Capacity enhancement by virtual subcarrier assignment for OFDM-based wireless systems

The capacity of wireless systems can be enhanced by means of effectively utilizing "spatial resource". However, even if transmitters and receivers are equipped with adaptive array antennas, a special training symbol is required in the preamble of a signal burst to distinguish one user from the other users. The distinguishability of users, the re-solvability of received paths and the array beamforming capability depend much on the auto- and cross-correlation properties of the training symbols. This paper proposes a novel spatial filtering technique for orthogonal frequency division multiplexing (OFDM) signals called "virtual subcarrier assignment (VISA)". Here, the virtual subcarrier, which is also called "(sub)-carrier hole", is a subcarrier which is not used for data transmission, in other words, transmits zero-information. VISA can easily achieve a space division multiple access (SDMA) and is applicable for already-existing OFDM-based wireless systems such as IEEE 802.11a and HIPERLAN/2.