HIROSHIMA, Japan — The city of Hiroshima is the largest city in the southwestern part of Honshu, Japan’s largest island. Several national and local broadcasters, including RCC Broadcasting Co. and its RCC Radio division serve Hiroshima’s population of approximately 1,200,000.
RCC Radio’s AM broadcasts cover the entire Hiroshima prefecture with seven medium-wave transmitters. In compliance with international broadcast regulations, certain sites operate on the same frequency, creating two islands of single-frequency networks that share synchronous signals.
“Japan’s proximity to other countries means that medium-wave radio broadcast signals, which can travel long distances at night, can potentially interfere with signals in other countries,” said Shotaro Umezawa, representative director, Maple Audio Technology, a distributor, consultant and system integration firm based in Shizuoka, Japan.
“To avoid any potential interference problems or lengthy delays, RCC Radio opted to transmit some of their stations on the same frequencies about 20 to 30 years ago. The other benefit is that listeners do not have to change stations as they drive through the region.”
The launch of those transmitter sites many years ago means that much of the infrastructure is aging. This is especially true of three stations operating on 1458 kHz in the cities of Miyoshi, Shobara and Tojo. Since launching, all three sites have been fed from RCC’s headquarters in Hiroshima.
RCC’s headquarters feeds the AM signal over a BSU (Broadcast Service Unit), which operates on a TDM-based T2 digital network — four times the speed of T1 — from NTT. The signal is sent to the Miyoshi site, which is the closest in proximity. From Miyoshi, the feeds are delivered to a repeater site in Saijo and then onto the other two sites. These sites are fed via redundant Toshiba TTL systems, using dedicated 160 MHz analog links.
While all of these TTL links have been reliable, redundancy requirements that the Japanese government recently issued have forced an infrastructure change for RCC Radio.
“The requests require redundant links for signal transport for all radio stations, including those operating across synchronous networks,” said Umezawa. “Though it is possible to do this via TDM fiber-based connections, the only real cost-effective way to achieve this is over IP.”
IP IN JAPAN
There remains much uncertainty about IP for broadcasting in Japan, he said, while adding that TDM links have grown increasingly more expensive.
“The expense of a second, backup TDM link is far from desirable,” he said. “So, while IP has not been embraced for television, radio broadcasters here are slowly adopting IP to save money.”
Introducing IP to an existing SFN, particularly in an AM system, is not without its challenges. As Umezawa explains, the headend and transmitter sites are isolated by approximately 150 kilometers/93 miles from each other, yet some areas of overlap can create areas of interference in the middle.
“Each site is trying to adjust to the same reception level, typically in areas with minimal population,” he said. “But for people listening in their cars, there will be noise about every 300 meters as they drive through. This is due to AM radio waves and how they operate with single-frequency networks. Making an AM SFN architecture work over IP is new territory in Japan.”
CONNECTING THE DOTS
The three sites, as Umezawa explains, are separated by a series of mountains and valleys. To ensure proper timing across the challenging terrain, he and his team required exact GPS clocking to ensure synchronized networking of signals across each transmitter site. Two of the transmitter sites — Shobara (1 kW) and Tojo (100 W) — use GatesAir (formerly Harris) Flexiva DAX-1 transmitters, and the Miyoshi site uses two redundant Toshiba AM 100 W transmitters.
Once new fiber lines were laid and the network was secured, it came down to finding codecs that would deliver the precise GPS timing that was required to eliminate the interference challenges in an AM SFN, while ensuring reliable service.
“I have been doing research over the past four years about fulfilling the technical requires of AM SFNs,” he said. “I found three companies that provided a working AM SFN solution. GatesAir was the only company that could, with certainty, meet RCC Radio’s requirement for one microsecond of accuracy as it relates to arrival timing.”
Umezawa ultimately selected the Intraplex IP Link 100p, which supports a single bidirectional feed to each site with virtually no packet loss to optimize performance. This is made possible through GatesAir’s Dynamic Stream Splicing application, which provides TDM-like reliability over IP or Ethernet networks.
Built-in SynchroCast software in each codec is responsible for dynamic alignment of audio output at each transmitter site, eliminating interference while ensuring properly timed broadcasts for listeners throughout the region.
“Each site’s delay target is configured to match the primary BSU and TTL delay time systems, so the Miyoshi site has the largest delay while Tojo has the smallest,” said Umezawa.
The big differences in IP and TDM delay times means that even though the correlation of network delay is the same, upon choosing the IP feed at one of three sites, they must switch all three to get the audio feeds from IP.
“In that scenario, all three sites will be delayed from 11 millseconds with an appropriate adjustment rate,” he said.
The network, which launched in May 2018, is monitored through web-based controls for each codec. These log performance data such as packet loss, burst loss and other metrics. While Umezawa was only responsible for the IP network deployment, he set an alarm threshold on each codec to alert him and RCC technicians if a technical support issue arises.
“RCC Radio continues to monitor their primary audio links, and the level of those outputs, through an existing 160 MHz receiver,” he said. “If that goes offline, the feeds are automatically switched to the IP Link codecs via an RF Design ADIPS-2500 audio switcher within 30 seconds, in compliance with government regulations. The backup IP network is built with the most reliable systems available for the purpose of eliminating those situations.”Umezawa expects that as time goes on and the technology proves reliable, RCC Radio will eventually retire their TDM links and migrate to IP completely.
“Their TDM links are the speed of a T2, which is quite fast and very reliable,” he said. “Given the performance they enjoy with IP, it would not surprise me if they move away from that next year.”