Stefano Sorrentino

Device-to-Device Communications for National Security and Public Safety

Device-to-device (D2D) communications have been proposed as an underlay to long-term evolution (LTE) networks as a means of harvesting the proximity, reuse, and hop gains. However, D2D communications can also serve as a technology component for providing public protection and disaster relief (PPDR) and national security and public safety (NSPS) services. In the United States, for example, spectrum has been reserved in the 700-MHz band for an LTE-based public safety network. The key requirement for the evolving broadband PPDR and NSPS services capable systems is to provide access to cellular services when the infrastructure is available and to efficiently support local services even if a subset or all of the network nodes become dysfunctional due to public disaster or emergency situations. This paper reviews some of the key requirements, technology challenges, and solution approaches that must be in place in order to enable LTE networks and, in particular, D2D communications, to meet PPDR and NSPS-related requirements. In particular, we propose a clustering-procedure-based approach to the design of a system that integrates cellular and ad hoc operation modes depending on the availability of infrastructure nodes. System simulations demonstrate the viability of the proposed design. The proposed scheme is currently considered as a technology component of the evolving 5G concept developed by the European 5G research project METIS.

Network Assisted Device-to-Device Communications: Use Cases, Design Approaches, and Performance Aspects

Network assisted device-to-device (D2D) communications have emerged as a means of increasing spectral and energy efficiency, reducing latency and creating a platform for proximity-based services. Application areas of D2D communications include cellular network offloading and coverage extension, proximity-based social networking, and providing national security and public safety (NSPS) in infrastructure-less situations. This broad range of applications has led to a large set of technical requirements that must be taken into account when designing physical layer algorithms, user and control plane protocols, and network architecture. In this chapter we review the key requirements and current approaches to network assisted service and device discovery, radio resource management and tuning the performance of integrated D2D, and cellular networks.

On pilot dimensioning in multicell single input multiple output systems

Resource management schemes in multicell orthogonal frequency division multiplexing (OFDM) networks typically assume perfect channel knowledge at the transmitter or employ a statistical channel estimation error. In this paper we propose a model that explicitly captures the inherent tradeoff between the power allocated to transmitting data and pilot signals in multicell single input multiple output (SIMO) systems. We first study the asymptotic behavior of the required data power to reach a predefined signal-to-noise ratio (SNR) target as a function of the employed pilot power in a single OFDM cell, then develop a distributed multicell algorithm that strives to minimize the multi-cell sum data power with respect to a predefined signal-to-interference-and-noise-ratio (SINR) target vector. The results provide new insights in dimensioning the pilot and data transmit power levels and serve as a basis for developing distributed power control schemes in multicell systems.

On the impact of uplink power control in network MIMO systems with MMSE and SIC receivers

Network multiple input, multiple output (MIMO) systems are built around a broadband backbone network that allows for the fast communication of channel state information (CSI) as well as user data between different base stations. Previous works have shown that multicell channel adaptive (opportunistic) power control can minimize the sum power or maximize the sum rate when the backbone is used for the exchange of CSI in network MIMO systems. In this work we investigate the gains of multicell opportunistic power control under per user fairness constraints when both CSI and user data are shared between multiple sites. We find that multicell opportunistic power control working in concert with uplink joint signal detection is an efficient means both for the capacity and the power control problems that not only minimizes sum power or maximizes overall capacity, but is also able to provide arbitrary level of fairness.

Multiple Access Schemes for DCT-Based OFDM: Derivation and Comparison

DCT-based OFDM has been proposed as a promising multicarrier transmission scheme which, compared to the widely employed DFT-based OFDM, trades improved robustness against frequency offset for a more complex receiver implementation. However, in order to allow the introduction of DCT-based OFDM in practical systems, efficient multiple access schemes characterized by low peak-to-average power ratio (PAPR) need to be derived. In this work three different multiple access chemes for DCT based OFDM are derived and compared in terms of bit errorprobability and PAPR. These schemes have similar characteristics to corresponding DFT-based OFDMA, LFDMA and IFDMA. It is shown that, while OFDMA and LFDMA are easily adapted to DCT-based OFDM, a new multiplexing algorithm needs to be derived in case of DCT-based IFDMA. The transfer function of this novel scheme is derived and an efficient implementation is proposed which is attractive for terminal devices with limited computational capacity.

Performance Optimization for Multi-User Orthogonal Space-Time Block Coding with Maximum Likelihood and Zero-Forcing Receivers

A multi-user MIMO channel is characterized by multiple degrees of freedom that can be alternatively exploited for increasing the link quality through diversity or improving the achievable data-rate through spatial multiplexing. A convenient trade-off between diversity and multiplexing gain is achieved by multi-user orthogonal space-time block coding (OSTBC): an independent space-time code is employed on each user link, while multiple users are spatially multiplexed for additional capacity. This paper addresses the optimization of multi-user OSTBC systems where the receiver is provided with multiple antennas. The study explicitly addresses both ideal maximum likelihood receivers and linear zero-forcing receivers in a general setting that is able to model, e.g., a multiple access channel with uncorrelated receive antennas. Assuming K scheduled users, it is shown that system performance optimization can be decoupled into K simpler independent convex optimization problems that are conveniently solved in a distributed fashion.