NTTドコモのHome-U(http://www.nttdocomo.co.jp/service/convenience/homeu/)やT-MobileのUnlimited Hotspot callingのような外ではセルラー回線を使用し家ではWiFi経由でインターネットを使用して通信を行う(Wifi+セルラーの)デュアル端末サービスがある。一方フェムトセル、すなわちセルラー回線を提供するスモールボックスを自宅に置き、これを介してインターネット経由で通信を行うサービスのどちらが主流になるのだろうか？
最近VodafoneがUKでフェムトセルを始めたことや、NTTドコモやT-mobileもフェムトセルのサービス開始をアナウンスする様子を見ると、フェムトセルが勢いを増しているように思える。
この二つの比較はあちらこちらで散々行われているが、以下の記事がよくまとまっている。
http://iphone.sys-con.com/node/1068599
1. Limited number of dual-mode phones and cost. As an example, AT&T has around 80mln mobile customers and pundits estimate about 5 mln iPhone subscribers. Most people still use a pretty dumb/cheap phone. The selections of dual-mode phones is comparatively small and cost is higher due to less competition and more components/complexity. It may change over time, but today, this is an obstacle when a customer calls SP and says they have bad coverage at home. I do believe most phones will be dual-mode down the road because "data wants to be free".
2. Battery life. WiFi consumes more power. Apparently, this is quickly improving, but may require new base stations and new phone models. Also, if you wanted seemless hand-in/out from/to macro network, you'd need both WiFi and 3G radios operating at the same time. Certainly, this would consume more power than 3G alone and some smart technology would be needed to minimize this to be negligible.
3. Quality of service. First, WiFi is an unlicensed spectrum. You can't completely control quality if you can't control what your neighbor does. Second, it operates at higher frequencies which offers weaker penetration. Third, if customer wants to use their own WiFi base station, it is a huge headache for SP to support configuration and quality issues with zillion different vendor devices (half of which don't work reliably based on my personal experience at home anyway).
By contrast, the biggest benefits of femtocell are that (a) it works with existing phones, (b) improves battery life, (c) provides managed quality of service. Albeit, many SPs may limit femtocells to 3G where they may have more spectrum, so it would only work with 3G phones (and not 2G). But in time for mass femtocell roll outs, most customers should renew subscriptions and get new phones with 3G. Since the phone requires no WiFi, you get better battery power and no extra headaches to manage quality of yet another radio network, unlicensed to boot. It is also a no brainer that SPs would prefer to leverage their investment into spectrum and proliferate the coverage of 3G services with more base stations rather than prompte the "dump pipe"
iphoneのようなwifi付きデュアル端末が売れたといっても、全体から見ればマイノリティということだ。
ところで、フェムトセルは携帯電話キャリアにどんなメリットをもたらせるのだろうか？キャリアの設備投資の抑制という利点はあるにせよ、先行してサービスを開始した会社のサービスメニューを見ると、儲けが増えるようなサービスでは無いように思える。サービスに関してもイノベーションが必要ということであろう。
