Abstract-We investigate the spectral efficiency of full-duplex small cell wireless systems, in which a full-duplex capable base station (BS) is designed to send/receive data to/from multiple halfduplex users on the same system resources. The major hurdle for designing such systems is due to the self-interference at the BS and co-channel interference among users. Hence, we consider a joint beamformer design to maximize the spectral efficiency subject to certain power constraints. The design problem is first formulated as a rank-constrained optimization one, and the rank relaxation method is then applied. However the relaxed problem is still nonconvex, and thus optimal solutions are hard to find. Herein, we propose two provably convergent algorithms to obtain suboptimal solutions. Based on the concept of the Frank-Wolfe algorithm, we approximate the design problem by a determinant maximization program in each iteration of the first algorithm. The second method is built upon the sequential parametric convex approximation method, which allows us to transform the relaxed problem into a semidefinite program in each iteration. Extensive numerical experiments under small cell setups illustrate that the full-duplex system with the proposed algorithms can achieve a large gain over the half-duplex one.Index Terms-Full-duplex, self-interference, transmit beamforming, D.C. program, semidefinite programming.

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This paper summarizes the main initiatives toward 5G wireless communication networks. Emphasis is paid on the program and project activities as well as on the recent literature. A closer look to a wide range of European Union 5G related projects is conducted. Literature review is restricted to recent thematic IEEE Communications Magazine 5G issues and relevant white papers from different sources. The aim is to shed some light on what 5G is about: what are the building blocks of core 5G system concept, what are the main challenges and how to tackle them. The studied references indicate that in addition to capacity boosting technologies 5G needs to offer, e.g., low latency, ultra-reliable communications, and massive connectivity. Thus, the most demanding part in 5G development will be the design of flexible enough system concept platform that allows successful integration and management of various distinct technologies optimized for diverse use cases.

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To tackle the challenge of providing higher data rates within limited spectral resources we consider the case of multiple operators sharing a common pool of radio resources. Four algorithms are proposed to address co-primary multi-operator radio resource sharing under heterogeneous traffic in both centralized and distributed scenarios. The performance of these algorithms is assessed through extensive system-level simulations for two indoor small cell layouts. It is assumed that the spectral allocations of the small cells are orthogonal to the macro network layer and thus, only the small cell traffic is modeled. The main performance metrics are user throughput and the relative amount of shared spectral resources. The numerical results demonstrate the importance of coordination among co-primary operators for an optimal resource sharing. Also, maximizing the spectrum sharing percentage generally improves the achievable throughput gains over non-sharing

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As the wireless and mobile world is turning its interest into beyond 5G development, industry and research community are gradually taking up this colossal challenge. This paper discusses the readiness and capacity needed to develop beyond 5G (B5G) and 6G technology and their associated businesses and applications. The wireless landscape is analyzed in different timeframes covering roughly the period between 2020 and 2030, the decade where B5G and 6G are expected to be fully developed. After discussing relevant trends and key requirements needed to develop B5G and 6G in general, the paper will consider, as a particular example, the current development and readiness of Finland. With a strong background in 5G, Finland is one of the first countries to start doing 6G development following a large research project where key industrial and academic players of the country participate. Hopefully, the conceived developing path to 6G presented in this paper will serve a motivational guide to other developers.

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