Gu Xuemai

Automatic digital modulation recognition using artificial neural networks

This paper presents a modified structure and learning algorithm of artificial neural networks (ANN) for recognizing baseband signal modulation types in the presence of additive white Gaussian noise. The new method employs a layer with less output nodes and an error back propagation learning algorithm with momentum to improve the recognition performance. Simulation results and performance evaluation of the ANN are given and it is shown that the benefits of the developed method are that its structure is simple and it performs well at low signal to noise ratio (SNR) with high overall success rates.

Joint optimal sensing threshold and subcarrier power allocation in wideband cognitive radio for minimising interference to primary user

Cognitive Radio (CR) can use the frequency band allocated to a Primary User (PU) on the premise that it will prevent significant of avoiding causing great interference to the PU. In this paper, we consider a wideband CR system where the Secondary User (SU) minimises its interference to the PU by jointly allocating the optimal sensing threshold and subcarrier power. A multi-parameter optimization problem is formulated to obtain the joint optimal allocation by alternating direction optimization, which minimises the total interference to the PU over all of the subcarriers subject to the constraints on the throughput, Bit Error Rate (BER) and maximal total power of the SU, the subcarrier rate and interference power of the PU, and the false alarm and mis-detection probabilities of each subcarrier. The simulation results show that the proposed joint allocation algorithm can achieve the desired mitigation on the interference to the PU at the different subcarrier gains.

Channelized receiver platform of SDR based on FPGAs

In this paper, a channelized receiver platform of software defined radio is developed which is mainly to realize wideband quadrature digitization, modulation classification and demodulation exploiting A/D converters. FPGAs with the combination of programmable DSPs. The front-end of researched receiver based on polyphase filter quadrature digitization processors, where digitization takes place at intermediate frequencies (IF), adopts a wideband design with a bandwidth of up to 100MHz and a centered carrier frequency of up to 250MHz. The low-complexity high-speed digital IF signal processing is carried out with CORDIC algorithm on FPGAs, then to realize the recognition of several modulation schemes such as 2ASK, 4ASK, 2PSK, 4PSK, 2FSK, 4FSK, 16QAM to implement communication protocols fairly flexibly.In this paper, a channelized receiver platform of software defined radio is developed which is mainly to realize wideband quadrature digitization, modulation classification and demodulation exploiting A/D converters. FPGAs with the combination of programmable DSPs. The front-end of researched receiver based on polyphase filter quadrature digitization processors, where digitization takes place at intermediate frequencies (IF), adopts a wideband design with a bandwidth of up to 100MHz and a centered carrier frequency of up to 250MHz. The low-complexity high-speed digital IF signal processing is carried out with CORDIC algorithm on FPGAs, then to realize the recognition of several modulation schemes such as 2ASK, 4ASK, 2PSK, 4PSK, 2FSK, 4FSK, 16QAM to implement communication protocols fairly flexibly.

Multi-QoS Routing for LEO Satellite Networks

The paper proposed a routing algorithm with multi-quality of service constraint conditions for low earth orbit satellite network, based on tuning architecture of ant colony optimization and updating strategy of pheromone. The routing algorithm was capable of adjusting current optimization path in time according to change of traffics distribution, balancing the network load, avoiding network congestion, and achieving optimization combined with multi-QoS. The results showed that in the nearly full load of the network, routing algorithm guaranteed QoS of traffic while making full use of network resource.

Classification using a novel support vector machine fuzzy network for digital modulations in satellite communication

To make the modulation classification system more suitable for signals in a wide range of signal to noise rate (SNR), a novel support vector machine fuzzy network (SVMFN) is presented in this paper. The SVMFN employs a new definition of fuzzy density which incorporates accuracy and uncertainty of the classifiers to improve recognition reliability. Further, three efficient features with high robustness and less computation are extracted from intercepted signals to classify eleven digital modulation types (i.e. 2ASK, 4ASK, 2FSK, 4FSK, 2PSK, 4PSK, 8PSK, 16QAM, TFM, /spl pi//4QPSK and OQPSK). Computer simulation shows that the proposed scheme has the advantages of high accuracy and reliability (success rates are over 97.5% when SNR is not lower than 0 dB), and adapt to engineering applications.

Based on 2.4G Wireless Communications System Design

ZigBee is a wireless technology developed as an open global standard. With the application of wireless sensor networks, many applications not only have low-power, low-complexity and cost-effective, but also should have high confidentiality. So the research of the security of ZigBee is becoming very important. Based on the ZigBee network protocol stack structure, in this paper, we mainly discuss the ZigBee data transmission security services, the encryption techniques, security key, the trust center, secured Frames Format and security Level. At last we introduce the security application in the ZigBee application layer.

Wireless Communications Network Design Based on the LPC2138

In the framework of the hardware platform, CC2420 chip which supports IEEE 802.15.4 protocol is used as RF transceiver controlling chip. 32-bit high-performance ARM processor LPC2138 is used as both protocol controller and data acquisition. Through the OP to improve the transmitting power and receiving sensitivity. The system adapts to the Universal 2.4 GHz band and it has a high transfer rate and multi-channel features. Finally, the testing result shows that the transmitting power for the platform is more than 25 dBm, the communication distance is more than 3km. It realizes the communication between platforms.

Multi-constraint quality of service routing algorithm for dynamic topology networks

Abstract An adaptive multi-QoS routing algorithm called AMQRA is proposed for dynamic topology networks, such as satellite networks and Ad-hoc networks. The AMQRA is a distributed and mobile-agents-based routing algorithm, which combines ant quantity system (AQS) with ant colony optimization (ACO) that is used in AntNet routing algorithm. In dynamic topology networks, the AMQRA achieves timely optimization for concave metric QoS constraint and fast convergence. The proposed routing algorithm is simulated in Iridium satellite constellation on OPNET. The results show that AMQRA not only outperforms the AntNet in convergence rate in dynamic topology networks but also can optimize concave metric QoS constraint and reasonably allot bandwidth to the load to avoid networks congestion.

An Onboard ATM Switching Fabric Based on Ant Algorithm with Blocking Avoidance

In this paper, an onboard asynchronous transfer mode (ATM) switching fabric based on ant algorithm with blocking avoidance is proposed in satellite ATM network. The onboard ATM switching fabric is an improved Benes network based on ants flooding mechanism and blocking avoidance mechanism to solve bandwidth-limited and delay-bounded problems in satellite communication network. Compared with traditional self-routing Benes network, better performances of proposed onboard ATM switching fabric are achieved

A new approach of 2D discrete cosine transform with Mobius inverse formula

The 2D discrete cosine transform (DCT) is an important mathematical tool in digital image processing and many other fields. Our aim is mainly to present an algorithm of 2D DCT, which turns N/spl times/N DCT into N separate 1D DCT and addition operations, and then to implement DCT with an arithmetic Fourier transform (AFT), which has turned out to be an important alternative to the known traditional methods of fast Fourier transform (FFT) in terms of accuracy, complexity and speed. The total number of multiplications and additions is only half of that required for the corresponding traditional method. Simulation results show that this method is feasible and its computational complexity is lower than the row-column algorithm.