Cooperative communication is a powerful technology combating fading in wireless medium. In contrast to conventional cooperation (CC) which allows the relay to simply process and forward what it has heard, network-coded cooperation (NCC) endows network coding capability with the relay, i.e., allows the relay to first encode the data it has received from different sources and then forward the network-coded data to corresponding destinations. In this paper we systematically investigate the performance of NCC in terms of diversitymultiplexing tradeoff as well as exact system outage behavior. Under the assumption (denoted as A) that each destination can reliably overhear the data from other sources, we prove the diversity-multiplexing tradeoff of NCC outperforms that of CC. Moreover, we derive the close form of the system outage probability of NCC as a function of signal-to-noise ratio (SNR). The analytical and numerical results show that by requiring less bandwidth cost, NCC offers a similar or even reduced system outage probability compared with CC, and achieves the same full diversity order as CC at high SNR. Finally we discuss the performance of NCC in case the assumption A is removed. For a wireless network composed of N s-d pairs and a single relay, although there is a certain system outage probability increase for NCC, it still provides the same full diversity order of 2 as CC at high SNR, and has a diversity-multiplexing tradeoff superior to CC.

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Recently, Li proposed a new password authentication and user anonymity scheme based on elliptic curve cryptography. In this paper, we will show that Li's scheme is vulnerable to the impersonation attack and the denial of service attack. Moreover, we also point out that there is an error in his scheme. To overcome the weaknesses of Li's scheme, we proposed an efficient password authentication scheme based on elliptic curve cryptography. The proposed scheme improves the security and efficiency of the authentication process.

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As one of the essential applications of Health Information Technology (HIT), the eHealth system plays a significant role in enabling various internet medicine service scenes, most of which primarily rely on service recommendation or evaluation mechanism. To avoid privacy leakage, some privacy-preserving mechanisms must be adopted to protect raters' privacy and make evaluation trust reliable. To tackle this challenge, this paper proposes an efficient service recommendation and evaluation scheme, called EPRT, which is based on similarity calculation and trust discovery method. This scheme uses homomorphic encryption technology to encrypt the sensitive data and combines the threshold mechanism and double-trap mechanism to realize the security processing on the encrypted data, so as to ensure that the plaintexts of the final calculation results (e.g. recommendation value and evaluation truth) are only obtained by the authorized subject. Also, a detailed security analysis is conducted to show that the proposed EPRT scheme can achieve the expected security. In addition, a set of performance comparison results are carried out, demonstrating its effectiveness and accuracy.