As mobile network and device makers explore many paths to using wireless spectrum more efficiently, one possible solution is still hard to achieve: Sending and receiving data on the same frequency at the same time, in the same space.
There are multiple ongoing efforts to reuse spectrum for mobile data. Equipment vendors are working out how to have traditional "macro" base stations and smaller cells serve the same neighborhood, with automatic coordination. There are also efforts to let mobile operators and government agencies share the same spectrum while staying out of each other's way. Each of these has its own challenges.
But when it comes to a particular base station transmitting and receiving signals on the same channel at the same time, it can't be done on current 3G or 4G mobile networks, according to researchers at the University of California, Riverside. Today's networks send and then receive, or do each on a different frequency. In fact, most mobile broadband networks are built around two separate "paired" blocks of spectrum, one for "upstream" signals coming from devices to the network and one for "downstream" traffic going the other way.
The Riverside researchers think they are close to solving this limitation in a way that would only slightly increase the cost of a cellular base station. Their so-called full-duplex radio could be technically ready by the end of next year, according to Ping Liang, a member of the Riverside team. He and Professor Yingbo Hua are leading a project funded partly by a grant from the U.S. Department of Defense. Liang said a major vendor of mobile equipment, whom he can't name, is actively pursuing full-duplex and is interested the team's work. The technology might also be applied to Wi-Fi, he said.
Doubling efficiency?
通过在相同频率上同时发送和接收数据，理论上可以提高无线网络的效率。如果移动操作员可以这样做，它可以为用户提供相同的速度和容量，只需一半的频谱，节省数十亿款用于扫描许可证。更有可能的是，该载体可以采取相同数量的频谱，它已经持续时间更长，服务于越来越多的用户和更高的数据需求而不需要超过更多频率。
实际上，大多数应用程序的好处将更少，因为少数移动手机涉及订户发送他们接收的数据量相同的数据。但它仍然可以产生区别，网络运营商预计将在未来几年内能够在有效使用光谱方面来寻找任何优势。
Full-duplex could deliver a big benefit if it let carriers take their paired upstream and downstream bands and talk both directions on each, said Ovum analyst Daryl Schoolar. "Any serious base station vendor would want to at least explore it," he said.
f的问题ull-duplex operation isn't radio waves on the same frequency crashing into each other in the air, turning YouTube videos into fuzz. The problem is that signals coming from within a cellular base station drown out the ones that the base station is trying to pick up from across the wireless network. The outgoing signals are about 10 billion times more powerful than the ones coming in over the air, so the external signals get drowned out. The same thing happens inside a phone or tablet as in a base station.
取消信号
梁先生称，需要的是信号消除电路。他的团队正在建造产生相反的信号，取消传输信号。它仅在无线电中取消信号，所以在网络上，传输工作正常。关键是收音机现在可以“听到”较弱的传入信号。Riverside团队于2010年作为一个理论开发并获得了其方法，然后继续进行测试。
梁和华不是第一个建立一个全双工无线电的人。梁先生说，由Intersil获得的硅卖方，由Intersil获得的硅助商在市场上有一个，梁说。Intersil拒绝评论Quellan Radio。Quellan的技术已被用于GPS和其他应用程序。然而，在今天的移动宽带网络上说，Quellan开发的Quellan不能用于全双工操作。
For one thing, the Quellan radio only works on spectrum bands that are 5MHz wide or less. Most 3G and 4G networks today use far more bandwidth than that: Both AT&T's and Verizon's LTE networks, for example, use two paired bands, each of which is 10MHz wide. The other limitation of the Quellan technology is that it can only cancel out those loud transmission signals by 30 decibels, Liang said. That leaves a signal that's still 1 million times stronger than what's coming in over the air.
梁说，来自微软，斯坦福大学和赖斯大学的其他研究人员最近推进了超越Quellan的技术，在宽更宽的10MHz通道上取消了30dB的信号。
首先瞄准基站
Liang said his team is aiming for 96dB of signal cancellation. There should be no theoretical limit to the width of the band it can work in, he said. The best place to start implementing it will be network infrastructure, partly because it takes longer to replace millions of handsets than a much smaller number of base stations, Liang said.
具有全双工无线电的基站可以从一个电话接收信号，并同时在相同的频率上传输到另一个电话。如果手机还有全双工无线电，那么基站可以在相同频率上使用相同的手机发送和接收数据，实现更高的效率。
然而，在开发，测试，标准工作和规则之间，全双工可以面对蜂窝网络中的商业用途的漫长道路。事实上，标准和调节是如此根深蒂固，可能永远不会是细胞中的全双工无线电，托拉加研究分析师Phil Marshall说。但工作应该仍然回报，他说：“你不会用这种技术转变[变换]频谱分配，你只是为了获得更多的效率。”
Ovum的校园认为，该概念对移动网络具有很大的潜力，但采用可能需要十年。硕士说，Wi-Fi行业可能更快地采用该技术，因为它建立了未经许可的网络，但它不会在一夜之间达到市场。
"Anything like that is probably going to be long term. I mean, very long term," Schoolar said.
斯蒂芬·劳森covers mobile, storage and networking technologies forIDG新闻服务。Follow Stephen on Twitter at@sdlawsonmedia。斯蒂芬的电子邮件地址是stephen_lawson@idg.com