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Passive bistatic radars (PBR) are receiver-only radar systems which utilize available communication signals from the environment for surveillance and tracking applications. An approach to improve the range resolution is to resort to a passive multistatic radar systems where range (and/or Doppler) information from multiple bistatic transmit-receive pairs are fused. However, localization process for multiple targets usually faces ghost-targets problem due to the large number of target-to-measurements associations possibilities. In this paper, we explore the performance of few reported multistatic localization methods in conjunction with a closed-form deghosting technique. Specifically, a novel data-association approach was implemented in a multistatic data fusion set-up to assess the effectiveness for localization and deghosting performance for multiple targets.

Efficient spectrum utilization lies at the heart of next generation (xG) wireless communication networks. In this context, a thorough investigation into new and innovative spectrum management techniques as well as additional regulatory procedures are deemed necessary to evaluate the practical feasibility of these xG networks. This paper reviews the three possible modes for multi-operator spectrum sharing based on dynamic spectrum access (DSA) in 5th Generation (5G) networks, and identifies Licensed/Authorized Shared Access (LSA/ASA) mode to be practically most suitable candidate for better spectrum utilization. Existing spectrum sharing techniques exploiting time, frequency and space domain to realize efficient co-existence of multiple operators are discussed, and game theory (GT) framework has been recognized as an appropriate tool to model the interactions among multiple operators accessing the shared spectrum resources. In particular, the hybrid cooperativecompetitive game has been proposed as a promising model to incorporate key parameters that play a significant role in the practical Deployment of DSA-enabled xG networks.

Spectrum scarcity is impeding practical implementations of emerging wireless multimedia applications requiring significantly more frequency spectrum. Cognitive radio (CR) has emerged as a promising solution to the current spectral congestion problem by imparting intelligence to the conventional software defined radio that allows spectrum sharing through opportunistic spectrum access. The principal objective of CR is to optimize the use of under-utilized spectrum through robust and efficient spectrum sensing (SS). This paper introduces cognitive functionality and provides an in-depth comparative survey of various spectrum awareness techniques in terms of their sensing accuracy and computational complexities along with their merits and demerits. Specifically, key challenges in SS are highlighted and possible solutions are discussed. A classification of SS is presented to address the sensing method selection criterion. Both non-cooperative and cooperative sensing schemes are reviewed and open research problems are highlighted to identify future research directions.

Cognitive radio based on dynamic spectrum access has emerged as a promising technology to meet the insatiable demand for radio spectrum by the emerging wireless applications. In this chapter, the authors address the problem of throughput-efficient spectrum access in Cognitive Radio Networks (CRNs) using Coalitional Game-theoretic framework. They model the problem of joint Coalition Formation (CF) and Bandwidth (BW) allocation as a CF game in partition form with non-transferable utility and present a variety of algorithms to dynamically share the available spectrum resources among competing Secondary Users (SUs). First, the authors present a centralized solution to reach a sum-rate maximizing Nash-stable network partition. Next, a distributed CF algorithm is developed through which SUs may join/leave a coalition based on their individual preferences. Performance analysis shows that the CF algorithms with optimal BW allocation provides a substantial gain in the network throughput over existing coalition formation techniques as well as the simple cases of singleton and grand coalition.

In this paper we consider the problem of joint coalition formation and bandwidth allocation in cognitive radio networks. We assume that the secondary links will be partitioned into disjoint coalitions, by which the available spectrum will be reused. On the other hand, we assume that the members of each coalition will transmit over orthogonal sub-bands with the available spectrum being optimally allocated among them. We formulate the problem as a coordinated coalition formation game where the optimization is held at a secondary coordinator (SC) that has all the required channel information. Given these assumptions, we use a closed form expression of the optimal bandwidth allocation for any given network partition, and we propose an algorithm to reach a Nash-stable partition (coalition structure), with the objective of maximizing the network through-put. Performance analysis shows that the proposed coalition formation algorithm with optimal bandwidth allocation provides a substantial gain in the network throughput over existing coalition formation techniques as well as the simple cases of singleton and grand coalition.

Existing wireless networks are unable to fulfill the insatiable demand of radio spectrum by emerging wireless services and applications. To address the current spectrum scarcity problem, next generation wireless networks are required to be comprising of intelligent and reconfigurable radios (popularly known as Cognitive Radios (CRs)) that can interact with their continuously changing environment to capture real time spectrum awareness and avail any spectrum usage opportunity. Dynamic and opportunistic spectrum access is identified as an enabling technology for Cognitive Radio Oriented Wireless Network (CROWN) wherein low-priority secondary users (CRs) are allowed to communicate over licensed frequency bands when the legacy users of that spectrum are not fully utilizing it. As most of the spectrum is already allocated to primary users with exclusive legacy rights of the frequency bands, the key challenge for CROWN is to reuse/share licensed spectrum without interfering with primary transmissions. This paper highlights fundamental challenges in getting multi-dimensional spectrum awareness under practical constraints and provides viable solutions. Furthermore, limitations of both transmitter detection based non-cooperative spectrum sensing techniques and cooperative sensing strategies are discussed, open research challenges are investigated and possible solutions are presented.

Cognitive radio (CR) has emerged as a smart solution to spectrum bottleneck faced by current wireless services, under which licensed spectrum is made available to intelligent and reconfigurable secondary users. CR technology enables these unlicensed secondary users to exploit any spectrum usage opportunity by adapting their transmission parameters on the run. In this chapter, the authors discuss the characteristic features and main functionality of CR oriented technology. Central to this chapter is Spectrum sensing (SS), which has been identified as a fundamental enabling technology for next generation wireless networks based on CR. The authors compare different SS techniques in terms of their sensing accuracy and implementation and computational complexities along with merits and demerits of these approaches. Various challenges facing SS have been investigated, and possible solutions are proposed.

Purpose: Tamoxifen remains an important hormonal therapy for ER-positive breast cancer; however, development of resistance is a major obstacle in clinics. Here, we aimed to identify novel mechanisms of tamoxifen resistance and provide actionable drug targets overcoming resistance. Experimental Design: Whole-transcriptome sequencing, downstream pathway analysis, and drug repositioning approaches were used to identify novel modulators [here: phosphodiesterase 4D (PDE4D)] of tamoxifen resistance. Clinical data involving tamoxifen-treated patients with ER-positive breast cancer were used to assess the impact of PDE4D in tamoxifen resistance. Tamoxifen sensitization role of PDE4D was tested in vitro and in vivo. Cytobiology, biochemistry, and functional genomics tools were used to elucidate the mechanisms of PDE4D-mediated tamoxifen resistance. Results: PDE4D, which hydrolyzes cyclic AMP (cAMP), was significantly overexpressed in both MCF-7 and T47D tamoxifen-resistant (TamR) cells. Higher PDE4D expression predicted worse survival in tamoxifen-treated patients with breast cancer (n = 469, P = 0.0036 for DMFS; n = 561, P = 0.0229 for RFS) and remained an independent prognostic factor for RFS in multivariate analysis (n = 132, P = 0.049). Inhibition of PDE4D by either siRNAs or pharmacologic inhibitors (dipyridamole and Gebr-7b) restored tamoxifen sensitivity. Sensitization to tamoxifen is achieved via cAMP-mediated induction of unfolded protein response/ER stress pathway leading to activation of p38/JNK signaling and apoptosis. Remarkably, acetylsalicylic acid (aspirin) was predicted to be a tamoxifen sensitizer using a drug repositioning approach and was shown to reverse resistance by targeting PDE4D/cAMP/ER stress axis. Finally, combining PDE4D inhibitors and tamoxifen suppressed tumor growth better than individual groups in vivo. Conclusions: PDE4D plays a pivotal role in acquired tamoxifen resistance via blocking cAMP/ER stress/p38-JNK signaling and apoptosis. Clin Cancer Res; 24(8); 1987–2001. ©2018 AACR.