Td Network Construction In The Special Scene Of A Comprehensive Solution (figure)

1, Introduction China Mobile Undertaken in eight cities nationwide TD-SCDMA trial

network construction tasks, the current trial network construction is being carried out in the. In the complex, where various scenes to provide integrated solutions targeted at the same time ensuring high quality network coverage, the network that we must face and solve problems. In this paper, a number of issues in building a network, select a representative two questions?? Highway / railway and covered a large upscale residential district, to carry out the solution of.

2, highway / railway scenes coverage With the continuous improvement of the user moving speed, for example, "Harmony" has reached 200km per hour over the train, in order to ensure that the highway / railway along the coverage, improve TD-SCDMA in the speed of 250km / h around the coverage performance, has become priority.

Doppler effect and the impact of rapid switching of high-speed mobile environment, two problems must be solved, the faster the greater the effect, to solve the greater the difficulty, the higher technical requirements. If no measures are taken, Communicate Quality will seriously deteriorate or even dropped. In addition to baseband processing and intelligent Antenna Carry out the optimization algorithm such as outside, in the construction of good network planning is the key to solving the problem.

2.1 Equipment Selection In equipment selection, the use of distributed fiber-optic networking equipment, base stations BBU + RRU. Advantage in a given area can only place a BBU, link along multiple RRU for coverage, while RRU with cascading feature can save by way of cascade fiber network construction to provide a flexible way.

2.2 Antenna Selection Choice of the antenna, according to the simulation and actual test results, 6 and 8 antenna array antenna array compared to coverage in the uplink, downlink channel coverage and public coverage are some difference. Therefore, highway coverage, in order to maintain good performance, suggested the use of 8 array antenna.

2.3 base station layout Base station arrangement can be distributed along both sides of the railway may also be unilateral distribution, there is no better or worse, completely under the propagation environment and topography. Along the distance covered

2.4 and consider Doppler shift and insertion loss as to take into account the transmitting antenna to cover objects (high-speed railway and highway) in the distance. According to the Doppler frequency offset feature, the same velocity, the base station and the vertical distance from the road longer, the smaller the effective fixed Doppler frequency offset, the more favorable the baseband demodulator.

The average speed as high-speed rail is higher than the average highway speed, under the same conditions (distance and offset angle), high-speed rail's Doppler frequency offset is greater than highway, the design base station from high-speed railway slightly larger than the vertical distance from the base station to the vertical distance from the highway in order to achieve better performance of the baseband demodulator.

Studies have shown that the insertion loss and the angle between the incident waves have correspondence in the wave perpendicular to the barrier, the transmission loss of the smallest, with oblique incident waves gradually obstacles, radio waves through the barrier and the losses are increased. In the high-speed railway and road scenes, we must consider the train and the car itself penetration loss. Base station along with the cover needed to maintain a certain distance to ensure that the antenna sidelobe beam injected into the body, the insertion loss is not too much. Without loss of generality, the base station and the base station coverage in high-speed rail connection with the coverage radius of the edge of the object should exist at least 30 angle.

Contrast, closed road running vehicles, body structure and thickness so determined to run in road vehicles under the same conditions of insertion loss is less than the railway locomotive. Therefore, the direction of the antenna design to reduce.

2.5 switch problem In super-fast moving situation, when the Doppler effect caused by the relative frequency offset with the frequency of adjacent areas greater than a certain threshold, the connection state of the user terminal adjacent areas measuring less than the same frequency, can not trigger Relay switch Relay switch leading to useless. At this point, using different frequency hard handoff scheme to counter the Doppler shift effect, switch the program better than the Relay for continuous coverage.

In addition, the design of the switch to switch the region have very important implications. Switch region is too small will switch because they can not meet the requirements of delay caused by switch failure. Overlapping coverage area is too small, usually easy to make wireless links in the target cell before a successful re-allocation has been out of step with the source cell, resulting in switching processes in the physical channel reconfiguration failure stage. Switch start threshold according to the design parameters, and the switching process time required to complete the conservative statistics estimate the switching area for the size of the overlapping coverage areas, two cells are designed to cover overlapping area is large enough to ensure the UE will meet the conditions of the measurement switching After the incident report, UE has enough time to cross the overlapping coverage area.

Assume that high-speed users maximum moving speed is 250km / h, distance of movement per second 69m. According to the performance, the hard-switching delay required for an average of 1000ms (from the measurement control message sent to the physical channel reconfiguration complete), then the need to plan to switch the scope of the region should be greater than 69m; switching is carried out in two-way, so switching zone should be 138m, while the signal field should be added from the same region (district boundaries) to the strong field on both sides of the transition region. This constitutes a switch with the way the transition region overlapping coverage areas. Shown in Figure 1.

Figure 1 Schematic diagram of switch region

Td Network Construction In The Special Scene Of A Comprehensive Solution (figure)

By: blairzhang

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