TitanMIMO-6 Elements

Remote Radio Head (RRH)

 

The RRH includes Nutaq’s second generation radio FMC modules, the Radio640x. The core technology of these radios is the AD9361 agile RF transceiver ICs, which provide the synchronisation capabilities to implement large antenna system arrays that are accurately phased aligned (common LOs).

The RRHs are based on radio carriers (Nutaq’s Perseus 611x) that support 8x RF transceivers while providing a large FPGA for pre/post-processing and 7x user-defined 20 Gbps P2P cable interfaces for channel aggregation or mesh-processing between multiple RRHs, or to a Nutaq’s Octal Virtex-6 Baseband Core module (Kermode XV6).

This powerful baseband processor unit (Kermode XV6) offers tremendous FPGA processing capabilities (8x Virtex-6) and up to 32x user-defined 20 Gbps P2P cable interfaces for channel aggregation and mesh processing by stacking cards together to scale processing or channel count to very large numbers.

Octal Virtex-6 Baseband Core Module

This baseband processing module (Nutaq’s Kermode XV6) provides tremendous processing capabilities through its on-board 8x Virtex-6 large FPGAs (SX475T).

The aggregation of all channels to a common central processing unit without real-time restriction or bandwidth compromise is just one of the features this module provides. Additionally, each FPGA interfaces with two DDR-3 SDRAM SODIMM modules, capable of supporting up to 4 GBytes, for an aggregate memory capacity of 64 GBytes.

The Kermode-XV6 supports various user-defined interconnection modes with the RRH or between multiple baseband processor through its RTM interface (Rear Transition Module).

  • 16x 20 Gbps full-duplex P2P cable connection on the Front Panel (typically interfacing RRH)
  • 16x 20 Gbps full-duplex P2P cable connection on the RTM side (typically for interconnection between multiple Octal V6 Baseband Core Modules)

Octal Virtex-6 Kermode XV6 interfacing with Rear Transition Module (RTM)

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System Synchronization

Radio Remote Heads (RRH)

Each Nutaq RRH includes two Radio640 FMC double-stack modules, each providing four TRX, thus a total of eight TRX per RRH.

Each Radio640 has onboad CLK & LO(s) but also can accept an external CLK/REF input as well as one or two external LO(s) input used for TDD or FDD topologies respectively.

In order to synchronise all radios, Nutaq provides uSync CLKs & LOs 19″ rackmount modules to accomplish these tasks. The uSync systems are specifically designed to ensure phase coherency between all CLKs as well as all LOs, and are stackable to scale for clocking very large systems.

A Common Time Base

On top of synchronising radio heads for beamforming applications, the uSync CLK module allows CLK disciplining to an external reference or embedded GPS.

The user selected reference can then be distributed on all RRH and Octal V6 Baseband Processor Cores to ensure precise time-based communication between all FPGAs within the system, through the use of VITA49 communication protocols.Through the uTCA/ATCA backplane, the PPS and 10 MHz time signals are distributed to ensure a deterministic communication system.

uSync Clock Module

uSync LO Module

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User Defined Cable Link Topologies

Nutaq’s RRHs and Octal V6 Baseband Core modules are interconnected using cabled link technology that supports multiple communication topologies and which are user-defined, adaptable and scalable to multiple baseband processing schemes.

This provides the TitanMIMO testbed with almost infinite flexibility and reduces the risk associated with fixed solution that can’t be adapted and can’t scale.

These 20 Gbps full-duplex link per cable are offered over Mini-SAS physical interfaces. Nutaq selected these interfaces due to their small form factor, high speed rate available, and low cost compared to existing SFP-type interfaces. Each of the Mini-SAS connection are directly interfaced to 4x Virtex-6 FPGA’s full-duplex high speed MGT (Multi-Gigabit Transceiver) interface.

These physical interfaces can support multiple protocol layers. Provided with the TitanMIMO development software are high-speed and low-latency Aurora-4x protocol (20 Gbps) full duplex interfaces. Users may employ these physical interface to support other telecom standard such as the CPRI protocol to validate scenarios which are similar to final deployment scenarios.

These Mini-SAS cable link can be offered in either copper or optical versions, enabling the RRH to be at a distance from the baseband processing if needed.

To illustrate the enormous throughput capacity and flexibility of the TitanMIMO-6 series, for each RRH (consisting of 8x TRXs) only one of the seven available 20 Gbps links is required to support the entire data rate of the all eight TRXs in sustained real-time operation. This assumes no decimation/upconversion within the RRH’s FPGA, i.e. in bypass-mode. The remaining 6x links are therefore available for other interconnection topologies.

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Massive MIMO Reference Design

As part of the TitanMIMO-6 system, a reference design is provided which enables developers to rapidly implement Massive MIMO applications without dealing with TRX calibration, data communications issues, data synchronization and using the right sets of APIs etc.

The provided reference design supports the data transfer, aggregation and control of all radio channels, automatic calibration, from the radio nodes (RF Modules) through to the central baseband processing engine, and back to the radio nodes.

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Record & Playback

Each RRH (8 TRXs) is equipped with a 4 GB SDRAM FPGA memory, which allows for recording of the full signal bandwidth, as shown in the example below:

  • Eight RF channels sampled at 122.88 MSPS.
  • Each sample has 2 Bytes.
  • Therefore 1966.08 MBps throughput are needed to record all 8 TRX at full speed to the SDRAM (8 x 122.88 MSPS x 2 Byte/Sample = 1966.08 MBps).
  • Maximum SDRAM throughput: 5700 MBps.

Thus, the record/playback FPGA module provided within each RRH enables record or playback of all channels within the Massive Mimo testbed.

A maximum of 250 Mega-Samples per channel can be recorded to the SDRAM (4 GB divided by 8 channels divided by 2 Bytes per channel). This translates to a total recording of 2 seconds (or a continuous playback) for all channels of the testbed at full rate (122.88 MSPS). Additionally, synchronous record (or playback) of all channels can be performed though the time based control of each RRH (see synchronisation section above).

 

Record & Playback Operating Modes

Single Shot:

  • Record: Fill up memory from RF, stop, then download data to PC.
  • Playback: Upload file, playback from memory to RF.
Normal:

  • Record: Fill up memory, stop, download data to PC, then re-arm trigger.
  • Playback: Upload file, playback from memory to RF.
Continuous:

  • Playback: Upload file, playback memory in a continuous loop.

Record & Playback Trigger Modes

External:

  • An external trigger for each 4×4 MIMO subsystem is available.
FPGA based:

  • The trigger signal can be defined by user logic within the FPGA of each 4×4 MIMO subsystem.
Time-based software:

  • The trigger signal can be sent from the central processor unit using time based events.

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OFDM Reference Design

Please click here.

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High Speed Real-Time Data Exchange (RTDEx) with embedded CPU (4C i7)

Nutaq RTDEx IP core provide extensive framework to exchange data with the embedded host device for transport layer implementation through the PCIe or GigE links with the highest bandwidth and lower latency possible. On both interfaces (FPGA & CPU), DMA engines initiates data transfer at very high speed through simple API calls; enabling the channel aggregates processed in the last FPGA in the baseband processing chain to send/receive the demodulated data to the embedded CPU at up to 10 Gbps.

Typical RTDEx performances (Linux OS)
HOST – FPGA StreamingGigEDual PCIe 4x (Gen 1)
Theoretical Data Rate1 Gbps20 Gbps
Effective Data Rate~ 900 Mbps~ 12.8 Gbps

Roundtrip Latency (4 kB, send & receive)

~ 1 msec~ 75 – 300 µsec
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