Mobile operators face significant challenges, given the rapid growth in mobile broadband traffic. They are starting to roll out the latest mobile technology, Long Term Evolution (LTE), as yet another overlay alongside the existing wideband CDMA and GSM networks. Mobile sites are thus being crammed with antennas and basestation equipment.
"The cellular network is 30 years old," said Tom Gruba, marketing director for wireless activities at Alcatel-Lucent. "You cannot just keep adding more basestations in the network to solve the [data] capacity problem; the business model doesn't work." Alcatel-Lucent's solution is lightRadio, which moves the processing power to the antenna or into the network, like cloud computing. The system vendor points out that architecture change is being industry led; what Alcatel-Lucent is claiming is that the lightRadio portfolio of products is the first to support the new architecture.
Announced in the run up to Mobile World Congress 2011, lightRadio promises to double network capacity, while halving power consumption. The lightRadio products include a wideband active array antenna that integrates the amplifier and antenna elements, a radio SoC developed with Freescale, and a multimode radio controller platform being developed with HP. Integrating the amplifier alongside the antenna achieves better coupling of the signal to the antenna. Less power is wasted, such that a smaller amplifier can be used.
The wideband active array antenna is implemented as a 6cm cube, pictured left. The wideband operation covers 400 to 4000MHz, allowing one cube to support 700MHz and 2600MHz bands. "These can be stacked, depending on how much power is needed, and you can have two or three columns to serve two or three frequencies and any technologies you want," said Gruba.
Being an active design, the antenna boosts cell capacity through beam forming and multiple input, multiple output (MIMO) technology. Combining the amplifier-antenna with the radio chip forms a compact basestation that can be mounted on masts or within buildings. Such a combined baseband/remote radio head takes little space and avoids the need for air conditioned cooling associated with traditional basestations.
Fig 1: Key components of the lightRadio architecture.
LightRadio will also enable a cloud computing style radio network architecture, where the basestation is separated from the antenna-amplifier. Traditionally, the radio amplifier was connected to the baseband via a backplane. The advent of the remote radio head led to the creation of the common public radio interface (CPRI) to connect the amplifier at the antenna with the baseband unit. With a cloud based radio network, basestations from 25 or 30 cell sites could be placed in a facility up to 40km away, with the CPRI signal carried over an optical link.
Alcatel-Lucent estimates the maximum lightRadio bit stream needed to be carried over the CPRI link is 10Gbit/s. Compression technology will reduce this by a factor of three, so operators can avoid installing a dedicated 10Gbit optical link. At the core of the baseband processing is the SoC developed with Freescale.
"Dimensioning the various aspects of the SoC is critical," said Preet Virk, Freescale's director, networking segment. The SoC design uses Freescale's recently announced QorIQ Qonverge technology that supports designs spanning femtocells to macro basestations. Two devices have been announced – for femtocells and picocells – that are implemented using a 45nm cmos process. Alcatel-Lucent's radio ic will be implemented in 28nm cmos and will be available from 2012.
Freescale is not willing to detail the basestation SoC yet, but the scalable design uses cores and IP blocks that are shipping in Freescale products, such as the e500 Power Architecture core and the StarCore SC3850 dsp as well as baseband acceleration blocks.
"Scalability comes in many forms," said Barry Stern, Freescale's baseband DSP & SoC products, marketing manager, wireless access division, networking and multimedia group. "From a few users to hundreds of users; from 1.25 to 20MHz bandwidths and beyond; simultaneous multimode support; and enabling OEMs to use the same software across different basestation designs, saving on development costs."
Fig 2: Block diagram of Freescale's PSC9132 wireless chip.
Freescale's femtocell SoC supports 8 to 16 users and uses an e500 core and a dsp core. The picocell SoC supports 32 to 64 users and uses two e500s and two dsp cores. Freescale's metro and macro cell SoCs will support hundreds of users, requiring multiple dsp and cpu cores. Other features will include several DDR3 memory controllers; baseband acceleration for turbo coding, fast Fourier transforms and MIMO; and interfaces for Ethernet, PCI Express and CPRI, according to Virk.
"The SoC in the cloud is going to give us the ability to do all sorts of new things," said Tod Sizer, head of Alcatel-Lucent's Bell Labs' wireless research domain.
Intercell communication
Having baseband processors concentrated at one location enables intercell communication. One application is Coordinated Multipoint (CoMP), what Alcatel-Lucent calls networked MIMO, which will be a feature of the 3rd Generation Partnership Project's (3GPP) Release 10 cellular standard.
Currently, only one cell serves a user, even if the user is commonly near the cell edge and is sensed by adjacent cells. With CoMP, MIMO technology can be used such that different streams are transmitted between the basestations and the user, boosting throughput. And it is this technique, says Alcatel-Lucent, which will double overall capacity.
The cloud like architecture will also enable new uses that benefit energy consumption. "One we are going to see in the coming years is coordination on the basis of energy usage," said Sizer, citing how, for example, all users could be moved to the 3G network, with the LTE basestations turned off to save power, based on time of day and subscriber requirements. "You have that capability of moving users if you have control of both technologies from a single cloud," said Sizer.
Power consumption has become a key issue for operators, with the likes of France Telecom looking to reduce the energy consumption in its network by 15% by 2020. In turn, US operator Verizon stipulates that each new piece of equipment must be at least 20% more energy efficient than its predecessor if it is to be deployed. Alcatel-Lucent is developing a virtualised radio controller architecture as part of the portfolio, working with HP to consolidate three generations of radio controllers into one platform. In GSM, the basestation controller (BSC) connects to multiple cell sites, while a radio network controller (RNC) is used in 3G.
"If I make the BSC or RNC a software routine, the software becomes independent of the platform and I can put both functions in one box," said Gruba. Alcatel Lucent is basing the design on an ATCA version 2 based general purpose processor design, while HP is providing server and virtualisation expertise to the controller design. Alcatel-Lucent expects to be trialling the wideband active array antenna in the autumn before it becomes commercially available in 2012.
The remaining lightRadio elements will appear from 2012 onwards. Ken Rehbehn, principal analyst at the Yankee Group, says lightRadio is arguably the most important wireless equipment development made by Alcatel-Lucent since its 2006 merger. However, he points out that other vendors are pursuing comparable strategies that might challenge much of the lightRadio vision.
