This letter proposes a multiuser switched scheduling scheme with per-user threshold and post user selection and provides a generic analytical framework for determining the optimal feedback thresholds. The proposed scheme applies an individual feedback threshold for each user rather than a single common threshold for all users to achieve some capacity gain due to the flexibility of threshold selection as well as a lower scheduling outage probability. In addition, since scheduling outage may occur with a non-negligible probability, the proposed scheme employs post user selection in order to further improve the ergodic capacity, where the user with the highest potential for a higher channel quality than other users is selected. Numerical and simulation results show that the capacity gain by post user selection is significant when random sequence is used.

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Three synchronization issues, i.e., phase, frequency, and symbol time, have to be properly controlled to achieve distributed beamforming gain. In orthogonal frequency division multiplexing (OFDM) systems, frequency offset in cooperating signals is more important than other synchronization issues since it results in SNR degradation as well as inter-carrier interference (ICI). In this paper, the impact of frequency offset in distributed beamforming is analyzed for OFDM systems. ICI resulting from frequency offset between cooperating signals is also investigated and approximated. Performance degradation due to frequency offset is shown with various numbers of cooperating signals and offset values. We show that frequency offset between cooperating signals is critical in OFDM systems since it leads to interference from the other subcarriers as well as power loss in the desired signal.

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In this work, we analyze the performance of cognitive amplify-and-forward (AF) relay networks under the spectrum sharing approach. In particular, by assuming that the AF relay operates in the semi-blind mode (fixed-gain), we derive the exact closed-form expressions of the outage probability for the cognitive relaying (no direct link) and cognitive cooperative (with direct link) systems. Simulation results are presented to verify the theoretical analysis.

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Flow mobility is an emerging technology to support flexible network selection for an application flow and to spread concentrated load to less-overloaded Internet access. Network-based flow mobility (FMO) does not require a massive amount of software logic and system resources on the mobile node. Under this approach, there are two kinds of modes available: network-initiated and user-initiated. Network-initiated FMO decides the best access network suited for a specific flow, but the decisions depend on the operator's policy. Therefore, it has limitations in supporting the user's preference and private network selection. In the user-initiated mode, users can hand off specific flow so that information of both the current user's preference and the conditions of private network are reflected. User-initiated flow mobility method has not been what should be specified and how it can be supported with the protocol sequence for real deployment. This paper extends Internet Exchange Key v2 (IKEv2) and an Attach request message to support user-initiated FMO when a flow moves between 3G and Wi-Fi access. Through performance analysis, we confirm that user-initiated FMO is superior to network-initiated FMO in terms of signaling overhead and handover latency costs.

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This letter proposes a multiple symbol differential detection (MSDD) with majority decision method for differentially coded quadrature phase-shift keying (DQPSK) in Rician fading channels. The proposed method shows better BER performance than the conventional MSDD. Simulation results show that the proposed MSDD with a majority decision method improves the system's BER performance for DQPSK signals under the AWGN channel and it approaches asymptotically the theoretical BER performance of coherent detection. Furthermore, the proposed method shows better BER performance under the Rician fading channel with large frequency offsets especially for the range of C/M > 12dB in comparison with the conventional MSDD.

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