Abstract-In current cooperative communication schemes, to achieve cooperative diversity, synchronization between terminals is usually assumed, which may not be practical since each terminal has its own local oscillator. In this paper, we first present a necessary and sufficient condition for the space-time trellis codes based on the stack construction proposed by Hammons and El Gamal to possess the full cooperative diversity order without the synchronization assumption. The condition is that the binary generator metrices of the trellis codes are shift full rank (SFR) matrices, i.e., have full row rank no matter the shifts of their row vectors, where a row corresponds to a terminal (or transmit antenna) and the length of a row vector is the memory size of the corresponding trellis code on the corresponding terminal. We then present a simple construction of SFR for any number of rows, whose number of columns, however, grows exponentially with the number of rows. We finally present some systematic SFR matrix constructions including shortest, i.e., square, SFR matrices.

Intrusion detection can identify unknown attacks from network traffics and has been an effective means of network security. Nowadays, existing methods for network anomaly detection are usually based on traditional machine learning models, such as KNN, SVM, etc. Although these methods can obtain some outstanding features, they get a relatively low accuracy and rely heavily on manual design of traffic features, which has been obsolete in the age of big data. To solve the problems of low accuracy and feature engineering in intrusion detection, a traffic anomaly detection model BAT is proposed. The BAT model combines BLSTM (Bidirectional Long Short-term memory) and attention mechanism. Attention mechanism is used to screen the network flow vector composed of packet vectors generated by the BLSTM model, which can obtain the key features for network traffic classification. In addition, we adopt multiple convolutional layers to capture the local features of traffic data. As multiple convolutional layers are used to process data samples, we refer BAT model as BAT-MC. The softmax classifier is used for network traffic classification. The proposed end-to-end model does not use any feature engineering skills and can automatically learn the key features of the hierarchy. It can well describe the network traffic behavior and improve the ability of anomaly detection effectively. We test our model on a public benchmark dataset, and the experimental results demonstrate our model has better performance than other comparison methods.

Abstract-Vector Orthogonal Frequency Division Multiplexing (OFDM) for single transmit antenna systems is a general transmission scheme, where OFDM and Single-Carrier Frequency Domain Equalization (SC-FDE) can be treated as two special/extreme cases. Due to its flexibility, it has drawn more and more attention recently. So far, all the studies about Vector OFDM assume the Maximum Likelihood (ML) receiver. In this paper, we investigate the performance of Vector OFDM with linear receivers, i.e., the Zero-Forcing (ZF) and Minimum Mean Square Error (MMSE) receivers. We first show that the detection SNR gap between the MMSE and ZF receivers increases with both channel SNR and the vector blocks (VB) size defined in Vector OFDM. Then, it is proved that for both ZF and MMSE receivers, all the transmitted symbols have equal performance. This is different from the Vector OFDM with ML receiver, where different VBs may have different coding gain, and thus may have different performances. We analyze the diversity order for Vector OFDM with MMSE receiver, and show that, regardless of the Vector OFDM symbol length , the diversity order can be represented as , where is the VB size, is the spectrum efficiency in bits/symbol, and is the maximum delay of the multipath channel. For Vector OFDM with ZF receiver, we show that the diversity order equals 1 and the performance is the same as the conventional OFDM at high SNR.

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Organic field-effect transistors based on two derivatives of annelated b-oligothiophenes are fabricated. High mobility of 2.2 cm 2 V À1 s À1 is obtained for 2,5-distyryl-dithieno[2,3-b:3 0 ,2 0 -d]thiophene (DEP-DTT) while 2,5-diphenyl-dithieno[2,3-b:3 0 ,2 0 -d]thiophene (DP-DTT) presents no field-effect characteristics. The existence of S-p intermolecular interaction in DEP-DTT, which is introduced by C]C double bonds, plays an important role in the molecular arrangement both in single crystal and thin film structures, and the charge transport of organic field-effect transistors.

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