Graceful CDMA to LTE Evolution

The estimation of global wireless subscriber growth made by CDG shows that 2G, 3G and 4G technologies cannot be simply substituted for one another, but they can complement one another and coexist in the next 5 to 10 years (see Figure 1).

Since Qualcomm announced terminating its research on the UMB technology at the end of 2008, the global leading mobile operators have gradually chosen LTE as their 4G technology. Therefore, how to gracefully evolve CDMA to LTE with minimum investment is becoming a major concern of the traditional CDMA operators.

CDMA to LTE Evolution Strategy
ZTE started research into the unified platform strategy two years ago, which laid a sound foundation for the evolution from CDMA to LTE. Its Software Defined Radio (SDR) base station platform based on the microTCA standard makes possible unified hardware architectures of all wireless products, thus avoiding the investment risk caused by the technology evolution route. Furthermore, the supply of traditional CDMA/GSM/UMTS base stations in large quantities greatly reduces the hardware cost in the evolution to LTE and thus reduces the operators’ CAPEX and OPEX.

Baseband evolution
At the initial stage of the CDMA/LTE development, separate LTE Baseband Processing (BP) boards are rolled out into the market. As the CDMA/LTE market grows on a large scale, ZTE will launch its highly-integrated CDMA/LTE dual-mode BP board (see figure 2).

RF evolution
The traditional CDMA RF units provide 1Tx/2Rx MISO. In order to support 2Tx/2Rx MIMO on the legacy system, two RRUs need to be combined. Besides, ZTE has developed CDMA/LTE dual-mode RRU (see Figure 3), with a single RRU enabling the coexistence of CDMA and LTE systems.

CDMA-to-LTE Evolution Cases
Based on the abovementioned CDMA-to-LTE evolution strategy and the global CDMA network applications, typical CDMA-to-LTE evolution cases are introduced as follows:

Case 1: Traditional CDMA/LTE dual-mode
For the evolution from the traditional CDMA network to LTE, when using the original 1Tx/2Rx RRU, it is necessary to add a conventional RRU to support 2Tx/2Rx MIMO, add a LTE BP board to the baseband part, and implement required software upgrade (see Figure 4).

Case 2: CDMA/LTE dual-mode RF
In this case, CDMA/LTE dual-mode RRU is adopted for networking. The evolution from CDMA to LTE can be accomplished simply by adding a LTE BP board and implementing necessary software upgrade (see Figure 5). 

Case 3: CDMA/LTE dual-mode BP
In this case, CDMA/LTE dual-mode BP board and CDMA/LTE dual-mode RRU are adopted for networking. The evolution from CDMA to LTE can be achieved only by software upgrade without any hardware change (see Figure 6).

Conclusion
With the deepening development of globalization and the increasing maturity of the telecommunication industry, the debate on the evolution of wireless communications tends to focus on the unified standard. This is not only an inherent demand of the telecommunications industry for low cost operation, but also the driving force behind the tendency toward LTE standard.
As a leading global provider of telecommunications equipment and network solutions, ZTE has launched its industry’s first future-proof SDR solution to adapt to the trend of the telecommunication industry. With the innovative SDR solution, ZTE achieved some significant successes in the global CDMA/GSM/UMTS market. The SDR solution runs radio functionality as software modules on an integrated, unified hardware platform, allowing CDMA operators to cost-effectively upgrade their networks to LTE.