Converged with the existing GSM/UMTS network, FDD LTE communication systems emerge in time to support higher efficiency and data throughputs. The FDD LTE network includes macro coverage and complementary coverage. The macro coverage network provides the main part of the total solution, and is the focus of this article.
1.FDD LTE Macro Coverage Market Requirements
Considering engineering and funding requirements, it is a challenge for operators to build a high-speed and high-quality FDD LTE macro network rapidly and cost-effectively. The market has imposed the following requirements on mobile macro network products.
Smallest possible size with equivalent performance
With environmental awareness on the rise, it is becoming more and more difficult to acquire a site. Products of small size are easily accepted and conveniently installed, requiring less roof footprint. When mounted on a tower, small modules cause lower wind loads, which aids site selection. The product size must be minimized while its performance must still be guaranteed.
Supporting high data rates with 4*4 MIMO technology
To support higher data rates, 4*4 MIMO technology was first introduced in FDD LTE network. Traditional products usually support 4T4R but with a very large size or combination of two 2T2R modules. A small integrated 4T4R RRU should be designed to meet difficult site selection challenges.
Supporting full working bandwidth in each frequency band
It is necessary to support the full working bandwidth in each frequency band, especially in 1800MHz. The 1800MHz band has the largest working bandwidth - 75MHz. Initially, products can only support 55MHz, located at the upper part or the lower part of the 75MHz range. With many operators merging to save cost, their frequency licenses become scattered across the whole spectrum. Products that support the full working bandwidth will greatly reduce the amount of RRUs needed and hence the network convergence cost.
Supporting multi-mode and multi-band within one module
FDD LTE wireless communication system is converged with the existing GSM/UMTS network. However, the multi-band and multi-mode network results in a large number of RRUs. Products supporting multi-band and multi-mode require fewer modules and less roof or tower footprints. The output power can be allocated to multi-band and multi-mode according to different requirements, providing high-quality network coverage for each system.
Supporting antenna and radio frequency (RF) module integration
Products must be more integrated. Antennas are being integrated into RF modules, following the development trend of flat networks. High integration enables smaller sizes, requiring less roof/tower footprints and achieving flexible and rapid system deployments.
2.New Product Solutions
In response to the above market demands, ZTE introduced many new types of product solutions, described below.
New generation Remote Radio Units (RRUs) solution
To improve the traditional RRUs, a series of new generation RRUs are being released. The volume of the first generation 2T2R/2T4R RRUs is 23L, and the second generation RRUs (magic RRUs) are downsized by 47.8%. Moreover, in the third generation, volume is reduced by 33%, to 8L. The same downsizing happens on the 4T4R RRUs. The newly released 4T4R RRU has a size of 12L, reduced nearly by half when compared with the previous one. The size drops sharply while the performance remains the same or even better, as illustrated in Figure 1. Not only roof resources are minimized but the installation period is shortened significantly. Thus, network construction becomes easier and faster.
Figure1 Much Smaller New Generation RRUs
Full Working Bandwidth (FWB) RRUs solution
The FWB RRUs cover the full bandwidth, suitable for operators with scattered bandwidth or spectrum. For example, in Hong Kong, operator A has the frequency bandwidth colored by green in Figure 2, and operator B has the frequency in orange. Now operator A is acquired by operator B. As a consequence, the merged operator has a bandwidth extending to 68 MHz. The FWB RRU supports the full 75 MHz in 1,800MHz, as shown in blue in Figure 3, below. One module is enough for one sector, while in traditional cases two RRUs are needed. Nearly half of the total cost of operation (TCO) is saved.
Figure 2 FWB RRU Covering Full Bandwidth
Ultra Broadband RRU (UBR) solution
Each RF channel of the ZTE UBR product supports an ultra broadband of 365 MHz, from 1,805 MHz to 2,170 MHz, ranking number one in the industry. One UBR supports GL1800 and UL2100 multi-band and multi-mode networks, as shown in Figure 3. The G1800 and U2100 networks which previously required at least two RRUs per sector can now be replaced by one UBR product per sector. And then it can be upgraded to GL1800 and UL1800 only via a software upgrade. RRUs and feeders are cut by 50%. UBRs supporting DD and 900 MHz and supporting 2.3 GHz and 2.6 GHz are in planning stage, and will be released as per market requirements.
Figure 3 One UBR Supporting GL1800+UL2100
The total output power of 100W of each channel of the UBR product is shared between 1800MHz and 2100MHz. According to real-time traffic conditions, network coverage requirements, and operation strategies, it is flexibly allocated to different services in different frequency bands. The dynamic output power adjustment responds to the traffic and coverage requirements in a more efficient way than a fixed power configuration, achieving a high-quality network and improving the user experience.
iMacro (AAU) solution
An Active antenna unit (AAU) is the integration of the traditional RRU and the antenna. One of ZTE AAU products uses ultra broadband technology to meet the multi-band and multi-mode network construction requirements of operators. With this integrated architecture, the AAU has less feeders and signal loss, which enhances coverage. It requires less space and is easy to be hidden from sight, which makes site acquisition and rapid deployment easier.
All the solutions above are summarized in the following table:
Table 1 Solutions and Benefits
Technology development never stops, and we are still on the road. ZTE is committed to continuous innovation, strives to provide quality service, novel solutions and business models, and collaborates to construct a brilliant win-win future with our customers and partners.