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In a typical wireless LAN application exploiting the OFDM technology, the preamble is usually used to acquire the channel state information in front of data payload. However, if the length of the frame is short, the bandwidth efficiency is restricted by the overhead due to the frame. For such an application that the length of the frame is long, we have to take into account the time-varying effect...
We study a cyclic prefix (CP) assisted method used for the uplink of code division multiple access (CDMA) systems in which the code despreading is performed in front of the frequency domain equalizer (FDE). The main advantage of the new despreading scheme is that the required points of discrete Fourier transform in the FDE are significantly reduced compared to the conventional CDMA scheme. Although...
In some frame-based OFDM applications such as WLAN and WMAN, the channel estimation is accomplished through the aid of the preamble. By means of the preamble, the estimated channel is only well applied under the assumption of a static channel status within the frame. If we consider a time-varying channel status in those applications, the channel tracking has to be performed without the aid of pilots...
The multi-access orthogonal frequency division multiplexing (OFDMA) technology has drawn a lot of attention in next generation wireless mobile communications. It is well-known that carrier frequency offsets in OFDMA systems can destroy the orthogonality among subcarriers and produce intercarrier interference (ICI) and multiuser interference (MUI). In our previous works, we proposed a common carrier...
One primary challenge in an OFDMA system is that different carrier frequency offsets (CFOs) simultaneously present at the transmitters. In spite of some peripheral synchronization methods already adopted for coarse estimation of CFO values, residual CFOs can exist and degrade system performance at the OFDMA receiver. A popular post-processing method, called the CLJL scheme, can be used to reduce the...
An interleaved OFDMA system with a new carrier frequency offset (CFO) correction scheme is studied. The previous proposals for OFDMA compensating for the CFO effect at the OFDMA receiver can remain multiple access interference (MAI). Although some MAI cancellation schemes have been proposed to mitigate the MAI effect, we found that the minimum mean square error (MMSE) performance of demodulated signals...
The effect of a common carrier frequency offset (CFO) at the OFDMA receiver is explored in this paper. In conventional CFO compensation methods for OFDMA systems, the CFOs are usually compensated for by directly eliminating the intercarrier interference (ICI) caused by the residual CFOs for individual users. Besides the ICI, the multiuser interference can be also introduced at the OFDMA receiver due...
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