CN114024813A

CN114024813A - Low earth orbit satellite constellation system broadcast control channel design and configuration method

Info

Publication number: CN114024813A
Application number: CN202111259900.4A
Authority: CN
Inventors: 周微; 王力男; 张庆业; 王力权; 王永超; 王雨晴; 卢向雨
Original assignee: CETC 54 Research Institute
Current assignee: Hebei Shenzhou Satellite Communication Co ltd; CETC 54 Research Institute
Priority date: 2021-10-28
Filing date: 2021-10-28
Publication date: 2022-02-08
Anticipated expiration: 2041-10-28
Also published as: CN114024813B

Abstract

The invention discloses a design and configuration method of a broadcast control channel of a low earth orbit satellite constellation system, and relates to the field of satellite mobile communication. The method designs a broadcast control channel in a low-orbit constellation system and adopts an OFDM subcarrier combined CDMA frequency domain spread spectrum system to complete a main synchronous channel, an auxiliary synchronous channel, a public broadcast channel and a public pilot channel; aiming at the rapid change of the relative position of a satellite and a terminal in a low-orbit constellation, which causes rapid change of Doppler frequency, a PSS channel can be used for rapid synchronous capture in a large dynamic environment, meanwhile, a SSS channel is designed to complete Cell identification Cell _ ID analysis and wireless frame synchronization, then, PBCH channel is used for analysis to complete wireless superframe synchronization, and finally, common pilot frequency design can be used for completing timing frequency tracking in the Doppler environment.

Description

Low earth orbit satellite constellation system broadcast control channel design and configuration method

Technical Field

The invention belongs to the field of satellite mobile communication, and particularly relates to a design and configuration method of a broadcast control channel of a low-earth-orbit satellite constellation system.

Background

Foreign low-frequency low-orbit mobile communication constellations Iridium, Globalstar and Orbcomm are already put into operation and start upgrading and updating; at present, the low orbit constellation operated in China does not exist, and a plurality of domestic units propose different types of low orbit constellation design schemes such as rainbow clouds, swan geese, heaven and earth integration and the like. The current low-orbit satellite network is used as an important component of the satellite network, is a dense-personnel area relative to the main coverage area of the ground mobile communication system, and is an important supplement of the ground mobile communication system in the face of the poor areas of rare personnel and natural geographical obstacles; in addition, the low-orbit satellite communication system can provide services at any time and at any place for access users by virtue of the unique advantages of low operation orbit, short transmission delay, wide coverage range, flexible networking and the like; plays an important role in the actions of anti-terrorism, field operation, airplane ocean and the like.

At present, a link transmission system of a low-earth-orbit satellite mobile communication system mainly has two development trends, one trend is to adopt a CDMA transmission technology, such as a Globalstar low-earth-orbit satellite system; another trend is for hybrid transmission technologies, such as the Iridium low-earth satellite system to employ MF-TDMA transmission technology combining FDMA and TDMA. However, the link transmission of the low-earth satellite system has certain disadvantages no matter FDMA, TDMA or CDMA transmission technology; CDMA can effectively suppress multipath fading through diversity reception, as opposed to TDMA; and for a transmission link with a large number of multipaths, the complexity of the receiver equipment of the CDMA transmission system needs to be increased. In the low orbit satellite MF-TDMA transmission system, the transponder bandwidth is divided into a plurality of frequency segments, then share for a plurality of mobile user terminals through the way of time division, the disadvantage of this transmission technology is that the frequency band utilization is low, need to unite two kinds of transmission systems at the same time, make the complexity of the transmitter and receiving arrangement high.

In the current low-earth transmission technology research, the design of a main transmission system is to move partial transmission systems in the third generation, fourth generation and 5G standards to a satellite scene and perform relevant applicable system demonstration and design work. In the aspect of improving the utilization rate of frequency bands, the OFDM technology can be used for solving the restriction of limited frequency band resources so as to obtain better frequency band resource allocation performance, and the OFDM technology improves the performance of resisting frequency selective fading channels of a low-orbit broadband satellite system by taking a cyclic prefix as a protection interval; meanwhile, the spectrum density of the satellite transmitting power can be further effectively reduced by utilizing CDMA spread spectrum in OFDM, and multipath fading can be effectively inhibited. However, aiming at the large doppler characteristic of the low earth orbit satellite constellation and the requirement of the ground base station for loading on the satellite, the prior art has not proposed a method for designing and configuring the broadcast channel of the low earth orbit satellite constellation system by combining OFDM with CDMA frequency domain spread spectrum.

Disclosure of Invention

In view of this, the present invention provides a method for designing and configuring a broadcast control channel of a low earth orbit satellite constellation system, which can design a synchronization channel and a common broadcast channel in the low earth orbit satellite constellation system, and configure broadcast channels of cells of a satellite beam.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for designing and configuring a broadcast control channel of a low earth orbit satellite constellation system comprises the following steps:

(1) designing a radio frame format of a common broadcast channel, wherein the radio frame format comprises subframes and a radio frame, each subframe comprises 14 OFDM symbols in a time domain and occupies 2 in a frequency domainⁿN is greater than or equal to 7, and the interval of each subcarrier is designed to be 7.5

K

2^u，0≤u≤4；

(2) Designing the primary synchronization signal to use small m-sequencesGeneration of small m-sequences of length 2ⁿ-1 and the last frequency domain subcarrier position is padded with 0 to form a length of 2ⁿA long synchronization sequence;

(3) design of secondary synchronization signal with length of 2^k-1 small m-sequence cyclic shift generation and 2^(n-k)Repeating the mapping for the second time, wherein the first and the last subcarrier positions in the frequency domain mapping need to be uniformly filled with 0 to be recombined into 2ⁿA long sequence;

(4) the broadcasting channel is designed to adopt BPSK/QPSK modulation, and each modulation symbol adopts 2ⁿThe long OVSF code carries out frequency domain spreading, a spreading code channel and a Cell identification Cell _ ID are in a corresponding relation and occupy all 2ⁿA subcarrier;

(5) the transmission of the common pilot channel is designed as a fixed modulation symbol, with 2 being used per modulation symbolⁿThe long OVSF code carries out frequency domain spreading, a spreading code channel and a Cell identification Cell _ ID are in a corresponding relation and occupy all 2ⁿA subcarrier;

(6) corresponding to the design of the main synchronization signal in the step (2), configuring the main synchronization signal to occupy any symbol in the first half sub-frame in each sub-frame of each Cell, wherein the signal formats of the main synchronization signal in all sub-frames are the same, and the specific time domain symbol position of the main synchronization signal is correspondingly related to the Cell identification Cell _ ID number modulo 7;

(7) corresponding to the design of the auxiliary synchronization signal in the step (3), configuring the auxiliary synchronization signal to generate an m sequence in each subframe, wherein the m sequence is only related to Cell _ ID and subframe number of a Cell in cyclic shift, and the auxiliary synchronization signal occupies one symbol in a second-half subframe in each subframe, and the specific time domain symbol position is in a corresponding relation with a Cell identification Cell _ ID numbering module 7;

(8) corresponding to the broadcast channel design in the step (4), configuring the broadcast channel to occupy all the rest time domain symbol positions in a wireless frame except the time domain symbol positions of the main synchronization signal and the auxiliary synchronization signal in each cell;

(9) corresponding to the design of the common pilot channel in the step (5), the common pilot channel is configured to have the same symbol format in each cell, but adopts different spreading code channels and occupies all time domain symbol positions in a wireless frame;

(10) corresponding to the design of the steps (2) - (5), except for the channels of the primary synchronization signal and the secondary synchronization signal, the broadcast channel and the common pilot channel are scrambled after each Cell completes frequency domain spreading, and the scrambling code number and the Cell identification Cell _ ID number module 7 are in a corresponding relation.

The invention has the beneficial effects that:

1. the invention can effectively complete the rapid synchronous capture and the downloading wave tracking at the large Doppler change rate under the large Doppler environment of the low-orbit constellation based on the large Doppler environment of the low-orbit satellite constellation system and the requirement of transmitting the low-power spectrum by the satellite load common channel.

2. The invention adopts OFDM technology, can effectively resist multipath effect under high-speed movement, reduces intersymbol interference and can improve the frequency spectrum efficiency.

3. The invention adopts the code division multiple access technology, can effectively reduce the power spectral density of the satellite load by using the spread spectrum gain, simultaneously improves the receiving performance of the ground terminal in the interference environment, and enhances the anti-interference capability of the system.

Drawings

FIG. 1 is a block diagram of a broadcast channel time and frequency domain frame structure in an embodiment of the present invention;

FIG. 2 is a diagram of a low earth orbit satellite cell beam division in an embodiment of the present invention;

FIG. 3 is a symbol composition diagram per subframe according to the present invention;

fig. 4 is a flow chart of digital signal processing for each channel according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

A method for designing and configuring broadcast control channels of a low-orbit satellite constellation system is characterized in that a primary synchronization channel PSS, a secondary synchronization channel SSS, a common broadcast channel PBCH and a common pilot channel CPICH are designed in the low-orbit satellite constellation system by adopting an OFDM combined CDMA frequency domain spread spectrum system.

The specific design idea is as follows:

(1) the public broadcast channel adopts the multi-address technology of OFDM + CDMA frequency domain spread spectrum; the radio frame format is composed of subframes and a radio frame, wherein each subframe comprises 14 OFDM symbols in a time domain, and a frequency domain occupies 2ⁿA number of consecutive subcarriers (n ≧ 7), and the subcarrier spacing is typically designed to be 7.5K 2^u(u is more than or equal to 0 and less than or equal to 4); and the 1 st and 7 th OFDM symbols in each wireless subframe adopt a cyclic prefix format 0(160Ts), the rest symbols adopt a cyclic prefix format 1(144Ts), and the specific cyclic prefix length is related to the subcarrier spacing;

(2) based on the content of the first aspect, the Primary Synchronization Signal (PSS) design is generated by using a small m sequence, wherein the length of the small m sequence is 2ⁿ-1 and the last frequency domain subcarrier position is padded with 0 to form a length of 2ⁿA long synchronization sequence; the design of auxiliary synchronous signal (SSS) adopts length of 2^kSmall m-sequence cyclic shift composition of-1 and 2 on each OFDM symbol^(n-k)Repeating the mapping for the second time, uniformly filling 0 in the first and the last subcarrier positions in the frequency domain mapping, and recombining 2ⁿA long sequence;

(3) based on the first aspect, the broadcast channel (PBCH) is BPSK/QPSK modulated with 2 modulation symbols per modulation symbolⁿThe long OVSF code is used for frequency domain spreading, specifically, a spreading code channel and a satellite beam Cell identification Cell _ ID are in a corresponding relation and occupy all 2ⁿA subcarrier; the common pilot channel (CPICH) is transmitted as fixed modulation symbols, using 2 per modulation symbolⁿThe long OVSF code is used for frequency domain spreading, specifically, a spreading code channel and a satellite beam Cell identification Cell _ ID are in a corresponding relation and occupy all 2ⁿA subcarrier;

(4) in the second aspect, the time domain occupies symbol positions and Cell identifiers Cell _ ID are combined in the design of the primary/secondary synchronization signals, and the PSS/SSS of different cells occupy different symbol positions and are distributed discretely in time, so that the peak power of a satellite can be effectively reduced, and the terminal can complete beam measurement; and common channels of the cell and the adjacent cell adopt same-frequency multiplexing, and PBCH and CPICH channels are configured in a frequency domain by adopting code division multiple access and scrambling treatment, so that the transmitting power spectral density of the common channels of the satellite can be obviously reduced, and the anti-interference capability of the common channels can be enhanced.

(5) On the basis of the content of the second aspect, the specific configuration standard of the PSS is that any one symbol in the first half subframe is occupied in each subframe of each Cell, the PSS signal formats in all subframes are the same, and the specific time domain symbol position of the PSS is correspondingly related to the Cell identifier Cell _ ID numbering module 7; the SSS is configured to generate a small m sequence in each subframe, the small m sequence and cyclic shift are only related to a Cell identifier Cell _ ID and a subframe number, the SSS occupies one symbol in a second-half subframe in each subframe, and a specific time domain symbol position and a Cell identifier Cell _ ID number modulo 7 are in a corresponding relation;

(6) on the basis of the content of the second aspect, the PBCH is specifically configured to occupy all the remaining time domain symbol positions in a radio frame except the time domain symbol positions where the PSS and the SSS are located in each cell; the CPICH is specifically configured to have the same modulation symbol in each cell, but different spreading code channels are adopted, and all time domain symbols in a wireless frame are occupied;

(7) on the basis of the content of the second aspect, besides the PSS and SSS channels, the PBCH and CPICH channels need to be scrambled after each Cell completes frequency domain spreading, and the specific scrambling code number and the Cell identification Cell _ ID number modulo 7 are in a corresponding relationship.

The following is a more specific example:

referring to fig. 1 and 3, assuming that Cell identification Cell _ ID% 7 is 0, PSS is set to occupy the 1 st OFDM symbol of each subframe, SSS occupies the 7 th OFDM symbol of each subframe, PBCH occupies all symbols except PSS and SSS, and CPICH occupies all time domain symbols.

Referring to a beam division diagram of a low-and-medium orbit satellite Cell in fig. 2, cells in the whole satellite beam coverage area are distributed in a cellular manner, common broadcast channels of the Cell and adjacent cells adopt a same-frequency multiplexing mode, and different beam cells have different Cell identifications Cell _ ID, so that the PSS and SSS signals of the Cell and the adjacent cells are distributed in a time discrete staggered manner, the instantaneous peak power of a satellite is reduced, and the terminal is facilitated to perform adjacent Cell measurement.

Still referring to fig. 1, the PSS and SSS channels occupy 512 subcarriers in the frequency domain, and the PSS channel format is designed using 511 ═ (2)⁹-1) long and small m-sequences, the generator polynomial of which is: d9 + D4 + D3 + D1 +1, register initial value [110010010 ^ D]The generated m sequence is x (n), wherein n is more than or equal to 0 and less than 511; the following relation dpss 1-2x (m), m (n +43) mod 511 is set, where n is 0 ≦ 511, and dpss (511) is 0.

The PSS and SSS channel frequency domains occupy 512 subcarriers, assuming that a radio frame includes 10 radio subframes, each subframe has 1 SSS signal, i.e. the SSS can be used to find the radio frame header position and the modulo 7 value corresponding to the Cell _ ID, and the SSS channel format is described as follows: frequency domain signal generation for SSS 127 ═ (2)⁷-1) m sequence generation format dsssm (n) ═ 1-2x ((n + m) mod127)]Wherein m is N_{Cell_ID}mod 112, where 0 ≦ n < 127, x (i +7) ≦ x (i +1) + x (i)) mod2, x register initial value [ x (6) x (5) x (4) x (3) x (2) x (1) x (0)]＝[0000001]And proceed with 4 ═ 2^(9-7)The secondary repetition mapping is that dsss (0) ═ 0, dsss (1) ═ 0, dsss (2:128) ═ dsssm, dsss (129:255) ═ dsssm, dsss (256:382) — dsssm, dsss (383:509) — dsssm, dsss (510) ═ 0, and dsss (511) ═ 0; corresponding N in each subframe of SSS_{Cell_ID}The value and the Cell identifier Cell _ ID and the radio subframe number sfn _ num in each radio frame are related, and the specific corresponding relationship is as follows: n is a radical of_{Cell_ID}10 × (Cell _ ID mod 7) + sfn _ num, where the Cell identification Cell _ ID mod7 ranges from 0,1,2, …, 6; sfn _ num ranges from 0,1,2, … 9, N_{Cell_ID}The variation range is 0-69, the terminal can carry out fast Hadamard transform and combine continuous 10 subframe peak values, and the subframe number of the cell ID number and the subframe number of the wireless frame head position can be found. It can be seen that the symbol positions occupied by the PSS and the SSS are only related to 3 bits after the Cell identifier Cell _ ID, radio frame timing information can be completely obtained through the PSS and the SSS, and then the timing synchronization of the Cell _ ID number of the whole Cell and the radio superframe frame can be obtained through PBCH demodulation and decoding.

Referring to fig. 4, a common pilot channel (CPICH) is a fixed-rate downlink channel, each subframe occupies 14 OFDM symbols, and occupies all 512 subcarriers in the frequency domainThe channelisation code of CPICH of wave, all wave beam cells is fixed as C_ch,512,511. The Physical Broadcast Channel (PBCH) is a downlink common physical channel with fixed rate, is used for transmitting system broadcast information, configures the frame length according to the specific PBCH information rate, and can configure to occupy a plurality of wireless frame lengths, and occupy all 512 subcarriers in the frequency domain, corresponding to a spreading factor of 512 channelization codes, the channelization codes are fixed as C channelization codes_ch,512,nN takes 1-7, and the specific N takes value and obtains the cell identifier (N) by the access network through SSS meter_{Cell_ID}) Determining; the PBCH may employ BPSK/QPSK modulation and requires channel coding design. Because CPICH and PBCH occupy all 512 subcarriers and occupy the whole wireless frame in the frequency domain, different cells adopt the same-frequency multiplexing mode, although different cells adopt different spreading codes, in order to reduce the mutual interference between the same-frequency cells to the maximum extent, the invention carries out scrambling processing on PBCH and CPICH channels after frequency domain spreading before IFFT, and the corresponding scrambling code numbers of different cells are Cell identification Cell _ ID mod 7.

CPICH/PBCH channel mapping parameters

In a word, the invention designs a broadcast control channel in a low-orbit constellation system, and adopts an OFDM subcarrier combined CDMA frequency domain spread spectrum system to complete a primary synchronization channel PSS, a secondary synchronization channel SSS, a common broadcast channel PBCH and a common pilot channel CPICH; aiming at the rapid change of the relative position of a satellite and a terminal in a low-orbit constellation, which causes rapid change of Doppler frequency, a PSS channel can be used for rapid synchronous capture in a large dynamic environment, meanwhile, a SSS channel is designed to complete Cell identification Cell _ ID analysis and wireless frame synchronization, then, PBCH channel is used for analysis to complete wireless superframe synchronization, and finally, common pilot frequency design can be used for completing timing frequency tracking in the Doppler environment.

By utilizing the method, the rapid synchronous capture and the carrier tracking under the large Doppler environment of the low-orbit constellation can be effectively finished, the primary/secondary synchronous signal design combines the symbol positions occupied by the time domain and the Cell identification Cell _ ID, and the PSS/SSS of different cells occupy different symbol positions and are in discrete distribution in time, so that the peak power of the satellite can be effectively reduced, and the terminal can finish the beam measurement; and common channels of the cell and the adjacent cell adopt same-frequency multiplexing, and the PBCH and CPICH channel configuration frequency domain adopts a code division multiple access mode, so that the transmitting power spectral density of the common channels of the satellite can be obviously reduced, and the anti-interference capability of the common channels can be enhanced.

Claims

1. a low-orbit satellite constellation system broadcast control channel design and configuration method, is characterized in that, comprises the following steps:

(1) Designing the radio frame format of the public broadcasting channel is composed of subframes and radio frames, in which each subframe contains 14 OFDM symbols in the time domain, and occupies 2 ⁿ consecutive subcarriers in the frequency domain, n≥7, and the subcarrier spacing is designed as 7.5K*2 ^u , 0≤u≤4;

(2) The main synchronization signal is designed to be generated by the small m sequence, where the length of the small m sequence is 2 ⁿ -1, and the last frequency domain subcarrier position is filled with 0 to form a long synchronization sequence with a length of 2 ⁿ ;

(3) The secondary synchronization signal is designed to be generated by a small ^m -sequence cyclic shift with a length of 2 ^k -1, and 2 ^(nk) times of repeated mapping are performed. long sequence;

(4) The broadcast channel is designed to use BPSK/QPSK modulation, and each modulation symbol uses a ²ⁿ -long OVSF code for frequency-domain spreading. The spread-spectrum code channel has a corresponding relationship with the cell ID Cell_ID, and occupies all ²ⁿ subcarriers;

(5) The transmission of the common pilot channel is designed as a fixed modulation symbol. Each modulation symbol uses a ²ⁿ -long OVSF code for frequency-domain spreading. The spread-spectrum code channel has a corresponding relationship with the cell ID Cell_ID, and occupies all ²ⁿ subcarriers. ;

(6) Corresponding to the design of the primary synchronization signal in step (2), the primary synchronization signal is configured to occupy any symbol in the first half of the subframe in each subframe of each cell, and the format of the primary synchronization signal in all subframes is the same, The specific time domain symbol position of the primary synchronization signal is correspondingly correlated with the cell identifier Cell_ID number modulo 7;

(7) Corresponding to the secondary synchronization signal design in step (3), configure the secondary synchronization signal such that the generation and cyclic shift of the small m sequence in each subframe are only related to the cell Cell_ID and the subframe number, and in each subframe The synchronization signal occupies one symbol in the second half of the subframe, and the specific time domain symbol position and the cell ID Cell_ID number modulo 7 are in a corresponding relationship;

(8) Corresponding to the broadcast channel design in step (4), configure the broadcast channel to occupy all other time-domain symbol positions in a radio frame except for the time-domain symbol positions where the primary synchronization signal and the secondary synchronization signal are located in each cell ;

(9) Corresponding to the design of the common pilot channel in step (5), configure the common pilot channel to have the same symbol format in each cell, but use different spread spectrum code channels, and occupy the entire time domain in a radio frame symbol position;

(10) Corresponding to the design of steps (2) to (5), in addition to the channels of the primary synchronization signal and the secondary synchronization signal, the broadcast channel and the common pilot channel are scrambled after the frequency domain spreading is completed in each cell. The code number and the cell identifier Cell_ID number modulo 7 are in a corresponding relationship.