在直接序列分碼多重存取(DS-CDMA)通訊系統中，每一位使用者擁有各自獨特的展頻碼來做為使用者之間傳輸的保護以及區分，進而達到更佳的頻譜使用效益，使其在區域無線網路中有非常高的傳輸能力。然而，由於展頻碼的不完全正交及多重路徑有著延遲的問題，導致了多重路徑干擾(MAI)，而在微細胞通訊系統中，此現象(MAI)將會限制通訊系統的品質以及使用者的容量。功率控制被提出來對付這個問題(MAI) ，利用功率的調節，以克服干擾的影響，達到較有效益的通訊品質。
本篇論文提出ㄧ個狀態空間模型，利用狀態回授及 最佳預測器追蹤指定的功率對干擾雜訊比(SINR)。由於要達到 最佳預測控制太困難及複雜，因此將此問題轉換為次最佳化預測，此次最佳預測問題可推導成線性矩陣不等式(LMI)，且由Matlab LMI 工具函式可以容易的得到其解。

Power control is an important topic in direct-sequence code division multiple access (DS-CDMA) cellular mobile radio systems, to achieve higher communication link quality
and better system capacity under fading, noise, and interference. In order to track a desired signal-to-interference-plus-noise ratio (SINR) under transmission delay, multiple access interference (MAI), channel fading and noise, a robust state feedback control via a desired pole (eigenvalue) placement and an L1 optimal prediction is proposed for the power tracking control of CDMA systems. The L1 predictor is to predict the tracking error to compensate the effect of round-trip delay, such that the peak of prediction error due to the uncertainties of channel fading, interference, and noise is as small as possible.
Then the optimal L1 predictor design problem is transformed to a suboptimal prediction problem by minimizing the upper bound of L1 norm of tracking error of dynamic system and solving the eigenvalue problem (EVP) under some linear matrix inequality (LMI) constraints. The Matlab LMI toolbox can be applied to efficiently solve the EVP via convex optimization to achieve a SINR tracking design via L1 optimal prediction scheme.

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