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This paper experimentally investigates the scheme of time reversal (TR) combined with multiple-input single-output (MISO) antennas over ultra-wideband (UWB) channels. In particular, temporal and spatial focusing as well as array gain are studied based on a (4times1) MISO scheme in an office environment. The results confirm that the energy of UWB signals in an MISO scheme is more spatial-temporally...
A CPM modulator can be decomposed into a recursive encoder followed by a memoryless mapper. For modulation indices of the form h=K/P with an odd K, the encoder generates a time-varying phase trellis with 2PML-1 states. For symmetric and analytically tractable premodulation filters, like GMSK, this time-varying trellis can be implemented efficiently in VLSI, allowing for very low storage requirements...
Mobile ad hoc networks suffer from route breakups caused by nodal mobility. In a network that aims to support critical interactive real time data and flows, as well as the uninterrupted transport of a complete file or a critical series of messages, it is essential to identify robust routes that can be used for the un-interrupted transport execution of such transactions. Noting that route failures...
The current Internet protocol (IP) architecture model for mobile ad hoc network (MANET) routing protocol development ignores cross-layer effects by seeking to emulate as closely as possible the wireline architecture. Nevertheless, cross-layer effects are unavoidable and it is actually desirable to exploit these interactions to achieve greater performance. Further, support for cross-layer information...
With ever increasing mobility of the workforce and of the communication infrastructure itself, we will continue to see the growth in diversity of network domains and diversity of applications. The global information grid (GIG) is a prime example of such a networking environment. In most networking scenarios, the component network domains are owned and operated by different organizations. This paper...
This paper provides a perspective and brief analysis of the U.S. Government's Department of Defense precedence and preemption (P&P) technical requirements for precedence-based assured service (PBAS) capabilities in the global information grid (GIG). Precedence is the user's indication of the importance of a message. In voice networks, the PBAS capabilities are implemented using multilevel precedence...
The mobile user objective system (MUOS) is DoD's next generation military UHF SATCOM system. MUOS is an integrated system that includes an advanced satellite constellation as well as all supporting ground radio access and switching facilities to support the worldwide transport of voice and data. For the last thirty years UHF SATCOM has operated over individual 5-kHz and 25-kHz bandwidth transponders,...
This paper proposes an efficient approach of secure clustering in distributed sensor networks. The clusters or groups in the network are formed based on offline rank assignment and predistribution of secret keys. Our approach uses the concept of weakly connected dominating set (WCDS) to reduce the number of cluster-heads in the network. The formation of clusters in the network is secured as the secret...
In a military communications environment, multiple communication links could exist between senders and receivers. This feature enhances communication connection reliability and throughput. Since each link may not use the same type of device or transmission method and links' characteristics may not be the same, sometimes, the link availability and link data rate could fluctuate significantly, which...
This paper presents a novel keystream generator using pseudorandom binary sequences (PRBS) with irregular clocking that is based on the A5/1 stream cipher which is used to secure GSM conversations. An improvement in security is obtained by introducing dynamic polynomial switching in the Linear Feedback Shift Registers (LFSRs) present in the architecture for pseudo noise sequence generation. A basic...
The secure communication interoperability protocol (SCIP) is a newly emerging application layer interoperability standard that is being developed for secure voice and voice band data communication between international coalition partners. It was designed to operate independently of the characteristics of underlying media layers. This paper will present the results of the first phase of an investigation...
This paper evaluates the performance of several alternative reliable unicast transport mechanisms in a hybrid network. Options investigated include end-to-end TCP (different flavors), end-to-end space communications protocol standards-transport protocol (SCPS-TP), and performance enhancing proxies (PEPs) (also called transport layer proxies). Our approach is to analyze these options in a specific...
When directional antennas are used in 802.11 based wireless LANs, higher network capacity is often accompanied with more collisions. This is due to the enhanced hidden node problem and the deafness problem that arise in the directional transmission/reception scenario. These problems are caused by an inconsistent view of the medium status by neighboring nodes. We have developed a new variation to the...
The classical technique for measuring the time-difference of arrival (TDOA) of a signal between two sensors has always been a filtered cross correlation. Recent papers, however, have suggested that cyclostationary correlation methods may achieve a much better TDOA estimate in the presence of strong interference for signals that are not truly stationary-such as digital communications signals. Of these,...
A military ad hoc network has to have a good LPI (low probability of intercept) and LPJ (low probability of jamming) capabilities. These requirements can be met by using a combined frequency hopping/direct sequence (FH/DS) spread spectrum (SS) system. Due to characteristics of an ad hoc network, the network wide synchronization has to be achieved distributely, which makes especially FH-code phase...
Multi-carrier code division multiple access (MC-CDMA) systems are well suited for high data rate wireless multimedia services due to their capability of converting the frequency-selective fading channels to distinct frequency-flat ones with low-complexity fast Fourier transform (FFT) devices. However, in multiuser MC-CDMA systems, the frequency selectivity and variation of the users' geographical...
Multicarrier code-division multiple access (MC-CDMA) system with adaptive frequency hopping (FH) has attracted significant attention in the literature due to its excellent spectral efficiency. A suboptimal water-filling (WF) channel allocation algorithm was previously proposed for the conventional matched filter (MF) detector in the reverse link of this system. However, the performance of the WF algorithm...
This paper discusses the side effects of sanitizing IT security event messages in a cooperative multi-domain intrusion warning system (IWS). To enhance detection capabilities of conventional IT security tools like intrusion detection systems (IDS), virus scanners and packet filters, a centralized, so-called intrusion warning system can be deployed, which collects and analyzes event messages from the...
The spectrum of deployed wireless cellular communication systems is found to be under-utilized, even though licensed spectrum is at a premium. To efficiently utilize the band-width left unused in a cellular system, which we denote as the primary system (PRI), we design a system with an ad hoc/mesh overlay network, which we denote as the secondary system (SEC). The basic design principle is that the...
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