WO2021248784A1 - 一种基于交叉子带划分的多带双曲调频扩频通信方法 - Google Patents

一种基于交叉子带划分的多带双曲调频扩频通信方法 Download PDF

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WO2021248784A1
WO2021248784A1 PCT/CN2020/125523 CN2020125523W WO2021248784A1 WO 2021248784 A1 WO2021248784 A1 WO 2021248784A1 CN 2020125523 W CN2020125523 W CN 2020125523W WO 2021248784 A1 WO2021248784 A1 WO 2021248784A1
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spread spectrum
subband
frequency
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余华
张雅琦
季飞
陈芳炯
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South China University of Technology SCUT
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details 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
    • H04B1/69—Spread spectrum techniques
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details 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
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00
    • H04B13/02—Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H04L27/20—Modulator circuits; Transmitter circuits

Definitions

  • the invention relates to the field of underwater acoustic communication, in particular to a spread spectrum communication method that combines a hyperbolic frequency modulation signal with a cross subband and an up-and-down HFM signal.
  • the underwater acoustic channel Due to the complexity of the marine environment, the underwater acoustic channel has serious multipath effects and time-varying characteristics.
  • the seawater medium attenuates high frequencies very seriously, resulting in very small available bandwidth for underwater acoustic communication.
  • Underwater acoustic communication has experienced the development from incoherent technology to coherent technology.
  • coherent technology Compared with incoherent technology, coherent technology has high spectrum utilization rate and can greatly improve the efficiency of communication system.
  • severe multipath effects and time-varying characteristics are the main limiting factors for underwater acoustic coherent communication. At the same time, it is difficult to ensure the reliability of communication in an environment with low signal-to-noise ratio.
  • SS Spread spectrum
  • DSSS Direct Sequence Spread Spectrum
  • FHSS Frequency Hopping Spread Spectrum
  • SCS Frequency Modulation Spread Spectrum
  • the hyperbolic FM signal is selected as the spread spectrum signal.
  • Hyperbolic frequency modulation as a spread spectrum communication method suitable for underwater acoustic communication, has its unique advantages.
  • the hyperbolic FM signal model is as follows:
  • Hyperbolic Frequency Modulation (HFM) signal can be defined as
  • f b represents the frequency of the start point of the HFM signal
  • f e represents the frequency of the end point of the HFM signal
  • B
  • T represents the duration of the HFM signal
  • f e > f b it is called frequency up, at this time the frequency modulation ⁇ ⁇ 0; if f e ⁇ f b , it is called frequency down, at this time the frequency modulation ⁇ > 0.
  • the instantaneous frequency of the HFM signal is,
  • the instantaneous frequency is a hyperbolic function that changes with time t, so the signal is called a hyperbolic FM signal.
  • Hyperbolic FM signal has good pulse compression and Doppler tolerance. Its pulse compressibility is reflected in the fact that after the received signal is correlated with the local HFM signal, it can present a pulse with a sharp main valve and a rapidly weakening sidelobe, so it has a good anti-noise performance.
  • the high-speed relative movement of the transceiver will cause a serious Doppler scale effect, and the signal will be compressed or expanded in time.
  • the receiving end can still form a good pulse through matched filtering, and the signal is considered to be Doppler tolerant.
  • the time delay ⁇ t is a constant that is determined by the scale factor and has nothing to do with time. That is, after the HFM signal undergoes the Doppler effect, its instantaneous frequency is only on the time axis compared to before the scale change. A shift has occurred, so that after matched filtering at the receiving end, a better pulse can still be formed, but the position of the pulse will shift by ⁇ t, so the HFM signal has Doppler tolerance.
  • the orthogonality between the sequences is very important.
  • the duration of the sequence must exceed the maximum delay of the channel to ensure the orthogonality of the received signal sequence as much as possible.
  • the multi-band hyperbolic frequency modulation spread spectrum communication method based on cross subband division in the present invention is proposed based on the above-mentioned signal model and background.
  • the available bandwidth of the system is only used for a single HFM frequency modulation signal, so the frequency band utilization rate of the system is very low.
  • the general underwater acoustic spread spectrum communication scheme is usually designed based on the principle that a single spread spectrum period exceeds the channel delay.
  • the orthogonality of the receiving end sequence will be affected to a certain extent, increasing the interference between adjacent symbols.
  • the present invention proposes a new spread spectrum communication scheme, that is, a multi-band hyperbolic frequency modulation spread spectrum communication method based on cross subband division.
  • the purpose of the present invention is to propose a new spread spectrum communication scheme based on the HFM signal, by dividing the available bandwidth of the underwater acoustic communication system into different numbers of subbands according to the parity of the spreading period sequence number, thereby reducing the number of adjacent symbols.
  • the interference of the communication signal improves the tolerance of the communication signal to the channel delay.
  • the sub-band selective activation mode and QPSK modulation mode are adopted to realize multi-band parallel transmission and improve the utilization rate of the frequency band.
  • the activated subbands respectively use the up and down HFM signals as the frequency modulation signals to spread the modulated QPSK symbols.
  • a multi-band hyperbolic frequency modulation spread spectrum communication method based on cross subband division includes the following steps:
  • the sub-band adopts the corresponding up and down hyperbolic FM signals for frequency modulation respectively;
  • a spreading period with an odd spreading period number divides the bandwidth used by the system into K 1 subbands
  • a spreading period with an even spreading period number divides the used bandwidth into K 2 subbands
  • each sub-band uses the rising and falling HFM signals to generate two kinds of weakly correlated spreading signals, and performing hyperbolic frequency modulation.
  • p is the sequence number of the spread spectrum; when p is odd or even, the modulation frequency is respectively
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • p is the sequence number of the spread spectrum; when p is odd or even, the modulation frequency is respectively
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • the data and subbands are grouped, and the grouping is specifically:
  • the bits to be transmitted are divided into a group every 3 bits.
  • every two adjacent subbands of K 1 subbands are divided into a group.
  • Grouping; for the even-numbered spreading cycle, divide the K 2 subbands into a group for every two adjacent subbands.
  • the result of the grouping in this scheme For each group of 2 subbands, 3 bits are transmitted.
  • step S3 subband selection and symbol mapping are performed according to the transmitted data, and signal modulation and spreading are performed, specifically:
  • Each sub-band group transmits 3 bits, and the first bit is used for sub-band selection: when the bit is 0, the first sub-band of the sub-band group is selected for spread spectrum transmission, and when the bit is 1, the sub-band is selected.
  • the second subband of the band group is used for spread spectrum transmission,
  • the second and third bits are used for QPSK symbol mapping, and the subbands activated by the first bit perform corresponding spread spectrum transmission.
  • the frame header uses the rising and falling HFM signals and the zero interval that occupy the entire communication frequency band
  • the guard interval uses the falling HFM signals and the zero symbol that occupy the entire communication frequency band as the interval.
  • the present invention achieves the beneficial effects: adopting the cross-subband division scheme, improving the tolerance to the maximum delay of the channel; using the weak correlation of the up and down hyperbolic FM signals, and carrying different transmissions Information; Multi-band parallel transmission scheme based on QPSK modulation is adopted to further improve the frequency band utilization and transmission rate of the system.
  • Fig. 1 is a schematic diagram of frequency modulation of an underwater acoustic hyperbolic frequency modulation spread spectrum communication scheme combining cross subband and raising and lowering HFM signals according to the present invention.
  • Figure 2 is a schematic diagram of subband selection corresponding to the example.
  • Fig. 3 is a flow chart of spread spectrum modulation at the transmitting end of the communication scheme of the present invention.
  • Figure 4 is a frame diagram of the transmitted signal frame.
  • Fig. 5 is a flow chart of demodulation and despreading at the receiving end of the communication scheme of the present invention.
  • T H periodic signal HFM
  • T G Symbol guard interval period.
  • T L duration of the frame header.
  • f s the sampling rate of the hyperbolic FM signal.
  • f s 100KHz.
  • f kb Represents the starting frequency of the k-th subband, which is further divided into four cases: frequency up and frequency down, odd symbol period number and even symbol period number.
  • f ke Represents the cut-off frequency of the k-th subband, which is further divided into four cases: frequency up and frequency down, odd symbol period number and even symbol period number.
  • the k-th sub-band raises the frequency modulation of the HFM signal, and is further divided into two cases: odd symbol period number and even symbol period number.
  • the k-th subband reduces the frequency modulation of the HFM signal, and further divides the odd symbol period sequence number and the even symbol synchronization sequence number into two cases.
  • an underwater acoustic hyperbolic frequency modulation spread spectrum communication method combining cross subbands and raising and lowering HFM signals includes the following steps:
  • sub-band HFM signal generation S2, sub-band HFM signal generation.
  • the sub-bands respectively adopt the corresponding up and down hyperbolic FM signals for frequency modulation.
  • Up HFM signal corresponding to each sub-band Expressed as
  • p is the sequence number of the spreading period
  • n represents the nth sampling point in a spreading period
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • p is the sequence number of the spread spectrum; when p is odd or even, the modulation frequency is respectively
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • the start frequency and cut-off frequency of the k-th subband are respectively
  • the first bit is used for subband selection: when the bit is 0, the first subband of the subband group is selected for spread spectrum transmission; when the bit is 1, the second subband of the subband group is selected for spread spectrum transmission transmission.
  • the transmitted random bit stream is 001110100101111010...
  • the first bit (underlined bit) of each group is used For subband selection, the activated subband is shown in Figure 2.
  • the first bit in the first group of bits is 0, so the first subband group in the first spreading cycle selects the first subband; the first bit in the second group of bits is 1, so the first spreading cycle The second subband group selects the second subband; the first bit in the third group of bits is 1, so the first subband group of the second spreading period selects the second subband, and the spreading period has only 1 subband.
  • subsequent bits will be modulated to the next spread spectrum period; other bit groups are analogously followed.
  • the second and third bits are used for QPSK symbol mapping, and the subbands activated by the first bit perform corresponding spread spectrum transmission.
  • the specific modulation process is shown in Figure 3.
  • the frame header uses the rising and falling HFM signals and the zero interval that occupy the entire communication frequency band for synchronous detection, and the guard interval uses the falling HFM signals and the zero symbol that occupy the entire communication frequency band as the interval.
  • the transmitted signal frame structure is shown in Figure 4.
  • the signal After the signal is band-pass filtered at the receiving end, it uses the rising and falling HFM signal that occupies the entire communication frequency band for synchronization and channel estimation.
  • the result of channel estimation is: the number of multipaths is L, and the parameter corresponding to the l(1,...,L) path is the amplitude Time delay Doppler factor
  • the peak offset of each path is calculated separately. For the current spreading cycle in a data frame, the peak offset of the l(1,...,L) path ⁇ n k,l is
  • ⁇ k is the modulation frequency of the k-th subband
  • f kb represents the start frequency of the k-th subband.
  • the corresponding values of ⁇ k and f kb need to be determined according to the up-frequency down-frequency and the parity of the current spreading cycle sequence number, see the definition in S2 for details.
  • r[n] represents the current spreading cycle symbol in the data frame.
  • the first subband of the qth subband group is considered to be the active subband. According to the activation scheme in S3, it is determined that the first bit transmitted by the qth subband group is
  • the second subband of the qth subband group is considered to be the active subband. According to the activation scheme in S3, it is determined that the first bit transmitted by the qth subband group is
  • q f and q s are between 1,...,K 1
  • q f and q s are between 1,...,K 2 value.
  • S8 Perform symbol demodulation on the active subband. According to the detection result of S7, it can be determined that the sequence number of the activated subband is k, and symbol demodulation is performed on the subband. Using the maximum combining ratio criterion, the peaks of the L paths are combined and the symbol is judged. The demodulated symbol is

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Abstract

本发明公开了一种基于交叉子带划分的多带双曲调频扩频通信方法。本方案提出将水声系统可用带宽按照当前扩频周期序号的奇偶性进行不同子带数量的多带划分，以达到交叉子带划分的目的。在此基础上，将划分的多个子带两两分组，每个分组采用子带选择激活的方式根据传输数据的不同进行子带的选择，实现多带并行传输。同时，每个扩频周期内，被激活子带分别采用升、降双曲调频信号对调制后的信号进行调频。相对于其他水声双曲扩频调频方案，本发明采用交叉子带划分的方案，提高了对信道最大时延的容忍度；利用升、降双曲调频信号的弱相关性，承载传输不同的信息；采取基于QPSK调制的多带并行传输方案，进一步提高了系统的频带利用率与传输速率。

Description

一种基于交叉子带划分的多带双曲调频扩频通信方法 技术领域
本发明涉及水声通信领域，具体涉及一种双曲调频信号，结合交叉子带与升降HFM信号的扩频通信方法。
背景技术
由于海洋环境的复杂性，水声信道存在严重的多径效应和时变特性。而海水介质对高频衰减非常严重，导致水声通信可用带宽非常小。水声通信经历了从非相干技术到相干技术的发展，相较于非相干技术而言，相干技术的频谱利用率高，可以大大提高通信系统的效率。然而严重的多径效应与时变性，是水声相干通信主要的制约因素，与此同时在信噪比较低的环境下，较难确保通信的可靠性。
扩展频谱(spread spectrum，SS)技术是一种能有效对抗干扰的技术，它以其自身的优势，在低信噪比以及存在多径扩展的复杂信道情况下，仍可以在保证一定通信速率的前提下，实现可靠信息的传输。常见的扩频方式主要有三种，分别是直接序列扩频(DSSS)，跳频扩频(FHSS)以及调频扩频(CSS)等。本发明中选取双曲调频信号作为扩频信号。双曲调频作为一种适用于水声通信的扩频通信方式，具备其独特的优势。
为了便于对后续算法的理解，双曲调频信号模型如下所示：
双曲调频(HFM)信号，可以定义为
Figure PCTCN2020125523-appb-000001
其中，f b表示HFM信号起始点的频率，f e表示HFM信号截止点的频 率，B＝|f e-f b|表示带宽(调频区间)，T表示HFM信号持续周期，
Figure PCTCN2020125523-appb-000002
表示调频率。特别地，若f e＞f b，则称为升频，此时调频率β＜0；若f e＜f b，则称为降频，此时调频率β＞0。HFM信号的瞬时频率为，
Figure PCTCN2020125523-appb-000003
瞬时频率是一个随时间t变化的双曲函数，因此该信号被称为双曲调频信号。双曲调频信号具有良好的脉冲压缩性和多普勒宽容性。其脉冲压缩性体现在，在接收信号与本地HFM信号进行相关后能够呈现主瓣尖锐、旁瓣迅速衰弱的脉冲，因此具备良好的抗噪性能。与此同时，在信号传输过程中，由于收发端的高速相对运动会造成严重的多普勒尺度效应，信号会产生时间上的压缩或者扩展。在信号经历了多普勒尺度效应之后，接收端经过匹配滤波依旧可以较好的形成脉冲，则认为该信号具有多普勒宽容性。
假设一个HFM信号发生了大小为α的尺度变换。对应接收到的HFM信号可以表达为
Figure PCTCN2020125523-appb-000004
发生尺度变化后，信号的瞬时频率变为
Figure PCTCN2020125523-appb-000005
这里我们可以找到一个合适的Δt，使得f α(t-Δt)＝f(t)，即
Figure PCTCN2020125523-appb-000006
Figure PCTCN2020125523-appb-000007
由此可见，该时延Δt是一个由尺度因子决定且与时间无关的常数，即 HFM信号在经历了多普勒效应之后，其瞬时频率相较于未发生尺度变化之前，只是在时间轴上发生了一个平移，这样在接收端进行匹配滤波后，依旧可以形成较好的脉冲，只是脉冲的位置会平移Δt，因此HFM信号具备多普勒宽容性。
此外，对于多序列扩频通信而言，各序列之间的正交性十分重要。同时序列的持续时间长度必须要超过信道的最大时延，以尽可能的保证其接收信号序列的正交性。
使用HFM进行扩频通信虽然能增强抗干扰能力和抗多普勒效应，但是面临的一个较为严重的问题就是频带利用率比较低。另外，若信道的最大时延超过扩频周期，接收信号序列的正交性将会受到影响，为了能一定程度缓解以上两种情况，提高HFM扩频通信的频带利用率以及对信道最大时延的容忍度是值得研究的问题。
本发明所述的一种基于交叉子带划分的多带双曲调频扩频通信方法，正是基于如上所述的信号模型和背景所提出的。
发明内容
对一般的HFM扩频通信方法而言，系统可用带宽只用于单个HFM调频信号，因此系统的频带利用率很低。此外，一般的水声扩频通信方案，通常是基于单个扩频周期超过信道时延这样的原则进行方案设计。但当信道最大时延超过扩频周期时，接收端序列的正交性会受到一定的影响，增加相邻符号之间的干扰。为此，本发明提出一种新的扩频通信方案，即一种基于交叉子带划分的多带双曲调频扩频通信方法。
本发明的目的在于基于HFM信号提出一种新的扩频通信方案，通过将水声通信系统可用带宽按照扩频周期序号的奇偶性进行不同数量的子带划分，以此降低相邻符号之间的干扰，提升通信信号对信 道时延的容忍度。另外，采用子带选择激活的方式，以及QPSK调制方式，实现多带并行传输，提升频带利用率。同时在一个调频周期内，被激活子带分别采用升、降HFM信号作为调频信号，对调制后的QPSK符号进行扩频。
为了解决上述技术问题，本发明采用的技术方案如下。
一种基于交叉子带划分的多带双曲调频扩频通信方法，包括以下步骤：
S1、将通信系统带宽按照扩频周期序号的奇偶性划分为不同数量的若干子带；
S2、子带分别采用对应的升、降双曲调频信号进行调频；
S3、将数据、子带进行分组，根据传输的数据进行子带选择与符号映射，并进行信号调制与扩频；
S4、对扩频后的传输信号添加帧头与保护间隔，生成信号帧。
进一步地，在所述步骤S1中，扩频周期序号为奇数的扩频周期将系统使用带宽分为K 1个子带，扩频周期序号为偶数的扩频周期将所用带宽分为K 2个子带，后续分别进行双曲调频，提高频带利用率。
进一步地，在所述步骤S2中，每个扩频周期内，每个子带分别使用升、降HFM信号生成两种弱相关的扩频信号，进行双曲调频。
进一步地，每个子带对应的升HFM信号
Figure PCTCN2020125523-appb-000008
表示为
Figure PCTCN2020125523-appb-000009
其中，p为扩频周期序号；当p为奇数或偶数时的调频率分别为
Figure PCTCN2020125523-appb-000010
当p为奇数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000011
当p为偶数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000012
同理，每个子带对应的降HFM信号
Figure PCTCN2020125523-appb-000013
可表示为：
Figure PCTCN2020125523-appb-000014
其中，p为扩频周期序号；当p为奇数或偶数时的调频率分别为
Figure PCTCN2020125523-appb-000015
当p为奇数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000016
当p为偶数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000017
进一步地，在所述步骤S3中，将数据、子带进行分组，分组具体为：
待传比特每3个比特分成一组，对于第奇数个扩频周期，将K 1个子带每两相邻子带分成一组，一共有K 1/2个组，每组承载前述的3比特分组；对于第偶数个扩频周期，将K 2个子带每两相邻子带分成 一组，一共有K 2/2个组，每组承载前述的3比特分组，本次方案中分组的结果为，每组2个子带传输3个比特。
进一步地，在所述步骤S3中，根据传输的数据进行子带选择与符号映射，并进行信号调制与扩频，具体为：
每个子带组传输3个比特，第1个比特用于子带的选择：该比特为0时，选择该子带组的第1个子带进行扩频传输，当该比特为1时选择该子带组的第2个子带进行扩频传输，
第2、3个比特则用于QPSK符号映射，由第1个比特激活的子带进行相应的扩频传输。
进一步地，在所述步骤S4中，帧头采用占用整个通信频段的升、降HFM信号与零间隔，保护间隔采用占用整个通信频段的降HFM信号与零符号作间隔。
与现有技术相比，本发明实现的有益效果是：采用交叉子带划分的方案，提高了对信道最大时延的容忍度；利用升、降双曲调频信号的弱相关性，承载传输不同的信息；采取基于QPSK调制的多带并行传输方案，进一步提高了系统的频带利用率与传输速率。
附图说明
图1为本发明一种结合交叉子带与升降HFM信号的水声双曲调频扩频通信方案的调频示意图。
图2为实例对应的子带选择示意图。
图3为本发明通信方案发送端的扩频调制流程图。
图4为发送信号帧结构图。
图5为本发明通信方案接收端的解调解扩流程图。
具体实施方式
为使本发明的目的、技术方案及优点更加清楚、明确，以下参照附图并举实施例对本发明进一步详细说明。各标号的含义如下：
f 0：通信频段的起始频率，本实例取f 0＝9KHz。
f 1：通信频段的截止频率，本实例取f 1＝15KHz。
B：带宽，本实例取B＝6KHz。
T H：双曲调频信号的周期，本实例取T H＝20.48ms。
T G：符号保护间隔周期。
T L：帧头持续时间。
f s：双曲调频信号采样率，本实例取f s＝100KHz。
N：双曲调频信号一个扩频周期的采样点数，N＝T H*f s，本实例中N＝2048。
K 1：第奇数个扩频周期的子带个数，本实例取K 1＝4。
K 2：第偶数个扩频周期的子带个数，本实例取K 2＝2。
M：每帧数据包含的扩频周期数，本实例取M＝10。
f kb：表示第k个子带的起始频率，进一步分升频与降频、奇数符号周期序号与偶数符号周期序号4种情况。
f ke：表示第k个子带的截止频率，进一步分升频与降频、奇数符号周期序号与偶数符号周期序号4种情况。
Figure PCTCN2020125523-appb-000018
第k个子带升HFM信号的调频率，进一步分奇数符号周期序号与偶数符号周期序号2种情况。
Figure PCTCN2020125523-appb-000019
第k个子带降HFM信号的调频率，进一步分奇数符号周期序 号与偶数符号同期序号2种情况。
本实施案例中一种结合交叉子带与升降HFM信号的水声双曲调频扩频通信方法，包括以下步骤：
S1、子带划分。将系统带宽按照扩频周期序号的奇偶性划分为不同数量的若干子带。对于通信频段的起始频率为f 0，截止频率为f 1，带宽为B＝f 1-f 0的系统，我们将系统带宽分别划分成2种情况：分成K 1、K 2个子带，K 1、K 2为2的整数倍，K 1≠K 2。其中K 1个子带用于扩频周期序号为奇数的扩频调制，K 2个子带用于扩频周期序号为偶数的扩频调制，扩频周期均为T H。设采样率为f s，一个扩频周期的采样点数为N，每帧数据包含M个HFM扩频周期。本实例交叉子带划分方式具体可见图1。
S2、子带HFM信号生成。子带分别采用对应的升、降双曲调频信号进行调频。每个子带对应的升HFM信号
Figure PCTCN2020125523-appb-000020
表示为
Figure PCTCN2020125523-appb-000021
其中，p为扩频周期序号，n表示一个扩频周期内的第n个采样点；
当p为奇数或偶数时的调频率分别为
Figure PCTCN2020125523-appb-000022
当p为奇数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000023
当p为偶数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000024
同理，每个子带对应的降HFM信号
Figure PCTCN2020125523-appb-000025
可表示为：
Figure PCTCN2020125523-appb-000026
其中，p为扩频周期序号；当p为奇数或偶数时的调频率分别为
Figure PCTCN2020125523-appb-000027
当p为奇数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000028
当p为偶数时，第k个子带的起始频率与截止频率分别为
Figure PCTCN2020125523-appb-000029
本实例通信方案的子带HFM信号生成方式如图1所示，其中箭头向右上表示升频，箭头向右下表示降频；f 2、f 3、f 4分别表示将B＝f 1-f 0的通信带宽划分为四个子带后，各子带的起始与截止频率。
S3、信号调制。将数据、子带进行分组，根据传输的数据进行子带选择与符号映射，并进行信号调制与扩频。待传比特每3个比特分成一组。对于第奇数个扩频周期，将K 1个子带每两相邻子带分成一组，一共有K 1/2个组；对于第偶数个扩频周期，将K 2个子带每两相邻子带分成一组，一共有K 2/2个组；每个子带分组将承载前述的3比特分组。本方案中分组的结果为，每组2个子带，携带3个比特。
第1个比特用于子带的选择：该比特为0时，选择该子带组的第1个子带进行扩频传输；该比特为1时选择该子带组的第2个子带进 行扩频传输。假设传输的随机比特流为001110100101111010…，按照每3个比特为一组，即： 001  110  100  101  111  010…，每组的第1个比特(带下划的比特)用于子带选择，那么被激活的子带如图2所示。即，第1组比特中第1比特为0，因此第1个扩频周期的第1个子带组选择第1个子带；第2组比特中第1比特为1，因此第1个扩频周期的第2个子带组选择第2个子带；第3组比特中第1比特为1，因此第2个扩频周期的第1个子带组选择第2个子带，同时该扩频周期只有1个子带组，后续比特将调制到下一个扩频周期；其它比特组依次类推。
第2、3个比特则用于QPSK符号映射，由第1个比特激活的子带进行相应的扩频传输。
记第q组的3个比特为b q1b q2b q3，则当前多带双曲调频扩频符号的发送信号表示为
Figure PCTCN2020125523-appb-000030
Figure PCTCN2020125523-appb-000031
其中，Q为当前扩频周期的子带组数，在第奇数个扩频周期中Q＝K 1/2，在第偶数个扩频周期中Q＝K 2/2；k q＝2q+b q1-1为第q组激活的子带编号；上式中
Figure PCTCN2020125523-appb-000032
表示对第q组的第2、3个比特则采用QPSK符号映射，其中j为虚数单位。具体调制流程如图3所示。
S4、信号帧生成。帧头采用占用整个通信频段的升、降HFM信号与零间隔以便同步检测，保护间隔采用占用整个通信频段的降 HFM信号与零符号作间隔。发送的信号帧结构如图4所示。
S5、接收同步。信号在接收端经过带通滤波后，利用占用整个通信频段的升降HFM信号进行同步和信道估计。假设信道估计的结果为：多径数为L条，第l(1,…,L)条路径对应的参数为幅度
Figure PCTCN2020125523-appb-000033
时延
Figure PCTCN2020125523-appb-000034
多普勒因子
Figure PCTCN2020125523-appb-000035
根据信道参数，分别计算每条路径的峰值偏移量。对于一个数据帧中的当前扩频周期，其第l(1,…,L)条路径的峰值偏移量Δn k,l为
Figure PCTCN2020125523-appb-000036
其中，
Figure PCTCN2020125523-appb-000037
为多普勒扩展导致的偏移；β k为第k个子带的调频率，f kb表示第k个子带的起始频率。β k与f kb需要根据升频降频以及当前扩频周期序号的奇偶性确定相应的值，具体见S2中定义。
S6、相关运算。将接收信号与每个子带的升HFM扩频符号，分别做互相关运算，根据峰值偏移量Δn k,l，在相关运算后的对应点获得峰值。第k个子带，第l条路径的峰值
Figure PCTCN2020125523-appb-000038
表示为
Figure PCTCN2020125523-appb-000039
其中，r[n]表示数据帧中的当前扩频周期符号。同理，接收信号与子带的降HFM扩频符号做互相关运算后，峰值
Figure PCTCN2020125523-appb-000040
表示为
Figure PCTCN2020125523-appb-000041
S7、确定激活子带。根据峰值
Figure PCTCN2020125523-appb-000042
和
Figure PCTCN2020125523-appb-000043
进行激活子带的判决。对数据帧中的当前扩频周期的第q个子带组，激活子带的判决规则如下：
若
Figure PCTCN2020125523-appb-000044
则认为第q个子带组的第1个子带为激活子带，根据S3中的激活方案，判定第q个子带组传输的第1个比特为
Figure PCTCN2020125523-appb-000045
若
Figure PCTCN2020125523-appb-000046
则认为第q个子带组的第2个子带为激活子带，根据S3中的激活方案，判定第q个子带组传输的第1个比特为
Figure PCTCN2020125523-appb-000047
其中，q f＝2q-1表示第q个子带组的第1个子带；q s＝2q表示第q个子带组的第2个子带。在第奇数个扩频周期中，q f与q s在1,…,K 1之间取值；在第偶数个扩频周期中，q f与q s在1,…,K 2之间取值。
S8、在激活子带上进行符号解调。根据S7的检测结果可确定激活的子带序号为k，对该子带进行符号解调。利用最大合并比准则，对L条路径的峰值作合并处理并进行符号判决，解调出的符号为
Figure PCTCN2020125523-appb-000048
其中，j为虚数单位，
Figure PCTCN2020125523-appb-000049
表示第l(1,…,L)条路径对应幅度
Figure PCTCN2020125523-appb-000050
的共轭。而后根据S进行QPSK符号解映射得b q2b q3，最终获得该子带组传输的3个比特b q1b q2b q3。数据帧中每个扩频周期符号各子带组的解调流程如图5所示。

Claims (7)

  1. 一种基于交叉子带划分的多带双曲调频扩频通信方法，包括以下步骤：
    S1、将通信系统带宽按照扩频周期序号的奇偶性划分为不同数量的若干子带；
    S2、子带分别采用对应的升、降双曲调频信号进行调频；
    S3、将数据、子带进行分组，根据传输的数据进行子带选择与符号映射，并进行信号调制与扩频；
    S4、对扩频后的传输信号添加帧头与保护间隔，生成信号帧。
  2. 根据权利要求1所述的一种基于交叉子带划分的多带双曲调频扩频通信方法，其特征在于：在所述步骤S1中，扩频周期序号为奇数的扩频周期将系统使用带宽分为K 1个子带，扩频周期序号为偶数的扩频周期将所用带宽分为K 2个子带，后续分别进行双曲调频。
  3. 根据权利要求1所述的一种基于交叉子带划分的多带双曲调频扩频通信方法，其特征在于：在所述步骤S2中，每个扩频周期内，每个子带分别使用升、降HFM信号生成两种弱相关的扩频信号，进行双曲调频。
  4. 根据权利要求3所述的一种基于交叉子带划分的多带双曲调频扩频通信方法，其特征在于：每个子带对应的升HFM信号
    Figure PCTCN2020125523-appb-100001
    表示为
    Figure PCTCN2020125523-appb-100002
    其中，p为扩频周期序号；当p为奇数或偶数时的调频率分别为
    Figure PCTCN2020125523-appb-100003
    当p为奇数时，第k个子带的起始频率与截止频率分别为
    Figure PCTCN2020125523-appb-100004
    当p为偶数时，第k个子带的起始频率与截止频率分别为
    Figure PCTCN2020125523-appb-100005
    同理，每个子带对应的降HFM信号
    Figure PCTCN2020125523-appb-100006
    可表示为：
    Figure PCTCN2020125523-appb-100007
    其中，p为扩频周期序号；当p为奇数或偶数时的调频率分别为
    Figure PCTCN2020125523-appb-100008
    当p为奇数时，第k个子带的起始频率与截止频率分别为
    Figure PCTCN2020125523-appb-100009
    当p为偶数时，第k个子带的起始频率与截止频率分别为
    Figure PCTCN2020125523-appb-100010
  5. 根据权利要求1所述的一种基于交叉子带划分的多带双曲调频扩 频通信方法，其特征在于：在所述步骤S3中，将数据、子带进行分组，分组具体为：
    待传比特每3个比特分成一组，对于第奇数个扩频周期，将K 1个子带每两相邻子带分成一组，一共有K 1/2个组，每组承载前述的3比特分组；对于第偶数个扩频周期，将K 2个子带每两相邻子带分成一组，一共有K 2/2个组，每组承载前述的3比特分组，本次方案中分组的结果为，每组2个子带传输3个比特。
  6. 根据权利要求1所述的一种基于交叉子带划分的多带双曲调频扩频通信方法，其特征在于：在所述步骤S3中，根据传输的数据进行子带选择与符号映射，并进行信号调制与扩频，具体为：
    每个子带组传输3个比特，第1个比特用于子带的选择：该比特为0时，选择该子带组的第1个子带进行扩频传输，当该比特为1时选择该子带组的第2个子带进行扩频传输，
    第2、3个比特则用于QPSK符号映射，由第1个比特激活的子带进行相应的扩频传输。
  7. 根据权利要求1～6任一项所述的一种基于交叉子带划分的多带双曲调频扩频通信方法，其特征在于：在所述步骤S4中，帧头采用占用整个通信频段的升、降HFM信号与零间隔，保护间隔采用占用整个通信频段的降HFM信号与零符号作间隔。
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