In orthogonal frequency division multiplexing （OFDM） systems, spectrum notch can be generated to mitigate interference to other narrow-band services by turning off corresponding subcarriers. However, the inter-carrier interference may limit considerably the produced notch depth. Another problem in OFDM is the high peak-to-average power ratio （PAPR）. In this paper, a technique combining subcarriers precoding with tone reservation is proposed to deepen spectrum notch and simultaneously reduce peak-to-average power ratio. Simulation results show that this presented joint algorithm can produce satisfied results to solve these problems at the expense of a moderate loss in bit error rate （BER） performance.
ZHAO Cheng-lin LIU De-qiang SUN Xue-bin JIANG Ting
Impulse systems do not undergo the multi-path destructive interference that manifests itself as Rayleigh fading prevalent in continuous wave systems, but rather show up as delayed replications of the direct impulse. In this paper, the model for impulse signals propagation over a plane earth is proposed. The condition for direct pulse and its replication overlapping each other was investigated. The model described here also takes into account the polarization of the transmission signals and the reflection coefficient of the plane, which was always neglected by previous approaches. The simulation result shows that the path loss can be characterized as 3 zones with different path loss exponents as the distance between transmitter and receiver (T-R) increasing.
