In my previous blog post in this series, we looked at how the different parts of Nutaq’s massive MIMO system achieved the necessary throughput to support the routing of data for 100 channels of RF sampling with a bandwidth of up to 28 MHz. In this post, we describe how to improve Nutaq’s massive MIMO system by providing it with a huge processing unit to handle the heavy baseband processing.
The Kermode XV6 is the most powerful AdvancedTCA computing blade ever built. It is specifically designed to tackle the most demanding signal processing applications.
Figure 1: Kermode AdvancedTCA computing blade
The Kermode XV6 as a processing monster
The Kermode XV6 packs eight Xilinx Virtex-6 SX475T field-programmable gate arrays (FPGAs), delivering an incredible 8.8 TeraMACs solely from their DSP48E1 dedicated multiply-accumulate engines. Each FPGA interfaces with two DDR3 SDRAM SODIMM modules capable of supporting up to 4 GBytes, for an aggregate memory capacity of 64 GBytes.
The Kermode replaces the Perseus 6113 in the massive MIMO system described in the previous blog posts. It has the advantages of more miniSAS connectors (thus increasing the throughput) and more processing power. It supports a mesh configuration between FPGAs as well as between the ATCA backplane’s zone 2 and zone 3 (see Figure 2). The advanced mesh topology enables a unique very large virtual FPGA.
Figure 2: Kermode functional diagram
Figure 3: Communication topology with the Kermode board
Figure 3 shows the benefits of Kermode upgrade. When compared to the previous system, there are fewer Perseus cards, which frees up one rear-transition module connector in order to have more data links out of the subgroups. More data links enable a higher throughput and the eight FPGAs provide sufficient power for heavy waveform processing.
Using the MI125 and the MO1000 with higher bandwidths (millimeter waves)
Figure 4: MI125 and MO1000 A/D D/A boards
Such a massive MIMO system requires that the antennas be small enough to fit within a reasonable space. Smaller antennas imply higher frequencies. This explains the tendency to move towards millimeter waves in the development of future wireless technologies. The MI125 and the MO1000 can be used as analog-digital (A/D) and digital-analog (D/A) converters to replace the Radio420 front-end. An RF front-end must be provided by the user.
The MI125 can be used to digitize IQ samples. One channel digitizes in-phase samples at a rate of 125 MSPS while the other channel digitizes quadrature samples at 125 MSPS. The total maximal theoretical bandwidth of the MI125 is therefore 125 MHz.
The MO1000 is the D/A counterpart to the MI125. It is a 16-channel D/A board and is currently in development at Nutaq. It will look identical to the MI125 shown above.
Figure 4 shows where the MI125 and MO1000 are inserted in the system in relation to the user-provided RF front-end and antenna array.
Figure 4: MI125 and MO1000 placement
This blog post showed how some of Nutaq’s actual products could be used in the massive MIMO testbed described in the previous blog articles. By increasing the processing power, covered frequencies, and bandwidth, the products make the testbed highly scalable at a reasonable cost.