功率動態範圍有限蜂巢式行動通訊系統之功率控制

Abstract

蜂巢式無線通訊系統應用頻道重用技術，因此共頻干擾被視為系統容量之 主要限制。欲克服此一問題，可於傳輸介質上設計精密之調變/解調架構 ，或於基地台上採用指向天線等。另一種方式為，在系統中，適當控制各 基地台傳輸端之輸出功率，使得除滿足本身訊號品質要求外，並儘可能減 低對於其他通訊鏈結造成之干擾。 應用結合特徵值-特徵向量計算、以 上/下限(UB/LB)法則使功率調整於有限之動態範圍內、當調整後功率無法 使系統滿足CIR要求時鏈結移除之Z/MI-法則作為功率控制方法。就同一問 題，亦可將其視為線性聯立不等式(SLI)求解。因此，吾人將其轉換為線 性規劃(LP)問題後，判斷其解是否存在。若是，則找出其中一組作為各基 地台傳輸端輸出功率；否則採用Z/MI-法則移除一鏈結，亦即取消一不等 式，再對此降階SLI問題求解。經移除若干鏈結後，若功率控制問題有解 ，由於結合UB/LB與Z/MI之架構盲目地調整，可能使產生之功率不為功率 控制問題之適當解，造成非必要之鏈結移除。另一方面，只要存在功率控 制解，於LP-架構下必可找出其中一組，因此就同一移除鏈結序列而言將 為較佳之選擇。 The presence of cochannel interference because of frequency reuse is seen to be a major problem in cellular radio systems. To overcome this problem on the physical medium, one has to either design an elaborate modulation/demodulation scheme or adopt directional antenna on base stations. On the system level, one may properly control the transmitter powers to alleviate cochannel interference. In this thesis, we propose a power control algorithm based on the eigensystem, upper-bounded( UB)/lower-bounded(LB) power adjustment and communication link removal to satisfy both the CIR requirement for all the mobiles and finite power range constraint for all the base stations. A different approach is to consider the problem as finding the solution of a set of simultaneous linear inequalities (SLI). Such a problem can be transformed into the linear programming (LP) problem to see if it is solvable. If so, find a set of solutions to determine the transmission power of each base station. If this problem is found unsolvable, remove one link, which means cancel an inequality, and solve the reduced SLI problem. For the scheme which combines UB/LB and link removal algorithms, it may happen that a link is removed unnecessarily. For the LP-scheme, however, the solution can always be found as long as it exists. We also compare the performance of these two schemes.