Location-aware Communications for 5G Networks

5G networks will be the first generation to benefit from location information that is sufficiently precise to be leveraged in wireless network design and optimization. We argue that location information can aid in addressing several of the key challenges in 5G, complementary to existing and planned technological developments. These challenges include an increase in traffic and number of devices, robustness for mission-critical services, and a reduction in total energy consumption and latency. This paper gives a broad overview of the growing research area of location-aware communications across different layers of the protocol stack. We highlight several promising trends, tradeoffs, and pitfalls. I. 5G: INTRODUCTION AND CHALLENGES 5G will be characterized by a wide variety of use cases, as well as orders-of-magnitude increases in mobile data volume per area, number of connected devices, and typical user data rate, all compared to current mobile communication systems [1]. To cope with these demands, a number of challenges must be addressed before 5G can be successfully deployed. These include the demand for extremely high data rates and much lower latencies, potentially down to 1 ms end-to-end for certain applications [2]. Moreover, scalability and reduction of signaling overhead must be accounted for, as well as minimization of (total) energy consumption to enable affordable cost for network operation. To fulfill these requirements in 5G, network densification is key, calling for a variety of coordination and cooperation techniques between various kinds of network elements in an ultra-dense heterogeneous network. Moreover, by implementing sharing and coexistence approaches, along with new multi-GHz frequency bands, spectrum efficiency can be improved. An overview of a number of disruptive technologies for 5G is provided in [1]. It is our vision that context information in general, and location information in particular, can complement both traditional and disruptive technologies in addressing several of the challenges in 5G networks. While location information was available in previous generations of cellular mobile radio systems, e.g., cell-ID positioning in 2G, timing-based positioning using communication-relevant synchronization signals in 3G, and additionally dedicated positioning reference signals in 4G, accuracy ranged from hundreds to tens of meters, rendering position information insufficiently precise for some communications operations. In 5G, for the first time, a majority of R. Di Taranto, L. S. Muppirisetty, and H. Wymeersch are with the Department of Signals and Systems, Chalmers University of Technology, Sweden. R. Raulefs is with German Aerospace Center (DLR) in Wessling, Germany. D. Slock is with EURECOM, France. Corresponding email: [email protected]. This work is supported, in part, by the European Research Council under Grant No. 258418 (COOPNET), by the European Union under ICT-248894 FP7 project WHERE2, and by the Swedish Research Council under Grant No. 2011-6864 and 2009-4555. spatial'correlation shadowing interference spatial'reuse propagation'delay distance routing next'hop proactive'allocation p(x(t)) predictable' behavior' Doppler velocity angle'of'arrival' MIMO path'loss distance fD = ||ẋ(t)||/ ||x xs|| ⌘ ⌧ = ||x xs||/c h( (x,xs)) min j ||xj xd|| exp ✓ ||xi xj || dc ◆ ||xi xs|| < R ||xi xj || > Rint Fig. 1. Communication systems are tied to location information in many ways, including through distances, delays, velocities, angles, and predictable user behavior. The notations are as follows (starting from the top left downward): x is the user location, xs is the base station or sender location, η is the path loss exponent; xi and xj are two user location, dc is a correlation distance; φ(.) is an angle of arrival between a user and a base station, h is a MIMO channel; c is the speed of light and τ a propagation delay; fD is a Doppler shift, ẋ(t) is the user velocity, λ is the carrier wavelength; R is a communicate range, Rint is an interference range; xd is a destination; p(x(t)) is a distribution of a user position at a future time t. devices can benefit from positioning technologies that achieve a location accuracy on the order of one meter. In this paper, we argue why and how such precise location awareness can be harnessed in 5G networks. We first present technologies providing seamless and ubiquitous location awareness for 5G devices, identify associated signal processing challenges, and describe at a high level how location information can be utilized across the protocol stack. We then zoom in on each layer of the protocol stack, and provide an overview of recent and relevant research on locationaware communications. We conclude the paper by identifying a number of issues and research challenges that must be addressed before 5G technologies can successfully utilize location information and achieve the predicted performance gains. II. LOCATION AWARENESS IN 5G NETWORKS A majority of 5G devices will be able to rely on ubiquitous location awareness, supported through several technological developments: a multitude of global navigation satellite systems (GNSS) are being rolled out, complementing the current global positioning system (GPS). Combined with ground support systems and multi-band operation, these systems aim to offer location accuracies around 1 meter in open sky [3]. In scenarios where GNSS is weak or unavailable (in urban