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We develop new transmission schemes for multipoint-to-multipoint (M2M) networks which, unlike the existing approaches, address duplexing/multiplexing and multiple access jointly and possess true M2M characteristics in the physical layer. In the proposed schemes, all forward and reverse links of the M2M network share the overall spectrum concurrently in an orthogonal frequency division manner. This provides increased degrees of freedom and enhanced diversity in scheduling and resource allocation, thus leading to performance enhancement. We first discuss practical implementation issues. Next, we develop our proposed schemes for both centralized and distributed access scenarios. Under the centralized access, we illustrate advantages of the proposed approach for M2M networks using a scheduling algorithm and provide a closed-form analytical throughput upper-bound. Next, we extend the proposed approach to multicasting and present a new scheduling strategy and its closed-form analytical approximate throughput expression. Under the distributed access, we develop a generalized multi-channel carrier sensing multiple access/collision avoidance scheme for M2M networks and propose a new scheme which exploits local channel information. Closed-form analytical throughput expressions for a specific scenario are also presented. Simulation results corroborate substantial performance gains of the proposed schemes over the conventional schemes in both centralized and random access scenarios. [ABSTRACT FROM AUTHOR]

Carrier frequency offset (CFO) causes spectrum misalignment of transmitter and receiver filters. This misalignment leads to energy loss and distortion of received signal, resulting in performance degradation of the whole system. However, these issues are often overlooked by existing works. This paper presents an exact signal model for OFDM that takes into account the CFO-induced spectral misalignment and related aliasing effects. Incorporating these practical issues, we also propose a new preamble structure and a new CFO compensation approach to mitigate their negative effects. Theoretical analysis and simulation results substantiate the importance of the exact signal model and the advantage of the proposed CFO compensation scheme. [ABSTRACT FROM PUBLISHER]

Interference control is crucial in cognitive radio networks and the existing related works focus on quasi-static channels. The expansion of wireless services and applications in everyday life has necessitated support of higher mobility, as evident from the emerging wireless standards. This results in time-varying fading channels within a transmission frame for which the interference power control schemes and power allocation strategies have not been developed yet. This paper proposes several interference control and power allocation strategies with different criteria for underlay cognitive radios in time-varying frequency-selective fading channels and extend the transmission schemes to multiple secondary systems. The transmission schemes are evaluated in terms of interference statistics at the primary receiver and the ergodic capacity of the secondary user link. Simulation results over the wide Doppler range show how the proposed schemes with different criteria shape the interference at the primary receiver and the capacity of the secondary user. The results also illustrate better interference control capability of the proposed approaches over the existing scheme. [ABSTRACT FROM PUBLISHER]

Diversity exploitation is a proven efficient means for addressing detrimental effects of wireless channel fadings. User channelization, where the frequency and time resources are structured into several user channels, can substantially help to capture the diversity, but it has not been well investigated. In this paper, we develop theoretical formulation of optimal resource structures under different performance metrics and then analyze them in frequency-selective time-varying channels. We propose a simplified system model which maintains the main features, and based on which, we develop a new practical approach of user channelization or user resource structuring which captures better diversity for OFDMA systems in multiuser time-varying frequency-selective fading channels. In contrast to the existing user resource structures where relative locations of the resources in the time-frequency grid remain the same throughout the transmission frame, the proposed resource structures evolve within the frame to enjoy better diversity gain. Example designs of the proposed evolving structures are presented from the 3GPP LTE perspective. Simulations done under LTE system environments validate that the proposed practical approach can obtain a near-optimal structure design, and provide significant performance advantage over the existing structures at the mobile speeds ranging from 3 km/h to 350 km/h. [ABSTRACT FROM PUBLISHER]