Fujitsu and NI Demonstrate the Interoperability of the ORI Specification for Base Stations, Incorporating a Fujitsu-Branded RRH and a BBU Simulator Developed Using NI in Its Testing

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"Thanks to the RRH testing platform from NI, we were able to complete our interoperability testing in just half a day. This enabled us to verify that there were no problems relating to the ORI specification. In addition, we were able to demonstrate to the telecommunications market and business operators that a device implemented according to the specification, and a measurement environment for developing and deploying such a device, was already complete."

- Masaki Taniguchi, Wireless Systems Business Division, Network Products Business Unit, Fujitsu Limited

The Challenge:
Performing connection tests using remote radio heads (RRHs) and baseband units (BBUs) compliant with the ORI specification, in order to verify its interoperability.

The Solution:
Using NI’s flexible PXI-based RRH tester (BBU simulator) as the BBU to test interoperability.

Author(s):
Masaki Taniguchi - Wireless Systems Business Division, Network Products Business Unit, Fujitsu Limited
Kazuhiko Yamaguchi - Wireless Systems Business Division, Network Products Business Unit, Fujitsu Limited
Takefumi Miyamoto - Global Access Business Unit, Network Products Business Unit, Fujitsu Limited

Background

Traditionally, the base station device for mobile phones was an integrated system comprising a wireless section and a baseband unit (BBU), housed in a single chassis. However, the system currently gaining popularity separates the wireless section (the remote radio head, or RRH) and the BBU. The RRH comprises elements such as an RF amplifier, A/D converter, D/A converter, and a logic circuit for processing orthogonal modulation and demodulation. Conversely, a BBU comprises logic circuits for processing baseband modulation/demodulation and controls. The mainstream system separates these components so multiple RRHs can connect to a single BBU with an optical cable, as shown in Figure 1. The small cell system incorporates RRHs that are far smaller than conventional base station devices, and deploys them with a high degree of flexibility, such as in higher volumes, more extensively, or in higher densities. This allows for adaptability in the case of an increase in subscribers, expanded coverage area, or improved throughput.

Figure 1. A Base Station System Comprising a Combination of a BBU and RRHs

Three standard specifications are available for the interface between the BBU and RRHs (CPRI, ORI, and OBSAI from Nokia). The first is Common Public Radio Interface (CPRI), effectively known as the industry standard. CPRI defines only the specifications for the low layer near the physical layer, while RRH/BBU control signals corresponding to the upper layer are not strictly defined. In other words, the main objective of CPRI is to obtain cost effectiveness through volume production by standardizing aspects relating to hardware. Conversely, the upper layer can be tweaked using software, so vendors have a high degree of flexibility for expanding functionality and other features.

Fujitsu has a solid history of developing business for wireless infrastructure. Since 2004, we have brought CPRI-compliant BBU/RRH products to market, targeting standards such as W-CDMA, CDMA 1X/2000, and LTE. However, we have also focused a lot of attention on ORI (Open Radio equipment Interface), which is another specification for interfaces between BBU and RRH.

In addition to the low layer, the ORI specification aims to standardize aspects including the upper layer, such as control signals. The CPRI specification is more or less adopted without modification for the lower layer. Despite CPRI already being effectively accepted as the industry standard, the new ORI specification was formulated for various reasons.

Besides migrating to small cell systems, new technologies are being sequentially developed and implemented to cope with high traffic volumes. These include carrier aggregation; multiple input, multiple output (MIMO); enhanced Inter-Cell Interference Coordination (eICIC); and Coordinated MultiPoint (CoMP) transmission and reception. Under these circumstances, it seems that a variety of RRHs are needed to adapt to the various technologies. However, the CPRI standard commonly used as the specification for the interface between BBUs and RRHs then becomes a problem. This is because CPRI only defines the low layer, so individual vendors can use their own specifications for other aspects. In this scenario, telecommunications business operators must procure their BBUs and RRHs from the same vendor, unless such vendors publicly disclose their individual specifications so that other companies can adopt them. In other words, a complete ‘vendor lock-in’ situation would occur, which would inhibit the principles of competition, and costs would be unlikely to fall.

The desire to prevent vendor lock-in motivated business operators to actively drive the European Telecommunications Standards Institute (ETSI) to begin formulating the ORI specification. Fujitsu endorsed this movement, and has been participating in the formulation of this new specification since the inception of the ETSI ORI Industry Specification Group (ISG) in 2010. This is because, as a device vendor, we believe that we can expand our business opportunities further by promoting this kind of standardization and normalized specification.

The ORI specification has major benefits for those business operators driving its formulation. Popularization of ORI can help business operators construct systems and procure RRHs and BBUs from separate vendors, in accordance with their respective strategies, or to suit particular conditions when installing base stations. RRHs and BBUs that are compliant with ORI, which fully regulates the interface specification, can help products from any vendor to be “plugged and played.” As a result, flexibility for developing base stations dramatically improves, and it becomes easier to provide various services. It is also possible to rapidly introduce services in response to investments such as for frequency resources. If various vendors supply various RRHs and BBUs based on a standard specification rather than their own proprietary specs, business operators can immediately introduce and operate existing products that meet different requirements, such as corresponding frequencies, rather than developing new products from scratch.

Another advantage is that base station device vendors could enter the market solely for RRHs, or only for BBUs, if so desired. For RRHs in particular, various vendors could use their strengths in certain technologies when developing products. In Fujitsu’s case, our RRH products boast features such as compact size and low energy consumption. There are other vendors whose strengths lie in lowering costs or whose focus is on advanced functionality, and there is an opportunity for each respective company to enter the RRH market. Indeed, telecommunications business operators would love the opportunity to be able to deploy suitable products with these kinds of characteristics, if the timing and location were appropriate. If the market can offer a supply of products with various characteristics in terms of features, performance, and price, the laws of competition can help ensure that even better products are generated.

Challenges

The main issue for business operators and vendors promoting ORI, such as Fujitsu, is the concern about whether there may be any omissions or oversights in the ORI specification. If such concerns exist, individual vendors might respond by creating their own specifications (individual implementation), which would prevent any chance of guaranteeing interoperability.

Accordingly, Fujitsu attempted to confirm the interoperability of the ORI specification by independently developing BBUs and RRHs that were compliant with this specification and then testing their connection. Both products could be connected and passed with flying colors. However, we decided that a successful connection test involving BBUs and RRHs developed by the same vendor was not sufficient to prove that the ORI specification ensured interoperability with plug-and-play functionality. The spec sheet is written in natural prose rather than in a precise format such as a computer language. Accordingly, the language contains a degree of vagueness that is open to interpretation by the reader. For example, even if there were no major issues such as omissions or oversights, if a company misinterpreted the standard in the same way for both BBUs and RRHs, it might still be possible to connect the devices without any problem. This situation would be particularly likely if the same vendor developed both BBUs and RRHs. To eliminate this possibility, we began by getting two separate vendors to independently interpret the ORI specification. Next, we asked one company to implement the standard in a BBU, and the other in an RRH, based on their respective interpretations. In order to prove the interoperability of the ORI specification, we needed to connect BBUs and RRHs developed in this way, without any issues arising.

Solution and Effects

Fujitsu required support from NI to resolve the aforementioned issues. The main reason we chose NI was that it already offered an RRH tester (BBU simulator) compliant with CPRI at that stage. This RRH tester was composed of a PXI-based chassis, controller, high-speed serial module, RF attenuator, and a vector signal transceiver (VST) (See Figure 2). The VST combines the functionality of a vector signal generator and a vector signal analyzer so the bidirectional properties (up/down) of RRHs can be evaluated using this tester alone. Knowing that NI provided this caliber of product, we felt sure that the company could help us with an RRH tester that was similarly compliant with the ORI specification.

Figure 2. Composition of the RRH Tester. NI developed an ORI-compliant RRH tester by making modifications at the software level, including FPGA programming.

NI listened to our briefing and complied with our wishes by modifying a CPRI-compliant RRH tester to suit our needs. Specifically, the team performed developments based on the ORI specification (Release 1) by making modifications at the software level, including FPGA programming, and provided it to us as an ORI-compatible RRH tester. We assessed the functionality and RF properties stipulated in the ORI specification, and the results confirmed that the Fujitsu-branded RRH could be connected to the RRH tester from NI with no issues. According to this experiment, two different companies had developed an RRH and BBU respectively, based on the same single standard. The fact that these components could be connected with no problems proved that there were no omissions or oversights in the ORI specification, and interoperability could be guaranteed.

We also considered that some degree of trial and error would probably be involved before we could establish a connection. However, we connected successfully in just half a day after bringing in the RRH tester. We believe that these results indicate that it would also take an extremely short time to deploy a device if ORI were adopted in commercial networks. Also, the results prove that migration to an ORI-compliant RRH or BBU can easily be achieved.

Although this test study used NI’s RRH tester as a solution for demonstrating interoperability, the actual use of this tester helped us see many more potential opportunities. In particular, the introduction of NI’s RRH tester at the development stage and volume production stage for ORI-compliant RRHs manufacturing suggests even greater benefits.

Various measurement devices are required for evaluating wireless properties at the RRH development stage, such as a spectrum analyzer, RF signal generator, and power meter. Furthermore, the configuration of each measurement device must be changed for each property being measured, which means that the structure of the measurement environment can become extremely complicated. The development stage also requires error case testing in addition to the verification of basic functionality and attributes. It is therefore preferable to use a BBU simulator, which enables the creation of various software-oriented conditions. However, developing a BBU simulator at Fujitsu would require vast amounts of manpower. In contrast, NI’s RRH tester provides the functionality of measurement devices as well as a BBU simulator. It is extremely effective because users can perform all kinds of RRH assessments with a single system.

In contrast to the development stage, which tests a product from every perspective, a volume production inspection checks only for whether manufacturing has been carried out correctly. It’s only natural that measurement systems for such different objectives would be different for the respective stages. The need to build two different measurement systems to correspond to development and volume production was a potential problem due to the vast amounts of manpower and costs involved. We believe that NI solutions also resolved this issue.

Systems that are extremely versatile and easily customized, as NI products are, can be applied to both the development stage and the volume production stage. If the same measurement device can be used for both stages, then some of the various scripts (testing programs) used for testing during the development stage can later be selected as required, and reused without modification, for shipping inspections. The benefits are enormous in terms of cost reduction and timely supply. If more business operators adopt the ORI specification, and Fujitsu can mass produce and ship its ORI-compliant RRHs, we would be extremely likely to use NI’s RRH tester in our testing system during development, as well as for our inspection device during volume production.

NI solutions also benefit vendors of RRH devices. If a specification for the interface between BBUs and RRHs were made publicly available, there would likely be many vendors interested in participating in the market. In Fujitsu’s case, we have already brought BBUs to market, so although we have accumulated enough knowledge to develop simulators at Fujitsu, other companies that specialize in RF or other technologies do not necessarily have equivalent capabilities sufficient for developing BBUs. NI products would be extremely useful for those vendors, as they would no longer need to develop their own BBU simulators.

NI solutions also carry many advantages for business operators. If an operator uses BBUs and RRHs from separate vendors instead of procuring them as a set from a single vendor, the business operator would essentially be the one responsible for ensuring the interoperability of those devices. This case study has also demonstrated that even if some kind of trouble occurred after the ORI specification had been implemented, a measurement environment already exists for resolving any such issues. This further encourages business operators to have confidence in introducing the ORI specification.

Future Developments

Fujitsu has decided to continue with both its CPRI and ORI businesses, even if the ORI specification is standardized and popularized. We based this decision on the fact that it is unlikely that every operator would suddenly have an immediate need for ORI-compliant products exclusively, and there are also some business operators who would be thankful if both BBUs and RRHs can be supplied as a complete system. However, even those business operators might migrate from CPRI to ORI. Accordingly, we believe that ORI can provide expanded business opportunities for Fujitsu.

We announced Release 1 of the ORI specification in August 2012. Since then, we have released new versions sequentially with added functionality. By February 2015, we made Release 4, with added compression functionality, available. As a vendor of base station products, Fujitsu plans to continue following this trend by developing products that are compatible with a wide range of applications, so that business operators can select even better BBUs and RRHs with even more advanced flexibility. Also, as part of our efforts to promote the popularization of the ORI specification, we will demonstrate to the market and business operators that there are already products suited to practical use, by carrying out tests on actual equipment. We also hope that as a business partner of Fujitsu, NI will promote the fact that it already offers a measurement environment that can be used for development, manufacturing, and deployment, as shown by the RRH tester (BBU simulator) in this case study.

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