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Monday, July 25, 2011

Fiber - Wireless Convergence: Will it influence the future Mobile Backhaul

Currently, the standardization of 3G partnership project (3GPP) specifies next generation of cellular wireless networks to deliver broadband - like data rates. Besides MIMO and advanced antenna configurations, next generation cellular standards look into aggressive use of radio spectrum and advanced inter - cell interference (ICI) mitigation techniques to increase network capacity. In the former case, cellular operators have adopted the use of universal frequency reuse, that is, no frequency reuse among neighboring cells (and fractional frequency reuse at cell edge), and are considering the use of additional radio spectrum if necessary. However, with such an aggressive use of spectrum, ICI is fast becoming the limiting factor not only to the throughput performances of cell edge users but also cell throughput. ICI mitigation techniques are proposed to reduce or even avoid interferences altogether by coordinating decisions among multiple cellular sites. Therefore, they promise more efficient use of the scarce radio spectrum resource.
The performance of ICI mitigation hinges on how well the coordination is performed in the backhaul. In general, cell throughput can increase with higher degree of coordination and with greater number of coordinating cells. Recent studies have suggested the use of fiber backhaul with very high bandwidth capacity to support ICI mitigation.
These studies employ Common Public Radio Interface (CPRI) standard, or CPRI - like digital formats, to transport radio signals over simple fiber backhaul. While these backhauls can effectively support ICI mitigation for a very small number of cells, cellular operators have very strong interests to increase both the degree and number of coordinating cells. This is because reduction of signal processing performed at the base station level can reduce the energy footprint and complexity on these remote sites. Moreover, consolidation on the number of centralized control sites can further lower the total cost of ownership (TCO) for operators.

Very recently, the Cloud Infrastructure Radio Access (C - RAN) architecture has been proposed to centralize base station processing to a super central site. In particular, C - RAN proposes a very large - scale and centralized architecture to encourage centralized coordination and management. In C - RAN or other large - scale next - generation cellular architectures, advanced fiber backhaul are desirable over conventional ones. Reconfigurable and WDM fiber architectures such as MARIN and GROW - Net would allow the network to flexibly allocate backhaul resources to meet the dynamic needs of the wireless networks. Moreover, they enable the operators to scale their wireless network infrastructure in a graceful way. In addition, in anticipation of greater wireless broadband capacity demands, radio frequency over fiber (RoF) technologies are the focus of many active researches due in large part to their ability to substantially reduce the complexity of the remote base stations. Therefore, the combination of advanced fiber backhaul architectures and RoF technologies are expected to play a key role in the development of next generation mobile backhauls.

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