How TitanMIMO solves the channel aggregation problem?
One of the main challenges of today’s Massive MIMO testbeds resides in the need to aggregate the entire set of RF channel baseband digitized samples within a single and common baseband processing engine, a key requirement for any Massive MIMO algorithms implementation.
The maximum data rate that can be managed by the baseband processing is defined as the system throughput, and contributes to defining the maximum RF over-the-air (OTA) bandwidth that the testbed would be able to process for real-time scenarios.
For example, let’s take a 802.11ac waveform with a 40 MHz channel BW as a scenario for a 100 antenna elements Massive MIMO testbed implementation. Assuming a baseband sample rate of at least 80 MSPS (Nyquist) for 12-bit samples, the minimum system throughput required would be defined by:
- 100 * 80MSPS * 12-bit = 96 Gbps (Minimum system throughput for a 100 antenna elements, 40 MHz OTA BW, 802.11ac)
Consequently, for 5G implementations (more than 100MHz channel BW), the minimum system throughput would be defined by:
- 100 * 200MSPS * 12-bit = 240 Gbps (Minimum system throughput for a 100 antenna elements, 100 MHz OTA BW, 5G)
Existing testbeds have been constrained by aggregation issues due to standard PCIe backplanes or 10 GigE network infrastructure with limited system throughput….thereby limiting the amount of "real world" Massive MIMO waveform propagation scenarios that could be investigated, while being limited to a few OTA MHz of real-time bandwidth.
The maximum system throughput for topologies as illustrated below is directly defined by the shared backplane or network infrastructure, since all channels need to go across the interface for channel aggregation at baseband.
Here are the maximum theoretical system throughputs (overhead not included) for different scenarios:
- 10GigE systems: 10 Gbps
- PCIe 4x Gen 2 : 20 Gbps
- PCIe 8x Gen 2 : 40 Gbps
From these system throughputs, the maximum OTA real-time baseband bandwidth can easily be derived by dividing the maximum throughput the backplane or network can support by the number of transceivers in the system and correlating the resulting channel maximum data rate to the corresponding maximum baseband OTA bandwidth supported.
Thus, for a 100 antenna elements, the theoretical maximum data throughput such systems can support are:
Maximum theoretical OTA BW for a 100×100, 12-bit / sample resolution
= System throughput / (N channels * 12-bit * 2 Nyquist )
PCIe 4x Gen 2
PCIe 8x Gen 2
Nutaq's TitanMIMO series systems overcome these infrastructure bottlenecks by using these interfaces exclusively for system control, while managing channel aggregation on additional user-defined ultra high speed point-to-point interfaces.