CN116980031B - Method for generating downlink spread spectrum signal of low-orbit satellite communication system - Google Patents

Method for generating downlink spread spectrum signal of low-orbit satellite communication system Download PDF

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CN116980031B
CN116980031B CN202311238605.XA CN202311238605A CN116980031B CN 116980031 B CN116980031 B CN 116980031B CN 202311238605 A CN202311238605 A CN 202311238605A CN 116980031 B CN116980031 B CN 116980031B
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spread spectrum
channel
downlink
data
satellite
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CN116980031A (en
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张庆业
王力男
王力权
袁旭彬
周微
王雨晴
王永超
肖娜
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CETC 54 Research Institute
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/14Relay systems
    • H04B7/15Active relay systems
    • H04B7/185Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851Systems using a satellite or space-based relay
    • H04B7/18513Transmission in a satellite or space-based system
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B1/00Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69Spread spectrum techniques

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
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Abstract

The invention provides a downlink spread spectrum signal generation method of a low-orbit satellite communication system, and relates to the field of wireless communication. The invention comprises the following steps: carrying out channel coding on multi-beam and multi-channel data transmitted by a satellite system in a downlink mode; modulating; multi-beam spread spectrum code allocation; spreading; performing gain control processing on the data after the spread spectrum of each channel; accumulating the business and control channels in the wave beam according to the frame structure; scrambling code generation; scrambling treatment; generating downlink spread spectrum synchronous channel data; the scrambled data and the downlink spread spectrum synchronous channel data are configured according to beam mapping and then accumulated; and performing up-sampling and shaping filtering on the processed data to finish the generation of the downlink spread spectrum signal. The invention adopts a spread spectrum mode, adopts scrambling code distinction for different satellites, adopts a multicolor code division mode for different beams under the same satellite and a special time division channel, and solves the problem of limited downlink power of a low-orbit constellation.

Description

Method for generating downlink spread spectrum signal of low-orbit satellite communication system
Technical Field
The invention relates to the field of wireless communication, in particular to a downlink spread spectrum signal generation method of a low-orbit satellite communication system.
Background
At present, a common wireless communication mode is ground wireless communication, and the communication network mainly completes signal forwarding and transmission through a ground base station. However, due to economic cost, technology and other natural environmental factors, the area covered by ground base stations occupies only about 20% of the total global area. Meanwhile, the ground base station is easy to destroy in special scenes with extremely strong destructive power such as earthquake, tsunami, storm or fire disaster, and cannot be quickly repaired in a short period, so that timely communication service cannot be provided. At the moment, the satellite communication network is not affected by ground disasters due to the characteristics of large coverage area, flexible networking and the like, and plays an irreplaceable important role in the fields of emergency rescue, navigation, aviation safety guarantee and the like. Meanwhile, satellite mobile communication, in particular to a low orbit satellite mobile communication constellation system, has the advantages of smaller communication time delay, smaller signal propagation loss and the like due to lower orbit height. However, because of the small coverage area of a single satellite, in order to achieve global or large-scale coverage, a plurality of low-orbit satellites are required to be cooperatively designed into a low-orbit constellation communication system.
In the radio rule formulated by the ITU, the requirements of signal landing power flux density set in a specific frequency band and different countries are different, but the downlink signal single carrier transmitting power of the conventional low-orbit satellite constellation does not meet the requirements of the ITU, so that a downlink multiple access mode and a channel design method which can meet the requirements of the ITU and simultaneously meet the application of the low-orbit constellation need to be designed.
Disclosure of Invention
The invention designs a downlink spread spectrum signal generating method of a low-orbit satellite communication system aiming at the problems. The method adopts a spread spectrum mode, adopts scrambling code distinction for different satellites, adopts a multicolor code division mode for different beams under the same satellite and a special time division channel, and solves the problem of limited downlink power of a low-orbit constellation.
The technical scheme adopted by the invention is as follows:
a method for generating a downlink spread spectrum signal for a low-orbit satellite communication system, comprising the steps of:
step 1, carrying out channel coding on original data of a plurality of beams and a plurality of channels transmitted by a satellite system in a downlink mode;
step 2, modulating the data after channel coding according to a MPSK modulation mode;
step 3, carrying out multi-beam spread spectrum code allocation on service and control channels in a plurality of beams of a satellite, wherein the spread spectrum codes adopt OVSF codes with different lengths according to different spread spectrum multiples SF, and the spread spectrum code allocation adopts a multi-beam same-frequency multi-color code division multiplexing mode;
step 4, replacing the data symbol of the channel with the allocated spreading code according to the bit, and performing spreading operation;
step 5, gain control processing is carried out on the data after the spread spectrum of each channel;
step 6, accumulating the business and control channels in the wave beam according to the frame structure;
step 7, each satellite is distributed with a scrambling code generation sequence and a scrambling code number, and scrambling code generation is carried out according to the scrambling code generation sequence and the scrambling code number;
step 8, multiplying the data processed in the step 6 by the scrambling code of the satellite to finish scrambling processing;
step 9, generating downlink spread spectrum synchronous channel data according to a synchronous sequence format;
step 10, carrying out accumulation processing on scrambled data and downlink spread spectrum synchronous channel data after configuration according to beam mapping;
and step 11, carrying out up-sampling and shaping filtering processing on the data processed in the step 10, and completing the generation of the downlink spread spectrum signal.
Further, in step 1, channels in a single beam of the satellite include a downlink spread spectrum synchronization channel, a downlink spread spectrum common pilot channel, a downlink spread spectrum physical broadcast channel, a downlink spread spectrum physical paging channel, and a downlink spread spectrum physical dedicated channel;
in step 3, different fixed OVSF codes are allocated to downlink spread spectrum common pilot channel, downlink spread spectrum physical broadcast channel and downlink spread spectrum physical paging channel in a single wave beam, and R channel OVSF codes are reserved for use as paging channels, and each wave beam uses r+3 control channels; according to the beam polychromatic multiplexing coefficient L, channels of adjacent (L-1) beams use different OVSF codes, and all beams of the whole star use L (3+R) OVSF codes in total; these OVSF codes can be multiplexed in addition to the L beams; the downlink spread spectrum physical dedicated channel adopts a multi-beam same-frequency multi-color code division multiplexing mode, and the intra-beam dedicated channel can use all spread spectrum codes except the control channel.
Further, in step 7, scrambling code allocation adopts the same mode of adjacent star dissimilarity and star separation, adjacent satellites in the constellation are distinguished by using different scrambling codes, and non-adjacent satellites can multiplex the same scrambling codes.
Further, in step 10, the specific manner of the beam mapping configuration is that the spread synchronization channels of the adjacent beams are offset by different chips N with respect to the time slot starting time:
N=SeqNum*Chip_offset
the SeqNum is 0 to L-1, and chip_offset is the chip offset.
The invention has the beneficial effects that:
1. the downlink spread spectrum channel of the low-orbit satellite constellation system can support different spread spectrum OVSF (Orthogonal Variable Spreading Factor) codes, adopts different spread spectrum ratios and spread spectrum bandwidths according to different use scene requirements, and meets the requirements of different regions on the floor power spectral density.
2. The downlink spread spectrum channel of the low orbit satellite constellation system supports the control and service channel configuration of different beams of the same satellite by adopting different scrambling code configuration modes for a plurality of satellites in the low orbit constellation.
3. The invention provides a low-orbit constellation system downlink spread spectrum channel configuration meeting the requirements of the ground power flux density and the large-scale frequency offset change of different areas, so that the channel meets the use requirements of low-orbit satellite services in specific areas.
Drawings
Fig. 1 is a schematic diagram of a downlink spread spectrum signal generating method of a low-orbit satellite communication system according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a frame format in an embodiment of the present invention.
Fig. 3 is a beam polychromatic multiplexing diagram of the same satellite in an embodiment of the invention.
Fig. 4 is a schematic diagram of a synchronization signal transmission structure in an embodiment of the present invention.
Fig. 5 is a schematic diagram of a structure of a spread spectrum downlink traffic channel in an embodiment of the present invention.
Fig. 6 is a schematic diagram of satellite scrambling code allocation according to an embodiment of the present invention.
Detailed Description
The technical scheme of the invention is described in detail below with reference to the accompanying drawings.
A method for generating a downlink spread spectrum signal of a low-orbit satellite communication system, as shown in fig. 1, comprises the following steps:
step 1, carrying out channel coding on original data of a plurality of beams and a plurality of channels transmitted by a satellite system in a downlink mode;
step 2, modulating the data after channel coding according to a MPSK modulation mode;
step 3, carrying out multi-beam spread spectrum code allocation on service and control channels in a plurality of beams of a satellite, wherein the spread spectrum codes adopt OVSF codes with different lengths according to different spread spectrum multiples SF, and the spread spectrum code allocation adopts a multi-beam same-frequency multi-color code division multiplexing mode;
step 4, replacing the data symbol of the channel with the allocated spreading code according to the bit, and performing spreading operation;
step 5, gain control processing is carried out on the data after the spread spectrum of each channel;
step 6, accumulating the business and control channels in the wave beam according to the frame structure;
step 7, each satellite is distributed with a scrambling code generation sequence and a scrambling code number, and scrambling code generation is carried out according to the scrambling code generation sequence and the scrambling code number;
step 8, multiplying the data processed in the step 6 by the scrambling code of the satellite to finish scrambling processing;
step 9, generating downlink spread spectrum synchronous channel data according to a synchronous sequence format;
step 10, carrying out accumulation processing on scrambled data and downlink spread spectrum synchronous channel data after configuration according to beam mapping;
and step 11, carrying out up-sampling and shaping filtering processing on the data processed in the step 10, and completing the generation of the downlink spread spectrum signal.
Further, in step 1, channels in a single beam of the satellite include a downlink spread spectrum synchronization channel, a downlink spread spectrum common pilot channel, a downlink spread spectrum physical broadcast channel, a downlink spread spectrum physical paging channel, and a downlink spread spectrum physical dedicated channel;
in step 3, different fixed OVSF codes are allocated to downlink spread spectrum common pilot channel, downlink spread spectrum physical broadcast channel and downlink spread spectrum physical paging channel in a single wave beam, and R channel OVSF codes are reserved for use as paging channels, and each wave beam uses r+3 control channels; according to the beam polychromatic multiplexing coefficient L, channels of adjacent (L-1) beams use different OVSF codes, and all beams of the whole star use L (3+R) OVSF codes in total; these OVSF codes can be multiplexed in addition to the L beams; the downlink spread spectrum physical dedicated channel adopts a multi-beam same-frequency multi-color code division multiplexing mode, and the intra-beam dedicated channel can use all spread spectrum codes except the control channel.
Further, in step 7, scrambling code allocation adopts the same mode of adjacent star dissimilarity and star separation, adjacent satellites in the constellation are distinguished by using different scrambling codes, and non-adjacent satellites can multiplex the same scrambling codes.
Further, in step 10, the specific manner of the beam mapping configuration is that the spread synchronization channels of the adjacent beams are offset by different chips N with respect to the time slot starting time:
N=SeqNum*Chip_offset
the SeqNum is 0 to L-1, and chip_offset is the chip offset.
The signal generated by the method has the following characteristics:
the spread spectrum signal transmission process includes: data coding, modulation, multi-beam spread spectrum code allocation, spread spectrum, satellite scrambling code allocation, scrambling, multi-beam synchronous signal configuration, synchronous signal accumulation and shaping treatment;
the satellite mobile communication downlink spread spectrum signal at least comprises a synchronous channel which is used for completing downlink synchronization; a broadcast channel for broadcasting broadcast messages; and a paging message used for broadcasting the paging message in the system, a dedicated channel, and carrying and transmitting user data and control information.
The multiplexing mode is multi-beam multi-color code division multiplexing; the multiple access mode is a CDMA system;
the multi-beam spread spectrum codes are distributed into multi-beam same-frequency multi-color code division multiplexing modes, and the multiplexing number is L; the channels in the same beam of the same satellite are distinguished by using different OVSF codes, and the service channels of adjacent beams can share and use code resources;
the satellite wave beam scrambling codes are distributed in the same mode that adjacent satellites are different and separated, the adjacent satellites in the constellation are distinguished by using different scrambling codes, the same scrambling codes can be multiplexed by non-adjacent satellites, and P scrambling codes can be adopted by a system according to the satellite deployment conditions of the same track surface and different track surfaces of the constellation;
the multi-beam synchronizing signal is configured to be the downlink synchronizing signal of the adjacent beam and offset by different chips, so that the terminal can search and fully utilize satellite power.
The method includes spreading downlink time division service channel, reserving K chip guard time channels before and after the channel, using configured spreading code, determining the length of K chips by uplink and downlink switching time of TDD terminal, and configuring multiple time division service channels with the same spreading code in one frame and multiple time division channels with different spreading codes in the same time.
The following is a more specific example:
as shown in fig. 2, the low orbit satellite downlink spread spectrum adopts a CDMA system, and the spread spectrum chip rate is 5.12Mcps. A 60ms spread spectrum frame includes 5 spread spectrum subframes and a 12ms radio spread spectrum subframe is divided into 10 spread spectrum slots (6144 chips/slot at a chip rate of 5.12 Mcps).
The spread spectrum channels comprise 5 channel types of physical synchronous channels, common pilot channels, physical broadcast channels, physical paging channels and physical downlink dedicated channels, and each channel function is described as follows:
1) SCH: a physical synchronization channel, the payload transmits a beam Primary Synchronization Sequence (PSS) and a beam Secondary Synchronization Sequence (SSS) using the channel.
2) The CPICH common pilot channel, which is used by the payload to transmit the beam common pilot.
3) The PBCH physical broadcast channel, which the payload uses to broadcast common information.
4) The PPCH physical paging channel, which is used by the payload to send paging messages.
5) PDTCH: the physical downlink dedicated channel comprises three channel types of PDTCH1\PDTCH2\PDTCH3, carries information data with different lengths, and uses the channel to send service data and dedicated control information by load.
In the method, different beams of the same satellite adopt a multicolor multiplexing mode, and multicolor spread spectrum code multiplexing of 4 colors, 7 colors, 12 colors and the like can be supported. As shown in fig. 3, taking 4-color multiplexing as an example, 512 spread code words are divided into four groups, respectively: 0-127, 128-255, 256-383, 384-511. Satellite coverage areas are also divided into four types of multiplexing areas. The multiplexing area 0 occupies a spreading code range of 0-127, the multiplexing area 1 occupies a spreading code range of 128-255, the multiplexing area 2 occupies a spreading code range of 256-383, and the multiplexing area 3 occupies a spreading code range of 384-511. Adjacent multiplexing areas must not use the same spreading code word. This approach allows the same frequency to be used between a large number of non-adjacent beams, significantly increasing frequency utilization and satellite communication capacity. If no interference between beams is to be ensured, narrow beams are required to be used and the beam intervals are far, but in practice, in order to ensure the coverage continuity, the beams are overlapped, so that the frequency can be reused by combining polarization multiplexing and regional isolation, thereby expanding the communication capacity.
The PSS synchronization signal and the SSS synchronization signal sent by the payload occupy 512 chips, in the same satellite, each beam PSS is offset by N chips with respect to the slot header, SSS is offset by n+512 chips with respect to the slot header, and the specific N value is related to the current beam multiplexing sequence number, n=seqnum×256 (for example, 7-color multiplexing, l=7, and SeqNum takes the value of 0-6). The synchronization signal transmission structure is shown in fig. 4. The PSS transmits signal sequence codes every time slot and keeps unchanged, SSS generates different sequence codes according to the time slot number, and the SSS transmits the signal sequence codes according to time slot conversion by taking a subframe as a conversion period.
The channelization codes are defined as Cch, SF, k, where SF is a spreading factor, k represents a kth spreading codeword, each stage of the code tree defines a channelization code of length SF, in this embodiment sf=512 for pilot channel, broadcast channel, paging channel and DTCH1 channel, sf=256 for DTCH2 channel, sf=128 for DTCH3 channel.
Taking 7-color multiplexing as an example, the system defines 7 groups of channelization codes for controlling channel allocation of maximum common-frequency 7-color spread spectrum code multiplexing wave beams, wherein k=0, 1, 2, 3, 4, 5 and 6, and the channelization code allocation mode of the same satellite is as follows:
(1) Control channel
The adjacent wave beams comprise control channels such as broadcasting, paging, public control and the like, and the system determines code resources according to the wave beam number and the multicolor multiplexing number so that the terminal can search on the set code resources.
The OVSF channel allocation is shown in the table below:
table 1 OVSF channel allocation table
(2) Traffic channel
The 512 spreading codes of the whole star are used as the downlink public code domain resources of the system, the spreading codes except the spreading broadcast channel can be dynamically allocated according to the actual user quantity, and all the code resources can be allocated to the same wave beam in the satellite power concentration mode.
In the method, a system spread spectrum downlink time division traffic channel is also designed, as shown in fig. 5. The front and back of the channel leave a protection time of K chips, and the length of K is determined by the uplink and downlink switching time of the TDD terminal. In terms of channelization code allocation, dynamically allocated spreading codes other than broadcast channels are also used. A plurality of time division service channels adopting the same spreading code can be arranged in one frame, and the time division channel configuration of a plurality of different spreading codes can be also arranged at the same time, so that the frequency spectrum utilization rate is greatly improved;
in the method, scrambling codes are used for distinguishing satellites, adjacent satellites adopt different scrambling codes, the system provides 4 basic scrambling codes, the numbers are respectively 0, 16, 32 and 48, as shown in fig. 6, the adjacent satellites in the constellation are distinguished by using the different scrambling codes, and the basic scrambling codes adopted by the satellites are designated by an upper network. All beams of each satellite are only allocated with one basic scrambling code, and the control channel and the service channel are scrambled by using the scrambling codes and then transmitted.

Claims (3)

1. A method for generating a downlink spread spectrum signal for a low-orbit satellite communication system, comprising the steps of:
step 1, carrying out channel coding on original data of a plurality of beams and a plurality of channels transmitted by a satellite system in a downlink mode; the channels in the satellite single wave beam comprise a downlink spread spectrum synchronous channel, a downlink spread spectrum public pilot channel, a downlink spread spectrum physical broadcast channel, a downlink spread spectrum physical paging channel and a downlink spread spectrum physical special channel;
step 2, modulating the data after channel coding according to a MPSK modulation mode;
step 3, carrying out multi-beam spread spectrum code allocation on service and control channels in a plurality of beams of a satellite, wherein the spread spectrum codes adopt OVSF codes with different lengths according to different spread spectrum multiples SF, and the spread spectrum code allocation adopts a multi-beam same-frequency multi-color code division multiplexing mode; different fixed OVSF codes are allocated to a downlink spread spectrum common pilot channel, a downlink spread spectrum physical broadcast channel and a downlink spread spectrum physical paging channel in a single wave beam, R channel OVSF codes are reserved to be used as paging channels, and each wave beam uses R+3 control channels; according to the beam polychromatic multiplexing coefficient L, channels of adjacent L-1 beams use different OVSF codes, and all beams of the whole star use L (3+R) OVSF codes in total; these OVSF codes can be multiplexed in addition to the L beams; the downlink spread spectrum physical dedicated channel adopts a multi-beam same-frequency multi-color code division multiplexing mode, and the dedicated channel in the beam can use all spread spectrum codes except the control channel;
step 4, replacing the data symbol of the channel with the allocated spreading code according to the bit, and performing spreading operation;
step 5, gain control processing is carried out on the data after the spread spectrum of each channel;
step 6, accumulating the business and control channels in the wave beam according to the frame structure;
step 7, each satellite is distributed with a scrambling code generation sequence and a scrambling code number, and scrambling code generation is carried out according to the scrambling code generation sequence and the scrambling code number;
step 8, multiplying the data processed in the step 6 by the scrambling code of the satellite to finish scrambling processing;
step 9, generating downlink spread spectrum synchronous channel data according to a synchronous sequence format;
step 10, carrying out accumulation processing on scrambled data and downlink spread spectrum synchronous channel data after configuration according to beam mapping;
and step 11, carrying out up-sampling and shaping filtering processing on the data processed in the step 10, and completing the generation of the downlink spread spectrum signal.
2. The method for generating downlink spread spectrum signals in a low orbit satellite communication system according to claim 1, wherein in step 7, scrambling code allocation is performed in the same manner as adjacent satellites are different and spaced apart, adjacent satellites in a constellation are distinguished by using different scrambling codes, and non-adjacent satellites can multiplex the same scrambling codes.
3. The method for generating a downlink spread spectrum signal in a low orbit satellite communication system according to claim 1, wherein in step 10, the specific manner of beam mapping configuration is that the spread spectrum synchronization channels of adjacent beams are offset by different chips N with respect to the time slot start time:
N=SeqNum*Chip_offset
the SeqNum is 0 to L-1, and chip_offset is the chip offset.
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