Thursday, July 18, 2024

5G Connectivity For Motorsports

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The article explores the feasibility and design considerations for providing 5G connectivity for motorsports.

There has been interest in the motorsports industry to provide 5G connectivity for the cars on track. Typically, the cars use legacy technologies like Wi-Fi or digital video broadcast (DVB) to provide the connectivity for backhauling telemetry, video, and audio data from the cars back to the pit and media centre for broadcasting. However, the current solutions provide a limited bandwidth, and throughput is in the range of 10 to 12Mbps. This throughput is insufficient for advanced use cases and capabilities like 4K streaming, 360-degree video, and telemetry for the racing cars.5G connectivity for motorsports

The automotive industry is also moving towards a software defined vehicle (SDV) strategy, where the cars will need a highly reliable and low latency connectivity for frequent updates to the software, and to push gigabytes of data from the hundreds of different sensors on the cars. The move to electrification and softwarisation also needs a connectivity solution that is future-proof and ready for these requirements and remain relevant for the next decade.

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Hence the option of using private 5G networks to provide connectivity for the motorsports industry cars is an attractive proposition. 5G is an option for the motorsports industry as it is designed to overcome and mitigate some of the issues involved in using wireless communications technologies for the motorsports use cases.

System Bandwidth Calculations
The following table shows the system bandwidth required for a typical racing circuit.

System Characteristics
UL/DL Uplink Downlink
FDD/TDD TDD
Number of component carriers 1
MIMO number of layers 2
MU-MIMO beamforming Yes, 2 beams
Modulation order 16QAM
Sub-carrier spacing 60kHz
Per channel bandwidth 15MHz
Slot format (uplink heavy) Format 11
Coding rate (robust coding) 658/1024 (robust coding)
Per radio unit throughput 90Mbps 10Mbps
Number of cars per channel 2
Throughput per car 45Mbps 5Mbps
Number of channels for 28 cars 14
System bandwidth (standard guard band) 210MHz (14x15MHz)

If using a higher order 64QAM modulation, the system bandwidth required is approx. 100MHz.

Proposed solution architecture

The figure on previous page shows the proposed ORAN disaggregated architecture for the motorsports use case. The solution uses the 7.2 split architecture, which is modular and extensible for the motorsports use case.

In this architecture, the distributed units (DUs) run some of the physical layer algorithms besides the radio link control (RLC) and media access control (MAC) layers. The DUs are housed in the track side units (TSU), which also provide the power for the DUs.

The centralised unit (CU) runs the radio resource control (RRC) and packet data convergence protocol (PDCP) layers. There is a redundant 25G fibre ring to backhaul the traffic from the DU to the CU. The CU and 5G core are centralised at the event technical centre.

This split architecture makes the solution scalable as the number of radios will depend on the track layout and dimensions. The CU can control multiple DUs and run the required algorithms specific to the motorsports use cases.

Design considerations

Some of the design considerations and proposed solutions when using 5G to provide the throughput requirements for racing cars are described below.

High speed

The cars move at a very high speed on track, up to 350 kilometres an hour. This high speed introduces unique design challenges in the design of a 5G solution. The Doppler shift or Doppler spread is a concern because of the shift in the frequency of the signals sent and received by the fixed radios from the moving cars. The Doppler shift is directly proportional to the speed of the car. This also results in inter-carrier interference.

Solution. Algorithms need to be designed to compensate for the Doppler shift introduced due to the speed at which the cars are travelling. The Doppler shift depends on the speed and direction of movement of the car relative to the trackside radio. Thus, the Doppler results in an increase or a decrease in the frequency, depending on the direction and speed of movement of the car relative to the radio. The transmit frequency is adjusted in the RF front end to compensate for the Doppler shift.

Street circuits

Several racing tracks, for example in Formula One, are in cities where there is infrastructure like buildings, fences, trees, grandstands, and street furniture. This infrastructure causes interference and scattering of the 5G radio signals to and from the cars, degrading the signal quality.

Solution. Antenna diversity and multipath reception needs to be implemented to maintain the quality of the received signals at the radio and the UE. The channel state information (CSI) can also be computed and predicted more frequently to determine the channel condition. Machine language algorithms can be used to make a more accurate estimation of the channel condition. This will require a higher compute power at the base station to accurately calculate the CSI and compensate accordingly.

Handover

A unique challenge faced due to the high speed at which the car travels is that the time for handover between the neighbouring cells is small. It is of the order of a few tens of milliseconds to prevent drops or glitches in the telemetry audio and video data that is sent from the car. Hence the seamless handover needs to be implemented for these racing cars.

Solution. Multi-TRxP features like co-ordinated multi-point (CoMP) and multi-panel beamforming can be used to cancel out the interference from neighbouring cars. CoMP utilises different techniques to dynamically coordinate the transmission and reception for a particular UE to and from multiple base stations.

The UE is connected to more than one base station and transmitting/receiving is both at the same time. The CoMP algorithm resolves duplicate packets received. At the cell edge, when moving from one cell to another, the handover time is very low, and the packet loss is minimised. This improves robustness of the transmission, and the connection is more reliable. This results in no dropped video frames in the transmission from the cars.

Interference

The cars typically have several sensors that take measurements like acceleration, speed, temperature, vibration, and tire pressure. These sensors can create electromagnetic interference, which can hinder the reception and transmission of the 5G radio signals.

Solution. The antennas need to be mounted strategically on the racing cars so that they are not prone to the interference from other components in the car. The radio frequency circuit needs to be designed with a high level of tolerance against spurious signals.

Bandwidth

The racing cars are travelling at a very high speed, hence a lower modulation and coding scheme (MCS) is required to be used to provide a robust transmission and reception of signals. Similarly, a robust code rate with more redundant bits is needed for the forward error correction (FEC) to recover from any transmission errors.

Hence the bandwidth required can be as large as 200MHz to provide the required throughput for the racing cars. This raises the issue of which spectrum to use where a sufficiently large bandwidth is available.

Solution

The unlicensed 5GHz or 6GHz bands are an option where a large bandwidth can potentially be available for use. However, this band is currently also shared for Wi-Fi, and hence the reliability and guaranteed availability of this spectrum may be an issue.

Another option is to use the custom band like the 10GHz band, which is currently used by the military for radar stations. The requirement is to keep the transmit power low so that there is no interference to incumbent users in this band.

Custom radios and trackside infrastructure would need to be developed when using these bands to provide the required quality of service and reliability for the racing cars.

Table 1 Private Use Spectrum
Country Band (MHz)
Germany 3700-3800 (100M)
USA 3550-3700 (150M)
UK 3800-4200 (400M)
Canada 3500 planned
Japan 4500-4800 (300M)
Table 2 5G NR FR2 Frequency Bands
Band Frequency (GHz) Common Name Uplink/Downlink (TDD) Channel Bandwidth (MHz)
n257 28 LMDS 26.50 – 29.50 50, 100, 200, 400
n258 26 K-band 24.25 – 27.50 50, 100, 200, 400
n259 41 V-band 39.50 – 43.50 50, 100, 200, 400
n260 39 Ka-band 37.00 – 40.00 50, 100, 200, 400
n261 28 Ka-band 27.50 – 28.35 50, 100, 200, 400

5G spectrum

One of the key decisions for the solution is the choice of spectrum to be used for the 5G system, so that the system can operate in all the countries while providing consistent KPIs like throughput and latency. So, following are the options for the operating frequency of the solution, along with the pros and cons of each option.

3.5GHz mid band

The 3.5GHz mid-band spectrum is crowded and is allocated to the operators in most countries, with the operators having about 20 to 50MHz bandwidth. There are a few countries, such as Spain, where the individual operators like Telefonica, Vodafone, and Orange have 90 to 100MHz of bandwidth. In Great Britain the operators have about 20 to 60MHz of bandwidth each. In countries like Bahrain, Canada, Russia, Netherlands, and Turkey the 3.5GHz spectrum has not yet been auctioned.

Hence to operate in the 3.5GHz band, we would need to have partnerships with two or more operators to be able to get the 100MHz spectrum needed. Some countries have reserved part of spectrum in the mid band for unlicensed and shared use (not available universally), as shown in Table 1. The available spectrum is primarily for private indoor use and should not interfere with incumbents operating in the same frequency band.

mmWave bands

The licensed mmWave spectrum is available in a few different bands: 26GHz, 28 GHz, 37GHz, 39GHz, and 47GHz. Typically, the amount of frequency allocated to each operator in the mmWave bands is higher—from 200MHz to 400MHz or more. This is ideal in terms of a large chunk of bandwidth required for the motorsport solution. Some of the unlicensed bands are:
• USA: 37 to 37.6GHz (3x200MHz) has been allocated by FCC for shared/unlicensed use
• Germany, UK, Australia: 24.25 to 27.5GHz for local licenses
• Japan: 28.3 to 29.1GHz (150MHz outdoor use) for local license


Varadaraj Yatirajula is 5G Solution Architect at Wipro and Distinguished Member of Technical Staff

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