個人行動通訊系統高斯濾波最小移鍵數據機架構研究

Abstract

這一篇論文研究的是高斯最小移鍵 (GMSK) 調變技術。GMSK 的優點是頻 寬利用效率高，而且其振幅保持固定因而可以使用效率高的 C 類放大器 。除此之外，GMSK 可以用簡單的非同調解調也可以用複雜的同調解調。 所以 GMSK 非常適合應用在行動與室內無線通訊方面。這一篇論文討論了 不同的傳送機和接收機的架構， 特別是直接降頻 (Direct Conversion) GMSK 數據機的架構以及其設計時需要克服的問題。 這一篇論文同時提出 了一種新的 GMSK 同步演算法， 這個演算法運用鑑頻器 (Frequency Discriminator) 和快速傅利葉轉換 (FFT) 很快的估計出頻率偏移和訊 號時序不準度， 進而做訊號時序調整和頻率偏移補償。此演算法相當的 簡單而且可以用 VLSI 技術加以製作。GMSK 在加成性白色高斯雜訊和雙 路徑半靜態 (Two-Path Quasi-Static) 頻道的效能分別以電腦模擬的方 式求出。 In this paper we investigate Gaussian-Filtered Minimum Shift Keying（ GMSK ）modulation which is suitable for mobile and indoor communications. GMSK, as we know, is a bandwidth efficient digital modulation scheme and satisfies the requirement of constant envelope such that it is also power efficient. In addition, coherent or noncoherent detection can be applied to GMSK. Various transmitter realizations and receiver detection schemes are discussed and the direct conversion GMSK modem architecture is emphasized. This architecture is attractive recently because of its good integration capability and the ease for DSP implementation. Finally, we suggest a new algorithm for joint carrier and bit synchronization. This algorithm uses frequency discriminator and fast Fourier transform（ FFT ）to estimate the frequency offset and sample timing error quickly, and then uses these estimation to correct the sample timing error and compensate the frequency offset. This algorithem has the advantage of simple and can be implemnen ted through current VLSI technology. It is proved in this paper that this algorithm is an approximately unbiased estimator of carrier frequency and sampling time instant and the simulation results shows the superiority of the algorithm. The performance of GMSK(BbT=0.25 and 0.5) in AWGN and a two-path quasi-static channel are derived using computer simulation.