Abstract-We consider sporadic ultra-reliable and low latency communications in the uplink 5G cellular systems. Reliable low latency access for randomly emerging packet transmission needs cannot be guaranteed in current wireless systems. To achieve the goal of low latency and high reliability simultaneously, we propose a contention-based transmission scheme aimed for the users with small payloads. We target to reduce collision probability by considering multiple transmissions for the same packet for reliable reception. We find the optimal number of consecutive multiple transmissions that reduces collisions and achieves target reliability within the latency window. By means of intended frame structure design for the 5G cellular systems, results are drawn and comparisons are made with default multi-channel slotted ALOHA access scheme.

The upcoming fifth generation (5G) wireless communication system is expected to support a broad range of newly emerging applications on top of the regular cellular mobile broadband services. One of the key usage scenarios in the scope of 5G is ultra-reliable and low-latency communications (URLLC). Among the active researchers from both academy and industry, one common view is that URLLC will play an essential role in providing connectivity for the new services and applications from vertical domains, such as factory automation, autonomous driving and so on. The most important key performance indicators (KPIs) related to URLLC are latency, reliability and availability. In this paper, after brief discussion on the design challenges related to URLLC use cases, we present an overview of the available technology components from 3GPP Rel-15 and potential ones from Rel-16. In addition, coordinated multi-cell resource allocation methods are studied. From the system level simulation results in an urban macro environment, it can be observed that effective multi-cell cooperation, more specifically soft combining, can lead to a significant gain in terms of URLLC capacity.

Abstract-We consider two small cell operators deployed in the same geographical area, sharing spectrum resources from a common pool. A method is investigated to coordinate the utilization of the spectrum pool without monetary transactions and without revealing operator-specific information to other parties. For this, we construct a protocol based on asking and receiving spectrum usage favors by the operators, and keeping a book of the favors. A spectrum usage favor is exchanged between the operators if one is asking for a permission to use some of the resources from the pool on an exclusive basis, and the other is willing to accept that. As a result, the proposed method does not force an operator to take action. An operator with a high load may take spectrum usage favors from an operator that has few users to serve, and it is likely to return these favors in the future to show a cooperative spirit and maintain reciprocity. We formulate the interactions between the operators as a repeated game and determine rules to decide whether to ask or grant a favor at each stage game. We illustrate that under frequent network load variations, which are expected to be prominent in small cell deployments, both operators can attain higher user rates as compared to the case of no coordination of the resource utilization.Keywords-Co-primary spectrum sharing, repeated games, spectrum pooling. I. INTRODUCTIONIn the state-of-art mobile communication systems, a network operator possesses a spectrum license that provides exclusive transmission rights for a particular range of radio frequencies. Spectrum assignment based on dedicated licenses resolves the issues related to inter-operator interference but it also results in low spectrum utilization efficiency. Inter-operator spectrum sharing is envisioned as one of the viable approaches to achieve higher operational bandwidth efficiency and meet the increasing mobile data traffic demand in a timely manner [1].In the limited spectrum pool (LSP) scenario, a limited number of operators share a common resource pool by relying on more flexible and adaptive prioritization policies than is currently possible with dedicated licenses [2]. Cognitive radio technologies are effective measures to resolve the sharing conflicts over the LSP under vertical spectrum sharing [3], where the lessor (owner) operator has higher legacy rights over the spectrum than the lessee operator. On the other hand, the co-primary or horizontal spectrum sharing scheme conceptualizes the case where authorized operators possess equal ownership on the spectrum being adopted [4]. However, a priori agreements should be made on the spectrum usage with regard to the long term share of an individual operator.The multilateral use of shared resources in the LSP can, for instance, be achieved with channel allocation schemes originally developed for single-operator systems. These schemes

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We consider spectrum sharing between a limited set of operators having similar rights for accessing spectrum. A coordination protocol acting on the level of the Radio Access Network (RAN) is designed. The protocol is noncooperative, but assumes an agreement to a set of negotiation rules. The signaling overhead is low, and knowledge of competitor's channel state information is not assumed. No monetary transactions are involved; instead, spectrum sharing is based on a RAN-internal virtual currency. The protocol is applicable in a scenario of mutual renting and when the operators form a spectrum pool. The protocol is reactive to variations in interference and load of the operators, and shows gains in a simulated small cell scenario compared to not using any coordination protocol.