Dynamic time-division duplexing (TDD) enables adjustments of uplink (UL) and downlink (DL) resources flexibly according to the instantaneous traffic load. Long-Term Evolution (LTE) systems can be implemented in TDD mode (TD-LTE). However, the dynamic change of a TDD configuration has not been well supported and investigated. In large macro cells, the high transmit power of base stations (BSs) easily blocks the weaker user equipment's (UE) UL signal (called the UL-DL interference); and therefore, neighboring cells usually operate with the same TDD configuration. In small cells, such as femtocells, the BS and UE transmission powers are in the same order and the system can afford to have overlapping UL-DL subframes. In addition, when DL load is light, the BS transmits empty DL subframes with only a reference signal (RS). In this paper, we measured the interference caused by DL RS. This interference is not negligible; and therefore, it is beneficial to reduce the amount of DL subframes by switching lightly loaded BSs to UL-heavy subframe configuration. We illustrate with simulations that this can improve system efficiency. Changing the subframe configuration dynamically has a switching-related cost. Frequent switching between subframe configurations can actually decrease throughput. We describe conditions where configuration change is beneficial. We also propose an algorithm that decreases the switching overhead and improves the ability to adapt to varying loads.
Abstract-The Extensible Messaging and Presence Protocol (XMPP) is one of the most popular Instant Messaging (IM) protocols which uses a client-server working mode. This protocol uses different connection primitives for both client-to-server (c2s) and server-to-server (s2s) connections. It is actively used in mission-critical operations where the reliability and security of communication systems is always imperative. One approach to secure services and private networks is to use proxy services as security gateways. Proxies enable interoperability between different security domains acting as Information Exchange Gateways (IEGs).In this paper we present an architecture of the XMPP proxy for s2s connections. The system is based on an Openfire XMPP server with a Hazelcast clustering plugin, and a Hazelcast clustering link is used between the XMPP server and the XMPP Proxy. We have constructed an implementation to verify and validate the presented approach. Our proposal enables an effective seamless connection for XMPP proxies. Furthermore, it increases the system security for example, terminating both TCP and XMPP flows to prevent malicious attacks. Finally, we show that the proposal does not significantly increase the anticipated delay of the communication.
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