| This paper first analyse how power- ontrol works and its use in CDMA system. CDMA achieve the change from time devision multiple address to code multiple address, allow one frequency to be used time after tme in different section, increase the capacity of the system consumedly. The system distinguish every user with expanding-frenquency code , so it is the most important to use expanding-frenquency code which is correlation oneself ly and not correlation commutatively. But the number of this ideal expanding-frenquency code is limited , and enven the ideal expanding-frenquency code will not be plumb each other after they go through many different pathway , so reduce multi-adress interfere between the user and restrict the increasing of the system capability. multi-adress interfere mostly behave as the Far-Near effect in up way and the Edge effect in dowen way. The power-control technology must be used to control the transmit power and reduce multi-adress interfere . Originally only opend-loop power-control technology is used , subsequently cosed-loop power-control technology is used to advance the control precision consumedly. but there are still some problem . (1)the transmit speed of the power-control command. (2)the peak value of the power. (3)the power excursion in dowen way. (4)the descend of the system capability conduced by nonideal power-control. The most important is that power-control can't wipe off multi-adress interfere indeed , it is just passive to settle isuue .Multi-user detection is only a effective means to counteract multi-adress interfere. This paper then analyse how Multi-user detection works and its use in CDMA system. Multi-user detection think that the statistic characteristic of multi-adress interfere is different from the white Gauss noise , so it can be estimated and wiped off. Thare are some kind of Multi-user detection technology. (1) the optimal Multi-user detector.(2) the linear Multi-user detector. (3)the non-linear Multi-user detector. the blind Multi-user detector is lucubrated widely these year because it can reduce the calculate complexitygreatly. Multi-user detector has its localization too. one is the complexity , the second is the delay made by calculate, on the side Multi-user detector can only clear up the multi-address interfere in one section but between sections.Actually , thare is internal affiliation between Multi-user detector and power control, they interact exch other . All the Multi-user detector are restrained by near-far effect, power control is needed even Multi-user detector has been used. More over faultly power control can depress the capability of Multi-user detector, on the other hand , perfect Multi-user detector can cut down the request for power control. So we can take the combine of two kind of technology into account . The research has being made but not gain evidence advance. WCDMA' s adhibiting of multi-operation bring higher request for both power control and Multi-user detector. Along with the construction and developing of 3G in our country, continue to research the combine of the two kind of technology in WCDMA system to increase furthest the capability is actual.This paper analyzes their operation principle and point out their relations and bring forword a kind of power control arithmetic base on LSCMA Multi-user detector .Emulation can prove that when the system capability increase , the constringency speed of the arithmetic is more higher then that only use power control. |
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