Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 5 Articles
The implementation of efficient baseband receivers characterized by affordable computational load is a crucial point in the\r\ndevelopment of transmission systems exploiting diversity in different domains. This would be a crucial point in the future\r\ndevelopment of 4G systems, where space, time, and frequency diversity will be combined together in order to increase system\r\nthroughput. In this framework, a linear multiuser detector for MC-CDMA systems with Alamouti�s Space-Time Block Coding\r\n(STBC), which is inspired by the concept of MinimumConditional Bit Error Rate (MCBER), is proposed. The MCBER combiner\r\nhas been implemented in adaptive way by using Least-Mean-Square (LMS) optimization. The estimation of Channel State\r\nInformation (CSI), necessary to make practically feasible the MCBER detection, is aided by a Genetic Algorithm (GA). The\r\nobtained receiver scheme is near-optimal, as both LMS-based MCBER and GA-assisted channel estimation perform closely to\r\noptimum in fulfilling their respective tasks. Simulation results evidenced that the proposed receiver always outperforms state-ofthe-\r\nart receiver schemes based on EGC andMMSE criterion exploiting the same degree of channel knowledge....
In side channel analysis, an attacker utilizes some legitimate function queries in order to collect the corresponding responses of a cryptographic system while it is functioning in a normal mode. If those responses reveal some unwanted information about the secrecy or privacy, this leakage is called side channel information and these responses are called side channels. In this respect, careless deployments of ââ?¬Å?secureââ?¬Â RFID authentication protocols are not exceptions and subject to side channel attacks. Focusing on lightweight RFID security protocols; we examine the server responses for several RFID tags and realize that if the database querying is performed through a static process, the RFID system is subject to timing attacks that could easily jeopardize the system's untraceability criteria. We demonstrate our attack on some well-known protocols and outline a countermeasure by precisely describing the database query mechanism. Furthermore, we analyze the success probability of the attack in terms of the system parameters such as the number of tags, number of cryptographic operations that have to be carried out, and server's computational power....
With the advances of wireless communication technologies, wireless networks gradually become the most adopted communication networks in the new generation Internet. Computing devices and mobile devices may be equipped with multiple wired and/or wireless network interfaces. Stream Control Transmission Protocol (SCTP) has been proposed for reliable data transport and its multihoming feature makes use of network interfaces effectively to improve performance and reliability. However, like TCP, SCTP suffers unnecessary performance degradation over wired-wireless heterogeneous networks. The main reason is that the original congestion control scheme of SCTP cannot differentiate loss events so that SCTP reduces the congestion window inappropriately. In order to solve this problem and improve performance, we propose a jitter-based congestion control scheme with end-to-end semantics over wired-wireless networks. Besides, we solved ineffective jitter ratio problem which may cause original jitter-based congestion control scheme to misjudge congestion loss as wireless loss. Available bandwidth estimation scheme will be integrated into our congestion control mechanism to make the bottleneck more stabilized. Simulation experiments reveal that our scheme (JSCTP) gives prominence to improve performance effectively over wired-wireless networks....
A relatively recent idea of extending the benefits of MIMO systems to multiuser scenarios seems promising in the context of achieving high data rates envisioned for future cellular standards after 3G (3rd Generation). Although substantial research has been done on the theoretical front, recent focus is on making Multiuser Multiple-Input Multiple-Output (MUMIMO) practically realizable. This paper presents an overview of the different MU-MIMO schemes included/being studied in 3GPP standardization from LTE (long-term evolution) to LTE Advanced. MU-MIMO system concepts and implementation aspects have been studied here. Various low-complexity receiver architectures are investigated, and their performance assessed through link-level simulations. Appealing performance offered by low-complexity interference aware (IA) receivers is notably emphasized. Furthermore, system level simulations for LTE Release 8 are provided. Interestingly, it is shown that MU-MIMO only offers marginal performance gains with respect to single-user MIMO. This arises from the limited MU-MIMO features included in Release 8 and calls for improved schemes for the upcoming releases....
An adaptive symbol mapping scheme is proposed for single-user point-to-point and multiuser downlink multiple-input multiple output (MIMO) systems aiming at the minimization of the overall system bit error rate. The proposed scheme introduces a disorder to the symbols to be transmitted within a MIMO subframe by means of dynamic mapping, with the objective to optimise the interference between them and enhance the received symbols' power. This is done by either changing the allocation order of the symbols to the antennas or by applying a scrambling process that alters the symbols sign. This procedure is targeted to optimizing, rather than strictly minimizing the interference between the symbols such that constructive instantaneous interference is utilized in enhancing the decision variables at the receiver on a symbol-by-symbol basis so that detection is made more reliable. In this way, the overall system performance is improved without the need to raise the transmitted power. The proposed scheme can be used in conjunction with various conventional MIMO precoding and detection techniques. The presented results show that for a given transmit power budget this scheme provides significant benefits to the corresponding conventional system's error rate performance....
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