Microsoft to test sub-THz links for use in datacenters

Microsoft is to begin research into communication links in the sub-terahertz (sub-THz) band for datacenters and, to this end, has submitted a licence application to the Federal Communications Commission (FCC), the agency that regulates radio, television, satellite and cable communication services, among other means, in the country.

As initially reported by the 6G World website, the application documents submitted by Microsoft to the FCC in December 2023 reinforce that sub-THz frequency bands (for example) offer directional radio frequency communication links, with high bandwidth and short range. Microsoft wants to exploit wireless communication on these frequencies to complement wired links in datacenters. The FCC approved Microsoft’s request on 8 February 2024.

In Microsoft’s view, in addition to high performance, links in the sub-THz band have several features that make them attractive for use in datacenters. Firstly, highly directional beams using antenna arrays allow multiple communication links to coexist by means of spatial multiplexing. The short communication range of sub-THz beams, due to high atmospheric attenuation, also extends spatial reuse. In addition, directional antenna arrays make it possible to assemble and disassemble links on demand. And, as a fourth advantage, it is possible to establish links with high bandwidth and high data transfer rates with minimal interference to possible external deployments, promoting efficient spectrum sharing and coexistence.

In the documents requesting use of the spectrum, Microsoft points out that there are already sub-THz test benches in place for academic and cooperative laboratory research, but this new proposal for experiments will focus exclusively on evaluating the use of multi-hop links to mitigate obstacles present in datacenters and on topologies suitable for structures and layouts typical of large-scale datacenters.

Previous work has examined optical links in open space for similar purposes. However, Microsoft argues that this solution performs poorly in datacenters because of the challenge of accurately pointing optical beams in the presence of vibrations. The company predicts that in sub-THz frequency bands, there will be no alignment problems due to the relatively large and adjustable beam width.

Microsoft’s expectation is that the ability to electronically direct radio frequency beams quickly will also make it possible to develop appropriate control circuits to further mitigate the challenges caused by equipment vibrations.

To achieve the test objectives, the entire experimental research programme will be carried out indoors in Redmond, the city where Microsoft’s headquarters are located in Washington state (USA), and will use the frequency bands 246 GHz-249.5 GHz, 252 GHz-257 GHz, 275.4 GHz-275.5 GHz and 258.5 GHz-260.5 GHz.

Keysight Technologies equipment

Microsoft’s experiments will use equipment from Keysight Technologies. On its website, the company presents its 6G sub-terahertz test environment for R&D that caters for a multitude of frequency bands, bandwidths and waveform types, with flexibility and expandability.

In April last year, Keysight Technologies, in collaboration with the National Physical Laboratory (NPL) and the University of Surrey, claimed to have established the first 6G connection with speeds of over 100 Gbps at sub-THz frequencies in the UK.

The company pointed out that in order to achieve the data speeds and low latencies required by use cases such as autonomous vehicles and augmented reality, data transfer speeds of 100 Gbps to 1 Tbps will be needed. For these situations, the use of sub-THz frequencies is being researched, but these present challenges of signal integrity and path loss.

The global market for datacenter networks, which involves interconnection elements via switching systems, routing, load balancing and analysis, among other means, for data sharing, is expected to reach US$38.3 billion by 2030.

Own interface

Seeking to reduce its dependence on NVidia hardware for datacenters, Microsoft is also developing its own network interface, according to The Information. The project, which is expected to take more than a year to complete, will help optimise the Microsoft Azure infrastructure used in its datacenters, including for customers who want to take advantage of Artificial Intelligence (AI) solutions.

The first major move towards this initiative was the acquisition of startup Fungible for $190 million in early 2023, a provider of disaggregated and scalable infrastructures to accelerate the performance of datacenter networks and storage with high-efficiency, low-power data processing units (DPUs). According to Microsoft at the time, the Fungible team would join the company’s datacenter infrastructure engineering group and focus on offering DPU solutions, network innovation and advances in hardware systems.

Development work on Microsoft’s new network interface is being led by Pradeep Sindhu, co-founder of Juniper Networks and former CEO of Fungible. By developing its own network chip, Microsoft is looking to solve data traffic problems that arose during the deployment of NVidia AI chips in the company’s datacenters. In general, AI systems in these environments move large volumes of data between servers and require reliable and fast connections.

According to The Information’s sources, Microsoft’s new network chip will be similar to NVidia’s ConnectX-7, available in one-, two- or four-port configurations and up to 400 Gb/s of bandwidth. This isn’t Microsoft’s only recent initiative in the field of datacenter hardware. In November last year, the company presented two customised chips developed in its lab in Redmond, Washington (USA): the Azure Maia 100 AI Accelerator and the Azure Cobalt 100 CPU. They are expected to be deployed in Microsoft’s datacenters to run its Copilot, Azure OpenAI and other services.