Hybrid Correlatively Encoded Multi-h CPFSK

[[abstract]]在這篇論文中，我們考慮一種數位式的調變方式，它叫做多值調變係數連續相位頻率偏移鍵 ( multi-h CPFSK )。此多值調變係數連續相位頻率偏移鍵是一種連續相位頻率偏移鍵的特殊個案。它是利用調變指數做週期性的變化，且信號的相位是連續的。當信號的相位被限制為連續的，此調變器必須有記憶性。此記憶的特性是表示信號的相位從這區間到下一個區間時相位是呈現連續的現象。並且，為了加強多值調變係數CPFSK的功率效能 ( power efficiency )，一種相關性編碼應用於多值調變係數 CPFSK 信號的技術可有效的去增加最小歐式距離，尤其是應用於較小的平均調變係數。較小的平均調變係數意味著有較窄的頻寬。此外，一種混合式相關性編碼應用於多值調變係數 CPFSK 信號的技術也將被介紹。它是結合兩種不同的編碼規則去獲得較大的不可避免的合併區間，也就是增加限制長度 ( constrain length )。 儘管有較大的不可避免的合併區間並不是代表有較大的歐式距離，但是無論如何，這也表示可能有較好的機會可提供較大的最小歐式距離 ( minimum Euclidean distance )。在相關性編碼中，它是靠著現在的資料符號 ( data symbol ) 和 L-1 個之前的資料符號去決定編碼的信號。在這裡 L 是一種整數型態的值。 在 L = 2 的情況下，數值結果證明這新的混合式相關性編碼方法可勝過先前相關性編碼的技術。並且，在 L = 2 情況下的系統比在 L = 3 下有較低的複雜度。並且，相關性編碼多值調變係數CPFSK的頻譜特性將會被討論在這篇論文中。且在公平的比較下，我們會秀出相關性編碼多值調變係數CPFSK有較低的平均調變係數。最後，在論文中的表格列出混合式相關性編碼中較好的碼可達到較佳的編碼增益。[[abstract]]In this thesis we consider a class of digital modulation techniques, called multi-h continuous phase frequency shift keying ( CPFSK ). Multi-h CPFSK is a special form of CPFSK that employs periodically variable modulation indexes, and the phase of the multi-h CPFSK signal is continuous. The multi-h CPFSK is a modulation with memory. The memory results from the phase continuity from one signal interval to the next. In order to enhance power efficiency of multi-h CPFSK, a correlatively encoding approach is known to be an effective way to increase the minimum Euclidean distance of multi-h CPFSK, especially for smaller average modulation index. Small average modulation index usually means narrower bandwidth occupancy. A new correlatively encoding technique [37,38], called hybrid correlatively encoding, is constructed to improve previous work. The approach is to alternatively employ different correlative encoding rules to multi-h CPFSK, and with these rules it is possible to achieve larger inevitable merging interval. Although, larger inevitable merging interval does not mean larger Euclidean distance, however, it is known that larger merging events may have better chance to produce larger minimum Euclidean distance. The correlatively encoding rule is a function of the present data symbol and previous L-1 data symbols. Numerical results verify that this new proposed approach consistently outperforms previous works for systems with L = 2. It is also found that systems using L = 2 is better than L = 3 with lower receiver complexity. Moreover, the spectral properties of correlatively encoded multi-h CPFSK are discussed. We show that correlatively encoded multi-h CPFSK has a very low average modulation index and fair comparison should be based on this new observation. Tables of good codes are given and significant coding gains are obtained compared to previous works