SDR in 5G Networks
As the name suggests, a Software-Defined Radio (SDR) is an RF unit that implements most signal processing and communication functions in the digital domain, leaving only the essential components to analog circuits. The general architecture of an SDR consists of an Analog Front-End (AFE) and a Digital Back-End.
Analog Front-End (AFE)
The AFE includes both receive and transmit functionalities and may comprise multiple channels for MIMO operations. Each AFE channel can be tuned across a wide frequency range, including the 5G frequency bands. Analog signals amplified and filtered by the AFE are digitized using dedicated ADCs and DACs with high phase coherence and stability.
Digital Back-End
The true core of the SDR lies in its digital back-end, typically implemented using high-end FPGAs. These FPGAs feature onboard DSP capabilities and are responsible for fundamental radio functions such as modulation/demodulation, upconversion/downconversion, and filtering. Additionally, they can execute complex communication tasks, including the latest 5G communication protocols and DSP algorithms. Furthermore, they can packetize and transmit Ethernet data at speeds exceeding 10 to 100 Gb/s via SFP+/qSFP+ links. The FPGA-based back-end enables SDRs to be designed for various SWaP (Size, Weight, and Power) requirements.
Role in 5G Networks
SDRs serve as fundamental building blocks for universal 5G RF networks. They can be implemented in:
Radio Remote Units (RRUs): For fronthaul networks to receive and transmit data from user equipment.
Baseband Units (BBUs): Particularly as Distributed Units (DUs) and Centralized Units (CUs) in O-RAN network standards.
SDRs can be applied at any stage of the network chain, playing critical roles in midhaul and backhaul operations. Moreover, they provide off-the-shelf solutions with high flexibility, low power consumption, and compact size, making them ideal for femtocells (small, low-power cellular base stations) that combine RRU and BBU functionalities.
Applications
SDR-based femtocells can be used in various applications, including:
Tactical wireless networks.
Embedded communication systems for Unmanned Aerial Systems (UAS).