Face sky array communications non-orthogonal multiple access downlink transmission methodTechnical field
The invention belongs to face sky field of communication technology, specifically a kind of sky array communications non-orthogonal multiple access downlink of facing is passedTransmission method.
Background technique
With the development of information technology, the growth of communication requirement amount exponentially utilizes near space dirigible and low latitudeUnmanned plane effectively can supplement and improve existing communication system as null base station services terrestrial user is faced.Due to dirigible and nothingIt is man-machine that all there is good mobility, it can fast implement the traffic demands for meeting specific region, such as remote districtsCommunication support, the communication service of emergency communication and high business demand area in the case of natural calamity.
On the one hand, growing communication requirement is unable to satisfy since bandwidth limits in traditional microwave frequency range.And millimeterWave (30-300GHz) possesses frequency spectrum resource abundant, shows huge advantage and potentiality increasing spectral bandwidth this aspect,The growth of bandwidth directly will effectively improve the capacity of communication system.However, due to millimeter wave propagation loss with higher,Face in empty communication at a distance and faces huge challenge.
The size of antenna and the wavelength direct proportionality of carrier wave in usual mobile communication, millimeter wave is due in higherFrequency band, wavelength are less than the wavelength of traditional communication band, thus the size of antenna can design it is smaller.ThisSample, identical space size can accommodate more antennas, can also be easier deployment aerial array, with reach enter it is moreThe purpose of the array gain of (Multiple-Input Multiple-Output, MIMO) out.So-called mimo systems, justIt is traditional single antenna transmissions to be become array antenna, transmitting terminal and receiving end all respectively carry out reasonable wave beam forming, so thatThe beam gain of multiple antennas is respectively directed to hair/receiving end, this makes it possible to realize array gain, in the feelings for not changing total transmission powerThe intensity for increasing receiving end received signal under condition can effectively resist the range attenuation faced in empty communication.
On the other hand, it with the raising of number of users and communication requirement, needs to increase the quantity for facing sky aircraft, ground masterBase station needs effectively to control and communicate to facing null base station real-time perfoming, while facing null base station and wanting the multiple users in real time service ground.In traditional method, the base station of single radio frequency can only connect one in same time domain/frequency domain/code domain and face null base station or user, thisJust greatly limit the access quantity for facing null base station and user.
In millimere-wave band, in order to make up gain loss caused by high propagation attenuation, generally realized using aerial arrayArray gain, in order to meet the needs of low hardware deterioration, using the method for analog beam figuration, all antennas share a radio frequencyLink, and the weight coefficient of each antenna has the long constraint of identical mould.Using a small amount of radio frequency link and large scale array dayLine is accessed by millimeter wave non-orthogonal multiple, ground base station may be implemented when identical/frequency/code resource under connect and multiple face skyBase station, and face null base station may be implemented when identical/frequency/code resource under connect multiple terrestrial users.
Summary of the invention
To solve the above-mentioned problems, the present invention accesses (Non Orthogonal Multiple using non-orthogonal multipleAccess, NOMA) mode, it proposes one kind and faces sky array communications non-orthogonal multiple access downlink transmission method, sent out by designIt penetrates the wave beam forming vector at end while aiming at two long-range receiving ends and distributing different transmitting signal powers for them, thusRealize the purpose maximized up to the sum of rate.
Specific step is as follows:
Step 1: facing sky non-orthogonal multiple access communications system for downlink, constructing ground base station and facing between null base stationCommunication scenes.
Communication scenes include: 1. ground base stations to multiple downlink transfers for facing null base station；2. facing null base station to multiple groundThe downlink transfer of user；3. the downlink transfer that ground base station services multiple low latitude unmanned planes.
For the first ground base station to the scene of multiple downlink transfers for facing null base station, specific building is as follows:
Ground base station has N member aerial array, and 2 single antenna are connected in same time domain/frequency domain/code domain resource block and are remotely facedNull base station, it is respectively space base 1 and space base 2 that two, which are faced null base station,.In ground base station one end, every antenna branch has a phase to turnParallel operation and power amplifier, all power amplifiers have identical scale factor, therefore wave beam forming vector, i.e. antenna power systemThe mould length of each component of number vector is equal, referred to as permanent modular constraint.
Step 2: being directed to the first model of place, ground base station will believe all power normalizations for facing null base station transmissionNumber it is overlapped transmitting；
Superposed signal expression formula are as follows:
siIndicate ground base station to the transmitting signal for facing null base station i transmission, piFor to the transmitting signal power for facing null base station i；I=1,2.
Step 3: superposed signal s by ground base station and after facing the channel response between null base station and antenna noise shapeAt mixed signal, and faces null base station by two and respectively receive；
Face the received mixed signal of null base station 1 are as follows:
Face the received mixed signal of null base station 2 are as follows:
Wherein hiIt is the channel response vector of ground base station and space base i, w indicates the wave beam forming vector under permanent modular constraint,Its permanent modular constraint is that each component mould length is equalN is ground base station antenna number, niIndicate emptyWhite Gaussian noise on base i antenna, mean power are denoted as σ2。
Step 4: ground base station uses the uniform linear array antenna of half-wave spacing, and each faces between null base station and carry outMillimeter wave beam communication obtains and respectively faces the channel response vector of null base station；
Ground base station and the channel response vector h for facing null base station iiFormula are as follows:
Wherein λi,lIndicate the complex coefficient of the l articles diameter of space base i, LiIndicate the multipath component total number for facing null base station i,Ωi,lIndicate that cosine value of the l articles diameter in the ground base station angle of departure of space base i, a () indicate the function for being directed toward vector, expressionFormula are as follows:
A (N, Ω)=[ejπ0Ω,ejπ1Ω,ejπ2Ω,…,ejπ(N-1)Ω]
A (N, Ω) depends on the geometry of array antenna；
Step 5: selecting the channel response vector on most strong path as ground base station for each path for facing null base station iWith the efficient channel response vector h for facing null base station ii；
hi=λia(N,Ωi)
Wherein λiIndicate the complex coefficient in the most strong path of space base i, i.e., | λi|≥|λi,l|。
Step 6: using the wave beam forming vector w under permanent modular constraint, the efficient channel gain to null base station is respectively facedCorresponding sequence is made, the decoding priority orders of each space base signal are obtained.
Efficient channel gain depends on channel gain and array gain, and efficient channel gain is lower, and decoding priority is higher；
For efficient channel gainPriority when the signal decoding of space base 2 is higher than the signal of space base 1Decode priority；
For efficient channel gainPriority when the signal decoding of space base 1 is higher than the signal of space base 2Decode priority；
Step 7: being ordered as efficient channel gainSpace base 1 will emit signal s2Preferential decoding is simultaneouslyIt is eliminated in the signal of superposition, further decoding emits signal s1, space base 2, which directly decodes, emits signal s2, obtain the reachable of each space baseRate；The reachable rate of two space bases is calculated separately using shannon formula, as follows:
The reachable rate R of space base 11Are as follows:
The reachable rate R of space base 22Are as follows:
Step 8: when all the sum of reachable rates for facing null base station reach maximization, the distribution of design joint Power and wave beamThe constraint condition that figuration need to meet.
Reach maximization i.e. objective function up to the sum of rate, as follows:
The constraint condition that need to meet is as follows:
p1+p2=P
Wherein riIndicate the minimum reachable rate constraint for facing null base station i；P is the maximum power for facing the transmitting signal of null base station.
Step 9: solving to the constraint condition that need to meet, respectively faced the corresponding power distribution of null base station and ground base stationBeamforming scheme, obtain good performance.
Specific step is as follows:
First, by maximized each the sum of reachable rate for facing null base station, power control and beam gain distribution are split asSubproblem and wave beam forming two sub-problems, and introduce intermediate variableIt is converted.
Under ideal wave beam forming, beam gain meets:
Power control and beam gain distribution subproblem statement as a result, are as follows:
Reach maximization up to the sum of rate are as follows:
The condition that need to meet is as follows:
p1+p2=P
The statement of wave beam forming subproblem are as follows:
Wherein, α is the intermediate variable introduced, so that each component of wave beam forming vector approaches permanent modular constraint condition；[w]iIndicate i-th of element of w；
Then, to after conversion power control and beam gain distribution subproblem solve；
The reachable rate of space base 2 is equal to its minimum reachable rate and constrains when the problem acquires optimal solution, i.e.,
Power control is obtained by derivation and beam gain distributes the optimal solution of subproblem are as follows:
Simultaneously, the wave beam forming subproblem after conversion is solved；
DefinitionWave beam forming subproblem becomes:
Suitable the amount of phase rotation is selected by phase rotationSo thatIt is real number, wave beam forming subproblem is convertedAre as follows:
The convex optimization problem of several standards is further decomposed into, it is corresponding when by search w acquirement optimal solutionPhase,It givesSo that it is become linear restriction multiplied by different phases, obtain the convex optimization problem of a series of standard of equal value:
Wherein M is phase search total number, m=1,2..., M.
It is solved with the convex optimization tool of standard, that solution that α is minimized in all optimization problems is selected to be denoted asThenPower normalization is carried out to wave beam forming vector
Finally, rightPermanent mould normalization is carried out, is keptThe phase invariant of each component uniformly becomes lengthTableIt is as follows up to formula:
Final power distribution and beamforming scheme as a result, respectivelyAnd w*。
The present invention has the advantages that
1), one kind faces sky array communications non-orthogonal multiple access downlink transmission method, can double up and face empty communicationIn face null base station/terrestrial user access quantity；
2), one kind faces sky array communications non-orthogonal multiple access downlink transmission method, co-design transmitting terminal wave beam formingPower distribution can effectively improve spectrum efficiency, that is, maximize up to the sum of rate；
3), one kind faces sky array communications non-orthogonal multiple access downlink transmission method, has lower computation complexity, energyEnough realize fast beam figuration and power distribution.
Detailed description of the invention
Fig. 1 is model of place schematic diagram of the ground base station of the present invention to multiple downlink transfers for facing null base station；
Fig. 2 is downlink phased-array antenna structure schematic diagram in the present invention；
Fig. 3 is a kind of flow chart for facing sky array communications non-orthogonal multiple and accessing downlink transmission method of the present invention.
Specific embodiment
Below in conjunction with drawings and examples, the present invention is described in further detail.
One kind of the present invention faces sky array communications non-orthogonal multiple access downlink transmission method, with ground base station to facing null base stationFor downlink transfer, ground base station accessed on same time domain/frequency domain/code domain resource block it is multiple face null base station, in power domainThey are distinguish.Ground base station faces empty signal mixing transmission multiple, respectively faces null base station and is done according to efficient channel gainCorresponding sequence out, channel gain is lower, and priority is higher, and assigned power is also higher.In this manner it is achieved that being adopted in receiving endIt is decoded with serial interference elimination (SIC) method, the high signal priority of priority is decoded, and is each faced null base station and is only needed to decodeThe signal higher than oneself priority, and these strong jammings are cut in mixed signal, finally decode the signal of oneself.By thisNon-orthogonal multiple access way not only increases the quantity for facing null base station, and improves the availability of frequency spectrum.The present invention is this non-Orthogonal access mode is equally applicable to face the downlink transfer scene and ground base station of null base station and terrestrial user while takeIt is engaged in the scenes of multiple low latitude unmanned planes.
As shown in Figure 3, the specific steps are as follows:
Step 1: facing sky non-orthogonal multiple access communications system for downlink, constructing ground base station and facing between null base stationCommunication scenes.
Communication scenes include: 1. ground base stations to multiple downlink transfers for facing null base station；2. facing null base station to multiple groundThe downlink transfer of user；3. the downlink transfer that ground base station services multiple low latitude unmanned planes.
For the first ground base station to the scene of multiple downlink transfers for facing null base station, as shown in Figure 1, specific building is such asUnder:
Ground base station has N member aerial array, and 2 single antenna are connected in same time domain/frequency domain/code domain resource block and are remotely facedNull base station, it is respectively space base 1 and space base 2 that two, which are faced null base station,.As shown in Fig. 2, every antenna branch has in ground base station one endOne phase converter (Phase Shifter) and power amplifier (Power Amplifier, PA), own under normal conditionsPower amplifier have identical scale factor, therefore wave beam forming vector, i.e. antenna weight coefficient vector (Antenna WeightVector, AWV) each component mould length it is equal, referred to as permanent modular constraint (Constant-modulus, CM).
Step 2: being directed to the first model of place, ground base station will believe all power normalizations for facing null base station transmissionNumber it is overlapped transmitting；
Ground base station is s to the power normalization signal that space base i (i=1,2) is senti, wherein the expectation of each signalSignal siTransmission power be pi, ground base station is by s1And s2Superposition transmitting, expression formula are as follows:
Step 3: superposed signal s by ground base station and after facing the channel response between null base station and antenna noise shapeAt mixed signal, and faces null base station by two and respectively receive；
2 space base received signals are respectively as follows:
y1To face the received mixed signal of null base station 1；y2To face the received mixed signal of null base station 2.
Wherein hiIt is the channel response vector of ground base station and space base i, w indicates the wave beam forming vector under permanent modular constraint,Its permanent modular constraint is that each component mould length is equalN is ground base station antenna number, niIndicate emptyWhite Gaussian noise on base i antenna, mean power are denoted as σ2。
Step 4: ground base station uses the uniform linear array antenna of half-wave spacing, and each faces between null base station and carry outMillimeter wave beam communication obtains and respectively faces the channel response vector of null base station；
Ground base station and the channel response vector h for facing null base station iiFormula are as follows:
Wherein λi,lIndicate the complex coefficient of the l articles diameter of space base i, LiIndicate the multipath component total number for facing null base station i,Ωi,lIndicate the l articles diameter of space base i in the cosine value of the ground base station angle of departure, i.e. cos (AoD)；A () indicates to be directed toward vectorFunction, expression formula are as follows:
A (N, Ω)=[ejπ0Ω,ejπ1Ω,ejπ2Ω,…,ejπ(N-1)Ω] (4)
A (N, Ω) depends on the geometry of array antenna；Use θi,lIndicate the angle of departure for facing the l articles diameter of null base station iValue, and Ωi,l=cos (θi,l)。
Step 5: selecting the channel response vector on most strong path as ground base station for each path for facing null base station iWith the efficient channel response vector h for facing null base station ii；
hi=λia(N,Ωi) (5)
Wherein λiIndicate the complex coefficient in the most strong path of space base i, i.e., | λi|≥|λi,l|。
Step 6: using the wave beam forming vector w under permanent modular constraint, the efficient channel gain to null base station is respectively facedCorresponding sequence is made, the decoding priority orders of each space base signal are obtained.
Efficient channel gain depends on channel gain and array gain, and efficient channel gain is lower, and decoding priority is higher；
For | λ1| > | λ2|, i.e. the channel gain of space base 1(NOMA) is accessed according to non-orthogonal multipleCriterion, ground base station will carry out corresponding power distribution, the lower space base priority of channel gain according to the priority of space baseIt is higher；The signal that priority when the signal decoding of space base 2 is higher than space base 1 decodes priority；
For efficient channel gainPriority is higher than the signal solution of space base 2 when the signal decoding of space base 1Code priority；
Step 7: being ordered as efficient channel gainGround base station will emit signal s2Preferential solutionCode simultaneously eliminates in the signal of superposition, and further decoding emits signal s1, space base 2, which directly decodes, emits signal s2, obtain each space baseUp to rate；
It is eliminated from the signal of superposition using serial interference elimination method (SIC) by signal is emitted at space base end；Optimal solutionCode sequence is successively decoded from low to high according to channel gain, and in this order, each space base first decodes priorityHigh space base signal is deleted them in receiving signal, finally decodes the signal of oneself and no longer by the high (power of priorityIt is high) space base effect of signals.In this way, space base 1 can be deleted by serial interference and be avoided in space base NOMA system of the inventionThe influence of 2 signal of space base；The space base high as priority of space base 2 need not be deleted using serial interference.In brief, space base 1 is firstFirst decode s2, in its reception signal y1It is middle s2It deletes, then decodes s1；And space base 2 is s1Interference as noise processed, directlyDecode s2。
The reachable rate of two space bases is calculated separately using shannon formula, as follows:
R1For the reachable rate of space base 1；R2For the reachable rate of space base 2；
Step 8: when all the sum of reachable rates for facing null base station reach maximization, the distribution of design joint Power and wave beamThe constraint condition that figuration need to meet.
Reach maximization i.e. objective function up to the sum of rate, as follows:
The above space base up to rate calculation formula obtain premise have it is assumed hereinafter that: space base 1 decode s2When Signal to Interference plus Noise Ratio(SINR) otherwise s is decoded lower than space base 22Signal to Interference plus Noise Ratio, otherwise will lead to space base 1 decode s2Rate be lower than space base 2, thenAccording to above-mentioned reachable rate calculation formula, space base 1 is in decoding s1Shi Wufa deletes s completely2Interference；This is claimed to be assumed to be implicit letterIt is dry to make an uproar than it is assumed that as follows:
To obtain reasonable power distribution and beam form-endowing method, the constraint condition that need to meet is as follows:
Wherein riIndicate the minimum reachable rate constraint for facing null base station i；P is the maximum power for facing the transmitting signal of null base station.
Step 9: solving to the constraint condition that need to meet, respectively faced the corresponding power distribution of null base station and ground base stationBeamforming scheme, obtain good performance.
Specific step is as follows:
First, by maximized each the sum of reachable rate for facing null base station, power control and beam gain distribution are split asSubproblem and wave beam forming two sub-problems, and introduce intermediate variableIt is converted.
Under ideal wave beam forming, beam gain meets:
Power control and beam gain distribution subproblem statement as a result, are as follows:
Reach maximization up to the sum of rate are as follows:
The condition that need to meet is as follows:
The statement of wave beam forming subproblem are as follows:
Wherein, α is the intermediate variable introduced, so that each component of wave beam forming vector approaches permanent modular constraint condition；[w]iIndicate i-th of element of w；
Then, to after conversion power control and beam gain distribution subproblem solve；
By to the problem objective function derivation, it can be found that objective function is p1Increasing function, and the reachable rate of space base 1It is p1Increasing function, the reachable rate of space base 2 is p1Subtraction function, then the reachable rate of space base 2 is necessarily etc. when the problem takes optimal solutionIt is minimum up to rate constraint in it, it may be assumed that
P as a result,1,p2,c2C can be used1It indicates, which becomes about c1Single argument optimization problem, can by derivationTo obtain its optimal solution are as follows:
Simultaneously, the wave beam forming subproblem after conversion is solved；
DefinitionWave beam forming formula (11) becomes:
Obviously, wave beam forming vector w can integrally carry out phase rotation, and not interfere with the value of beam gain,So if w is optimal solution,It is also optimal solution, whereinRepresent the amount of phase rotation, value range be [0,2 π).Do not lose oneAs property, suitable the amount of phase rotation is selected by phase rotationSo thatIt is real number, wave beam forming subproblem is converted are as follows:
Further decompose into the convex optimization problem of several standards, it can be seen that the last one constraint condition of formula (15)The sign of inequality left side is the ABS function of a linear function, and the right is a constant, is substantially to requireMould length be not less thanBecause not knowing that optimal solution is correspondingPhase, therefore cannot be equally simpleIt regards real number as, but passes through corresponding when search w acquirement optimal solutionPhase, giveMake its change multiplied by different phasesLinear constraint can always find the optimal solution of the problem as long as the phase of search is accurate enough；It finally obtains and formula (15)The convex optimization problem of a series of standard of equal value:
Wherein M is phase search total number, m=1,2..., M.Correspondence is searched for each time, it is clear that M is bigger, and search precision is got overHeight, obtained solution are more accurate；This M problem can be solved with the convex optimization tool of standard, and α in all optimization problems is selected to takeThat solution of minimum value is denoted asThen power normalization is carried out to wave beam forming vector
Finally, rightPermanent mould normalization is carried out, is keptThe phase invariant of each component uniformly becomes lengthTableIt is as follows up to formula:
In final power distribution and beamforming scheme as a result, respectively formula (13)In formula (17)W*。