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As the world becomes increasingly dependent on dynamic and up-to-the-moment information, we recognize that broadband networks must be able to convey this information timely and wirelessly, to and from users in motion. Varieties of 802.11 compliant equipment and other types of broadband wireless equipment have been proposed for, and in some areas, being used to meet this need. There have been questions...
For the uplink transmission of an orthogonal frequency division multiple access (OFDMA) system, frequency synchronization is particularly challenging due to the presence of multiple Carrier Frequency Offsets (CFOs), which destroy the orthogonality among subcarriers and introduce massive multiuser interference (MUI) and inter-carrier interference (ICI). To prevent the consequent performance degradation,...
We introduce complete analytical characterization of the nonlinear interference that results when passing more than one high-order modulation carrier through the same nonlinear transponder HPA. Based on this analysis, a novel Volterra filter is proposed that models nonlinear intersymbol interference (ISI) and adjacent channel interference (ACI). Our focus is on adaptive algorithms so that the solutions...
A key enabling functionality in implementing Cognitive Radio is to reliably detect the licensed users. In recent literature, cooperation among spectrum sensing terminals is suggested to offer reliable sensing performance. We consider the problem that the presence of malfunctioning or malicious sensing terminals will severely degrade the performance of cooperative spectrum sensing. In this paper, we...
Mobile ad-hoc networks, such as tactical networks, are frequently implemented using multiple subnets, or tiers, so that nodes in one tier can communicate to nodes in another tier only through gateways that can communicate in two of the tiers. The selection of the gateway nodes affects the robustness and performance of the connected subnets. This paper presents an algorithm for selecting gateways in...
This paper describes the complex behavior of receive phased array antennas with high level incident signals with respect to generation and suppression of intermodulation and harmonic products. The resulting complex spatial dependencies are described and demonstrated with a Matlab??-based nonlinear phased array antenna analysis tool whose results are compared to phased array antenna measurements.
Several concepts for more dynamic spectrum access have been suggested: 1. terminals making autonomous decisions without coordination 2. Networks cooperating in peer-to-peer (P2P) constellations without an infrastructure 3. Centralized spectrum server concepts which makes local decisions and coordinate through a broker hierarchy. In this paper we compare these three types of concepts in terms of spectrum...
The Link-16 is the tactical data link utilized by the Joint Tactical Information Distribution System (JTIDS). The JTIDS system is important due to its wide use by U.S. armed forces, NATO, and other allied militaries. Link-16 is a hybrid frequency-hopped/direct sequence spread spectrum system that utilizes minimum-shift keying (MSK) to modulate the chips, cyclical code-shift keying (CCSK) to modulate...
Iterative signal processing has gained in popularity over the last decade as a way of reducing the effects of interference in a communication system. In previous work, the expectation maximization (EM) algorithm was used to estimate the parameters and data of colliding transmissions in a slow frequency-hopping spread-spectrum (FHSS) system using binary frequency-shift keying (BFSK). As in many FHSS...
In this paper, we propose orthogonal frequency division duplex (OFDD) which combines orthogonal division duplex (ODD) and frequency division duplex (FDD) as a new hybrid division duplex scheme. In the asymmetric traffic environment, the mismatch of uplink and downlink between adjacent cells results in co-channel interference (CCI) which degrades the system performance. The proposed scheme can remove...
Multicarrier (MC) CDMA systems have been developed and rapidly gained popularity as they capitalize on both MCM (multicarrier modulation)'s resilience to multi-path fading and direct-sequence (DS) CDMA's simplicity in multi-access and synchronization design to mitigate both multiple access interference (MAI) and the inter-symbol interference (ISI) caused by time dispersive channels with the aid of...
In this paper, we provide a feasibility analysis of non-contiguous orthogonal frequency division multiplexing (NC-OFDM) transceivers based on different operating configurations. The selection of these configurations conform to the constraints defined by the spectral masks of the Federal Communications Commission's (FCC), such as out-of-band radiation. Actual spectrum measurement data collected from...
In this paper, sensing algorithms to select the available sub-bands in the cognitive UWB system are proposed; grouped time division sensing technique and decision methods for sub-channel selection. We employ energy detection method for spectrum sensing, which has low complexity in the wide spectrum sensing. Grouped time division sensing technique is proposed to transmit training symbols and to measure...
In recent years there was much attention about connected dominating set as a backbone for wireless networks. The aim is changing much nodes' state to inactive as possible and keep smallest number of nodes active and leave communication duty of inactive group to active group. In previous algorithms for attaining this goal, nodes with greater degree were kept active and trees were grown over nodes with...
As the wireless access technology evovles to wider and wider bandwidth, orthogonal frequency division multiplex (OFDM) becomes the fundamental technology component to provide efficient data transmission. However, compared to code division multiplex access (CDMA), OFDM has no capability to mitigate the intercell interference though it can provide orthogonality among the intracell users. To build a...
Conflict-free power allocation for secondary user (SU) in cognitive networks is a challenging problem since the accessible spectrum of the SU is shared with the primary user (PU); the problem becomes to be especially difficult when it is wanted to achieve the maximum network capacity considering the mutual interference between PU and SU. In this paper, specifying the single SU case with multiple PUs,...
This paper discusses the interaction of technology and policy in enabling widespread rural access to clean solar electric power using retail delivery of beamed power. Recent advances in power beaming have made it possible to deliver electric power to off-grid locations using millimeter-wave beams and compact, efficient transmitters and receivers. The research question is how to bring about the public...
This paper reports on visual position measurement based on space-frequency analysis of a pseudo-periodic pattern. This approach can be seen as a two-dimensional extension of the Vernier principle as used in the Vernier caliper. The pseudoperiodic pattern fixed on the target is seen as a secondary scale that is compared to the reference scale formed by the image pixel frame. By performing space-frequency...
As a theoretical concept, and a means to understand the potential of interference alignment, in this paper we investigate possibilities to place n transmitter-receiver pairs in n - 1 dimensions such that the interference from unintended transmissions is aligned at each receiving node. By such an arrangement each link has half of the capacity available, at least in theory. Regular patterns of stations...
In this paper, an algorithm reprocessing of the power spectrum density (RPSD) is proposed to detect and estimate the PN code's period of the multipath direct sequence spread spectrum (DS/SS) signal in low SNR, which develops the previous processing method based on the single path environment. It can solve the difficult problem of PN code's period detection and estimation in multipath environment....
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