R&D Trends in Communications Infrastructure to Achieve Safe and Secure Access Networks

1.1 Advancing deterioration of facilities

If current trends continue, in 20 years, approximately 80% of all conduits and manholes will be more than 50 years old and entering their old age (Fig. 2). Approximately half of existing conduits are steel and have advanced rust and corrosion, which is becoming an obstacle in installing cable. Moreover, weakening of concrete components such as manholes and cable tunnels due to cracking, peeling, and corrosion of rebar is becoming a concern. It would be ideal to handle these age-related issues by systematically renewing the facilities, but the cost and time required to renew the large amount of infrastructure buried underground would be huge, and it is therefore not practical. Excavation of roadways also significantly disrupts the surrounding environment. Accordingly, a major R&D issue is determining how to enable continuous use of old facilities without renewing them.

Fig. 2. Amount of infrastructure construction, indicated in 5-year periods.

1.2 The need to earthquake-proof existing facilities

Developing technology for earthquake-proofing infrastructure facilities has been an ongoing theme at the laboratories ever since its inception. Many large earthquakes have occurred since then, and the knowledge gained from each experience has been accumulated and used to improve earthquake-proofing technologies. The 1964 Niigata earthquake, the 1978 Miyagi earthquake, and the 1995 Kobe earthquake in particular provided opportunities to radically revise earthquake-proofing capabilities because of the extent of the damage that occurred.

The Great East Japan Earthquake in 2011 was the largest in recorded history in Japan, and it provided an opportunity to evaluate the performance of infrastructure earthquake-proofing technology applied up to that point. The evaluation revealed that only 1–3% of infrastructure facilities were damaged in most cases, a very low figure. This verified that underground facilities are highly earthquake-proof infrastructures. Furthermore, the facilities that were damaged were built during periods when older standards applied and earthquake-proofing capabilities were lacking. This also confirmed the effectiveness of current standards. In fact, there are still many older facilities that were built before the current standards were introduced. However, even if the renewal of such facilities was restricted to those along major routes and in areas where earthquakes were expected to occur, the cost of renewing all of them to current standards would still be prohibitive and impractical, just as it is in the case of aging infrastructure. Consequently, we expect that developing effective methods of predicting damage to facilities and applying earthquake-proofing measures where they are most needed will be an important R&D theme in the future.

2.1 Concrete pole inspection technology (automating and streamlining inspection)

NTT has approximately eight million concrete poles nationwide. Inspections of these poles are done mainly by visually inspecting them for cracks, which requires a certain level of skill. Furthermore, the upper part of concrete poles must be checked using binoculars, which is labor intensive and raises concerns that problems could be overlooked. Three technologies have been developed to enable this inspection work to be done more efficiently and effectively (Fig. 4).

Fig. 4. Technology for inspecting concrete telephone poles.

The first is a technology to detect cracks using image processing. Software is used to eliminate factors such as cables and dirt, which obstruct the detection of cracks, from the color and texture of images captured using an off-the-shelf digital camera. This enables automatic detection of cracks.

The second technology uses millimeter-wave radiation to detect cracks underneath the anti-posting sheet placed on the concrete pole. The previous image-processing technique is unable to detect cracks hidden by the anti-posting sheet, but millimeter waves are reflected by cracks and scattered in all directions, and this can be used to automatically detect cracks that are concealed by the anti-posting sheet.

The third technology is used to assess the condition of the pole by analyzing the vibrations that result from striking it. The purpose of this is not to detect cracks, but to measure the characteristic frequencies generated when striking the concrete with a hammer to automatically determine if the pole’s rigidity has decreased.

2.2 PIT (pipe insertion type) new-conduit method for facility repair, maintenance-free conversion, and earthquake-proofing

One problem with conduit facilities is deterioration of steel pipes. Over 60% of conduits, where multi-cable installations are planned, are diagnosed as faulty. Most of this is due to rust and corrosion of steel pipes. Technology to repair empty conduits that were faulty due to rust and corrosion already existed, but there was no way to repair them after the cable had been installed. The PIT new-conduit method resolves this issue (Fig. 5).

Fig. 5. PIT new-conduit method.

This method involves inserting a PVC inner pipe into a metal conduit that already has a cable installed. This new pipe encompasses the existing cable. The duct is replaced by the PVC pipe, so rust is no longer an issue, and no further maintenance is required. Use of this method can create capacity for three cables in one duct. The space for the existing cable (35 mm in diameter) accommodates up to a 1000-fiber optical cable, and the remaining two spaces (28 mm in diameter) can accommodate two new thin 1000-fiber cables, for a total capacity of 3000 fibers. The inner conduit also protects the cables, which increases the earthquake resistance of the conduit. This enables conduit earthquake-proofing without having to do the construction work of excavating roadways.

We are currently studying ways to expand the range of application areas for this technology. This includes reducing the diameter of the PVC pipe to apply it to narrower conduits that are weak or deteriorated, increasing the lengths of spans in which installation is possible, and supporting use in colder regions where cables must be protected from freezing groundwater.