CN107070515B - D2D cooperative transmission method under Rice fading channel condition - Google Patents

D2D cooperative transmission method under Rice fading channel condition Download PDF

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CN107070515B
CN107070515B CN201710238088.4A CN201710238088A CN107070515B CN 107070515 B CN107070515 B CN 107070515B CN 201710238088 A CN201710238088 A CN 201710238088A CN 107070515 B CN107070515 B CN 107070515B
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CN107070515A (en
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史锋峰
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Southeast University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0417—Feedback systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/70—Services for machine-to-machine communication [M2M] or machine type communication [MTC]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/12—Wireless traffic scheduling
    • H04W72/1215—Wireless traffic scheduling for collaboration of different radio technologies
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/12—Wireless traffic scheduling
    • H04W72/1263—Mapping of traffic onto schedule, e.g. scheduled allocation or multiplexing of flows
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria

Abstract

The invention discloses a D2D cooperative transmission method under the condition of a Rice fading channel, which comprises the following steps of (1) scheduling cell users and D2D users participating in cooperative transmission; (2) estimating cell users US0And D2D Link receiver user D1Obtaining a channel delay correlation coefficient by the Doppler frequency offset; (3) evaluating performance gains obtained by the two transmission modes, and determining a cooperative transmission mode to be adopted by the base station; (4) the users estimate respective channel information and feed back the information to the base station after quantizing; (5) and transmitting data under the precoding scheme of the selected mode. The achievable rate of the cooperative transmission method can be well fitted with the statistical characteristics of an actual system, the closed expression is utilized to help the base station to quickly and effectively make a decision before the system actually feeds back channel information, and then according to the cooperative requirement, a user only feeds back necessary channel state information to the base station, so that the transmission load of a feedback link is reduced.

Description

D2D cooperative transmission method under Rice fading channel condition
Technical Field
The invention relates to a cooperative transmission method in a mobile communication multiple-input multiple-output (MIMO) system, in particular to a D2D cooperative transmission method under the condition of a Rice fading channel.
Background
In order to overcome the difficulty that some users in cellular mobile communication systems are unable to effectively obtain high data transmission rate due to low useful signal power and high interference signal power, recent researchers have proposed that the data rate of the users can be effectively increased by establishing a direct communication link between a Device and a Device (D2D).
This D2D technology enables users located at the edge of a cell to establish a link directly with a neighboring terminal for data transmission by sharing the frequency resources of other users of the cell in the existing cellular mobile communication environment. Because the distance between two users of D2D communication is very close, can utilize less transmit power to obtain higher data transmission rate, utilize multiplexing technique to fully excavate the space resource, improve frequency spectrum utilization ratio and power efficiency to the utmost extent.
The wireless link between the close-range D2D users can have a line-of-sight path to a great extent, the wireless channel is more likely to be fitted with a rice channel model, the analysis of the transmission performance of a rice fading channel is a difficulty in the field of wireless communication, and when the amplitude peak of a line-of-sight main signal tends to 0, and the ratio K → -infinity of the line-of-sight energy and the non-line-of-sight energy of the D2D link, the rice distribution is converted into a special Rayleigh distribution thereof.
The introduction of the D2D link inevitably brings about significant co-channel interference (ICI), which restricts the increase of the achievable transmission rate of the system. When a base station transmits a signal, there are two common precoding processing modes, a Maximum Rate (MR) precoding and Interference Cancellation (IC) precoding mode: in IC mode, the base station utilizes D2D user D1The feedback channel information carries out interference suppression on the feedback channel information; in the MR mode, a base station needs to acquire a cell user US0And the fed back channel information is used for carrying out maximum rate precoding processing on the cell communication link. The difference between the two cooperation modes is that in the IC mode, the base station needs not only the cell user US0Fed back channel information while requiring D2D user D1The fed back channel information is needed to be additionally fed back to eliminate the interference suffered by the D2D user; whereas in the MR mode, the base station only needs the cell users US0The feedback channel state information and the feedback link load are obviously reduced, and the system delay is also reduced.
Existing MR and IC mode evaluation schemes are based on the assumption that the base station can know the ideal channel information, but in practical application scenarios, the assumption is difficult to satisfy in both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) systems. If the system adopts Time Division Duplex (TDD), the transmitting end can estimate the uplink channel information at the base station and use it as the downlink channel information by using the reciprocity principle, but the uplink and the downlink are not completely symmetrical, so that the channel information obtained by the base station through reciprocity inevitably has estimation errors. If the system employs Frequency Division Duplex (FDD), the downlink channel information is usually estimated by the user terminal, and then the user feeds back the downlink channel information to the base station through a feedback link, but the amount of information that can be fed back by the user in the actual system is limited. In order to meet the capacity requirement of the feedback link, the user usually quantizes the channel information first, then feeds back the quantized information to the base station through limited bits, and finally the base station recovers the channel information as much as possible according to the feedback information. This scheme will result in a certain quantization error between the system channel information obtained by the base station and the actual channel information, and the size of this quantization error is determined by the capacity of the feedback link. In addition, when a feedback mechanism is adopted, the problem of information delay caused by a feedback link also exists, namely, the feedback information obtained by the base station is not the channel information at the current moment but the channel information before a period of delay.
Under the influence of the above factors, the downlink information obtained by the base station is not completely matched with the actual channel information, which results in a significant performance degradation of the adaptive transmission scheme based on the ideal channel information.
Disclosure of Invention
The purpose of the invention is as follows: in order to solve the defects of the prior art, a self-adaptive cooperative transmission method in a cellular mobile communication D2D system is provided, which can be effectively applied to an actual scene, and can support device-to-device direct communication and effectively improve the reachable transmission rate and the spectrum utilization rate of the system under the conditions that a direct path exists between adjacent D2D users, only delay limited feedback channel information can be obtained at a base station end, and non-ideal factors such as quantization errors, feedback delay, path loss and the like exist in the obtained channel information.
The technical scheme is as follows: the invention discloses a D2D cooperative transmission method under the condition of a Rice fading channel, which comprises the following steps:
(1) scheduling cell users and D2D users participating in the cooperative transmission;
(2) estimating cell users US0And D2D Link receiver user D1Obtaining a channel delay correlation coefficient by the Doppler frequency offset;
(3) evaluating performance gains obtained by the two transmission modes, and determining a cooperative transmission mode to be adopted by the base station;
(4) the users estimate respective channel state information, and feed back the information to the base station after quantizing;
(5) and transmitting data under the precoding scheme of the selected mode.
The step (1) comprises the following steps: base station scheduling and selecting one cell user US0Share its frequency band resource to neighboring users Ds and D with direct path1Device-to-device D2D communication, user Ds and D1The wireless channel between approximately follows a rice fading channel.
The step (2) comprises the following steps:
(21) estimating cell users US0And D2D Link receiver user D1Doppler frequency shift of
The base station investigates the average moving speed of the user terminal participating in the cooperation in the cell and estimates the cell user US0Doppler frequency shift f0The formula is as follows:
f0＝fcv0/c；
estimating D2D Link receiver user D1Doppler frequency shift f1The formula is as follows:
f1＝fcv1/c；
wherein c represents the speed of light, fcRepresenting the carrier frequency, v0Representing cell users US0Average moving velocity of v1Representation D2D Link receiver user D1Average moving rate of (2).
(22) Obtaining channel delay correlation coefficient
Calculating cell users US0Is channel delay correlation coefficient rho0The formula is as follows:
ρ0＝J0(2πf0Ts)；
computing D2D Link receiver user D1Is channel delay correlation coefficient rho1The formula is as follows:
ρ1＝J0(2πf1Ts)；
wherein π represents the circumference ratio, TsDenotes the length of each symbol period, J0(.) represent a first class of zero order bessel functions.
The step (3) comprises the following steps:
(31) closed form solution R of achievable transmission rate of system under calculation maximization rate precoding modeMR
First of all, the first step is to,calculating the cell user US according to0Closed form solution to achievable transmission rate in maximum rate precoding mode
Figure GDA0002376661790000031
Figure GDA0002376661790000032
Where the subscript b denotes the cell base station and the subscript 0 denotes the scheduled cell users US0The subscript s denotes the sending end user Ds of the D2D link; l isb0Indicating cell base station b to cell user US0The formula is: l isb0＝(db0/d0)-l；Ls0Representing the D2D link sender s to the cell user US0The formula is: l iss0＝(ds0/d0)-l；d0Denotes the transmit power reference distance, l denotes the signal propagation path loss attenuation factor, PbRepresenting the transmission power, P, of the cell base station bsRepresents the transmit power, ρ, of the D2D link sender s0Representing cell users US0Of the channel delay correlation coefficient, B0Representing cell users US0The quantization bit number of the feedback channel state information, M represents the number of the transmitting antennas of the base station.
Second, the device-to-device link receiver user D is calculated according to1Closed form solution to achievable transmission rate in maximum rate precoding mode
Figure GDA0002376661790000041
Figure GDA0002376661790000042
Where the subscript 1 denotes the receiving end user D of the D2D link1；Lb1Indicating cell base station b to D2D link receiving end user D1The formula is: l isb0＝(db1/d0)-l；Ls1Representing a D2D link sender s to receiver user D1The formula is: l iss1＝(ds1/d0)-l。
Then, calculating a closed type solution R of the achievable transmission rate of the system under the precoding mode of the maximum rate according to the following formulaMR：
Figure GDA0002376661790000043
(32) Closed-form solution R of achievable transmission rate of system in calculation interference elimination precoding modeIC
First, the cell user US is calculated according to the following formula0Closed-form solution to achievable transmission rates in interference cancellation precoding mode
Figure GDA0002376661790000044
Figure GDA0002376661790000045
Second, the device-to-device link receiver user D is calculated according to1Closed-form solution to achievable transmission rates in interference cancellation precoding mode
Figure GDA0002376661790000046
Figure GDA0002376661790000047
Where ρ is1Representing device-to-device link receiver user D1The channel delay correlation coefficient of (2); b is1Representing device-to-device sink user D1The bit number of the channel state information fed back to the base station; k represents the rice channel factor, which is the ratio of D2D link line-of-sight energy to non-line-of-sight energy.
Then, calculating a closed type solution R of the achievable transmission rate of the system under the interference elimination precoding mode according to the following formulaIC：
Figure GDA0002376661790000051
(33) Calculating the performance gain obtained in both modes
Calculating the performance gain R obtained by the system under the mode of maximizing the rate precoding according to the following formulaMR,↑：
Figure GDA0002376661790000052
Calculating the performance gain R obtained by the system under the interference elimination precoding mode according to the following formulaIC,↑：
Figure GDA0002376661790000053
Wherein R is0For cell users US0The achievable rate without introducing device-to-device communication is calculated according to the following formula:
Figure GDA0002376661790000054
the performance gains obtained for the system in the two transmission modes after introduction of D2D communication were then compared: if R is satisfiedMR,↑≥RIC,↑Selecting a maximum rate precoding mode as a transmission mode adopted by a near base station user; otherwise, selecting the interference elimination precoding mode as the transmission mode adopted by the near base station user.
Wherein the function F1(x0,x1,x2M) is calculated as:
Figure GDA0002376661790000055
wherein x is0，x1，x2M is the independent variable of the function, and M is the number of the base station transmitting antennas; i, ζ, j is an index of the operation sequence of the summation operator; j! Represents a factorial of the number j;log2(e) is the logarithm of a base-2 natural number e, which is reciprocal to the natural logarithm of 2, i.e. log2(e)＝1/ln2，
Function I (x)0,x1,x2The formula for m, n) is as follows:
Figure GDA0002376661790000061
wherein x is0，x1，x2M, n are the arguments of the function, q, k are the index indices of the sequence of operation of the summation operator,
Figure GDA0002376661790000062
to take the number of combinations of q elements out of m different elements,
Figure GDA0002376661790000063
in order to be an incomplete gamma function,
Figure GDA0002376661790000064
is a gamma function, wherein u, x are arguments of the gamma function;
when x is2When 1, m 0, n 1, function I (x)0,x1,x2M, n) is reduced to:
Figure GDA0002376661790000065
wherein the content of the first and second substances,
Figure GDA0002376661790000066
is a first order exponential integration function, k being the argument of the function.
Calculation of R0Calling function F1(x0,x1,x2And M) if x is present2In the case of 0, the above formula cannot be used to calculate directly, and the special formula is derived as follows:
Figure GDA0002376661790000067
function F2(x0,x1,x2M) is calculated as:
F2(x0,x1,x2)＝log2(e)(Iξ(x0,x1,x2,K)+Iξ(x0,x2,x1,K))；
wherein the content of the first and second substances,
Figure GDA0002376661790000068
Figure GDA0002376661790000071
wherein x is0，x1，x2K is the argument of the function, K is the rice channel factor of the corresponding channel, and m, K, ζ are index indices of the sequence of operation of the summation operator.
The step (4) comprises the following steps:
(41) cell user US0And D2D Link receiver user D1Respectively carrying out channel estimation to obtain channel state information and path loss;
(42) and quantizing the channel state information in real time according to a codebook known by the user and the base station, and feeding back the quantized channel state information to the base station.
The step (5) comprises:
(51) the base station calculates a precoding vector by using the fed back channel state information according to the selected transmission mode;
(52) will be sent to the cell user US0Then data transmission is carried out, and the D2D user carries out data transmission by using the same-frequency resources.
Has the advantages that: compared with the prior art, the invention has the following advantages: (1) the invention can fully estimate the performance deterioration caused by non-ideal factors such as path loss, quantization error, feedback delay error and the like in the actual system, and selects a more suitable transmission mode, thereby obtaining higher system transmission rate. (2) When the method is applied to a cellular mobile communication D2D system, the closed-type solution of the reachable rate can be utilized, and before the feedback link feeds back the real-time channel state information, the method can estimate in advance which precoding scheme is adopted between the base station and the cell user, so that the system performance is better, different precoding schemes are selected in a self-adaptive manner in different system environments, the feedback channel can be fully utilized, the realization complexity is reduced, and better system performance is obtained.
Drawings
FIG. 1 is a system schematic of the process of the present invention;
FIG. 2 is a graph of the achievable rate of the system in MR mode as a function of the reference SNR;
FIG. 3 is a graph of the achievable rate of the system in IC mode as a function of the reference SNR;
FIG. 4 is a user US0And user D1The achievable rate change is a function of the reference signal-to-noise ratio.
Detailed Description
The technical solution of the present invention is further explained with reference to the accompanying drawings.
As shown in the system diagram of FIG. 1, the BSbIs a base station, US0For selected cell users, D1And Ds is selected adjacent user of D2D link with direct path, users Ds and D1The wireless channel between approximately follows a rice fading channel.
In fig. 1 solid arrows indicate active links, dashed arrows indicate interfering links, hb0Is a base station BSbAnd cell user US0Channel state information of, hb1Is a base station BSbAnd D2D Link user D1Channel state information of, hs1For D2D link users Ds and D1Channel state information of, hs0For D2D link user Ds and cell user US0Channel state information in between.
A D2D cooperative transmission method under the condition of a Rice fading channel comprises the following steps:
(1) scheduling cell and D2D users participating in cooperative transmissions
Base station scheduling and selecting one cell user US0Share its frequency band resource to neighboring users Ds and D with direct path1Device-to-device D2D communication, user Ds and D1The wireless channel between approximately follows a rice fading channel.
(2) Estimating cell users US0And D2D Link receiver user D1Obtaining the channel delay correlation coefficient
(21) Estimating cell users US0And D2D Link receiver user D1Doppler frequency shift of
The base station investigates the average moving speed of the user terminal participating in the cooperation in the cell and estimates the cell user US0Doppler frequency shift f0The formula is as follows:
f0＝fcv0/c；
estimating D2D Link receiver user D1Doppler frequency shift f1The formula is as follows:
f1＝fcv1/c；
wherein c represents the speed of light, fcRepresenting the carrier frequency, v0Representing cell users US0Average moving velocity of v1Representation D2D Link receiver user D1Average moving rate of (2).
(22) Obtaining channel delay correlation coefficient
Calculating cell users US0Is channel delay correlation coefficient rho0The formula is as follows:
ρ0＝J0(2πf0Ts)；
computing D2D Link receiver user D1Is channel delay correlation coefficient rho1The formula is as follows:
ρ1＝J0(2πf1Ts)；
wherein π represents the circumference ratio, TsDenotes the length of each symbol period, J0(.) represent a first class of zero order bessel functions.
(3) Evaluating the performance gains obtained for the two transmission modes, the base station determines the cooperative transmission mode to be used
(31) Closed form solution R of achievable transmission rate of system under calculation maximization rate precoding modeMR
First, the cell user US is calculated according to the following formula0Closed form solution to achievable transmission rate in maximum rate precoding mode
Figure GDA0002376661790000091
Figure GDA0002376661790000092
Where the subscript b denotes the cell base station and the subscript 0 denotes the scheduled cell users US0The subscript s denotes the sending end user Ds of the D2D link;
Lb0indicating cell base station b to cell user US0The formula is: l isb0＝(db0/d0)-l；
Ls0Representing the D2D link sender s to the cell user US0The formula is: l iss0＝(ds0/d0)-l；
d0Represents a transmit power reference distance;
l represents a signal propagation path loss attenuation factor;
Pbrepresents the transmit power of cell base station b;
Psrepresenting the transmitting power of a D2D link transmitting terminal s;
ρ0representing cell users US0The channel delay correlation coefficient of (2);
B0representing cell users US0The quantization bit number of the feedback channel state information;
m denotes the number of base station transmit antennas.
Second, the device-to-device link receiver user D is calculated according to1In maximum rate precoding modeClosed-form solution of achievable transmission rate
Figure GDA0002376661790000093
Figure GDA0002376661790000094
Where the subscript 1 denotes the receiving end user D of the D2D link1；Lb1Indicating cell base station b to D2D link receiving end user D1Path loss of (D) is represented by Lb0＝(db1/d0)-l；Ls1Representing a D2D link sender s to receiver user D1Path loss of (D) is represented by Ls1＝(ds1/d0)-l。
Then, calculating a closed type solution R of the achievable transmission rate of the system under the precoding mode of the maximum rate according to the following formulaMR：
Figure GDA0002376661790000101
(32) Closed-form solution R of achievable transmission rate of system in calculation interference elimination precoding modeIC
First, the cell user US is calculated according to the following formula0Closed-form solution to achievable transmission rates in interference cancellation precoding mode
Figure GDA0002376661790000102
Figure GDA0002376661790000103
Second, the device-to-device link receiver user D is calculated according to1Closed-form solution to achievable transmission rates in interference cancellation precoding mode
Figure GDA0002376661790000104
Figure GDA0002376661790000105
Where ρ is1Representing device-to-device link receiver user D1The channel delay correlation coefficient of (2); b is1Representing device-to-device sink user D1The bit number of the channel state information fed back to the base station; k represents the rice channel factor, which is the ratio of D2D link line-of-sight energy to non-line-of-sight energy.
Then, calculating a closed type solution R of the achievable transmission rate of the system under the interference elimination precoding mode according to the following formulaIC：
Figure GDA0002376661790000106
(33) Calculating the performance gain obtained in both modes
Calculating the performance gain R obtained by the system under the mode of maximizing the rate precoding according to the following formulaMR,↑：
Figure GDA0002376661790000107
Calculating the performance gain R obtained by the system under the interference elimination precoding mode according to the following formulaIC,↑：
Figure GDA0002376661790000108
Wherein R is0The achievable rate for the cell user US0 without introducing device-to-device communication conditions is calculated according to the following equation:
Figure GDA0002376661790000111
the performance gains obtained for the system in the two transmission modes after introduction of D2D communication were then compared: if R is satisfiedMR,↑≥RIC,↑Selecting a maximum rate precoding mode as a transmission mode adopted by a near base station user; otherwise, interference cancellation precoding is selectedThe mode is used as a transmission mode for the near base station user.
In addition, function F1(x0,x1,x2M) is calculated as:
Figure GDA0002376661790000112
wherein x is0，x1，x2M is the independent variable of the function, and M is the number of the base station transmitting antennas; i, ζ, j is an index of the operation sequence of the summation operator; j! Represents a factorial of the number j; log (log)2(e) Is the logarithm of a base-2 natural number e, which is reciprocal to the natural logarithm of 2, i.e. log2(e)＝1/ln2。
Function I (x)0,x1,x2The formula for m, n) is as follows:
Figure GDA0002376661790000113
wherein x is0，x1，x2M, n are the arguments of the function; q, k are index subscripts of the operation sequence of the summation operator;
Figure GDA0002376661790000114
the number of combinations for taking q elements out of m different elements;
Figure GDA0002376661790000115
is an incomplete gamma function;
Figure GDA0002376661790000116
is a gamma function, where u, x are the arguments of the gamma function.
When x is2When 1, m 0, n 1, function I (x)0,x1,x2M, n) is reduced to:
Figure GDA0002376661790000121
wherein the content of the first and second substances,
Figure GDA0002376661790000122
is a first order exponential integration function, k being the argument of the function.
When calculating R0Calling function F1(x0,x1,x2M), x appears2In the case of 0, this time it cannot be directly calculated using the above formula, and we derive the formula for this particular case as follows:
Figure GDA0002376661790000123
function F2(x0,x1,x2M) is calculated as:
F2(x0,x1,x2)＝log2(e)(Iξ(x0,x1,x2,K)+Iξ(x0,x2,x1,K))；
wherein the content of the first and second substances,
Figure GDA0002376661790000124
Figure GDA0002376661790000125
wherein x is0，x1，x2K is the argument of the function, K is the Rice channel factor of the corresponding channel; m, k, ζ are index indices of the sequence of summation operator operations.
(4) The users estimate their own channel information, and feed back the information to the base station after quantizing according to the codebook
(41) Cell user US0And D2D Link receiver user D1Respectively carrying out channel estimation to obtain channel state information and path loss;
(42) and quantizing the channel state information in real time according to a codebook known by the user and the base station, and feeding back the quantized channel state information to the base station.
The channel state information h system can adopt a random vector quantization method to carry out limited feedback on the channel state information. The channel norm h can be defined as channel quality information, which is a representation of channel quality and occupies a small amount of channel feedback. Channel direction information is usually fed back when channel state information is fed back
Figure GDA0002376661790000126
Accounting for the main feedback quantity.
Figure GDA0002376661790000127
The receiving end maps the channel direction information to a codebook with the smallest included angle between the codebook space and the direction thereof, the codebook label is fed back to the transmitting end through a feedback link, and the transmitting end recovers the channel direction information into a quantized vector through the codebook
Figure GDA0002376661790000131
The angle between the quantized vector and the actual channel vector is the finite feedback quantization error
Figure GDA0002376661790000132
If the number of feedback bits is B, the size of the codebook space is 2B(ii) a The smaller B, the smaller the required feedback bandwidth, but the poorer the quantization accuracy; conversely, the larger B, the larger feedback bandwidth is required, but the quantization accuracy can be improved.
In the MR precoding mode, the base station only needs to obtain the cell base station b to the cell user US from the feedback link0Channel state information h ofb0. In IC precoding mode, the base station needs to obtain the cell base station b to the cell user US from the feedback link at the same time0Channel state information h ofb0And cell site b to D2D link receiving end user D1Channel state information h ofb1. In an actual system, two precoding modes have advantages respectively, and the invention provides a scheme for adaptively selecting a precoding mode.
(5) Data transmission under selected mode precoding scheme
(51) The base station calculates a precoding vector by using the fed back channel state information according to the selected transmission mode;
(52) will be sent to the cell user US0Then data transmission is carried out, and the D2D user carries out data transmission by using the same-frequency resources.
Example (b):
for uniform reference comparison, the noise variance is normalized, and the base station transmission power P is represented by the signal-to-noise ratio of the base station transmission signal at the reference distancebIn the following drawings, the reference distance d is assumed0100m, the signal propagation path loss attenuation factor l is 3.5.
In the maximum rate precoding mode, the total achievable transmission rate of the system and the cell users US after D2D communication is introduced0And D2D user D1The respective achievable transmission rates, which vary with the signal to noise ratio, are shown in fig. 2. As can be seen from fig. 2:
in MR mode, D2D is used to indicate1The curve of the rate theoretical result changing with the signal-to-noise ratio by adopting the method and the curve of the numerical simulation rate numerical value changing with the signal-to-noise ratio by adopting the method can be seen that the theoretical calculation result by adopting the method is very similar to the numerical simulation result, namely the theoretical calculation result by adopting the method can better fit the simulation result.
In MR mode, by cell user US0The curve of the rate theoretical result changing with the signal-to-noise ratio by adopting the method and the curve of the numerical simulation rate numerical value changing with the signal-to-noise ratio by adopting the method can be seen, the theoretical calculation result by adopting the method is consistent with the numerical simulation result, namely the theoretical calculation result by adopting the method can well fit the simulation result.
In addition, in the MR mode, by the cell user US0And D2D user D1The two curves of the sum rate theoretical result and the sum rate numerical result show that the calculation result of the sum rate theoretical result and the calculation result of the sum rate numerical result are basically consistent with the calculation result of the sum rate theoretical result and the calculation result of the sum rate numerical result, namely the calculation result of the sum rate theoretical result and the calculation result of the rate theoretical result are basically consistentAnd fitting and speed simulation results can be better.
In the interference elimination precoding mode, the total achievable transmission rate of the system and the cell users US after D2D communication is introduced0And D2D user D1The respective achievable transmission rates are plotted against the signal-to-noise ratio in fig. 3. Therefore, the following steps are carried out:
in IC mode, user D is connected by D2D1The curve of the rate theoretical result changing with the signal-to-noise ratio by adopting the method and the curve of the numerical simulation rate numerical value changing with the signal-to-noise ratio by adopting the method can be seen that the theoretical calculation result by adopting the method is very similar to the numerical simulation result, namely the theoretical calculation result by adopting the method can better fit the simulation result.
In IC mode, by cell user US0The curve of the rate theoretical result changing with the signal-to-noise ratio by adopting the method and the curve of the numerical simulation rate numerical value changing with the signal-to-noise ratio by adopting the method can be seen, the theoretical calculation result by adopting the method is consistent with the numerical simulation result, namely the theoretical calculation result by adopting the method can well fit the simulation result.
In addition, in IC mode, by cell user US0And D2D user D1The curves of the sum rate theoretical result and the sum rate numerical result show that the calculation result of the sum rate theoretical result and the calculation result of the sum rate numerical result are basically consistent with the calculation result of the sum rate theoretical result and the calculation result of the sum rate numerical result, namely the calculation result of the sum rate theoretical result and the calculation result of the sum rate theoretical result can be better fitted and the speed simulation result.
Through comparison of the theoretical calculation result and the numerical simulation result, the invention verifies that the provided expression can better fit the simulation result in the two pre-coding modes.
The specific parameters are as follows: m is 4, Ps＝Pb/20，db0＝50m，db1＝450m，ds0＝500m，ds1＝10m，f0Ts＝0.1，f1Ts＝0.01，B0＝B1＝8，K＝3dB。
In two collaboration modes, D2D user D1The achievable rate increment obtained, andcell user US0The rate loss as a function of signal to noise ratio is shown in fig. 4. As can be seen from fig. 4:
when the transmit power is low and the two precoding modes are relatively good, the MR precoding mode which is easy to implement and requires less channel state information is preferably adopted from the viewpoint of system implementation complexity.
When the sending power is larger, when the error of the channel state information fed back by the feedback channel is smaller, the quantization error and the delay error are smaller, the performance of the IC precoding mode is obviously superior to that of the MR precoding mode, and the IC precoding mode is suitable for being adopted.
The specific parameters are as follows: m is 4, Ps＝Pb/20，db0＝50m，db1＝450m，ds0＝500m，ds1＝10m，f0Ts＝0.1，f1Ts＝0.01，B0＝B1＝8，K＝3dB。
In the simulation process, it is found that due to a lot of factors affecting the system performance, the related parameters include the transmission power of each signal source, the distance between each communication terminal, the feedback channel bandwidth, the feedback information delay length, and the like. Therefore, in an actual system, the choice of which cooperation strategy is adopted by the D2D system base station is a multidimensional decision problem. In an actual system, besides selecting a proper transmission precoding mode, the power proportional relation between the base station and the D2D transmitting device is not maintained, and the transmission power of the D2D link is reduced, because the D2D communication is typical short-distance communication, and a transmitting end can transmit signals with lower power to transmit data. Also, in a practical system, feedback of channel state information is also an inevitable heavy overhead in the system. According to simulation results, the achievable rate of the cooperative transmission method can be well fitted with the statistical characteristics of an actual system, the closed expression is utilized to help the base station to quickly and effectively make a decision before the system actually feeds back channel information, and then according to cooperative requirements, a user only feeds back necessary channel state information to the base station, so that the transmission load of a feedback link is reduced.

Claims (6)

1. A method for cooperative D2D transmission under rice fading channel conditions, comprising the steps of:
(1) scheduling cell users and D2D users participating in the cooperative transmission;
(2) estimating cell users US0And D2D Link receiver user D1Obtaining a channel delay correlation coefficient by the Doppler frequency offset;
(3) evaluating performance gains obtained by the two transmission modes, and determining a cooperative transmission mode to be adopted by the base station; the method specifically comprises the following steps:
(31) closed form solution R of achievable transmission rate of system under calculation maximization rate precoding modeMR
First, the cell user US is calculated according to the following formula0Closed form solution to achievable transmission rate in maximum rate precoding mode
Figure FDA0002376661780000011
Figure FDA0002376661780000012
Where the subscript b denotes the cell base station and the subscript 0 denotes the scheduled cell users US0The subscript s denotes the sending end user Ds of the D2D link; l isb0Indicating cell base station b to cell user US0Path loss of (D) is represented by Lb0＝(db0/d0)-l；Ls0Representing the D2D link sender s to the cell user US0The formula is: l iss0＝(ds0/d0)-l；d0Denotes the transmit power reference distance, l denotes the signal propagation path loss attenuation factor, PbRepresenting the transmission power, P, of the cell base station bsRepresents the transmit power, ρ, of the D2D link sender s0Representing cell users US0Of the channel delay correlation coefficient, B0Representing cell users US0The quantization bit number of the feedback channel state information, M represents the number of the transmitting antennas of the base station;
second, the device-to-device link receiver user D is calculated according to1Closed form solution to achievable transmission rate in maximum rate precoding mode
Figure FDA0002376661780000013
Figure FDA0002376661780000014
Where the subscript 1 denotes the receiving end user D of the D2D link1；Lb1Indicating cell base station b to D2D link receiving end user D1Path loss of (D) is represented by Lb0＝(db1/d0)-l；Ls1Representing a D2D link sender s to receiver user D1The formula is: l iss1＝(ds1/d0)-l；
Then, calculating a closed type solution R of the achievable transmission rate of the system under the precoding mode of the maximum rate according to the following formulaMR：
Figure FDA0002376661780000021
(32) Closed-form solution R of achievable transmission rate of system in calculation interference elimination precoding modeIC
First, the cell user US is calculated according to the following formula0Closed-form solution to achievable transmission rates in interference cancellation precoding mode
Figure FDA0002376661780000022
Figure FDA0002376661780000023
Second, the device-to-device link receiver user D is calculated according to1Closed-form solution to achievable transmission rates in interference cancellation precoding mode
Figure FDA0002376661780000024
Figure FDA0002376661780000025
Where ρ is1Representing device-to-device link receiver user D1The channel delay correlation coefficient of (2); b is1Representing device-to-device sink user D1The bit number of the channel state information fed back to the base station; k represents a Rice channel factor, which is the ratio of D2D link line-of-sight energy to non-line-of-sight energy;
then, calculating a closed type solution R of the achievable transmission rate of the system under the interference elimination precoding mode according to the following formulaIC：
Figure FDA0002376661780000026
(33) Calculating the performance gain obtained in both modes
Calculating the performance gain R obtained by the system under the mode of maximizing the rate precoding according to the following formulaMR,↑：
Figure FDA0002376661780000027
Calculating the performance gain R obtained by the system under the interference elimination precoding mode according to the following formulaIC,↑：
Figure FDA0002376661780000028
Wherein R is0For cell users US0The achievable rate without introducing device-to-device communication is calculated according to the following formula:
Figure FDA0002376661780000031
then comparePerformance gains obtained by the system in two transmission modes after introduction of D2D communication: if R is satisfiedMR,↑≥RIC ,↑Selecting a maximum rate precoding mode as a transmission mode adopted by a near base station user; otherwise, selecting an interference elimination precoding mode as a transmission mode adopted by a near base station user;
(4) the users estimate respective channel state information, and feed back the information to the base station after quantizing;
(5) and transmitting data under the precoding scheme of the selected mode.
2. The method for D2D cooperative transmission under rice fading channel conditions as claimed in claim 1, wherein said step (1) comprises: base station scheduling and selecting one cell user US0Share its frequency band resource to neighboring users Ds and D with direct path1Device-to-device D2D communication, user Ds and D1The wireless channel between approximately follows a rice fading channel.
3. The method for D2D cooperative transmission under rice fading channel conditions as claimed in claim 1, wherein said step (2) comprises:
(21) estimating cell users US0And D2D Link receiver user D1Doppler frequency shift of
The base station investigates the average moving speed of the user terminal participating in the cooperation in the cell and estimates the cell user US0Doppler frequency shift f0The formula is as follows:
f0＝fcv0/c；
estimating D2D Link receiver user D1Doppler frequency shift f1The formula is as follows:
f1＝fcv1/c；
wherein c represents the speed of light, fcRepresenting the carrier frequency, v0Representing cell users US0Average moving velocity of v1Representation D2D Link receiver user D1Average moving rate of (d);
(22) obtaining channel delay correlation coefficient
Calculating cell users US0Is channel delay correlation coefficient rho0The formula is as follows:
ρ0＝J0(2πf0Ts)；
computing D2D Link receiver user D1Is channel delay correlation coefficient rho1The formula is as follows:
ρ1＝J0(2πf1Ts)；
wherein π represents the circumference ratio, TsDenotes the length of each symbol period, J0(.) represent a first class of zero order bessel functions.
4. The method of claim 1, wherein the method comprises the following steps:
function F1(x0,x1,x2M) is calculated as:
Figure FDA0002376661780000041
wherein x is0，x1，x2And M is an independent variable of the function, and M is the number of the corresponding base station transmitting antennas; i, ζ and j are index indices of the operation sequence of the summation operator; j! Represents a factorial of the number j; log (log)2(e) Is the logarithm of a base-2 natural number e, which is reciprocal to the natural logarithm of 2, i.e. log2(e)＝1/ln2；
Function I (x)0,x1,x2The formula for m, n) is as follows:
Figure FDA0002376661780000042
wherein x is0，x1，x2M and n are arguments of a function; q, k are index subscripts of the operation sequence of the summation operator;
Figure FDA0002376661780000043
the number of combinations for taking q elements out of m different elements;
Figure FDA0002376661780000044
is an incomplete gamma function;
Figure FDA0002376661780000045
is a gamma function, wherein u, x are arguments of the gamma function;
when x is2When 1, m 0, n 1, function I (x)0,x1,x2M, n) is represented by:
Figure FDA0002376661780000051
wherein the content of the first and second substances,
Figure FDA0002376661780000052
is a first order exponential integration function, k being the argument of the function;
calculation of R0Calling function F1(x0,x1,x2And M) if x is present2In the case of 0, the above formula cannot be used to calculate directly, and the special formula is derived as follows:
Figure FDA0002376661780000053
function F2(x0,x1,x2M) is calculated as:
F2(x0,x1,x2)＝log2(e)(Iξ(x0,x1,x2,K)+Iξ(x0,x2,x1,K))；
wherein the content of the first and second substances,
Figure FDA0002376661780000054
Figure FDA0002376661780000055
wherein x is0，x1，x2K is the independent variable of the function, and K is the Rice channel factor of the corresponding channel; m, k, and ζ are index indices of the sequence of summation operator operations.
5. The method for cooperative D2D transmission under rice fading channel conditions according to claim 1, wherein the step (4) comprises:
(41) cell user US0And D2D Link receiver user D1Respectively carrying out channel estimation to obtain channel state information and path loss;
(42) and quantizing the channel state information in real time according to a codebook known by the user and the base station, and feeding back the quantized channel state information to the base station.
6. The method for cooperative D2D transmission under rice fading channel conditions according to claim 1, wherein the step (5) comprises:
(51) the base station calculates a precoding vector by using the fed back channel state information according to the selected transmission mode;
(52) will be sent to the cell user US0Then data transmission is carried out, and the D2D user carries out data transmission by using the same-frequency resources.
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