Xuemai Gu

Improved Channel Estimation Method Based on Time-Domain Processing for OFDM Systems

Channel impulse response (CIR) can be estimated by time-domain processing (TDP) based on cyclic correlation in orthogonal frequency division multiplexing (OFDM) systems. We propose an improved generalized TDP method to reduce the estimation error by taking the average of different CIR values which are derived according to the different starting points of cyclic correlation. Moreover, an effective channel length estimation method which is performed by reverse detection processing to search the last effective CIR is also proposed. The whole proposed method is more efficient to OFDM systems with long cyclic prefix (CP) because the CP information is sufficiently utilized during the CIR estimation. The analysis and the simulation results verify that the mean square error (MSE) performance of the proposed method is 4-5 dB better than the conventional method under the same conditions.

Estimation-Based Blind Detection in Low SNR on Direct-Sequence Spread Spectrum Signal

In nowadays, the Direct-Sequence Spread Spectrum (DSSS) technology has been widely used. Its necessary to research blind detection algorithms on DSSS signal. Many studies before successfully detect the parameters of the signal, like carrier frequency, code rate, code period etc. The current main problem is that signal-noise ratio (SNR) required is much higher than which DSSS signal working at. Therefore these algorithms are difficult to carry out practical applications. The proposed algorithm can effectively suppresses the noise through estimating data and code information, thus achieving a low SNR threshold of the blind detection of DSSS signals. For DSSS signal using 15 bits spreading code, algorithm proposed can easily complete the detection in the SNR lower than -8 dB. The threshold could be even lower if spreading code is longer or there are more signal samples. Algorithm in this paper can also demodulate data blindly with good BER performance.

A Robust FLOM Based Spectrum Sensing Scheme under Middleton Class A Noise in IoT

Accessibility to remote users in dynamic environment, high spectrum utilization, and no spectrum purchase make Cognitive Radio (CR) a feasible solution of wireless communications in the Internet of Things (IoT). Reliable spectrum sensing becomes the prerequisite for the establishment of communication between IoT-capable objects. Considering the application environment, spectrum sensing not only has to cope with man-made impulsive noises but also needs to overcome noise fluctuations. In this paper, we study the Fractional Lower Order Moments (FLOM) based spectrum sensing method under Middleton Class A noise and incorporate a Noise Power Estimation (NPE) module into the sensing system to deal with the issue of noise uncertainty. Moreover, the NPE process does not need noise-only samples. The analytical expressions of the probabilities of detection and the probability of false alarm are derived. The impact on sensing performance of the parameters of the NPE module is also analyzed. The theoretical analysis and simulation results show that our proposed sensing method achieves a satisfactory performance at low SNR.

Demodulation of Low SNR QPSK Signal Based on Chaotic Synchronization

Signal restoration utilizing chaotic synchronization can resist strong noise and it can make signal demodulation more easy in low SNR channel. In this paper, BPSK signal restoration is introduced and a new QPSK signal demodulation based on chaotic synchronization which is used to restore QPSK signal to increase SNR is put forward. The characteristic of QPSK signal in chaotic synchronization is analyzed and two path systems is brought in to deal with the complexity of QPSK signal. Then a global design of new QPSK signal demodulation is set up and finally it is proved through simulation and compared with the traditional coherent demodulation.

Frequency Detection of Weak Signal in Narrowband Noise Based on Duffing Oscillator

Duffing oscillator is used to detect weak signal in strong noise because traditional linear methods cannot work correctly in this situation. Normal Duffing oscillator is used under broadband noise because it is immune to broadband noise. But it is not suitable in narrowband noise because zero expectation of noise is damaged in narrowband noise. In this paper, the difference influence to Duffing oscillator between broadband noise and narrowband noise is analyzed and the resistance of Duffing oscillator to narrowband noise is proved. Then a new frequency detection method based on higher initial driving force amplitude and duration of cycle state is developed. Finally, the appropriate initial amplitude needed in this method is confirmed and the method is verified that it can detect frequency in narrowband noise by simulation.

A Novel UWB System with CSS BOK Technique

Chirp signal has the feature of low power consumption, high processing gain and low cost. However, little work has been done to use a chirp signal in a UWB system. This paper proposed a novel idea to make use of chirp spread spectrum in a UWB system and designed a simple UWB system based on Binary Orthogonal Keying. Simulation results show that, compared with TH-UWB system, this system has better performance in 802.15.4a multipath channel model, and more suitable to worse environment.

An efficient OFDM channel estimation method for satellite and intermediate module repeater channels in DMB system

A noise reduction channel estimation method is needed to improve the performance for digital multimedia broadcasting (DMB) systems with intermediate module repeater (IMR). It is based on correlation channel estimation method with the aid of the time-domain received signal and pilot signal. Channel impulse response can be derived by the output of cyclic correlation directly. Moreover, the information contained in the received signal with the cyclic prefix is made use of in the proposed method at the receiver. However, the errors caused by the coarse channel impulse response estimation degrade the performance severely. The noise reduction method is processed by using the time-averaging of channel impulse responses. The simulation results about the satellite and IMR channels show that the symbol error rate (SER) performance of the proposed method is much better than other conventional methods.