The method that suppresses interference
(1) technical field
The present invention relates to a kind of method that suppresses interference in mobile communication system, this communication system has a kind of sectorized cells structure.Said method can be used for for example TD-SCDMA (time division duplex-S-CDMA) mobile communications network.
(2) background technology
To CDMA (code division multiple access) system, CDMA2000 for example, W-CDMA (wideband CDMA) or TD-SCDMA, employing be a kind of same frequency multiplexing scheme, wherein the mobile subscriber in all sub-districts of an operator uses identical frequency.For seamless covering being provided and guaranteeing the safety switching, between neighbor cell, there is an overlapping region.The mobile subscriber is in above-mentioned overlapping region and can communicates with different base stations, but use is same frequency.But although processing gain is arranged, network still can be subjected to serious disturbance.
The sectorized cells structure be generally used for second and 3-G (Generation Three mobile communication system) (2G 3G), utilizes above-mentioned sectorized cells structure, and same website can be shared in several base stations, and operator can save the investment of configuration network thus.Above-mentioned interference problem is especially serious in a mobile communications network with sectorized cells structure, because in fact the base station of serving different sectorized cells is positioned at same website.
Can utilize smart antenna to improve the performance of mobile communication system, for example in the TD-SCDMA system, just utilized smart antenna, this smart antenna is a beam controlling antenna, and it follows the tracks of the mobile subscriber of whole sub-district, and only the cell area at mobile subscriber place is distributed power.If there is not smart antenna, power will be distributed to whole sub-district.The use of smart antenna has reduced multi-user interference, thereby by the interference minimization between the sub-district and the sub-district having been increased the capacity of system, has increased the reception susceptibility, has reduced through-put power, has enlarged cell range simultaneously.Utilize smart antenna, the capacity of system significantly increases.
Adopt smart antenna, each mobile subscriber (or one group of mobile subscriber) can obtain the wave beam of oneself by beam shaping, a kind of simple and effective beam shaping algorithm for example is to select optimum beam from the predetermined wave beam of a series of arrival directions according to the mobile subscriber (DOA).These a series of wave beams are called as wave beam grid (GOB).Usually, the relevant criterion of generation wave beam is the received power maximization with desired mobile subscriber.
In mobile communications network, the sectorized cells structure also can be used with smart antenna, and still, the interference in this system between the sectorized cells is especially remarkable, and with the performance of restriction system.
In a mobile network environment with sectorized cells structure, the work of existing GOB algorithm must be not as good like that in the omni cell network.Will limit the performance performance of whole system in the interference of the fringe region of sector boundary.
In order to improve the QoS of customer in the critical zone, CDMAIS-95 and W-CDMA system all adopt soft handover, and for soft handover, the mobile subscriber provides service by a more than base station in above-mentioned critical zone.
Though soft handover can improve the service quality of above-mentioned critical zone, its shortcoming is additionally to take Internet resources, and therefore, in some mobile communication system, for example soft handover is not used among the TD-SCDMA.What adopt in TD-SCDMA is direct-cut operation and smart antenna.
In theory, utilize an optimal algorithm, above-mentioned smart antenna can provide optimal performance.Yet in reality, because the limitation of signal of base station disposal ability and existing knowledge, what extensively adopt at present all is the shortcut calculation of performance suboptimum.Simple algorithm is to produce a series of wave beams in advance, and they are stored in the base station, in case estimate according to arrival direction (DOA) and need to produce an optimized wave beam, it can be easy to recover to take out and be used for down link (DL) transmission, promptly from NodeB to the subscriber equipment.
In a kind of known wave beam grid (GOB) algorithm, suppose on sense, to have the disturbed condition of maximum gain or hypothesis sectorized cells, thereby can produce a series of wave beam.In addition, according to the arrival direction (DOA) of the signal of uplink direction (from the subscriber equipment to NodeB), select optimal beam adaptably.Yet people wish that further inhibition is to the interference of adjacent sectorized cells.
(3) summary of the invention
The objective of the invention is to suppress in the mobile communication system with a sectorized cells structure method of interference, this method makes all little to the existing technology of the interference ratio of neighbor cell.
Above-mentioned purpose of the present invention is achieved in that a kind of method that suppresses interference in the mobile communication system with sectorized cells structure, and wherein, first subscriber equipment is positioned at first fan section and the second adjacent fan section is produced an interference.First subscriber equipment is in communications status by a smart antenna and a base station.According to the present invention, above-mentioned smart antenna is removed from the desirable direction of first subscriber equipment facing to the wave beam main lobe of first subscriber equipment, and the main lobe of this intelligent antenna beam preferably moves towards the center direction in above-mentioned first fan section.
Above-mentioned subscriber equipment can be any communicator that can communicate by letter in mobile communication system, for example, and mobile phone or PDA(Personal Digital Assistant).Above-mentioned base station can for example be the NodeB of TD-SCDMA.
In one embodiment of the invention, first subscriber equipment is positioned at the fringe region of first fan section and boundary, second fan section.This fringe region is called as the critical zone.Above-mentioned main lobe preferably shifts out above-mentioned critical zone and to the central mobile in this fan section.
Preferably produce a series of intelligent antenna beams in above-mentioned base station, this series wave beam produces in advance and is stored in the base station, according to the position of desired subscriber equipment, can select a suitable wave beam from the intelligent antenna beam series of above-mentioned storage.
In one embodiment of the invention, for selecting an optimized intelligent antenna beam, should consider the directive gain (Gs) of the wave beam on the direction of first subscriber equipment, and (G_int) disturbed in the equivalence that is produced when adopting a concrete wave beam, that is, to the interference of other subscriber equipment on other directions.The directive gain of above-mentioned wave beam on the first subscriber equipment direction provides carrier power for subscriber equipment self.
In another embodiment of the present invention, the receiving algorithm of above-mentioned first subscriber equipment is considered so that the calculating of disturbing.For example, in TD-SCDMA, by utilizing orthogonal factor or utilizing interference suppression algorithm, the joint-detection in first subscriber equipment (JD) is for example suppressed the interference of other subscriber equipmenies in the sub-district.So-called " joint-detection " all detailed description in following white paper: " solution of TD-SCDMA:TDD frequency range " Siemens AG Representation, in April, 2002, information and mobile communication group.By means of joint-detection, can eliminate for the descending interference of other users in the sub-district.Therefore, in the calculating of G_int, the i.e. interior interference of the first fan section scope of Serving cell can be provided with to such an extent that be close to 0.
In addition, the subscriber equipment on other websites of the direction scope in first fan section that is positioned at above-mentioned service, interference may also can exist.But most of times of the subscriber equipment in other websites are positioned at least one cell range away from above-mentioned serving BS, and therefore, the interference meeting decays because of propagation loss, so this interference cases is not very serious.
In a most preferred embodiment of the present invention, the direction of above-mentioned intelligent antenna beam is round the direction of first subscriber equipment and change, and this direction can be the direction of first subscriber equipment of the hope determined according to arrival direction (DOA).
For each intelligent antenna beam, should calculate it at directive gain Gs on the first subscriber equipment direction and the mean direction gain G _ int on all directions except that first fan section.
In another embodiment, the beam feature of each the separate antenna element in the antenna array of smart antenna is comprised in the calculating of a Gs/G_int ratio.
Preferably determine to have that wave beam of maximum Gs/G_int ratio.This wave beam is the optimization wave beam of selecting for desired above-mentioned subscriber equipment direction.The calculating of the maximum rate of Gs/G_int is preferably calculated on a plurality of potential direction of first subscriber equipment, thus, can obtain a series of optimized wave beams.
In another embodiment of the present invention, one second subscriber equipment is positioned at the fringe region of second fan section and boundary, first sector, this second subscriber equipment is carried out those calculating identical with first equipment equally, calculate according to these, determine the optimized intelligent antenna beam of one second subscriber equipment at least.
Purpose of the present invention can also be realized by a kind of method that suppresses to disturb in the mobile communication system of the structure with sectorized cells.Wherein, first subscriber equipment is positioned at first fan section and the second contiguous sector is produced interference, and this first subscriber equipment communicates through a smart antenna and a base station.According to the present invention, in above-mentioned base station, generate a series of intelligent antenna beams, and the critical zone of first sector is positioned at the marginal zone of the intersection of first sector and second sector, and an intelligent antenna beam that points to this critical zone is substituted by the intelligent antenna beam of this critical zone of sensing with external position.
(4) description of drawings
The present invention will be described in more detail with reference to the accompanying drawings.Wherein,
Fig. 1 represents the schematic diagram of a sectorized cells structure;
Fig. 2 is illustrated in two intelligent antenna beams of the boundary vicinity in different fan sections;
Fig. 3 represents the example of the intelligent antenna beam figure on certain direction of a plurality of candidates;
Fig. 4 represents the calculating of the Gs/G_int ratio of the intelligent antenna beam on certain direction of a plurality of candidates;
(5) embodiment
Fig. 1 illustrate schematicallys a TD-SCDMA network with sectorized cells structure, and a NodeB (NodeB) is served three fan section C1, C2, C3.A user equipment (UE) 1 is in the critical zone E1 of fan section boundary edge.Above-mentioned NodeB and above-mentioned user equipment (UE) 1 communicate.Fig. 1 represents the main lobe SAB1 of the smart antenna of NodeB, and it points to above-mentioned user equipment (UE) 1.Because UE1 is arranged in the critical zone, another user equipment (UE) 2 that is positioned at adjacent sectors C2 can be subjected to very strong interference, thereby service quality is bad.Fig. 1 is another main lobe SAB2 of the smart antenna of the above-mentioned NodeB of expression further, and it points to above-mentioned another calculated user equipment (UE) 2.
Fig. 2 represents the array gain of two intelligent antenna beam SAB1 and SAB2, and the trunnion axis among the figure is represented the emission angle of smart antenna, and vertical pivot is represented array gain.Fan section between above-mentioned fan section C1 and the C2 has a common boundary and locates about 60 °.As shown in the figure, at the critical zone of fan section C2 E2, promptly the interference between 60 ° to 82 ° is very high.Equally, disturb also very big to the critical zone E1 between 38 ° to 60 °.
Fig. 3 represents the computational process of a mobile subscriber's optimization beam pattern, and its direction is 55 °.Trunnion axis among the figure is represented beam direction from 0 °-90 °, and vertical pivot is represented antenna gain.At first near 55 °, generate some candidate's wave beams, in 45 ° to 60 ° scopes, generate 8 wave beams 45,47,49,51,53,55,57,59 with maximum directive gain.In the present embodiment, adopt 90 ° of angle of release antenna elements, calculated the Gs/G_int ratio of each candidate's wave beam 45,47,49,51,53,55,57,59 then.
Fig. 4 represents the Gs/G_int ratio of a plurality of candidate's wave beams, and its trunnion axis is represented the principal direction of initial beam, and its vertical axes is represented the Gs/G_int value.Obviously, principal direction is that 50 ° initial beam is the user's optimization wave beam on 55 ° of directions.But also must consider following factor: the change of the kind of the change of number of antenna elements and the wave beam of each antenna element, they can influence above-mentioned result of calculation.
Above-mentioned calculating not only can be used for the critical zone, can also be used for whole fan section, i.e. 360 ° of scopes.Because there is not the serious disturbance problem in middle section, therefore, can not change on the main lobe direction of intelligent antenna beam.Above-mentioned antenna beam calculates in advance, therefore, does not need real-time processing power.
In another embodiment, according to a supposition interference profile characteristic, a signal power distributes and system's specific criteria, generate a series of wave beam, these with in the critical zone in fan section, reach the corresponding wave beam of direction (DOA), do not substituted by its arrival direction at the wave beam of above-mentioned critical zone.
By means of the present invention, on basis, generate the predetermined wave beam of wave beam grid for the arrival direction (DOA) of mobile subscriber equipment more than a kind of criterion.With only compare with regard to the situation that generates above-mentioned predetermined wave beam according to a criterion, mobile subscriber's service quality is able to remarkable improvement in the critical zone in fan section.Further advantage of the present invention is the change that does not need hardware and software.