A wireless power supply network resource allocation method based on time reversal technology

Abstract

The invention belongs to the field of wireless communication technology, and specifically relates to a wireless power supply network resource allocation method based on time reversal technology; the method comprises: constructing a wireless power supply network system model based on time reversal technology; calculating a channel impulse response of all terminals sending signals to an AP at the same time according to the wireless power supply network system model based on time reversal technology; calculating an equivalent channel after time reversal processing according to the channel impulse response; calculating a signal to interference noise ratio of a terminal according to the equivalent channel; calculating a total rate of a wireless power supply network according to the signal to interference noise ratio of the terminal; constructing an optimization objective function according to the total rate of the wireless power supply network, solving the optimization objective function to obtain an optimal time allocation result, an optimal subcarrier allocation result and an optimal power allocation result; the system allocates resources according to the optimal resource allocation result; the invention significantly improves the sum rate of users, obtains better throughput performance, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to a wireless power supply network resource allocation method based on time reversal technology. Background Art

[0002] The rapid development of connected devices in recent years has led to the rise of IoT applications. In IoT networks, multiple devices and machines can exchange information through wireless communication functions. Nowadays, IoT devices are commonly used in smart homes, smart transportation, medical monitoring, and disaster warnings. In traditional wireless networks, node devices are powered by fixed energy sources such as batteries. The network life is limited due to battery exhaustion, which affects the performance of wireless sensor networks. In order to extend the operation time of the network, it is necessary to replace or replenish the battery after the battery is exhausted. However, in some applications, wireless nodes are deployed in large-scale sensor networks or implanted in the human body, making regular replacement or charging technically and economically unfeasible. Energy harvesting (EH) is considered to be a promising technology that can replace traditional energy sources such as batteries. It can provide a more cost-effective energy supply for wireless networks. Due to the dual use of energy harvesting (EH) in wireless information transmission (WIT) and wireless energy transmission (WET), the collection of radio frequency (RF) signals has attracted great attention. RF wireless power transmission is an EH technology in which wireless network nodes collect energy from RF signals and convert it into electrical energy. Among various energy transmission systems, wireless power communication network (WPCN) has been widely studied. For WPCN, wireless energy transmission (WET) and wireless information transmission (WIT) are completely separate. Compared with traditional wireless networks where user devices are powered by batteries or power grids, WPCN is more suitable for small wireless networks and can provide permanent energy for user devices such as small wireless sensors. Therefore, WPCN has received widespread attention. The energy-constrained devices in WPCN adopt the "harvest first, then transmit" protocol, that is, obtain energy from a dedicated wireless energy transmitter and use the obtained energy for information transmission.

[0003] In order to meet the rapidly growing demand for wireless data traffic, rate maximization is considered an important indicator, and resource allocation has been widely studied due to the trade-off between WET and WIT in wireless packet networks. In the prior art, a variety of resource allocation methods have been studied, for example, a WPCNs protocol in which users first obtain energy through a hybrid access point (HAP), then transmit data to the HAP through time division multiple access (TDMA), and then obtain the optimal time allocation for wireless power transmission and information transmission through analytical demonstration to maximize the total throughput of all users. A multiple access fading network for TDMA or frequency division multiple access (FDMA) that derives the optimal power allocation for downlink power transmission and uplink information transmission. A WPCN technology based on TDMA optimizes the joint power allocation of downlink power transmission and the time allocation of uplink information transmission. A WPCN based on full-duplex HAP using orthogonal frequency division multiplexing (OFDM) studies the subcarrier allocation and power allocation problems under ideal and non-ideal self-interference elimination.

[0004] However, the above existing methods only focus on downlink WET and uplink WIT in WPCN. However, some practical scenarios involving energy-constrained nodes located in toxic environments, underground, tunnels, remote locations, or disaster areas increase the difficulty of replacing batteries or deploying fixed power supplies. Therefore, it is necessary to obtain energy from the RF signal of a dedicated wireless transmitter to communicate with IoT devices. Moreover, as the number of terminals increases, interference is inevitable. There is an urgent need for a wireless power supply network that can suppress system interference and improve system performance. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a wireless power supply network resource allocation method based on time reversal technology, the method comprising:

[0006] S1: Construct a wireless power supply network system model based on time reversal technology; the model includes a single-antenna power beacon PB, an energy-constrained multi-antenna access point AP, and an IoT terminal device;

[0007] S2: Calculate the channel impulse response of all terminals sending signals to the AP at the same time according to the wireless power supply network system model based on time reversal technology;

[0008] S3: Calculate the equivalent channel after time inversion processing according to the channel impulse response;

[0009] S4: Calculate the signal to interference and noise ratio of the terminal according to the equivalent channel;

[0010] S5: Calculate the total rate of the wireless power supply network based on the time reversal technology according to the signal interference and noise ratio of the terminal;

[0011] S6: construct an optimization objective function according to the total rate of the wireless power supply network based on the time reversal technology, and solve the optimization objective function to obtain the optimal time allocation result, the optimal subcarrier allocation result and the optimal power allocation result;

[0012] S7: The system performs resource allocation according to the best time allocation result, the best subcarrier allocation result and the best power allocation result.

[0013] Preferably, constructing a wireless power supply network system model based on time reversal technology includes:

[0014] During time τ0, PB transmits wireless energy to AP and terminal nodes, and AP and terminal nodes receive energy and store it in rechargeable batteries;

[0015] At time τ tr Within, the terminal node sends a time-reversed detection signal to the AP;

[0016] During time τ1, the AP receives the detection signal and transmits wireless information to the terminal node.

[0017] Preferably, the formula for calculating the channel impulse response when all terminals simultaneously send signals to the AP is:

[0018]

[0019] in, represents the channel impulse response, represents the amplitude of the lth multipath in the multipath channel, L represents the number of multipaths, Represents the delay of the lth multipath in a multipath channel.

[0020] Preferably, the process of calculating the equivalent channel after time reversal processing is: calculating the channel tap value after time reversal processing according to the channel impulse response; calculating the equivalent channel after time reversal processing according to the channel impulse response and the channel tap value after time reversal processing.

[0021] Furthermore, the formula for calculating the channel tap value after time inversion processing is:

[0022]

[0023] in, represents the tap value of the pth multipath between the jth antenna and the mth terminal on subcarrier n, represents the channel response on the lth multipath between the jth antenna and the mth terminal on subcarrier n, It represents the conjugate of the channel response between the j-th antenna and the m-th terminal on subcarrier n, L represents the total number of multipaths, and p represents the p-th multipath.

[0024] Furthermore, the formula for calculating the equivalent channel after time reversal processing is:

[0025]

[0026] in, represents the tap value of the pth multipath between the jth antenna and the mth terminal on subcarrier n, represents the channel response on the lth multipath between the jth antenna and the mth terminal on subcarrier n, It represents the conjugate of the channel response between the j-th antenna and the m-th terminal on subcarrier n, L represents the total number of multipaths, and p represents the p-th multipath.

[0027] Preferably, the formula for calculating the signal to interference and noise ratio of the terminal is:

[0028]

[0029] Among them, SINR m,n represents the signal-to-interference-to-noise ratio at the mth terminal on subcarrier n, p m,n represents the transmit power of the mth terminal on subcarrier n, represents the channel response between the jth antenna and the mth terminal on subcarrier n, represents the channel tap value between the jth antenna and the mth terminal on subcarrier n, B represents the bandwidth, N represents the total number of subcarriers, L represents the total number of multipaths, and N T represents the total number of antennas at the AP end, σ 2 represents the noise power, It represents the interference of the i-th antenna (i≠j) of the AP end antenna to the j-th antenna on subcarrier n.

[0030] Preferably, the formula for calculating the total rate of the wireless power supply network based on the time reversal technology is:

[0031]

[0032] Among them, R sum represents the total rate of the wireless power supply network, r mn represents the rate of the mth terminal on subcarrier n, x m,n Indicates whether the nth subcarrier is allocated to the mth terminal, SINR m,n represents the signal to interference and noise ratio at the mth terminal on subcarrier n, τ1 represents the time used in the WIT phase, B represents the bandwidth, N represents the total number of subcarriers, and M represents the number of terminals.

[0033] Preferably, the optimization objective function is:

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] C5: 0≤τ0≤1

[0040] Among them, R sum represents the total rate of the wireless power supply network, p m,n represents the transmit power of the mth terminal on subcarrier n, x m,n Indicates whether the nth subcarrier is allocated to the mth terminal, τ0 indicates the time used in the WET phase, τ tr represents the time of the time reversal phase, N represents the total number of subcarriers, M represents the number of terminals, and E represents the total energy collected by the AP in the WET phase.

[0041] The beneficial effects of the present invention are as follows: the present invention introduces time reversal technology based on the original WPCN model, and uses the space-time focusing of time reversal to suppress interference in the system, thereby obtaining better throughput performance. The present invention adopts the classic "receive first and transmit later" protocol, and divides time into three stages, one for power transmission, one for time reversal detection, and one for information transmission. Among them, the energy-constrained access point (AP) and the terminal node obtain energy from the radio frequency signal sent by the power beacon (PB) to assist the terminal data transmission. In the time reversal (TR) stage and the wireless information transmission (WIT) stage, the terminal uses the collected energy to transmit the time reversal special measurement signal to the AP, and the AP uses the collected energy to transmit independent signals to multiple terminals through orthogonal frequency division multiple access (OFDM). In order to maximize the total rate of WPCN, the present invention jointly optimizes the energy collection time and AP power allocation, studies the subcarrier allocation, power allocation and time allocation problems of the three stages of the whole process under the energy causal constraint, and adopts binary search to obtain the optimal solution; the present invention significantly improves the sum rate of users, obtains better throughput performance, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram of a wireless power supply network system model based on time reversal technology in the present invention;

[0043] Figure 2 Schematic diagram of time slot allocation of a wireless power supply network based on time reversal technology in the present invention. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] The present invention proposes a wireless power supply network resource allocation method based on time reversal technology, the method comprising:

[0046] S1: Construct a wireless power supply network system model based on time reversal technology; the model includes a single-antenna power beacon PB, an energy-constrained multi-antenna access point AP, and an IoT terminal device;

[0047] S2: Calculate the channel impulse response of all terminals sending signals to the AP at the same time according to the wireless power supply network system model based on time reversal technology;

[0048] S3: Calculate the equivalent channel after time inversion processing according to the channel impulse response;

[0049] S4: Calculate the signal to interference and noise ratio of the terminal according to the equivalent channel;

[0050] S5: Calculate the total rate of the wireless power supply network based on the time reversal technology according to the signal interference and noise ratio of the terminal;

[0051] S6: construct an optimization objective function according to the total rate of the wireless power supply network based on the time reversal technology, and solve the optimization objective function to obtain the optimal time allocation result, the optimal subcarrier allocation result and the optimal power allocation result;

[0052] S7: The system performs resource allocation according to the best time allocation result, the best subcarrier allocation result and the best power allocation result.

[0053] like Figure 1 As shown in the figure, the wireless power supply network system model based on time reversal technology includes a single-antenna power beacon PB, a T There are energy-constrained access points AP with root antennas and M single-antenna IoT users, where M>1; in the WPCN system, PB first performs wireless energy transmission WET to AP and terminal nodes, and AP and terminal nodes store the energy in rechargeable batteries after receiving it. Different from the traditional WPCN system, after the WET stage, the terminal node sends a time-reversed detection signal to AP. After receiving the detection signal, AP performs wireless information transmission WIT, specifically, the data signal to be sent is sent to the terminal node after time reversal processing.

[0054] Assume that all channels are quasi-static flat fading, that is, the channel power gain remains constant during a transmission block and may change between blocks. The time of a transmission block is normalized to 1, and the total transmission time block is denoted by T max Indicates that T max = 1; it is assumed that the channel state information at the AP and all terminals is completely known. In the IoT network, all transceivers including the AP should be low-cost and low-power devices. Therefore, Figure 2 As shown in the figure, the “harvest first, transmit later” protocol is adopted on the energy-constrained AP, and a transmission block is divided into three stages, namely τ0+τ tr +τ1=1, the first stage is that PB transmits RF energy, AP and terminal collect energy, the duration is τ0; the second stage is that the terminal sends a time reversal detection signal, the duration is τ tr ; The third stage is that the AP node transmits information to the terminal node, which lasts for τ1.

[0055] In the WET phase, the AP and the terminal obtain energy from the PB, and the total power received by the AP is:

[0056] P T =P B ||h p || 2

[0057] Where P B is the transmitted power at PB, is the channel vector from PB to AP.

[0058] In the energy harvesting EH model, the energy collected at the AP can be expressed as:

[0059] E=ηP T τ0

[0060] Among them, η∈(0,1] is the energy conversion efficiency.

[0061] In WPCN networks, the interference between symbol blocks caused by the multipath environment affects the system performance. Time reversal technology is considered to be an effective technology to combat multipath and time selective fading in the field of wireless communications. The present invention utilizes the spatiotemporal focusing of time reversal technology in multipath channels to suppress the interference between transmission blocks caused by the multipath effect during OFDM transmission.

[0062] Assuming that the terminal channel gains are sorted from low to high, the AP sends data to the terminal using OFDM through N orthogonal subcarriers (SC) within the same duration τ1 in the WIT phase. A binary SC allocation variable x is introduced in the WIT phase. m,n , the n∈Nth orthogonal subcarrier SC nAssigned to the mth terminal, x m,n =1, otherwise, x m,n =0; AP j∈{1,2,...,N T} antennas and the m∈{1,2,..,M}th terminal in SC n The channel impulse response on Considering the impact of multipath effect on the system in practice, assuming that all terminals send signals to the AP at the same time, the channel impulse response for:

[0063]

[0064] in, represents the channel impulse response, represents the amplitude of the lth multipath in the multipath channel, L represents the number of multipaths, Represents the delay of the lth multipath in a multipath channel.

[0065] The channel impulse response is discretized in the time domain and expressed as:

[0066]

[0067] Discrete operations in the time domain satisfy the mean and

[0068] The terminal node obtains energy in the τ0 time slot. In the time reversal phase, the terminal node uses the energy obtained in the τ0 time slot to send a time reversal detection signal to the AP node and obtain channel state information. At this time, the AP receives and records the detection signal and then performs time reversal preprocessing on the obtained channel state, that is, inverts it in the time domain. After time reversal processing, the equivalent channel between the AP and the terminal node can be obtained. The process of obtaining the equivalent channel is as follows:

[0069] The channel tap value after time inversion is calculated based on the channel impulse response, which is expressed as:

[0070]

[0071] in, represents the channel tap value between the jth antenna and the mth terminal on subcarrier n, and L represents the total number of multipaths.

[0072] Each element in the matrix is ​​a normalized tap value after time reversal processing. The calculation formula for the elements in the matrix is:

[0073]

[0074] in, represents the tap value of the pth multipath between the jth antenna and the mth terminal on subcarrier n, represents the channel response between the jth antenna and the mth terminal on subcarrier n, represents the conjugate of the channel response between the j-th antenna and the m-th terminal on subcarrier n, and p represents the p-th multipath.

[0075] The equivalent channel after time reversal processing is calculated based on the channel impulse response and the channel tap value after time reversal processing. The calculation formula is:

[0076]

[0077] in, Represents the convolution operation, p∈{0,1,...,2L-2}.

[0078] When p = L-1, an autocorrelation function will be generated, and the above formula takes the maximum power center peak at this time; since most of the signal power will be focused on the center tap, that is, the L-1th tap, the power on the L-1th tap is considered as the transmission power of the ideal signal; it is allocated to SC n The transmission power of the AP used to send information to the mth terminal is denoted as p m,n , the achievable rate of the mth terminal on the nth SC is:

[0079]

[0080] Among them, SINR m,n represents the signal to interference and noise ratio at the mth terminal on subcarrier n, τ1 represents the time used in the WIT phase, and B represents the bandwidth.

[0081] The signal to interference plus noise ratio (SINR) of the terminal is calculated based on the equivalent channel. The SINR at the mth terminal is:

[0082]

[0083] Among them, σ 2 represents the noise power, It represents the interference of the i-th antenna (i≠j) of the AP end antenna to the j-th antenna on subcarrier n.

[0084] The total rate of the wireless power supply network based on time reversal technology is calculated according to the signal-to-interference-to-noise ratio of the terminal. The calculation formula is:

[0085]

[0086] The optimization goal of the present invention is to maximize the system and rate of the wireless power supply network based on the time reversal technology; the optimization objective function is constructed according to the total rate of the wireless power supply network based on the time reversal technology, and the optimization objective function is constructed by jointly optimizing τ0, x m,n , p m,n , the optimization objective function is constructed as:

[0087]

[0088]

[0089]

[0090]

[0091]

[0092] C5: 0≤τ0≤1

[0093] Constraints C2 and C3 indicate that one SC is accurately assigned to each link; constraint C4 indicates that the total energy consumed by the AP in the WIT phase should be less than the energy collected in the WET phase; from the optimization objective function, we can see that τ0,p m,n and x m,n The strong coupling between leads to the non-concavity of its objective and the non-convexity of C4. In addition, due to the binary assignment variable x m,n Due to the existence of , the above optimization objective function belongs to the mixed integer non-convex programming problem.

[0094] In order to obtain the best time allocation result, the best subcarrier allocation result and the best power allocation result, the optimization objective function is solved, and the solution process is as follows:

[0095] Rewrite C4 in the optimization objective function as:

[0096]

[0097] Obviously, the original optimization objective function is a non-increasing function of τ0. Therefore, according to constraint C4 in the original optimization objective function, for a given power allocation, the optimal τ0 should maintain the following equation:

[0098]

[0099] Substituting the above formula into the formula for calculating the total rate of the system, we get:

[0100]

[0101] According to the above formula, the original optimization objective function is rewritten as:

[0102]

[0103]

[0104]

[0105]

[0106] Next, the rewritten optimization objective function is solved, and the solution process is as follows:

[0107] A1: Calculate τ based on the given distance d between the terminal and the AP and the speed of light v0 tr ;

[0108] Since time τ0 has an analytical solution, according to τ0, τ tr τ1 can be calculated to obtain the optimal time allocation result.

[0109] A2: Initialization: θ l =0,θ u =ω, m = 0, ε is the error threshold

[0110] A3: Solve for p m,n and x m,n , the process is shown in A31-A36;

[0111] A31: Let θ(m)=(θ l +θ u ) / 2;

[0112] A32: Find the optimal p m,n , the formula is:

[0113]

[0114]

[0115] Among them, μ represents the non-negative Lagrange multiplier in the Lagrange function, which is a constant, and θ represents the introduced slack variable, which is a constant.

[0116] A33: Find the optimal x m,n , the formula is:

[0117]

[0118] m · =argminΠ(m,n)

[0119]

[0120] C=(1-μ)ηBP T (1-τ tr )

[0121] in, Represents x m,n The optimal value of , m represents the mth terminal.

[0122] A34: Add the p calculated in steps A32 and A33 to the m,n , x m,n Substitute the following formula:

[0123]

[0124] A35: If L(p m,n ,μ)>0, then let θ u =θ; otherwise, let θ l =θ;

[0125] A36: Let m=m+1, and repeat A31-A36 until L(p m,n ,μ)>0 holds.

[0126] A4: Determine θ u -θ l <ε is true; if true, output p m,n and x m,n .

[0127] The optimal time allocation result, the optimal subcarrier allocation result and the optimal power allocation result are obtained by solving the optimization objective function; the system can allocate resources according to the optimal time allocation result, the optimal subcarrier allocation result and the optimal power allocation result.

[0128] The present invention studies a wireless power communication network (WPCN) based on orthogonal frequency division multiplexing (OFDM), introduces time reversal technology on the basis of the original WPCN model, and uses the space-time focusing of time reversal to suppress interference in the system, so as to obtain better throughput performance. The present invention adopts the classic "receive first and then transmit" protocol, and divides time into three stages, one for power transmission, one for time reversal detection, and one for information transmission. Among them, the energy-limited access point (AP) and the terminal node obtain energy from the radio frequency signal sent by the power beacon (PB) to assist the terminal data transmission. In the time reversal (TR) stage and the wireless information transmission (WIT) stage, the terminal uses the collected energy to transmit the time reversal special measurement signal to the AP, and the AP uses the collected energy to transmit independent signals to multiple terminals through orthogonal frequency division multiple access (OFDM). In order to maximize the total rate of WPCN, the present invention jointly optimizes the energy collection time and AP power allocation, studies the subcarrier allocation, power allocation and time allocation problems of the three stages of the entire process under energy causal constraints, and adopts binary search to obtain the optimal solution; the present invention significantly improves the user's sum rate, obtains better throughput performance, and has broad application prospects.

[0129] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A wireless power supply network resource allocation method based on time reversal technology, characterized in that: include: S1: Construct a wireless power supply network system model based on time reversal technology; the model includes a single-antenna power beacon PB, an energy-constrained multi-antenna access point AP and an IoT terminal device; constructing a wireless power supply network system model based on time reversal technology includes: During time τ0, PB transmits wireless energy to AP and terminal nodes, and AP and terminal nodes receive energy and store it in rechargeable batteries; At time τ tr Within, the terminal node sends a time-reversed detection signal to the AP; During time τ1, the AP receives the detection signal and transmits wireless information to the terminal node; S2: Calculate the channel impulse response when all terminals send signals to the AP at the same time according to the wireless power supply network system model based on the time reversal technology; the formula for calculating the channel impulse response when all terminals send signals to the AP at the same time is: in, represents the channel impulse response, represents the amplitude of the lth multipath between the jth antenna and the mth terminal on subcarrier n, L represents the total number of multipaths, represents the time delay of the lth multipath between the jth antenna and the mth terminal on subcarrier n; S3: calculating the equivalent channel after time reversal processing according to the channel impulse response; the process of calculating the equivalent channel after time reversal processing is: calculating the channel tap value after time reversal processing according to the channel impulse response; calculating the equivalent channel after time reversal processing according to the channel impulse response and the channel tap value after time reversal processing; The formula for calculating the channel tap value after time reversal processing is: in, represents the tap value of the pth multipath between the jth antenna and the mth terminal on subcarrier n, represents the channel response on the lth multipath between the jth antenna and the mth terminal on subcarrier n, represents the conjugate of the channel response between the jth antenna and the mth terminal on subcarrier n, and P represents the pth multipath; The formula for calculating the equivalent channel after time reversal processing is: S4: Calculate the signal to interference plus noise ratio of the terminal according to the equivalent channel; the formula for calculating the signal to interference plus noise ratio of the terminal is: Among them, SINR m,n represents the signal-to-interference-to-noise ratio at the mth terminal on subcarrier n, p m,n represents the transmit power of the mth terminal on subcarrier n, represents the channel response between the jth antenna and the mth terminal on subcarrier n, represents the channel tap value between the jth antenna and the mth terminal on subcarrier n, B represents the bandwidth, N represents the total number of subcarriers, N T represents the number of antennas at the AP end, σ 2 represents the noise power, Indicates the interference of the i-th (i≠j)th antenna of the AP end to the j-th antenna on subcarrier n; S5: Calculate the total rate of the wireless power supply network based on the time reversal technology according to the signal to noise ratio of the terminal; the formula for calculating the total rate of the wireless power supply network based on the time reversal technology is: Among them, R sum represents the total rate of the wireless power supply network, r mn represents the rate of the mth terminal on subcarrier n, x m,n Indicates whether the nth subcarrier is allocated to the mth terminal, τ1 indicates the time of the WIT phase, and M indicates the number of terminals; S6: construct an optimization objective function according to the total rate of the wireless power supply network based on the time reversal technology, and solve the optimization objective function to obtain the optimal time allocation result, the optimal subcarrier allocation result and the optimal power allocation result; the optimization objective function is: Among them, τ0 represents the time of WET stage, τ tr represents the time of the time reversal phase, and E represents the total energy collected by the AP in the WET phase; S7: The system performs resource allocation according to the best time allocation result, the best subcarrier allocation result and the best power allocation result.

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