A Novel Discovery Channel Scheduling for Inter-Cell Device-to-Device Discovery in 3GPP LTE Asynchronous Network

Kyunghoon LEE  Wonjun HWANG  Hyung-Jin CHOI  

IEICE TRANSACTIONS on Communications   Vol.E98-B   No.2   pp.370-378
Publication Date: 2015/02/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E98.B.370
Type of Manuscript: PAPER
Category: Terrestrial Wireless Communication/Broadcasting Technologies
asynchronous network,  D2D,  inter-cell discovery,  LTE,  

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In recent 3GPP (3rd Generation Partnership Project) standardization meetings, D2D (Device-to-Device) discovery has been a major issue to support commercial/social services and public safety in disaster environment, and TDM (Time Division Multiplexing) based discovery channel structure is mainly considered to prevent mutual interference between D2D and cellular traffic. In this structure, D2D discovery among the same cell UEs (User Equipment) has no problem because they have the same timing source. However, LTE (Long Term Evolution) assumes an asynchronous network where two adjacent eNBs (evolved Node B) have a symbol-level timing offset. For that reason, asynchronous interference among discovery signals can appear in inter-cell D2D discovery. Therefore, channel re-use scheduling was studied previously in which neighboring cells do not use the same portion of the extended discovery channel and other non-neighboring cells re-use it. However, it still shows interference problems in small cell networks which cause substantial cellular traffic loss. Therefore, in this paper, we propose a novel discovery channel scheduling in which eNBs time-align their discovery channels from each other by sample-level. In the proposed scheme, serving eNB requests cell edge UEs to estimate NTD (Network Time Difference) between serving eNB and neighboring eNB. Then, considering multiple NTDs, eNB adjusts the sample position of its discovery channel based on a novel decision rule. We verify that the proposed scheme can match the discovery performance of a synchronous network with less cellular uplink loss.