FPGAs Target Remote Radio Heads
By Loring Wirbel
Remote radio heads (RRHs)—small mixed-signal platforms attached to walls and telephone poles—play an important role in macro cellular networks by combining RF/IF analog functions and digital front ends. As the RRH becomes a main element in small-cell networks based on a cloud-RAN (C-RAN) topology, FPGAs may play an important part. These devices could also become common in centralized baseband-unit (BBU) platforms for C-RANs.
In a typical C-RAN, several RRHs share a central baseband-processing pool. Initial implementations replace the base station with the RRH, supported by central BBUs. This approach is possible using the Common Public Radio Interface (CPRI) over fiber, which supports up to 40km fronthaul links. The BBU can perform baseband processing in the traditional fashion—using a combination of DSPs and CPUs—or it can employ more-general-purpose processors, such as Intel’s Xeon, and accelerators.
The challenge with the C-RAN approach is the need for high bandwidth between a simple RRH and the central BBU. So far, this requirement has limited the C-RAN to operators such as China Mobile that have access to dark fiber. The industry, however, is considering new partitions between the BBU and RRH to reduce the fronthaul bandwidth requirements and initiate broader deployments. FPGAs in the BBU still must confront a dual-switching architecture that incorporates both Ethernet and I&Q data switching, as well as I&Q data channels based on either CPRI physical links or future 10Gbps extensions of Synchronous Ethernet.
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