CN105763309A - Chain-typed net large-scale MIMO system pilot frequency pollution mitigating scheme - Google Patents
Chain-typed net large-scale MIMO system pilot frequency pollution mitigating scheme Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
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- H04B17/00—Monitoring; Testing
- H04B17/30—Monitoring; Testing of propagation channels
- H04B17/309—Measuring or estimating channel quality parameters
- H04B17/336—Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
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- 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
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- H04B7/024—Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
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- H04L25/0204—Channel estimation of multiple channels
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- H04L5/1469—Two-way operation using the same type of signal, i.e. duplex using time-sharing
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Abstract
The invention discloses a chain-typed net large-scale MIMO system pilot frequency pollution mitigating scheme, and provides a new pilot frequency pollution mitigating scheme specific to characteristics of a chain-typed net large-scale MIMO time-division duplex (TDD) system. In the scheme, each district is divided into a left zone and a right zone, and orthogonal pilot frequency sequences are divided into three sets. Three sets of pilot frequency sequences are successively and circularly distributed to users of left and right zones in a chain-typed net, thereby arranging orthogonal pilot frequency sequences for a target user and adjacent areas, allowing the target user and farther area users to reuse the pilot frequency sequences, and thereby mitigating pilot frequency pollution. Simulation results show that the scheme saves uplink channel estimation time, and obtains a throughput capacity better than a pilot frequency power control method; in addition, compared with a pilot frequency enumeration method, the scheme has a small calculated amount, and possesses certain practical values.
Description
Technical field
Present invention relates particularly to pilot pollution in the extensive mimo system of chain network and alleviate scheme, belong to radio communication uplink channel estimation technical field.
Background technology
Extensive MIMO (" Large-ScaleMIMO " or " MassiveMIMO ") technology, just can increase power system capacity by directly increasing the antenna number of base station, reduce user emission power.And along with the increase of antenna for base station number, noise and the interference in community can be left in the basket.
1. the pilot pollution problem analysis
In the uplink channel estimation of extensive MIMO multiple cell TDD (Time-divisionDuplex) system, adopting mutually orthogonal pilot tone in each community, minizone adopts identical pilot frequency sequence group.All community users send the pilot tone vector that length is τ (τ >=N) simultaneously.If all community kth users send pilot tone simultaneously(meet normalizing condition), base station and user locate mean power (during transmitting) respectively pfAnd ρr, now the reception signal of i-th base station is:
Wherein ginlIt is nth user's channel vector to i-th cell base station of l community, ziSeparate additive noise for M × τ.The kth subscriber channel estimates of parameters of i-th base station is
WhereinIt can be seen that the channel parameter estimated exists the interference that Target cell is estimated by other communities from the Section 2 of formula (2), i.e. pilot pollution (PilotContamination).The main cause that it produces is in uplink channel estimation, same set of pilot frequency sequence or non-orthogonal pilot frequency sequence is used as the user of different districts, cause that the result that base station end carries out channel estimating is not the channel between local user and base station, but sent the estimation after user's pollution of non-orthogonal pilot sequence by other communities.
Assume that the upstream data power that each user sends is identical.According to the channel parameter that formula (2) obtains, upstream data is carried out MRC (Maximum-ratiocombining) and merges by base station side.As antenna for base station M → ∞, the i-th base station upstream data s to kth userkiThe signal interference ratio SIR (SignaltoInterferenceRatio) of estimated value is
It can be seen thatIt is limited mainly by other communities and adopts the channel slow fading factor beta of same pilot or non-orthogonal pilot signaling useriklImpact.When the interference user of distribution same pilot is more remote to Target cell distance, its slow fading coefficient is more little,It is worth more big.
It is similarly assumed that the downlink data power that each base station sends is identical.According to the channel parameter that formula (2) obtains, downlink data is carried out linear predictive coding by base station side.As antenna for base station M → ∞, the signal interference ratio of kth user's downlink reception data estimation value of i-th base station is
It can be seen that as antenna for base station M → ∞,WithDifferent, it is with slow fading factor betalkiRelevant, namely closely related to the distance of base station, interfered cell with targeted customer.Targeted customer is more little to the slow fading coefficient of base station, interfered cell,It is worth more big.
As can be seen from the above analysis, pilot pollution seriously limits the value of signal interference ratio, thus also limit the channel capacity that extensive MIMO communication system can reach.
2, correlational study scheme
For the pilot pollution problem that extensive MIMO uplink channel estimation exists, domestic and international researcher has be carried out correlational study.(the Wang Hairong such as Wang Hairong, Wang Yuhui, yellow Yongming, Yang Lvxi. the pilot pollution in extensive MIMO beehive network system alleviates method [J]. communication journal, 2014,35 (1): 24-33.) all communities in cellular network being divided into two classes, each community within same class adopts identical pilot frequency sequence group, and the community between inhomogeneity adopts pilot power control method, alleviate each district pilots within same class and pollute.The program has certain practicality, but is only applicable to cellular network.(the Wang Hairong such as Wang Hairong, Wang Yuhui, yellow Yongming, Yang Lvxi. the pilot pollution in extensive MIMO multiple cell TDD system alleviates method [J]. signal processing, 2013,29 (2): 171-180.) the neighboring cell pilot sequence that staggers in one-dimensional Multi-cell model sends the time, thus avoiding the pilot pollution of neighbor cell.Program channel estimation time is longer, and signal interference ratio is limited to the interference simultaneously sending pilot cell.(the NEUMANNDavid such as NEUMANNDavid, etal..Pilotcoordinationforlarge-scalemulti-cellTDDsystem s [C] .201418thInternationalITGWorkshoponSmartAntennas (WSA), Erlangen, Germany, 2014:1-6.) according to extensive mimo system data transmission signal interference ratio only this conclusion relevant to slow fading coefficient, list the situation that all pilot tones distribution of all communities is possible, calculate the total speed of system in every kind of possible situation.The total speed of system is allowed to reach that maximum group pilot tone distribution, it is simply that optimal pilot distributes.The program is along with the increase of community number, number of users, and algorithm amount of calculation increases therewith.
From above existing algorithm, any pilot pollution alleviates scheme and all to pay a price.And can not be completely eliminated in pilot pollution real system, alleviate pilot pollution only by effective ways.
Summary of the invention
For overcoming the defect of prior art, alleviating pilot pollution, the present invention proposes pilot pollution in the extensive mimo system of chain network and alleviates mainly comprising the following steps of scheme:
1, initial scene setting:
1-1) in the extensive mimo system model of Fig. 1 chain network multiple cell, the system that arranges adopts tdd mode.
Community 1-2) arranging L non-cooperating uses same frequency band.
1-3) heart arranges base station in each cell, and there is M root antenna base station.
1-4) centered by base station, each community arranges and is divided into Zuo Qu and You Qu.Each community arranges N number of single-antenna subscriber, is evenly distributed in community, and namely each community Zuo Qu is identical with the number of users in right district, is
2, scheme realizes step:
Zuo Qu and You Qu 2-1) arranging each community has identical number of users.Namely the left district Customs Assigned Number arranging each community is Right district Customs Assigned Number is
2-2) when system carries out uplink channel estimation, employing length isPilot tone vectorAnd meet normalizing condition
2-3) pilot frequency sequence that length is τ is divided into three groups, namely obtains mutually orthogonal pilot frequency sequence group
2-4) as shown in Figure 1.By three groups of pilot frequency sequence groups successively, be cyclically allocated.Namely the right district user of i-th community adopts pilot frequency sequence groupThen the left district user of (i+1) community adopts pilot frequency sequence groupThe left district user of i-th community and the right district user multiplexed pilot sequence set of (i+1) communityBy that analogy.Namely targeted customer is adjacent the closely user in region and arranges orthogonal pilot frequency sequence, and targeted customer and zone user multiplexed pilot sequence farther out.
2-5) as shown in Figure 1.For the user of multiplexed pilot sequence set, arrange the left district the of i-th communityThe right district of individual user and (i+1) community theIndividual user uses identical pilot frequency sequence.The right district of the 1st, the left district of such as i-th community user and (i+1) community theIndividual user uses identical pilot frequency sequence.By that analogy.
Beneficial effect
Length, to chain network extensive MIMO multiple cell TDD system feature, when uplink channel estimation is by this programmePilot frequency sequence be divided into mutually orthogonal pilot frequency sequence group so that the closely user that targeted customer is adjacent arranges orthogonal pilot frequency sequence, and targeted customer and relatively remote subscriber's multiplexed pilot sequence, is effectively reduced pilot pollution.As antenna for base station M → ∞, this paper new departureIt is limited mainly by relatively remote and is arranged the same pilot sequence user channel slow fading index impacts to Target cell,It is limited mainly by targeted customer's channel slow fading index impacts to the cell base station being arranged same pilot sequence user, is effectively increased signal interference ratio.Simulation result shows, this programme is more suitable for the situation that community user number is many, and simple, more has significant practical applications.
Accompanying drawing explanation
Fig. 1 is chain network multiple cell extensive mimo system model: each cell base station is located at center of housing estate, and there is M root antenna base station.Centered by base station, little divide into Zuo Qu and You Qu by each.There is N number of single-antenna subscriber each community, is evenly distributed in community, and namely each community Zuo Qu is identical with the number of users in right district, is
Fig. 2 is TDD host-host protocol in coherence time: have T OFDM symbol within coherence time.In Fig. 2, in coherence time, TDD host-host protocol is divided into four parts: 1. τupThe transmission of individual upstream data；2. the transmission of τ uplink pilot sequence；3. the process etc. of channel estimating, upstream data and pre-coding matrix, amounts to a symbol；④τdownThe transmission of individual downlink data.Therefore T=τ in each coherence timeup+1+τ+τdown。
Tu3Wei community number, slow fading coefficient are certain, and when number of users is different, community user uplink throughput compares (L=5, b1=0.5；B2=0.11；B3=0.0625；B4=0.04).
Tu4Wei community number, number of users are certain, cell uplink throughput ratio relatively (N=6, L=5, B1:b1=0.4 under slow fading coefficient different situations；B2=0.11；B3=0.0625；B4=0.04, B2:b1=0.7；B2=0.21；B3=0.05；B4=0.01)
Fig. 5 is that slow fading coefficient, number of users are certain, cell uplink throughput ratio relatively (N=6, b1=0.5 when community number is different；B2=0.11；B3=0.0625；B4=0.04).
Tu6Wei community number, slow fading coefficient are certain, and under number of users different situations, community user downlink throughput capacity compares (L=5, b1=0.5；B2=0.11；B3=0.0625；B4=0.04).
Tu7Wei community number, number of users are certain, cell downlink throughput ratio relatively (N=6, L=5, B1:b1=0.4 under slow fading coefficient different situations；B2=0.11；B3=0.0625；B4=0.04, B2:b1=0.7；B2=0.21；B3=0.05；B4=0.01).
Fig. 8 is that slow fading coefficient, number of users are certain, cell downlink throughput ratio relatively (N=6, b1=0.5 under the number different situations of community；B2=0.11；B3=0.0625；B4=0.04).
Detailed description of the invention
Below in conjunction with accompanying drawing, technical scheme is further detailed.
1, the channel estimating of new departure
The symbol definition used in this programme is as follows: (Α)T、(A)*、(A)+The transposition of representing matrix Α, conjugation, conjugate transpose respectively.Operative symbol E{ } represent mathematic expectaion.
In Fig. 1, system adopts tdd mode.Assume that the community having L non-cooperating uses same frequency band.Each cell base station is located at center of housing estate, and there is M root antenna base station.Centered by base station, little divide into Zuo Qu and You Qu by each.There is N number of single-antenna subscriber each community, is evenly distributed in community, and namely each community Zuo Qu is identical with the number of users in right district, isThe channel parameter assumed between kth user and the m root antenna of (i-1) individual community of i-th community isChannel parameter constitutes vector g(i-1)ki=(g1(i-1)ki,g2(i-1)ki,…,gM(i-1)ki)T.Wherein hm(i-1)ki～CN (0,1) (meets the multiple Gauss of Cyclic Symmetry) for rapid fading coefficient, h within coherence timem(i-1)kiKeep constant, i.e. flat fading.Rapid fading coefficient constitutes rapid fading vector h(i-1)ki=(h1(i-1)ki,h2θii-1)ki,…,hM(i-1)ki)T, and h(i-1)ki～CN (0, IM)。For slow fading coefficient, mainly include shadow fading and path fading.Wherein α(i-1)kiFor constant, it it is the shadow fading coefficient obeying logarithm normal distribution；d(i-1)kiFor the kth user of i-th community to the distance of (i-1) individual cell base station；γ is path fading index, and span is generally 2～6.Assume that the aerial array that the M root antenna of same base station forms is sufficiently compact, then the M root antenna of same base station is had identical slow fading coefficient by a certain user, and thinks that slow fading coefficient is the constant that anticipated that.It can be seen that the size of slow fading coefficient is closely related to the distance of base station with user, distance is more remote, and slow fading coefficient is more little.
This programme discusses for left district user.Assume that all community users send pilot tone simultaneously.Base station and user locate mean power (during transmitting) respectively pfAnd ρr.This programme considers in chain network, i-th community only receive be adjacent (i+1), (i+2), (i-1), (i-2) individual community user send signal, ignore other distant community interference to Target cell.
Now i-th base station received signal is:
Wherein ψnlIt it is the pilot tone vector of the nth user of l community；ziSeparate additive noise for M × τ.If for the left district user of i-th base station, then the left district of i-th base stationIndividual subscriber channel estimates of parameters is
Wherein
In like manner, the of i-th base stationGe You district subscriber channel estimates of parameters is
From formula (6) (7) although second and third it can be seen that the channel parameter estimated still suffers from the interference that Target cell user is estimated by other communities, but interference is both from relatively remote subscriber, is effectively reduced pilot pollution.
2, the transmitting uplink data analysis of new departure
When transmitting uplink data, herein for the left district user of i-th base station, namelyAssume that the nth user of l community sends upstream data snl, then N number of user of l community sends upstream data Sl=[s1l,…sNl]T。SlMeet E{Sl}=0,Now i-th base station received signal is:
Wherein υi∈M×1It is additive noise, υi～CN (0,1).
I-th base station uses MRC (Maximum-ratiocombining) method to estimate skiValue:
In order to calculate as M → ∞, the value of formula (9), we use following lemma 1.
Lemma 1: if x, y be ∈ CM×1Two Independent Vector obey CN (0, cI), then
With
As antenna for base station M → ∞, owing to the channel vector of different user is statistical iteration, and hikl～CN (0, IM).According to lemma 1, can obtain
As antenna for base station M → ∞, the channel parameter of each terminal to base station is statistical iteration, and each subscriber channel parameter is also independent with noise.According to lemma 1 and formula (12) conclusion, can obtain in formula (9)
According to above analysis, it is possible to obtain skiEstimated value be
Assume that each user sends upstream data power identical.The i-th base station upstream data s to kth user (left district) is obtained according to formula (17)kiThe signal interference ratio of estimated value is
It can be seen that as antenna for base station M → ∞, adopt pilot arrangement scheme herein,It is limited mainly by relatively remote and is arranged the same pilot sequence user channel slow fading index impacts to Target cell.
3, the downlink data transmission analysis of new departure
When downlink data transmission, herein for the left district user of i-th base station, namelyDuring downlink data transmission, base station side precoding beam forms vector and is
Due to the reciprocity of TDD system channel, namely think that channel parameter when uplink and downlink data are transmitted is identical.Assume qnlBe the downlink data that sends to nth user of the l community, then the downlink data that the l community sends N number of user is ql=[q1l,…qNl]T。qlMeet E{ql}=0,The kth left district user downlink data q of i-th communitykiEstimated value be
Wherein to user additive noise z usedkiIt is independent identically distributed, and zki～CN (0,1).Order receives the mean power of signal
Five kinds of situations of lower surface analysis.
1. as l=i,
According to lemma 1 and formula (12) conclusion,
2. as l=i-2,
Because the right district of the left district kth user of i-th community and (i-2) community theIndividual user uses identical pilot tone sequence
Row.According to lemma 1 and formula (12) conclusion,
3. as l=i+1,Analysis method, with 2. identical, obtains
4. as l=i+2,
According to lemma 1 and formula (12) conclusion, obtain
5., as l=i-1, method of analyzing, with 4. identical, obtains
Owing to the variance of noise is definite value, as antenna for base station M → ∞, effect of noise is almost nil.By above analysis, it can be seen that kth user (left district) the downlink data q of i-th communitykiEstimated value be made up of formula (23) (25) (26) three.
As antenna for base station M → ∞, adopt pilot arrangement scheme herein, kth user (left district) the downlink data q of i-th communitykiThe signal interference ratio of estimated value is
It can be seen that as antenna for base station M → ∞,WithDifferent, it is limited mainly by targeted customer's channel slow fading index impacts to the cell base station being arranged same pilot sequence user.
In above-mentioned analysis, it is considered to be chain network middle cell.For the most community, two ends of chain network, owing to interfered cell is reduced, pilot pollution can be less, and uplink and downlink data signal interference ratio improvement amount can be bigger.
4, scheme measurement index
Assume in TDD host-host protocol, within coherence time, have T OFDM symbol, and channel keeps constant.TDD host-host protocol according to Fig. 2, in scheme, the handling capacity of i-th community kth user uplink is herein
In scheme, the total throughout of i-th cell uplink is herein
In downlink data transmission, in scheme, i-th community kth user's downlink throughput capacity is herein
In downlink data transmission, in scheme, the total throughout of i-th cell downlink is herein
From formula (31)-(34) it can be seen that in same coherence time, handling capacity is not only relevant with the signal interference ratio of each user, also relevant with channel estimation time.In same coherence time, channel estimation time is more long, and the ratio that data transmission period accounts for coherence time is more little.
5, simulation result
5.1 simulated conditions
Due to this programme is thought chain network i-th community only receive be adjacent (i+1), (i+2), (i-1), (i-2) community user send signal, ignore other distant community interference to Target cell.Therefore in numerical simulation model, emphasis considers the situation that community number is 3 and 5.
In numerical simulation, it is assumed that community number is L, community user number is that N, base station and user locate mean power (during transmitting) respectively Pf=20dB, Pr=10dB.For chain network feature, to slow fading factor betalkiTake normalized value, if i.e. l=i, direct gain (directgain) βiki=1；If l ≠ i, due to dikl> dikiAnd γ > 1, so cross-gain (crossgain) βikl< 1, and from i-th Target cell more away from, βiklMore little.Emulation defines: whenTime, βik(i+1)=b1、βik(i+2)=b3、βik(i-1)=b2、βik(i-2)=b4；WhenTime, βik(i+1)=b2、βik(i+2)=b4、βik(i-1)=b1`、βik(i-2)=b3.Pilot frequency sequence adopts Zadoff-Chu (ZC) sequence with constant amplitude, zero autocorrelation.In order to effectively analyze the performance of various pilot tone delivery plan, it is assumed that only catch row or downlink data in each coherence time.It is the same when each subcarrier of each OFDM symbol.Emulate the situation only considering an OFDM symbol single carrier herein.
In numerical simulation, relative for this paper scheme pilot power control method, pilot tone listing technique have been carried out com-parison and analysis by emphasis.Feature according to chain network, the interference of the uplink channel estimation of the kth user of the i-th base station of pilot power control method uses same pilot sequence user from (i-2), (i+2) two community farther out.Its upstream data skiThe signal interference ratio of estimated value is
The i-th base station of the pilot power control method downlink data q to kth userkiThe signal interference ratio of estimated value is
Pilot tone listing technique is listed under the optimal pilot allocative decision premise selected, and the interference of the uplink channel estimation of the kth user of its i-th base station uses same pilot sequence user from (i-2), (i+2), (i+1), (i-1) community.Its upstream data skiThe signal interference ratio of estimated value is
The i-th base station of the pilot tone listing technique downlink data q to kth userkiThe signal interference ratio of estimated value is
5.2 transmitting uplink data analysiss of simulation result
1. community number, slow fading coefficient are certain, when number of users is different
From figure 3, it can be seen that under the same conditions, every community user number N is more big, and scheme user uplink handling capacity to be more better than pilot power control method herein.This is because pilot power control method staggers in chain network neighboring cell pilot sequence send the time, its pilot pollution from community farther out, by formula (18) (35) it can be seen that itThan scheme is bigger herein.But scheme uplink channel estimation within each coherence time needs hereinThe individual OFDM symbol time, and pilot power control method needs 2N OFDM symbol time.Scheme saves hereinThe individual OFDM symbol time.Under the same conditions, N is more big, and the time that scheme channel estimating is saved herein is more many, and user uplink handling capacity is more better than pilot power control method.Such as, when working as M=200, N=6, the user uplink throughput ratio big 0.85bit/s/Hz of pilot power control method of scheme herein.When every community user number N is less, the time that scheme channel estimating is saved herein diminishes along with the reduction of N, and again because the pilot pollution of pilot power control method is more smaller than this paper scheme, therefore the uplink user handling capacity of pilot power control method is slightly better than scheme herein.Such as, when working as M=200, N=2, the user uplink throughput ratio of pilot power control method scheme herein is than bigger 0.2bit/s/Hz.
From analogous diagram 3 it can be seen that under the same conditions, when n is large, pilot tone listing technique is better than scheme herein.Such as, when working as M=200, N=6, the user uplink throughput ratio of pilot tone listing technique is the big 0.7bit/s/Hz of scheme herein.This is because by formula (18) (37) although it can be seen that pilot tone listing technique selects optimal pilot allocative decision, but its pilot pollution is bigger than scheme herein, itsThan scheme is little herein, and in each coherence time, channel estimating needs N number of OFDM symbol time.And scheme needs hereinThe individual OFDM symbol time.When N is more big, it is more long that pilot tone listing technique uplink channel estimation saves the time, and therefore user uplink handling capacity is more big.But pilot tone listing technique need to list the situation that all pilot tones distribution of all communities is possible, calculatesPlant the total speed of system in the situation of possibility.Such as τ=N=6, L=5, about 2.69 × 10 need to be calculated11Planting the total speed of system in the situation of possibility, amount of calculation is quite big, and practical application is not strong.When N is less, pilot tone listing technique advantage is also inconspicuous.This is because every community user a few hours, time phase difference shared by both scheme channel estimating is little, and the pilot pollution of pilot tone listing technique is bigger than this paper scheme.
2. community number, number of users are certain, the situation that slow fading coefficient is different
N=6, L=5 is set during emulation.Slow fading coefficient two groups different is adopted to combine, wherein B1 scheme: neighbor cell decline is very fast, slow fading coefficient is less；B2 scheme: neighbor cell slowly declines, slow fading coefficient is bigger.From fig. 4, it can be seen that this paper scheme and pilot tone listing technique, the cell uplink handling capacity of employing B1 scheme is better than adopting situation during B2 scheme.This is because by formula (18) (37) it can be seen that in chain network, the decline of employing B1 scheme neighbor cell is very fast, slow fading coefficient is less, pilot pollution is also little, itsJust big.The cell uplink handling capacity of pilot power control method employing B1, B2 scheme is close.This is because by the pilot pollution of pilot power control method in formula (35) known chain network from community farther out, and the slow fading coefficient of community is all less farther out, therefore adopts B1, B2 scheme pilot pollution not have significant change.
When community number, number of users are certain, when slow fading coefficient changes, the pilot pollution of scheme and pilot tone listing technique reduces therewith simultaneously or increases herein, itsAlso increase therewith simultaneously or reduce.By the pilot pollution of the known pilot power control method of formula (35) from community farther out, affected less by slow fading index variation.According to 5.2 analyses 1., scheme is better than pilot power control method, is inferior to pilot tone listing technique herein.
3. slow fading coefficient, number of users are certain, the situation that community number is different
N=6 is set during emulation.From figure 5 it can be seen that as community number L=3, the cell uplink handling capacity of every kind of scheme is slightly better than situation during L=5.This is because in chain network, community decline is very fast farther out, slow fading coefficient is all less.When community number reduces, by formula (18) (35) (37) it can be seen that the pilot pollution of uplink channel estimation also slightly reduces, itsAlso increase therewith.Therefore along with the reduction of community number, the cell uplink handling capacity of every kind of scheme slightly promotes.When community number reduces or increases, the pilot pollution of various schemes also reduces therewith or increases.According to 5.2 analyses 1., scheme is better than pilot power control method, is inferior to pilot tone listing technique herein.
5.3 downlink data transmission analysiss of simulation result
1. community number, slow fading coefficient are certain, the situation that number of users is different
From fig. 6, it can be seen that under the same conditions, N is more big, and scheme user's downlink throughput capacity to be more better than pilot power control method herein.This is because by formula (30) (36) although it can be seen that herein the distracter of scheme downlink data estimated value is more bigger than pilot power control method, itsMore smaller than pilot power control method, but within each coherence time, channel estimation time is fewer than pilot power control methodThe individual OFDM symbol time.When N is more big, the time that scheme channel estimating is saved herein is more many, and user throughput is more better than pilot power control method.Such as, when working as M=200, N=6, user's downlink throughput capacity 1.2bit/s/Hz bigger than pilot power control method of scheme herein.When every community user number N is less, the time that scheme channel estimating is saved herein diminishes along with the reduction of N, and therefore user's downlink throughput capacity of pilot power control method is slightly better than scheme herein.Such as, when working as M=200, N=2, the user throughput of pilot power control method 0.2bit/s/Hz more bigger than scheme herein.
It can be seen that N is more little from analogous diagram 6, scheme user's downlink throughput capacity to be more better than pilot tone listing technique herein.Such as, when working as M=200, N=6, user's downlink throughput capacity 0.8bit/s/Hz bigger than pilot tone listing technique of scheme herein.When working as M=200, N=2, user's downlink throughput capacity 2.45bit/s/Hz bigger than pilot tone listing technique of scheme herein.This is because known by formula (4), as antenna for base station M → ∞,Closely related to the distance of base station, interfered cell with targeted customer.Although pilot tone listing technique channel estimating within each coherence time is fewThe individual OFDM symbol time, but by formula (38) it can be seen that the distracter of its downlink data estimated value is than scheme is much bigger herein, itsThan scheme is little herein.And pilot tone listing technique is as τ=N=6, L=5, need to calculate about 2.69 × 1011Planting the total speed of system in the situation of possibility, amount of calculation is quite big.
2. community number, number of users are certain, the situation that slow fading coefficient is different
N=6, L=5 is set during emulation.Slow fading coefficient two groups different is adopted to combine.B1 scheme: neighbor cell decline is very fast, slow fading coefficient is less；B2 scheme: neighbor cell slowly declines, slow fading coefficient is bigger.From figure 7 it can be seen that this paper scheme and pilot tone listing technique, the cell downlink handling capacity of employing B1 scheme is better than adopting situation during B2 scheme.This is because by formula (30) (38) it can be seen that in chain network, the decline of employing B1 scheme neighbor cell is very fast, slow fading coefficient is less, when downlink data is estimated, interference value is also little,Also increase.The cell downlink handling capacity of pilot power control method employing B1, B2 scheme is close.This is because interference value is from community farther out when in chain network, the downlink data of pilot power control method is estimated, and the slow fading coefficient of community is all less farther out, by formula (36) it can be seen that itsChange is little, therefore adopts B1, B2 scheme pilot pollution not have significant change.
When community number, number of users are certain, when slow fading coefficient changes, when scheme is estimated with pilot tone listing technique downlink data herein, interference value reduces therewith simultaneously or increases.When the downlink data of pilot power control method is estimated, interference value is from community farther out, is affected less by slow fading index variation.According to 5.3 analyses 1., scheme is better than pilot power control method, pilot tone listing technique herein.
3. slow fading coefficient, number of users are certain, the situation that community number is different
N=6 is set during emulation.As can be seen from Figure 8, as community number L=3, the cell downlink handling capacity of every kind of scheme is slightly better than situation during L=5.This is because according to formula (30) (36) (38) it can be seen that when chain network small area number reduces, the distracter of the downlink data estimated value of targeted customer reduces,Increasing therewith, the cell throughout of every kind of scheme slightly promotes.
When community number reduces or increases, the pilot pollution of various schemes also reduces therewith or increases.According to 5.3 analyses 1., scheme is better than pilot power control method, pilot tone listing technique herein.
By up, downlink data transmission simulation analysis it can be seen that along with antenna for base station number increases, herein the handling capacity of new departure also increases therewith, and level off to definite value gradually, demonstrate formula (18) (30).Scheme is relative to pilot power control method herein, saves the uplink channel estimation time, and is more suitable for the situation that number of users is many.Scheme is relative to pilot tone listing technique herein, simple, has more practicality.
Claims (1)
1. in the extensive mimo system of chain network, pilot pollution alleviates scheme, it is characterised in that comprise the following steps:
1) initial scene setting:
1-1) in the extensive mimo system model of Fig. 1 chain network multiple cell, the system that arranges adopts tdd mode；
Community 1-2) arranging L non-cooperating uses same frequency band；
1-3) heart arranges base station in each cell, and there is M root antenna base station；
1-4) centered by base station, each community arranges and is divided into Zuo Qu and You Qu, and each community arranges N number of single-antenna subscriber, is evenly distributed in community, and namely each community Zuo Qu is identical with the number of users in right district, is
2) scheme realizes step:
Zuo Qu and You Qu 2-1) arranging each community has identical number of users, and the left district Customs Assigned Number namely arranging each community is Right district Customs Assigned Number is
2-2) when system carries out uplink channel estimation, employing length is τPilot tone vectorAnd meet normalizing condition
2-3) pilot frequency sequence that length is τ is divided into three groups, namely obtains mutually orthogonal pilot frequency sequence group
2-4) three groups of pilot frequency sequence groups successively, being cyclically allocated, namely the right district user of i-th community adopts pilot frequency sequence groupThen the left district user of (i+1) community adopts pilot frequency sequence groupThe left district user of i-th community and the right district user multiplexed pilot sequence set of (i+1) communityBy that analogy, namely targeted customer is adjacent the closely user in region and arranges orthogonal pilot frequency sequence, and targeted customer and zone user multiplexed pilot sequence farther out；
2-5) for the user of multiplexed pilot sequence set, orderArrange the right district the of left district kth user and (i+1) community of i-th communityIndividual user uses identical pilot frequency sequence, for instance the right district of the 1st, the left district of i-th community user and (i+1) community theIndividual user uses identical pilot frequency sequence, by that analogy.
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Application publication date: 20160713 Assignee: Nanjing Nanyou Communication Network Industry Research Institute Co.,Ltd. Assignor: NANJING University OF POSTS AND TELECOMMUNICATIONS Contract record no.: X2021980014811 Denomination of invention: Pilot pollution mitigation method in chain network large-scale MIMO system Granted publication date: 20190531 License type: Common License Record date: 20211213 |