Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 5 Articles
In this article, we apply different adaptive transmission techniques to dual-hop multiple-input multiple-output\r\namplify-and-forward relay networks using orthogonal space-time block coding over independent Nakagami-m\r\nfading channels. The adaptive techniques investigated are optimal simultaneous power and rate (OSPR), optimal\r\nrate with constant power (ORCP), and truncated channel inversion with fixed rate (TCIFR). The expressions for the\r\nchannel capacity of OSPR, ORCP, and TCIFR, and the outage probability of OSPR, and TCIFR are derived based on\r\nthe characteristic function of the reciprocal of the instantaneous signal-to-noise ratio (SNR) at the destination. For\r\nsufficiently high SNR, the channel capacity of ORCP asymptotically converges to OSPR while OSPR and ORCP\r\nachieve higher channel capacity compared to TCIFR. Although TCIFR suffers from an increase in the outage\r\nprobability relative to OSPR, it provides the lowest implementation complexity among the considered schemes.\r\nAlong with analytical results, we further adopt Monte Carlo simulations to validate the theoretical analysis....
In this paper, an adaptive resource management scheme for hybrid WWAN/WLAN is proposed. Based on proposed\r\njoint velocity and average received power (ARP) estimation algorithms, a novel vertical handoff (VHO) for efficient\r\nload balancing in multitier network is developed. Simulation results show that proposed scheme achieves\r\nsignificant improvements over conventional schemes...
We consider a carrier sense multiple access(CSMA) in an unslotted cognitive radio network under a mixed\r\nspectrum environment of licensed channels and unlicensed channels. In this system, primary users use only\r\nlicensed channels, while secondary users use unlicensed channels and opportunistically can use licensed channels\r\nunused by primary users temporally. If an arriving secondary user(SU) does not find any idle channels, then the SU\r\neither enters the retrial group with probability q for later retrial or gives up its service and leaves the system with\r\nprobability 1 - q. SUs in the retrial group retry independently after exponentially distributed random time. We\r\nanalyze the system by continuous time Markov chain(CTMC) with level dependent QBD structure and obtain the\r\nsteady state probability of the system by matrix analytic method. In numerical results, we compare the\r\nperformance of two systems with retrial(q > 0) and without retrial(q = 0). It is shown that the retrial phenomenon\r\nof SUs has an impact on the performance of SUs in cognitive radio networks....
Vehicular delay-tolerant network (VDTN) is a network architecture based on the delay-tolerant network paradigm,\r\nwhich was designed to provide low-cost asynchronous vehicular communications in environments with\r\ndisruptions, intermittency, variable delays, and network partition. This article proposes a laboratory testbed for\r\nVDTNs, called VDTN@Lab. It aims to support research studies related with the design, emulation, performance\r\nevaluation, and diagnose of new VDTN protocols, services, and applications. It intends to demonstrate the\r\napplicability of VDTNs over multiple application environments. VDTN@Lab features an emulation capability,\r\nallowing live experiments with prototyped hardware and software embedded into robotic cards, desktop, and\r\nnetbooks computers. The proposed prototype is demonstrated and evaluated with Epidemic, and Spray, and Wait\r\nrouting protocols, using different combinations of scheduling and dropping policies, in scenarios with different\r\nvehicular mobility models (bus movement and random movement across roads)....
Received signal strength (RSS) can be used in sensor networks as a ranging measurement for positioning and\r\nlocalization applications. This contribution studies the realistic situation where neither the emitted power nor the\r\npower law decay exponent be assumed to be known. The application in mind is a rapidly deployed network\r\nconsisting of a number of sensor nodes with low-bandwidth communication, each node measuring RSS of signals\r\ntraveled through air (microphones) and ground (geophones). The first contribution concerns validation of a model\r\nin logarithmic scale, that is, linear in the unknown nuisance parameters (emitted power and power loss constant).\r\nThe parameter variation is studied over time and space. The second contribution is a localization algorithm based\r\non this model, where the separable least squares principle is applied to the non-linear least squares (NLS) cost\r\nfunction, after which a cost function of only the unknown position is obtained. Results from field trials are\r\npresented to illustrate the method, together with fundamental performance bounds. The ambition is to pave the\r\nway for sensor configuration design and more thorough performance evaluations as well as filtering and target\r\ntracking aspects....
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