SoftBank’s LTE TDD network impresses in Japan
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By Yu Xiangyang
At ten months after its launch, the SoftBank group’s LTE TDD/AXGP (LTE TDD) network attracted more than 260,000 customers, and this number will continue to grow, thanks to its expanding network coverage and the introduction of multi-mode data cards.
Mobile data traffic is expected to increase eighteen fold over the next five years, representing a compound annual growth rate (CAGR) of 78%. Yoshioki Chika, CTO of Wireless City Planning, a member of the SoftBank group (SoftBank), has stated that the data traffic over the Japanese operator’s mobile network has been doubling each year and will increase 32 fold over the same period (65% of its ARPU stemmed from data services in 2011, among the highest percentages in the world).
This increase in data services is creating a need for spectrum, which LTE TDD can meet for the next decade, not only in Japan but globally as well. At the Mobile World Congress 2012, China Mobile confirmed that it will have over 20,000 LTE TDD base stations in operation by the end of 2012. In India, BhartiAirtel is launching LTE services in four telecom circles. In Japan, SoftBank’s LTE TDD service went online commercially in November 2011, and the network is expected to cover 100% of the population of 12 major cities by 2013, making the operator a model for others to follow.
Consolidated leadership
After SoftBank’s 2006 acquisition of Vodafone Japan, its mobile customers doubled over the next five years to 30 million by November 2011. In 2010, its 3G penetration passed 100%, far ahead of the global average of 22%. In the same year, SoftBank took aboard WILLCOM, a Personal Handy-phone System (PHS) operator with TDD spectrum & site resources, and promptly founded Wireless City Planning (WCP) by reorganizing the team that had been developing the eXtended Global Platform (XGP) network at WILLCOM. WCP took over the development of XGP and upgraded it to AdvancedeXtended Global Platform (AXGP), which conforms to the LTE TDD standard.
With WILLCOM now under the SoftBank flag, the operator had the site resources and the spectrum to move ahead. WCP then assigned WILLCOM’s 1.9GHz spectrum to its PHS service, with 1.5GHz/2.1GHz assigned to 3G and 2.6GHz (30MHz) assigned to LTE TDD.
According to SoftBank CEO Masayoshi Son, LTE TDD has two unique advantages – asymmetric uplink/downlink and abundant spectrum resources, which he believes can fully meet the needs of mobile Internet service and enhance user experience for the foreseeable future.
Tokyo: As crowded as it gets
Tokyo, Nagoya, and Osaka have been the starting points for SoftBank’s LTE TDD network. As a megacity in one of the world’s most demanding mobile markets, Tokyo’s wireless communications environment is both extremely dense and extremely complex. Many of its residents are accustomed to web surfing, online video, and online gaming on the go; all require high network throughput and access success rates.
SoftBank plans to deploy 50 to 100 base stations per square kilometer, with a site spacing of 100 to 150 meters in certain areas of Tokyo. In a city where a hotel room might be scarcely bigger than a telephone booth, the CAPEX involved in this sort of density will give the bean counters sleepless nights. However, if uptake is sufficient, all will be forgiven, and SoftBank will be able to replicate this process in other regions.
SoftBank grouped its coverage scenarios into three classes – dense urban areas that will use distributed base stations with four transmitters and four receivers (4T4R) for seamless coverage; hotspots such as shopping malls and other centers of gravity that may adopt picoRRU for network access; and suburban and rural areas that need not require such elaborate planning.
Joint innovations
Joint innovation efforts have been taking place between Softbank and Huawei with the aim of simplifying network deployment; Single Frequency Network (SFN) and Intelligent Baseband Array (IBA) have been among the fruit.
The latter is scalable (supporting the interaction of dozens of BBUs), coordinated (enhancing base station-cell coordination, reducing interference, and increasing the gain for both transmission & reception), and reliable (supporting mutual backup of baseband data), leading to spectrum efficiency enhancements of up to 30%, while the SFN technology effectively inhibits inter-cell interference; users can enjoy 38.7% faster Internet speed at cell edges.
User experience has also been enhanced thanks to the 4T4R and beamforming technologies, with the latter changing array directionality to ensure optimal signaling. SoftBank has also used antenna sharing and reused all of its existing 1.9GHz PHS sites to accelerate network deployment.
Before its commercial launch, SoftBank’s network performance tests were quite impressive. The average network entry and inter-cell handover success rate exceeded 98.8% and 99%, respectively, while the packet loss rate was below 0.25%. In the Ginza district of Tokyo (that neon-lit shopping district that finds its way into pretty much every travelogue or Hollywood movie set in Tokyo), an interior user could enjoy downlink/uplink rates of 11Mbps/5Mbps, respectively; while 60Mbps could be enjoyed near a window and up to 58Mbps (30Mbps average) could be achieved outdoors. All these figures greatly strengthened the operator’s confidence.
Enhanced terminals & services
On February 24, 2012, SoftBank officially launched LTE TDD services in its three target cities. The operator evaluated the UMTS and LTE TDD networks at Ginza, and the results were impressive; LTE TDD delivered nearly ten times the speed (34.13Mbps) that UMTS did, and service handover between LTE TDD base stations was smooth.
Mr. Son was also further convinced that LTE TDD could help achieve Softbank’s strategic goal and its rollout pace could be sped up.
SoftBank had enjoyed exclusive distributions rights for the iPhone until October 2011, but as a lot of users around the world found out the hard way, the iPhone did not yet support LTE. SoftBank’s first commercial LTE TDD Mobile Wi-Fi terminal uses the category-3 chipset, which delivers a downlink rate of 76Mbps and uplink rate of 10Mbps, while supporting simultaneous LTE TDD access for up to ten Wi-Fi devices. In May 2012, the operator launched another LTE terminal based on the category-4 chipset. In addition, SoftBank launched a number of LTE TDD smartphones in Q3 of this year.
SoftBank has used an LTE TDD tariff plan similar to its 3G plan – users can enjoy faster services for almost the same pricing, with a monthly package running JPY3,880 (USD50). Each user’s data cap is 5GB, with the network speed reduced to 128Kbps until the next billing month if it’s exceeded. If users want their regular speed back, they must pay roughly USD33 per 2GB of traffic.
In its marketing efforts, SoftBank has highlighted its network as the country’s fastest, with high-speed Internet access available anywhere, anytime; ads have been sent out through customer service centers, subway screens, broadcast TV, and other channels; the operator also markets through service centers, handset outlets, and home appliance stores.
Thanks to the expanded terminal and network coverage, SoftBank attracted 260,000 LTE customers by August 2012, and more can be expected as the operator strengthens its leadership in the mobile Internet landscape.
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