| Wireless Local Area Network(WLAN) is the outcome that the computer networks combine the advantages of wireless communication technique in 90s 20th century. It provides convenient way to make communication mobilization and personal and multimedia. In order to gain high data rate and combat multi-path fading, Orthogonal Frequency Division Multiplexing (OFDM) technique is applied. This technique is the combination of multi-carrier modulation (MCM) and frequency shift key modulation (FSK). It divides the broad-width channel into a lot of independent and orthogonal sub-channels. The date is parallel mapped and modulated into these sub-channels, which increases the OFDM signal period. And it reduce the deterioration of Rayleigh fading.This thesis makes profound research and analysis on WLAN communication system based on OFDM. And discusses some viable design.In second section, the structure of RF receiver used in WLAN and its performance related specification is discussed. The IQ circuits and signals unbalanced affects to the system performance are analyzed in detail. Then presents the derivation of the relationship that exists between the phase noise of local carrier and the demodulated OFDM signals. And explain how to test I/Q circuit unbalance and how to settle IQ signal difference time delay in application.In chapter 4, thesis dwells on the structure, theory and filter characteristic of the PLL. And analyze PLL circuit characteristic how to affect the phase noise of out frequency.In chapter 5, the design of oscillator is discussed. First introduced the condition of how to make circuit oscillate and keep stabilization. And compared the advantage and shortcoming of design oscillator with S parameter or Bessel Function method. Finally design a Colpitts oscillator with ADS and analyze its performance.All in all, this thesis introduces the effect of key module on WLAN system capability. And discusses how to improve its performance and how to resolve design difficulty. |
PDF Full Text Request