Background technology
Multimedia broadcasting and multicast (MBMS, Multimedia Broadcast and Multicast Service) technology is by sharing a transmission link, multimedia data broadcast or be multicasted to portable terminal, its objective is in mode efficient, economic, that share to be that the multi-user provides folk prescription from any to multiple spot to descending multi-medium data.Present user's request is demanding message transmission rate, and the transfer of data of two-forty must need big transmission bandwidth to satisfy, and along with the increase of bandwidth, the performance of selectivity of channel frequency is more outstanding.OFDM (OFDM, Orthogonal Frequency Division Multiplex) technology has been introduced Cyclic Prefix (CP, Cyclic Prefix) technology, can effectively overcome the influence of frequency selective fading, and the OFDM technology can be easy to support the expansion of bandwidth, guarantee system's compatibility technically of different bandwidth, for diversity of operations provides strong support.MBMS in Long Term Evolution (LTE, LongTime Evolution) technology and back 3G (B3G, the Back 3G) system is based on OFDM (OFDM, Orthogonal Frequency Division Multiplexing) technology at present.
In conjunction with the strong characteristics of MBMS one-way, present MBMS system is based on that separate carrier designs more, and in a MBMS coverage, the user can receive relevant MBMS business; Simultaneously, in order to obtain macro diversity, separate carrier MBMS system often covers big zone.For example a MBMS coverage comprises a plurality of nodes (Node B), perhaps a plurality of base stations, and perhaps a plurality of sub-districts utilize identical frequency resource in each coverage, the identical data of transmission under the synchronous condition of strict time.Because a MBMS coverage is bigger, and subscriber equipment (UE, User Equipment) will be to from different N ode B, different base station, the MBMS signal of different districts carries out diversity and merges, therefore, the signal that requires to arrive UE all drops within the CP scope of OFDM symbol, to guarantee the correct demodulation of ofdm signal.
In order to improve the band efficiency of MBMS system, the MBMS business of covering area overlapping can be carried out multiplexing in same MBMS system.In present MBMS system, be to adopt time division multiplexing (TDM, Time Division Multiplexing) mode to carry out multiplexing between the MBMS business of overlapped coverage.
In the MBMS of covering area overlapping service time division multiplex system, also need to consider to carry the CP Design of length of inserting in each OFDM symbol in the TDM time slot of MBMS business.
Embodiment
The service integration technical scheme of overlapped coverage is in the MBMS system that the embodiment of the invention proposes: in the MBMS system based on OFDM, in regional extent, described at least two MBMS business are carried out TDM handle by the professional overlapping covering of at least two MBMS; Based on the MBMS Service coverage, with be used for carrying the relation that the CP length value that inserts in each OFDM symbol of TDM time slot of MBMS business is directly proportional, according to the magnitude relationship of coverage between described at least two business, insert the CP of different length value respectively in each the OFDM symbol in the TDM time slot of each corresponding business of carrying.
Below in conjunction with Figure of description the specific embodiment of the present invention is described.
Fig. 1 has schematically provided the structure chart of the service integration of overlapped coverage in the MBMS system, comprises four MBMS business that coverage is different in this MBMS system, and is specific as follows:
Professional one coverage is sub-district A, and professional two coverage is sub-district B, and professional three coverage is sub-district C, and the coverage of the common service four of sub-district A, B, C is sub-district A, B, C.The MBMS business of these four different coverages is undertaken multiplexing by same communication system.
Succinct for what explain, the method of the service integration of overlapped coverage in the MBMS system is described with the system of the MBMS service integration of two different coverages below, as shown in Figure 2, the separate carrier MBMS system based on the OFDM technology in a city, only the little covering of coverage cell A is professional to comprise one, and big the coverings business of coverage cell A, a B, C.Among the figure, UE1 is for only using the little professional subscriber equipment that covers, and UE2 is for using the total professional subscriber equipment of sub-district A, B and C.Use the little MBMS signal that cover business of the UE1 reception of the peculiar business of sub-district A from sub-district A, use the MBMS business of corresponding this sub-district, use the total professional UE2 of sub-district A, B and C then the big MBMS signal that covers business from sub-district A, B and C to be carried out diversity and merge, use the common MBMS business in these three sub-districts.At the MBMS system among the A of sub-district, carry out multiplexing problem with regard to the business that has overlapped coverage, and these two different coverages belong to the same MBMS communication system in this city.
In an embodiment of the present invention, the MBMS communication system in this city adopts the TDM mode to cover professional and little the multiplexing of business that cover greatly.There is N time slot in the separate carrier MBMS system of supposing this city, wherein the professional N that uses of the big covering of coverage cell A, B, C
LIndividual time slot, and only the little covering business of coverage cell A is used N
SIndividual time slot, and N
L+ N
S=N.N wherein
LAnd N
SSpan all be from 0 to N, specifically can carry out the dynamic-configuration adjustment, specifically referring to shown in Fig. 3 a according to the demand of business.Simultaneously, can continuous dispensing between the time slot of corresponding different coverages, also can carry out the interval and distribute, specifically referring to shown in Fig. 3 b, whether carry out continuous dispensing and be configured according to concrete service needed.
This city adopts the TDM mode to realize in the system of MBMS service integration, and the method for designing of concrete CP is seen shown in Figure 4, and the business of different coverages is used each self-corresponding CP, uses long CP to merge with the diversity that satisfies UE in big covering business; In little covering business, use short CP, to improve the efficient of MBMS system.
For clean culture, CP length is the time elongatedness of subscriber equipment receiving multipath signals in the clean culture sub-district, generally gets 5us and gets final product, and in the present embodiment, the little coverage that covers business only is sub-district A, the value of the professional CP length of little covering can be decided to be 5us; MBMS business for large coverage, owing to need consider the consolidation problem of a plurality of cell base station signals, it is longer that CP length can be provided with, can determine that the length of CP is generally the distance of the professional middle distance of this MBMS two base stations farthest divided by the light velocity by the distance of the professional middle distance of this MBMS two base stations farthest.
When specific design, for band efficiency, complete unification that guarantees frame structure that improves system and the complexity that reduces terminal processes, a kind of preferable mode is to adjust CP length according to the OFDM number of symbols in the professional shared time slot of different coverages, make that the OFDM symbol lengths of K long CP is identical with the OFDM symbol lengths of M short CP, the professional time slot that takies of just big covering is identical with the slot time length that little covering business takies.
Can certainly adjust the length of data in the OFDM symbol according to the OFDM number of symbols in the professional shared time slot of different coverages, make that the OFDM symbol lengths of K long CP is identical with the OFDM symbol lengths of M short CP.
In the present embodiment, suppose that the distance between sub-district A and the sub-district C is 10km farthest, the length of so big covering CP is: 10km/ (3 * 10
8M/s)=33.33 * 10
-6S=33.33us.
In order to guarantee the complete unification of frame structure, suppose that big the covering in the professional time slot has K OFDM symbol, in the time slot of little covering business M OFDM symbol arranged, need to satisfy following relation between them:
The length (formula 1) of K * (data length of the length of long CP+OFDM symbol)=M * (data length of length+OFDM symbol of short CP)=time slot
Suppose that a slot length is 1ms in the MBMS system in the present embodiment, the data length of OFDM symbol is 57.5us, calculates in the substitution formula 1:
K * (33.33us+57.5us)=M * (5us+57.5us)=1ms (formula 2)
Through type 2 specifically calculates, and obtains M=16, K=11.0095, and the promptly big number that covers OFDM symbol in the corresponding time slot of business is 11, the little number that covers OFDM symbol in the corresponding time slot of business is 16.If the K value or the M value of trying to achieve by this calculating are not integer or the number that approaches very much integer, can make the K value and the M value that calculate be integer by the length of CP being carried out adjustment among a small circle so.
By being carried out multiplexing CP length, the business of overlapped coverage in the MBMS system designs, business for large coverage, its CP length is longer, all sub-district A, B, C in the corresponding institute coverage, can guarantee to use sub-district A, B, the total professional UE of C to carry out effective diversity and merge, obtain macro diversity, improve the quality and the receiving efficiency of MBMS business; Professional for little covering, its CP length is shorter, and the sub-district in the corresponding little coverage only is sub-district A here, does not exist UE to carry out the problem that diversity merges; Even little covering business also is to cover several sub-districts, UE still can carry out effective diversity merging so, to improve the band efficiency of MBMS system.
Wherein the CP Design of length thought in the service integration system of overlapped coverage can be applied to time division duplex (TDD in the MBMS system that proposes here, Time division duplex) MBMS system, and in the MBMS system of Frequency Division Duplexing (FDD) (FDD, Frequency division duplex).
The present invention proposes the method for the service integration of overlapped coverage in a kind of MBMS system, this method proposes same business based on the overlapped coverage in the MBMS system of OFDM technology and uses different time slots to transmit, and just carries out the multiplexing of TDM mode.Slot length is identical, and OFDM number of symbols difference in each time slot, by the concrete number of the length decision OFDM symbol of CP.The time slot of different coverage business can continuous dispensing, also can distribute at interval, also be can carry out between the time slot that covers of different business multiplexing flexibly.Carry out the demand that diversity merges in order to satisfy the UE that uses the large coverage business in addition, and improve the little professional receiving efficiency that covers, different business is covered the CP that uses different length, improved the band efficiency of MBMS system.Use the inventive method can guarantee in the different business coverage, to carry out on the basis of reliable transmission, reduce the waste of CP, improve the band efficiency of system.
According to the embodiment of technical solution of the present invention, the present invention provides the device of the service integration of overlapped coverage in a kind of MBMS service integration system that implements this technical scheme here, and as shown in Figure 5, this device comprises:
Time-division multiplexing unit 51 is used at the broadcast/multicast system based on OFDM, in the regional extent by at least two overlapping coverings of broadcasting multicast service, described at least two broadcasting multicast services is carried out time division multiplexing handle;
Cyclic Prefix inserts unit 52, be used for based on the broadcasting multicast service coverage, with be used for carrying the relation that the circulating prefix-length that inserts in each OFDM symbol of time division multiplexing time slot of broadcasting multicast service is directly proportional, according to the magnitude relationship of coverage between described at least two business, insert the Cyclic Prefix of different length value respectively in each OFDM symbol in the time division multiplexing time slot of each corresponding business of carrying.
If the coverage of described broadcasting multicast service is a sub-district, then Cyclic Prefix inserts unit 52 and determines to be inserted into circulating prefix-length value in each OFDM symbol in the time division multiplexing time slot of this broadcasting multicast service of carrying according to the time elongatedness of this community user equipment receiving multipath signals.
If the coverage of described broadcasting multicast service is at least two sub-districts, then Cyclic Prefix inserts unit 52 according to the distance between farthest two base stations in the described coverage, determines to be inserted into the circulating prefix-length value in each OFDM symbol in the time division multiplexing time slot of this broadcasting multicast service of carrying.
Also comprise Cyclic Prefix adjustment unit 53, be used for inserting the circulating prefix-length value that unit 52 inserts according to data length value of inserting at each OFDM symbol and Cyclic Prefix, determine in the time of to carry integer OFDM symbol in the time division multiplexing time slot of each regular length in broadcast/multicast system, be inserted into circulating prefix-length value in each OFDM symbol by adjustment, guarantee to carry an integer OFDM symbol in each time division multiplexing time slot.
Also comprise data length adjustment unit 54, be used for inserting the circulating prefix-length value that unit 52 inserts according to data length value of inserting at each OFDM symbol and Cyclic Prefix, determine in the time of to carry integer OFDM symbol in the time division multiplexing time slot of each regular length in broadcast/multicast system, be inserted into data length value in each OFDM symbol by adjustment, guarantee to carry an integer OFDM symbol in each time division multiplexing time slot.
Need to prove that each functional unit of being mentioned in the said apparatus can be realized based on software programming, also can realize based on transforming existing hardware device.
Obviously, those skilled in the art can carry out various changes and modification to the present invention and not break away from the spirit and scope of the present invention.Like this, if of the present invention these are revised and modification belongs within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also is intended to comprise these changes and modification interior.