CN108390945A - A kind of file transmission of wireless buffer network and wave beam forming design method - Google Patents

Abstract

The invention discloses a file transmission and beamforming design method of a wireless cache network, which belongs to the technical field of beamforming design and power allocation. The steps are: 1. The user initiates a request for the required file to the base station; 2. The user feeds back the channel gain and noise power obtained from the path loss and channel measurement information to the associated base station; 3. The base station obtains the cache status of the requested file, and at this time the base station sends The central node feeds back h _ij , q _fi , c _fj , p _i,noise , and the transmission delay d _jf of the requested file from the central node to the base station; 4. The central node calculates the transmit beamforming value of the base station to the user and the base station The file transfer ratio requested by the user; 5. The central node sends the corresponding beamforming value and file transfer ratio to the base station; 6. The base station initiates file transfer to the user according to the corresponding beamforming value and file transfer ratio. The invention can dynamically adjust the size of the files sent by the base station to the users, and ensures the fairness among users.

Description

A file transfer and beamforming design method for wireless caching network

technical field

The invention provides a file transmission and beamforming design method of a wireless cache network, and belongs to the technical fields of wireless access cloud network, beamforming design and power allocation.

Background technique

The development of fifth-generation wireless networks (5G) paves the way for wireless networks to support more data-hungry applications, such as augmented and virtual reality (AR/VR), video games, and more. The low-latency nature of data transmission is critical for these data-intensive applications, as excessive network latency will affect the overall quality of experience (QoE) for users. In order to reduce the download latency of users in cloud radio networks (C-RANs), caching files in base stations and designing corresponding effective beamforming design methods have attracted extensive attention from academia and industry.

In the wireless caching network, the probability of users requesting different files varies greatly in certain time periods, that is, according to the tidal effect of the network, the probability of some files being requested by users is much higher than that of other requested files, that is to say, they have a high probability of being requested by users. Popularity. Due to the unbalanced distribution of file popularity, a corresponding cache device is installed on the base station side to cache files with high popularity, so as to reduce the transmission distance from the file to the user, thereby reducing the network transmission delay for the user to obtain the desired file. At the same time, this network transmission method prevents the files requested by the user from being obtained from the remote file server every time, reducing the load on the core network and the backhaul link.

Although the existing cache file transfer strategy and beamforming design method can reduce the user's download delay, these two important factors that affect the user's file download delay are studied separately. The transmission strategy of the cache file only affects the size of the backhaul delay, while the beamforming design method is to reduce the transmission delay between the base station and the user. The previous literature only studied the transmission strategy of the cache file or the beamforming design algorithm, and the result is that it can only reduce the backhaul delay or the transmission delay between the base station and the user. Therefore, how to comprehensively consider the cache file transmission strategy and the beamforming design method to reduce the user's download delay has become an urgent problem to be solved. The purpose of the present invention is to solve the joint design of the above cached file transfer strategy and beamforming design method, so as to reduce the user's file download delay.

Contents of the invention

The purpose of the present invention is to reduce the user's file download delay by comprehensively considering the transmission strategy and beamforming of cached files in a wireless cache network, and proposes a design method for file transmission and beamforming of a wireless cache network.

A file transmission and beamforming design method of a wireless cache network, referred to as this method; the wireless cache network system relied on includes: 1 single-antenna user, J base stations, and a central node, wherein 1 single-antenna user and The positions of J base stations are random, and the number of antennas of each base station is N _T . Each base station is equipped with a storage device to cache files, and the central node stores all files requested by users. Each base station is connected to the central node through a wired or wireless backhaul link. ; and the central node can perceive the channel state information of the link between the base station and the user in real time, as well as the cached files of each base station;

The method includes file transfer strategies from the central node to the base station and from the base station to the user;

Among them, the file transfer strategy from the central node to the base station is embodied as follows: for a file requested by a user, the design of the proportion of the base station transmitting the file to the user, that is, the proportion of files sent by the central node to the base station;

Among them, the ratio of files delivered by the central node to the base station is referred to as the file transfer ratio;

The file transfer strategy from the base station to the user, that is, the transmit beamforming design for transmitting files from the base station to the user, referred to as the beamforming design; the specific design: consider the path loss, fading and noise on the wireless link between the base station and the user, The transmission delay of the backhaul link from the central node to each base station, and the popularity distribution of the file; among them, the transmission delay of the backhaul link from the central node to each base station, and the return delay;

The file transfer strategy from the base station to the user, specifically: the central node stores all the files requested by the user, and the base station storage device caches a part of the files requested by the user; the user can access one or more base stations, and multiple base stations can initiate collaborative files to the user Transmission, each base station determines the file transfer ratio for each user, and the ratio also affects the file transfer from the central node to the base station; when a user initiates a file request, according to the channel quality of the wireless link between the base station and the user, and the cache of the user file by the base station The status and return delay determine the file transfer ratio between the base station and the user, whether the central node transmits files to the base station, and the transmit beamforming design of the base station to the user;

The distance between user i and base station j is d _ij , and the path loss is The channel h _ij between user i and base station j obeys a certain fading distribution, the noise is additive white Gaussian noise with power p _{i, noise} , p _j is the maximum transmit power of base station j; S _i is all base stations accessed by user i set, all base stations in S _i can transmit files to users;

A file transmission and beamforming design method of a wireless caching network, comprising the steps of:

Step 1. When user i needs file f, it initiates a file transfer request for f to the base station in S _i . After receiving the file transfer request sent by user i, the base station updates the file request variable q _fi :

Step 2, user i feeds back channel gain h _ij and noise power p _i,noise based on path loss and channel measurement information to all base stations j belonging to S _i ;

Step 3. The base station obtains the cache status of the requested file f, and updates c _fj :

After obtaining c _fj , the base station feeds back h _ij , q _fi , c _fj , p _{i , noise} to the central node, and the transmission delay d _jf from the central node to the base station for file f;

Step 4. After the central node obtains h _ij , q _fi , c _fj , p _{i , noise} fed back from the base station to the central node in step 3, and the transmission time delay d _jf from the central node to the base station for file f, it is determined by the following sub-steps The transmit beamforming value w _ij of base station j to user i, the file transfer ratio x _{i, f, j} of file f requested by base station j to user i;

Step 4.1 The system initializes the count value of the iteration counter, and the count value of the iteration counter is recorded as t; initialize the iteration counter t=0, and initialize the transmit beamforming vector file transfer ratio variable iteration termination threshold ∈ ₁ ;

Step 4.2 Calculation Set the iteration termination threshold ∈ ₂ , iteration counter n=0, where

Step 4.3 If n=0, use initialization Adopt f ⁽ⁿ⁾ = f ^(t) to initialize f ⁽ⁿ⁾ ;

Step 4.4n=n+1, solve the following problem to obtain

exp(-β _ij )≤log ₂ (1+r _ij ),

Step 4.5 Obtain the current optimal target value pass renew update f ⁽ⁿ⁾ by f ⁽ⁿ⁾ =f ^* ;

Step 4.6 calculates |f ⁽ⁿ⁾ -f ^(n-1) |, if |f ⁽ⁿ⁾ -f ^(n-1) |<∈ ₁ , go to step G; otherwise return to step 4.3;

Step 4.7 t=t+1, calculate

in

Step 4.8 According to the file popularity distribution p _f and file size L _f , get the transmission delay from user base station j to user i for file f

Step 4.9 For user i and file f, obtain the base station j ^* = argmin _j τ _i f _j with the smallest transmission delay, and calculate according to the following formula

Step 5, update the count value of the iteration counter, calculate Calculate |f ^t -f ^(t-1) |=|f ^t -f _pre |, if |f ^t -f _pre |<∈ ₂ , go to step 6; otherwise return to step 4.2;

Step 6. The central node sends a corresponding message to the base station j and if And c _fj =0, then the central node sends file f to base station j at the same time;

Step 7, base station j according to the received Decide whether to transfer file f to user i, if Base station adopts File transfer is initiated to user i for transmit beamforming, otherwise no file transfer is initiated.

Beneficial effect

Compared with other file transfer strategies and beamforming design methods, a file transmission and beamforming design method of a wireless cache network in the present invention has the following beneficial effects:

1. It can support the base station to dynamically adjust the file size sent by the base station to the user according to the link status between the base station and the user;

2. The proposed design method of file transmission and beamforming of wireless caching network takes the average download delay of users as the optimization target to make the difference of download delay between users smaller and ensure the fairness among users.

Description of drawings

1 is a downlink wireless cache network scene diagram of a file transmission and beamforming design method of a wireless cache network according to the present invention;

2 is a downlink wireless cache network scene diagram of a file transmission and beamforming design method of a wireless cache network according to the present invention;

FIG. 3 is a comparison diagram of the average user download delay between the file transmission and beamforming design method in the present invention and embodiments and other schemes under different Zipf situations;

Fig. 4 is a comparison diagram of the user average delay between the file transmission and beamforming design method in the present invention and the embodiment and other schemes under different base station antennas.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. This embodiment is guided by the technical solution of the present invention to conduct actual practice verification, and at the same time provides detailed implementation methods and specific operation procedures, but the scope of protection of the present invention is not limited to the following embodiments.

Example 1

Assume that the network topology is three 500m*500m rectangular areas, each with a macro base station in the center of each area, this macro base station covers the entire rectangular network area, and each macro base station is configured with 4 antennas and has the same storage space. 9 users are randomly distributed in the simulation area, the user equipment is equipped with a single antenna, the minimum distance from the user to the base station is 400m; the system bandwidth is 1MHz, the noise power spectral density is -106dBm/Hz, and the channel path loss and shadow fading are expressed as 128.1 +37.6log ₁₀ (d)+N(0,8)dB, where d (unit: km) is the distance from the user to the serving micro base station. The maximum transmission power of each micro base station is the same, which is 5W. The number of files is 15, the size of each file is randomly selected between 8 and 10Mbit, and the file popularity obeys the Zipf distribution.

The process flow of the file transmission and beamforming design method of the wireless cache network proposed by the present invention is as follows:

Step A, when user i needs file f, initiate a file transfer request for f to the base station in S _i ; after receiving the file transfer request sent by the user, the base station updates the file request variable q _fi :

Step B, user i feeds back channel gain h _ij and noise power p i obtained based on path loss and channel measurement information to all base stations j belonging to S _{i , noise} =10 ^-10 W;

Step C, the base station obtains the cache status of the requested file f, and updates c _fj :

After obtaining c _fj , the base station feeds back h _ij , q _fi , c _fj , p _{i , noise} to the central node, and the transmission delay d _jf from the central node to the base station for file f;

Step D. After the central node obtains the above values, the following steps are used to determine the transmit beamforming value w _ij of base station j to user i, and the file transfer ratio x _ifj of file f requested by base station j to user i.

A. Set iteration counter t=0, initialize transmit beamforming vector file transfer ratio variable iteration termination threshold ∈ ₁ ;

b. Calculate Set the iteration termination threshold ∈ ₂ , iteration counter n=0, where

C. If n=0, use initialization Initialize f ^{(n) with f (n)} = f ^{(t )}

Dn=n+1, solve the following problems to get

exp(-β _ij )≤log ₂ (1+r _ij ),

E. Obtain the current optimal target value pass renew Update f ⁽ⁿ⁾ by f ⁽ⁿ⁾ = f ^* ,

F. Calculate |f ⁽ⁿ⁾ -f ^(n-1) |, if |f ⁽ⁿ⁾ -f ^(n-1) |<0.005, go to step G; otherwise return to step C.

Gt=t+1, calculate

in

H. According to the file popularity distribution p _f and file size L _f , get the transmission delay from user base station j to user i for file f

I. For user i and file f, obtain the base station j ^* = argmin _j τ _ifj with the smallest transmission delay, and calculate according to the following formula

j. Calculate |f ^t -f ^(t-1) |=|f ^t -f _pre |, if |f ^t -f _pre |<0.005, go to step 5; otherwise return to step B.

Step E, the central node sends the corresponding and if And c _fj =0, then the central node sends the file f to the base station j at the same time.

Step F, base station j according to the received Decide whether to transfer file f to user i, if Base station adopts File transfer is initiated to user i for transmit beamforming, otherwise no file transfer is initiated.

In the test, the five schemes in the table below were compared respectively, and the test performance was the average performance under 1000 groups of topologies.

The file transfer and beamforming design method of the wireless caching network proposed in Table 1 is compared with the other four schemes

Program User Access and Power Allocation Scheme plan 1 Proposed beamforming algorithm and file transfer strategy Scenario 2 Proposed beamforming algorithm, equal file ratio transmission strategy Option 3 Proposed beamforming algorithm, random file ratio transfer strategy Option 4 Proposed beamforming algorithm, only transfer cached file strategy Option 5 Proposed beamforming algorithm, no cache file transfer strategy

Figure 3 shows the variation of the user's average time delay as the file popularity parameter increases. It can be seen that the average user delay can be greatly reduced by adopting the file transmission and beamforming design method of the wireless cache network of the present invention. Figure 4 shows the change of the average download delay of users with the increase of the number of antennas of the base station when the file popularity parameter is constant. Delay is down 47.4% compared to the no-cached file transfer strategy.

To sum up, the file transmission and beamforming design method of the wireless caching network proposed by the present invention can effectively reduce the average download delay of users, thereby improving the advantages of system performance, which has practical application significance.

The specific description above has further explained the purpose, technical solution and advantages of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. file transmission and the wave beam forming design method of a kind of wireless buffer network, it is characterised in that：It is arrived including Centroid The file transmitting policy of base station and base station to user；

Wherein, the file transmitting policy of Centroid to base station is embodied as：For the file of user's request, base station is to the use Transmit the Proportionality design of this document, i.e., the file percentage that Centroid is issued to base station in family；

Wherein, the file percentage that Centroid is issued to base station, abbreviation file transfer ratio；

The launching beam Shape design of file, abbreviation wave beam are transmitted to user to the file transmitting policy of user, i.e. base station in base station Shape design；When specific design：In view of path loss, decline and noise between base station and user on Radio Link, center Node is distributed to the propagation delay time of each base station return link and the popularity of file；Wherein, Centroid is to each base station The propagation delay time of return link returns time delay；

Base station to user file transmitting policy, specially：Centroid stores the file of all user's requests, and base station stored is set The standby a part of file for having cached user's request；User can access one or more base station, and multiple base stations can be to user Cooperation file transmission is initiated, each base station determines that the ratio influences Centroid to base station simultaneously to each user file transfer ratio File transmission；When user initiates file request, according to the channel quality of Radio Link between base station and user, base station to The buffer status of family file, passback time delay determine file transfer ratio of the base station to user, and it is literary whether Centroid transmits to base station The launching beam Shape design of part and base station to user；

The distance of user i and base station j are d_ij, path loss isChannel h between user i and base station j_ijObey certain decline point Cloth, noise are that power is p_i,noiseAdditive white Gaussian noise, p_jFor base station j maximum transmission power；S_iFor the institute of user's i accesses There are collection of base stations, S_iIn all base stations can to user transmit file.

2. file transmission and the wave beam forming design method of a kind of wireless buffer network as described in claim 1, referred to as we Method；The wireless buffer network system relied on, it is characterised in that：Including：I single-antenna subscriber, J base station, a centromere Point, the wherein position of I single-antenna subscriber and J base station are random, and the antenna number of each base station is N_T, each base station is equipped with storage Device carrys out cache file, and Centroid stores the All Files of user's request, and each base station passes through wired or wireless backhaul chain Road is connected to Centroid；And Centroid being capable of the channel state information of link and each between real-time perception base station and user The case where a node B cache file.

3. a kind of file transmission of wireless buffer network as described in claim 1 and wave beam forming design method, feature exist In：Include the following steps：

When step 1, user i need file f, to S_iIn base station initiate to transmit request to the file of f, base station receives user i and sends File transmission request after, update file request variable q_fi：

Step 2, user i belong to S to all_iThe channels that are obtained based on path loss and channel measurement information of base station j feedbacks increase Beneficial h_ijWith noise power p_i,noise；

Step 3, base station obtain the buffer status for being requested file f, update c_fj：

Obtain c_fjAfterwards, h is fed back in base station to Centroid_ij, q_fi, c_fj, p_i,noise, and for file f Centroid arrive base station Propagation delay time d_jf；

Step 4, Centroid obtain the h that base station is fed back to Centroid in step 3_ij, q_fi, c_fj, p_i,noise, and it is directed to file Propagation delay time d of the f Centroids to base station_jfAfterwards, launching beam figuration values of the base station j to user i is determined by following sub-step w_ij, file transfer ratio xs of the base station j to the user i file fs asked_i,f,j；

The count value of step 4.1 system initialization iteration count, iteration count count value are denoted as t；Initialize iteration count Device t=0 initializes launching beam forming vectorsFile transfer ratio variableIteration ends thresholding ∈₁；

Step 4.2 calculatesIteration ends thresholding ∈ is set₂, Iteration count n=0, wherein

If step 4.3 n=0, useInitializationUsing f⁽ⁿ⁾=f^(t)Initialize f⁽ⁿ⁾；

Step 4.4n=n+1 solves problems with and obtains

exp(-β_ij)≤log₂(1+r_ij),

Step 4.5 obtains current optimal objective valuePass throughUpdatePass through f⁽ⁿ⁾=f^*More New f⁽ⁿ⁾；

Step 4.6 calculates | f⁽ⁿ⁾-f^(n-1)|, if | f⁽ⁿ⁾-f^(n-1)|<∈₁, arrive step G；Otherwise return to step 4.3；

Step 4.7t=t+1 is calculated

Wherein

Step 4.8 is according to file popularity distribution p_fWith file size L_f, obtain the biography for file f user base station j to user i Defeated time delay

Step 4.9 obtains the base station j of propagation delay time minimum for user i and file f^*=argmin_jτ_ifj, and according to such as following formula Son calculates

Step 5, the count value for updating iteration count calculateCalculate | f^t-f^(t-1)|=| f^t-f_pre|, if | f^t-f_pre|<∈₂, arrive step 6；Otherwise return to step 4.2；

Step 6, Centroid issue correspondence to base station jWithIfAnd c_fj=0, then Centroid is same When issue the documents f to base station j；

Step 7, base station j are according to receivingDecide whether to transmit file f to user i, ifBase station usesFile transmission is initiated to user i for launching beam figuration, does not otherwise initiate file transmission.