Joint PHY-MAC cross-layer design in wireless ad hoc networks

This work deals with joint PHY-MAC cross-layer designs in wireless ad hoc networks. The goal of a joint design is to exploit the advantages of the respective physical layer technique regarding multiple access interference suppression. To this end, an appropriate MAC protocol design is required that meets the specific needs of the underlying physical layer technology. Within this work, the physical layer technologies investigated are multiuser detection at the receivers, power control at the transmitters, and MIMO multiple antenna signal processing technologies. The work investigates existing cross-layer designs for all specified physical layer technologies with respect to their practical functionality. The first part of this work presents an in-depth comparison of power control based cross-layer designs and multiuser detection based cross-layer designs. While power control suppresses multiple access interference at the transmitters, multiuser detection cancels multiple access interference at the receivers. It could be shown that power control based cross-layer designs generally suffer from strong disadvantages compared with multiuser detection based cross-layer designs, if applied in ad hoc networks. The second part of this work presents newly developed protocols that meet the specific requirements of MIMO signal processing technologies as physical layer strategy. The proposed channel Information Exchange-MAC protocol avoids multiple access interference by a combination of beamforming and spatial nulling. In contrast to this protocol, the Fully Distributed Spatial Multiplexing-MAC protocol exploits the multiple antennas by spatial multiplexing to avoid multiple access interference and to transmit multiple streams in parallel. Both protocols avoid known disadvantages from existing approaches and are fully applicable in fading environments.