Home base station (FemtoCell) coverage solution
FemtoCell technology has the characteristics of efficient and flexible networking and low cost. It can be used to quickly expand network coverage, increase network capacity, provide users with a better business experience, and have broad application prospects. Network coverage in high-speed mobile scenarios, such as high-speed railways, has become an important part of 3G wireless network construction. Based on the research and analysis of network coverage in high-speed mobile scenarios, this paper proposes a solution for high-speed mobile scenario coverage using home base station technology. This solution can improve or solve the problems of mobility management, limited network capacity and carriage penetration loss in mobile coverage in high-speed railway scenarios, and effectively improve the service experience of end users in high-speed mobile scenarios.
introduction
TD-SCDMA is a 3G mobile communication system independently developed in China. After years of large-scale network construction, network coverage has become increasingly mature. In recent years, with the continuous development of domestic high-speed railways, wireless network coverage in high-speed mobile scenarios has become an important part of TD-SCDMA network construction. In high-speed mobile scenarios, end users are provided with seamless coverage and higher System capacity and data rate have become one of the major challenges in the field of mobile communications.
Relying on the 2010 Shanghai Science and Technology Commission Key Project (No.10511500402), the author conducted research and analysis on network coverage solutions in high-speed mobile scenarios, and proposed a solution for high-speed mobile scenario coverage using TD-SCDMA FemtoCell technology. This article includes the following chapters: The second section introduces the high-speed mobile communication scenario, and gives an analysis of the mobile communication traffic demand in this scenario, and introduces the difficult problems of network coverage in the high-speed scenario; the third section summarizes the current Some high-speed mobile scene coverage schemes; Section IV proposes a coverage solution based on FemtoCell, gives analysis of key technical issues, and gives details on the details that require further research; Section V summarizes the full text.
Introduction to high-speed mobile scenarios
High-speed mobile communication scenarios
High-speed railway as a safe, reliable, fast and comfortable, ultra-large capacity, low-carbon and environmentally friendly transportation method has become an important trend in the development of railways in the world. Up to now, the high-speed railways put into operation in mainland China have reached 6,920 kilometers, with the highest operating mileage in the world, and the high-speed railways under construction have reached more than 10,000 kilometers. High-speed railways from Beijing to Tianjin, Wuhan to Guangzhou, Zhengzhou to Xi'an, Shanghai to Nanjing and other high-speed railways with a speed of 350 kilometers per hour have been opened for operation, with the highest operating speed in the world. Shanghai's maglev high-speed railway has reached 431 kilometers per hour. The line scale and hourly speed of high-speed railways are constantly improving. High-speed mobile scenarios have become an important networking scenario for 3G mobile communications and attract more and more attention.
Compared with ordinary scenarios, mobile network coverage in high-speed mobile scenarios usually has the following characteristics:
a) End users in high-speed mobile scenarios are all concentrated in the car, and all users move synchronously with the train.
b) The user's handover and cell reselection in the wireless network are very concentrated, and the use of wireless network resources is sudden; frequent inter-cell handover and reselection in a short time have a certain impact on the network KPI index .
c) The high-speed movement makes the time for a user to pass through a cell very short. Signaling and service delay have a great impact on the user's mobile performance in the wireless network.
d) Car bodies in high-speed mobile scenes usually have large penetration loss: For the common frequency band of TD-SCDMA, the penetration loss of high-speed train cars is usually 15-20 dB, and that of Shanghai Maglev high-speed trains (up to 431 kilometers per hour) The penetration loss is between 30 and 35 dB. This puts higher requirements on the continuous coverage of wireless networks and terminal power consumption.
e) In high-speed mobile scenarios, the Doppler effect is obvious, and the resulting Doppler frequency offset has a greater impact on service quality.
f) In high-speed mobile scenarios, the potential demand for end-user data services is relatively large.
In the high-speed mobile scenario, wireless network coverage must be planned and designed in combination with the above characteristics to ensure the business needs of end users to the greatest extent and improve user experience.
Business requirements for high-speed mobile communication scenarios
With the expansion of domestic TD-SCDMA network scale and user scale, the demand for data services of TD-SCDMA terminal users has also shown a large upward trend, and end users potentially hope to get a better business experience in various environments.
For high-speed mobile scenarios, here is an analysis of end-user business needs based on a series of assumptions:
Assumptions: High-speed trains each have 16 cars, and each car has 50 passengers.
Passenger voice communication requirements: 16 & TImes; 50 & TImes; 0.02 & TImes; 0.8 = 12.8 erl
Among them, the mobile user penetration rate is 80%, and the traffic volume per user is 0.02 erl.
Passenger data communication requirements: 16 & TImes; 50 × 0.384 × 0.25 × 0.25 × 0.8 = 15.36 Mbps
Among them, the communication capacity of each passenger is 0.384 Mbps, the convergence ratio is 4: 1 (coefficient 0.25), the data communication utilization rate is 25%, and the mobile user penetration rate is 80%.
Taking into account the two-way travel, based on the calculation of up to 2 vehicles per cell, the traffic demand per cell is shown in the following table:
The above parameters assume that the actual capacity budget can be adjusted appropriately, but overall the comparison trend will not be changed.
According to the above business demand analysis, the demand for data services in high-speed scenarios is very large. Taking the current commercial TD-SCDMA system 2 as an example, the ratio of 4 timeslots to 4 timeslots, a single carrier can provide a theoretical maximum throughput of 560 kbps and a theoretical downlink throughput of 1.68 Mbps. Due to factors such as the Lele effect and large penetration loss, the actual uplink and downlink data rates that a single carrier can provide are very low.
Therefore, under the condition of available spectrum resources of the existing TD-SCDMA, it is difficult to meet the service needs of end users in high-speed mobile scenarios.
Difficulties in covering high-speed mobile scenes
In the scenario where the terminal is moving at high speed, there are a series of problems in directly using conventional TD-SCDMA macro cells for coverage, including:
Doppler shift
The Doppler frequency shift is caused by the relative motion between the terminal and the base station, and this effect is particularly obvious in high-speed scenarios. The Doppler frequency shift causes a frequency deviation between the signal received by the UE and the signal sent by the Node B. The frequency deviation will cause a phase rotation of the data symbol received by the UE, thereby affecting the accuracy of data demodulation. After calculation, the speed limit supported by QPSK demodulation in the TD-SCDMA system is 200 km / h. For higher speed mobile scenes, the phase calibration algorithm must be improved to ensure transmission performance. In fact, due to the limited phase compensation capability of the phase calibration algorithm, it is impossible to fundamentally solve the effect of Doppler frequency offset, which will inevitably have a negative impact on the quality of the communication link.
Carriage penetration loss
The penetration loss of the following cars in high-speed scenes is large. After measurement, the high-speed train car penetration loss is usually around 15 ~ 20dB, and the Shanghai Maglev high-speed train car penetration loss is around 30 ~ 35dB. Therefore, if the users in the car are covered outside the car, the penetration loss of the car is also a problem that cannot be ignored and will directly affect the quality of the communication link.
Mobility management
Compared with ordinary scenes, high-speed mobile scenes such as high-speed railways have very short moving times due to their very high moving speed. In the high-speed mobile environment, due to the deterioration of the link quality, the communication process of the end user's cell camping, access, reselection and handover requires longer time for measurement and signaling interaction, and the conventional macro cell coverage is used The main consideration is the low- and medium-speed scenarios. The processes of reselection, handover, and access with large delays may not be completed within the coverage of a single base station site. At the same time, frequent handovers will also lead to poor user experience and handovers. The possibility becomes larger.
Limited network capacity
With reference to the analysis in Section 2.2, a large number of high-speed mobile scenarios require high end user service capacity. Under the existing spectrum resources available for TD-SCDMA, it is difficult to meet the requirements of high-speed mobile scenarios using TD-SCDMA macro cell coverage. The business needs of end users.
In addition, when the high-speed train runs to the edge of the cell or location area, a large amount of handover or location area update signaling will be generated, which will cause system load overload in a short time.
Existing coverage solutions for high-speed mobile scenarios
Multi-cell merged networking solution
The multi-cell merged networking method solves the problem of continuity coverage in high-speed environments by expanding the coverage area of ​​a single cell and increasing the reselection / switching band, thereby solving the terminal parking, access, and call in high-speed mobile environments Problem, improve the terminal cell reselection and cell handover success rate, and reduce the terminal drop rate.
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