From connectivity to awareness: how 6G makes network a sensor

Future wireless networks will integrate sensing, learning and communication to provide new services beyond communication and to become more resilient. Sensors at the network infrastructure, sensors on the user equipment and the sensing capability of the communication signal itself provide a new source of data that connects the physical and radio frequency environment.

A wireless network that harnesses all this sensing data, not only enables additional sensing services but also becomes more resilient to channel-dependent effects like blockage and supports better adaptation in dynamic environments as networks reconfigure.

Typical sensing applications include target detection, target range calculation, velocity calculation and target tracking etc.

Positioning is determining the location of an object connected to the network. Sensing is determining the location of an object not connected to the network, commonly done using RADAR (Radio Detection and Ranging).

In sensing applications the target is passive, so the wireless system transmits signals and receives them. Target is detected by sending known signal pulses towards target location.

Integrated Sensing and Communication (ISAC) or Joint Sensing and Communication (JSAC) is defined as one of the new 6G usage scenarios and one of the new capabilities in IMT-2030. It is expected to play a crucial role in enhancing communication capabilities and enabling new applications.

‘Network as sensor’ has been identified as a key enabling technology that supports the vision of bringing the digital and physical worlds together. Sensing will be fully integrated into the wireless network and operate simultaneously with communication services.

Fusion of sensing and communication became possible when the communication systems began to use mmWave bands, which is the spectrum range used for RADAR, leading to cost savings.

A receiver located near the transmitter listens to the noisy echoes of the transmitted signal, which might be reflected off the target. Detectors determine whether there is a target or not by processing received signals and exploiting prior information regarding the signal characteristics.

The key properties of ISAC are 1. Multi-element sharing (Hardware and Software sharing, Spectrum sharing, Air interface sharing) 2. Multi- band coordination:

1) Low frequency: basic communication and IOT perception 2) Mid frequency: high throughput communication and wide area detection 3) High frequency: improved communication throughput, high resolution sensing application 3. Multi-node collaboration (Full sensing coverage, smart collaboration to improve sensing resolution)

ISAC Diversity Modes to enable variable scenarios

There are six sensing modes which are included for channel model study:

Mode1 : same gNB (5G Base Station) as transmitter and receiver

Mode 2 : one gNB as transmitter and another gNB as receiver

These modes find application in V2X (Vehicle to Everything) communication, UAV (Unmanned Aerial Vehicle) and Weather Forecast. High transmission power, large antennas and high sensing accuracy are the features of these Modes.

Mode 3: gNB as transmitter, UE (User Equipment) as receiver

Mode 4: UE as transmitter and gNB as receiver

Coordination between gNB and UE, sensing of non cooperative UE are the challenges in these Modes.

Mode 5: Same UE as transmitter and receiver

Mode 6: one UE as transmitter and another UE as receiver.

Applications of these Modes are indoor, office and factory. These modes have Low transmission power, small antenna and low sensing accuracy.

3GPP (3rd Generation Partnership Project) status of ISAC

In 5G Advanced Rel (Release)-19 RAN1, Rel-20 RAN1, Rel-20 RAN3, Rel 20 SA2, Rel -20 SA3 and Rel -20 SA6 deal with RAN/System Architecture aspects of ISAC. In 6G, Study Items (SI) Rel-20 RAN1/4, Rel-20 RAN2 and Rel-20 SA2 deal with ISAC.

Release 19 identified 32 use cases for ISAC, detailed 8 KPIs (Key Performance Indicators) for Sensing (position accuracy, velocity estimation accuracy, confidence levels, sensing resolution, miss detection probability, false alarm probability, sensing service latency and refresh rates) and studied Channel modelling on ISAC.

Release 20 studied architecture aspects of ISAC, gNB based sensing for UAV use case and procedures/signalling between RAN and CN (Core Network) to support ISAC. Sensing was recognised as one of the 9 objectives of 6G Radio. OFDM (Orthogonal Frequency Division Multiplexing) has been confirmed as the DL (Down LInk)/UL (Up Link) waveforms for 6 GR.

In ISAC, there are two sensing methods: Pulse Wave Sensing and Continuous Wave Sensing. The former has applications in long range aircraft detection, military surveillance.

Later has applications in Traffic speed guns, proximity sensors and non contact vital sign monitoring. Long range is possible in the former due to high peak power and it has minimal self interference. It has high hardware complexity and cost.

Policy dimensions of ISAC development

Spectrum requirements

The right spectrum is to be identified to enable contiguous bandwidth per carrier/TSP (Telecom Service Provided) in FR3 (7.125 GHz-24.25 GHz). Coexistence with the incumbent services, harmonization across regions and flexible licensing models should be considered to encourage innovation while ensuring efficient spectrum utilisation.

Security, privacy, trustworthiness

Policies around collecting user consents, secure data collection and authorised access to sensing data and/or sensing results must be clearly defined. It should be ensured that sensing enabled applications adhere to National security priorities while maintaining transparency and accountability to build user confidence.

Monetisation

Policy support for open ecosystems, fair revenue- sharing models and interoperability standards will be crucial to unlock sustainable economic value from ISAC deployments.

Wayforward

Various Network Sensing Use Cases are Traffic monitoring, Weather forecasting, Intrusion Detection, Factory floor monitoring, Factory automation and Self-driving cars. Sensing technologies can be used for monitoring elderly people living alone to track their movement and activity.

The military worldover is taking keen interest in the concept of ISAC which is part of the 6G standard. Today’s 5G networks are for voice and data connectivity. 6G technology can turn these networks into radars, pinpointing objects within a coverage area, determining their size and shape.

Both 4G and 5G are based on a waveform technology called OFDM. After standards meeting this year, OFDM has been confirmed as the DL/UL waveforms for 6 GR also. An alternative waveform technology, OTFS (Orthogonal Time Frequency Space), is also being advocated.

It is claimed that OFTS produces 4 times better resolution than OFDM and can track 4 times as many targets and has a better link budget. US defence is taking an interest in OFTS.

References: 1. Webinar conducted by NCAT, Ghaziabad 2. Intel-backed Cohere launches Pulsone in bid to disrupt 6G- an article in Light Reading.

(The author is former advisor to DoT)