TWI641235B - Differential cyclic-frequency shift orthogonal frequency division multiplex spread spectrum device - Google Patents

Abstract

A differential cyclic frequency shift orthogonal frequency division multiplexing spread spectrum device, wherein a communication device is configured to perform conversion between a series of bits and a plurality of frequency domain symbols by using a plurality of cyclic frequency shift values. Moreover, the frequency domain symbols include a first frequency domain symbol and a second frequency domain symbol, and the cyclic frequency shift value of the second frequency domain symbol is a cyclic frequency displacement value according to the first frequency domain symbol. And ask for it.

Description

Differential cyclic frequency shift orthogonal frequency division multiplexing multi-function spread spectrum device

The present invention relates to a spread spectrum device, and more particularly to a differential cyclic frequency shift (hereinafter referred to as differential CFS) Orthogonal Frequency Division Multiplex Spread Spectrum (hereinafter referred to as OFDM). ) device.

Spread spectrum technology is a communication technology that intentionally transmits messages with a bandwidth that is several times higher than the basic required message bandwidth, in order to achieve more stable transmission and resist interference.

Currently known spread spectrum technologies include Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and Chirp Spread Spectrum (hereinafter referred to as Chirp Spread Spectrum). CSS). DSSS spread spectrum technology is to modulate the original single bit (bit) message with a long string of pseudo-random sequences (Pseudo Noise Sequence). The length of the original single bit is equal to the length of the pseudo-random sequence, that is, It is said that the chip time of the pseudo-random sequence is very short, thus forming Broadband transmission. The FHSS subdivides the available bandwidth into a number of small frequency bands, and randomly transmits a small frequency band to repeat transmission when the message is transmitted. Each bit of the CSS spread spectrum technology is transmitted by a chirp signal. Since the chirp signal itself is a wideband signal, the effect of the spread spectrum is obtained.

The shortcoming of DSSS spread spectrum technology is that the first is because each pseudo-random chip has a very short time, so the ability to resist multiple transmission paths is poor, and the second is because of the high-speed transmission, which also results in relatively high power consumption. The disadvantage of FHSS spread spectrum is that the first is that the synchronization between the transmission end and the reception end is more difficult. The second is that each frequency hopping needs to be synchronized, thus reducing the bandwidth usage rate, resulting in the final transmission rate compared to the DSSS spread spectrum method. It’s slow. The disadvantage of CSS spread spectrum is that the first is that the resistance to multiple paths is poor, and the second is that each click signal only carries one bit, and the transmission rate is slow.

Orthogonal frequency-division multiplexing (OFDM) is a special case of multi-carrier transmission. It has the capability of high-speed data transmission, and it can effectively resist the frequency selective attenuation, and gradually gains attention and adoption. For example, U.S. Patent No. 7,839,880, an OFDM communication system is proposed.

Orthogonal frequency division multiplexing is a multi-carrier modulation technique that effectively partitions the entire system bandwidth into multiple (N) orthogonal sub-bands. These subbands are also known as tones, subcarriers, bins, and channels. With OFDM, each subband is associated with a subcarrier of a respective modulatable material. Since the signal received by the receiving end is the result of the transmission signal and the channel response during the signal transmission, it is necessary to obtain the channel response in order to understand the transmission signal, so the channel estimation is performed. Bad channel estimation Will cause the bit error rate to rise. Traditionally, channel estimation is performed by transmitting a pilot from the transmitting end and measuring the pilot at the receiving end. Since the pilot consists of modulation symbols known to the receiving end, for each subband used for pilot transmission, the channel response can be estimated as the ratio of the received pilot symbols to the transmitted pilot symbols.

According to an embodiment of the invention, a spread cycle frequency shift orthogonal frequency division multiplexing spread spectrum apparatus is provided, comprising at least one communication device. The at least one communication device is configured to perform conversion between a series of bits and a plurality of frequency domain symbols by using a plurality of cyclic frequency shift values. The cyclic frequency shift values are a frequency ordering loop, and different cyclic frequency shift values correspond to different bit values. The frequency domain symbols include a first frequency domain symbol and a second frequency domain symbol, and the cyclic frequency shift value of the second frequency domain symbol is obtained according to a cyclic frequency shift value of the first frequency domain symbol. Got it.

In one embodiment, the communication device includes a transmitting device. The transmitting device includes a modulation unit and an OFDM transmission unit. The modulation unit converts the serial bit into the frequency domain symbols formed by the N frequency domain subcarriers, the frequency domain symbols being a function of the cyclic frequency shift values, wherein the second frequency domain symbol The cyclic frequency shift value is a function of the cyclic frequency shift value of the first frequency domain symbol and a desired cyclic frequency shift value, and the string bit includes the bit value corresponding to the desired cyclic frequency shift value. The OFDM transmission unit converts the frequency domain symbols into a plurality of time domain symbols, and forms a time domain packet with the time domain symbols.

In an embodiment, the time domain symbols satisfy the following formula: , m =0~ N -1

t=0:

t >0:

Where N is the number of all frequency domain subcarriers, S(k) is the frequency domain symbol, k is the kth subcarrier, s(n) is the time domain symbol, and n is the nth time point. m represents the cyclic frequency shift value in units of subcarriers, mod(.,N) is the remainder for N, and N can be the power of two.

The frequency domain symbols S(k) satisfy the following formula: , k =0~ N -1, and the cyclic frequency shift value of the second frequency domain symbol is the cyclic frequency shift value of the first frequency domain symbol plus a desired cyclic frequency shift value.

In an embodiment, the OFDM transmission unit includes an N-point inverse Fourier transform unit, a cyclic preamble (CP) unit, a window unit, and a packet component unit. The N-point inverse Fourier transform unit is configured to convert the frequency domain symbols into the time domain symbols. A cyclic preamble (CP) unit is configured to copy a partial symbol in each end of the time domain symbol to a front end of each of the time domain symbols to generate each of the time domain symbols. The window unit is coupled to the cyclic preamble unit and is configured to reduce interference of each of the time domain symbols in an adjacent frequency band. The packet forming unit generates the time domain packet by using the time domain symbols. In an embodiment, the transmitting device further includes a Gray code encoding unit. A Gray code coding unit is used to convert the format of the string bit from a binary code to a Gray code.

In an embodiment, the communication device includes a receiving device. The receiving device includes an OFDM connection Receive unit and a demodulation module. The OFDM receiving unit is configured to convert the time domain packet into the frequency domain symbols. The demodulation module is configured to demodulate the frequency domain symbols, and obtain a desired cyclic frequency displacement value according to the cyclic frequency displacement value of the second frequency domain symbol and the cyclic frequency displacement value of the first frequency domain symbol. And converting the desired cyclic frequency shift value into the string of bits.

In an embodiment, the demodulation module includes a cyclic convolution unit and a peak determination unit. The circular convolution unit cyclically convolves the first frequency domain symbol with the second frequency domain symbol. The peak determining unit is coupled to the circular convolution unit, and determines a plurality of peaks of the cyclic convolution result as the cyclic frequency displacement values of the first and second frequency domain symbols, and obtains the desired cyclic frequency displacement value, and The desired cyclic frequency shift value is converted into the string of bits.

In an embodiment, the expected cyclic frequency displacement value satisfies the following formula: Where R ^t (k) represents the second frequency domain symbol, and R ^t-1 (k) represents the first frequency domain symbol, Represents a circular convolution, conj() represents a conjugate complex function, argmax represents a function that takes the maximum value of the circular convolution, and k represents the kth subcarrier.

In an embodiment, the demodulation module includes a cyclic convolution unit and a peak determination unit. The circular convolution unit is configured to cyclically convolve the phase of the first frequency domain symbol with the second frequency domain symbol, or to cycle the phase of the first frequency domain symbol with the phase of the second frequency domain symbol convolution. The peak determining unit is coupled to the circular convolution unit, and determines a plurality of peaks of the cyclic convolution result as the cyclic frequency displacement values of the first and second frequency domain symbols, and obtains the desired cyclic frequency displacement value, and The desired cyclic frequency shift value is converted into the string of bits.

In an embodiment, the expected cyclic frequency displacement value satisfies the following formula: Or, satisfy the following formula: Where R ^t (k) represents a second frequency domain symbol, and R ^t-1 (k) represents a first frequency domain symbol, Represents a circular convolution, argmax represents a function that takes the maximum value of the circular convolution, and k represents the kth subcarrier.

In an embodiment, the OFDM receiving unit includes a packet detection unit, a cyclic preamble removal unit, and an N-point Fourier transform unit. The packet detection unit estimates whether the time domain packet exists. The loop preamble removal unit removes the loop preamble in the time domain packet to restore to multiple time domain symbols. The N-point Fourier transform unit restores the time-domain symbols to the frequency-domain symbols. The receiving device further includes a Gray code decoding unit. The Gray code decoding unit is configured to convert the format of the serial bit from the Gray code to the binary code.

According to the differential CFS-OFDM according to an embodiment of the invention, the transmission information is obtained according to the relationship between the cyclic frequency displacement values between the two frequency symbols. In an embodiment, the cyclic frequency displacement value of the second frequency domain symbol is obtained. It is based on the cyclic frequency shift value of the first frequency domain symbol. Therefore, the demodulation can eliminate the need for channel estimation, frequency offset estimation, and time shift estimation steps, and is a spread spectrum modulation technique suitable for harsh environments.

100‧‧‧Differential CFS-OFDM device

110‧‧‧Communication device

200‧‧‧Transfer

210‧‧‧ Gray code coding unit

220‧‧‧Modulation unit

230‧‧‧OFDM transmission unit

231‧‧‧Package unit

232‧‧‧window unit

233‧‧ Circulation preamble unit

234‧‧‧N-point anti-Fourier transform unit

240‧‧‧Transmission circuit Tx

300‧‧‧ receiving device

310‧‧‧Gray decoding unit

320‧‧‧Demodulation Module

321‧‧‧ Peak Judging Unit

322‧‧‧Circular convolution unit

330‧‧‧OFDM receiving unit

331‧‧‧Package detection unit

332‧‧‧Circular leading removal unit

333‧‧‧N-point Fourier transform unit

340‧‧‧Receiving circuit Rx

Figure 1 shows a schematic diagram of a different cyclic frequency combined pattern corresponding to a bit value.

2 is a functional block diagram of a differential CFS-OFDM device in accordance with an embodiment of the present invention.

Fig. 3 is a functional block diagram showing a transmitting apparatus of a differential CFS-OFDM apparatus according to an embodiment of the present invention.

4 is a functional block diagram of a receiving apparatus of a differential CFS-OFDM apparatus according to an embodiment of the present invention.

FIG. 5A is a diagram showing the result of cyclic convolution when demodulating by the CFS-OFDM method according to an embodiment of the present invention.

FIG. 5B is a diagram showing the result of cyclic convolution when demodulating by the differential CFS-OFDM method according to another embodiment of the present invention.

In an embodiment of the present invention, a Cyclic-Frequency Shift Orthogonal Frequency Division Multiplex (CFS-OFDM) is proposed, which is a novel spread spectrum technology, and the message is through wideband OFDM. The cyclic frequency shift value of the signal (as described later) is transmitted. The advantage is that it can still be transmitted with very low signal-to-noise ratio, which is very suitable for long-distance communication applications. By looping the preamble, the channels in the multipath have better performance than the traditional spread spectrum techniques such as DSSS, FHSS and CSS. By properly selecting the frequency domain signal, the signal in the time domain has a very low power peak-to-average ratio, so the RF at the transmitting end The linearity requirements of the gain amplifier are very low, which can significantly reduce the cost of the amplifier.

In an embodiment, the sequentially arranged cyclic frequency ordering may be regarded as the first combined aspect, and the frequencies are shifted to the left or right in a cyclic manner as other combined manners, and each combined aspect corresponds to one Cyclic frequency shift value. More details are as follows. Figure 1 shows a schematic diagram of a different cyclic frequency combined pattern corresponding to a bit value. As shown in FIG. 1 , in the present embodiment, the sequentially arranged frequencies are sorted as S ₀ S ₁ S ₂ S ₃ S ₄ S ₅ S ₆ S ₇ as the first combined aspect, and the cyclic frequency displacement value m= is specified. 0. After the frequencies are shifted to the left by one unit in a cyclic manner, a frequency order S ₁ S ₂ S ₃ S ₄ S ₅ S ₆ S ₇ S _{0 is formed} , as a second combined state, at which time the cyclic frequency displacement value m=1 . Other combinations, and so on. In this embodiment, different cyclic frequency combinations correspond to different cyclic frequency displacement values, and different cyclic frequency displacement values correspond to different bit values, and the bit values may be binary code or Gray coded.

For example, when N=8, a message of k=3 bits can be transmitted through the cyclic frequency shift value. As shown in Table 1 above, m is a three-bit message with a cyclic frequency shift value, the binary value is b ₂ b ₁ b ₀ , the Gray code is g ₂ g ₁ g ₀ , and the original subcarrier content is S ₀ S ₁ S ₂ S ₃ S ₄ S ₅ S ₆ S ₇ , when the cyclic frequency shift = 1, the subcarrier sequence becomes S ₁ S ₂ S ₃ S ₄ S ₅ S ₆ S ₇ S ₀ , when the cyclic frequency shift = 2, The subcarrier order becomes S ₂ S ₃ S ₄ S ₅ S ₆ S ₇ S ₀ S ₁ , and so on. The example of Table 1 is a cyclic shift to the left, but the cyclic shift of the present invention is not limited to cyclic shifts to the left or to the right.

More specifically, k=0 to 7, m=0 to 7 and N=8 are substituted into the mathematical formula S(mod(k+m, N)), and mod(.,N) is module N, ie, N Taking the remainder, the following Table 2 can be obtained.

Referring to Table 2 above and the mathematical formula S (mod(k+m, N)), in an embodiment, the transmission signal of CFS-OFDM can satisfy the following formula (1): Where N is the number of all frequency domain subcarriers, S(k) is the frequency domain symbol, k is the kth subcarrier, s(n) is the time domain symbol, n is the nth time point, and m is the The cyclic frequency shift value is in units of subcarriers, mod(.,N) is module N, that is, the remainder is taken for N, and N can be implemented by the power of two.

Since the possible value of the cyclic frequency shift amount m is 0~N-1, a symbol of CFS-OFDM can transmit up to K=log2(N) bit messages.

In theory, S(k) can be used as a CFS-OFDM signal as long as it is a non-periodic signal, but a proper choice of S(k) can achieve better transmission quality. The so-called appropriate selection includes the selection of the best auto-correlation characteristics and the lowest peak-to-average power ratio (PAPR) in the time domain. For example, when the selected S(k) is as shown in the following formula (4), the above two advantages are obtained:

In this embodiment, the PAPR of the real or imaginary part in the time domain is about 3 dB, and the auto-correlation is far greater than 0 only when k=0, in the case of k≠0. 0, so it is a very good choice as CFS-OFDM. This embodiment can reduce the linearity requirement of the RF gain amplifier at the transmitting end, and can greatly reduce the cost of the amplifier.

However, CFS-OFDM belongs to a coherent modulation method, which requires a certain degree of channel estimation, frequency offset compensation, time shift compensation, and demodulation to achieve the expected performance. In the harsh channel environment, the estimation of channel and frequency offset and time shift is very likely to be inaccurate, resulting in an increase in bit error rate.

In view of this, according to another embodiment of the present invention, a differential cyclic frequency shift orthogonal frequency division multiplexing spread spectrum device (hereinafter referred to as a differential CFS-OFDM device) is proposed, which can be in a poor channel environment. Such as power line transmission systems, providing stable data transmission. Moreover, it can effectively improve the problem that the channel, the frequency offset, and the time shift estimation are not accurate enough to cause an increase in the bit error rate.

2 is a functional block diagram of a differential CFS-OFDM device in accordance with an embodiment of the present invention. As shown in FIG. 2, in accordance with an embodiment of the present invention, a differential CFS-OFDM device 100 includes at least one communication device 110, and the communication device 110 uses a plurality of cyclic frequency shift values to perform a series of bits and a plurality of frequency domain symbols. The conversion between the elements, the cyclic frequency displacement value is a frequency sorting cycle, and different cyclic frequency displacement values correspond to different bit values. The plurality of frequency domain symbols include a first frequency domain symbol and a second frequency domain symbol. The cyclic frequency shift value of the second frequency domain symbol is obtained according to the cyclic frequency shift value of the first frequency domain symbol.

In one embodiment, at least one communication device 110 includes a transmitting device 200. In one embodiment, a receiving device 300 can be further included. The transmitting device 200 is configured to convert a series of bits into a plurality of frequency domain symbols, and convert the frequency domain symbols into a transmission signal St. The receiving device 300 is configured to receive the transmission signal St and convert the transmission signal St into a plurality of frequency domain symbols, and then convert the frequency domain symbols into a series of bits.

Fig. 3 is a functional block diagram showing a transmitting apparatus of a differential CFS-OFDM apparatus according to an embodiment of the present invention. As shown in FIG. 3, the transmitting device 200 of the differential CFS-OFDM device 100 includes: a modulation list Element 220 receives a series of bits and converts into a plurality of frequency domain symbols formed by combining N frequency domain subcarriers, wherein the frequency domain symbols are a function of a cyclic frequency displacement value. The frequency domain symbols include a first frequency domain symbol and a second frequency domain symbol, and the cyclic frequency shift value of the second frequency domain symbol is a function of a cyclic frequency shift value of the first frequency domain symbol.

According to an embodiment of the present invention, the transmission signal of the differential CFS-OFDM can be expressed by the following equation (2).

Initial symbol:

The tth symbol: Wherein, the cyclic frequency shift of the initial differential CFS-OFDM symbol (symbol) (0) = m (0), the cyclic frequency shift of the t-th differential CFS-OFDM symbol is the cyclic frequency shift of the previous t-1th differential CFS-OFDM symbol plus m(t), It can be represented by the following formula (3).

Referring to FIG. 3, the transmitting device 200 of the differential CFS-OFDM device 100 may further include: a Gray code encoding unit 210, an OFDM transmitting unit 230, and a transmitting circuit Tx 240. The Gray code encoding unit 210 is configured to convert the format of the serial bit from the binary code to the Gray code to minimize the one bit error rate when the symbol is demodulated. The OFDM transmission unit 230 converts the frequency domain symbols into a time domain packet. The transmission circuit Tx 240 converts the time domain packet into a transmission signal St, and transmits it through a network route or a wireless signal.

In an embodiment, the OFDM transmission unit 230 includes an N-point inverse Fourier transform unit 234, a cyclic preamble (CP) unit 233, a window unit 232, and a packet composition unit 231. The N-point Inverse Fast Fourier Transform (N-IFFT) unit 234 is coupled to the modulation unit 220, and the N-point inverse Fourier transform unit 234 converts to the N-point time-domain symbol according to the N-point frequency domain symbol. The loop preamble unit 233 copies part of the symbols in the end of the N-point time-domain symbol packet to the front end of the N-point time-domain symbol. The window unit 232 is coupled to the cyclic preamble unit 233 for reducing interference of time domain packets in adjacent frequency bands. The packet composition unit 231 combines a preamble, a header, a payload, and generates a time domain packet using the N-point time domain symbol.

The message length is K bits, and K can be less than or equal to log ₂ (N). When K is equal to log ₂ (N), it means that all cyclic frequency shifts are used, including 0~N-1. Conversely, when K is less than log ₂ (N), it means that only part of the cyclic frequency shift is used. For example, if only an even cyclic frequency shift is used, the adjacent loop frequency displacement false detection can be avoided, which is a method of reducing the rate for higher stability. Another reason for using only partial cyclic frequency shifts is that due to limitations in spectrum regulations, certain frequency bands are not available, so only M is used. The N subcarriers are used to generate the differential CFS-OFDM signal, and the N of the formulas (1) to (5) should be replaced by M. After determining the K value, the K-bit message is first converted by Gray code. The Gray code can ensure that the K bits represented by the adjacent cyclic frequency shifts differ from each other by only one bit, because the most common error is when When the cyclic frequency shift is equal to ±1, the bit error rate can be minimized by Gray code. The decimal digit value after the Gray code conversion is the value of the cyclic frequency displacement. According to the cyclic frequency displacement value, the signal is converted to the time domain by the inverse Fourier according to the formula (1). Next, a Cyclic prefix (CP) is added to boost immunity to multiple paths. Finally, windowing is added to reduce interference to adjacent frequency bands.

4 is a functional block diagram of a receiving apparatus of a differential CFS-OFDM apparatus according to an embodiment of the present invention. As shown in FIG. 4, the receiving device 300 of the differential CFS-OFDM device 100 may include: a receiving circuit Rx 340, an OFDM receiving unit 330, a demodulation module 320, and a gray decoding unit 310. After receiving the transmission signal St through the network route or the wireless signal, the receiving circuit Rx converts the transmission signal St into a time domain packet. The receiving circuit Rx 340 may include an analog front end AFE, and the analog front end circuit AFE may include, for example, an analog filter, a signal gainer, and an analog digital conversion circuit to process the Transmission signal St.

The OFDM receiving unit 330 receives the time domain packet and converts the time domain packet into the frequency domain symbols. In an embodiment, the OFDM receiving unit 330 includes a packet detection unit 331, a loop preamble removing unit 332, and an N-point Fast Fourier Transform (N-FFT) unit 333. The packet detection unit 331 is configured to monitor the time domain signal, and estimate whether the domain packet exists sometimes according to the frame preamble, and adjust the gain size. The loop preamble removal unit 332 removes the loop preamble in the time domain packet to reduce to a plurality of N point time domain symbols. The N-point Fourier transform unit 333 converts a plurality of N-point time-domain symbols into a plurality of frequency-domain symbols.

The demodulation module 320 is configured to demodulate the frequency domain symbols into a series of bits. The Gray code decoding unit 310 is configured to convert the format of the string bit from the Gray code to the binary code when the format of the string bit is Gray code. In this embodiment, the demodulation module 320 includes a circular convolution unit 322 and peak determination. The unit 321 is broken. The circular convolution unit 322 cyclically convolves the first frequency domain symbols of the frequency domain symbols with the second frequency domain symbols. The peak determining unit 321 is coupled to the circular convolution unit 322 and determines the peak value of the cyclic convolution result, and regards the difference between the cyclic frequency displacement values corresponding to the two peaks as a desired cyclic frequency displacement value m, and utilizes The desired cyclic frequency shift value m outputs the string of bits.

In one embodiment, during demodulation, the circular convolution is performed by the received frequency domain symbol and the previous frequency domain symbol, and then the cusp of the circular convolution is sought. The value is equivalent to the highest cross-correlation cyclic frequency shift value. The received t-th frequency domain symbol is cyclically convolved with the previous t-1th frequency domain symbol. At this time, the expected cyclic frequency displacement value m can be expressed by the following equation (5).

Where R ^t (k) represents the t-th frequency domain symbol received, Represents a circular convolution, conj() represents a conjugate complex function, and argmax represents a function that takes the maximum value of the circular convolution.

Since the received signal may carry a lot of noise and interference, it will cause a great change in the amplitude of the signal. In order to reduce the influence of the sharp amplitude change, another demodulation method is to use the phase of a frequency domain symbol to perform the cyclic volume. In this case, the expected cyclic frequency shift value m can be expressed by the following formula (6).

To further reduce the complexity, in another embodiment, two frequency domain symbols can be utilized. The phase is subjected to cyclic convolution. At this time, the expected cyclic frequency shift value m can be expressed by the following formula (7).

When CFS-OFDM demodulation is performed, the received frequency domain symbols are cyclically convolved with conj(S(-k)), so they are sensitive to frequency offset or time offset, and need to frequently perform frequency offset or time offset. Estimate. 5A is a diagram showing the result of cyclic convolution when demodulating by the CFS-OFDM method according to an embodiment of the present invention, in which the solid line is the result due to the frequency offset, and the broken line is the correct result. As shown in Figure 5A, the estimated value is The actual value is m. It can be seen that the peak value of the circular convolution has an error due to the frequency offset of the signal, and thus the wrong cyclic frequency shift value is estimated during demodulation.

FIG. 5B is a diagram showing the result of cyclic convolution when demodulating by the differential CFS-OFDM method according to another embodiment of the present invention. According to the demodulation method of the differential CFS-OFDM, the cyclic frequency shift value of the second frequency domain symbol is obtained according to the cyclic frequency shift value of the first frequency domain symbol. More specifically, the cyclic frequency shift of the t-th differential CFS-OFDM symbol ( t ) is the cyclic frequency shift of the t-1th differential CFS-OFDM symbol ( t -1) plus m(t). Even if there is an error between the actual value and the peak position of the estimated value due to the frequency offset, the difference is the previous symbol as the reference point, so the frequency offset effect will be offset and then offset, the estimated value It is equal to the actual value m, so the correct cyclic frequency displacement value is obtained. Therefore, channel estimation, frequency offset estimation, and time shift estimation are not required for demodulation, which is a spread spectrum modulation technique suitable for harsh environments.

According to the differential CFS-OFDM according to an embodiment of the present invention, the information is transmitted according to two frequency symbols. The relationship between the cyclic frequency displacement values between the elements is obtained. Differential CFS-OFDM is a CFS-OFDM-based communication technology that transmits information relative to the difference in the cyclic frequency shift value of the previous symbol. Therefore, the demodulation can eliminate the need for channel estimation, frequency offset estimation, and time shift estimation steps, and is a spread spectrum modulation technique suitable for harsh environments.

Claims (11)

A spread-frequency frequency-shifting orthogonal frequency division multiplexing multiplexer device comprises: at least one communication device, configured to perform conversion between a series of bits and a plurality of frequency domain symbols by using a plurality of cyclic frequency shift values, The cyclic frequency shift values are a frequency ordering loop, and different cyclic frequency shift values correspond to different bit values, and the frequency domain symbols include a first frequency domain symbol and a second frequency domain symbol. And a cyclic frequency shift value of the second frequency domain symbol is obtained according to a cyclic frequency shift value of the first frequency domain symbol. The spread spectrum device according to claim 1, wherein the at least one communication device comprises a transmitting device, and the transmitting device comprises: a modulation unit that converts the serial bits into the plurality of frequency domain subcarriers. a frequency domain symbol, wherein the frequency domain symbols are a function of the cyclic frequency shift values, wherein the cyclic frequency shift value of the second frequency domain symbol is a cyclic frequency shift value of the first frequency domain symbol and a hope a function of the cyclic frequency shift value, and the string of bits includes a bit value corresponding to the desired cyclic frequency shift value; and an OFDM transmission unit that converts the frequency domain symbols into a plurality of time domain symbols and The time domain symbols form a time domain packet. The spread spectrum device according to claim 2, wherein the time domain symbols satisfy the following formula: , m =0~ N -1 t=0: t >0: Where N is the number of all frequency domain subcarriers, S(k) is the frequency domain symbol, k is the kth subcarrier, s(n) is the time domain symbol, and n is the nth time point. m represents the cyclic frequency shift value in units of subcarriers, mod(.,N) is a remainder for N, and N can be a power of two, and the frequency domain symbols S(k) satisfy formula: , k =0~ N -1, and the cyclic frequency shift value of the second frequency domain symbol is a cyclic frequency shift value of the first frequency domain symbol plus a desired cyclic frequency shift value. The spread spectrum apparatus according to claim 3, wherein the OFDM transmission unit comprises: an N-point inverse Fourier transform unit for converting the frequency domain symbols into the time domain symbols; a loop preamble (CP) a unit for copying a partial symbol in each end of the time domain symbol to the front end of each of the time domain symbols to generate each of the time domain symbols; a window unit coupled to the loop The preamble unit is configured to reduce interference of each of the time domain symbols in an adjacent frequency band; and a packet forming unit is configured to generate the time domain packet by using the time domain symbols. The spreading device according to claim 2, wherein the transmitting device further comprises: a Gray code encoding unit for converting the format of the serial bit from the binary code to the Gray code. The spread spectrum device of claim 1, wherein the at least one communication device comprises a receiving device, and the receiving device comprises: an OFDM receiving unit, configured to convert the time domain packet into the frequency domain symbols; And a demodulation module, configured to demodulate the frequency domain symbols, and obtain a desired position according to a cyclic frequency displacement value of the second frequency domain symbol and a cyclic frequency displacement value of the first frequency domain symbol The frequency shift value is cyclically converted and the desired cyclic frequency shift value is converted into the string of bits. The spread spectrum device of claim 6, wherein the demodulation module comprises: a circular convolution unit, wherein the first frequency domain symbol and the second frequency domain symbol are cyclically convolved; and The peak determining unit is coupled to the circular convolution unit, and determines a plurality of peaks of the cyclic convolution result as the cyclic frequency displacement values of the first and second frequency domain symbols, and obtains the desired cyclic frequency displacement value. And converting the desired cyclic frequency shift value into the string of bits. The spread spectrum device according to claim 7, wherein the expected cyclic frequency shift value satisfies the following formula: Where R ^t (k) represents the second frequency domain symbol, and R ^t-1 (k) represents the first frequency domain symbol, Represents a circular convolution, conj() represents a conjugate complex function, argmax represents a function that takes the maximum value of the circular convolution, and k represents the kth subcarrier. The spread spectrum device of claim 6, wherein the demodulation module comprises: a circular convolution unit for cyclically convolving the phase of the first frequency domain symbol with the second frequency domain symbol Or cyclically convolving the phase of the first frequency domain symbol with the phase of the second frequency domain symbol; and a peak determining unit coupled to the circular convolution unit and determining the cyclic convolution result The plurality of peaks are used as the cyclic frequency shift values of the first and second frequency domain symbols, and the desired cyclic frequency shift value is obtained, and the desired cyclic frequency shift value is converted into the serial bit. The spread spectrum device according to claim 9, wherein the expected cyclic frequency displacement value satisfies the following formula: Or, satisfy the following formula: Where R ^t (k) represents the second frequency domain symbol, and R ^t-1 (k) represents the first frequency domain symbol, Represents a circular convolution, argmax represents a function that takes the maximum value of the circular convolution, and k represents the kth subcarrier. The spreading device according to claim 6, wherein the OFDM receiving unit comprises: a packet detecting unit, estimating whether the time domain packet exists; and a looping preamble removing unit to remove the loop in the time domain packet The preamble is restored to the plurality of time domain symbols; and an N-point Fourier transform unit is used to restore the time-domain symbols to the frequency domain symbols, and the receiving device further comprises: a Gray code decoding unit, The format used to convert the string bit from the Gray code to the binary code.