TRP vs TIS: Key OTA Measurement Differences

In Over The Air (OTA) testing, evaluating how well a wireless device communicates with a network requires looking at both sides of the conversation i.e. how loudly it can “speak” and how well it can “hear.” To quantify this, engineers use two fundamental OTA metrics viz. TRP (Total Radiated Power) and TIS (Total Isotropic Sensitivity). Let us understand these terms and explore difference between TRP and TIS.

In OTA certification for smartphones, IoT devices and 5G equipment, a device must pass strict thresholds for both TRP and TIS to be allowed onto a carrier’s network, ensuring that the device will neither drop network connections nor drain its battery trying to communicate.

TRP (Total Radiated Power)

TRP is a measure of the total RF power radiated by a device’s antenna in all directions. It evaluates the overall performance of the device’s transmitter (Tx).

TRP Measurement Procedure:

• A device is placed in an anechoic chamber.
• The test equipment measures the Effective Isotropic Radiated Power (EIRP) at dozens or hundreds of different points across a full 3D sphere surrounding the device.
• All of these EIRP measurements are then mathematically integrated (averaged) to calculate a single TRP value.

TRP represents the “true” output power of the device. Even if the internal radio amplifier is pushing exactly 23 dBm of power, a poorly designed antenna, internal cabling losses, or interference from the device’s battery/casing will cause the actual radiated power to drop. TRP captures all of these real-world losses.

TRP determines the device’s uplink coverage. A high TRP means the device can reliably push its signal back to a distant cell tower, reducing dropped calls and increasing uplink data speeds, especially at the edge of a cell network.

TIS (Total Isotropic Sensitivity)

TIS is a measure of the device’s overall receiver performance. It represents the lowest possible signal strength the device can receive from all directions while still maintaining a reliable data connection. It evaluates the performance of the device’s receiver (Rx).

TIS Measurement Procedure:

• In the anechoic chamber, the test equipment sends a signal to the device.
• At each point on the 3D sphere, the equipment gradually lowers the signal power until the device’s error rate (Bit Error Rate or Block Error Rate) exceeds a acceptable threshold (e.g. 5 % drop rate).
• This point is called the Effective Isotropic Sensitivity (EIS).
• All the EIS points across the sphere are integrated to calculate the TIS.

TIS accounts for antenna efficiency on the receiving side, but more importantly, it captures internal noise and self interference. If a device has a noisy digital screen or processor that interferes with its own antenna, the TIS will be severely degraded.

TIS determines the device’s downlink coverage. A good (i.e. very low) TIS means the device can successfully decode faint, degraded signals from a distant cell tower, ensuring high download speeds and preventing “dead zones” where the device shows bars but cannot load data.

Difference Between TRP and TIS

Limits for User Equipment (UEs / Smartphones) – 5G-Advanced

TRP Limits for UEs:

• A standard 5G mmWave smartphone (Power Class 3) is typically specified with a maximum TRP of +23 dBm.

Receiver sensitivity (Spherical Coverage / TIS equivalent):

• The UE is tested across a 3D sphere. 3GPP dictates that the device’s EIS must be below a certain threshold (e.g. -88.3 dBm for a 50 MHz channel in band n257) for at least 50% of the spherical surface.

6G specifications

In 6G which is 3gpp rel-21 and beyond, FR3 band (7 GHz to 24 GHz) and Sub-THz bands (100 GHz to 300 GHz) are currently being explored. Following specifications documents mention details of TRP and TIS.

• TS 38.101-1 & TS 38.101-2: UE TRP and EIS/Spherical Coverage Limits.
• TS 38.104: Base Station (gNodeB) TRP, EIRP, and OTA Sensitivity limits.
• TS 38.115-2: Network Controlled Repeater (NCR) radiated conformance limits

Summary

If you think of wireless communication as a conversation in a noisy room:

• TRP measures how loudly and clearly the device can shout so the network can hear it.
• TIS measures how incredibly sensitive the device’s ears are to hear the network whispering back.