A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each u...A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each user are generated by circularly shifting the prototype spreading code. A feedback pre-equalizer is employed to process the M-ary MC- CDMA signal before transmitted. The received signal is multiplied by the Inverse Discrete Fourier Transform (IDFT) result of the mirror image code of the prototype spreading code, and then demodulated by Orthogonal Frequency-Division Multiplexing (OFDM) demodulator. Compared with the conventional M-ary MC-CDMA receiver, the proposed scheme increases bandwidth efficiency, meanwhile, it achieves M-ary despread spectrum and multi-carrier demodulation, which reduces computation complexity remarkably.展开更多
It is well-known that the multi-valued CDMA spreading codes can be designed by means of a pair of mirror multi-rate filter banks based on some optimizing criterion. This paper indicates that there exists a theoretical...It is well-known that the multi-valued CDMA spreading codes can be designed by means of a pair of mirror multi-rate filter banks based on some optimizing criterion. This paper indicates that there exists a theoretical bound in the performance of its circulating correlation property, which is given by an explicit expression. Based on this analysis, a criterion of maximizing entropy is proposed to design such codes. Computer simulation result suggests that the resulted codes outperform the conventional binary balanced Gold codes for an asynchronous CDMA system.展开更多
Frequency Hopping Spread Spectrum (FHSS) system is often deployed to protect wireless communication from jamming or to preclude undesired reception of the signal. Such themes can only be achieved if the jammer or unde...Frequency Hopping Spread Spectrum (FHSS) system is often deployed to protect wireless communication from jamming or to preclude undesired reception of the signal. Such themes can only be achieved if the jammer or undesired receiver does not have the knowledge of the spreading code. For this reason, unencrypted M-sequences are a deficient choice for the spreading code when a high level of security is required. The primary objective of this paper is to analyze vulnerability of linear feedback shift register (LFSRs) codes. Then, a new method based on encryption algorithm applied over spreading codes, named hidden frequency hopping is proposed to improve the security of FHSS. The proposed encryption security algorithm is highly reliable, and can be applied to all existing data communication systems based on spread spectrum techniques. Since the multi-user detection is an inherent characteristic for FHSS, the multi-user interference must be studied carefully. Hence, a new method called optimum pair “key-input” selection is proposed which reduces interference below the desired constant threshold.展开更多
Long PN-code acquisition is a difficult and time-consuming task due to long code period.To accelerate acquisition,folding methods like XFAST are widely used.In highdynamic environment however,the application of those ...Long PN-code acquisition is a difficult and time-consuming task due to long code period.To accelerate acquisition,folding methods like XFAST are widely used.In highdynamic environment however,the application of those methods are largely restricted due to nonnegligible residual frequency.This paper proposes a new dual-channel method for fast acquisition of long PN-code.In the proposed method,both non-overlapping local PNcode blocks are employed to correlate with input sample block;the detection process is eased through finding the maximum value among correlation results and verification is made with all the full and partial peaks taken into account.False alarm probabilities from analysis of the verification process are derived.Both theoretical and Monte Carlo simulations reveal that,with respect to acquisition probability and mean acquisition time under the same false alarm rate,dual-channel method has advantage over zero-padding and XFAST based folding methods under certain false alarm probabilities.展开更多
Space-time coding is an important technique that can improve transmission performance at fading environments in mobile communication systems. In this paper, we propose a novel diversity scheme using spread spacetime b...Space-time coding is an important technique that can improve transmission performance at fading environments in mobile communication systems. In this paper, we propose a novel diversity scheme using spread spacetime block coding （SSTBC） in multiple antenna systems. At the transmitter, the primitive data are serial to parallel converted to multiple data streams, and each stream is rotated in constellation. Then Walsh codes are used to spread each symbol to all antenna space in a space-time block. The signals received from all receiver antennas are combined with the maximum ratio combining （MRC）, equalized with linear equalizer to eliminate the inter-code interference and finally demodulated to recover to transmit data by using the one-symbol maximum likelihood detector. The proposed scheme does not sacrifice the spectrum efficiency meanwhile maintains the transceiver with low complexity. Owing to the transmission symbols of different transmit antennas passing through all the spatial subchannels between transceiver antenna pairs, the system obtains the partial additional space diversity gain of all spatial paths. It is also shown that the diversity gain is better than the previous space-time block coding （STBC） schemes with full transmission rate.展开更多
In this paper, we propose a new en /de coding scheme of spreading time OCDMA utilizing the dispersion of grating and filter in frequency domain. The key components of the scheme are grating pair, Fourier transformat...In this paper, we propose a new en /de coding scheme of spreading time OCDMA utilizing the dispersion of grating and filter in frequency domain. The key components of the scheme are grating pair, Fourier transformation lens, phase filter etc. The results of design and calculation are shown that the spreading time of input pulse can be up to nanosecond duration and the phase filter can provide pseudo noise bursts in time domain. The requirements for Laser and optical detection equipment in the scheme are reduced. So the new scheme proposed by us is effective for OCDMA en /de coding of coherent ultra short pulses.展开更多
An improved technique with a fractional sampling based on two samples per chip, according to the Nyquist criterion, has been employed by the authors to enhance the performance in the code synchronization of UMTS (or W...An improved technique with a fractional sampling based on two samples per chip, according to the Nyquist criterion, has been employed by the authors to enhance the performance in the code synchronization of UMTS (or W-CDMA) systems. In this paper, we investigate on the theoretical rationale of such a promising behavior. The performance is analyzed for several wireless channels, in the presence of typical pedestrian and vehicular scenarios of the IMT2000/UMTS cellular systems.展开更多
Self-encoded spread spectrum eliminates the need for traditional pseudo noise (PN) code generators. In a self-encoded multiple access (SEMA) system, the number of users is not limited by the number of available sequen...Self-encoded spread spectrum eliminates the need for traditional pseudo noise (PN) code generators. In a self-encoded multiple access (SEMA) system, the number of users is not limited by the number of available sequences, unlike code division multiple access (CDMA) systems that employ PN codes such as m-, Gold or Kassami sequences. SEMA provides a convenient way of supporting multi-rate, multi-level grades of service in multimedia communications and prioritized heterogeneous networking systems. In this paper, we propose multiuser convolutional channel coding in SEMA that provides fewer cross-correlations among users and thereby reducing multiple access interference (MAI). We analyze SEMA multiuser convolutional coding in additive white Gaussian noise (AWGN) channels as well as fading channels. Our analysis includes downlink synchronous system as well as asynchronous system such as uplink mobile-to-base station communication.展开更多
In this work, we observe the behavior of block space-time code in wireless channel dynamics. The block space-time code is optimally constructed in slow fading. The block code in quasistatic fading channels provides af...In this work, we observe the behavior of block space-time code in wireless channel dynamics. The block space-time code is optimally constructed in slow fading. The block code in quasistatic fading channels provides affordable complexity in design and construction. Our results show that the performance of the block space-time code may not be as good as conventionally convolutional coding with serial transmission for some channel features. As channel approaches fast fading, a coded single antenna scheme can collect as much diversity as desired by correctly choosing the free distance of code. The results also point to the need for robust space-time code in dynamic wireless fading channels. We expect that self-encoded spread spec-trum with block space-time code will provide a robust performance in dynamic wireless fading channels.展开更多
基金Supported by the National Natural Science Foundation of China (No.60172029).
文摘A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each user are generated by circularly shifting the prototype spreading code. A feedback pre-equalizer is employed to process the M-ary MC- CDMA signal before transmitted. The received signal is multiplied by the Inverse Discrete Fourier Transform (IDFT) result of the mirror image code of the prototype spreading code, and then demodulated by Orthogonal Frequency-Division Multiplexing (OFDM) demodulator. Compared with the conventional M-ary MC-CDMA receiver, the proposed scheme increases bandwidth efficiency, meanwhile, it achieves M-ary despread spectrum and multi-carrier demodulation, which reduces computation complexity remarkably.
基金Supported by the National Natural Science Foundation of China(No.69872027)
文摘It is well-known that the multi-valued CDMA spreading codes can be designed by means of a pair of mirror multi-rate filter banks based on some optimizing criterion. This paper indicates that there exists a theoretical bound in the performance of its circulating correlation property, which is given by an explicit expression. Based on this analysis, a criterion of maximizing entropy is proposed to design such codes. Computer simulation result suggests that the resulted codes outperform the conventional binary balanced Gold codes for an asynchronous CDMA system.
文摘Frequency Hopping Spread Spectrum (FHSS) system is often deployed to protect wireless communication from jamming or to preclude undesired reception of the signal. Such themes can only be achieved if the jammer or undesired receiver does not have the knowledge of the spreading code. For this reason, unencrypted M-sequences are a deficient choice for the spreading code when a high level of security is required. The primary objective of this paper is to analyze vulnerability of linear feedback shift register (LFSRs) codes. Then, a new method based on encryption algorithm applied over spreading codes, named hidden frequency hopping is proposed to improve the security of FHSS. The proposed encryption security algorithm is highly reliable, and can be applied to all existing data communication systems based on spread spectrum techniques. Since the multi-user detection is an inherent characteristic for FHSS, the multi-user interference must be studied carefully. Hence, a new method called optimum pair “key-input” selection is proposed which reduces interference below the desired constant threshold.
文摘Long PN-code acquisition is a difficult and time-consuming task due to long code period.To accelerate acquisition,folding methods like XFAST are widely used.In highdynamic environment however,the application of those methods are largely restricted due to nonnegligible residual frequency.This paper proposes a new dual-channel method for fast acquisition of long PN-code.In the proposed method,both non-overlapping local PNcode blocks are employed to correlate with input sample block;the detection process is eased through finding the maximum value among correlation results and verification is made with all the full and partial peaks taken into account.False alarm probabilities from analysis of the verification process are derived.Both theoretical and Monte Carlo simulations reveal that,with respect to acquisition probability and mean acquisition time under the same false alarm rate,dual-channel method has advantage over zero-padding and XFAST based folding methods under certain false alarm probabilities.
基金This project was supported by the National Science Foundation of China (60496314)
文摘Space-time coding is an important technique that can improve transmission performance at fading environments in mobile communication systems. In this paper, we propose a novel diversity scheme using spread spacetime block coding （SSTBC） in multiple antenna systems. At the transmitter, the primitive data are serial to parallel converted to multiple data streams, and each stream is rotated in constellation. Then Walsh codes are used to spread each symbol to all antenna space in a space-time block. The signals received from all receiver antennas are combined with the maximum ratio combining （MRC）, equalized with linear equalizer to eliminate the inter-code interference and finally demodulated to recover to transmit data by using the one-symbol maximum likelihood detector. The proposed scheme does not sacrifice the spectrum efficiency meanwhile maintains the transceiver with low complexity. Owing to the transmission symbols of different transmit antennas passing through all the spatial subchannels between transceiver antenna pairs, the system obtains the partial additional space diversity gain of all spatial paths. It is also shown that the diversity gain is better than the previous space-time block coding （STBC） schemes with full transmission rate.
文摘In this paper, we propose a new en /de coding scheme of spreading time OCDMA utilizing the dispersion of grating and filter in frequency domain. The key components of the scheme are grating pair, Fourier transformation lens, phase filter etc. The results of design and calculation are shown that the spreading time of input pulse can be up to nanosecond duration and the phase filter can provide pseudo noise bursts in time domain. The requirements for Laser and optical detection equipment in the scheme are reduced. So the new scheme proposed by us is effective for OCDMA en /de coding of coherent ultra short pulses.
文摘An improved technique with a fractional sampling based on two samples per chip, according to the Nyquist criterion, has been employed by the authors to enhance the performance in the code synchronization of UMTS (or W-CDMA) systems. In this paper, we investigate on the theoretical rationale of such a promising behavior. The performance is analyzed for several wireless channels, in the presence of typical pedestrian and vehicular scenarios of the IMT2000/UMTS cellular systems.
文摘Self-encoded spread spectrum eliminates the need for traditional pseudo noise (PN) code generators. In a self-encoded multiple access (SEMA) system, the number of users is not limited by the number of available sequences, unlike code division multiple access (CDMA) systems that employ PN codes such as m-, Gold or Kassami sequences. SEMA provides a convenient way of supporting multi-rate, multi-level grades of service in multimedia communications and prioritized heterogeneous networking systems. In this paper, we propose multiuser convolutional channel coding in SEMA that provides fewer cross-correlations among users and thereby reducing multiple access interference (MAI). We analyze SEMA multiuser convolutional coding in additive white Gaussian noise (AWGN) channels as well as fading channels. Our analysis includes downlink synchronous system as well as asynchronous system such as uplink mobile-to-base station communication.
文摘In this work, we observe the behavior of block space-time code in wireless channel dynamics. The block space-time code is optimally constructed in slow fading. The block code in quasistatic fading channels provides affordable complexity in design and construction. Our results show that the performance of the block space-time code may not be as good as conventionally convolutional coding with serial transmission for some channel features. As channel approaches fast fading, a coded single antenna scheme can collect as much diversity as desired by correctly choosing the free distance of code. The results also point to the need for robust space-time code in dynamic wireless fading channels. We expect that self-encoded spread spec-trum with block space-time code will provide a robust performance in dynamic wireless fading channels.
