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TD indoor distribution system design

发布日期:2012-03-20 点击次数:2518

TD-SCDMA, indoor distribution system rehabilitation programs
With the high-speed advancement of information technology, individual users of hand-held communication devices increasing number of demand for communication services is also rising, followed by the wireless coverage requirements are also increasing. According to statistics, used in mobile phones, the number of indoor users greater than the number of outdoor users than 2 times, the users tend to use the mobile phone in the indoor. However 3G band higher signal penetration is weak, it is difficult to realize the depth of indoor coverage.
TD-SCDMA network-based data services, while most of the data traffic occurred in the room, so early in the TD-SCDMA network construction, the introduction of TD-SCDMA indoor hot spots in some indoor distribution system is very necessary. Implementation of indoor coverage projects, buildings traffic can generally be increased 1.4 times, and at the same time reduce the the outdoor network load and expansion pressure, reducing the the outdoor network's overall interference and improve the quality of network services.
1 TD-SCDMA indoor distribution system characteristics
TD-SCDMA indoor distribution system compared to other indoor distribution system of the communication system has the following characteristics:
(1) TD-SCDMA indoor distribution system using smart antenna system coverage, capacity and quality are affected. No shaping gain downlink traffic channel, business channel downlink power 6dB ~~ 8dB lower compared with outdoor coverage. Due to the lack of smart antenna uplink interference is not well controlled.
(2) the coverage of the common channel and the traffic channel be considered separately. Since forming gain smart antenna indoor business channel, so it is a business channel coverage limited system. TD-SCDMA pilot power can be flexibly set according to the requirements of, not a fixed value.
(3) business coverage is basically the same. Respiratory effects of the TD-SCDMA system is not obvious, the business of various rate basically covered the same diameter.
(4) support asymmetric data services, according to the traffic up and down to adjust the time slot configuration.
(5) working band, big loss, poor signal indoor propagation, deep cover difficult.
(6) To reduce indoor, outdoor interference, indoor, outdoor is more suitable for using different frequency Zuwangfangshi.
(7) In the indoor distribution area to the outdoor coverage area movement, can not use relay switching, can select only the hard handover.
(8) for control system equipment delay. The maximum radius of the TD-SCDMA base stations covering 11.25km, which requires indoor distribution system relay device is not large transmission delay, to ensure that the interference between downlink.
(9) using the uplink synchronous technology, improve the technical requirements of the repeater and dry amp.
(10) The majority of sources need to introduce a separate GPS antenna, and select a suitable location for installation.
2 TD-SCDMA indoor distribution system construction principles
TD-SCDMA indoor distribution system construction should consider the needs of the coverage, capacity, quality unified. Constrained by the proximity effect, consider a single antenna coverage should be balanced design. And other communication systems between interference and multi-system power sharing 2G indoor distribution system, you need to pay attention to the match. According to the TD-SCDMA technology features, this paper presents the following TD-SCDMA indoor distribution system construction principles.
(1) meet the target area of ​​coverage, capacity, quality demand;
(2) to build a comprehensive distribution system, using broadband passive devices;
(3) To conserve resources, try to share the existing indoor antenna distribution system;
(4) to minimize the impact on existing 2G systems;
(5) reasonable power configuration to minimize the use of the TD-SCDMA dry release;
(6) to minimize passive components, reduce device insertion loss;
(7) considering the construction and operation and maintenance costs;
(8) take full account of the system compatible, upgrade, expansion capability.
According to the above principles, the source selection need to consider the following factors: coverage, capacity and quality requirements of the building, and give due consideration to the long-term business development needs of buildings; whether the source installation location, whether to meet to take power conditions ; Third, network conditions, and signal transmission in place around.
Coverage, such as switching and interference factors to consider in the design of the distribution system. Which coverage should take into account the distribution of signal power, signal link loss, terminal receiver sensitivity and power margin factor; switch including outdoor indoor switch, indoor switch, switch elevators inside and outside, and should also consider switching area, switch, handover success rate factors; interference should take into account the interaction of the original system and the 3G system before and after the opening of the 3G system.
According to the TD-SCDMA indoor distribution test, Table 1 lists the service quality indicators of TD-SCDMA indoor distribution system design requirements.
Table 1 TD-SCDMA indoor distribution system construction quality indicators

To reduce the impact of indoor distribution system for outdoor systems need to meet the following conditions: In addition to the provisions of the edge of the indoor signal level, indoor coverage system is not over covers outdoor and indoor distribution system in a building 10 meters away from built indoor signal should be higher than 9dB ​​above outdoor strongest signal level is low, or indoor signal from leaking to the outside at 10 meters of the pilot signal strength is not higher than-95dBm.
3 distribution system shared analysis
When multiple systems share a common distribution system, power matching is the biggest problem. Power matching the need to consider the difference of the signal source output power, different band signals in the difference of the transmission loss in the distribution system, the edge coverage field strength of the different requirements of the different frequency bands in the signal space propagation loss differences and other factors. Table 2 is a comprehensive consideration of the above factors, related Typical parameter values ​​obtained in each of the communication system.
Table 2 indoor distribution system power matching comprehensive analysis

As can be seen from Table 2, in the same distribution system to a plurality of system signal source coupled directly huge the remaining allowable loss difference obtained by the different systems. In all systems, CDMA800, GSM, and DCS1800 coverage effect is best, WCDMA and TD-SCDMA effect, followed by the worst effects of the PHS and WLAN coverage. In the distribution system, the system branch loss of about 5dB, an insignificant difference, so share the branch of the distribution system is not difficult. The same time, the system of trunk loss of 2dB, seems more suitable shared. Various systems, however, due to the need for capacity and power to match, in the dry roads to do a different approach, TD-SCDMA multi-system shared distribution system, the trunk is difficult to share, except small-scale distributed systems.
4 distribution system reform program
Indoor distribution system to solve the primary problem, which is a good wireless signal coverage for indoor users. Usually in accordance with the size and type of buildings, indoor distribution application scenarios are divided into: the miniature building area (6000m2), a small building (6000m2 ~ 12000m2 area), medium-sized buildings (12000m2 ~ 60000m2 area) and large building area (60000m2). Retrofitting existing indoor coverage system, you can perform the following steps:
(1) to collect the existing distribution system design, information including topology interface, power configuration and cable type, length, etc.;
(2) verification of existing passive devices, some devices need to be replaced to ensure its support for TD-SCDMA band;
(3) the input power of each distributed antenna recalculated;
(4) the typical floors calculate the coverage of each antenna distance and blocking;
(5) According to the topology diagram of the antenna of each antenna input power and typical floor, verification of the signal coverage of the floors;
(6) based on each floor of the signal output power and topology, to identify the active node of the device erected position;
(7) to determine the trunk routing and TD-SCDMA signal source location.
The following four different specifications of TD-SCDMA indoor distribution system rehabilitation programs.
4.1 micro-architectural
Micro-architectural interior area is smaller, the input power of the signal source is limited, distribution systems using passive devices, the TD-SCDMA signal input port coupled directly in the 2G signal source, using the same position combiners achieve distribution system shared, see Figure 1 .

Figure 1 micro-distribution system transformation methods
Micro-distribution system in the transformation of the way, we need to confirm two things: First, check whether the original passive devices support TD-SCDMA bands, if not support, couplers, power dividers and other passive components to be replaced as broadband devices. The second is to check the adequacy the original distributed antenna density propagation loss, according to the interior space. If the original distribution system can not be used directly, we need to increase the distribution of the number of antennas, and based on this, reducing the 2G signal source power.
4.2 small construction
In the the early 2G distribution system, the use of many 6D, 8D feeder, which make the the 2G/3G communication system loss difference to increase. In this case, can be used the same position subcircuit simply part of the feeder replacement more coarse attenuation smaller feeder can be, see Figure 2.

2 small distribution systems transform the way
Small distribution system, the same should be to consider the passives bandwidth and distributed antenna density TD-SCDMA system meets the requirements of (the same). In this scenario, it is necessary to reduce the output power of the original 2G equipment, in order to ensure that the power constant of the antenna port.
4.3 medium-sized buildings
In a medium-sized indoor distribution system, often dry release and other active equipment. At this time, TD-SCDMA signal source of a single channel can not meet the power requirements of the distribution system, and therefore can not use the same location subcircuit, only end combiners shared branch distribution system, but can not share a dry road distribution system , see Figure 3.

Figure 3 medium-sized distribution system transformation
The figure above, 2G/3G dry put is an optional device, not mandatory devices. In this scenario, in the case does not increase the number of distributed antenna, due to the introduction of the TD-SCDMA combiner, brought the power of the insertion loss, the output of the original 2G equipment should be slightly improved, in order to ensure that the power constant of the antenna port.
4.4 large buildings
In large indoor distribution system, usually in the optical fiber distribution system, comprising the optical amplifier and an optical coupling device. At this point, the use of a single TD-SCDMA signal source has failed to meet the power requirements of the distribution system, BBU + RRU as the signal source end Combiner, see Figure 4.

Figure 4 large-scale distributed systems transform the way
Figure above, the the 2G/3G transformation box, 2G and 3G signal light dry put at combiner and convert the RF signal coverage branch distribution system in buildings. 2G Distributor distribution system using the optical transmission system in the premises the 3G Distributor distribution systems can take advantage of the building existing optical fiber, or re-laying fiber.
5 Summary
The construction of the TD-SCDMA indoor coverage system, to make full use of the buildings has been indoor distribution system. In this paper, the characteristics of TD-SCDMA indoor distribution system, come to the basic principle of the construction of the TD-SCDMA indoor distribution system. TD-SCDMA and other communication systems shared indoor distribution system power matching, micro, small, medium and large four typical 2G distribution system rehabilitation programs of the TD-SCDMA. The rehabilitation programs take full account of the 2G indoor distribution system status and technical characteristics of TD-SCDMA, change the existing distribution system and building a faster, less investment, easy maintenance.
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