LANs(Wireless Local Area Networks) have emerged as a powerful architecture capable of meeting the needs of next generation broadband wireless communications. The IEEE 802.11a 5 GHz WLAN standard employs OFDM in its physical layer. The OFDM is a kind of transmission method that provides high-speed data transmission by converting serial data into parallel first, and then modulates them into a carrier orthogonal to each datum. This is the standard of high-speed wireless LAN, and is also the standard of digital broadcasting in Europe. Recently, A new method of transmission, CIMA was developed, which uses the orthogonality of CI signal and provides phase offset to each carrier. CIMA excels any other conventional methods using multi-carrier in performance by increasing the efficiency of the frequency spectrum via reiteration the orthogonal multi-carrier.
The OFDM processes data in high-speed and increases the efficiency of frequency spectrum. However there is a weakness that the performance of the system will become worse, but if time delay in transmission channel is greater than the capacity of the OFDM's guard band. Moreover, due to the fact that carriers with orthogonality are reiterated one another in the OFDM, There is a problem that PAPR will become bigger when they are in-phase. In order to improve the defects, CI-OFDM that incorporates the CI signal into OFDM is has been proposed. While each bit is modulated into its own carrier in the conventional OFDM, each bit in the CI-OFDM is modulated into a whole carrier. Data bits transformed into identical carriers are divided by phase offset. Because the signals in the CI-OFDM have phase offset, a in-phaseing condition is reduced and PAPR can be significantly improved. For the reason, the performance of CI-OFDM is highly improved compared with the conventional methods. CI-OFDM improves the deficiency of the traditional OFDM and raises the system considerably. Therefore, if the CI-OFDM mode is applied for upcoming wireless multimedia communication, it will make it possible to achieve not only high-speed data transmission, but also high-performance communication.