Abhinav Kumar

Energy and Throughput Trade-Offs in Cellular Networks Using Base Station Switching

Base station operation consumes a lot of energy, a considerable amount of which can be saved by switching off base stations during low user demand (for example, at night). Base station switching (BSS) can result in loss in coverage if not performed properly. We show that coverage is closely related to scheduling via power management and that the bottleneck is typically the uplink. To save energy, we propose a set of BSS patterns, at a global system-level, that have the potential to provide full coverage if the appropriate schedulers are used. We further show that the existing benchmark uplink scheduling schemes do not provide full coverage when BSS is used in urban as well as rural macro-cell environments (the downlink benchmark scheduling scheme provides full coverage only for some of the BSS patterns). Hence, we propose novel scheduling schemes for both uplink and downlink that realistically model interference, ensure full coverage, and provide good energy-performance trade-offs for the proposed BSS patterns. We also present a low complexity high performance heuristic for the proposed uplink scheduler. Finally, we show the presented models and results can be used to quantify, offline, the energy-performance trade-offs under different operating scenarios.

Base station switching with CoMP in cellular networks

Base station switching (BSS) during low traffic load can ensure significant reduction in energy consumption of a cellular network. However, it has been shown that BSS can result in loss of coverage, specially in the uplink. Hence, in this paper, we consider coordinated multipoint (CoMP) transmission and reception to compensate for the loss in coverage due to BSS. We formulate the BSS with CoMP as an optimization problem. We numerically compute the optimization problem and present simulation results that show significant improvement in uplink coverage for BSS with CoMP. The improved coverage ensures more base stations can be switched off in BSS with CoMP in comparison to BSS without CoMP. Further, with suitable scheduling schemes, we show that BSS with CoMP does not result in significant loss in overall network throughput performance. Hence, BSS with CoMP can ensure in more energy savings without compromising on the network throughput performance.

Duopoly price competition of WLAN service providers in presence of heterogeneous user demand

In the presence of several wireless local area network (WLAN) service providers, the users have to make a choice. The price charged and the congestion experienced by the users play an important role in making this choice. In this paper, we analyze the duopoly price competition between two WLAN service providers in the presence of four types of users. We prove that the distribution of heterogeneous user demand is governed by the Wardrop equilibrium. We also show the existence of the Nash equilibrium between competing WLAN service providers. It is further shown through analysis that the social welfare in Nash equilibrium is close to its maximal value. We find that compared to a strictly regulated monopoly, an unregulated WLAN duopoly market results in significant transfer of the surplus from service providers to users with negligible losses in efficiency.

Security Analysis of LTE/SAE Networks Under De-synchronization Attack for Hyper-Erlang Distributed Residence Time

In this letter, we analyze the security of a long term evolution/system architecture evolution-based network in the presence of de-synchronization attack. For a random mobile user, with the mobility management entity residence time distributed as a Hyper-Erlang random variable, we derive closed form expressions for the distribution of key exposure time, expected volume of exposed packets, and expected additional signaling overhead rate. Furthermore, we present a novel framework for a cellular operator to select the trade-off between security and computational complexity for various practical scenarios. Finally, we verify the proposed results through extensive simulations.

Energy efficient rate coverage with base station switching and load sharing in cellular networks

During low user demand, significant energy can be saved in a cellular network by using base station switching (BSS). However, coverage restrictions limit the number of base stations (BSs) a cellular operator can turn off. In this work, we examine the scenario when multiple cellular operators cooperate by sharing the load of their users with BSS (for example, on weekends). We show that significantly more energy can be saved by performing BSS with load sharing between the cellular operators. We formulate this cooperative BSS as an optimization problem. Further, for suitable service level agreements between the cellular operators, we show that the proposed optimization problem is real time solvable. Finally, we present results that quantify the achievable gains obtained by BSS with cooperation among the cellular operators. We also present the rate and coverage trade-off results which can be used by the cooperative cellular operators to find suitable points of operation.

Key exchange protocols for secure Device-to-Device (D2D) communication in 5G

In this paper, we consider network assisted device-to-device (D2D) communication between two user equipments (UEs) in a cellular network. For the scenario, when both the UEs are in network coverage, we propose novel key exchange protocols for D2D communication. The proposed protocols are based on the standard Diffie-Hellman (DH) based key exchange and other cryptographic functions. We present detailed threat analysis for the proposed protocols and show their resilience against man-in-the-middle attack. Further, through numerical results, we show that the proposed protocols have low computational time and low communication overhead in comparison with existing key exchange protocols for D2D communication. The proposed protocols are practically implementable and highly suitable for D2D communications in 5G cellular networks.

Fuzzy Logic Based Cell Selection Framework for Downlink Uplink Decoupled Cellular Networks

Deployment of small cell base stations (BSs), like pico BSs (PBSs), alongside macro BSs (MBSs) in cellular network leads to increased data rates for the users. However, asymmetric transmission power of BSs and received power based user association (UA) necessitates some form of user offloading between MBSs and PBSs on both the downlink and uplink to maximize system performance. In this work, we formulate optimal downlink and uplink decoupled UA as an optimization problem. We show that this network wide optimization problem is not real time solvable. Hence, we propose a novel fuzzy logic based cell selection framework that can be tuned for system level performance gains. Further, we show that in certain scenarios, careful tuning of fuzzy logic system based UA results in significant increase in system performance compared with existing techniques.

Poster: Feasibility of Desynchronization Attack in LTE/SAE Networks

The long term evolution/system architecture evolution (LTE/SAE) networks have been shown vulnerable to desynchronization attack. In this attack, the adversary compromises a legitimate evolved NodeB and gains access to the encryption keys. The essential feasibility conditions have not been considered in the existing work. Hence, in this paper, we propose the conditions essential for the occurrence of DA. Through numerical results, we evaluate the feasibility of DA for various network scenarios.

Poster: Uplink and Downlink Resource Allocation for Energy Efficient Cellular Networks with Dual Connectivity

In heterogeneous cellular networks (HCNs), dual connectivity (DC) has been introduced to increase throughput of the system. Base station sleeping (BSS) techniques has been proposed to reduce the power consumption of the under-utilized base stations (BSs). In this paper, given a partially shared deployment (PSD) of subchannels between macro BS (MBS) and the small cell base stations (SCBSs), the DC uplink (UL) resource allocation problem is formulated. Given such PSD system, the optimum number of subchannels that can be allocated for SCBSs for a DC user in UL are computed. The computation of MBS and SCBSs thresholds for selection of DC user in downlink is also presented. Further, a framework to select the operating point based on energy, throughput, user density, and SCBSs density is presented.

Improved magnetization and reduced leakage current in Sm and Sc co-substituted BiFeO3

BiFeO3 (BFO) and Bi0.85Sm0.15Fe0.90Sc0.10O3 (BSFSO) ceramics were synthesized by conventional solid state route. X-ray diffraction measurements revealed that an orthorhombic Pnma structure evolved with a phase fraction of 84% in the rhombohedral R3c structure of BFO upon the substitution of Sm and Sc. The changes in the intensity and the frequency of Raman modes also corroborated the structural transformation in the BSFSO compound. A decrease in grain size, reduction in porosity, and improved density were observed in the BSFSO compound. An enhanced remanent magnetization of 0.2 emu/g and coercive field of 6.2 kOe were observed, which were attributed to the structural change as well as the destruction of the spin structure with the substitution. Impedance and leakage current measurements revealed that the insulating character of BFO was improved with the substitution of Sm and Sc in BFO and was explained based on the bond enthalpy concept. The enhanced magnetic properties along with the improved insulating character of BSFSO compound will be suitable for device applications.BiFeO3 (BFO) and Bi0.85Sm0.15Fe0.90Sc0.10O3 (BSFSO) ceramics were synthesized by conventional solid state route. X-ray diffraction measurements revealed that an orthorhombic Pnma structure evolved with a phase fraction of 84% in the rhombohedral R3c structure of BFO upon the substitution of Sm and Sc. The changes in the intensity and the frequency of Raman modes also corroborated the structural transformation in the BSFSO compound. A decrease in grain size, reduction in porosity, and improved density were observed in the BSFSO compound. An enhanced remanent magnetization of 0.2 emu/g and coercive field of 6.2 kOe were observed, which were attributed to the structural change as well as the destruction of the spin structure with the substitution. Impedance and leakage current measurements revealed that the insulating character of BFO was improved with the substitution of Sm and Sc in BFO and was explained based on the bond enthalpy concept. The enhanced magnetic properties along with the improved insulating...