Shiju Li

An On-demand and Dynamic Slot Assignment Protocol for Ad Hoc Networks

An on-demand and dynamic slot assignment (ODSA) protocol for ad hoc networks is proposed. The protocol assigns slots for nodes basing on information in their two-hop neighborhood, which can be collected by listening before slot assignment. In ODSA, a slot is divided into several mini-slots, and the reservation procedure is realized in the selected idle slot by message exchanging. ODSA can adapt to variations of application and network topology. Furthermore, it can ensure the time delays of nodes owning slots. ODSA has been studied in different network situations, and the results show that ODSA has smaller average access delay and higher channel utilization compared with FPRP

A Flexible Bit Allocation Algorithm Based on Adaptive Method for OFDM Channels

This paper presents a new bit and power allocation scheme for OFDM systems with low computational complexity in which the overall transmission power is minimized by constraining the fixed data rate and bit error rate. The algorithm and simulation include two stages. The first stage involves the application of a target BER and SNR of each sub-carrier for a variable-rate bit pre-allocation. The second stage applies greedy and Campello approach to achieve constant channel rate of bit allocation. In a word, bit allocation with constant rate performs variable rate bit allocation first, and then modifies the overall bits to a constant. The simulation results demonstrate that the scheme has significant computational advantages over the conventional algorithms while providing optimal performance. It also provides considerable universality and flexibility for both the fixed rate voice data and variable rate multimedia data of the broadband wireless communication.

Blind Separation of DS-CDMA Signals with ICA Method

The estimation of pseudo noise sequence and information sequence is of great importance in the security of DS-CDMA system, which remains a hot research problem in reconnaissance and supervision of wireless communication. In DS-CDMA system, the pseudo noise sequences of different users are uncorrelated and the information sequences of different users are statistical independent, thus independent component analysis (ICA) could be introduced to separate the DS-CDMA signals with little prior knowledge. In multipath situations, the recovered pseudo noise sequence with ICA is overlapped. For DS-CDMA signals which utilize m-sequence as pseudo noise sequence, the triple correlation function (TCF) is introduced to eliminate the influence of overlap in this paper , which increases the estimation correct ratio greatly. Under the non - cooperative conditions, it is very difficult for the interceptor to aim at the very beginning of the transmitted signal. Certain offset s between the interceptor and the transmitter deteriorate the blind separation method obviously. The relationship between none convergence and the offset is found out and explained from eigen value decomposition. The validity of the proposed method and theory analysis is proved well by the simulation results at last.

Cross-Layer Iterative Decoding of Irregular LDPC Codes using Cyclic Redundancy Check Codes

This paper presents a cross-layer iterative decoder for irregular Low-Density Parity-Check (LDPC) codes which uses Cyclic Redundancy Check (CRC) codes. The key idea of the decoder is to use correctly decoded frames as an aid for correcting the remaining erroneous frames. To accomplish this, the decoder exchanges the relevant information between layers by using the cross-layer design method and an iterative decoding architecture. Moreover, the Unequal-Error Protection (UEP) property of irregular LDPC is exploited and both the multiple-error detection and single-error correction capabilities of the CRC code are used. Simulation results show that the proposed decoder outperforms the pure Sum-Product Algorithm (SPA) decoder by a considerable gain while the increase in complexity is moderate. Furthermore, the error floor of irregular LDPC codes in the high Eb/N0 regime can be lowered effectively. The proposed cross-layer iterative decoder can be used for any irregular LDPC coded wireless system to boost the performance and lower the error floor.

Average filtered blind separation of DS-CDMA signals with ICA method

In DS-CDMA system, the pseudo random sequences are none correlation and the information sequences of different users are independent, thus Independent Component Analysis (ICA) is appropriate for the blind separate the DS-CDMA signals with little prior knowledge. Original blind separation method of DS-CDMA signals with ICA utilized only one sample value in each chip. However, in common DS-CDMA communication systems, the sample rate is much faster than the chip rate, so there are many samples during a chip interval. A method of average filtered blind separation of DS-CDMA signals with ICA is proposed in this paper. When noise is stationary, the method proposed could increase the input SNR of ICA greatly. The validity of the method is proved by the simulation results at last.

Convergence characteristics analysis on blind separation of DS-CDMA signals with ICA method

Blind estimation of information sequences and pseudo random sequences is of great importance for the security in DS-CDMA system, which remains a hot research topic in reconnaissance and supervision of wireless communication. In DS-CDMA system, the information sequences of different users are independent and the pseudo random sequences are none correlation, thus independent component analysis (ICA) technology can be adopted to separate the DS-CDMA signals with little prior knowledge. Under non-cooperative situations, the interceptor could not aim at the beginning of the symbol accurately. The offset between the transmitter and the interceptor has great influence on the convergence characteristic of the blind separation algorithm of DS-CDMS signals with ICA method. Certain offsets deteriorate the convergence characteristic obviously. The relationship between the offset and the convergence characteristics is found out, which has great importance in choosing the offset in practice. The reason why certain offsets deteriorate the algorithm is analyzed from the idea of eigen value decomposition. The correctness of theory analysis is proved by the simulation results at last.

Study of a Novel Key Feature in Non-Cooperative Modulation Automatic Recognition

For both analogue and digital modulation types, we proposed a general signal expression and studied the non-cooperative automatic recognition synthetically, which is more useful and universal than separate research. The proposal of a new key feature, i.e. the variance of normalized instantaneous amplitude, with the benefit of less computationally demanding and excellent correct classification rate in low SNR, can be used to discriminate between the signals that have amplitude information and that have no amplitude information. We concluded a set of the parameters whole and accurate theoretical expressions for several signals, especially for the amplitude modulated signals with different modulation depths and audio modulated single side band signals. Illustrative simulation examples were provided at last.

Blind Estimation of Pseudo Random Sequence of DS-CDMA Signals with ICA Method

The estimation of pseudo random sequence is of great importance of the security in DS-CDMA system, which remains a hot research topic in reconnaissance and supervision of wireless communication. In DS-CDMA system, the information sequences of different users are independent and the pseudo random sequences are none correlation, thus Independent Component Analysis (ICA) technology can be adopted to separate the DS-CDMA signals with little prior knowledge. An estimation method of pseudo random sequences based on ICA is proposed, projected with the unmixing matrix calculated through ICA, the pseudo random sequences could be estimated from the eigenvector subspace. In multipath situations, the estimation is the overlapped form of the pseudo random sequences, a triple correlation function is introduced to eliminate the influence of multipath, which increases the estimation correct ratio more than 18%. The validity of the method proposed is proved well by the simulation results at last.

An Improved Joint Synchronization and Channel Estimation Algorithm for MIMO-OFDM System

This paper proposes an improved synchronization and channel estimation solution for multi-input multi-output orthogonal frequency division multiplex (MIMO-OFDM) system. We present a novel preamble design, on this basis, the performance of synchronization and channel estimation can be improved in an iterative way. Simulation results demonstrate that the proposed algorithm have a satisfactory performance even at low SNR in rich multipath, fast moving environment.

Constructions of Euclidean Geometry LDPC Codes and Performance Analysis in MIMO-OFDM System

In this paper, we introduce the history and basic characteristic of low density parity check codes, then emphasize on the construction of Euclidean geometry LDPC code and take it as the channel code into IEEE802.16d MIMO-OFDM system simulation and compare it with RS-CC codes. Finally we makes a conclusion that Euclidean geometry LDPC codes are strong competitors to FEC codes for error control in communication systems