CN114095324B - Framing method and apparatus for narrowband data broadcasting - Google Patents
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Abstract
The invention discloses a framing method of narrow-band data broadcasting and equipment thereof, physical layer signal frames, which are characterized in that two paths of pseudo-random sequences are subjected to a series of transformations to form synchronous beacons, 32 MID sequences are subjected to a series of transformations to form transmission mode beacons, the synchronous beacons and the transmission mode beacons form beacons, 58 OFDM symbols and the beacons form physical layer signal frames, and 1 or 4 physical layer signal frames form superframes, and the method adopts a shorter frame structure and a smaller interleaving block structure, so that the modulation and demodulation delay of digital signals is smaller, and the requirement of differential data on high transmission delay is better met; the mode of a single transmission channel different from HDradio and CDR is adopted without transmitting program information in an audio program, and all channel resources can be used for transmitting differential data, so that the transmission efficiency is high.
Description
Technical Field
The present invention relates to the field of communications, and in particular, to a framing method of narrowband data broadcasting, a device thereof, and a physical layer signal frame.
Background
With the continuous development of global satellite navigation GNSS technology, satellite navigation standard positioning accuracy of several meters to tens of meters cannot meet the requirement of users for high-precision positioning. Differential GNSS technology which can effectively improve positioning accuracy by utilizing the space and time correlation characteristics of GNSS observation errors is widely used. At present, differential GNSS equipment mainly comprises pseudo-range differential GNSS and carrier phase differential GNSS, and the positioning accuracy of the differential GNSS equipment can reach sub-meter level and centimeter level respectively. With the rapid development of the differential satellite navigation positioning field, such as a real-time dynamic carrier phase technology, a network dynamic carrier phase technology and the like, the differential satellite navigation positioning field is generated; meanwhile, a continuously-running reference station system based on a network dynamic carrier phase technology is rapidly developed in countries around the world, theoretical technical achievements in the field are greatly applied to actual life and production application, the accuracy of satellite navigation and positioning is effectively improved, and the use experience of users is improved. Differential data transmitted in a continuously operating reference station system is encoded mainly in the rules of the RTCM (Radio Technical Commission for Maritime services, differential positioning signal data format made by the international maritime service radio technical commission) protocol. The current mainstream high-precision positioning service transmits differential data in a mode of transmitting and sharing data information in the internet based on an Ntrip (Networked Transport of RTCM via Internet Protocol protocol for RTCM network transmission through the internet).
With the development of intelligent driving technology and intelligent cities, the requirements of various industries on high-precision positioning services are becoming more popular, and the number of users with high-precision positioning is also becoming larger. In the future, high-precision positioning is required not only in the professional field, but also by common consumers. Based on future popularization expectations for high-precision positioning, the manner of transmitting differential data through the internet (end users usually through wireless networks such as 4G, 5G and the like) can cause a plurality of problems after large-scale business, and the popularization of high-precision positioning services is affected. Thus, a method for transmitting differential data using fm digital broadcasting technology has been proposed, and new technology will be able to solve some of the problems and bottlenecks encountered in the prior art during the future popularization of high-precision positioning services. For convenience of description, a technology of transmitting differential data using the internet is referred to as a network differential technology, and a technology of transmitting differential data using a fm digital broadcasting technology is referred to as a broadcasting differential technology.
The network differential technology adopts a client-server mode to access a server to establish a link, the approximate position of a terminal user is reported, the server generates differential data at the user position in real time, the terminal acquires the differential data from a service through an Ntrip protocol, and high-precision positioning and resolving are carried out after the terminal acquires the differential data to acquire high-precision position information. The client-server access mode is easy to form congestion when massive user services are concurrent access. The broadcast differential technology adopts a broadcast single-point to multi-point transmission mode, a data center generates differential data of all places in a service area at regular time according to a fixed time period to form a differential data group, the differential data group is continuously broadcast to all users in the service area through a broadcast station, the users can continuously receive the broadcast differential data group without reporting positions and start up, a terminal selects one differential data which most meets the high-precision positioning requirement of the terminal according to the position of the terminal, and the terminal acquires the differential data and then performs high-precision positioning calculation to acquire high-precision position information.
The network differential technology utilizes the existing mobile network, and when each terminal uses the mobile network, network use cost is generated, so that huge cost is generated by integrating mass users by using the mobile network. Broadcast differential technology adopts point-to-multipoint transmission in the differential data transmission process, and theoretically, the transmission cost of one user and infinite users in a service area is the same, so that infinite user numbers can be served with very little fixed cost. Broadcast differential technology will create a significant cost advantage in terms of network transmission costs when a large number of users are present.
The 4G and 5G mobile networks used by the network differential technology are easy to generate large network delay and even network congestion due to the reasons of base station user capacity, concurrent user access and the like, so that differential data transmission delay is unstable and transmission delay is large. The existing 4G and 5G mobile networks often adopt cellular networks, for fast switching between different base stations in the mobile networks of users moving at high speed, when the base stations are switched, the time delay of network communication is unstable, and sometimes, problems of overlong delay occur. The satellite navigation differential data are data sensitive to the stability and the size of the transmission delay, the instability of the transmission delay is unfavorable for the deep optimization of a high-precision calculation algorithm, and the overtime of the differential age can be caused by the overlarge transmission delay so as to reduce the positioning precision. The broadcast differential technology uses a broadcast technology, the service area of a broadcast station is large, broadcast signals continuously cover the whole area in the service area, the frequency modulation broadcast carrier frequency is low, the penetrating power is strong, and the signal coverage effect is good. In the service area, the delay of the broadcast signal reaching each user is almost the same, so that the stability of the differential age is ensured. The fm digital broadcasting technique, narrowband data broadcasting (NBB), is specifically designed to transmit differential data with very little NBB broadcast transmission delay, thereby optimizing differential age. For the user moving at high speed, the differential age is not stable or even exceeds the differential age caused by frequent switching of the base station in the broadcast differential technology. In areas with poor coverage of the 4G and 5G mobile networks, the coverage advantage of the frequency modulation broadcasting technology is more obvious. Broadcast differential techniques have higher reliability availability.
The network differential technology must upload the outline position of the user when the terminal user obtains the differential data, and the server can generate the differential data for the user after receiving the user position and send the differential data to the user through the network. The network differential technology users must upload own position information, which is unfavorable for data security and unfavorable for privacy protection of the users. The broadcast differential technology adopts a broadcast transmission technology, is connected in one way, does not need to upload any information, does not collect any user information by a broadcast station, and ensures better data security and user information privacy.
The network optimization of the mobile network aims at the ground direction because the main users of the 4G mobile network and the 5G mobile network used by the network differential technology are all located on the ground, and the network quality of mobile communication cannot be ensured even most areas cannot normally communicate in the air direction. Fm broadcast is an omni-directional antenna coverage, a global coverage of signals on the ground and in the air. For unmanned aerial vehicles and other equipment needing to fly in low altitude, high-precision positioning service is used, a mobile network is adopted for differential data transmission, communication cannot be guaranteed, and broadcast technology is adopted for differential data transmission, so that air and ground services are consistent. Broadcast differential technology has absolute advantages over low-altitude coverage.
The broadcasting technology has a plurality of advantages in differential data transmission, and the adoption of the broadcasting transmission of differential data can be more optimized, more practical and more satisfied for high-precision positioning service. However, not all broadcasting techniques are suitable for transmitting differential data, narrowband data broadcasting, which is called NBB (Narrow Band data Broadcast) for short, is designed for transmitting satellite navigation positioning foundation enhanced differential data, and the advantages of broadcasting techniques can be exerted only by using NBB to transmit differential data.
The NBB technology is a parasitic fm broadcast technology developed based on fm bands, and the differences and technical advantages of this new broadcast technology and other parasitic fm broadcast technologies will be briefly described below.
Conventional FM audio signal transmissions typically use only a portion of the bandwidth within the FM band to transmit sound signals using analog modulation techniques. In order to utilize the residual spectrum resources of the FM, a plurality of digital modulation techniques are designed in the development of the FM to transmit data in-band or out-of-band of the FM, so that the simultaneous same-frequency broadcasting of the digital signals and the analog signals in the FM frequency band is realized, and the FM spectrum resources are effectively utilized. The more well-known digital transmission standards in the FM band are RDS and DARC, and the more well-known transmission standards in the FM band are HDradio in the United states and the CDR in China, as shown in FIG. 1.
FM in-band digital transmission systems such as RDS, DARC and FMextra are called digital subcarrier communication systems, and can be directly connected to an FM exciter through an SCA subcarrier interface, so that most of the FM exciters in the market support the SCA interface. Part of the FM exciter is embedded with an RDS modulator and a DARC modulator which can be directly used, and a digital subcarrier communication system without embedded support can be accessed to the FM exciter through an SCA port.
The techniques of HDradio, CDR, and NBB utilize FM out-of-band frequencies to transmit digital signals, which may be referred to as FM out-of-band digital transmission systems.
HDradio and CDR are digital transmission systems developed specifically for digital audio broadcasting. Digital audio broadcasting is a third generation broadcasting after amplitude modulation and frequency modulation broadcasting, and all of it uses digital processing mode to make audio broadcasting. Digital audio broadcasting has become a necessary trend of broadcasting development. The introduction of digital technology can effectively improve the sound quality of audio broadcasting, improve the frequency spectrum utilization rate, effectively reduce the power of a transmitter and reduce electromagnetic pollution. HDradio and CDR broadcasts utilize the free frequency resources between existing analog broadcast channels for digital audio broadcasting while keeping the existing equipment and frequency division unchanged and minimizing interference with the existing analog broadcast. Over a period of time, HDradio and CDR digital audio broadcasts will coexist with analog FM audio broadcasts and gradually transition smoothly to the digital audio broadcasting era.
The NBB digital broadcasting technology and HDradio and CDR are the same as FM out-of-band digital transmission system, and the main technical architecture adopts COFDM modulation, but NBB is not designed for digital audio broadcasting. The NBB digital broadcasting technology is a data transmission system specially designed for transmitting satellite navigation differential data, and compared with the HDradio and CDR technology, the NBB has lower transmission delay, higher data organization flexibility and higher transmission efficiency, and is more suitable for transmitting satellite navigation differential data.
Both HDradio and CDR use longer signal frame lengths and longer interleaving blocks, which makes the delay of modulation and demodulation of digital signals relatively large, and are not suitable for the high requirements of differential data on transmission delay. The HDradio and CDR techniques customize interface protocols for audio transmission, and the frame structure is strongly related to audio transmission, so that the interfacing with multiple data formats of differential data on a data organization is inflexible, the interfacing efficiency is low, the idle running of the transmission data frame is easy to occur, and the transmission bandwidth is wasted. The HDradio and CDR techniques are divided equally into control data transmission channels and traffic data transmission channels in a design structure that satisfies channel division requirements in digital audio broadcasting, the control data transmission channels transmitting configuration information and program information, and the traffic data transmission channels transmitting audio data streams. The dual-channel design has great waste for differential data transmission, the differential data transmission can only utilize a service data transmission channel, and the control data transmission channel can not transmit effective information. HDradio and CDR techniques are inefficient in transmitting differential data. The HDradio adopts error correction coding with weaker error correction capability, and the transmission interference resistance is insufficient. The CDR is coarser in frequency spectrum utilization design, so that the out-of-band frequency spectrum of FM can not be fully utilized, and the frequency spectrum utilization rate of a transmission system is reduced.
The NBB technology is specially designed for transmitting differential data, and a shorter frame structure and a smaller interleaving block structure are adopted, so that the modulation and demodulation delay of digital signals is smaller, and the requirement of high transmission delay of the differential data is better met. The NBB technology is more flexible in frame structure and interface protocol, can realize more efficient butt joint with the data structure of differential data, and improves the transmission efficiency of the system. The NBB technology adopts a mode of a single transmission channel different from HDradio and CDR, and all channel resources can be used for transmitting differential data, so that the transmission efficiency is high. The NBB adopts LDPC error correction coding which is stronger in error correction capability and interference resistance capability and better in receiving effect than convolutional coding adopted by HDradio. The NBB adopts a more flexible and finer spectrum mode than the CDR, so that the spectrum utilization rate is higher, and the future expandability is stronger.
HDradio, CDR, NBB are parasitic fm broadcast techniques, but both HDradio and CDR broadcast techniques are not suitable for transmitting differential data.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a framing method of narrow-band data broadcasting, equipment thereof and a physical layer signal frame, and aims at the transmission of differential data, a shorter frame structure and a smaller interleaving block structure are adopted, so that the delay of digital signal modulation and demodulation is smaller, and the requirement of the differential data on high transmission delay is better met.
In a first aspect, the present invention provides a framing method for narrowband data broadcasting, including the steps of:
step 1: generating 58 OFDM symbols by OFDM modulation of service data;
step 2: defining and generating two paths of pseudo-random sequences, and modulating data generated by the two paths of pseudo-random sequences to generate synchronous pilot symbols;
step 3: mapping and transforming the synchronous pilot frequency symbols according to the mapping relation between the NBB system spectrum mode and the subcarriers to form OFDM symbols of synchronous beacons;
step 4: copying the OFDM symbols in the step 3 to generate 2 identical OFDM symbols, forming a synchronous head by the 2 identical OFDM symbols, and adding a cyclic prefix to the synchronous head to form a synchronous beacon;
step 5: defining and generating an MID bit sequence, and modulating the MID bit sequence into a complex symbol sequence;
step 6: mapping and transforming the complex symbol sequence according to the corresponding relation between the transmission mode spectrum mode and the NBB system spectrum mode and the mapping relation between the transmission mode spectrum mode and the sub-carrier wave to form an OFDM symbol of a transmission mode beacon;
step 7: adding a cyclic prefix to the OFDM symbol in the step 6 to form a transmission mode beacon;
Step 8: and forming a beacon by the synchronous beacon and the transmission mode beacon, forming a physical layer signal frame by the beacon and 58 OFDM symbols in the step 1, and forming a superframe by 1 or 4 physical layer signal frames.
Further, in the step 2, the specific modulation process of the synchronization pilot symbol is:
step 2.1: two paths of pseudo-random sequences are defined, and the two paths of pseudo-random sequences are respectively:
pI＝{pI 1 ，pI 2 ，…，pI i ，…，pI pl }，pQ＝{pQ 1 ，pQ 2 ，…，pQ i ，…，pQ pl }
wherein pl is the pilot frequency length, pl is Nv, and Nv is the effective carrier number;
step 2.2: generating two paths of pseudo-random sequences defined in the step 2.1 by adopting a pseudo-random sequence generator;
step 2.3: in each spectrum mode of NBB system, bit stream pair pI synthesized by two pseudo random sequences 1 pQ 1 ，pI 2 pQ 2 ，…，pI i pQ i ，…，pI pl pQ pl Which in turn is QPSK mapped to synchronization pilot symbols.
Further, in the step 3, the NBB system spectrum mode includes a class a spectrum and a class B spectrum;
the class A spectrum comprises spectrum modes A1 to A16, wherein:
the frequency range of the lower sideband of the frequency spectrum mode A1 is-200 KHz to-150 KHz, the frequency range of the upper sideband is 150KHz to 200KHz, the number of the contained sub-bands is 2, and the bandwidth is 100KHz;
the frequency range of the lower sideband of the frequency spectrum mode A2 is-250 KHz to-150 KHz, the frequency range of the upper sideband is 150KHz to 250KHz, the number of the contained sub-bands is 4, and the bandwidth is 200KHz;
The frequency range of the lower sideband of the frequency spectrum mode A5 is-150 KHz to-100 KHz, the frequency range of the upper sideband is 100KHz to 150KHz, the number of the contained sub-bands is 2, and the bandwidth is 100KHz;
the frequency range of the lower sideband of the frequency spectrum mode A6 is-200 KHz to-100 KHz, the frequency range of the upper sideband is 100KHz to 200KHz, the number of the contained sub-bands is 4, and the bandwidth is 200KHz;
the frequency range of the lower sideband of the frequency spectrum mode A9 is-200 KHz to-130 KHz, the frequency range of the upper sideband is 130KHz to 200KHz, the number of the contained sub-bands is 2.5, and the bandwidth is 140KHz;
the frequency range of the lower sideband of the frequency spectrum mode A10 is-250 KHz to-130 KHz, the frequency range of the upper sideband is 130KHz to 250KHz, the number of the contained sub-bands is 4.5, and the bandwidth is 240KHz;
the spectrum modes A3, A4, A7, A8 and A11-A16 are reserved;
the class B spectrum comprises spectrum modes B1-B8, wherein:
the frequency range of the lower sideband of the frequency spectrum mode B1 is-50 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-50 KHz, the number of the contained sub-bands is 2, and the bandwidth is 100KHz;
the frequency range of the lower sideband of the frequency spectrum mode B2 is-100 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-100 KHz, the number of the contained sub-bands is 4, and the bandwidth is 200KHz;
the frequency range of the lower sideband of the frequency spectrum mode B3 is-150 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-150 KHz, the number of the contained sub-bands is 6, and the bandwidth is 300KHz;
The frequency range of the lower sideband of the frequency spectrum mode B4 is-200 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-200 KHz, the number of the contained sub-bands is 8, and the bandwidth is 400KHz;
the frequency range of the lower sideband of the frequency spectrum mode B5 is-250 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-250 KHz, the number of the contained sub-bands is 10, and the bandwidth is 500KHz;
the spectrum modes B6 to B8 are reserved.
Further, in the step 3, the specific forming process of the OFDM symbol of the synchronization beacon is:
step 3.1: filling the synchronous pilot symbols into effective subcarriers in a corresponding frequency spectrum mode, and filling zero complex symbols into virtual subcarriers which are not filled with synchronous pilot symbols;
step 3.2: and performing IFFT transformation on the subcarriers filled with the synchronous pilot symbols and the zero complex symbols to form OFDM symbols of the synchronous beacons.
Further, in the step 4, the length of the synchronization beacon is:
T sb ＝T scp +2×T u
wherein T is sb For the length of the synchronization beacon, units ms, T scp For synchronizing the length of the beacon cyclic prefix, units ms, T u For the length of the sync beacon OFDM symbol, units ms.
Further, in the step 5, the specific modulation process of the complex symbol sequence is:
step 5.1: defining 32 MID bit sequences to correspond to 32 PN sequences, wherein the length of each PN sequence is 62 bits, each MID bit sequence MID (i) is expressed as MID (i) =PN [ 0:61 ], and the 32 PN sequences are sequentially generated by using a linear feedback shift register;
Step 5.2: each bit of each MID bit sequence MID (i) is modulated into a complex symbol by a BPSK modulation mode, each MID bit sequence MID (i) is modulated into 62 complex symbols, and 32 MID bit sequences form a 32×62 complex symbol sequence.
Further, in the step 6, the transmission mode spectrum modes are divided into three modes, namely mode 1, mode 2 and mode 3;
the lower sideband frequency range of the mode 1 is-50 KHz-0 KHz, the upper sideband frequency range is 0 KHz-50 KHz, the bandwidth is 100KHz, and the mode 1 corresponds to the NBB system frequency spectrum modes B1-B5;
the lower sideband frequency range of the mode 2 is-150 KHz to-100 KHz, the upper sideband frequency range is 100KHz to i50KHz, the bandwidth is 100KHz, and the mode 2 corresponds to the NBB system frequency spectrum modes A5 and A6;
the lower sideband frequency range of the mode 3 is-200 KHz to-150 KHz, the upper sideband frequency range is 150KHz to 200KHz, the bandwidth is 100KHz, and the mode 3 corresponds to NBB system frequency spectrum modes A1, A2, A9 and A10.
Further, in the step 6, the specific forming process of the OFDM symbol of the transmission mode beacon is:
step 6.1: filling the complex symbol sequence into effective sub-carriers in a transmission mode spectrum mode, and filling zero complex symbols into virtual sub-carriers which are not filled with the complex symbol sequence; the transmission mode spectrum mode corresponds to each spectrum mode of the NBB system;
Step 6.2: and performing IFFT transformation on the subcarriers filled with the complex symbol sequences and the zero complex symbols to form OFDM symbols of the transmission mode beacon.
Further, in the step 7, the length of the transmission mode beacon is:
T m ＝T mcp +T mu
wherein T is m For the length of the transmission mode beacon, units ms, T mcp For the length of the transmission mode beacon cyclic prefix, units ms, T mu For the length of the transmission mode OFDM symbol, in ms.
In a second aspect, the present invention provides a framing apparatus for narrowband data broadcasting, comprising: an OFDM generating unit, a synchronous beacon generating unit, a transmission mode beacon generating unit and a composing unit;
the OFDM generation unit is used for generating 58 OFDM symbols from the service data through OFDM modulation;
the synchronous beacon generation unit is used for defining and generating two paths of pseudo-random sequences and modulating data generated by the two paths of pseudo-random sequences to generate synchronous pilot symbols; mapping and transforming the synchronous pilot frequency symbols according to the mapping relation between the NBB system spectrum mode and the subcarriers to form OFDM symbols of synchronous beacons; copying the OFDM symbols of the synchronous beacons to generate 2 identical OFDM symbols, forming a synchronous head by the 2 identical OFDM symbols, and adding a cyclic prefix to the synchronous head to form the synchronous beacons;
The transmission mode beacon generation unit is used for defining and generating an MID bit sequence and modulating the MID bit sequence into a complex symbol sequence; mapping and transforming the complex symbol sequence according to the corresponding relation between the transmission mode spectrum mode and the NBB system spectrum mode and the mapping relation between the transmission mode spectrum mode and the sub-carrier wave to form an OFDM symbol of a transmission mode beacon; adding a cyclic prefix to the OFDM symbol of the transmission mode beacon to form the transmission mode beacon;
the composing unit is configured to compose a beacon from the synchronization beacon and the transmission mode beacon, compose a physical layer signal frame from the beacon and 58 OFDM symbols, and compose a superframe from 1 or 4 physical layer signal frames.
In a third aspect, the present invention provides a physical layer signal frame, which is composed of a beacon and 58 OFDM symbols, wherein the beacon is composed of a synchronization beacon and a transmission mode beacon; the synchronization beacon is formed by steps 2 to 4 in the framing method of the narrowband data broadcasting as described in the first aspect, and the transmission mode beacon is formed by steps 5 to 7 in the framing method of the narrowband data broadcasting as described in the first aspect.
The beneficial effects of the invention are as follows:
1. Compared with the HDradio and the CDR which both adopt longer signal frame length and longer interleaving blocks, the delay of digital signal modulation and demodulation is larger, the method is not suitable for the high requirement of differential data on transmission delay, the NBB system is specially designed for transmitting differential data, and a shorter frame structure and a smaller interleaving block structure are adopted, so that the delay of digital signal modulation and demodulation is smaller, and the high requirement of differential data on transmission delay is better met;
2. the invention adopts a minimum frame structure with 160ms length, uses two interleaving modes, and the longest interleaving mode interleaving depth is 640ms, which is far smaller than the frame length of HDradio and CDR;
3. compared with the HDradio and CDR technology which are divided into a control data transmission channel and a service data transmission channel in the design structure, the two-channel design has larger waste for differential data transmission, the differential data transmission can only utilize the service data transmission channel, the control data transmission channel can not transmit effective information, the HDradio and CDR technology has low efficiency in transmitting differential data, the NBB system does not need to transmit program information in an audio program, a mode of a single transmission channel different from the HDradio and CDR is adopted, all channel resources can be used for transmitting differential data, and the transmission efficiency is high;
4. The invention fuses the system control information into the transmission mode beacon head, transmits the system control information along with the frame head, does not need a special transmission channel for transmission, fully utilizes the channel transmission capability and improves the transmission efficiency.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawing in the description below is only one embodiment of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a diagram illustrating the utilization of FM in-band and out-of-band spectrum in the background of the invention;
FIG. 2 is a block diagram of an NBB system in accordance with an embodiment of the present invention;
fig. 3 is a flowchart of a framing method of narrowband data broadcasting according to an embodiment of the present invention;
FIG. 4 is a diagram of a pseudo-random sequence generator for synchronizing different frequencies in an embodiment of the present invention;
fig. 5 is a QPSK modulation constellation according to an embodiment of the present invention;
fig. 6 is a spectrum pattern diagram of an NBB system according to an embodiment of the present invention, where fig. (a) is a spectrum pattern A1 diagram, fig. (B) is a spectrum pattern A2 diagram, fig. (c) is a spectrum pattern A5 diagram, fig. (d) is a spectrum pattern A6 diagram, fig. (e) is a spectrum pattern A9 diagram, fig. (f) is a spectrum pattern a10 diagram, fig. (g) is a spectrum pattern B1 diagram, fig. (h) is a spectrum pattern B2 diagram, fig. (i) is a spectrum pattern B3 diagram, fig. (j) is a spectrum pattern B4 diagram, and fig. (k) is a spectrum pattern B5 diagram;
Fig. 7 is a diagram of a synchronous beacon OFDM symbol structure in an embodiment of the present application;
FIG. 8 is a schematic diagram of a linear feedback shift register of a transmission mode MID according to an embodiment of the present application;
fig. 9 is a diagram of a BPSK modulation constellation in an embodiment of the present application;
fig. 10 is a spectrum pattern diagram of a transmission mode beacon in an embodiment of the application;
fig. 11 is a diagram of a transmission mode beacon OFDM symbol structure in an embodiment of the application.
Detailed Description
The following description of the embodiments of the present application will be made more apparent and fully by reference to the accompanying drawings, in which it is shown, however, only some, but not all embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
The technical scheme of the application is described in detail below by specific examples. The following embodiments may be combined with each other, and some embodiments may not be repeated for the same or similar concepts or processes.
As shown in the block diagram of the NBB system in fig. 2, the service data to be transmitted in the upper layer enters the NBB system, scrambling, channel coding, framing and OFDM signal modulation are performed in the NBB system, and the modulated signal is converted into a radio frequency signal by a radio frequency module. The service data is composed of data from each service defined by the upper layer protocol of the NBB system. After the service data is subjected to scrambling, LDPC coding, bit interleaving and constellation mapping, OFDM symbols are generated through OFDM modulation, and corresponding pilot frequency is added in the OFDM symbols; and forming a physical layer signal frame by adding a plurality of OFDM symbols and beacon heads, forming a super frame by the physical layer signal frame according to different interleaving modes, modulating the super frame into a baseband signal, and finally modulating the baseband signal into a radio frequency signal for transmission. The NBB radio frequency signal can be transmitted through an antenna feed antenna system after power amplification by a power amplification device.
The invention provides a new NBB system frame framing method for an NBB system, which is shown in figure 3 and comprises the following steps:
step 1: the service data is subjected to OFDM modulation to generate 58 OFDM symbols.
Step 2: two paths of pseudo-random sequences are defined and generated, and data generated by the two paths of pseudo-random sequences are modulated to generate synchronous pilot symbols.
In this embodiment, the definitions of the two paths of pseudo random sequences are respectively:
pI＝{pI 1 ，pI 2 ，…，pI i ，…，pI pl } (1)
pQ＝{pQ 1 ，pQ 2 ，…，pQ i ，…，pQ pl } (2)
where pl is pilot length (pilot length), pl is Nv, nv is the number of effective carriers, and the effective carrier number can be referred to the effective subcarrier index table, i.e., tables 2 to 14.
As shown in fig. 4, the two paths of pseudo-random sequences defined by formulas (1) and (2) are generated by using a pseudo-random sequence generator with synchronous different frequencies, and the generating polynomial of the linear feedback shift register is as follows: x is x 11 +x 9 +1, initial value 01010100101 (0 x2a 5).
In each spectrum mode of NBB system, bit stream pair pI synthesized by two pseudo random sequences defined by formulas (1) and (2) 1 pQ 1 ，pI 2 pQ 2 ，…，pI i pQ i ，…，pI pl pQ pl Mapped sequentially by QPSK to synchronous pilot symbols, e.g. in spectral mode A1, bit stream pair pI 1 pQ 1 ，pI 2 pQ 2 ，…，pI i pQ i ，…，pI pl pQ pl Which in turn is QPSK mapped to a synchronization pilot symbol in spectral pattern A1.
QPSK modulation is prior art, as shown in FIG. 5, QPSK modulation uses two bits v in FIG. 5 0 v 1 Representing a two-bit sequence in QPSK modulation.
Step 3: and (3) mapping and transforming the synchronous pilot symbols in the step (2) according to the mapping relation between the NBB system spectrum mode and the subcarriers to form OFDM symbols of the synchronous beacons.
Modulating the synchronous pilot symbol into an OFDM symbol requires forming the OFDM symbol according to the spectrum mode set by the NBB system and the subcarrier mapping relation under each spectrum mode. The NBB system spectrum mode comprises a class A spectrum and a class B spectrum; the A-type frequency spectrum is used for a digital-analog simulcast transmission mode, and the B-type frequency spectrum is used for a full-digital transmission mode; class a spectrum includes spectrum patterns A1 to a16, and class B spectrum includes spectrum patterns B1 to B8, as shown in table 1.
Table 1 NBB system spectrum pattern list
Spectral pattern A9 includes 2 Subbands (SB) and 2 Extended Subbands (ESB), and the transmission payload may be equivalent to 2.5 subbands. Spectral pattern a10 includes 4 Subbands (SB) and 2 Extended Subbands (ESB), and the transmission payload may be equivalent to 4.5 subbands. A graph of the NBB system spectrum pattern is shown in fig. 6.
The subcarrier interval of the OFDM symbols in the synchronous beacon is 398.4375Hz, the number of effective subcarriers of different frequency spectrum modes is different, and in one effective subband, each OFDM symbol comprises Nv effective subcarriers, and the rest subcarriers are virtual subcarriers without modulating data. The effective subcarrier indexes are shown in tables 2 to 14:
Table 2 effective subcarrier index in each subband
| Sub-band | Spectrum corresponding range (kHz) | Corresponding subcarrier index |
| SBU5 | 250～200 | 626～503 |
| SBU4 | 200～150 | 501～378 |
| SBU3 | 150～100 | 375～252 |
| SBU2 | 100～50 | 250～127 |
| SBU1 | 50～0 | 124～1 |
| SBL1 | 0～-50 | -1～-124 |
| SBL2 | -50～-100 | -127～-250 |
| SBL3 | -100～-150 | -252～-375 |
| SBL4 | -150～-200 | -378～-501 |
| SBL5 | -200～-250 | -503～-626 |
Table 3 effective subcarrier index in extended subbands
| Extension subband | Spectrum corresponding range (kHz) | Corresponding subcarrier index |
| ESBU3 | 150～130 | 377～346 |
| ESBL3 | -130～-150 | -346～-377 |
Table 4 spectrum pattern A1 effective subcarrier index
TABLE 5 Spectrum Pattern A2 active subcarrier index
TABLE 6 Spectrum Pattern A5 active subcarrier index
TABLE 7 Spectrum Pattern A6 active subcarrier index
Table 8 spectrum pattern A9 effective subcarrier index
TABLE 9 Spectrum Pattern A10 active subcarrier index
TABLE 10 Spectrum Pattern B1 active subcarrier index
Table 11 spectrum pattern B2 valid subcarrier index
Table 12 spectrum pattern B3 valid subcarrier index
TABLE 13 Spectrum Pattern B4 active subcarrier index
Table 14 spectrum pattern B5 valid subcarrier index
The number of subcarriers of the OFDM symbol in the synchronization beacon is 2048, the number of effective subcarriers of different spectrum modes is defined in tables 2 to 14, and the effective subcarriers areThe subcarriers other than the carrier are null subcarriers. According to different spectrum modes and subcarrier mapping modes in different spectrum modes, pilot symbols are filled into corresponding effective subcarriers. Bit stream pair pI in each spectral mode 1 pQ 1 ，pI 2 pQ 2 ，…，pI i pQ i ，…，pI pl pQ pl Bit stream pair pI with minimum index number 1 pQ 1 The synchronous pilot symbol formed by QPSK modulation is put into the subcarrier with the minimum subcarrier index number under the spectrum mode, and the bit stream with the maximum subscript sequence number is opposite to the pI pl pQ pl And the synchronous pilot symbol formed by QPSK modulation is placed in the subcarrier with the largest subcarrier index number in the spectrum mode. Taking the spectrum pattern A1 as an example, as can be seen from table 4, the number of effective subcarriers of the spectrum pattern A1 is 248, and the effective subcarrier indexes are 501 to 378, -378 to-501, pI 1 pQ 1 Corresponding to the effective subcarrier index number-501, pi 248 pQ 248 Corresponding to the valid subcarrier index number 501, the bit stream pair pI will be in spectral mode A1 1 pQ 1 The mapped synchronous pilot symbols are put into the effective sub-carrier with index number-501 under the spectrum pattern A1, and the bit stream pair pI under the spectrum pattern A1 248 pQ 248 The mapped synchronization pilot symbols are placed in the active subcarriers with index number 501 in spectrum pattern A1.
Of 2048 subcarriers of the OFDM symbol of the synchronization beacon, the effective subcarriers are filled with synchronization pilot symbols, the remaining subcarriers are not filled with synchronization pilot data, which is called virtual subcarriers, and zero complex symbols 0+j0 are filled in the virtual subcarriers. After 2048 subcarriers are filled with data, IFFT is performed to form an OFDM symbol of a synchronization beacon.
Step 4: the OFDM symbols of the synchronous beacon are duplicated to generate 2 identical OFDM symbols, a synchronous head is formed by the 2 identical OFDM symbols, and a cyclic prefix is added to the synchronous head to form the synchronous beacon.
Step 3, obtaining OFDM symbol of time domain, wherein the time length is T u The OFDM symbol is duplicated to form two identical OFDM symbols, and then 2 identical OFDM symbols form a synchronous head. To be full ofBy utilizing the characteristic of OFDM modulation against multipath interference, a synchronous beacon is formed by adding a cyclic prefix to a synchronous head, wherein the time length of the cyclic prefix is T scp . The cyclic prefix is added as shown in fig. 7.
The synchronization beacon parameter values are shown in table 15.
Table 15 synchronization beacon parameter values
| Parameter definition | (symbol) | Parameter value |
| OFDM data volume length (ms) | T u | 2.51(2048T) |
| Cyclic prefix length (ms) of a synchronization beacon | T scp | 0.2525(206T) |
| Length of synchronization beacon (ms) | T sb ＝T scp +2×T u | 5.2721(4302T) |
In table 15, a unit time t=i/816000 s is defined, and a time expressed by T is an accurate time and a time expressed by ms is an approximate time.
Generating a synchronous beacon in the steps 2 to 4, and generating a transmission mode beacon in the steps 5 to 7.
Step 5: defining and generating an MID bit sequence, and modulating the MID bit sequence into a complex symbol sequence.
If the MID values in the transmission mode beacon are 32, defining 32 MID bit sequences corresponding to 32 PN sequences, wherein the length of each PN sequence is 62 bits, and each MID bit sequence MID (i) is expressed as MID (i) =pn [0 ]: 61], i is more than or equal to 1 and less than or equal to 32. The PN sequences have high autocorrelation and extremely low cross correlation.
Each MID (i) is a pseudo-random sequence: MID (i) =pn [0:61]The linear feedback shift register generates PN 0 in turn]To PN [61]]As shown in fig. 8, the generating polynomial of the linear feedback shift register is as follows: x is x 12 +x 11 +x 8 +x 6 +1。
The initial values of the linear feedback shift registers corresponding to the 32 MIDs (i) are shown in table 16.
Table 16 linear feedback shift register initial values for different MID bit sequences
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Each MID bit sequence MID (i) is a binary bit sequence, each bit is modulated into a complex symbol by adopting a BPSK modulation mode, 0 is modulated into 1+j, and 1 is modulated into-1-j. For a certain MID bit sequence MID (i) =PN [0:61], 62 bits total from PN [0] to PN [61] are modulated into 62 complex symbols. BPSK modulation is a prior art technique as shown in fig. 9.
Step 6: and (3) mapping and transforming the complex symbol sequence in the step (5) according to the corresponding relation between the transmission mode spectrum mode and the NBB system spectrum mode and the mapping relation between the transmission mode spectrum mode and the subcarriers to form an OFDM symbol of the transmission mode beacon.
The transmission mode beacon adopts a special spectrum mode, and the transmission mode spectrum mode is divided into 3 types, namely a mode 1, a mode 2 and a mode 3; the 3 special spectrum modes correspond to a normal operation spectrum mode (namely, an NBB system spectrum mode), and the synchronization beacon and the service data OFDM symbol adopt the normal operation spectrum mode, and the normal operation spectrum mode is shown in table 1.
Mode 1: corresponding to normal working spectrum modes B1, B2, B3, B4 and B5;
mode 2: corresponding to normal working spectrum modes A5 and A6;
mode 3: corresponding to normal operating spectrum modes A1, A2, A9, a10.
The transmission mode spectrum pattern is shown in table 17 and the graph of the transmission mode spectrum pattern is shown in fig. 10.
Table 17 transmission mode spectrum
| Spectral patterns | Lower sideband frequency range | Upper sideband frequency range | Bandwidth of a communication device |
| Mode 1 | -50KHz～0KHz | 0KHz～50KHz | 100KHz |
| Mode 2 | -150KHz～-100KHz | 100KHz～150KHz | 100KHz |
| Mode 3 | -200KHz～-150KHz | 150KHz～200KHz | 100KHz |
When the transmission mode beacon head carries out signal modulation, when the working spectrum modes are B1, B2, B3, B4 and B5, MID (i) is modulated on the subcarriers of the mode 1. When the operating spectrum modes are A5, A6, MID (i) is modulated onto the subcarriers of mode 2. When the operating spectrum modes are A1, A2, A9, a10, MID (i) is modulated onto the subcarriers of mode 3.
In the transmission mode beacon, the subcarrier interval is 1593.75Hz, the number of effective subcarriers in different modes is different, and in one effective subband, one OFDM symbol comprises 62 effective subcarriers, and the rest subcarriers are virtual subcarriers. The effective subcarrier indexes of the corresponding modes are shown in tables 18 to 21.
Table 18 transmission mode beacon effective subcarrier index
| Sub-band | Spectrum corresponding range (kHz) | Corresponding effective subcarrier index |
| SBU4 | 200～150 | 125～95 |
| SBU3 | 150～100 | 93～63 |
| SBU1 | 50～0 | 31～1 |
| SBL1 | 0～-50 | -1～-31 |
| SBL3 | -100～-150 | -63～-93 |
| SBL4 | -150～-200 | -95～-125 |
Table 19 transmission mode beacon mode 1 valid subcarrier index
| Sub-band | Spectrum corresponding range (kHz) | Corresponding effective subcarrier index |
| SBU1 | 50～0 | 31～1 |
| SBL1 | 0～-50 | -1～-31 |
Table 20 transmission mode beacon mode 2 active subcarrier index
| Sub-band | Spectrum corresponding range (kHz) | Corresponding effective subcarrier index |
| SBU3 | 150～100 | 93～63 |
| SBL3 | -100～-150 | -63～-93 |
Table 21 transmission mode beacon mode 3 active subcarrier index
| Sub-band | Spectrum corresponding range (kHz) | Corresponding effective subcarrier index |
| SBU4 | 200～150 | 125～95 |
| SBL4 | -150～-200 | -95～-125 |
The number of effective subcarriers of the transmission mode beacon using 3 spectrum modes is 62, and only the indexes of the subcarriers are different. The number of subcarriers of the OFDM symbol in the transmission mode beacon is 512, and different mode effective subcarriers are defined in tables 18 to 21, and subcarriers other than the effective subcarriers are ineffective subcarriers. In a certain mode, MID (i) =pn [0:61], the low order of the PN sequence corresponds to the low order of the active subcarrier index, and the high order of the PN sequence corresponds to the high order of the subcarrier index. For example, in mode 1, as can be seen from Table 19, in mode 1, the subcarrier indexes are 31 to 1, -1 to-31, 62 effective subcarriers are provided, PN [0] corresponds to the effective subcarrier index-31, and PN [61] corresponds to the effective subcarrier index 31. And filling 62 complex symbols corresponding to the PN sequences into the corresponding 62 effective subcarriers. The total of 512 subcarriers are in the OFDM modulation of the transmission mode beacon, the rest subcarriers except 62 effective subcarriers are virtual subcarriers, zero complex symbols 0+j0 are filled on the virtual subcarriers, and 512 subcarriers are filled with data and then are subjected to IFFT conversion to form the OFDM symbol of the transmission mode beacon.
Step 7: the OFDM symbol of step 6 is added with a cyclic prefix to form a transmission mode beacon.
Step 6, obtaining an OFDM symbol with the OFDM symbol as a time domain and the time length of T mu . In order to fully utilize the characteristic of OFDM modulation against multipath interference, a cyclic prefix is added to form a transmission mode beacon, wherein the time length of the cyclic prefix is T mcp . The cyclic prefix is added as shown in fig. 11.
The transmission mode beacon parameters are shown in table 22.
Table 22 transmission mode beacon parameter values
| Parameter definition | (symbol) | Parameter value |
| Cyclic prefix length (ms) of transmission mode beacons | T mcp | 0.1446(118T) |
| Symbol length (ms) of transmission mode beacon | T mu | 0.6275(512T) |
| Length of transmission mode beacon (ms) | T m ＝T mcp +T mu | 0.7721(630T) |
Step 8: the beacon is composed of a synchronous beacon and a transmission mode beacon, the physical layer signal frame is composed of the beacon and 58 OFDM symbols in the step 1, and the superframe is composed of 1 or 4 physical layer signal frames.
The invention also provides framing equipment of the narrowband data broadcasting, which comprises: OFDM generation unit, synchronous beacon generation unit, transmission mode beacon generation unit and constitution unit.
The OFDM generation unit is used for generating 58 OFDM symbols by OFDM modulation of the service data.
The synchronous beacon generation unit is used for defining and generating two paths of pseudo-random sequences and modulating data generated by the two paths of pseudo-random sequences to generate synchronous pilot symbols; mapping and transforming the synchronous pilot frequency symbols according to the mapping relation between the NBB system spectrum mode and the subcarriers to form OFDM symbols of synchronous beacons; and copying the OFDM symbols of the synchronous beacons to generate 2 identical OFDM symbols, forming a synchronous head by the 2 identical OFDM symbols, and adding a cyclic prefix to the synchronous head to form the synchronous beacons. The specific generation process of the synchronization beacon is referred to in steps 2-4, and will not be described here.
The transmission mode beacon generation unit is used for defining and generating an MID bit sequence and modulating the MID bit sequence into a complex symbol sequence; mapping and transforming the complex symbol sequence according to the corresponding relation between the transmission mode spectrum mode and the NBB system spectrum mode and the mapping relation between the transmission mode spectrum mode and the sub-carrier wave to form an OFDM symbol of a transmission mode beacon; and adding a cyclic prefix to the OFDM symbol of the transmission mode beacon to form the transmission mode beacon. The specific generation process of the transmission mode beacon is referred to steps 5-7, and will not be described here.
The composing unit is configured to compose a beacon from the synchronization beacon and the transmission mode beacon, compose a physical layer signal frame from the beacon and 58 OFDM symbols, and compose a superframe from 1 or 4 physical layer signal frames.
The invention also provides a physical layer signal frame, which consists of a beacon and 58 OFDM symbols, wherein the beacon consists of a synchronous beacon and a transmission mode beacon; the synchronization beacon is formed by steps 2 to 4 in the framing method of the narrowband data broadcasting according to the present embodiment, and the transmission mode beacon is formed by steps 5 to 7 in the framing method of the narrowband data broadcasting according to the present embodiment.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (7)
1. A framing method for narrowband data broadcasting, comprising the steps of:
step 1: generating 58 OFDM symbols by OFDM modulation of service data;
step 2: defining and generating two paths of pseudo-random sequences, and modulating data generated by the two paths of pseudo-random sequences to generate synchronous pilot symbols;
step 3: mapping and transforming the synchronous pilot frequency symbols according to the mapping relation between the NBB system spectrum mode and the subcarriers to form OFDM symbols of synchronous beacons; the specific forming process of the OFDM symbol of the synchronous beacon is as follows:
Step 3.1: filling the synchronous pilot symbols into effective subcarriers in a corresponding frequency spectrum mode, and filling zero complex symbols into virtual subcarriers which are not filled with synchronous pilot symbols;
step 3.2: performing IFFT transformation on the sub-carriers filled with the synchronous pilot symbols and the zero complex symbols to form OFDM symbols of the synchronous beacons;
step 4: copying the OFDM symbols in the step 3 to generate 2 identical OFDM symbols, forming a synchronous head by the 2 identical OFDM symbols, and adding a cyclic prefix to the synchronous head to form a synchronous beacon;
step 5: defining and generating an MID bit sequence, and modulating the MID bit sequence into a complex symbol sequence;
step 6: mapping and transforming the complex symbol sequence according to the corresponding relation between the transmission mode spectrum mode and the NBB system spectrum mode and the mapping relation between the transmission mode spectrum mode and the sub-carrier wave to form an OFDM symbol of a transmission mode beacon; the specific forming process of the OFDM symbol of the transmission mode beacon is as follows:
step 6.1: filling the complex symbol sequence into effective sub-carriers in a transmission mode spectrum mode, and filling zero complex symbols into virtual sub-carriers which are not filled with the complex symbol sequence; the transmission mode spectrum mode corresponds to each spectrum mode of the NBB system;
Step 6.2: performing IFFT transformation on the sub-carriers filled with the complex symbol sequence and the zero complex symbol to form OFDM symbols of the transmission mode beacon;
step 7: adding a cyclic prefix to the OFDM symbol in the step 6 to form a transmission mode beacon;
step 8: and forming a beacon by the synchronous beacon and the transmission mode beacon, forming a physical layer signal frame by the beacon and 58 OFDM symbols in the step 1, and forming a superframe by 1 or 4 physical layer signal frames.
2. The method for framing narrowband data broadcasting as recited in claim 1, wherein in step 2, a specific modulation procedure of the synchronization pilot symbol is:
step 2.1: two paths of pseudo-random sequences are defined, and the two paths of pseudo-random sequences are respectively:
pI＝{pI 1 ,pI 2 ,…,pI i ,…,pI pl }，pQ＝{pQ 1 ,pQ 2 ,…,pQ i ,…,pQ pl }
wherein pl is the pilot frequency length, pl is Nv, and Nv is the effective carrier number;
step 2.2: generating two paths of pseudo-random sequences defined in the step 2.1 by adopting a pseudo-random sequence generator;
step 2.3: in each spectrum mode of NBB system, bit stream pair pI synthesized by two pseudo random sequences 1 pQ 1 ,pI 2 pQ 2 ,…,pI i pQ i ,…,pI pl pQ pl Which in turn is QPSK mapped to synchronization pilot symbols.
3. The method for framing narrowband data broadcasting as defined in claim 1, wherein in step 3, the NBB system spectrum mode includes a class a spectrum and a class B spectrum;
The class A spectrum comprises spectrum modes A1 to A16, wherein:
the frequency range of the lower sideband of the frequency spectrum mode A1 is-200 KHz to-150 KHz, the frequency range of the upper sideband is 150KHz to 200KHz, the number of the contained sub-bands is 2, and the bandwidth is 100KHz;
the frequency range of the lower sideband of the frequency spectrum mode A2 is-250 KHz to-150 KHz, the frequency range of the upper sideband is 150KHz to 250KHz, the number of the contained sub-bands is 4, and the bandwidth is 200KHz;
the frequency range of the lower sideband of the frequency spectrum mode A5 is-150 KHz to-100 KHz, the frequency range of the upper sideband is 100KHz to 150KHz, the number of the contained sub-bands is 2, and the bandwidth is 100KHz;
the frequency range of the lower sideband of the frequency spectrum mode A6 is-200 KHz to-100 KHz, the frequency range of the upper sideband is 100KHz to 200KHz, the number of the contained sub-bands is 4, and the bandwidth is 200KHz;
the frequency range of the lower sideband of the frequency spectrum mode A9 is-200 KHz to-130 KHz, the frequency range of the upper sideband is 130KHz to 200KHz, the number of the contained sub-bands is 2.5, and the bandwidth is 140KHz;
the frequency range of the lower sideband of the frequency spectrum mode A10 is-250 KHz to-130 KHz, the frequency range of the upper sideband is 130KHz to 250KHz, the number of the contained sub-bands is 4.5, and the bandwidth is 240KHz;
the spectrum modes A3, A4, A7, A8 and A11-A16 are reserved;
the class B spectrum comprises spectrum modes B1-B8, wherein:
The frequency range of the lower sideband of the frequency spectrum mode B1 is-50 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-50 KHz, the number of the contained sub-bands is 2, and the bandwidth is 100KHz;
the frequency range of the lower sideband of the frequency spectrum mode B2 is-100 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-100 KHz, the number of the contained sub-bands is 4, and the bandwidth is 200KHz;
the frequency range of the lower sideband of the frequency spectrum mode B3 is-150 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-150 KHz, the number of the contained sub-bands is 6, and the bandwidth is 300KHz;
the frequency range of the lower sideband of the frequency spectrum mode B4 is-200 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-200 KHz, the number of the contained sub-bands is 8, and the bandwidth is 400KHz;
the frequency range of the lower sideband of the frequency spectrum mode B5 is-250 KHz-0 KHz, the frequency range of the upper sideband is 0 KHz-250 KHz, the number of the contained sub-bands is 10, and the bandwidth is 500KHz;
the spectrum modes B6 to B8 are reserved.
4. The method for framing narrowband data broadcasting as recited in claim 1, wherein in said step 4, the length of the synchronization beacon is:
T sb ＝T scp +2×T u
wherein T is sb For the length of the synchronization beacon, units ms, T scp For synchronizing the length of the beacon cyclic prefix, units ms, T u For the length of the sync beacon OFDM symbol, units ms.
5. The method for framing narrowband data broadcasting as recited in claim 1, wherein in step 5, the specific modulation procedure of the complex symbol sequence is:
Step 5.1: defining 32 MID bit sequences to correspond to 32 PN sequences, wherein the length of each PN sequence is 62 bits, each MID bit sequence MID (i) is expressed as MID (i) =PN [0:61], and the 32 PN sequences are sequentially generated by using a linear feedback shift register;
step 5.2: each bit of each MID bit sequence MID (i) is modulated into a complex symbol by a BPSK modulation mode, each MID bit sequence MID (i) is modulated into 62 complex symbols, and 32 MID bit sequences form a 32×62 complex symbol sequence.
6. The method for framing narrowband data broadcasting as defined in claim 1, wherein in said step 6, transmission mode spectrum modes are divided into three modes, namely mode 1, mode 2 and mode 3;
the lower sideband frequency range of the mode 1 is-50 KHz-0 KHz, the upper sideband frequency range is 0 KHz-50 KHz, the bandwidth is 100KHz, and the mode 1 corresponds to the NBB system frequency spectrum modes B1-B5;
the lower sideband frequency range of the mode 2 is-150 KHz to-100 KHz, the upper sideband frequency range is 100KHz to 150KHz, the bandwidth is 100KHz, and the mode 2 corresponds to the NBB system frequency spectrum modes A5 and A6;
the lower sideband frequency range of the mode 3 is-200 KHz to-150 KHz, the upper sideband frequency range is 150KHz to 200KHz, the bandwidth is 100KHz, and the mode 3 corresponds to NBB system frequency spectrum modes A1, A2, A9 and A10.
7. A framing device for narrowband data broadcasting, comprising: an OFDM generating unit, a synchronous beacon generating unit, a transmission mode beacon generating unit and a composing unit;
the OFDM generation unit is used for generating 58 OFDM symbols from the service data through OFDM modulation;
the synchronous beacon generation unit is used for defining and generating two paths of pseudo-random sequences and modulating data generated by the two paths of pseudo-random sequences to generate synchronous pilot symbols; mapping and transforming the synchronous pilot frequency symbols according to the mapping relation between the NBB system spectrum mode and the subcarriers to form OFDM symbols of synchronous beacons; copying the OFDM symbols of the synchronous beacons to generate 2 identical OFDM symbols, forming a synchronous head by the 2 identical OFDM symbols, and adding a cyclic prefix to the synchronous head to form the synchronous beacons; the specific forming process of the OFDM symbol of the synchronous beacon is as follows: filling the synchronous pilot symbols into effective subcarriers in a corresponding frequency spectrum mode, and filling zero complex symbols into virtual subcarriers which are not filled with synchronous pilot symbols; performing IFFT transformation on the sub-carriers filled with the synchronous pilot symbols and the zero complex symbols to form OFDM symbols of the synchronous beacons;
The transmission mode beacon generation unit is used for defining and generating an MID bit sequence and modulating the MID bit sequence into a complex symbol sequence; mapping and transforming the complex symbol sequence according to the corresponding relation between the transmission mode spectrum mode and the NBB system spectrum mode and the mapping relation between the transmission mode spectrum mode and the sub-carrier wave to form an OFDM symbol of a transmission mode beacon; adding a cyclic prefix to the OFDM symbol of the transmission mode beacon to form the transmission mode beacon; the specific forming process of the OFDM symbol of the transmission mode beacon is as follows: filling the complex symbol sequence into effective sub-carriers in a transmission mode spectrum mode, and filling zero complex symbols into virtual sub-carriers which are not filled with the complex symbol sequence; the transmission mode spectrum mode corresponds to each spectrum mode of the NBB system; performing IFFT transformation on the sub-carriers filled with the complex symbol sequence and the zero complex symbol to form OFDM symbols of the transmission mode beacon;
the composing unit is configured to compose a beacon from the synchronization beacon and the transmission mode beacon, compose a physical layer signal frame from the beacon and 58 OFDM symbols, and compose a superframe from 1 or 4 physical layer signal frames.
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