Based On The Multi-channel Mac Protocol Under The Ofdma System Research

Orthogonal frequency division multiplexing (OFDM) technology began to beapplied at the1960s, whose complex structure restrain it from further usage but mainlyin military field. In the1970s, as the discrete Fourier transformation (DFT) realized themulti-carrier modulation, OFDM stepped further into applications that are morepractical. With the development of digital signal processing and high speed hardware,OFDM became widely received by ADSL, VDSL and HDTV systems. After1990s itreached the area of broadband transmission under wireless channel condition.Under one OFDM system, a certain period of sub carriers can all be assigned toone user. Whereas in OFDMA, which developed from OFDM, different sub carriers canbe assigned to different users at a time in such a manner that the users with different subcarriers can send their packets within each other’s sending range at the same timewithout any interfere, theoretically. This formed a multi-channel network where eachnode is equipped with multiple half-duplex radio devices. A Pipelined OpportunisticMulti-channel MAC (POM) protocol is proposed, which implements the function ofmulti-channel access and multi-rate transmission. From the paper it can be observed thatthe protocol improves the channel efficiency and make the MAC layer work in apipeline style by dividing its control overhead into band-dependent andband-independent. Using NS2simulating tools we design and realize the multi-channelmodule under OFDMA system and proved the POM-MAC’s improvement on channelefficiency, packets delay, energy consumption and fairness.The paper have the following achievements: First, according to the features ofOFDMA system, we transform it into a multi-channel network with multiplehalf-duplex radio nodes, adding the function of rate control. Besides, we introduce anovel pipelined channel accessing and scheduling algorithm, which carries two phasesof backoff stages using CSMA/CA under OFDMA technology and the particle filter,respectively. And finally realize a better channel efficiency and guarantee the userfairness. Second, based on the above algorithm, a multi-channel MAC protocol usingparticle filter technique is proposed. At last the success demonstration of POM-MAC with the simulating tools NS2, which illustrate the improvement of channel efficiency,，and access delay.