Analysis of LTE Testing Difficulties

　　Long Term Evolution (LTE) is rapidly gaining popularity around the world. China Mobile has started the construction of more than 200,000 TD-LTE base stations across the country, and 100 key cities will achieve continuous coverage of the main urban areas. At the same time, 1 million TD-LTE terminals will be purchased. China Unicom and China Telecom are also actively increasing the construction of LTE test networks, and will prepare for the upcoming LTE commercialization in terms of networks, services and terminals.

　　The challenges to test equipment capabilities during the implementation and deployment of LTE networks exceed any technology upgrade and migration since the implementation of WLAN technology. The physical layer of LTE/LTE-Advanced is different from previous technologies, and the changes in test equipment requirements for LTE and LTE-Advanced are unprecedented since the introduction of 802.11 wireless LAN technology in the early 2000s.

　　Testing technology is a critical link in the LTE development industry chain. Faced with the development direction of multi-mode and multi-frequency terminals in the LTE industry and the complex network environment in the mobile Internet era, what are the difficulties in LTE testing that need to be solved?

　　Backward compatibility issues

　　The growing deployment of LTE has brought significant challenges to wireless test equipment suppliers. This requires ensuring that LTE terminals can work seamlessly on existing networks, and also ensuring that they comply with the latest LTE standards. As a new technology that is still being deployed by some operators around the world, these service providers will tend to purchase forward and backward compatible test tools for future use and LTE testing.

　　In mobile terminals, terminals need to switch seamlessly between the coexisting 2G, 3G, and LTE to provide users with a complete user experience; 2G and 3G services such as calls, text messages, multimedia messages, and positioning need to be well integrated into LTE terminals; LTE terminals also need many new applications to attract users. Therefore, terminal application testing is more diverse and requires more compatible standards.

　　Challenges brought by multi-standard coexistence. The emergence of multi-mode terminals and multi-mode base stations requires that the same device can still maintain good performance when multiple standard signals coexist. Therefore, multi-mode coexistence requires test instruments to be able to generate and simultaneously analyze signals of multiple standards that coexist.

　　Therefore, the parallel development of multiple LTE standards has become a complex technical problem to be solved, making interconnection with existing networks a challenge. The complexity of LTE testing and the unique application requirements from consumers have led to limited availability of LTE test tools in meeting multiple testing requirements.

　　The Challenge of Multi-Antenna Testing

　　Currently, TD-LTE, FDD-LTE and LTE-Advanced (LTE-A) wireless technologies use several different multiple-input multiple-output (MIMO) technologies. Given the increasing complexity of MIMO systems, the related test methods will also become more challenging. For example, currently deployed MIMO technologies use two antennas to improve channel performance. Some LTE communities have taken the lead in using eight-antenna technology to achieve higher performance. These advanced technologies will make the choice of test methods even more critical.

　　In order to form a simpler and flatter network structure, many network elements in the LTE network have been merged into the base station, and the functions of the base station itself have been enriched. Therefore, the base station test, which was not complicated in the past, has become very complicated and has high requirements. According to relevant manufacturers involved in foreign network testing, the core part of the new test is multi-antenna testing - 2 antennas, 4 antennas and even 8 antennas for TDD will greatly increase the air interface cost, so it is necessary to ensure that the performance of multiple antennas is best utilized to meet the cost investment, so this part of the test must be strict and demanding.

　　An eight-antenna system can quadruple the number of channels used by a 2x2 MIMO system. However, researchers have begun exploring techniques that require eight times the number of antenna elements in a 2x2 system. Reproducing reciprocal high-antenna-count test scenarios in the lab presents severe constraints in terms of space and other resources. Emerging advanced antenna technologies also present new challenges compared to traditional channel modeling. Testing the system in dynamic scenarios is essential when testers need to fully understand the performance of the system.

　　An effective test methodology that can address these challenges must use geometric channel modeling that supports a variety of advanced antenna technologies. It must also be able to run dynamic scenarios in real time. Finally, the test methodology must be able to reliably and efficiently create all the details of the bidirectional MIMO channel in an eight-antenna system, and it must do all of this within a small, portable device form factor.

　　As the industry pursues higher data rates for newer wireless applications, the number of antennas used and the complexity of advanced antenna technologies will inevitably increase. This trend will pose a huge challenge to LTE and LTE-A testing that includes advanced antenna technologies. Therefore, new methods and new ways of thinking about test scenarios will be indispensable.

　　Testing cost and time

　　New standards also mean new challenges. Compared with 3G mobile communication standards, 4G/LTE terminal products have nearly 100 more test items. Not only are wireless standards increasing, but the frequency bands supported by terminals are also increasing. This puts higher demands on production testing, with test items and test time several times higher than before. Increased test time means increased test costs, and how to find fast and effective test methods has become an important challenge for 4G/LTE system testing. On the other hand, as the amount of data transmission increases, the complexity of measurement also increases. The modulation and demodulation of 4G/LTE signals requires an order of magnitude increase in signal processing capabilities, which puts new demands on the test system.

　　Other Difficulties

　　LTE and LTE-Advanced bring huge changes to cellular communication systems. No other technology change can compare to this in the nearly 10 years since the transition from GSM to W-CDMA systems. LTE systems use OFDM modulation rules to send more data to more users more quickly. OFDM brings new challenges to testing. OFDM signals are composed of multiple subcarriers, which are arranged very precisely and occupy a higher bandwidth, so they are more complex and more difficult to test.

　　As LTE develops, core network traffic will grow exponentially. Whether the core network can handle this growth and whether the switch and server capacity are sufficient are crucial to network quality, which also requires repeated verification during the testing phase.

　　In addition, such as reduced waiting time, higher user data rates, improved system capacity and coverage, and reduced operating costs. The core network cannot obtain effective wireless data for analysis, which increases the complexity of network management and optimization. Traditional protocol analyzers are already difficult to meet these new challenges, and special solutions are needed to monitor and optimize network performance. For a period of time, this is still a difficulty that major test manufacturers need to overcome. Only by solving these difficulties can we lay a solid foundation for the development of the entire LTE industry.