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In this paper, we propose an opportunistic spectrum sharing protocol that exploits the situation when the primary system experiences weak channel conditions. Specifically, when the outage rate of the primary systeme falls below the target rate, the secondary system tries to help the primary system achieve its target rate by acting as a decode-and-forward(More)
To reduce interference to primary user and improve channel capacity with an acceptable detection probability in cognitive radio networks, we propose a relay-based cooperative spectrum sensing framework. Different from conventionally cognitive radio network, where spectrum sensing and signal transmission are performed separately, the proposed framework(More)
In order to achieve efficient dynamic spectrum access (DSA) in Cognitive Ultra-Wideband (C-UWB) systems, an orthogonal wavelets based dynamic pulse shaping method is proposed to obtain pulses which can adapt to any given spectral requirements. Using Meyer wavelet set as the orthogonal basis, pulses with high power efficiency can be achieved. The compact(More)
In this paper, weighted fractional Fourier transform (WFRFT) is employed to safeguard the physical layer (PHY) security of wireless communications. By leveraging the features of WFRFT, we propose a PHY security modulation scheme, which significantly degrades the equivalent signal-to-noise ratio (SNR) of the unauthorized receiver while imposing no impact on(More)
Sparse Code Multiple Access (SCMA) is a recently designed spreading technology in which QAM symbols are mapped to different OFDMA tones. The codebook based mapping can be regarded as a spreading encoding process, where the shaping gain helps promote spectral efficiency and enhance system performance. Based on the SCMA encoding scheme, this paper proposes a(More)
In the ultra-wideband (UWB) communication systems, a critical spectral mask is released to restrict the allowable interference to other wireless devices by the Federal Communications Commission (FCC), and then some pulse shaping methods have been presented to fulfil the mask. However, most pulse shaping methods do not consider the antenna distortion which(More)
In impulse radio ultra-wideband (IR-UWB) systems, Rayleigh pulse and Gaussian monocycle are usually the waveforms used to transmit data. However when all the users in a system transmit an identical waveform, the effects of multi-user interference (MUI) are great and therefore the system bit error rate (BER) is high. In order to reduce the effects of MUI,(More)
An adaptive MIMO detection algorithm for LTE-A system which is based on sphere detection is proposed in this paper. The proposed algorithm uses M-algorithm for reference to remove unreliable constellation candidates before search, and the number of constellation reservation is adaptively adjusted according to SNR. Simulations of LTE-A downlink show that the(More)