gho Jeon

LTE in the unlicensed spectrum: Evaluating coexistence mechanisms

The Long Term Evolution (LTE) in unlicensed spectrum is an emerging topic in the 3rd Generation Partnership Project (3GPP), which is about an operation of the LTE system in the unlicensed spectrum via license-assisted carrier aggregation. The 5 GHz Unlicensed National Information Infrastructure (U-NII) bands are currently under consideration, but these bands are also occupied by Wireless Local Area Networks (WLAN), specifically those based on the IEEE 802.11a/n/ac technologies. Therefore, an appropriate coexistence mechanism must be augmented to guarantee a peaceful coexistence with the incumbent systems. With this regard, our focus lies on the evaluation of all the proposed coexistence mechanisms so far in a single framework and making a fair comparison of them. The coexistence mechanisms covered in this work includes static muting, listen-before-talk (LBT), and other sensing-based schemes that make a use of the existing WLAN channel reservation protocol.

LTE in the unlicensed spectrum: A novel coexistence analysis with WLAN systems

In this paper, we consider the operation of the Long Term Evolution (LTE) systems in the unlicensed spectrum. Given the lack of the exclusive use of the spectrum, the operation in the unlicensed band is fundamentally limited by interference from other technologies using the same frequency band. By noting that the unlicensed spectrum is heavily used by Wireless Local Area Networks (WLAN), here we focus on the mutual effect between LTE and WLAN when they coexist. For this, we developed a novel inter-system interference analysis technique based on the continuum field approximation and spiral representation, which improves the accuracy of the previous approaches and is applicable to both large-scale and small-scale networks. To this end, we quantify the effect of inter-system interference when the LTE and WLAN systems operate in the same unlicensed spectrum.

LTE with listen-before-talk in unlicensed spectrum

We consider the adoption of listen-before-talk (LBT) for Long Term Evolution (LTE) in unlicensed spectrum, which is currently under discussion in the 3rd Generation Partnership Project (3GPP). The first and foremost task to be done to allow LTE to use unlicensed spectrum is to study the coexistence with incumbent system, such as the Wireless Local Area Network (WLAN). In our study, we observe that a proper coexistence mechanism is imperative especially when both LTE Evolved Node Bs (eNBs) and WLANs are located outdoor. The outdoor deployment scenario is considered by the next generation WLAN, the IEEE 802.11ax, with high importance. The implementation of LBT in LTE plays an effective role in this scenario in balancing the performance between LTE and WLAN. In the conventional scenario where WLANs are located indoor and LTE eNBs are located outdoor, a plain coexistence without additional mechanism could be acceptable due to high penetration loss of outdoor walls.

Licensed-Assisted Access to Unlicensed Spectrum in LTE Release 13

Exploiting the unlicensed spectrum is considered by 3GPP as one promising solution to meet ever-increasing traffic growth. As a result, one major enhancement for LTE in Release 13 has been to enable its operation in the unlicensed spectrum via licensed-assisted access (LAA). In this article, we provide an overview of the Release 13 LAA technology including motivation, use cases, LTE enhancements for enabling the unlicensed band operation, and the coexistence evaluation results contributed by 3GPP participants.

Optimal Resource Allocation and Mode Selection for D2D Communication Underlaying Cellular Networks

In this work, we consider the device-to-device (D2D) communications underlaying cellular networks to support local communication needs. In particular, we focus our attention on the design of an optimal resource allocation and mode selection algorithm for both cellular and D2D users. In the design, communication mode selection for D2D users is also taken into account so that a D2D source-destination pair has an option to either directly communicate or indirectly communicate through the base station (BS). On the other hand, it is necessary and important to provide a certain level of Quality of Service (QoS) to users. The users can be further differentiated by assigning different weighting factors and QoS requirements. To this end, we formulate a problem of maximizing the weighed sum rate of all the users constrained by their power and QoS requirements. The tool that we use to handle this problem is the primal-dual technique which transforms the original problem into the equivalent problem showing lower computational complexity. The simulation results verify that our proposed scheme outperforms the previous heuristic scheme by jointly optimizing the power and resource allocation along with the communication mode selection for the D2D communication pairs.