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Testing LTE Networks: Operators and equipment vendor concerns

March 31, 2014

The rapid increase in demand for bandwidth-intensive services as well as the proliferation of smartphones has led to a rise in the uptake of mobile broadband services. While HSPA and EVDO networks have traditionally been utilised to provide data services, operators are increasingly setting up long term evolution (LTE) networks to support the rising demand for high speed services. As compared to the former networks, LTE technology offers greater data throughput and speeds, higher spectral efficiency, and lower cost of ownership. To ensure that LTE networks provide optimum broadband connectivity (low latency and jitter, and high data transmission rates), adequate network testing is required at various deployment stages. However, due to the complexity of LTE network systems and constant technology innovation on the user equipment front, network testing is becoming an increasingly complicated process.

Given that the voice segment still contributes a major share of service revenues for operators across the world, ensuring backward compatibility of LTE networks with legacy technologies is crucial. Besides, as network roll-out for 4G services is usually undertaken in phases, most areas remain uncovered in the initial few phases. As a result, LTE subscribers are shifted to GSM/HSPA or CDMA/EVDO networks in areas not covered by LTE networks. Effective handover between these legacy networks and LTE infrastructure is, therefore, essential to ensure seamless service availability at all intervals. Consequently, testing compatibility and interoperability among these networks becomes imperative.

Network assessment entails significant challenges for operators that opt for the single radio access network strategy as against network overlay for rolling out LTE. This is primarily because testing networks that have been deployed using the former strategy, which involves replacing existing 2G and 3G base transceiver stations (BTSs) with multi-standard BTSs, results in service disruption and poor user experience. Besides, multi-vendor network deployment further complicates the testing process owing to varying configurations and standards used by different vendors.

A key challenge in testing of LTE networks is the lack of spectrum harmonisation for 4G services. Globally, operators are using different spectrum bands – Band 1, Band 7, Band 13 for frequency division duplex (FDD), and Band 30 and Band 48 for time division duplex (TDD) – for LTE networks. These bands conform to and operate on different standards and configurations. This requires equipment vendors to manufacture a wide range of testing instrument each specific to different standards.

Service providers are also implementing small cells in addition to a macro network to provide enhanced coverage and capacity in a HetNet set-up, especially in high density areas. With both small cells and macro networks using the same spectrum band, interference becomes a major concern. Also, hand-off issues between a macro network and small cells need to be addressed before deployment. Another aspect that requires extensive testing during the deployment of LTE networks and distributed antenna systems is passive intermodulation, which results in spurious signals in the network and affects service quality.

Meanwhile, the LTE-enabled test and measurement (T&M) equipment available at present can cater only to limited spectrum bands (particularly LTE-FDD) utilised in mature markets, which were the early adopters of the technology. However, several Asian operators, including those in China and India, have begun opting for LTE-TDD technology. Given that these two markets account for most of the global mobile subscribers and have significant growth potential in the mobile broadband segment, several original equipment manufacturers (OEMs) have been compelled to develop T&M instruments that support multiple technologies and multiple spectrum bands on the LTE network.

The deployment of varying antenna configurations and multiple input, multiple output (MIMO) antennas in LTE networks creates additional testing challenges. To offer higher bandwidth, operators are deploying multiple antennas (2x2 and 4x4) on tower sites. However, MIMO antennas, which use higher-order modulation

techniques, are more susceptible to signal interference. With the introduction of LTE Advanced technology, which involves the deployment of 4x4 and 8x8 MIMO antennas for signal transmission, there will be issues in ensuring different signals reach user equipment at the same interval. Further, OEMs have contended that installing additional transmitters and receivers in the test equipment (spectrum analyser) increases its cost significantly, thus limiting its demand. Also, test instruments are required to assess the performance of mobile handsets in real time and must have transmission and receiving characteristics similar to those of 4G BTSs.

Testing requirements have become more complex with the emergence of LTE-based networks and constant development of technology standards and protocols. For instance, several service providers are already undertaking a software-defined networking approach to automate operations and reduce the field maintenance requirement for their existing wireless networks. They are also planning to conduct trials of LTE Advanced networks to achieve higher mobile broadband speed.

Thus, vendors will have to offer more innovative T&M equipment to ensure that service providers are able to integrate new technologies in their 4G networks in a time-bound manner.

 
 

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