Cooperative diversity performance for OFDM transmission over partially jammed channels

Cooperative diversity is a transmission technique, where multiple terminals share their resources to form a virtual antenna array that realizes spatial diversity gain in a distributed fashion. In this paper, we focus on a performance evaluation for orthogonal frequency division multiplexing (OFDM) transmission in cooperative networks under partial-band jamming (PBJ) environments. We present a bit error rate (BER) analysis for a cooperative diversity system with amplifying-and-forward (AF) relays over partially jammed Rayleigh fading channels. In addition, a simple jamming mitigation technique, called relay-based sub-band shifting method, is proposed. Through this approach, each sub-band of the amplified OFDM symbol at the relay can be changed by the predefined shifting rule of each relay, and the jamming effects at the destination are partially removed. Simulation results show that the proposed method improves significantly the BER performance at a low signal-to-jamming ratio.     

A new preamble-based cell search algorithm for asynchronous MC-CDMA systems

In this paper, we propose a new cell search scheme for asynchronous multi-carrier (MC) CDMA systems. For initial cell search, the proposed scheme contains detection processes for symbol timing, fractional frequency offset, frame timing, cell-specific code group, integer frequency offset, and cell-specific code. In order to accomplish faster cell search by diminishing the effects of noise and interference, a new preamble structure with power-concentrated repeated symbols is proposed and efficient detection algorithms for the above parameters are also proposed. Then, the performances of the proposed cell search algorithms are evaluated in a multi-cell environment with 19-hexagonal cell layout. The proposed method can search the desired cell site nearly twice as fast as the conventional method when the cumulative cell detection probability is 0.95.