Beyond femtocells: smart distributed wireless broadband

Robert Syputa/Maravedis
04 Jun 2008

Femtocells have advanced into the market as a way to extend coverage and offload capacity of 3G networks.  This is a method of distributing the signaling and bandwidth load to local area networks, enhancing building penetration that is currently limited by 3G WCDMA technology and network architecture.

Femtocells have little ability to become self-organized or perform network management functions.  Wimax and LTE, on the other hand, are based on highly adaptive OFDMA air interfaces and IP communications that enable architecting of self-configured and distributed networks.  They become part of the broader unified communications industry movement toward smart, distributed networking that is augmented by distributed storage and application servers. The largest opportunities for Wimax are Smart Distributed Wireless broadband Networks (SDWN), and Purpose Use of Multiple Spectrum bands (PUMS).

This article will sketch the rationale and basics behind SDWN for key segments and players.

What is SDWN‾

The SDWN wireless interface layer is based on scalable OFDMA, adaptive modulation and power control methods that enable the network to adapt to a variety of channel bandwidths, range, multi-path environments, and attenuating signal conditions and usage.

The same factors that are now driving intelligent wired networks are amplified by the nature of wireless: limited available spectrum.  MIMO- beam forming, smart antenna and smart power regulation built into remote and mobile stations can achieve very high localized performance while working as an adaptive layer within the managed network.

Distributed and virtual SDWN networks  

Groups of aggregated remote stations (RS) and mobile stations (MS) can handle authentication, QoS, and security functions:

"¢ Virtual base station functionality: enables hand-offs and localized routing and network optimization.

"¢ Multiuser MIMO (MU-MIMO): enables a single base station to transmit to multiple remote (RS) or mobile stations (MS) simultaneously over the same frequency band, thereby increasing the sum and processing gain bandwidth, while decreasing latency and increasing signal path reliability.

"¢ Collaborative MIMO (Co-MIMO): as compared with conventional MIMO in which a terminal is served by one unique base station, a co-MIMO terminal is served by multiple base stations or RS. Inter-cell interference is very often a limiting factor to wireless network capacity. Co-MIMO uses non-coherent signal combining, which dramatically reduces inter-cell interference. This can be effective in cell edge and tiered networks.

"¢ Network MIMO-AAS: enables adaptive use of a variety of smart antenna techniques from multiple radios.

The sub-channel signal measurement, estimation and error correction techniques used in Wimax and LTE systems provide knowledge essential to building self-organized networks.  This capability combines with OFDMA's finely grained sub-channelization methods to enable an evolution of smart wireless broadband network architecture. Early manifestations can be seen in products and development plans from technology leaders including Alvarion, Alcatel-Lucent, DesignArt Networks and picoChip.

The term "ËœWiMAXmesh' is used by some companies to describe SDWN functionality for multi-hop relay network capabilities now being implemented into Wimax integrated circuits and network devices.  Currently, WiMAXmesh can include on-board or local memory and storage, support for multiple external network interfaces and optimized network routing capabilities. We prefer the term SDWN to signify a  richer set of capabilities that will lead to smart distributed network evolution well beyond that implied by WiMAXmesh, a take-off on the popular, but limited, WiFi mesh architecture.

The Scalable network architecture of SDWN includes:

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