| With the development of communication system, the high date rate traffic plays more and more important part in future communication system, the high date rate traffic is characterized by the uplink rate is asymmetric to downlink rate. Furthermore, with increase of transmission rate, the power is also enhanced and the impact on human and environment is growing. By calculation it shows that: under the restriction of electromagnetic radiation, the uplink transmission rate is limited; the downlink rate is much higher than that of uplink.To adapt to the asymmetric characteristic of future communication system, the problem of TDD (time division duplex) technology when supporting asymmetric transmission is analyzed in this article. TDD can allocate the slot of uplink and downlink dynamically according to traffic conditions, but it introduces the problem of crossed timeslot interference. Different from the. topic of the crossed timeslot interference in TDD\CDMA system which was well analyzed, the disadvantage of crossed timeslot interference in TDD\OFDMA system is analyzed in this article. And the scheme based on isolated area is put forward to solve this problem which can control the interference of the crossed timeslot and reduce the effect caused by synchronization errors.Besides TDD technique, frequency division duplex (FDD) is also analyzed in this article. A novel AFDD (Asymmetric Frequency Division Duplex) technique is put forward in this article. AFDD allocate the uplink (downlink) bandwidth according to the service circumstance, it divide the uplink (downlink) frequency into several frequency points, all the uplink (downlink) frequency points make up uplink (downlink) frequency pool, each cell use the frequency points dynamically according to the actual service circumstance. The performance of AFDD\CDMA and AFDD\CDMA system is analyzed in this article, it show that: AFDD technique can improve the system's capacity and efficiency of frequency resource. |
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