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60GHz Millimeter-Wave Backhaul Link Is Poised to Boost Cellular Capacity

Xilinx Employee
Xilinx Employee
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(Excerpted and adapted from the latest issue of Xcell Journal)


By John Kilpatrick and Robbie Shergill (Analog Devices), and Manish Sinha (Xilinx)


The ever-increasing demand for data on the world’s cellular networks has operators searching for ways to increase the capacity 5,000-fold by 2030. Getting there will require a 5x increase in channel performance, a 20x increase in allocated spectrum and a 50x increase in the number of cell sites. Many of these new cells will be placed indoors, where the majority of traffic originates, and fiber is the top choice to funnel the traffic back into the networks. But there are many outdoor locations where fiber is not available or is too expensive to connect, and for these situations wireless backhaul is the most viable alternative.


Unlicensed spectrum at 5GHz is available and does not require a line-of-sight path. However, the bandwidth is limited and interference from other users of this spectrum is almost guaranteed due to heavy traffic and wide antenna patterns. Communication links of 60GHz are emerging as a leading contender to provide these backhaul links for the many thousands of outdoor cells that will be required to meet the capacity demands. This spectrum is also unlicensed, but unlike frequencies below 6GHz, it contains up to 9GHz of available bandwidth. Moreover, the high frequency allows for very narrow and focused antenna patterns that are somewhat immune to interference.


A complete 60-GHz two-way data communication link developed by Xilinx and Hittite Microwave (now part of Analog Devices) demonstrates superior performance and the flexibility to meet the requirements of the small-cell backhaul market (Figure 1). Xilinx developed the digital modem portion of the platform and Analog Devices, the millimeter-wave radio portion.



60GHz Backhaul Comm Link Block Diagram.jpg



Figure 1 – High-level block diagram of the complete two-way communication link



An integrated millimeter-wave modem solution complete with PHY, controller, system interfaces and packet processor is shown in Figure 2.



Zynq task partitioning for 60GHz Backhaul Model.jpg 


Figure 2 – Wireless modem task partitioning using Zynq SoC



Some of the other important features of the Xilinx modem IP include automatic hitless and errorless state switching through adaptive coding and modulation (ACM) to keep the link operational; adaptive digital closed-loop predistortion (DPD) to improve RF power amplifier efficiency and linearity; synchronous Ethernet (SyncE) to maintain clock synchronization; and Reed-Solomon or low-density parity check (LDPC) forward error correction (FEC). The FEC choice is based on the design requirements. LPDC FEC is the default choice for wireless backhaul applications, whereas Reed-Solomon FEC is preferred for low-latency applications such as front-haul.


Xilinx and Analog Devices have jointly created a demonstration platform implementation featuring the FPGA- based modem on the Xilinx KC705 development board, an industry-standard FMC board containing ADCs, DACs and clock chip, and two radio module evaluation boards (Figure 3).



60GHz Wireless Backhaul Modem Demonstration Platform.jpg



Figure 3 – 60GHz Zynq-based wireless modem demonstration platform developed by Analog Devices/Hittite and Xilinx



The millimeter-wave modules snap onto the baseband board. The modules have MMPX connectors for the 60-GHz interfaces as well as SMA connectors for optional use of an external local oscillator. This platform contains all the hardware and software needed to demonstrate point-to-point backhaul connections of up to 1.1Gbps in 250MHz channels for each direction of a frequency-division duplex connection.



This blog is an excerpt. To read the full article in the latest issue of Xcell Journal, click here.


Note: If you need help understanding CloudRANs and Fronthaul (and Backhaul too), here’s Raghu Rau’s excellent tutorial on video.




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