Companding techniques for PAPR reduction of OFDM systems / Chung-Ping Liaw.

[[abstract]]在無線通訊系統中，隨著時代科技的進步，系統的傳送速率被要求愈來愈快。而正交分頻多工技術是一種多重載波調變系統，有很好的無線傳輸高資料率使用在正交頻率通道，而且可有效地抑制ISI導致多重路徑衰減在無線通道上。 但是正交分頻多工技術有一個重大缺點，就是傳送信號有很高的均峰值(PAPR)，使得系統放大器需要較大的線性區域範圍，避免產生非線性失真，導致位元錯誤率增加以及頻譜外散的現象。不過，操作線性區域變大，卻也浪費了放大器的使用效率。 因此，在本文中，我們主要比較三種訊號壓縮技術以解決正交分頻多工系統的高均峰值問題。首先我們分析μ-law和A-law壓縮技術，並推導出當量化誤差最小時的最佳壓縮係數。然後也分析了我們所提出的Hyperbolic Tangent transform壓縮技術，以及討論它相較於μ-law和A-law壓縮技術的優缺點。 再者，因為Hyperbolic Tangent transform在電路的設計上，可以輕易的被實現。因此由我們研究的結果顯示Hyperbolic Tangent transform壓縮技術是一種可行的方法。[[abstract]]In wireless system, and time of technology, the system is required faster speed rate of transmission. Orthogonal frequency division multiplexing is a kind of multi-carrier modulation system. It is good for high data rate in orthogonal frequency channel, and it is effective to reduce multi-path fading on wireless channel. However, there is a main drawback in OFDM system, where the signal is higher PAPR. The amplifier needs larger linear range in order to avoid producing non-linear distortion which leads to increase bit error rate and spread outside band, but it will enlarge linear range of operation, and waste the efficiency of amplifier. In the thesis, we focus on comparing the three companding techniques. We first analyze the -law and A-law companding techniques by deriving the optimal companding coefficients to attain the minimum quantization errors. We then analyze the proposed hyperbolic tangent transform and discuss its advantages and disadvantages in comparison with the -law and A-law methods. Furthermore, the hyperbolic tangent transform can be implemented practically in analog circuit design. It is the fact that it can be implemented very simply. According the result of our research, that hyperbolic tangent transform companding method should be a feasible method