[System Analysis] Difficulties in LTE Testing

Long-Term Evolution (LTE) technology is rapidly gaining popularity around the world. China Mobile has launched more than 200,000 TD-LTE base stations nationwide. 100 key cities will achieve continuous coverage in the main city and purchase 1 million TD-LTE terminals. China Unicom and China Telecom are also actively expanding the construction of the LTE trial network, preparing for the upcoming LTE commercialization from various aspects such as network, service and terminal.

The LTE network challenges the test equipment capability in implementation deployments over any technology upgrade and migration since the implementation of WLAN technology. The physical layer of LTE/LTE-Advanced is different from the previous technology. The changes required by LTE and LTE-Advanced for test equipment have never been introduced since the introduction of 802.11 wireless LAN technology in early 2000.

Test technology is a key link in the LTE development industry chain. In the face of the LTE industry's multi-mode multi-frequency terminal development direction and the complex network environment of the mobile Internet era, what are the test difficulties of LTE test?

Downward compatibility problem

The growing LTE deployment poses significant challenges for wireless test equipment vendors. This requires ensuring that LTE terminals work seamlessly on existing networks and that they are subject to the latest LTE standards. LTE is 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 the mobile terminal, the terminal needs to seamlessly switch between the coexisting 2G, 3G, and LTE to provide a complete user experience; 2G and 3G services such as call, SMS, MMS, and positioning need to be well integrated into the LTE terminal; LTE The terminal also needs many new applications to attract users. Therefore, terminal application testing is more diverse and requires more standards of compatibility.

The challenge of multi-standard coexistence. The emergence of multimode terminals and multimode base stations requires that the same device maintains good performance when multiple standard signals are present at the same time. Therefore, multimode coexistence requires that the test instrument can generate and simultaneously analyze multiple standard signals.

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

Multi-antenna test problem

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 associated test methods will be more challenging. For example, currently deployed MIMO technology utilizes two antennas to improve channel performance. There are also some LTE communities that have taken the lead in adopting 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 are merged into the base station, and the function of the base station itself is rich. Therefore, the base station test which is not complicated in the past becomes very complicated and requires very much. high. In the view of relevant vendors involved in foreign network testing, the most core part of the new test is multi-antenna testing - 2 antennas, 4 antennas and even TDD 8 antennas will greatly increase the air interface cost, so it is necessary to ensure the best performance of multiple antennas. The land is played to meet the cost of investment, so this test must be strictly high.

The eight-antenna system can increase the number of channels used in 2x2 MIMO systems to four times the original level. But researchers have begun to explore techniques that use 8x the number of antenna components for a 2x2 system. If you reproduce the reciprocal high antenna count test scenario in the lab, you will face many serious constraints on space and other resources. Compared with traditional channel modeling, emerging advanced antenna technology will also bring new challenges. Testing a system in a dynamic scenario is essential when testers need a complete understanding of the performance of the system.

Effective test methods that can address these challenges must be modeled using geometric channels that support a variety of advanced antenna technologies. It must also be able to run dynamic scenes in real time. Finally, this test method must also be able to reliably and efficiently create all the details of a bidirectional MIMO channel in an eight-antenna system, and all of these functions must be implemented within a small, portable device specification.

As the industry is pursuing higher data rates for newer wireless applications, the number of antennas used and the complexity of advanced antenna technology are bound to increase. This trend will pose a huge challenge for LTE and LTE-A testing with advanced antenna technology. Therefore, new methods and new test scenarios will be indispensable.

Test cost and time

The new standard also means new challenges. Compared to the 3G mobile communication standard, there are nearly 100 more test items for 4G/LTE terminal products. Not only is the wireless standard increasing, but the frequency band supported by the terminal is also increasing. This puts higher demands on production testing, and the test project and test time are several times higher than before. The increase in test time means an increase in test costs, and how to find a fast and effective test method becomes an important challenge for 4G/LTE system testing. On the other hand, as the amount of data transmission increases, the complexity of measurement increases. The modulation and demodulation of 4G/LTE signals requires an order of magnitude of signal processing capability, which puts new demands on the test system.

Other difficulties

LTE and LTE-Advanced have brought huge changes to cellular communication systems. In the past 10 years since the transition from GSM to W-CDMA systems, no other technological changes have been comparable. LTE systems use OFDM modulation rules to more quickly send more data to more users. OFDM will bring new challenges to testing. The OFDM signal consists of multiple subcarriers, which are arranged very accurately and occupy a high bandwidth, so it is more complicated and the test is more difficult.

After LTE is developed, the core network traffic will grow geometrically. Whether the core network can solve this growth problem, whether the switch and server capacity are sufficient, is critical to the network quality, which also requires repeated verification during the test phase.

In addition, such as reduced latency, 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 analysis instruments have been 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 difficult point for major test vendors to overcome. Only by solving these difficulties can we lay a solid foundation for the development of the entire LTE industry.

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