Bandwidth-adaptive MIMO OFDM for dynamic spectrum access networks

In a Dynamic Spectrum Access Network (DySPAN), nodes opportunistically make use of white spaces for transmission. The frequencies and bandwidth of available white spaces will of course vary in these networks. Hence a DySPAN transmitter will need to be capable of frequency agile and bandwidth-adaptive transmissions and a DySPAN receiver will need to accordingly respond to any changes made by a transmitter. This paper introduces a novel space–time (ST) scheme that facilitates the detection of bandwidth-adaptive transmissions without the need for a control channel. The scheme is based on orthogonal frequency-division multiplexing (OFDM) and ensures a high diversity gain. By using multiple transmit antennas, the proposed scheme also allows the application of ST block-coded OFDM (STBC-OFDM) which not only increases the robustness against bit errors but also preserves the spectral efficiency of the system. For frequency acquisition and bandwidth estimation, the receiving nodes in the DySPAN exploit the cyclostationary signatures intentionally embedded in the OFDM signals using a small set of subcarriers. In this way, communication links are established autonomously without any need for control channels.The ST scheme in this paper carries out appropriate multi-antenna transmissions of the signature information on the aforementioned subcarriers, which result in highly robust cyclostationary feature detection over the frequency selective multipath fading channels. Moreover, lower bit-error rates (BERs) are attained by applying STBC-OFDM to the data symbols on the rest of the subcarriers. Both feature detection and the BER performance are improved further by deploying multiple receive antennas. Detailed performance comparisons are presented by using simulation results.