China Railway has entered the high-speed era. It is expected that China's high-speed railway in 200km / h will exceed 18,000 kilometers. How to provide users with excellent service in the mobile communication network of high-speed mobile environment, mobile operators have been conducting research to solve the problem since the dawn of high-speed rail.
Conventional CDMA network coverage and planning compared to high-speed rail plan covering a certain degree of particularity. Identify the key issues covered by the high-speed rail in order to achieve more accurate in depth coverage of high-speed rail along fine optimization. As shown in Figure 1.
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Significance of high-speed rail coverage Figure 1
High-speed rail covered four iconic factor
HSR network coverage mainly in the four flags factors: Doppler shift, the vehicle body penetration losses, coverage area, and problems terrain switching diversity.
Doppler shift
Doppler frequency shift means in question is moving at a high speed, the frequency of the signal receiving side shift will occur, resulting in a base station and a receiver for coherent demodulation performance decreases.
◆ impact on the receiver
CDMA uses coherent demodulation, and requires local carrier demodulation carrier frequency of the received signal with a receiver, a carrier frequency jitter has an effect on the demodulation performance of the receiver; the same time, 1X CSM6700 Qualcomm chip, DO RevA CSM6800 Qualcomm chip, the maximum value of the frequency shift are 1440Hz and 960Hz. The formula for calculating the Doppler shift receiver allows maximum moving speed of 972km / h and 648km / h. This speed is much higher than the maximum operating speed of high-speed railway, the demodulation chip tolerances to meet the requirements.
◆ impact of base stations
Due to the presence of Doppler shift, resulting in reduced performance of coherent demodulation of the base station and mobile. It could be considered in the original Eb / Nt 3dB increase in the value of the link budget.
Switch problem
It refers to high-speed mobile switching problem more dropped calls leading to switching, the switching required is much higher than an ordinary scene.
In the handover without changing the size of the area, the faster the switching time of the terminal through the smaller area. Thus, when the moving speed of the terminal is fast enough, so that through the time of the switching system processing region is smaller than the minimum delay soft handover, this time will lead to a dropped call generation. When high speed railway coverage base station parameter to be considered a minimum set of handover region, to meet the demand for high-speed trains in the high-speed switching operation. Size of the smallest switching region may be calculated from the size and speed of the train according to the soft handover delay. Usually soft handoff delay take 300ms, therefore, the minimum size of the handover region depends on the moving speed of the train.
The current high-speed rail designed maximum speed of 350km / h, is calculated according to the formula 29m minimum soft handover region.
Shenyang-Dalian high-speed rail CDMA coverage Case
We will cover the Shenyang-Dalian high-speed CDMA wireless network research, mainly for covering the user's high-speed rail passenger line, including passengers waiting on the station and high-speed trains.
Shenyang-Dalian high-speed rail profile
Shenyang-Dalian high-speed rail throughout Tieling, Liaoning Province, Shenyang, Liaoyang, Anshan, Yingkou, Dalian six cities, a total length of 553km. For the double line electrified railway, the average speed of 200km / h or more. 2011 opened to traffic. Shenyang-Dalian high-speed rail has a total of 15 stations.
Shenyang-Dalian high-speed rail design uses a high-speed train to Changchun Railway Vehicles Company and French company Alstom joint efforts CRH5 models manufactured 8 grouping, a total length of 211.5m, the maximum body width 3200mm, high vehicle 4270mm. , Reading the full text, the technology area
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