of the corresponding subcarrier in the subcarrier allocation matrix I^M: I _n =0, / _nmV =1 and the corresponding Lagrangian multiplier: λ η, = λ η, +μ ' n, mk -μ * n,m _Ύ k .

Calculate the sum of the powers on all subcarriers and compare them with the total power of the base station until it is full. Claim

The total power limit of the base station is up to now.

3. The utility-based radio resource allocation method in an OFDMA system according to claim 1, wherein all users have their utility value ^ on any subcarrier, and the priority of the user to obtain the subcarrier depends on Utility value, the larger the utility value, the higher the priority.

4. The utility-based radio resource allocation method in an OFDMA system according to claim 1, wherein a user can divide a plurality of subcarriers, and each subcarrier can be allocated to at most one user.

5. The utility-based radio resource allocation method in an OFDMA system according to claim 1, wherein the design is based on the characteristic property of the ^=/(, ,Γ,Γ,α) function, following the exponential criterion and the proportional criterion. Different forms of utility functions.

6. The utility-based radio resource allocation method in an OFDMA system according to claim 5, wherein said ^ = /( , , Γ, , «) is one of the following utility functions:

L

f (L, N,, r, T, a) = ~ *are ^T ,

' L *N,

f(L,N _t ,r,T,a) = arTe ^N '

Or f(L, N _t , r, T, a) = raL(b + e ^N '),

Where is the length of the user data queue, L. Is the average data queue length for all users, b is a constant greater than 0, and the QoS coefficient is determined by the user's business type.

7. The utility-based radio resource allocation method in an OFDMA system according to claim 6, wherein said representation is =.

8. The utility-based radio resource allocation method in an OFDMA system according to claim 1, Claim

It is characterized in that the base station side knows the channel state information of all users on all subcarriers, and remains unchanged in one time slot, and the modulation modes are four, namely: BPSK, QPSK, 16QAM and 64QAM.