The Lower Bound of Open Loop Transmission Power Control Error in DS-CDMA System

Eisuke KUDOH  Isao OKAZAKI  Shigeaki OGOSE  

IEICE TRANSACTIONS on Communications   Vol.E80-B       pp.1805-1809
Publication Date: 1997/12/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Category: Mobile Communication
DS-CDMA,  transmission power control,  open loop,  wideband transmission,  

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TPC (transmission power control) can compensate the near-far problem and so is a key technology of DS (direct sequence) -CDMA (code divison multiple access) systems. There are two kinds of TPC. One is closed loop and the other is open loop. In practical systems, both methods are used to compensate the variation in reception signal level. However, adoption of one simple TPC scheme is preferable from the viewpoint of transceiver configuration at the BS (base station) and MSs (mobile stations). Reception signal variation in wide-band DS-CDMA systems is shallower and we have the possibility of using only open loop as the TPC method. To evaluate the TPC accuracy of open loop, it becomes important to estimate the lower bound of TPC error because TPC error directly influences user capacity. This paper evaluates the lower bound of open loop TPC error by a theoretical analysis and laboratory tests; both results agree well. It is found that as the average power difference between paths increases, the lower bound of open loop TPC error increases. Ir is also found if the number of paths increases, the lower bound of open loop TPC error decreases. If the number of paths is 10 and the power difference between the nearest paths is less than 0.2 dB, the lower bound of open loop TPC error is larger than 1 dB. When the TPC error is larger than 1 dB, the reduction in user capacity is above 30%.