TD-SCDMA系统中GPS失步对网络性能的影响2.docVIP

TD-SCDMA系统中GPS失步对网络性能的影响 ???????????????????????????????????????????????????????????????????????????????????????????????Impacts of GPS Loss of Synchronization on TD-SCDMA Network Performance 2010-01-29 ??????作者:姬舒平,刘志坚,董晖 英文摘要:There often occurs Global Positioning System (GPS) loss of synchronization in Time Division Synchronous Code Division Multiple Access (TD-SCDMA) system because GPS signals may be disturbed by other system signals and sheltered from some buildings. Long-time loss of synchronization will lead to time deviation between NodeBs. When this time deviation is big enough, neighboring cell searching of mobile phones and intercell handover may fail and Downlink Pilot Time Slot (DwPTS) interfere with Uplink Pilot Time Slot (UpPTS), which will make network quality bad with handover failure, call dropping and low call succeeding ratio. In such a case, user experience will be badly affected. With our tests and analysis, we find that the TD-SCDMA network quality has obvious decrease when the GPS loss of synchronization goes over 4 chips, that the mobile phone fails to search a neighboring cell when the loss of synchronization goes over 10 chips, and that there is little UpPTS interference in the first-circle and second-circle neighboring cells when the loss of synchronization goes below 16 chips. The study results show that the allowable GPS loss of synchronization should be below 4 chips in TD-SCDMA system.英文关键字:global positioning system loss of synchronization; TD-SCDMA; chip ? ? ? ??? 在3G三大标准中，CDMA2000和时分-同步码分多址(TD-SCDMA)均是基站同步系统，TD-SCDMA系统是全网同步系统，要求所有基站之间严格保持时间同步，小区间切换、漫游等都需要精确的时间控制，因此同步问题对于TD-SCDMA通信系统的重要性不言而喻。由于缺乏先进的网络同步技术，TD-SCDMA基站普遍采用全球定位系统(GPS)同步[1-14]。目前TD-SCDMA网络中，由于一些原因，基站无法收到GPS卫星信号，同步失效的现象。 ??? (1)GPS信号收到外界的干扰??? GPS工作频段为1 575 MHz，由于GPS信号从卫星发射到地面之后，已经非常微弱，所以很容易受到外界干扰的影响，很多因素都会对GPS信号造成干扰，比如外太空太阳耀斑的干扰、电离层和大气环境的干扰、雷电等异常天气的影响等。在存在干扰的情况下，接收机接收卫星的信号质量会变差，信噪比降低，误码率上升，某些时候就会导致接收不到卫星信号。 ??? (2)工程施工原因??? 在现实大规模建站时，如果GPS天线安装位置附近存在遮挡或者施工工艺问题造成馈线阻抗过大