Virtuelle Instrumente in der Praxis VIP 2016

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Setting a World Record in 5G Wireless Spectrum Efficiency With Massive MIMO

Paul HarrisUniversity of Bristol, Bristol, U.K.

Steffen MalkowskyLund University, Lund, Schweden

KurzfassungDie Aufgabe bestand in der Validierung von MIMO (MIMO = Massive multiple input, multi-ple output) als Technologie, die künftigen 5G-Netzwerken riesige Kapazitäts- und Ener-gieeffizienzsteigerungen bescheren und gesteigerte Datenraten ebenso handhaben kann wiedas schnelle Wachstum smarter vernetzter Geräte – ohne dabei mehr Bandbreite des Funk-spektrums zu nutzen.

Zur Lösung nutzten die Forscher die NI-Plattform für die Entwicklung eines Echtzeit-Mas-sive-MIMO-Testbeds mit 128 Antennen. Mit diesem technologisch topaktuellen Systemwaren sie in der Lage, nur 20 MHz des Spektrums (innerhalb des 3,5-GHz-Bands) zunutzen, um gleichzeitig 12 Client-Geräte über Funk zu bedienen – bei einer Datenrate von1,59 GB/s. Dies stellt einen neuen Weltrekord in Bezug auf 5G-Wireless-Spektrumeffizienzdar.

AbstractValidating massive multiple input, multiple output (MIMO) as a technology that can bringhuge capacity and energy efficiency gains to future 5G networks, which must accommo-date increased data rates and the rapid proliferation of smart connected devices, withoutconsuming any more of the radio spectrum.

Using the NI platform to develop a 128-antenna, real-time massive MIMO testbed. Usingthis cutting edge system, the scientists were able to use just 20 MHz of spectrum (within the3.5 GHz band) to simultaneously serve 12 client devices over-the-air, with an aggregatedata rate of 1.59 GB/s, and sets a new world record for 5G wireless spectrum efficiency.

IntroductionThe Communication Systems & Networks (CSN) Group at the University of Bristol formedin 1985 to address the research demands of the fixed and wireless communications sectors.It combines fundamental academic research with a strong level of industrial application.The group has well-equipped laboratories with state-of-the-art test and measurementequipment and first-class computational facilities. ‘Bristol Is Open’ (BIO) is a joint venturebetween the University of Bristol and Bristol City Council, which supports initiatives thatcontribute to the development of a smart city and the IoT.

Lund University seeks to be a world-class university that works to understand, explain andimprove our world and the human condition. The Electrical Engineering and Information

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Technology Department (EIT) at Lund University covers a wide range of research areas inthe fields of analog and digital as well as communications system design and has been atthe forefront of massive MIMO research including massive MIMO theory, channel measure-ments and accelerator design (Figure 1).

Figure 1: The Record Breaking ‘Bristol Is Open’ Massive MIMO System

The Journey to 5GIn addition to mobile phone subscribers, who are predicted to each consume 20 GB permonth in North America by 2020, networks will also need to provide broadband Internetaccess to rural areas. Most prominently, future networks must also accommodate the Inter-net of Things (IoT) and the proliferation of smart telemetry devices. By 2020, analysts pre-dict that each person in the United Kingdom will own and use 27 Internet-connecteddevices. This contributes to the expected 50 billion connected devices worldwide. Asidefrom connectivity, new industrial applications (smart factories and machine-to-machinecommunications) and consumer applications (4K video streaming and driverless vehicles)require high data rates, lower latencies, and improved reliability. This is challenging tele-communications engineers to innovate rapidly in order to ensure that the fifth generationof cellular networks (5G) can cope with these unprecedented demands.

A massive MIMO system can spatially multiplex more devices without consuming anymore radio spectrum, which is an extremely valuable and scarce resource. Coupled with itsability to average out the effects of fast fading in multipath propagation environments(most urban and industrial settings), it can also fundamentally improve latency at thephysical layer by reducing the number of errors caused by sudden drops in signal level.

The Many Benefits of Massive MIMOIn a multiuser MIMO communication system, devices can simultaneously transmit on thesame frequency band whilst the base station uses multiple antennas to unravel theirrespective data streams in the spatial domain. For downlink transmission, the base station

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performs the reverse process, transmitting back to all users simultaneously using a tech-nique known as beamforming. If the spatial signatures of each device are uncorrelatedenough, the result is a K-fold increase in system capacity, where K is the number of userspresent. For signal processing reasons, the base station requires at least the same number ofantennas as users. MIMO is currently found in both WiFi and 4G cellular operating with upto eight antennas (Figure 2).

Figure 2: The BIO 128-Antenna Massive MIMO System, with Researchers Paul Harris and Siming Zhang

Developing the Massive MIMO TestbedThrough a collaborative effort with the NI Advanced Wireless Research Group in Austin,Lund University in Sweden, and the Bristol City Council, researchers successfully imple-mented a 128-antenna massive MIMO system that can serve 12 wireless devices on thesame time-frequency resource (Figure 3).

Figure 3: Highly Scalable Massive MIMO System, Combining PXI and USRP RIO

The testbed is designed with the NI massive MIMO reference design, combining five NIPXEe-1085 chassis. The master chassis contains an NI PXIe-1085 controller, an NI PXIe-

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6674T timing module, and four NI PXIe-7976R FlexRIO FPGA modules. Four slave chassisare linked via x8 MXI. We connected 16 USRP-2943R software defined radios (SDRs) viax4 MXI links to each slave chassis, collectively providing a total of 128 RF chains. Theaccurate 10 MHz OXCO reference from the NI PXIe-6674T along with a digital trigger isdistributed to all USRP SDRs through eight OctoClock clock distribution modules, ensuringtight hardware synchronisation.

Finally, an additional six USRP-2953R SDRs with x1 MXI links to laptops were used thatmimic user clients. LabVIEW software, the LabVIEW FPGA Module, and NI-Sync were usedto develop the massive MIMO reference design that powers the system (Figure 4).

Figure 4: Six USRP RIO Clients in Front of the BIO Massive MIMO Testbed

In a large and complicated system such as this, there are many things that can go wrong.However, NI provided an unrivaled, ubiquitous level of integration between their softwaredevelopment tools and commercial hardware products, which helped the scientists to easilymodularise this complex system. A flexible, powerful solution built on a single, well-sup-ported platform was the goal.

The PXI Express platform is a solid foundation for any high-throughput, low-latency sys-tem, and it is well supported by NI from many years of experience. The scientists were ableto built upon this well-established standard and integrated nearly 100 different pieces ofhardware, yet seamlessly developed the entire application within a single software frame-work. This highly modular approach and tight software and hardware integration not onlygave the solution needed right now, but ensure that future changes to the hardware config-uration are cost and time effective.

To spatially separate and distinguish the signals from all 12 wireless devices whilst meetingreal-time constraints, parallel MIMO processing was implemented across the integratedFPGAs within the four FlexRIO modules. Each needed to perform 24 million 12x128-128x1matrix multiplies per second for signal detection alone.

This leads to another major benefit of PXI Express, peer-to-peer (P2P) streaming, which al-lows the deterministic transfer of data between cards within the PXI Express chassis. P2P

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was pivotal to the success of the application, enabling direct point-to-point transfer be-tween 68 FPGAs, without having to send any of the data through the host processor ormemory. This enabled the optimal throughput and latency performance required for real-time operation. The P2P functions in LabVIEW simplified the implementation of eachstream, so source, destination, and data type could easily be mapped.

Record-Breaking ResultsThis is the world’s first real-time demonstration of a 128-antenna massive MIMO systemsimultaneously serving 12 devices over-the-air in the same frequency band. With a sumrate of 1.59 GB/s in only 20 MHz of bandwidth, the researchers achieved 79.4 b/s/Hz, thehighest recorded spectral efficiency in the world to date. This technology can enable a 12-fold increase in spectrum efficiency compared with current LTE (4G) networks, whilst offer-ing the connection reliability and decreased latency required for Industrial IoT and real-time control applications (Figure 5 and 6).

Figure 5: Uplink Throughput in Real-Time at the Base StationLeft: Individual Stream Rates for Each User Right: System Sum Rate

Figure 6: Base Station Host Interface, Displaying Channel Information

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As the BIO testbed has proven, massive MIMO can deliver a strengthened network capacitythat will help network operators to reliably host an ever increasing number of wirelessdevices. Furthermore, with a 100X increase in radiated energy efficiency, power consump-tion and operating cost of a wireless network can be greatly reduced. From a consumer per-spective, wireless device and mobile handset will also experience improved battery life.

The Future of the ProjectThe NI PXI Express platform provided a solid framework to build the system on, which isrugged, easily reconfigured, and capable of meeting the demanding throughput require-ments for 128-antenna MIMO operation. By using NI commercial off-the-shelf hardwarecombined with LabVIEW and LabVIEW FPGA, the scientists could focus on implementingthe required functionality and rapidly testing new ideas. This resulted in a world-firstachievement for spectral efficiency of 79.4 b/s/Hz and paved the way for leading-edgeresearch with industrial collaborators that could move this new technology ever closer tothe radio mast.

The massive MIMO testbed will soon be deployed on a rooftop site within the city of Bristoland will be connected to the BIO fiber optic network in order to conduct further research inreal-world deployment scenarios.

Eventually, the system will be slpit into four 32-antenna subsystems and the fiber networkwill be used to implement a distributed massive MIMO configuration. All of this work ulti-mately pushes forward the validation of this promising technology, allowing network oper-ators to consider practical deployments for real networks.