Based on the electrical model of body area communication, the change tendency of chan nel gain in 100 kHz 10 MHz band was experimentally analyzed and verified. Results show that chan nel gain was flat and signal a...Based on the electrical model of body area communication, the change tendency of chan nel gain in 100 kHz 10 MHz band was experimentally analyzed and verified. Results show that chan nel gain was flat and signal attenuation was approximately 43 dB in 1 MHz 10 MHz band. The char acteristics of the channel were taken into account in the design of body area spread spectrum com munication and its multiuser receiver issue. BER Eb/No curves of single user and multiuser were de rived by simulation. The characteristics of body area commutation channel were studied and the fea sibility of introducing spread spectrum theory to body area communication was verified.展开更多
Traditional lapped transform domain excision techniques obtain good performance at the expense of increased processing delay. Extension of transform domain filtering techniques to the lapped biorthogonal transform dom...Traditional lapped transform domain excision techniques obtain good performance at the expense of increased processing delay. Extension of transform domain filtering techniques to the lapped biorthogonal transform domain can help solve the problem. By incorporating biorthogonality into the lapped transforms, more flexibility is obtained in the design of windows. Thus transform bases with better stopband attenuation can be generated by designing windows, but not by increasing the overlapping factor. In this paper, a new modulated lapped biorthogonal transform (MLBT) with optimized windows is introduced for efficient compression of multi-tone interfering signal energy. The bit error rate (BER) performance of the receiver employing the proposed MLBT excision technique is analyzed and compared with that of the lapped transform domain excision-based receivers. Simulation results demonstrate the improved performance and increased robustness of the proposed technique.展开更多
This paper presents a high efficiency spread spectrum scheme using approximate orthogonal complex (AOC) sequences. In this scheme, the 64 AOC sequences picked up from 84 complex sequences space are employed for spread...This paper presents a high efficiency spread spectrum scheme using approximate orthogonal complex (AOC) sequences. In this scheme, the 64 AOC sequences picked up from 84 complex sequences space are employed for spreading spectrum. In modulation, 6 input bits is used to select one AOC sequence, and the selected sequence is then phase-rotated by another 2 input bits. In demodulator, a complex correlator detects the transmitted AOC sequence. Simulation results show that the proposed scheme has better BER performance than the existing complementary code keying (CCK) modulation scheme. For AOC, additional processing gain of 1.79dB can be obtained when the sequence length is 8.展开更多
Aimed at the conventional serial communication system fails when the channel was frequency-selective,long delay and multi-paths effect,resulting in inter-symbol-interference( ISI),an iterative system for underwater ac...Aimed at the conventional serial communication system fails when the channel was frequency-selective,long delay and multi-paths effect,resulting in inter-symbol-interference( ISI),an iterative system for underwater acoustic communication( UWAC) was proposed,which employed iterative differential detection and spread spectrum technique. The proposed scheme adopts π /4-DQPSK soft demodulation to overcome the difficulty of phase ambiguity. For suppression of ISI in UWAC,joint demodulation and decoding iteration was used. The communication scheme has the characteristic of long communication range at low SNR,and the maximum range is up to 100 km. The theoretic analysis and simulation results show that the proposed scheme outperforms traditional serial one. When SNR is- 6 dB,after four joint iterations,compared with serial scheme,BER can decrease from 10- 2to 10- 5.展开更多
A satellite communication system consisting of small earth terminals which utilize spread spectrum multiple access (SSMA) techniques is introduced in this paper. Having no master station, the system is distributively ...A satellite communication system consisting of small earth terminals which utilize spread spectrum multiple access (SSMA) techniques is introduced in this paper. Having no master station, the system is distributively controlled. The frequency band used is 6/4GHz.展开更多
This paper designs an underwater acoustic communication system based on tamed spread spectrum and Frequency Hopping Multiple Access (FHMA) for multiple underwater vehicles. In this system, multiple underwater vehicles...This paper designs an underwater acoustic communication system based on tamed spread spectrum and Frequency Hopping Multiple Access (FHMA) for multiple underwater vehicles. In this system, multiple underwater vehicles can communicate with the console on the water surface simultaneously successfully. The communication system is com-posed of tamed spread spectrum modulation and demodulation, frequency hopping modulation and demodulation with synchronization function, 4FSK modulation and demodulation and Rake Receiver. In order to make the system more feasible, underwater channel and the effect of user number on Bit Error Ratio (BER) are also taken into account. The simulation results indicate that it is feasible to use this system to accomplish underwater communication reliably for multiple users due to the low BER.展开更多
Direct-sequence spread spectrum （DSSS） communication possesses low probability of detection and has been widely used in confidential communications. However, pseudo-noise （PN） sequences, used as spreading code in ...Direct-sequence spread spectrum （DSSS） communication possesses low probability of detection and has been widely used in confidential communications. However, pseudo-noise （PN） sequences, used as spreading code in conventional DSSS communications, possess peri- odic character and binary value. In hostile environments, these distinct characters may lead to some important parameters of signals being estimated accurately, and then lead to the leakage of transmitted information. To solve the problem, we propose the chaotic phase modulation （CPM） sequence alternating the PN sequences. CPM sequence has complex values and constant envelope, and also possesses large quantity and good correlation characteristics. Moreover, it has more hidden features than conventional sequences by modulating its phases using chaotic sequence. To improve the data rate, we apply it into the technique of multichannel communica-tion. Simulation results show this scheme＇s superior bit error ratio （BER） performance, which demonstrates its feasibility in underwater acoustic communications.展开更多
Coherent fast frequency hopping(CFFH)is attracting growing attention owing to its good antijamming performance and the coherent combining ability.However,compared with the conventional non-coherent fast frequency hopp...Coherent fast frequency hopping(CFFH)is attracting growing attention owing to its good antijamming performance and the coherent combining ability.However,compared with the conventional non-coherent fast frequency hopping,CFFH requires a more precise system synchronization.In this paper,we propose a new fine synchronization algorithm for CFFH.This algorithm consists two stages,namely,open-loop stage and closed-loop stage.In the openloop stage,a grid-based search parameter estimation method is proposed.In the closed-loop stage,we construct a fully coherent phase-locked loop(PLL)and a delay-locked loop(DLL)with decoding feedback structure to perform further fine estimation of the system clock skew and time delay,respectively.Moreover,we analyze the effect of the search parameter settings on the estimation error and derive the root mean squared error(RMSE)of estimates in the steady state of the closed-loop stage.Finally,through simulation,the RMSE performance are compared with the corresponding Cramer-Rao low bound(CRLB)and conventional code loop estimation to show the effectiveness of proposed algorithm.展开更多
With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based ...With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.展开更多
The statistic characteristics of chaotic sequences generated by improved logistic map are analyzed and it is found that improved logistic map chaotic sequences have good correlation and they can be used as address ...The statistic characteristics of chaotic sequences generated by improved logistic map are analyzed and it is found that improved logistic map chaotic sequences have good correlation and they can be used as address sequences in spread spectrum communication. The discrete time synchronization of Henon map is immediate. We apply the discrete time synchronization to chaotic spread spectrum communication and propose an original communication scheme. The simulation shows that the application is successful.展开更多
In underwater acoustic communication,because the available bandwidth of the channel is severely limited,the direct-sequence spread-spectrum scheme can only be realized at low bit rates.To improve the transmission spee...In underwater acoustic communication,because the available bandwidth of the channel is severely limited,the direct-sequence spread-spectrum scheme can only be realized at low bit rates.To improve the transmission speed,a multicode spread-spectrum scheme is considered.However,in this case,due to the rapid time-variability of the underwater channel,and the influence of inter-symbol interference(ISI)and inter-channel interference(ICI),the conventional rake receiver may fail to function.The hypothesis-feedback equalization algorithm has been proposed for the direct-sequence spread-spectrum system[1].By updating coefficients at chip rate and feeding back hypothesized chips,it can track time-variability and combat ISI effectively.However,for a multicode system,its performance will be degraded by ICI.An improved algorithm is proposed in this paper,which combines parallel interference cancellation(PIC)with hypothesis-feedback equalization(HFE),with the capabilities of tracking the time-varying channel and suppressing the ISI and ICI at the same time.Simulation results prove that the proposed algorithm can significantly improve the performance of a multicode system.展开更多
基金Supported by the Ministerial Level Advanced Research Foundation(7130819)
文摘Based on the electrical model of body area communication, the change tendency of chan nel gain in 100 kHz 10 MHz band was experimentally analyzed and verified. Results show that chan nel gain was flat and signal attenuation was approximately 43 dB in 1 MHz 10 MHz band. The char acteristics of the channel were taken into account in the design of body area spread spectrum com munication and its multiuser receiver issue. BER Eb/No curves of single user and multiuser were de rived by simulation. The characteristics of body area commutation channel were studied and the fea sibility of introducing spread spectrum theory to body area communication was verified.
文摘Traditional lapped transform domain excision techniques obtain good performance at the expense of increased processing delay. Extension of transform domain filtering techniques to the lapped biorthogonal transform domain can help solve the problem. By incorporating biorthogonality into the lapped transforms, more flexibility is obtained in the design of windows. Thus transform bases with better stopband attenuation can be generated by designing windows, but not by increasing the overlapping factor. In this paper, a new modulated lapped biorthogonal transform (MLBT) with optimized windows is introduced for efficient compression of multi-tone interfering signal energy. The bit error rate (BER) performance of the receiver employing the proposed MLBT excision technique is analyzed and compared with that of the lapped transform domain excision-based receivers. Simulation results demonstrate the improved performance and increased robustness of the proposed technique.
文摘This paper presents a high efficiency spread spectrum scheme using approximate orthogonal complex (AOC) sequences. In this scheme, the 64 AOC sequences picked up from 84 complex sequences space are employed for spreading spectrum. In modulation, 6 input bits is used to select one AOC sequence, and the selected sequence is then phase-rotated by another 2 input bits. In demodulator, a complex correlator detects the transmitted AOC sequence. Simulation results show that the proposed scheme has better BER performance than the existing complementary code keying (CCK) modulation scheme. For AOC, additional processing gain of 1.79dB can be obtained when the sequence length is 8.
基金Sponsored by the Advanced Research Project of"Twelve-Five-Year-Plan"of Weapon System(Grant No.4010201050201)the China Postdoctoral Science Foundation Founded Project(Grant No.2011M500640)+1 种基金the Postdoctoral Science Foundation of Heilongjiang Province(Grant No.LBHZ10206)the China Fundamental Research Funds for the Central Universities(Grant No.HEUCF130802)
文摘Aimed at the conventional serial communication system fails when the channel was frequency-selective,long delay and multi-paths effect,resulting in inter-symbol-interference( ISI),an iterative system for underwater acoustic communication( UWAC) was proposed,which employed iterative differential detection and spread spectrum technique. The proposed scheme adopts π /4-DQPSK soft demodulation to overcome the difficulty of phase ambiguity. For suppression of ISI in UWAC,joint demodulation and decoding iteration was used. The communication scheme has the characteristic of long communication range at low SNR,and the maximum range is up to 100 km. The theoretic analysis and simulation results show that the proposed scheme outperforms traditional serial one. When SNR is- 6 dB,after four joint iterations,compared with serial scheme,BER can decrease from 10- 2to 10- 5.
文摘A satellite communication system consisting of small earth terminals which utilize spread spectrum multiple access (SSMA) techniques is introduced in this paper. Having no master station, the system is distributively controlled. The frequency band used is 6/4GHz.
文摘This paper designs an underwater acoustic communication system based on tamed spread spectrum and Frequency Hopping Multiple Access (FHMA) for multiple underwater vehicles. In this system, multiple underwater vehicles can communicate with the console on the water surface simultaneously successfully. The communication system is com-posed of tamed spread spectrum modulation and demodulation, frequency hopping modulation and demodulation with synchronization function, 4FSK modulation and demodulation and Rake Receiver. In order to make the system more feasible, underwater channel and the effect of user number on Bit Error Ratio (BER) are also taken into account. The simulation results indicate that it is feasible to use this system to accomplish underwater communication reliably for multiple users due to the low BER.
文摘Direct-sequence spread spectrum （DSSS） communication possesses low probability of detection and has been widely used in confidential communications. However, pseudo-noise （PN） sequences, used as spreading code in conventional DSSS communications, possess peri- odic character and binary value. In hostile environments, these distinct characters may lead to some important parameters of signals being estimated accurately, and then lead to the leakage of transmitted information. To solve the problem, we propose the chaotic phase modulation （CPM） sequence alternating the PN sequences. CPM sequence has complex values and constant envelope, and also possesses large quantity and good correlation characteristics. Moreover, it has more hidden features than conventional sequences by modulating its phases using chaotic sequence. To improve the data rate, we apply it into the technique of multichannel communica-tion. Simulation results show this scheme＇s superior bit error ratio （BER） performance, which demonstrates its feasibility in underwater acoustic communications.
基金funded by National Scientific Foundation of China under grants(No.62101050 and No.62001022).
文摘Coherent fast frequency hopping(CFFH)is attracting growing attention owing to its good antijamming performance and the coherent combining ability.However,compared with the conventional non-coherent fast frequency hopping,CFFH requires a more precise system synchronization.In this paper,we propose a new fine synchronization algorithm for CFFH.This algorithm consists two stages,namely,open-loop stage and closed-loop stage.In the openloop stage,a grid-based search parameter estimation method is proposed.In the closed-loop stage,we construct a fully coherent phase-locked loop(PLL)and a delay-locked loop(DLL)with decoding feedback structure to perform further fine estimation of the system clock skew and time delay,respectively.Moreover,we analyze the effect of the search parameter settings on the estimation error and derive the root mean squared error(RMSE)of estimates in the steady state of the closed-loop stage.Finally,through simulation,the RMSE performance are compared with the corresponding Cramer-Rao low bound(CRLB)and conventional code loop estimation to show the effectiveness of proposed algorithm.
基金Project supported by the National Natural Science Foundation of China(Nos.61431005,51409235,and 61401111)the Fundamental Research Funds for the Central Universities,China(No.201213004)
文摘With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.
文摘The statistic characteristics of chaotic sequences generated by improved logistic map are analyzed and it is found that improved logistic map chaotic sequences have good correlation and they can be used as address sequences in spread spectrum communication. The discrete time synchronization of Henon map is immediate. We apply the discrete time synchronization to chaotic spread spectrum communication and propose an original communication scheme. The simulation shows that the application is successful.
文摘In underwater acoustic communication,because the available bandwidth of the channel is severely limited,the direct-sequence spread-spectrum scheme can only be realized at low bit rates.To improve the transmission speed,a multicode spread-spectrum scheme is considered.However,in this case,due to the rapid time-variability of the underwater channel,and the influence of inter-symbol interference(ISI)and inter-channel interference(ICI),the conventional rake receiver may fail to function.The hypothesis-feedback equalization algorithm has been proposed for the direct-sequence spread-spectrum system[1].By updating coefficients at chip rate and feeding back hypothesized chips,it can track time-variability and combat ISI effectively.However,for a multicode system,its performance will be degraded by ICI.An improved algorithm is proposed in this paper,which combines parallel interference cancellation(PIC)with hypothesis-feedback equalization(HFE),with the capabilities of tracking the time-varying channel and suppressing the ISI and ICI at the same time.Simulation results prove that the proposed algorithm can significantly improve the performance of a multicode system.
