Guo Jingbo

Performance of DSSS against Repeater Jamming

Direct sequence spread spectrum (DSSS) technique has been widely used in both military communications and commercial communications. The normal jamming types, including broadband noise, partial-band noise and so on, are ineffective at the current jamming power level when the processing gain is large enough. This paper proposes a design of the repeater jamming based on radio frequency memory (RFM). The interference effect of repeater jamming on victim receivers code acquisition is discussed, and the bit error probability of the DSSS system interfered by repeater jamming is obtained. Moreover, geometric limitation on repeater jamming is mentioned. The result of simulation shows the deduction is right. The repeater jamming proposed in this paper is a kind of correlative jamming types which are more effective than normal jamming types, and it can be used in the field of DSSS communication countermeasures.

Transmission characteristics of low-voltage distribution networks in China and its model

Communication over the low-voltage distribution networks is of great importance to the electrical engineering and networks engineering. The signal transmission characteristics over the distribution networks are the key factors to be considered in designing the communication systems. In this paper, the signal transmission characteristics in frequency band of 100 kHz /spl sim/400 kHz over 220-V distribution networks in China is investigated and its mathematical models are derived from the measured data. After the procedure of transmission measurement based on HP4395A is discussed briefly, the measurement results including in-phase and cross-phase transmission are described and analyzed. The impulse response of the channel is estimated from the frequency domain measurement based on the linear minimum mean square error in which the measurement noise is reduced during the parameters estimation processes, the estimation shows that the channel could be well described by the 20-taps finite-impulse response model. On the basis of a large amount measurements, we believe the transmission channel is the stationary stochastic process and a stochastic channel model of in-phase transmission is discussed and a six-order autoregressive of the channel model was given out.

Breaking a chaotic secure communication scheme

The chaotic direct sequence spread spectrum (CD3S) has been extensively studied and accepted as an approach of chaotic secure communication. However, we find that CD3S is insecure and present the results of breaking CD3S. A modified unscented-Kalman-filter chaos fitting method is proposed. With the proposed method, an intruder can use a different chaotic system to fit the transmitters chaotic system and break the CD3S scheme without any knowledge of the chaotic transmitters structure, parameters or initial value, even under the following conditions: (A) the chaotic spreading sequence is complex and generated by two chaotic maps; (B) there exists noise in the CD3S signal; (C) the CD3S signal is constructed in frames. Simulation results verify the method.

A Novel Sub-carrier and Power Allocation Algorithm for Multi-user OFDM Systems

In this paper, a novel sub-carrier and power allocation algorithm for downlink transmission of multi-user OFDM system is presented. The proposed algorithm tries to minimize the total transmission power, while satisfying the bit error rate constraint and rate requirement of each user. The proposed algorithm combines the sub-carriers and power allocation simultaneously, by comparing the power increment to swap the sub-carriers between users. As demonstrated in the simulation results, the proposed algorithm offers better performance than other sub-optimal algorithms, with the similar computational complexity.

Parameter estimation in chaotic interference

In many cases signals of interest are submerged by strong chaotic interference, how to extract the weak signal is of great importance and interest. In order to estimate the parameters representing the signal, a novel noise reduction method is proposed in which the chaotic interference is successfully separated from the received data, which is composed of the signal of interest, chaotic interference and measurement noise. The parameters can be precisely estimated from the residual error time series after the novel noise reduction method. Some simulations are given to verify the effectiveness of the estimation and some related discussions are also given.

A Novel UPF-Based Demodulator for Chaotic Parameter Modulation Systems

Chaotic parameter modulation is one kind of secure communications in which the system noise is merged into the dynamic evolution of modulating signal and the observed sequence is a chaotic signal plus non-Gaussian noise. So far the known demodulation algorithms for the sequence are limited to the Gaussian noises and high signal to noise ratios are required. To solve these issues, the idea of PF (particle filter) is introduced to deal with these issues in which the distribution of the noise could be any form. The state equations in UPF (unscented particle filter) form for the demodulation of chaotic parameter modulations are derived, and a novel modified algorithm based on UPF for the demodulation is presented. Because of the utilization of the nonlinear innovation hidden in the received chaotic signal and non-Gaussian noise, there is no limit to the Gaussian noise or not, and the requirement of signal to noise ratio is obviously decreased in the same time. The simulated results show that the presented algorithm can demodulate the messages from the received sequence accurately under the relatively low signal to noise ratio. The demodulation comparison with PF (particle filter) is also carried out and results show that the MSE(mean square error) of the UPF-based algorithm is better than PF about 10 dB.

A novel continuous-time current-mode biquad filter employing CCIIs

A novel configuration of a CCII-based continuous-time current-mode biquad filter is proposed in this paper. The filter is only made of minim CCII elements and grounded resistors and capacitors; the topology is really simple and the performance is really good, so it is suited for full integration. A computer simulation is carried out and the results show that the proposed circuits are effective.