HybridDCF Supporting HybridAntennas inaWLAN

Hybriddistributed coordination function (H-DCF), a modified mediumaccess control protocol ofIEEE802.11, is proposed inthis papertosupport hybrid antennas, i.e., smart adaptive arrayantennas andnormalomni-directional antennas inoneWLAN.Nodesequipped withsmartantennas follow directional DCF(D-DCF) andnodesequipped withomni- directional antennas follow DCF.InD-DCF,before sending any data-frames, thesender andreceiver nodetransmit itspilot sequence respectively bymeansofomni-directional RTS/omni- directional CTS(ORTS/OCTS) handshake mechanism. Basedon thepilot, thedirectional beamcanbeformedbythesmart antenna. Thenthesender cantransmit itsdata-frame inthe directional mode.Basedonvirtual carrier sensemechanism, the omni-directional transmission between thesender andreceiver cannotinterfere withtheother nodes. Whenthesender and receiver communicate inthedirectional mode,theother nodes cancontend thechannel tosendtheir data-frames. Hence, D- DCFsupports spacedivision multiplexing. D-DCFis compatibility withDCFbymeansofORTS/CTSorRTS/OCTS mechanism. Moreover, D-DCFsupports service differentiation. Smartantennas haveahigher priority toaccess channel than normalantennas bydifferentiating thecontention parameters, suchasinitial contention windowsize, themaximumbackoff stage andretry limit. A simple analytical modelispresented to computesaturation throughput andbandwidth. Simulation results showthatH-DCFcansupport hybrid antenna system effectively andprovide muchhigher network throughput, lower delay andjitter thanDCFdoes, andthattheanalytical modelis valid.