Current Issue : January - March Volume : 2013 Issue Number : 1 Articles : 5 Articles
Multipacket reception (MPR) is the capability of simultaneous decoding of more than one packet from multiple concurrent\r\ntransmissions. Continuous investigations on increasing the reception capability are giving new scientific contributions. In this\r\npaper, we provide an overview of MPR-related research work covering (1) the theoretically proved impacts and advantages of\r\nusing MPR from a channel perspective to network capacity and throughput; (2) the various technologies that enable MPR from\r\ntransmitter, transreceiver, and receiver perspectives; (3) previous work on protocol improvement to better exploit MPR. Indeed,\r\nMPR approaches have been applied in modern wireless mobile systems but the focus of this paper is to discuss MPR in random\r\naccess wireless networks. Using MPR in suchmultihop environments calls for new adaptation on protocols, especially a cross-layer\r\napproach. To this end, we detail a scheduling method that targets full utilization of MPR capability....
This paper studies the effect of ARQ retransmissions on packet error rate, delay, and jitter at the application layer for a realtime\r\nvideo transmission at 1.03 Mbps over a mobile broadband network. The effect of time-correlated channel errors for various\r\nMobile Station (MS) velocities is evaluated. In the context of mobile WiMAX, the role of the ARQ Retry Timeout parameter and\r\nthe maximum number of ARQ retransmissions is taken into account. ARQ-aware and channel-aware scheduling is assumed in\r\norder to allocate adequate resources according to the level of packet error rate and the number of ARQ retransmissions required.\r\nA novel metric, namely, goodput per frame, is proposed as a measure of transmission efficiency. Results show that to attain quasi\r\nerror free transmission and low jitter (for real-time video QoS), only QPSK 1/2 can be used at mean channel SNR values between\r\n12 dB and 16 dB, while 16QAM 1/2 can be used below 20 dB at walking speeds. However, these modes are shown to result in low\r\ntransmission efficiency, attaining, for example, a total goodput of 3 Mbps at an SNR of 14 dB, for a block lifetime of 90 ms. It is\r\nshown that ARQ retransmissions are more effective at higher MS speeds....
The cognitive radio (CR) concept has appeared as a promising technology to cope with the spectrum scarcity caused by increased\r\nspectrum demand due to the emergence of new applications. CR can be an appropriate mean to establish self-organization and\r\nsituation awareness at the radio interface, which is highly desired to manage unexpected situations that may happen in a disaster\r\nscenario. The scout node proposed in this paper is an extended concept based on a powerful CR node in a heterogeneous nodes\r\nenvironment which takes a leading role for highly flexible, fast, and robust establishment of cooperative wireless links in a disaster\r\nsituation. This node should have two components: one is a passive sensor unit that collects and stores the technical knowledge\r\nabout the electromagnetic environment in a data processing unit so-called ââ?¬Å?radio environment mapââ?¬Â in the form of a dynamically\r\nupdated database, and other is an active transceiver unit which can automatically be configured either as a secondary node for\r\nopportunistic communication or as a cooperative base station or access point for primary network in emergency communications.\r\nScout solution can be viable by taking advantage of the technologies used by existing radio surveillance systems in the context of\r\nCR....
Physical layers of communication systems using Filter Bank Multicarrier (FBMC) as a modulation scheme provide low out-ofband\r\nleakage but suffer from the large Peak-to-Average Power Ratio (PAPR) of the transmitted signal. Two special FBMC schemes\r\nare investigated in this paper: the Orthogonal Frequency Division Multiplexing (OFDM) and the Staggered Multitone (SMT). To\r\nreduce the PAPR of the signal, time domain clipping is applied in both schemes. If the clipping is not compensated, the system\r\nperformance is severely affected. To avoid this degradation, an iterative noise cancelation technique, Bussgang Noise Cancelation\r\n(BNC), is applied in the receiver. It is shown that clipping can be a good means for reducing the PAPR, especially for the SMT\r\nscheme. A novel modified BNC receiver is presented for SMT. It is shown how this technique can be implemented in real-life\r\napplications where special requirements must be met regarding the spectral characteristics of the transmitted signa...
Iterative and incremental mechanisms are not usually considered in existing approaches for information security management\r\nSystem (ISMS). In this paper, we propose SUP (security unified process) as a unified process to implement a successful and highquality\r\nISMS. A disciplined approach can be provided by SUP to assign tasks and responsibilities within an organization. The SUP\r\narchitecture comprises static and dynamic dimensions; the static dimension, or disciplines, includes business modeling, assets,\r\nsecurity policy, implementation, configuration and change management, and project management. The dynamic dimension, or\r\nphases, contains inception, analysis and design, construction, and monitoring. Risk assessment is a major part of the ISMS process.\r\nIn SUP, we present a risk assessment model, which uses a fuzzy expert system to assess risks in organization. Since, the classification\r\nof assets is an important aspect of risk management and ensures that effective protection occurs, a Security Cube is proposed\r\nto identify organization assets as an asset classification model. The proposed model leads us to have an offline system health\r\nmonitoring tool that is really a critical need in any organization....
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