eNodeB (enhanced Node B) simulators are an important piece of test networks that are used for a variety of user equipment tests. eNodeB simulators run as only one part of a simulated networks, so that interactions among the Radio Access Network and Evolved Packet Core can be tested as well as interactions between eNodeBs in LTE.
Node Bs, or base stations, were the predecessors of eNodeBs, in previous generations of network technology. Base stations used to only be able to communicate with the core of the network, and all information had to be conveyed to the core in order for network functions to be performed. In Long Term Evolution networks, the eNodeBs are able to communicate with each other via the X2 interface, which allows some network intelligence to be applied at the edge of the network rather than having to be carried back into the network core. This reduces latency and enables some peer-to-peer applications for functions that do not need to extend deep into the network.
Multi-format eNodeB simulators can emulate a variety of network technologies, according to Mike Barrick, business development manager for wireless at Anritsu: GSM, UMTS, wideband CDMA base stations or LTE base stations. This enables devices to be tested across both LTE and legacy technologies.
Barrick said that in order to perform testing using eNodeB simulators, the base stations are simulated as part of a radio access network (RAN) to test mobile devices’ interactions across a slice of the network, not merely with the base station alone.
“To really do our job, what you have to have is the eNodeB, plus the EPC to some degree, to do what needs to be done,” Barrick said.
Barrick said that simulated networks can be used for conformance testing of LTE devices, which involves a series of detailed tests laid out by the Global Certification Forum and/or the PTCRB, a wireless device certification forum formed by North American operators; and functional performance testing.
This testing enables new devices to be certified, and the device ecosystem for LTE is exploding. According to the Global Mobile Supplies Association, there were 821 LTE certified devices as of March 27. That number grew from 666 on January 13 of this year.
Simulators of LTE networks must be equipped to handle both FDD (frequency division duplexing) and TDD (time division duplexing) flavors of LTE in order to enable testing by operators across the ecosystem. Sprint has said it is in the process of launching a multi-mode network that includes both FDD and TDD LTE. Generally, though, TDD LTE is mostly used in the Asia-Pacific region, while FDD LTE is more commonly used across the ecosystem, particularly in the U.S. Barrick said that in Anritsu’s case, the testing of both FDD and TDD is enabled by software that runs on top of Anritu’s test hardware.
In addition, simulators also must allow testing in a wide range of frequencies, given that LTE bands are not standardized around the world and there are dozens of bands in use, varying based on a carrier’s spectrum holdings, license requirements and what spectrum they have been able to free for launching LTE networks. The fragmentation of the LTE spectrum ecosystem has been a point of concern for roaming, as devices are limited in the number of bands they can support; however, so far the wireless industry has managed to cope, although many international LTE networks are still in their early days.
eNodeB simulators can also be part of a test network that includes simulation of Voice over LTE servers, which are part of the IMS core. If a carrier wants to simulate a network in order to test VoLTE calls on wireless devices, the VoLTE servers must also be simulated or a VoLTE call can’t be set up, Barrick noted.
