CN104080109A - Synchronization and calibration method of densely-distributed mobile communication network system - Google Patents

Abstract

The invention provides a synchronization and calibration method of a densely-distributed mobile communication network system. Radio access units (RAU) are densely distributed in each cell, and all the RAUs are connected with a baseband processing unit (BPU) in the same cell through high-speed links. In a synchronization stage, the BPU sends carrier signals to all the RAUs connected with the BPU after receiving synchronization request signals; after the RAUs receive the carrier signals, phase-locked loops are adopted for obtaining the carrier signals, and time delay of transmission lines are estimated. In the calibration stage, the BPU carries out clustering on the RAUs connected with the BPU to form tree-shaped clustering topology; the RAUs in each cluster receive calibrating signals from one another and send calibrating signals to one another, and transmit the received calibrating signals to the BPU through the high-speed links, and the BPU calculates the corresponding calibration factor; calibration factors of the distributed RAUs in different clusters are obtained through indirect calculation to achieve calculation of all the distributed RAUs. The synchronization and calibration method of the densely-distributed mobile communication network system is low in system complexity and free of user participation or wireless feedback.

Description

Synchronous and the calibration steps of dense distribution formula mobile communication network

Technical field

The invention belongs to communication technical field, relate in particular to a kind of multi-user space that uses dense distribution formula Wireless Access Unit to lay and divide multi-address radio communication system.

Background technology

The sustainable growth of frequency spectrum resource day by day in short supply and wireless data service amount, becomes the key factor that drives wireless communication system to carry out new change.Along with the development of the communication technology, the methods such as high order modulation coding, chain circuit self-adaptive method, MIMO have all obtained application in radio communication.Can say, the property development of point-to-point communication link and engineering practice are own through almost having reached the limit.

In order to realize the more double goal of spectral efficient and green radio communication, people have proposed dense distribution formula mobile communication technology.Cooperation (joint transmission/cooperative scheduling) by the Wireless Access Unit on diverse geographic location (Radio Access Unit, RAU) improves systematic function.Dense distribution formula mobile communication network can reduce system interference by the cooperation between RAU, realizes cell-edge performance and promotes, and also to current techniques, provides effective integration simultaneously.

In dense distribution formula mobile communication network, the RAU of cooperation need to know descending channel information accurately, carries out downlink precoding, serves a plurality of users, improves systematic function.Adopt time division duplex (Time Division Duplexing, TDD) communication pattern, RAU can utilize channel reciprocity, by the uplink channel information of estimating, obtains descending channel information.According to EM theory, if the time interval is less than coherence time, signal transmission will experience identical decline in uplink and downlink direction so.Like this, greatly reduced the feedback overhead of system.

Yet dense distribution formula mobile communication network is to synchronously having a very high requirement between the RAU of cooperation.If asynchronous between the RAU of cooperation, can greatly reduce the cooperative gain of user side, also can produce between time slot and disturb and up-downgoing interference, have a strong impact on communication quality, even cause communication failure.

In addition, channel reciprocity theory is just applicable to aerial wireless transmission channel.And a complete communication channel not only comprises aerial wireless channel, also comprise radio frequency (Radio Frequency, the RF) circuit of transmitter and receiver.RF circuit comprises antenna, RF frequency mixer, and digital to analog converter, power amplifier etc., is also subject to the impact (such as temperature, humidity etc.) of surrounding environment.Like this, from the impact on signal, in fact each RF circuit is equivalent to sending and receiving signal has respectively been multiplied by an extra coefficient, i.e. RF gain, and RF gain is normally unmatched, this RF gain do not mate the reciprocity of having destroyed communication channel.So, in TDD system, while adopting downlink precoding technology, the antenna calibration that must cooperate between RAU.

Summary of the invention

Technical problem: the object of this invention is to provide a kind of complexity lower, the synchronous and calibration steps of the dense distribution formula mobile communication network that feasibility is stronger.

Technical scheme: the synchronous and calibration steps of dense distribution formula mobile communication network of the present invention adopts following technical scheme:

Each community intensive laying distributed wireless access unit (Radio Access Unit in mobile communications network, RAU), the center baseband processing unit (Baseband Processing Unit, BPU) that all RAU pass through high-speed link Yu Gai community is connected.At synchronous phase: send carrier signals by BPU to connected all RAU, realize the carrier frequency synchronization of all RAU carrier signals.At calibration phase: BPU, all RAU are carried out to sub-clustering, form the sub-clustering topology of tree type; With the RAU in cluster, receive and dispatch mutually calibrating signal, and the calibrating signal of receiving is transferred to BPU by high-speed link, directly calculate corresponding calibration factor; Calibration factor between distributed wireless access unit in different bunches obtains by indirect calculation, realizes the calibration of all RAU.

Beneficial effect: the synchronous and calibration steps of dense distribution formula mobile communication network provided by the invention, tool has the following advantages:

(1) carrier synchronization signal is sent to each RAU by high-speed link by BPU, and signal accuracy is high, and each RAU can lock very accurately to the carrier frequency of carrier signal, thereby realizes preferably the carrier frequency synchronization of all RAU.

(2) during carrier frequency synchronization, a part for RF gain phase place is regarded in the phase difference that each RAU is produced by PLL and the unification of time delay evaluated error as, by calibration, solves, will be synchronous and calibrate and effectively join together to process.

(3) calibration time is carried out sub-clustering to each RAU, and in the calibration problem of extensive node is turned to bunch, the calibration problem of less node, greatly reduces complexity.

(4), when calibration, between the RAU in bunch, receive and dispatch mutually calibrating signal, without user's participation.

(5) calibrating signal that RAU receives is transferred to by high-speed link the calculating that BPU carries out calibration factor, without the feedback of wireless channel, has reduced the feedback overhead of system, provides cost savings.

Accompanying drawing explanation

In order to be illustrated more clearly in technical solution of the present invention, to the accompanying drawing of required use in embodiment or description of the Prior Art be briefly described below, apparently, accompanying drawing in the following describes only shows some embodiments of the present invention, for those of ordinary skills, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings the accompanying drawing of other embodiment.

The schematic diagram of a kind of dense distribution formula mobile communication network framework that Fig. 1 provides for the embodiment of the present invention and the schematic diagram of RAU sub-clustering;

The flow chart of a kind of dense distribution formula mobile communication network synchronous method that Fig. 2 provides for the embodiment of the present invention;

The flow chart of a kind of dense distribution formula mobile communication network RAU cluster-dividing method that Fig. 3 provides for the embodiment of the present invention;

The flow chart of a kind of dense distribution formula mobile communication network calibration steps that Fig. 4 provides for the embodiment of the present invention.

Fig. 5 be one bunch in the schematic diagram of each RAU calibration.

Embodiment

In order to make those skilled in the art person understand better the present invention program, below in conjunction with the accompanying drawing in the embodiment of the present invention, technical scheme in the embodiment of the present invention is carried out to clear, complete description, obviously, described embodiment is only the present invention's part embodiment, rather than whole embodiment.Embodiment based in the present invention, those of ordinary skills, not making the every other embodiment obtaining under creative work prerequisite, should belong to the scope of protection of the invention.

(1) dense distribution formula mobile communication network framework

The dense distribution formula mobile communication network framework of the present embodiment as shown in Figure 1, the distributed single-antenna wireless access unit of the intensive laying in each community RAU in diagram scene in mobile communications network (also can many antennas, for discussing, be simply made as single antenna in an embodiment), the center baseband processing unit BPU that all RAU pass through high-speed link (for example optical fiber) Yu Gai community is connected.In definition community, all RAU set connect and compose a cell base station with BPU by high-speed link.

(2) carrier frequency synchronization of RAU carrier signal

The synchronous method flow process of the dense distribution formula mobile communication network of the present embodiment as shown in Figure 2.In community, to realize the process of carrier signal carrier frequency synchronization as follows for all RAU,

Step 1, RAU sends synchronous request signal by high-speed link to BPU;

Step 2, BPU sends carrier signal to connected all RAU after receiving synchronous request signal;

Step 3, after RAU receives carrier signal, adopts phase-locked loop pll to obtain carrier signal, and estimates the time delay of transmission line.

If the carrier frequency of the carrier signal that BPU sends is f _c, because carrier signal is transmitted by high-speed link, and PLL has very high Frequency Synchronization precision, so can think that the carrier frequency of each RAU carrier signal equates, only exists phase difference and the time delay evaluated error being produced by PLL.N RAU can be expressed as

Wherein, τ _nfor time delay evaluated error, φ _nfor the constant phase difference of PLL generation, for initial phase, change slowlyer, within a period of time, all can see constant as.The carrier signal that such n RAU produces only differs a phase difference with the carrier signal of BPU

And Δ θ _nthe part that can regard RF gain phase place as, will solve by calibration.

(3) coordination downlink precoded signal model

Be provided with M single antenna user of N single antenna RAU collaboration services (User Equipment, UE), downlink precoding adopts the mode of zero-forcing beamforming (Zero Forcing Beamforming, ZFBF) precoding.The transmission matrix of uplink and downlink is respectively

G _UL＝C _RAU,rH ^TC _UE,t

G _DL＝C _UE,rHC _RAU,t

Wherein, for air traffic channel transmission matrix, each element h wherein _mn(m=1 ..., M; N=1 ..., N) be m UE to the air traffic channel coefficient of n RAU, meet channel reciprocity theory, up-downgoing channel coefficients equates.C _{rAU, t}, C _{rAU, r}the sending and receiving RF gain matrix that represents respectively RAU, C _{uE, t}, C _{uE, r}the sending and receiving RF gain matrix that represents respectively UE, is diagonal matrix.

C _RAU,t＝diag(t _RAU,1,...,t _RAU,n,...,t _RAU,N)

C _RAU,r＝diag(r _RAU,1,...,r _RAU,n,...,r _RAU,N)

C _UE,t＝diag(t _UE,1,...,t _UE,m,...,t _UE,M)

C _UE,r＝diag(r _UE,1,...,r _UE,m,...,r _UE,M)

T wherein _{rAU, n}, r _{rAU, n}, t _{uE, m}, r _{uE, m}(n=1 ..., N; M=1 ..., the sending and receiving RF that M) is respectively RAU and UE gains.

When cooperation RAU adopts ZFBF downlink precoding, establish x=[x ₁..., x _m] ^tfor RAU sends to respectively the information symbol of M UE, and ignore the uplink channel estimation error of RAU, the signal that UE receives is

$\begin{array}{c}y=\mathrm{\β}{G}_{\mathrm{DL}}{G}_{\mathrm{UL}}^{*}{\left(G_{\mathrm{UL}}^T{G}_{\mathrm{UL}}^{*}\right)}^{-1}x+n\\ ={\mathrm{\βC}}_{\mathrm{UE},r}{\mathrm{HC}}_{\mathrm{RAU},t}{C}_{\mathrm{RAU},r}^{*}{H}^H{C}_{\mathrm{UE},t}^{*}{\left(C_{\mathrm{UE},t}{\mathrm{HC}}_{\mathrm{RAU},r}{C}_{\mathrm{RAU},r}^{*}{H}^H{C}_{\mathrm{UE},t}^{*}\right)}^{-1}x+n\\ =\mathrm{\β}{C}_{\mathrm{UE},r}\left({\mathrm{HC}}_{\mathrm{RAU},t}{C}_{\mathrm{RAU},r}^{*}{H}^H\right){\left({\mathrm{HC}}_{\mathrm{RAU},r}{C}_{\mathrm{RAU},r}^{*}{H}^H\right)}^{-1}{C}_{\mathrm{UE},t}^{-1}x+n\end{array}$

In above formula, for additive white Gaussian noise vector, represent complex field, β is the power normalization factor.Known according to above formula, due to matrix each element of diagonal unequal, thereby can cause the interference between downlink user.If in downlink precoding, then be multiplied by a calibration matrix C _cal, make C _{rAU, t}c _cal=α _calc _{rAU, r}, be the product of a complex scalar and unit matrix.After perfection calibration, the signal that UE receives is

$y={\mathrm{\α}}_{\mathrm{cal}}{\mathrm{\β}}_{\mathrm{cal}}{C}_{\mathrm{UE},r}{C}_{\mathrm{UE},t}^{-1}x+n$

Wherein, β _calfor the power normalization factor after calibration, α _calrepresent a complex scalar, in theoretical derivation, this complex scalar can be divided out, so actual value is how many performance not to be affected.Like this, just can eliminate because caused inter-user interference is not mated in RF gain.

(4) RAU cluster-dividing method

In practical communication, due to the variation of UE position and channel, in community, any number of RAU likely carry out collaboration communication.So will realisticly show the antenna calibration between all RAU in community.As shown in Figure 3, sub-clustering effect as shown in Figure 1 for the synchronous method flow process of the dense distribution formula mobile communication network of the present embodiment.Before carrying out sub-clustering, BPU produces the location matrix of position relationship between each RAU, and upgrades at any time and safeguard.Generate two set, not sub-clustering set, current sub-clustering set simultaneously.When initial, all RAU are all in sub-clustering set not, and current sub-clustering set is empty set.RAU cluster-dividing method is as follows:

Initial sub-clustering: from a RAU of center of housing estate, according to location matrix, according to sub-clustering rule, nearest with it RAU is divided into cluster.Sub-clustering rule is as follows:

1) in order to make the average signal-to-noise ratio between any two RAU in same cluster be greater than certain threshold value, thereby guarantee the precision of calibration factor, the distance that requires to be divided between the RAU of same cluster is less than distance threshold d ₀, system is according to antenna calibration determine precision threshold value d ₀.

2) because the RAU in same cluster need to send successively calibrating signal when calibrating, and calibration algorithm need to utilize the reciprocity of air traffic channel coefficient, with the RAU in cluster, must in coherence time, calibrating signal be sent at channel, requirement is no more than and sets numerical value K (K is channel coherence time and the ratio in calibrating signal cycle) with the RAU sum in cluster, if meet distance each other, is less than threshold value d ₀but unit sum has surpassed K, choose K-1 the nearest RAU from first RAU., the RAU of new sub-clustering is joined in current sub-clustering set meanwhile, and in never sub-clustering set, remove the RAU of new sub-clustering, initial sub-clustering finishes;

Sub-clustering successively: select any one RAU in current sub-clustering set, be then divided into cluster by sub-clustering rules selection RAU in never sub-clustering set, delete the RAU choosing simultaneously from current sub-clustering set.If current sub-clustering is not empty, continue to select in current sub-clustering set by sub-clustering rules selection RAU, to carry out sub-clustering in any one RAU never sub-clustering set, until current sub-clustering set this sub-clustering when empty finishes, the RAU of this new sub-clustering is joined in current sub-clustering set, and delete in never sub-clustering set.

Finish sub-clustering: according to the method in clustering process successively, continue sub-clustering next time, when sub-clustering set be not sky, sub-clustering finishes.

Upgrade sub-clustering: when there being RAU to exit because of fault, or there have new RAU to add to be fashionable, and BPU upgrades location matrix, and re-starts sub-clustering.

Like this, in calibration, time each RAU is carried out to sub-clustering, in the calibration problem of extensive node is turned to bunch, the calibration problem of less node, greatly reduces complexity.

(5) RAU antenna calibration

The calibration steps flow process of the dense distribution formula mobile communication network of the present embodiment as shown in Figure 4.In community, the process of all RAU realization calibrations is as follows,

Step 1, all RAU radio broadcasting calibrating signal successively in each bunch, and the calibrating signal of other RAU in receiving bunch;

Step 2, all RAU are transferred to BPU by the calibrating signal receiving by high-speed link, by it, calculate antenna calibration coefficient between corresponding RAU;

Step 3, with calibrating by direct wireless calibration channel between the distributed wireless access unit in cluster, between distributed wireless access unit in adjacent cluster, by total distributed wireless access unit, indirectly calibrate, thereby obtain the calibration factor between any two distributed wireless access units, realize the calibration of all distributed wireless access units.

Fig. 5 be one bunch in the schematic diagram of each RAU calibration.In bunch, there is L RAU, be made as set .Calibration is divided into L time slot, and RAU sends calibrating signal successively.I RAU and j mutual sending and receiving of RAU to signal be

y _ij＝t _ih _ijr _j+n _ij

y _ji＝t _jh _jir _i+n _ji

Wherein, h _ij(i, j=1 ..., L) represent the channel coefficients between i RAU and j RAU, and h _ij=h _ji.

N _ij(i, j=1 ..., L) be corresponding white Gaussian noise.

If vectorial for take i RAU as the alignment vector with reference to RAU, its element meets

$c_j^i=\left\{\begin{array}{cc}1& j=i\\ \frac{y_{\mathrm{ij}}}{y_{\mathrm{ji}}}& j\≠i\end{array}\right.$

Consider L calibration factor vector, can obtain final alignment vector and be

$c=\underset{i=1}{\overset{L}{\mathrm{\Σ}}}{c}^i$

Like this, can be in the hope of the calibration factor between i RAU in this RAU bunch and j RAU

${\mathrm{\α}}_{\mathrm{ij}}=\frac{c_i}{c_j},{\mathrm{\α}}_{\mathrm{ji}}=\frac{c_j}{c_i}$

Similarly, between the RAU in other bunches, calibration factor also calculates by said method.Like this, the calibration factor between the RAU in same bunch can directly obtain, and in adjacent cluster, the calibration factor between RAU can obtain indirectly by the total RAU of two bunches.

If there be N RAU to cooperate in community, u RAU and v RAU not in same bunch, and w RAU simultaneously with these two RAU in one bunch, the calibration factor between u RAU and v RAU is

α _uv＝α _uw·α _wv,α _vu＝α _vw·α _wu

Therefore, can realize the calibration between RAU arbitrarily in community.If n the RAU of take is reference, calibration matrix when this N RAU carries out coordination downlink precoding is

C _cal＝diag(α _n1,...α _nn,...α _nN)

Wherein, α _nn=1.Like this, can be in the hope of the calibration matrix of any number of cooperation RAU in community.

In the embodiment providing in the application, should be understood that disclosed method, not surpassing in the application's spirit and scope, can realize in other way.Current embodiment is a kind of exemplary example, should be as restriction, and given particular content should in no way limit the application's object.For example, a plurality of unit or assembly can in conjunction with or can be integrated into another system, or some features can ignore, or do not carry out.

The above; be only the specific embodiment of the present invention, but protection scope of the present invention is not limited to this, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; can expect easily changing or replacing, within all should being encompassed in protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of described claim.

Claims (6)

1. a synchronous and calibration steps for dense distribution formula mobile communication network, is characterized in that:

Each community intensive laying distributed wireless access unit in mobile communications network, all distributed wireless access units are all connected with the center baseband processing unit of community, place by high-speed link;

At synchronous phase: center baseband processing unit sends carrier signals to all distributed wireless access units of its connection, realizes the carrier frequency synchronization of all distributed wireless access unit carrier signals in community;

At calibration phase: center baseband processing unit carries out sub-clustering to all distributed wireless access units of its connection, form the sub-clustering topology of tree type; With the distributed wireless access unit in cluster, receive and dispatch mutually calibrating signal, and the calibrating signal of receiving is transferred to center baseband processing unit by high-speed link, directly calculate corresponding calibration factor; Calibration factor between distributed wireless access unit in different bunches obtains by indirect calculation, realizes the calibration of all distributed wireless access units.

2. the synchronous and calibration steps of a kind of dense distribution formula mobile communication network according to claim 1, is characterized in that: at synchronous phase, the process that in community, all distributed wireless access units are realized carrier signal carrier frequency synchronization is as follows,

Step 1, distributed wireless access unit sends synchronous request signal by high-speed link to center baseband processing unit;

Step 2, center baseband processing unit receives that all distributed wireless access units to its connection send carrier signals after synchronous request signal;

Step 3, after distributed wireless access unit is received carrier signal, utilizes phase-locked loop to obtain carrier signal, and estimates the time delay of transmission line.

3. the synchronous and calibration steps of a kind of dense distribution formula mobile communication network according to claim 2, is characterized in that: a part for RF gain phase place is regarded in the phase difference being produced by phase-locked loop and the unification of time delay evaluated error as, by calibration, solves.

4. the synchronous and calibration steps of a kind of dense distribution formula mobile communication network according to claim 1, it is characterized in that: center baseband processing unit generates the location matrix of position relationship between each distributed wireless access unit, and upgrades at any time and safeguard; Generate two set: not sub-clustering set and current sub-clustering set simultaneously; When initial, all distributed wireless access units are all in sub-clustering set not, and current sub-clustering set is empty set; Cluster-dividing method is as follows:

(1) initial sub-clustering: from a distributed wireless access unit of center of housing estate, according to location matrix, choose distributed wireless access unit according to sub-clustering rule and be divided into cluster; Described sub-clustering rule refers to: with the distance between any two distributed wireless access units in cluster, be less than distance threshold, with the sum of distributed wireless access unit in cluster, be no more than and set numerical value and nearest with first distributed wireless access unit; , the distributed wireless access unit of new sub-clustering is joined in current sub-clustering set meanwhile, and in never sub-clustering set, remove the distributed wireless access unit of new sub-clustering, initial sub-clustering finishes;

(2) sub-clustering successively: select any one distributed wireless access unit in current sub-clustering set, then in never sub-clustering set, by sub-clustering rules selection distributed wireless access unit, be divided into cluster, from current sub-clustering set, delete the distributed wireless access unit of choosing simultaneously; If current sub-clustering is not empty, continue to select in current sub-clustering set by sub-clustering rules selection distributed wireless access unit, to carry out sub-clustering in any one RAU never sub-clustering set, until current sub-clustering set this sub-clustering when empty finishes, the distributed wireless access unit of this new sub-clustering is joined in current sub-clustering set, and delete in never sub-clustering set;

(3) finish sub-clustering: according to the cluster-dividing method in step (2), continue sub-clustering next time, when sub-clustering set is not empty, sub-clustering finishes;

(4) upgrade sub-clustering: when there being distributed wireless access unit to exit because of fault, or there have new distributed wireless access unit to add to be fashionable, and center baseband processing unit upgrades location matrix, and re-starts sub-clustering.

5. the synchronous and calibration steps of a kind of dense distribution formula mobile communication network according to claim 4, is characterized in that: described distance threshold is according to antenna calibration determine precision, and described setting numerical value is channel coherence time and the ratio in calibrating signal cycle.

6. the synchronous and calibration steps of a kind of dense distribution formula mobile communication network according to claim 1, is characterized in that: at calibration phase, in community, the process of all distributed wireless access units realization calibrations is as follows,

Step 1, all distributed wireless access units radio broadcasting calibrating signal successively in each bunch, and the calibrating signal of other distributed wireless access units in receiving bunch;

Step 2, all distributed wireless access units are transferred to center baseband processing unit by the calibrating signal receiving by high-speed link, by it, calculate antenna calibration coefficient between corresponding distributed wireless access unit;

Step 3, with calibrating by direct wireless calibration channel between the distributed wireless access unit in cluster, between distributed wireless access unit in adjacent cluster, by total distributed wireless access unit, indirectly calibrate, thereby obtain the calibration factor between any two distributed wireless access units, realize the calibration of all distributed wireless access units.