In initial random access, base station (BS) estimates the distance between the user equipment (UE) and BS. In the mobile satellite system (MSS), however, the characteristics of large transmission delay makes the estimation method used in the terrestrial system not applicable in the MSS. To solve this problem, a two-step time delay difference estimation scheme is proposed for orthogonal frequency division multiple access (OFDMA) multi-beam satellite system. We first divide a beam cell into some layered small sub-areas according to the different delay difference values. Then, two types of Physical Random Access Channel (PRACH) preamble burst format are performed: the first one is for the fractional delay difference value measurement and the second one is for the integer part. Further, complete criteria for the designation of PRACH parameters are proposed and closed-form expressions of the system performance are also derived, including the false alarm probability and the missed detection probability. Finally, according to the numerical analysis, the method shows good performance.

Abstract-This paper investigates jammer selection in a twoway decode-and-forward (DF) relay network with imperfect channel state information (CSI). The proposed scheme enables an selection of one conventional relay and two jamming nodes to enhance communication security against eavesdropper. The conventional relay assists two sources to exchange their data via a DF protocol. The two jamming nodes are used to create interference signals to confuse the eavesdropper. Furthermore, the asymptotic performance of proposed scheme is analyzed in detail. Under the assumption that the relay can decode received signals perfectly and when the jamming power is higher than that of source nodes, we find that the proposed scheme has a high secrecy performance which is almost independent of the position of the eavesdropper.

No abstract

Abstract-As most of voice calls and data traffic originates indoors, femtocells have been one of the most promising trends in LTE, which are short-range, cost-beneficial and low-power cellular home base stations that can improve indoor coverage and voice/data quality of service (QoS). One of the major challenges for femtocell network is the access control. The hybrid access control mechanism, as a tradeoff between open and closed scenario, is the most promising access mechanism from which both users and operators benefit. Femtocell user equipments (FUEs) select femtocell access points (FAPs) according to their reported channel information which FAPs confidently own, and selfish FAPs have incentive to report larger information to win greater opportunity to be selected. Considering the aforementioned truth-telling in access control issue, this paper proposes access control scheme for hybrid femtocell network based on Arrow-d'AspremontGerard-Varet (AGV) mechanism. Close form for the payment is given. Moreover, the access control scheme is nearly optimal performances with low computational complexity compared with the optimal access scheme. Furthermore, the simulation results demonstrate that the access control scheme can be apply to hybrid femtocell network.