EN 300 328: Medium Utilization (MU) Requirements

Medium Utilization (MU) is a pivotal parameter in EN 300 328, dictating how effectively RF resources such as power and time are utilized within the 2.4 GHz ISM band. For original equipment manufacturers achieving compliance ensures not only adherence to regulatory standards but also harmonious operation in increasingly crowded spectrum environments.

Key aspects of Medium Utilization in EN 300 328

What is Medium Utilization?

Medium Utilization (MU) is defined by a straightforward formula:   

Where:

• P_{out}: RF output power in milliwatts
• DC: Duty Cycle (percentage of time the device is actively transmitting)

For non-adaptive equipment with declared maximum RF output power exceeding 10mW (10 dBm) e.i.r.p., EN 300 328 specifies a maximum MU factor of 10%, balancing operational needs with fair spectrum access. Complying with this requirement ensures devices minimize the risk of interference while coexisting efficiently with other equipment in the 2.4 GHz ISM band.

When and Why Medium Utilization is Not Required

1. When Medium Utilization is Not Required:
• Medium Utilization requirements do not apply to adaptive equipment, such as devices employing Listen Before Talk (LBT) or Detect And Avoid (DAA) mechanisms.
• MU is exempt for equipment operating with an RF output power level below 10mW (10 dBm) e.i.r.p., as specified in EN 300 328.
2. Why Medium Utilization is Not Required:
• Adaptive Equipment: These devices dynamically adjust their spectrum usage based on the presence of other transmissions, ensuring fair spectrum access without rigid MU constraints.
• Low-Power Devices: Equipment with lower RF output power inherently poses minimal risk of spectrum interference, removing the need for MU regulation.

Does Medium Utilization Apply to Wi-Fi, Bluetooth, LoRa, and Zigbee Devices?

Understanding whether medium utilization applies to various technologies operating in the 2.4 GHz ISM band is essential for ensuring compliance with EN 300 328. Here's how MU impacts these devices:

1. Wi-Fi (802.11):
• Applicability: MU does not apply to Wi-Fi devices, as they are classified as adaptive equipment.
• Why Exempt: Wi-Fi's Listen Before Talk (LBT) mechanism ensures spectrum efficiency without requiring additional MU constraints.
2. Bluetooth (BT):
   1. Note: Non-adaptive Bluetooth devices must comply with the 10% MU limit if operating above 10 dBm e.i.r.p.
• Applicability: Traditional Bluetooth devices using Frequency Hopping Spread Spectrum (FHSS) are subject to MU requirements unless they employ adaptive features.
3. Bluetooth Low Energy (BLE):
• Applicability: BLE devices are typically adaptive and exempt from MU requirements under EN 300 328.
4. LoRa:
• Applicability: Non-adaptive LoRa devices must comply with MU limits, while adaptive implementations with LBT mechanisms are generally exempt.
5. Zigbee (802.15.4):
• Applicability: Zigbee devices can be either adaptive or non-adaptive. Non-adaptive devices must comply with MU limits if exceeding 10 dBm e.i.r.p.

Challenges in EN 300 328 Medium Utilization Compliance

Real-world implementation of medium utilization compliance involves overcoming several technical hurdles:

1. Duty Cycle Configuration: Balancing duty cycle and throughput for high-performance devices while adhering to EN 300 328 limits can be challenging.
2. Power Management: Fine-tuning RF output power (P_{out}​) across various scenarios without breaching MU constraints.
3. Adaptive vs. Non-Adaptive Equipment: Adaptive systems gain flexibility through spectrum-sharing mechanisms, but non-adaptive devices must meet stricter limitations.

Testing Medium Utilization for EN 300 328 Compliance

Medium Utilization compliance is validated through testing methodologies:

• Conducted Testing: This is the preferred method for MU calculations, as it offers precise measurements by directly connecting to the device’s RF output, bypassing the antenna.
• Note: To accurately determine the equivalent isotropic radiated power (EIRP), the antenna gain must be considered in conjunction with the conducted RF output power.
• Radiated Testing: Used when RF connectors are unavailable, this approach estimates P_{out} out​ based on antenna characteristics and radiated performance.

Actionable Strategies for OEMs

1. Optimizing Duty Cycles
   1. Declare accurate duty cycle parameters during testing, as specified in Section 5.4.1 of EN 300 328.
   2. Use advanced modulation techniques to minimize transmit durations without compromising data rates.
2. Power Management
   1. Dynamically adjust RF output power P_{out} to reduce medium utilization in scenarios requiring less range or throughput.
3. Accounting for Blacklisted Frequencies
   1. Ensure accurate MU calculations by considering restricted frequencies as active during conformance testing, per Clause 5.4.2.2.1.4.
4. Leveraging Adaptive Capabilities
   1. For non-adaptive devices, incorporating adaptive features like LBT can simplify compliance by enabling dynamic channel access.

Practical Example: Meeting Medium Utilization Requirements

Consider a non-adaptive device with:

• P_{out}​: 50 mW (17 dBm)
• Duty Cycle (DC): 5%

The MU is calculated as:    

This value is well below the 10% threshold, demonstrating how precise adjustments to power and duty cycle can ensure compliance with EN 300 328 while maintaining optimal performance.

Figure 1 illustrates the relationship between the maximum allowable duty cycle (DC) and the device’s equivalent isotropic radiated power (e.i.r.p.) in dBm, based on regulatory limits. As the e.i.r.p. increases, the maximum allowable duty cycle decreases, reflecting stricter constraints for higher power emissions. The curve converges to the MU limit of 10%, indicating the minimum duty cycle permissible for devices operating at high e.i.r.p. levels.

Collaborating with Intertek Assurance for EN 300 328 Compliance

At Intertek Assurance Solutions, we provide a comprehensive suite of RF compliance services designed to streamline your product development process. Whether optimizing designs, navigating the complexities of medium utilization, or ensuring pre-compliance testing success, our experts support your team at every stage.

Our Key Services Include:

• Design for Compliance (DfC): Helping you identify and resolve potential issues early in the development process.
• Pre-Compliance Testing: Advisory and troubleshooting to ensure your product meets all relevant requirements before final certification.
• Global Market Access (GMA): Strategies for achieving certifications across over 150 countries.

By collaborating with Intertek, you gain access to industry-leading expertise that minimizes risk, accelerates market entry, and ensures product success.

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• RF, EMC, Safety, and Performance testing capabilities.
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