| ABSTRACT |
3G networks basically have evolved from a circuit-switched cellular network, they have their own gateways to interpret IP from the backbone network, and have their own protocols and interfaces for the communication within themselves. To get over these problems, 4G networks are expected to become an all-IP based packet-switched system like the IP backbone network. An OFDM system, which is capable to deliver high data rates in highly dispersive channels and is thus believed as a good candidate of modulation schemes for 4G.
In case of mobile radio with time-varying multipath propagation, OFDM performance degrades due to the absence of frequency diversity. Frequency selective fading, which could lead to carriers used, being heavily attenuated due to destructive interference at the receiver. This can result in the carriers being lost in the noise.
The performance of OFDM systems is not only devalued by inter-symbol interference (ISI) but also by the loss of orthogonality between subcarriers and inter-carrier interference (ICI) if the carrier frequency offset is not counterbalanced correctly.
Coherent OFDM systems cannot perform well without proper channel estimation and channel equalization.
Moreover, a new scheme for channel prediction in OFDM system is proposed. The technique adaptively estimates the channel conditions and eliminates the need for the system to transmit a request message prior to transmitting the packet data. The ready-to-use channel will be occupied with a Pseudonoise (PN) code and use for transmission or else, it will be banned.
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