ZTE's WiMAX Solution Helps Operators Lower TCO

Over the recent years, competition in the telecom industry has been intensified. Despite the richer and richer services provided, telecom operators have seen slow increase, or even decrease, of the Average Revenue Per User (ARPU). They pay increasing attention to how to decrease the network's Total Cost of Ownership (TCO) through saving the Capital Expenditures (CAPEX) and Operation Expenditures (OPEX).

Analysis of WiMAX TCO
For an operator, TCO mainly includes CAPEX and OPEX. In constructing and operating a WiMAX network, CAPEX mainly consists of purchase and construction expenditures. Purchase expenditures cover the purchases of WiMAX and supplementary equipment as well as upgrade and expansion equipment in the later phase. Construction expenditures cover site acquisition, civil works, and equipment installation.
OPEX is indirect costs related with routine network operation and maintenance. Operation expenditures cover the expenses on site rental, transmission rental, and power consumption.
TCO, which considers both CAPEX and OPEX, avoids the situation when the decrease of one kind of expenditure leads to a sharp rise in other expenditures, hence increasing the overall TCO. For example, if the operator pays much attention to the unit price of base stations, while ignoring the performance and power consumption of base stations, the number of sites in the network might increase greatly. As a result, the costs on base station equipment will increase greatly, leading to much higher TCO.

ZTE's WiMAX Solution Offering Lower TCO
With rich R&D experience in GSM, UMTS, CDMA2000 and TD-SCDMA systems, ZTE has taken into consideration operator's needs for lower TCO when designing and developing WiMAX products.

Distributed BBU+RRU solution
Figure 1 shows a distributed BBU+RRU solution for the WiMAX network. The Baseband Unit (BBU) is based on the MicroTCA architecture. MicroTCA standard-compliant modules can be applied to various types of sites. Therefore, the number of spare parts and turnover period can be decreased, hence saving OPEX.

The Remote Radio Unit (RRU) features small size and light weight, easy transportation and deployment. It supports outdoor installation modes, including wall-mount and pole-mount, and various networking methods, such as star, link, ring, and mixed networking. The RRU can support up to four levels of cascading, which offers placement flexibility while saving costs.
The GPS can be connected to BBU and shared by all BBU sectors, thus cutting the CAPEX.
Between the BBU and the RRU, the optical fiber is adopted to lower feeder losses, increase coverage, and decrease sites, hence decreasing the CAPEX and OPEX.
The site acquisition costs are a major part of the CAPEX. The WiMAX BBU adopts the box plug-in design. When the equipment room is available, the BBU can be placed in a standard 19-inch rack, or share the same rack with 2G/3G or transmission equipment. If there is no equipment room, the BBU can be placed in an outdoor cabinet, which saves the equipment room lease cost. The installation flexibility of the BBU decreases the site acquisition difficulty and avoids schedule delay, hence effectively controlling the CAPEX.

Serial coverage enhancement technologies
The WiMAX network uses higher frequency than 2G/3G networks, which causes problems like smaller coverage and larger number of sites. To solve these problems, the coverage enhancement technologies are introduced to improve coverage and save CAPEX and OPEX.
Major coverage enhancement solutions are the Multiple-Input Multiple-Output (MIMO) technology for dense urban areas and the Beamforming (BF) technology for rural areas.
Regarding link budgeting, the uplink is always limited, and the base station coverage is restricted, as the base station has big transmit power and high antenna gain, while the terminal has restricted transmit power and antenna gain. In ZTE's WiMAX solution, there are more uplink antennas than downlink antennas, for example, MIMO adopts 2Tx×4RX, and BF adopts 4Tx×8Rx, which effectively improves uplink budget, hence increasing coverage. Compared with the other vendor's MIMO (2Tx×2RX) and BF (4Tx×4Rx), ZTE's solution enables bigger coverage and less number of sites, thus decreasing TCO. By now, ZTE is the only vendor in the world that supports BF (4Tx×8Rx).
Cyclic Delay Diversity (CDD) is a technique, where multiple transmit antennas transmit delayed versions of the same signal. It can improve the downlink coverage performance. By using the CDD scheme, the 4-antenna transmit diversity provides 2~4dB higher gain over the 2-antenna transmit diversity.
With the introduction of coverage enhancement technologies, less number of sites will be necessary and the corresponding supplementary equipment will also be saved. This can significantly decrease the operator's CAPEX and OPEX.

Flexible, smooth upgrade and capacity expansion
In a mobile communications network, future capacity expansion should be taken into consideration at the initial stage of the network construction.
Figure 2 is ZTE's typical WiMAX network upgrade solution. The BBU supports Partial Usage of Subchannels (PUSC) with 3 Segments, PUSC with All Subchannels, and Full Usage of Subchannels (FUSC). In the early phase of network construction when fast network construction and complete coverage is required, the 10MHz PUSC with 3 Segment mode can be used. In the middle stage when the traffic of each subscriber increases, the system can be upgraded to support 3×5/10MHz PUSC with All Subchannels, and in the final stage, the system can be upgraded to support 2×10MHz PUSC with All Subchannels.

Each BBU supports up to 12 sectors and 120MHz bandwidth, and delivers up to 600Mbps peak throughput. Therefore, the upgrade requires only software upgrade or addition of boards in the rack. This solution is fast, cost-effective, and flexible.
The RRU supports up to two carriers, for example 2×5MHz or 2×10MHz. In the early phase of network construction, the RRU can support 5/7/10MHz single carrier; when capacity expansion is needed, it can support two carriers through software upgrade.
ZTE's BBU+RRU solution meets requirements of network upgrade while curtailing to the largest extent CAPEX for capacity expansion.

Future evolution of SDR-based BS 
ZTE's WiMAX products take into account network evolution risks and protect operator's investments. The base station equipment adopts the Software Defined Radio (SDR) technology, satisfying the needs for radio network evolution, superimposition, and convergence.
The BBU adopts the high-performance digital signal processor and supports WiMAX, GSM, WCDMA and CDMA2000 systems. Through software configurations, it can enable the convergence between WiMAX and 2G/3G systems. The future BBU can support 16m and Long-Term Evolution (LTE) through software upgrade as shown in Figure 3.


The RRU adopts different RF modules to support TDD or FDD and systems in different frequency bands. The RRU can support systems using the same frequency band and duplex mode through software upgrade; it can also support systems using different frequency bands and duplex modes through small hardware upgrade.
The BBU+RRU solution fully satisfies the operator's requirement for future evolution while maximally cutting the CAPEX for capacity expansion.

Conclusion
Based on rich R&D experience in wireless communications, ZTE fully considers the operator's need for lower TCO when designing WiMAX products.
ZTE provides end-to-end WiMAX solutions and makes use of serial coverage enhancement technologies to decrease the number of sites in target areas. It offers flexible upgrade and capacity expansion solutions to save expenditures. It enables real convergence between the WiMAX and the 2G/3G networks by utilizing SDR technology; and it can also support 16m and LTE with a software upgrade, meeting the network trend towards future evolution, superimposition, and convergence.
Featuring excellent performance and reduced TCO, ZTE's WiMAX products have commanded an industry-leading position. By the end of 2008, ZTE had deployed 30 mobile WiMAX commercial and trial networks in America, Africa, Asia and Europe. ZTE's full series WiMAX products are the best choice for operators in constructing WiMAX networks.