References of "Shankar, Bhavani 50002712"
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See detailRobust Precoding and Beamforming in a Multiple Gateway Multibeam Satellite System
Joroughi, Vahid UL; Shankar, Bhavani UL; Maleki, Sina UL et al

in Robust Precoding and Beamforming in a Multiple Gateway Multibeam Satellite System (2018, December)

This paper aims to design joint precoding and onboard beamforming at a multiple gateway multibeam satellite system. Full frequency reuse pattern is considered among the beams and each gateway serves a ... [more ▼]

This paper aims to design joint precoding and onboard beamforming at a multiple gateway multibeam satellite system. Full frequency reuse pattern is considered among the beams and each gateway serves a cluster of adjacent beams such that multiple clusters are served through a set of gateways. However, two issues are required to be addressed. First, the interference in both user and feeder links is the bottleneck of the whole system and employing interference mitigation techniques is essential. Second, as the data demand increases, the ground and space segments should employ extensive bandwidth resources in the feeder link accordingly. This entails embedding an extra number of gateways aiming to support a fair balance between the increasing demand and the corresponding required feeder link resources. To tackle these problems, this paper studies the impact of employing a joint multiple gateway architecture and on-board beamforming scheme. It is shown that by properly designing the on-board beamforming scheme, the number of gateways can be kept affordable even if the data demand increases. The proposed beamforming scheme can partially mitigate the interference in the user link. While the user and feeder link channels vary over time, this paper focuses on designing fixed beamforming which is sufficiently robust to the variations in both channels, leading to keep payload complexity low. Moreover, Zero Forcing precoding technique is employed at the gateways to reject the interference in the feeder links as well as it helps the proposed fixed on-board beamforming by partially equalizing the interference in user link. [less ▲]

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See detailA Statistically Efficient Estimator for Co-array Based DoA Estimation
Sedighi, Saeid UL; Shankar, Bhavani UL; Ottersten, Björn UL

Poster (2018, October)

Co-array-based Direction of Arrival (DoA) estimation using Sparse linear arrays (SLAs) has recently gained considerable interest in array processing due to the attractive capability of providing enhanced ... [more ▼]

Co-array-based Direction of Arrival (DoA) estimation using Sparse linear arrays (SLAs) has recently gained considerable interest in array processing due to the attractive capability of providing enhanced degrees of freedom. Although a variety of estimators have been suggested in the literature for co-array-based DoA estimation, none of them are statistically efficient. This work introduces a novel Weighted Least Squares (WLS) estimator for the co-array-based DoA estimation employing the covariance fitting method. Then, an optimal weighting is given so that the asymptotic performance of the proposed WLS estimator coincides with the Cram\'{e}r-Rao Bound (CRB), thereby ensuring statistical efficiency of resulting WLS estimator. This implies that the proposed WLS estimator has significantly better performance compared to existing methods in the literature. Numerical simulations are provided to corroborate the asymptotic statistical efficiency and the improved performance of the proposed estimator. [less ▲]

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See detailEnhancing mobile services with DVB-S2X superframing
Mazzali, Nicolò UL; Boumard, Sandrine; Kinnunen, Jouko et al

in International Journal of Satellite Communications and Networking (2018)

DVB-S2X is the cornerstone for satellite communication standards forming the state of the art of broadband satellite waveforms. In this paper, we propose new application scenarios and advanced techniques ... [more ▼]

DVB-S2X is the cornerstone for satellite communication standards forming the state of the art of broadband satellite waveforms. In this paper, we propose new application scenarios and advanced techniques, including a reference design implementing superframing, predistortion, a robust synchronization chain, and a plug-and-play channel interleaver. We demonstrate by means of software simulations and hardware tests that the DVB-S2X can be a common technology enabler for land-mobile, aeronautical, and maritime satellite scenarios in addition to the more traditional VSAT scenario, even in very challenging conditions (eg, very low signal-to-noise ratio). [less ▲]

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See detailInterference Localization On-Board the Satellite Using Drift Induced Virtual Array
Arora, Aakash UL; Maleki, Sina; Shankar, Bhavani UL et al

in Proc. 2018 International Conference on Signal Processing and Communications (SPCOM) (2018, July)

Herein, we investigate the interference received from other wireless networks into a satellite communication (SATCOM) link, and review approaches to identify the interference location using on-board ... [more ▼]

Herein, we investigate the interference received from other wireless networks into a satellite communication (SATCOM) link, and review approaches to identify the interference location using on-board satellite processing. Interference is an increasing problem for satellite communication links, and while receiving signals from gateways or user terminals, the uplink is prone to disturbance by interference due to jammers or unintentional transmissions. In this paper, our aim is to localize unknown interference sources present on the ground by estimating direction of arrival (DOA) information using onboard processing (OBP) in the satellite, and the satellite drift inducing a virtual array. In this work, the signal sampled by the drifting single antenna feed is modeled as using an arbitrary array. Building on this model, we perform the 2-D DOA (azimuth and elevation) estimation. The key challenges in such a design include single snapshot based DOA estimation with low complexity and robustness, arising out of limited on-board computational complexity as well as uncertainty in parameters like the drift speed. Employing realistic satellite drift patterns, the paper illustrates the performance of the proposed technique highlighting the accuracy in localization under adverse environments. We provide numerical simulations to show the effectiveness of our methodology. [less ▲]

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See detailBlock Circulant Decomposition of Cross-Correlation Matrix for Transmit MIMO Beamforming
Hammes, Christian UL; Shankar, Bhavani UL; Ottersten, Björn UL

Poster (2018, July)

This paper deals with the design of transmit probing signal under the trade-off between good target discrimination (low cross-correlation beam pattern) and beam pattern design (desired auto-correlation ... [more ▼]

This paper deals with the design of transmit probing signal under the trade-off between good target discrimination (low cross-correlation beam pattern) and beam pattern design (desired auto-correlation beam pattern) in a Multiple-Input- Multiple-Output (MIMO) radar configuration. The quartic optimization problem, with a finite alphabet constraint on the probing signal and using Quadrature Phase Shift Keying (QPSK) in a multiplexed antenna system, is solved through a Fourier series approximation of the desired beam pattern by exploiting a block circulant property of the transmit signal matrix. The mean square error between an ideal and the proposed crosscorrelation beam pattern is -35 dB enhancing the attractiveness of the proposed approach. [less ▲]

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See detailCONSISTENT LEAST SQUARES ESTIMATOR FOR CO-ARRAY-BASED DOA ESTIMATION
Sedighi, Saeid UL; Shankar, Bhavani UL; Maleki, Sina et al

Poster (2018, July)

Sparse linear arrays (SLAs), such as nested and co-prime arrays, have the attractive capability of providing enhanced degrees of freedom by exploiting the co-array model. Accordingly, co-array-based ... [more ▼]

Sparse linear arrays (SLAs), such as nested and co-prime arrays, have the attractive capability of providing enhanced degrees of freedom by exploiting the co-array model. Accordingly, co-array-based Direction of Arrivals (DoAs) estimation has recently gained considerable interest in array processing. The literature has suggested applying MUSIC on an augmented sample covariance matrix for co-array-based DoAs estimation. In this paper, we propose a Least Squares (LS) estimator for co-array-based DoAs estimation employing the covariance fitting method as an alternative to MUSIC. We show that the proposed LS estimator provides consistent estimates of DoAs of identifiable sources for SLAs. Additionally, an analytical expression for the large sample performance of the proposed estimator is derived. Numerical results illustrate the finite sample behavior in relation to the derived analytical expression. Moreover, the performance of the proposed LS estimator is compared to the co-array-based MUSIC. [less ▲]

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See detailReduced complexity satellite broadcast receiver with interference mitigation in correlated noise
Abu Shaban, Zohair UL; Mehrpouyan, Hani UL; Shankar, Bhavani UL et al

in International Journal of Satellite Communications and Networking (2018), 36(5),

ry The recent commercial trends towards using smaller dish antennas for satellite receivers and the growing density of broadcasting satellites necessitate the application of robust adjacent satellite ... [more ▼]

ry The recent commercial trends towards using smaller dish antennas for satellite receivers and the growing density of broadcasting satellites necessitate the application of robust adjacent satellite interference cancellation schemes. This orbital density growth along with the wider beamwidth of a smaller dish have imposed an overloaded scenario at the satellite receiver, where the number of transmitting satellites exceeds the number of receiving elements at the dish antenna. To ensure successful operation in this practical scenario, we propose a satellite receiver that enhances signal detection from the desired satellite by mitigating the interference from neighboring satellites. Towards this objective, we propose an enhanced list‐based group‐wise search detection (E‐LGSD) receiver under the assumption of spatially correlated additive noise. To further enhance detection performance, the proposed satellite receiver utilizes a newly designed whitening filter to remove the spatial correlation among the noise parameters, while also applying a preprocessor that maximizes the signal‐to‐interference‐plus‐noise ratio. We exploit the structure of this filter and propose a reduced complexity LGSD (RC‐LGSD) receiver. Extensive simulations under practical scenarios show that the proposed receiver enhances the performance of satellite broadcast systems in the presence of adjacent satellite interference compared with existing methods. Also, under pointing error, RC‐LGSD exhibits similar behavior to that of the optimum receiver. [less ▲]

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See detailPrecoding, Scheduling and Link Adaptation in Mobile Interactive Multibeam Satellite Systems
Vazquez, Miguel-Angel; Shankar, Bhavani UL; Kourogiorgas, Charilaos et al

in IEEE Journal on Selected Areas In Communications (2018), 36(5), 971-980

This paper deals with the problem of precoding, scheduling and link adaptation in next generation mobile interactive multibeam satellite systems. In contrast to the fixed satellite services, when the user ... [more ▼]

This paper deals with the problem of precoding, scheduling and link adaptation in next generation mobile interactive multibeam satellite systems. In contrast to the fixed satellite services, when the user terminals move across the coverage area, additional challenges appear. Due to the time varying channel, the gateway has only access to a delayed version of the channel state information (CSI) which can eventually limit the overall system performance. However, in contrast to general multiuser multipleinput- multiple-output terrestrial systems, the CSI degradation in multibeam mobile applications has a very limited impact for typical fading channel and system assumptions. Under realistic conditions, the numerical results show that precoding can offer an attractive gain in the system throughput compared to conservative frequency reuse allocations. [less ▲]

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See detailDesigning Joint Precoding and Beamforming in a Multiple Gateway Multibeam Satellite System
Joroughi, Vahid; Shankar, Bhavani UL; Maleki, Sina UL et al

in IEEE WCNC 2018 (2018, April 18)

This paper aims to design joint on-ground precoding and on-board beamforming of a multiple gateway multibeam satellite system in a hybrid space-ground mode where full frequency reuse pattern is considered ... [more ▼]

This paper aims to design joint on-ground precoding and on-board beamforming of a multiple gateway multibeam satellite system in a hybrid space-ground mode where full frequency reuse pattern is considered among the beams. In such an architecture, each gateway serves a cluster of adjacent beams such that the adjacent clusters are served through a set of gateways that are located at different geographical areas. However, such a system brings in two challenges to overcome. First, the inter-beam interference is the bottleneck of the whole system and applying interference mitigation techniques becomes necessary. Second, as the data demand increases, the ground and space segments should employ extensive bandwidth resources in the feeder link accordingly. This entails embedding an extra number of gateways aiming to support a fair balance between the increasing demand and the corresponding required feeder link resources. To solve these problems, this study investigates the impact of employing a joint multiple gateway architecture and on-board beamforming scheme. It is shown that by properly designing the on-board beamforming scheme, the number of gateways can be kept affordable even if the data demand increases. Moreover, Zero Forcing (ZF) precoding technique is considered to cope with the inter-beam interference where each gateway constructs a part of block ZF precoding matrix. The conceived designs are evaluated with a close-to-real beam pattern and the latest broadband communication standard for satellite communications. [less ▲]

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See detailMulticarrier phase modulated continuous waveform for automotive joint radar-communication system
Dokhanchi, Sayed Hossein; Shankar, Bhavani UL; Stifter, Thomas Stifter et al

in 2018 IEEE 19th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC) (2018)

Automotive radar implementation in the mm Wave band (79 G Hz) is being increasingly considered for the high bandwidths offered. While the radar systems and technology is maturing in mm Wave bands, the ... [more ▼]

Automotive radar implementation in the mm Wave band (79 G Hz) is being increasingly considered for the high bandwidths offered. While the radar systems and technology is maturing in mm Wave bands, the reuse of radar spectrum for low latency, limited throughput and safety critical communication has started to receive attention of late. Towards this, a joint radar-communication (JRC) system is proposed where the platform performs sensing and communication operations. The major challenge in JRC waveform design is the lack of degrees of freedom (DoF), due to need to estimate communication symbols in addition to the radar parameters. In this work, we propose a novel automotive JRC system based on multicarrier phase-modulated continuous waveform (MC-PMCW). MC-PMCW provides sufficient DoF to confine desired parameters, i.e., angles of arrival, Doppler shifts, ranges, and communication symbols in different dimensions. It can overcome the limitations of conventional PMCW and OFDM waveforms by leveraging the multicarrier feature of OFDM and the code sequence of PMCW to embed radar and communication. Further, the separation of parameters into different domains reduces complexity and enhances robustness; this is desirable in automotive scenarios characterized by dynamic scenes. Numerical results demonstrate the effectiveness of the proposed system. [less ▲]

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See detailPrecoder Design for Multibeam Mobile Satellite Systems
Joroughi, Vahid UL; Shankar, Bhavani UL; Maleki, Sina UL et al

in Proceedings of IEEE Asilomar Conference on Signals, Systems and Computers (2018)

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See detailOn-Board Precoding in a Multiple Gateway Multibeam Satellite System
Joroughi, Vahid UL; Shankar, Bhavani UL; Maleki, Sina UL et al

in Proceedings of IEEE VTC Fall 2018 (2018)

This paper present On-Board Precoding (OBP) for a multiple gateway multibeam satellite system where full frequency reuse pattern is employed at both user and feeder links. By reducing the Channel State ... [more ▼]

This paper present On-Board Precoding (OBP) for a multiple gateway multibeam satellite system where full frequency reuse pattern is employed at both user and feeder links. By reducing the Channel State Information (CSI) roundtrip delay to half, OBP offers significant benefits in the emerging multiple gateway scenario in terms of lower gateways coordination. However, two critical issues need to be addressed: (a) interference in both user and feeder links is the bottleneck of the whole system and employing interference mitigation techniques is essential, (b) clear push towards non-adaptive (fixed) payload implementation, leading to low computationally complex satellite architectures. In order to fulfill requirements (a) and (b), this paper studies the impact of employing a fixed OBP technique at the payload which is sufficiently robust to the variations in both user and feeder link channels. In addition to (a) and (b), the provided simulation results depict the performance gain obtained by our proposed OBP with respect to the conventional interference mitigation techniques in multiple gateway multibeam systems. [less ▲]

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See detailOFDM-based automotive joint radar-communication system
Dokhanchi, Sayed Hossein UL; Shankar, Bhavani UL; Stifter, Thomas et al

in 2018 IEEE Radar Conference (RadarConf18) (2018)

We propose a novel automotive joint radar-communication (JRC) system, where the system first transmits OFDM sub-carriers for radar processing followed by sub-carriers enabling radar and communication ... [more ▼]

We propose a novel automotive joint radar-communication (JRC) system, where the system first transmits OFDM sub-carriers for radar processing followed by sub-carriers enabling radar and communication functionalities. The receiver processing includes iterative estimation of parameters to alleviate the shortage of samples to estimate range. The receiver first estimates the target parameters from the sub-carriers dedicated to radar; these parameters then determine the channel for the communication link. The communication data is then extracted, thereby enabling the use of all the carriers for improving the range estimation. It is shown that the range estimation improves significantly after efficient use of all the sub-carriers. Furthermore, for radar parameter estimation, we propose an effective iterative method based on alternating least square (ALS) to recover the angle of arrival (AoA), Doppler and Range. Numerical results demonstrate the feasibility of our proposed system. [less ▲]

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See detailOn-Board Precoding in a Multiple Gateway Multibeam Satellite System
Shankar, Bhavani UL; Joroughi, Vahid UL; Maleki, Sina UL et al

Scientific Conference (2018)

This paper present On-Board Precoding (OBP) for a multiple gateway multibeam satellite system where full frequency reuse pattern is employed at both user and feeder links. By reducing the Channel State ... [more ▼]

This paper present On-Board Precoding (OBP) for a multiple gateway multibeam satellite system where full frequency reuse pattern is employed at both user and feeder links. By reducing the Channel State Information (CSI) round-trip delay to half, OBP offers significant benefits in the emerging multiple gateway scenario in terms of lower gateways coordination. However, two critical issues need to be addressed: (a) interference in both user and feeder links is the bottleneck of the whole system and employing interference mitigation techniques is essential, (b) clear push towards non-adaptive (fixed) payload implementation, leading to low computationally complex satellite architectures. In order to fulfill requirements (a) and (b), this paper studies the impact of employing a fixed OBP technique at the payload which is sufficiently robust to the variations in both user and feeder link channels. In addition to (a) and (b), the provided simulation results depict the performance gain obtained by our proposed OBP with respect to the conventional interference mitigation techniques in multiple gateway multibeam systems. [less ▲]

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See detailBinary Sequences set with small ISL for MIMO radar systems
Alaee-Kerahroodi, Mohammad; Modarres-Hashemi, Mahmoud; Naghsh, Mohammad Mahdi Naghsh et al

in 2018 26th European Signal Processing Conference (EUSIPCO) (2018)

In this paper, we aim at designing a set of binary sequences with good aperiodic auto- and crosscorrelation properties for Multiple-Input-Multiple-Output (MIMO) radar systems. We show such a set of ... [more ▼]

In this paper, we aim at designing a set of binary sequences with good aperiodic auto- and crosscorrelation properties for Multiple-Input-Multiple-Output (MIMO) radar systems. We show such a set of sequences can be obtained by minimizing the Integrated Side Lobe (ISL) with the binary requirement imposed as a design constraint. By using the block coordinate descent (BCD) framework, we propose an efficient monotonic algorithm based on Fast Fourier Transform (FFT), to minimize the objective function which is non-convex and NP-hard in general. Simulation results illustrate that the ISL of designed binary set of sequences is the neighborhood of the Welch bound, Indicating its superior performance. [less ▲]

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See detailLearning-based rainfall estimation via communication satellite links
Gharanjik, Ahmad UL; Mishra, Kumar Vijay; Shankar, Bhavani UL et al

in 2018 IEEE Statistical Signal Processing Workshop (SSP) (2018)

We present a method for estimating rainfall by opportunistic use of Ka-band satellite communication network. Our approach is based on the attenuation of the satellite link signal in the rain medium and ... [more ▼]

We present a method for estimating rainfall by opportunistic use of Ka-band satellite communication network. Our approach is based on the attenuation of the satellite link signal in the rain medium and exploits the nearly linear relation between the rain rate and the specific attenuation at Ka-band frequencies. Although our experimental setup is not intended to achieve high resolutions as millimeter wavelength weather radars, it is instructive because of easy availability of millions of satellite ground terminals throughout the world. The received signal is obtained over a passive link. Therefore, traditional weather radar signal processing to derive parameters for rainfall estimation algorithms is not feasible here. We overcome this disadvantage by employing neural network learning algorithms to extract relevant information. Initial results reveal that rainfall accumulations obtained through our method are 85% closer to the in situ rain gauge estimates than the nearest C-band German weather service Deutscher Wetterdienst (DWD) radar. [less ▲]

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See detailCoverage Extension via Side-Lobe Transmission in Multibeam Satellite System
Gharanjik, Ahmad UL; Kmieciak, Jarek; Shankar, Bhavani UL et al

in 23rd Ka and Broadband Communications Conference (2017, October 16)

In this paper, we study feasibility of coverage extension of a multibeam satellite network by providing low-rate communications to terminals located outside the coverage of main beams. Focusing on the MEO ... [more ▼]

In this paper, we study feasibility of coverage extension of a multibeam satellite network by providing low-rate communications to terminals located outside the coverage of main beams. Focusing on the MEO satellite network, and using realistic link budgets from O3b networks, we investigate the performance of both forward and return-links for terminals stationed in the side lobes of the main beams. Particularly, multi-carrier transmission for forward-link and single carrier transmission for return-link are examined and the resulting coverage and data rate for different setups are evaluated. Simulation results verifies that side-lobe transmission can extend the coverage area and provide considerable data rate, thereby providing a solution for enhancing capacity of existing networks. [less ▲]

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See detailOptical Feeder Links Study towards Future Generation MEO VHTS Systems
Mengali, Alberto UL; Lyras, Nikos K.; Shankar, Bhavani UL et al

in Proceedings of the 35th AIAA International Communications Satellite Systems Conference (ICSSC) (2017, October)

Detailed reference viewed: 97 (3 UL)