In recent years, the increasing demand for mobile data services has promoted the acceleration of LTE network commercialization. Throughout the world, LTE commercial networks are still dominated by lte fdd, but with the gradual development of their networks, users and businesses are increasing, lte fdd network frequency resources, insufficient capacity and other issues will gradually become prominent, and TD-LTE network in the spectrum resources have more resources, can effectively alleviate the FDD spectrum shortage problem. Therefore, the integration of TD-LTE and lte fdd will become the future trend.
However, because of the differences between TD-LTE and lte fdd in frequency band selection, antenna type, coverage characteristics, capacity characteristics and other aspects, TD-LTE and lte fdd fusion network still faces some challenges, in particular, it is necessary to solve four problems: Network Positioning, frequency band selection, Antenna Selection, and terminal strategy.
TD-LTE and lte fdd have their own merits
From the perspective of coverage performance, lte fdd is slightly better than TD-LTE network. According to the 3GPP TD-LTE and lte fdd Frequency Band distribution, the TD-LTE network frequency band is higher than the lte fdd network, so from the perspective of the use of frequency band, given the advantages of lte fdd network frequency band, it is superior to the TD-LTE network in terms of coverage performance.
In addition to the frequency band, the signal-to-noise ratio also affects the coverage performance of the LTE network to a certain extent. In the case that other configurations are the same, the thermal noise ratio of the 20 MHz bandwidth TD-LTE system is about greater than that of the 2 × 10 MHz bandwidth lte fdd system, the uplink coverage radius of the lte fdd network is about 18% larger than that of the TD-LTE network.
TD-LTE network can use 8 antenna network, and lte fdd network mainly uses 2 antenna network. When 8-antenna beam is used, the TD-LTE network can obtain 1dB ~ 3 dB gain; TD-LTE receives 3 dB ~ in uplink with 8 antenna diversity ~ The diversity gain of 5 dB.
All in all, from the domestic frequency distribution, TD-LTE mainly work in the 2.6 GHz band, while lte fdd has not yet issued a license, the frequency band is not fixed, we predict its possible frequency band is 1.8 GHz. In this context, the coverage performance of lte fdd is better than that of TD-LTE network.
In terms of capacity performance, lte fdd has some advantages over TD-LTE in capacity, but the gap is limited.
The main indicators of capacity performance in LTE Networks include average cell throughput, cell edge throughput, number of simultaneous online users, and number of simultaneous scheduling users, the preceding indicators are related to factors such as channel configuration, parameter configuration, scheduling algorithm, and inter-cell interference coordination algorithm.
TD-LTE and lte fdd system capacity difference, mainly manifested in three aspects: First, TD-LTE and lte fdd on the downlink network capacity has an advantage; second, the number of simultaneous online users and simultaneous scheduling users of TD-LTE and lte fdd have similar performance. Third, the cell throughput of lte fdd is higher than that of TD-LTE network.
Four major issues cannot be ignored
1. Network Positioning
TD-LTE and lte fdd integrated networking construction, first of all to solve the problem of two standard Network Positioning, through reasonable positioning, and strive to meet the development needs of users and businesses with minimum investment.
From the international TD-LTE and lte fdd fusion network deployment case, generally according to the work frequency band to determine the Network Positioning: the low frequency band of the system to play its wide coverage advantage, mainly to solve the network coverage; systems with high frequencies are mostly used for business absorption in hotspot areas due to insufficient coverage.
At present, China only issued a license for TD-LTE, TD-LTE network needs to focus on intensive urban areas, general urban areas and developed towns coverage and business absorption problems. With the development of TD-LTE and lte fdd hybrid networking experiment, our country will be the development of TD-LTE and lte fdd in the future. TD-LTE is mainly used in 2 GHz and above, and lte fdd is expected to work in 1 8 GHz band, from a long term development perspective, lte fdd network will be mainly used for coverage, TD-LTE network is mainly used for capacity absorption.
Due to the limitations of the GSM technology, the data service carrying capacity is weak, and it is not suitable for the mobile Internet era, and will gradually exit in the future. After the GSM network is switched back, the MHz band can be used for the construction of the lte fdd network to better utilize the wide coverage of the lte fdd network.
2. frequency policy
China's TD-LTE license issued, the relevant frequency band has been determined. From the current results of the TD-LTE Band Division, there are three main frequencies: 1.8 GHz, GHz and GHz, of which GHz is used for indoor coverage, while GHz and GHz are used for outdoor coverage. For China Mobile, it has two frequencies, namely, 1.8GHz and 2.6GHz. In terms of networking performance and investment, the wide coverage is dominated by 1.8GHz, which can take full advantage of its wide coverage and reduce site demands, reduces network investment. For the GHz frequency band, to take advantage of its rich spectrum resources, it is mainly used for capacity absorption in hotspot areas.
For the lte fdd network, it seems that the GHz and GHz frequencies may be used at present. According to the international networking experience and industry chain status, the GHz network has a high maturity and may become the mainstream band of the lte fdd network, however, the absence of a 1.8 GHz spectrum and a small band of isolation may cause inter-system interference, especially the interference to the GHz TD-LTE.
3. Antenna Policy
The 3GPP R9 version specifies eight transmission modes, but two antenna and eight antenna technologies are used in practical applications. These two antenna technologies complement each other, flexible use based on actual Channel Changes.
According to the test results of domestic TD-LTE test network and commercial network construction, there are differences between 8-antenna and 2-antenna networking: first, 8-antenna is more cost-effective than 2-antenna single equipment; secondly, in terms of network performance, the coverage and capacity of the 8-antenna TD-LTE network are better than those of the 2-antenna network. Thirdly, the 8-antenna has a large size in engineering construction and operation and maintenance, the construction is relatively difficult and requires a high level of site sky resources, while the 2-antenna is smaller in size and the construction is less difficult, which facilitates project construction and quick network construction.
For the construction of the lte fdd system, there are currently two types of antennas: 2T2R and 2T4R. Compared with 2T2R antenna, 2T4R antenna can obtain 3.5dB ~ in terms of coverage performance ~ The reverse gain of 4.5 dB, but the engineering cost and implementation difficulty are higher than 2T2R antennas. Therefore, in the actual network construction process, we should follow different scenarios and needs, flexible selection of 2T2R and 2T4R antennas for network deployment.
4. Terminal Policy
At present, LTE terminals mainly include data cards, CPE, modules, tablets, netbooks, and smart phones. In the early stages of the network, LTE terminals will be dominated by data cards, and later may gradually adopt LTE smartphones, tablets, and other terminals.
In the integration of TD-LTE and lte fdd networking, terminals need to support more standard. Considering the international roaming problem, the integrated terminal must support at least TD-LTE, lte fdd, GSM, WCDMA, WiFi and other systems.
There are 26 FDD frequencies defined by 3GPP and 12 TDD frequencies. The LTE band is discrete and the frequency span is large, and there is no concentrated global roaming band, multi-Mode band supported by terminals has become an inevitable choice. With the application of carrier aggregation technology, the multi-band support capability of TD-LTE and lte fdd converged network terminal will be higher, which will increase the difficulty of TD-LTE and lte fdd converged network terminal.
For LTE terminals, China Mobile has put forward requirements for a five-mode ten-frequency mechanism, making it more difficult for chip manufacturers to implement. Currently, only products from a few vendors, such as Qualcomm, haisi, and mediatek, are available, it can meet the requirements of Five-mode and ten-frequency. Therefore, from the chip point of view, to meet the future of TD-LTE and lte fdd fusion networking requirements, there is a long way to go.
Comments from the Chief Engineer
The integration of TD-LTE and lte fdd has become an inevitable trend. With the continuous opening of the global LTE commercial network, the increasing number of users and business volume, the problem of insufficient lte fdd spectrum resources is becoming more and more prominent, and TD-LTE has a wealth of spectrum resources, the two are integrated networking, it can effectively alleviate the FDD spectrum shortage problem. At the same time, it can be seen that, compared with lte fdd, TD-LTE in the industrial chain development and other aspects, there is a certain gap. To promote the development and maturity of TD-LTE, it is also necessary to take the international line of integrated development. In general, the integration of TD-LTE and lte fdd will become the inevitable trend of LTE network construction in the future. At present, China's "National tower" Company is in preparation, its establishment will further promote the construction and sharing of telecommunications infrastructure, is conducive to the development and maturity of TD-LTE and lte fdd multimode equipment.