1 Introduction
Currently, wireless communication technology is accelerating the evolution of higher-end 4G technology, TD-SCDMA technology will be the first to smooth the same as Time Division Duplex technology TD-LTE transition. TD-LTE as soon as possible whether commercial, and maximize the protection of existing investment in TD-SCDMA network, is one of the industry's concerns.
TD-LTE uses orthogonal frequency division multiplexing (OFDM) technology and multi-antenna MIMO technology, which allows for more flexible spectrum bandwidth allocation. Relative of TD-SCDMA network architecture, TD-LTE canceled RNC unit, while the flat all-IP architecture. Following through on the TD-SCDMA network with TD-LTE network analysis of the difference between its smooth evolution of the need to consider a comprehensive analysis of the issues, and on this based on the recommendations.
2, analysis of technical solutions were BBU
The current TD-SCDMA TD-LTE to co-evolution of the program are a total of BBU rack, dual-mode BBU support and expand box three kinds.
Total rack solution is achieved through the sharing of the rack, without equipment modification, its implementation is limited rack space left. The program is equivalent to a completely new BBU equipment, only power can be shared, therefore, expensive, not cost savings. Box support program is extended by adding an LTE baseband processing machine frame, and TD-SCDMA BBU via external cable connections, share transfer board. Which is subject to the TD-SCDMA equipment, software upgrades, some already have GE transport interfaces in TD-SCDMA devices without hardware upgrades on the existing network TD-SCDMA BBU relatively small changes, but also need to increase TD-LTE BBU equipment, from cost savings point of view is not the best option.
Dual-mode BBU programs that use TD-LTE and TD-SCDMA dual-mode BBU, only in a different board baseband processing, master control, transmission, chassis, backplane, and so completely shared. The program can share most of the existing resources, is very cost savings, but the need for the existing TD-SCDMA BBU equipment chassis and backplane upgrades, improved processing power, and need to upgrade the hardware platform, the larger changes, but the technical difficulty does not exist.
By this analysis, the proposed smooth evolution can be used in BBU following programs: early in building a network, by adding LTE baseband processing board, share transfer, backplane, chassis and other fast TD-LTE development; to the size of the latter part of the network larger and more mature devices when the key board of TD-SCDMA software upgrade directly for TD-LTE mode.
2.1 TD-SCDMA and TD-LTE work on the same frequency band
TD-SCDMA and TD-LTE working in the same band (such as A-band and E-band), it occupies a different frequency resources, namely, adjacent channel coexistence. At this point the device can share the RRU, RRU, but were limited by the following three conditions.
(1) bandwidth
Limited by the bandwidth capacity of the device, the program supports up to a total of RRU 30 MHz bandwidth.
(2) the ratio of slot
A total of transceiver channels, requires TD-SCDMA and TD-LTE line transfer point slot, this time between the two systems without interference isolation bandwidth. When the TD-SCDMA time slot with 3:3 ratio and the use of TD-LTE ratio of 2:2 time slot when no spectral efficiency loss can be carried out adjacent channel coexistence; and when to use TD-SCDMA time slot ratio of 2:4 The TD-LTE time slot with 1:3 ratio, the TD-LTE will bring the loss of spectral efficiency.
(3) output power
TD-SCDMA will be the output of existing power upgrade from the 2W 5W or more.
With the current TD-SCDMA TD-LTE adjacent A band co-existence is mainly used in outdoor and indoor E-band. A band, for example in outdoor, taking into account the PHS interference, you can use TD-LTE using the 1885 ~ 1895MHz, TD-SCMDA program using 1880 ~ 1885MHz.
2.2 TD-SCDMA and TD-LTE work in different frequency bands
When the TD-SCDMA and TD-LTE working in different frequency bands, due to use TD-LTE frequency bands adjacent to far this time because the major components such as PA RRU in the largest such support only 30 MHz bandwidth, limited by the current device support capabilities, RRU's share can not be achieved. TD-SCDMA and TD-LTE antenna is required by an external combiner to connect RRU.
2.3 RRU product support case
According to research we can see, the current F-band outdoor eight-channel RRU has supported common-mode and transfer mode, signal bandwidth of 30MHz, TD-LTE and TD-SCDMA signal bandwidth can be dynamically adjusted; output power greater than 9W / channel, Ir interface supports 6.144GHz × 2 or 6.144 GHz × 3, but by the Central Purchasing equipment for TD-SCDMA analysis shows that, TD-SCDMA third phase of the application devices support only 1880 ~ 1900MHz band, four engineering equipment to support 1880 ~ 1910MHz band, so When the PHS network back then, they can not fully utilize the existing equipment for smooth evolution.
E-band, the interior single / dual channel RRU has supported the common-mode and switch-mode approach, the current signal bandwidth of 30 MHz, push firms will support 40 ~ 50 MHz, TD-LTE and TD-SCDMA signal bandwidth can be dynamically adjusted; output power for the 20 ~ 50 W / channel, depending on the signal bandwidth may be, Ir interface supports 4.9152 GHz × 2.
2.4 TD-LTE RRU upgrade configuration
A band for outdoor and indoor E-band, RRU upgrade of TD-LTE configuration are shown in Figure 1, shown in Figure 2.
3, antenna analysis program
In TD-SCDMA TD-LTE evolution of the antenna depends on whether the share TD-SCDMA and TD-LTE's operating band. By planning to use TD-LTE spectrum analysis, we can draw the following conclusions:
For the D-band TD-LTE equipment, antennas can not be fully shared, to be newly installed antenna system;
A band for TD-LTE equipment, antennas can be shared;
For the E-band TD-LTE equipment, antennas can be shared.
In the future TD-SCDMA TD-LTE evolution, when the FAD antenna mature, the band currently in use should be replaced with FAD antenna broadband antenna, thereby reducing the difficulty of construction, to reduce antenna weight.
4, supporting the evolution of program analysis
4.1 Power
TD-LTE BBU support the-48V power supply, with power does not exceed the maximum full 660W; RRU way require a separate power supply with a maximum power does not exceed 450W.
4.2 rooms
TD-LTE equipment, high integration, BBU height of the equipment no more than 4U, and are in a standard 19 "rack mount with the existing base of computer room construction, if the original base station there is a corresponding 19" frame, and there 6U of space, you can install the BBU TD-LTE equipment. If the new base station, you need a flight to the installation of equipment to meet the requirements of BBU.
4.3 rooms divided building
If the original antenna position or density of sub-chamber is unreasonable, it would take to transform, to increase or adjust the antenna laying points to ensure coverage of TD-LTE network. Use of MIMO antenna options, at least need to add all the way Antenna. In order to ensure the MIMO performance, the proposed dual-wavelength antenna spacing of 10 times as far as possible, that is 1.5m, the actual installation space is limited, such as dual-antenna spacing should not be less than 4 times the wavelength, ie 0.5m.
4.4 Transmission facilities
Transmission facilities according to the bandwidth requirements of the E1 line to replace FE / GE optical interface (LC) or power port (RJ45). Can be calculated through the outdoor macro base station (S1/1/1) requires the convergence of bandwidth for the 120 ~ 170 MHz, the indoor distribution system (O1) of the convergence bandwidth of 40 ~ 60 MHz.
5 Conclusion
Through the above analysis we can see, TD-SCDMA TD-LTE with a smooth evolution to the conditions, if the TD-LTE and TD-SCDMA with the band, can be used TD / LTE dual-mode RRU, without changing the day surface; if the TD-LTE and TD- SCDMA different band, you need to add the corresponding band dual-mode RRU, RRU built-in dual-mode combiner, combiner to direct the antenna to be used FAD broadband antenna.
Author: China Mobile Group Design Institute REN Yi Lu Jiyu Wang Shen
Source: Third generation mobile communication network |
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