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Virtualised networks gain from programmable devices

Posted: 03 Dec 2015     Print Version  Bookmark and Share

Keywords:base station  FPGA  C-RAN  SDN  NFV 

Recently, there has been an ongoing trend of wireless networks going towards cloud radio access networks (C-RANs) that feature broader use of remote radio heads and small cells organised using SON techniques. In fact, virtualised networks exploit open-source software with a combination of software-defined networks (SDN) and network function virtualisation (NFV).

The SDN/NFV software is then matched with white box or bare metal switches to create the network. This hardware uses standardised commodity processors and is (often) shipped without proprietary software.

The reason networking companies such as AT&T are interested in this concept is not too difficult to understand. Operators want to avoid "vendor lock-in" and reduce their capital expenditure and their operational costs. Also, they ideally want to be more responsive in the ever-changing network environments. Open source software and white box hardware promise to deliver on all three counts.

So, what's the difference between white boxes for wired and wireless infrastructure?

Wireless white box hardware

Let's start with the fact that, for a number of reasons, the hardware for wireless systems is more complex. The primary problem is that cellular frequency allocations vary around the world, so a white box vendor would need to cater for this variation. Even within a single country there are many diverse frequencies used, say 800MHz, 1800MHz and 2600MHz, with different channel access and data transmission technologies such as TDMA, CDMA and OFDMA, as well as TDD and FDD systems. In all cases, the key to designing a global white box solution is to incorporate the maximum amount of programmability into the hardware.

Programmable hardware

Programmable devices offer a highly flexible solution for white boxes. The baseband requirement can be met by a range of FPGAs from vendors such as Altera and Xilinx. As an example, Altera Cyclone V FPGAs come in a range of sizes and include devices that boast both ARM processors and programmable logic on a single chip; these are termed SoC FPGAs. Tasks such as selecting the channel access and transmission standard can be programmed using high-level abstraction tools such as OpenCL to efficiently create C code for the ARM. The processor can run the open APIs that interface with the open source SDN software.

Programmable RF is more problematical, but recently introduced Field-programmable radio frequency (FPRF) devices from Lime Microsystems and software-defined radio (SDR) solutions from ADI provide the answer. These highly integrated chips contain complete transceivers that are programmable on the fly across all the cellular frequencies. Characteristics such as the bandwidth and gain are also fully programmable, making FPRFs amazingly flexible wireless solutions.

Open source software

Fortunately, Lime Microsystems is heavily committed to open sourcing and provides full visibility into how engineers can program its silicon. Open source hardware allows the freedom to study, share, and modify designs, and to sell products that are built using those designs. This openness permits engineers to innovate with FPRF devices in a way similar to how designers have used FPGAs. The flexibility of FPGAs has led to them being used in numerous applications and spawned an industry segment worth $4B. This is far ahead of the nascent FPRF market, of course, but FPRFs have been used in infrastructure projects to bring cellular connectivity to remote areas, as well as to build small cells and even enhancing PCs to act as cellular base stations.

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