CN108768602B - Method for selecting authorized user to feed back CSI (channel state information) in independent unlicensed frequency band cellular mobile communication system - Google Patents
Method for selecting authorized user to feed back CSI (channel state information) in independent unlicensed frequency band cellular mobile communication system Download PDFInfo
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Abstract
The invention discloses a method for selecting authorized users to feed back CSI (channel state information) in an independent unlicensed frequency band cellular mobile communication system, which comprises the following steps: (1) the base station receives the CSI fed back by the user and calculates the feedback time delay; (2) and the base station decides and selects which users are sent with the authorization signaling feedback CSI according to the CSI reported by the users and the feedback time delay through an optimization target model. The invention considers the premise that the feedback CSI resource of the authorized user is limited when the LTE-U independent system and the Wi-Fi system coexist, and the system can make self-adaptive adjustment of the number of the authorized feedback CSI users according to the number of the resource; meanwhile, different utility requirements of each user are considered, and when the relevant indexes of the throughput are optimization targets, the users authorized to feed back the CSI can be optimized and selected according to the CSI fed back by the users and the feedback time delay, so that the throughput performance of the LTE-U independent system is effectively improved.
Description
Technical Field
The invention belongs to the technical field of mobile communication, and particularly relates to a method for an independent unlicensed frequency band cellular mobile communication system to select an authorized user to feed back CSI.
Background
An independent Long term evolution (LTE-U) of an unlicensed frequency band is a technology that deploys a conventional LTE to an unlicensed frequency band without the assistance of an unlicensed frequency band, and may be used to increase the capacity of a cellular network and relieve the pressure caused by the increase of traffic of the licensed frequency band. In order to obtain a higher spectrum utilization rate, the LTE-U independent system may still use a reporting mode of Channel State Information (CSI) of the LTE system: the base station firstly selects an authorized user to feed back CSI; the user receiving the authorization signaling measures a channel at a designated position, and then feeds back the obtained CSI to the base station at the designated position in the uplink subframe; and the base station receives the CSI fed back by the user, calculates the feedback time delay of the CSI and then carries out data transmission in a downlink subframe according to the CSI and the time delay of the CSI. In this process, since data and signaling are transmitted in the unlicensed band, it will face several challenges:
challenge one: for fair coexistence with Wi-Fi and other systems, the 3rd generation partnership project (3 GPP) specifies that LTE-U independent systems access channels of unlicensed bands in a channel contention manner similar to the carrier sense lbt (listenbefore talk) of Wi-Fi systems. Meanwhile, 3GPP also specifies that the time duration for accessing the unlicensed frequency band channel each time cannot exceed the specified time duration, so that signaling interaction and data transmission processes of the LTE-U independent system can be completed only by multiple channel accesses. Compared with an LTE system, the method ensures that the access time of each channel of the LTE-U independent system is uncertain and has larger feedback delay. Different from the fixed feedback time delay of the LTE system, the time delay of the user for feeding back the CSI in the LTE-U independent system has randomness, and therefore the decision of the base station for selecting the authorized user for feeding back the CSI is influenced.
Challenge two: in order to be compatible with the Time Division Duplexing (TDD) characteristic of the LTE system, the LTE-U independent system should transmit signaling/data at the subframe alignment Time after each channel access. Due to the adoption of an LBT channel access mode, the time of accessing the channel by the LTE-U independent system is not always exactly aligned with the sub-frame, and from the time to the time of aligning the sub-frame, it is likely that systems such as Wi-Fi and the like can access the channel, so that the signaling/data transmission conflict between the LTE-U independent system and other systems is caused, and the conflicting sub-frames can cause the signaling sent by the base station of the LTE-U independent system and the CSI fed back by the user to be possibly conflicted and not to be successfully received.
In a cellular system, patent PCT/US2013/03283 discloses a system and method for user reference signal and channel state information feedback, and provides system and method embodiments for signaling reference signals and CSI feedback for wireless communication. Patent PCT/US2016/015464 discloses an uplink operation for LTE in unlicensed band, even if a Wireless transmit/receive unit (WTRU) receives configuration information from a secondary cell to perform a corresponding operation in uplink subframes. The patent WO2016/191091a1 discloses a system, a method and a device suitable for a control domain of an LTE-U system, which include operations such as control domain processing of a transmission time interval, an enhanced physical control channel, aperiodic CSI reporting and discontinuous reception, and these operations can be extended to an LTE-U independent system for use. However, since signaling of the LTE-U independent system is transmitted in the unlicensed frequency band and a channel needs to be shared with Wi-Fi, compared to the LTE system with an exclusive channel, time-frequency resources of the LTE-U independent system access channel are relatively less, so that control resources which are scarce originally are further reduced. Although the above patent proposes various CSI feedback schemes for the cellular system, the above patent does not consider the selection of the feedback CSI user on the premise that the resource consumed by the authorized user for feeding back CSI is limited.
Disclosure of Invention
In view of the above, the present invention provides a method for an independent unlicensed frequency band cellular mobile communication system to select an authorized user to feed back CSI, which can significantly improve the throughput of an LTE-U independent system.
A method for selecting authorized users to feed back CSI in an independent unlicensed frequency band cellular mobile communication system comprises the following steps:
(1) a base station in an LTE-U independent system receives CSI fed back by users and deduces feedback time delay of the CSI of each user when the base station is accessed into a channel to perform downlink transmission, so that a CSI matrix and a feedback time delay matrix are constructed;
(2) establishing a model for selecting authorized users to feed back CSI, and the base station of the LTE-U independent system decides and selects the users for feeding back the CSI next time through optimizing and solving the model, so as to generate an authorization signaling and send the authorization signaling to each user;
(3) and the user analyzes the received authorization signaling, detects a reference signal in a channel according to a corresponding time-frequency position in the authorization signaling and obtains CSI for the user selected for authorization, and then feeds back the CSI to the base station through the uplink subframe.
Further, the estimation of the CSI feedback delay of each user in step (1) is calculated according to a difference between a channel measurement time specified in the grant signaling and an actual data transmission time from the base station to the user.
Further, the size of the CSI matrix is K × S, the size of the feedback delay matrix is K × N, K is the number of users currently accessing the base station, S is the number of subbands in the channel, N is the number of subframes in which the base station occupies the channel last time, an element value in the CSI matrix is CSI on the corresponding subband when the corresponding user feeds back the channel gain last time, and an element value in the feedback delay matrix is a delay from a time when the corresponding user obtains CSI through the last measurement to a start time of the corresponding subframe in the channel last occupied by the base station.
Further, the authorization signaling includes time-frequency positions of behaviors of detecting the reference signal and feeding back the CSI in the channel and a user list of the base station selecting the next authorization to feed back the CSI.
Further, the model for selecting the authorized user to feed back the CSI is established in the step (2), and the specific process is as follows:
2.1 the base station counts the number N of the current Wi-Fi nodes by monitoring the frame head information of the control frames and the data frames of the Wi-Fi nodeswAnd calculating the packet sending probability tau of each Wi-Fi nodew；
2.2 the base station according to the MAC (Medium Access control) layer parameter of the LTE-U independent system and the N obtained in step 2.1wAnd τwCalculating the probability distribution of the LTE-U independent system channel competition time delay;
2.3 according to the probability distribution of the LTE-U independent system channel competition time delay, the probability that each subframe of the base station starts to be collided by Wi-Fi when the base station accesses the channel next time is obtained through calculation;
2.4, determining the upper limit of the number of users for authorizing and feeding back CSI next time by the base station;
2.5, according to the probability distribution of the LTE-U independent system channel competition delay, the CSI matrix and the feedback delay matrix, estimating the expected data transmission rate of each user on each sub-band in each sub-frame when the base station accesses the channel for the next time under the two conditions of authorized CSI feedback and unauthorized CSI feedback;
2.6 based on the obtained data, establishing the following model for the base station to select the authorized user to feed back CSI;
wherein:
when the independent variable is
Resource allocation utility function of the k-th user in the case ofkSelecting an indicator variable I for authorizing the kth user to feed back CSI for a base station k0 or 1, Ik1 means that the kth user is authorized to feed back CSI, Ik0 indicates that the kth user is not authorized to feed back CSI, NselAn upper limit of the number of users for the base station to authorize the feedback of the CSI next time,
an indicator variable pre-allocated to the kth user for the s sub-band of α th sub-frame of the next access channel start of the base station and
or 1 of the number of the groups in the group,
the s-th sub-band indicating the α th sub-frame from which the base station accesses the channel next time is allocated to the k-th user,
it means that the s-th sub-band of α th sub-frame of the next access channel of the base station is not allocated to the k-th user,
for corresponding indication of variable IkUnder the circumstance, the throughput expected by the pre-allocation of time-frequency resources is obtained when the kth user accesses the channel next time at the base station, K is the number of users currently accessing the base station, α and s are natural numbers, and N is more than or equal to 1 and less than or equal to αdS is more than or equal to 1 and less than or equal to S, and S is a sub-channelNumber of bands, NdAnd the number of the sub-frames occupying the channel for the next time by the base station.
Further, the step 2.1 calculates the packet sending probability tau of each Wi-Fi node through the following expressionw：
Further, the throughput
The calculation expression of (a) is as follows:
wherein: b is the channel bandwidth, pc,αIndicating the probability that the α th sub-frame of the next access channel of the base station is collided by Wi-Fi,
for corresponding indication of variable IkIn this case, the kth user starts the desired data transmission rate on the s sub-band in the α th sub-frame from the next access channel of the base station.
Based on the technical scheme, the invention has the following beneficial technical effects:
(1) the method for selecting the authorized user to feed back the CSI provided by the invention considers the premise that the authorized user feeds back the CSI resource is limited when the LTE-U independent system and the Wi-Fi system coexist, and the system can make self-adaptive adjustment of the number of the authorized CSI users according to the number of the resource.
(2) The method for selecting the authorized user to feed back the CSI of the LTE-U independent system considers the possible different utility requirements of each user, and when the throughput related index is the optimization target, the user authorized to feed back the CSI can be optimized and selected according to the CSI fed back by the user and the feedback time delay, so that the throughput performance of the LTE-U independent system is effectively improved.
Drawings
Fig. 1 is a flow chart of signaling and CSI interaction between a base station and a user in an LTE-U independent system according to the present invention.
Fig. 2 is a schematic flow diagram of an LTE-U independent system base station receiving CSI and issuing an authorization signaling in the present invention.
FIG. 3 is a schematic diagram of a model construction process of an LTE-U independent system base station selecting an authorization feedback CSI user.
FIG. 4 is a diagram illustrating a model of coexistence of an LTE-U independent system and Wi-Fi according to the present invention.
Fig. 5 is a schematic diagram of channel contention and access of an LTE-U independent system according to the present invention.
FIG. 6 is a graph of throughput simulation results for an LTE-U independent system of the present invention.
Fig. 7 is a flowchart of an algorithm for selecting an authorized user to feed back CSI in the LTE-U independent system of the present invention.
Detailed Description
In order to more specifically describe the present invention, the following detailed description is provided for the technical solution of the present invention with reference to the accompanying drawings and the specific embodiments.
The invention is provided based on a coexistence scene of an LTE-U independent system and a Wi-Fi system, wherein the coexistence scene is as follows: (a) a base station and a user in an LTE-U independent system access an unlicensed frequency band by adopting an LBE (load based demand) scheme; (b) after accessing the channel, the base station or the user sends a reservation signal to other systems until the first subframe of the transmission data is aligned; (c) the base station and the user access the channel alternately, and the number of the sub-frames accessing the channel for transmitting data each time is determined by the uplink and downlink services of the LTE-U independent system and the relevant regulations of 3 GPP.
As shown in fig. 1, the present invention designs a method for feeding back CSI by selecting authorized users in an independent unlicensed band cellular mobile communication system, which comprises the following steps:
(1) the base station in the LTE-U independent system receives the CSI fed back by the users in the uplink transmission stage, calculates the feedback time delay of the CSI of each user when the base station is accessed into a channel to carry out downlink transmission, and stores a matrix formed by the CSI fed back by the users and a matrix formed by the feedback time delay in the local part of the base station.
In the LTE system, the feedback delay from the measurement of CSI by a user to the actual transmission of data to the user is a fixed value, whereas in the LTE-U independent system, the feedback delay is variable. For the feedback delay of any user, the base station may obtain the feedback delay by recording a difference between a time when the user measures the channel and a time when the current base station transmits data to the user, and the operation steps are as shown in fig. 2.
(2) And establishing a model for selecting authorized users to feed back CSI, and deciding and selecting the users authorized to feed back the CSI by a base station of the LTE-U independent system through the model, wherein an authorization signaling comprises a measurement channel and a time-frequency position for feeding back the CSI.
And establishing a model for selecting the authorization feedback CSI user, and measuring the decision advantages of the current selection authorization feedback CSI user by the base station through the throughput which can be obtained by the LTE-U independent system under the given time-frequency resource allocation scheme when estimating the next access channel. The model construction process is shown in fig. 3, and the base station may obtain a decision to select a feedback CSI user through the following processes:
2.1 the base station of the LTE-U independent system counts the number N of the Wi-Fi nodes by monitoring the frame header information of the control frames and the data frames of the Wi-Fi nodeswAnd the packet sending probability tau of the Wi-Fi nodewThe probability is calculated as follows:
2.2 the base station calculates the probability distribution of the channel competition time delay of the independent system according to the MAC layer parameter of the LTE-U independent system and the Wi-Fi parameter in the a.
2.3 according to the probability distribution of the channel competition delay calculated in the step b, calculating and obtaining the probability p of each subframe being conflicted by the Wi-Fi when the base station accesses the channel next timec,α。
2.4 calculating the upper bound N capable of authorizing the number of the feedback CSI users at the current moment according to the number of the downlink transmission subframes of the access channel at the current moment of the base station and the number of the uplink transmission subframes of the access channel of the next usersel。
And 2.5, according to the probability distribution of the independent system channel competition delay, the CSI matrix and the feedback delay matrix, evaluating the expected data transmission rate of each user on each sub-band in each sub-frame when the base station accesses the channel next time under the two conditions of selecting authorization and not selecting authorization to feed back the CSI.
And 2.6, selecting the user authorized to feed back the CSI at the current moment according to the following optimization model decision.
Wherein: k represents a user index; k represents the number of users in the coverage area of the base station; i iskAn indicator variable, I, representing whether the base station authorizes the user k to feed back CSIk1 denotes authorized user k feedback, Ik0 denotes an unauthorized user k feedback;
representing the indicated variable as IkThe throughput expected by the time-frequency resource pre-allocation of the next time a base station accesses a channel is given by a time-frequency user K (═ 1,2, …, K), where the number of subframes of the access channel for transmitting data is NdEach sub-frame having a bandwidth B in the frequency domain and being divided into S mutually orthogonal sub-bands, pc,αIndicating the probability that the α th sub-frame from the next base station access channel start is collided by Wi-Fi,
an indicator variable indicating that the s sub-band of the α th sub-frame from which the access channel of the base station is started next time is pre-allocated to user k,
the s subband representing the α th subframe is assigned to user k,
the s-th sub-band representing the α -th sub-frame is not allocated to user k,
is represented by indicating that the variable is IkUnder the condition that the user k expects a data transmission rate on the s th sub-band in the α th sub-frame from the beginning of the next base station access channel;
is prepared by reacting with
A resource allocation utility function of a corresponding user k; to control the overhead of selecting authorized users for feedback of CSI resources, NselAnd the upper bound of the number of the CSI users which can be authorized to be fed back by the base station in the channel access process is shown.
(3) And the user receives the authorization signaling from the base station, measures the channel and obtains the CSI according to the indication of the signaling, and finally feeds the CSI back to the base station according to a specific feedback scheme on the uplink subframe.
And (3) periodically executing the steps (1) to (3) according to the characteristic that the LTE-U independent system base station and the user alternately access the channel, and deciding the user selected to authorize and feed back the CSI after the base station accesses the channel.
The following is an embodiment of the present invention, and the specific process is as follows:
FIG. 4 shows a scenario of coexistence of LTE-U independent systems in this embodiment, where the LTE-U independent system is composed of a base station and K users, and the Wi-Fi system is composed of N userswAnd the nodes share the channel with the bandwidth of B. Both systems are saturated traffic models. The LTE-U independent system divides the channel into S orthogonal subbands with the same bandwidth. In this embodiment, it is assumed that the CSI feedback mode of the user in the LTE-U independent system is a threshold feedback scheme, λ represents a threshold for feeding back CSI normalized by the user, and if a ratio of a subband channel gain measured by the user to an average value of the channel gain is not less than λ, the CSI of the subband is fed back by the userTo be fed back by the user; otherwise it is not fed back. Fig. 5 gives a schematic diagram of channel contention and access for an LTE-U independent system. In the LTE-U independent system, when a user and a base station compete for a channel, a channel contention scheme similar to LBT of carrier sense signaling of a Wi-Fi system is respectively performed, where a backoff window length Z is a fixed value and a Distributed inter-frame spacing (DIFS) needs to be waited after the channel is accessed every time. Let tdIndicating the duration of the contention phase of the downlink channel. The base station will send a reservation signal indicating that it has occupied the channel before the next subframe arrives. The duration of this phase is defined as td,rThis phase is called the downlink reservation phase. The total time length before the base station accesses the channel (called the downlink pre-transmission phase) is defined as
Wherein
Is an upward rounding function, TsbThe duration of a single subframe of the occupied channel. When transmitting data (defined as the effective downlink transmission phase), the base station access channel can continuously occupy the channel NdAnd a sub-frame. For uplink data transmission, the channel contention procedure is similar to the previous downlink transmission case, where the main difference is that the backoff value is selected by the base station (randomly selected from 0 to Z-1) and all users share the same backoff value. And the base station sends the backoff value to all users in the downlink data transmission. Further, when the reservation signal is transmitted for uplink data transmission, it is the user and not the base station that transmits the reservation signal. Similar to the case of downlink data transmission, let tu、tu,r、tu,pAnd NuRespectively showing the duration of an uplink channel competition stage, the duration of an uplink reservation stage, the duration of an uplink pre-transmission stage and the number of subframes of an uplink effective transmission stage. In this embodiment, let Nd＝Nu＝Nsb. Definition of qdAnd q isuAnd the uplink sub-frame and the downlink sub-frame respectively represent the upper bound of the number of users of which the base station can authorize to feed back the CSI in a single downlink sub-frame and the upper bound of the number of users of which the base station can feed back the CSI in a single uplink sub-frame.
According to the model of the LTE-U independent system base station selecting the authorization feedback CSI users described in the figure 3, the following solutions are sequentially carried out:
a. and calculating the probability distribution of the LTE-U independent system channel competition time delay.
Given a fixed contention window length Z of an LTE-U independent system and a number of nodes N of a Wi-Fi systemwAnd the probability of a hair packet τwChannel contention delay t for downlink transmission of LTE-U independent systemdOr the channel contention delay t of the uplink transmissionuThe probability mass function of (A) is The same and is expressed by p (t), which can be obtained by Poisson's mesh algorithm based on probability generating function proposed in The document "modeling of synchronization and energy generation for The FBE-and LBE-based station LTE-U networks" (Author J.Li et al, published in The Journal of engineering, vol.2017, No.7,2017).
b. The probability of each subframe being collided in the next downlink effective transmission stage.
Duration of one Wi-Fi collision transmission (defined as T)c w) Is less than the duration T of one sub-framesbTherefore, only the first subframe in a downlink or uplink active data transmission may collide with the Wi-Fi system. By pc,1And pLRespectively representing the collision probability of the first subframe in the effective data transmission stage and the probability of the base station or the user sending a reservation signal in the reservation period, then:
wherein: i belongs to { d, u },
denotes biIs a positive integer, pLThe numerical solution of (A) can be determined by The method described in The document "modeling of synchronization and energy performance of FBE-and LBE-based standing LTE-U networks" (Author J.Li et al, published in The Journal of engineering, vol.2017, No.7,2017).
In summary, the collision probability of each subframe in the next downlink effective transmission phase can be summarized as follows:
c. and calculating the maximum number of users which can be authorized in the downlink transmission stage.
Since the first subframe may be collided by Wi-Fi, neither control signaling nor CSI fed back by the user will be scheduled for transmission in the first subframe. Then, the maximum number of users that can be granted in any downlink transmission stage is:
Nsel≤min{qd(Nd-1),qu(Nu-1)}
d. and calculating the expected transmission rate of the user in the next downlink transmission stage.
When the indicator variable is IkUnder the condition of (a), the expected transmission rate of the user k for transmitting data on the s-th sub-band in the α -th sub-frame from the next base station access channel can be expressed as:
due to the indicator variable Ik0 or Ik1, need to be respectively paired
And
these two transmission rates are calculated.
At any moment, the base station of the LTE-U independent system stores the CSI reported recently by the user and the feedback time delay from the CSI to the current moment. Let matrix C and matrix d respectively represent the matrix formed by CSI reported by all users and the matrix formed by their feedback time delay, where element Ck,sAnd the CSI on the subband s when the user k feeds back the channel gain last time is shown in the kth row and the s column of the matrix C. Element dk,αIs located at the k-th row and α -th column of the matrix d and represents the slave Ck,sThe time delay of α th sub-frame starting time of the current downlink transmission phase is obtained by measurement of the user.
In the current downlink transmission phase, if the user k is not selected to authorize the feedback of CSI, IkIf 0, the expected data rate of user k on the s th sub-band in the α th sub-frame of the next downlink transmission phase is:
wherein: λ is a feedback threshold value of a threshold feedback scheme agreed by the user and the base station; gk,sRepresenting the channel power gain obtained when user k measures channel s;
denotes the actual channel gain, τ, when the base station transmits data to user k using sub-band s in sub-frame α of the next active downlink transmission phasek,αRepresenting the feedback delay from the channel measurement to the data transmission for user k. Under the rayleigh channel fading model, it is known from the literature "Digital communication over fading channels" (author m.simon et al, published by John Wiley Sons, 2000) that at a given feedback delay τk,αG under the conditionk,sAnd
the joint probability density function of (a) is:
omega herekIs the average of the user k channel gains, I0(. is) a Bessel function of the first kind of zero-order modification,
is the correlation coefficient, phidIs the maximum Doppler shift, J0(. is a first class zero order Bessel function; tau isk,αHas a lower bound of
A Tsb；
Indicates that a is
Is a positive integer of (1). P0{τk,α＝aTsbDenotes the feedback delay τk,α＝aTsbCan be calculated by:
when transmitting data, if the user is selected to transmit data, the transmission rate is selected according to the CSI reported by the user. The data rate associated with each CSI feedback is determined by the discrete levels of channel fading. Furthermore, we divide the range of subband gain into N +1 fading ranges, Rn＝[Ln,Ln+1) N is 0,100 and LN+1Infinity. If G isk,s∈RnThe CSI fed back by the user is Ck,sN, the base station will use the data rate rnTransmitting data to a user; accordingly, when the actual channel gain of the user is
The user may successfully receive the data.
In the current downlink transmission phase, if user k is authorized to feed back CSI, IkThen, in the next downlink transmission phase, the rate of transmitting data to user k by the base station will be scheduled based on the new CSI fed back by user k in the next uplink transmission phase, and on the s th sub-band in the α th sub-frame of the next downlink transmission, the expected data rate that user k can obtain is:
wherein: w is such that Lw≤λΩk<Lw+1A true discrete data rate index; feedback delay τk,αHas a lower bound of
A Tsb；
Indicates that e is
Is a positive integer of (1). P1{τk,α＝eTsbDenotes the feedback delay τk,α＝eTsbCan be calculated by:
e. when the scheduling algorithm is designed according to the proportional fairness principle, the utility function can be ordered
Accordingly, the optimization problem of selecting authorized users to feed back CSI can be expressed as:
wherein: x ═ x1,x2,...,xK]T，
I＝[I1,I2,...,IK]T。
By fixing one of the variables and solving the problem for the other variable, the above optimization problem can be split into two sub-problems:
wherein:
wherein:
for SOP1, the problem can be solved by the following algorithm:
step 1: setting the iteration number n as 1, initializing an iteration stop threshold epsilon, an iteration step length u e (0,1) and an increment of a utility function
Randomly setting indication variable of resource allocation of each user
And
and the given authorized user feeds back an indication variable vector I of the CSI.
Step 2: repeat calculation
And
and performing the following substeps until
Wherein
(a) And distributing the sub-bands in each sub-frame according to the following rules:
where k denotes that the s-th sub-band in the α -th sub-frame of the current downlink transmission phase is allocated to user k.
(b) According to the resource allocation result in (a), adopting
And calculating the transmission rate accumulated on all sub-frames and all sub-bands of the user in the next effective downlink transmission stage.
(c) Update increment of utility function:
and step 3: the algorithm is finished, and a resource allocation indicating variable vector x is outputopt＝x(n)(ii) a Presented in the above description of the algorithm (.)(n)To representThe value of the variable (-) set at the nth iteration.
For SOP2, the problem can be solved by the following algorithm:
step 1: given the indication variable of the resource allocation of each user, denoted xk。
Step 2: according to the indication variable xk of each user, calculating
And
step 3, according to βk,1/βk,0Sorting the users from big to small, and setting the indication variable I of the first Nsel userskThe indication variable of the other user is 0.
And 4, step 4: finishing the algorithm, and outputting an optimal indicator variable vector I for feeding back CSI by the authorized useropt＝I。
The original optimization problem can be solved iteratively through the algorithm of simultaneous SOP1 and SOP2 to obtain an indicator variable vector for the authorized user to feed back CSI. The solution algorithm DUS (dynamic user selection) process is shown in FIG. 7, and includes the following steps:
step 1: before performing scheduling decision, the base station needs to obtain a CSI matrix C of a user and a delay matrix d of a corresponding CSI.
Step 2: setting an iteration time indication variable n as 1, initializing an iteration stop threshold epsilon, an iteration step u e (0,1) and an increment of a utility function
Randomly setting indication variable of resource allocation of each user
And
indicator variable vector I for feeding back CSI with authorized user(n)。
And step 3: repeat calculation
And
and repeatedly executing the following substeps until
(a) And distributing the sub-bands in each sub-frame according to the following rules:
(b) calculating according to the resource allocation result in (a)
And
(c) push button
Ordering the users from big to small, and setting the top NselIndication variable of individual user
The other user's indication variable is 0.
(d) According to the decision result of resource block allocation in (a) and CSI feedback selected from authorized users in (c)
And calculating the transmission rate accumulated on all sub-frames and all sub-bands of the user in the next downlink effective transmission stage.
(e) Update utility function delta:
and 5: finishing the algorithm, and outputting an optimal indicator variable vector I for feeding back CSI by the authorized useropt＝I(n)。
The beneficial effects of the technical scheme of the embodiment can be verified through the following simulation.
Let us assume that there is one base station and multiple users in the LTE-U independent system and share a 20MHz bandwidth with the Wi-Fi system with a center frequency of 5.75GHz, and the LTE-U independent system divides the channel into 20 sub-bands which do not overlap each other. Length T of subframe in LTE-U independent systemsbAnd the number of sub-frames N of a continuous transmission occupying the channel at one timesb(the number of subframes for uplink active transmission and downlink active transmission is the same) is 1ms and 3 respectively. The size of the contention window length Z of the LTE-U independent system is set to 64. To simulate time-varying Rayleigh fading for different users, consider that users employ different moving velocities vk0.6+0.14 (k-1) m/s. Regarding the channel gains of users, similar to the document "Joint evaluation of channel gains, rate adaptation, and scheduling in OFDMA downlink with feedback delays" (author s. guharoy et al, published in IEEE trans. ve. technol. vol.62, No.4, pp.1719-1732,2013), the average of the channel gains of all users is set to ΩkIn this embodiment, Ω is 7.78 dB. For data rates in LTE-U independent systems, the reference "evolution and discovery of specific radio access (E-UTRA): Physical layer processes" (LTE-U Forum, Tech. Spe.36.300v.13.3.0), we assume that there are 15 different rates, r respectivelynN is 1, 2. According to the document "Performance characteristics of cellular systems with differential link adaptation" (Author K.Baum et al, published in IEEE Trans.Veh.Technol., vol.52, No.6, pp.1497-1507,2003), the threshold associated with the rate adaptation is defined by the value of the rate adaptation threshold
Is obtained in which
Is the coding loss in the actual coding. The feedback threshold of the threshold feedback scheme is λ 0.2. The parameter setting of the Wi-Fi system follows the IEEE802.11ac standard, and the time length of the backoff time slot, the maximum backoff order of the Wi-Fi and the minimum contention window length of the Wi-Fi are respectively 9us, 5 and 32. In The reference "Modeling of synchronization and energy performance of FBE-and LBE-based station LTE-U networks" (Author J.Li et al, published in The journal of engineering, vol.2017, No.7,2017), in The simulation, we set The duration T of channel occupation when Wi-Fi transmission conflictsc wAnd Wi-Fi successfully occupies the channel for 284.72us and 540.72us, respectively. For the algorithm presented, set u-0.1 and e-0.001. In order to ensure the accuracy of the numerical result and the simulation result, the simulation result is the average value of 5000 repeated experiments of downlink and uplink transmission.
In order to embody the advantages of the channel quality feedback user selection method, when the resources are actually allocated for data transmission, the resource allocation can be performed according to the algorithm of SOP1, and then the throughput is counted. Thus, the results of LTE-U independent system throughput for the proposed algorithm and the comparative algorithm are given in fig. 6. Different from the proposed algorithm, the comparison algorithm adopts a scheme of randomly selecting a user for CSI feedback when selecting an authorized feedback CSI user. As the number of users increases, the frequency of each user to be selected to feed back CSI decreases, and accordingly, the feedback delay increases, so that the probability of successful reception of the user when the base station transmits data and the downlink throughput of the LTE-U independent system decrease. However, compared with the use of a comparison algorithm, the reduction of the downlink throughput can be relieved more after the LTE-U independent system uses the method for selecting the authorization feedback CSI user. Take K as an example 10, when NwWhen the output value is 6, the algorithm improves the downlink throughput of the system by 4.6 percent compared with a comparison algorithm; when N iswAt 10, the proposed algorithm is 5.5% higher than the comparison algorithm.
The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.
Claims (4)
1. A method for selecting authorized users to feed back CSI in an independent unlicensed frequency band cellular mobile communication system comprises the following steps:
(1) a base station in an LTE-U independent system receives CSI fed back by users and deduces feedback time delay of the CSI of each user when the base station is accessed into a channel to perform downlink transmission, so that a CSI matrix and a feedback time delay matrix are constructed;
(2) establishing a model for selecting authorized users to feed back CSI, wherein the specific process is as follows, a base station of an LTE-U independent system selects users authorized to feed back CSI next time through optimizing and solving the model, so that an authorization signaling is generated and sent to each user;
2.1 the base station counts the number N of the current Wi-Fi nodes by monitoring the frame head information of the control frames and the data frames of the Wi-Fi nodeswAnd calculating the packet sending probability tau of each Wi-Fi node through the following expressionw；
2.2 base station according to MAC layer parameter of LTE-U independent system and N obtained in step 2.1wAnd τwCalculating the probability distribution of the LTE-U independent system channel competition time delay;
2.3 according to the probability distribution of the LTE-U independent system channel competition time delay, the probability that each subframe of the base station starts to be collided by Wi-Fi when the base station accesses the channel next time is obtained through calculation;
2.4, determining the upper limit of the number of users for authorizing and feeding back CSI next time by the base station;
2.5, according to the probability distribution of the LTE-U independent system channel competition delay, the CSI matrix and the feedback delay matrix, estimating the expected data transmission rate of each user on each sub-band in each sub-frame when the base station accesses the channel for the next time under the two conditions of authorized CSI feedback and unauthorized CSI feedback;
2.6 based on the obtained data, establishing the following model for the base station to select the authorized user to feed back CSI;
wherein:
when the independent variable is
Resource allocation utility function of the k-th user in the case ofkSelecting an indicator variable I for authorizing the kth user to feed back CSI for a base stationk0 or 1, Ik1 means that the kth user is authorized to feed back CSI, Ik0 indicates that the kth user is not authorized to feed back CSI, NselAn upper limit of the number of users for the base station to authorize the feedback of the CSI next time,
an indicator variable pre-allocated to the kth user for the s sub-band of α th sub-frame of the next access channel start of the base station and
or 1 of the number of the groups in the group,
it means that the base station starts the α th access channel next timeThe s-th sub-band of the sub-frame is allocated to the k-th user,
it means that the s-th sub-band of α th sub-frame of the next access channel of the base station is not allocated to the k-th user,
for corresponding indication of variable IkUnder the circumstance, the throughput expected by the pre-allocation of time-frequency resources is obtained when the kth user accesses the channel next time at the base station, K is the number of users currently accessing the base station, α and s are natural numbers, and N is more than or equal to 1 and less than or equal to αdS is more than or equal to 1 and less than or equal to S, S is the number of sub-bands in the channel, NdThe number of sub-frames occupying the channel for the next time by the base station, B is the channel bandwidth, pc,αIndicating the probability that the α th sub-frame of the next access channel of the base station is collided by Wi-Fi,
for corresponding indication of variable IkIn the case that the kth user starts the desired data transmission rate on the s sub-band in the α th sub-frame from the next access channel of the base station;
(3) and the user analyzes the received authorization signaling, detects a reference signal in a channel according to a corresponding time-frequency position in the authorization signaling and obtains CSI for the user selected for authorization, and then feeds back the CSI to the base station through the uplink subframe.
2. The method of claim 1, wherein: the estimation of the CSI feedback delay of each user in step (1) is calculated according to the difference between the channel measurement time specified in the grant signaling and the actual data transmission time from the base station to the user.
3. The method of claim 1, wherein: the CSI matrix is KxS, the feedback delay matrix is KxN, K is the number of users currently accessed to the base station, S is the number of sub-bands in the channel, N is the number of sub-frames of the channel occupied by the base station for the last time, the element value in the CSI matrix is the CSI on the corresponding sub-band when the corresponding user feeds back the channel gain for the last time, and the element value in the feedback delay matrix is the time delay from the moment when the corresponding user obtains the CSI by the last measurement to the moment when the base station occupies the corresponding sub-frame in the channel for the last time.
4. The method of claim 1, wherein: the authorization signaling comprises time-frequency positions of behaviors of detecting reference signals and feeding back CSI in a channel and a user list of the base station for selecting the next authorization to feed back the CSI.
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