Yi Kechu

Packet routing algorithm for polar orbit LEO satellite constellation network

Broadband satellite networks are capable of providing global coverage and support various services. The networks constructed by Low Earth Orbit (LEO) satellite constellations have attracted great interests because of their short round-trip delays and wide bandwidths. A challenging problem is to develop a simple and efficient packet routing algorithm for the LEO satellite constellation network. This paper presents a SpiderWeb Topological Network (SWTN) and a distributed packet routing algorithm for the LEO satellite constellation network based on the SWTN. The algorithm gives the minimum propagation delay paths with low computational complexity and requires no routing tables, which is practical for on-board processing. The performance of the algorithm is demonstrated through simulations.

A new method to design CDMA spreading sequences

It is well-known that multi-value 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 circulate correlation property, which is given by an explicit expression. Based on this analysis, a criterion of maximizing entropy is proposed to design such codes. A computer simulation result suggests that the resulting codes outperform the conventional binary balance Gold codes for an asynchronous CDMA system.

Blind Narrowband Interference Suppression in DS/CDMA Systems

This paper proposes a blind narrowband interference suppression algorithm based on FFT. By keeping the phase spectrum of the received signal and hard limiting the magnitude spectrum, the signal is reconstructed with the stored phase spectrum and limited magnitude spectrum. During the process, the power of NBIs is greatly decreased, thus the suppression of the NBIs is achieved. The method can be used to suppress various NBIs. The algorithm has a very low complexity that is very suitable to the real-time processing

A fast codebook design algorithm for vector quantization

This paper presents a fast codebook design algorithm for vector quantization, which eliminates distortion calculations by using inequality between the distortion and the means of two vectors as well as the partial distortion theorem during both the initial codebook splitting and LBG iteration procedures. Moreover, the partition information of vectors in the previous iteration is used in the repartition of the training set to make the employing of the two above eliminating rules more efficiently. This algorithm eliminates about 90% of unnecessary distortion calculations and can produce the same codebook as the LBG algorithm with only a little additional memory, thus outperforming other fast algorithms that always need much more additional memory which is impractical for big codebook cases.

A gradient algorithm for complex adaptive notch filters

This paper proposes a novel gradient algorithm for complex adaptive IIR notch filters with constrained poles and zeros. We applied the algorithm to a high-order adaptive notch filter structure with matrix form, which consists of first-order filters. Computer simulation shows that the convergence speed of the adaptive algorithm is faster than the conventional ones, moreover the stability of the resulted adaptive filters is sure.

Particle Filter Localization in Underground Mines Using UWB Ranging

Ultra Wideband technology is regarded by many as one of the future key technologies in communications and positioning. In this paper a positioning method is described for accurate underground mine localization of a sensor in a network of known beacons. The sensor measures the range to the beacons using an Ultra-Wideband (UWB) signal and uses statistical inference to correct for the error due to multipath and NLOS in underground mine. We show that a particle filter can be used to estimate the joint distribution over beacon measurement. Simulation results show perfect performance with UWB ranging and particle filter technology.

Performance analysis of RC-SRake receiver in ultra-wideband communication under IEEE 802.15.4a channel

In ultra-wideband impulse radio (UWB-IR) system, Rake receiver can take advantage of the high degree of diversity that results from a large number of multipath components (MPCs). In this paper, we propose a reduced-complexity selective Rake (RC-SRake) receiver scheme under ultra-wideband multipath channels. It employs a convolution based finger estimation algorithm, which has minimal complexity that does not require precise channel information. We derive a closed-form expression for symbol error probability (SEP) of the proposed Rake receiver in term of the combined fingers and impulse noise. We evaluate these expressions numerically under various IEEE 802.15.4a channel models. It is observed that a similar ability of energy capture can be obtained with less than 10 fingers as compared to the ideal SRake. More importantly, as the number of combined fingers increases, the performance of our RC-SRake receiver improves in general despite occasional degradation due to the estimation error of impulse noise.

Cepstrum digital image watermarking algorithm

A novel digital image watermarking technique in the cepstrum domain is proposed. The watermark is weighted in the cepstrum domain according to the distribution of cepstral coefficients and the characteristics of human visual system. The watermark is imperceptibly inserted in a spread-spectrum-like fashion into the cepstral components of the original image and the embedded watermark can be uniquely detected without the original image. Computer simulation results show that the proposed method is robust to multiple watermarks, JPEG compression, image cropping, multiplicative noise, and some other image processing operations.

On removing cloud interference in remote-sensing images

Improvements made to the cloud removal method for landsat MSS images proposed by O.R. Mitchell are presented. A more reasonable mathematical model for the cloud effect has been derived, and a two-stage filtering scheme based on this new model has been proposed. A filtering and a 3-D processing method for landsat MSS image noise cleaning has been developed to implement the scheme. A preliminary experiment shows promising results.

A scheme of M-ary multi-carrier spread spectrum based on wavelet packet

We propose a novel scheme of M-ary multicarrier spread spectrum based on wavelet packet. The scheme has good performance in multipath channel because of taking advantages of the properties of wavelet packet. Its performance is investigated for a multipath, slow Rayleigh fading channel. The performance advantages of the system over that based on DFT are demonstrated by both analytical and simulation methods.