Terminology » 5G O-RAN Conformance Testing: EVM, ACLR, OBW, TAE & More

5G O-RAN Conformance Testing: EVM, ACLR, OBW, TAE & More

5g open ran o-ran conformance tests

Introduction: Ensuring that O-RAN components (especially O-RU) meet performance standards is critical for interoperability and regulatory compliance. Core conformance tests include EVM (modulation accuracy), ACLR (Adjacent Channel Leakage Ratio), OBW (occupied bandwidth), TAE (time alignment error), transmit on/off & power and sensitivity. This page describes each test and how it’s performed and specifications requirement in 5G / O-RAN environments.

O-RAN Conformace tests

These tests verify that RF transmitter or receiver performance of RAN components (often O-RU / gNB / base station) comply with 3GPP / O-RAN standards (e.g. TS 38.104, TS 38.141-1, etc.). Conformance is needed for certification, regulatory, interoperability, performance and avoiding interference.

EVM Test

  • Definition & Purpose : EVM (Error Vector Magnitude) measures the difference between the ideal transmitted modulation symbols and the actual transmitted symbols.
  • Measurement : It is measured using VSA (Vector Signal Analyzer) specifically developed for such measurements. Use specific test modes e.g. PDSCH with 64QAM or 256QAM as per test requirements.
  • Standard requirements : EVM (256QAM PDSCH) should be <= 3.5%. Lower EVM means higher signal fidelity and better transmitter performance.

ACLR Test

  • Definition & Purpose : ACLR (Adjacent Channel Leakage Ratio) quantifies how much transmitted power “leaks” into adjacent frequency channels.
  • Measurement : It is the ratio of the power in the assigned channel to the power in the adjacent channel, showing spectral purity and interference potential to neighboring channels. This can be measured either using Spectrum Analyzer or using VSA. Tests usually done for both immediate adjacent and sometimes second adjacent depending on standard.
  • Standard requirements : ACLR should be approx. -45 dBc for many channel BWs.

OBW Test

  • Definition & Purpose : OBW (Occupied Bandwidth) is the portion of the transmitted spectrum that contains 99% of the total transmitted power, excluding out of band emissions.
  • Measurement : Measured with spectrum analyzer. Define lower and upper frequencies (f1 & f2) such that a specified percentage (often 99%) of transmitted power is between them. Often this must be less than or equal to declared channel bandwidth or aggregate BW in Carrier Aggregation (CA).
  • Standard requirements : Must be <= defined channel BW; e.g. For 100 MHz BW, OBW should be less or equal with tolerances of +/- 300-600 KHz as per BW etc.

TAE Test

  • Definition & Purpose : TAE measures the timing difference between signals transmitted from multiple radio units or antennas in a coordinated system.
  • Measurement : Use a reference trigger, frame synchronous measurement; compare when each of the signals from different antenna ports (or carriers) leaveing the transmitter.
  • Standard requirements : Should be <= 65 ns. Excessive TAE can cause signal overlap or degradation in multi-antenna or multi-cell systems, affecting synchronization and performance.

Transmit Power ON/OFF Test

  • Definition & Purpose : This parameter defines the power level accuracy and timing when a transmitter switches between ON and OFF states. It ensures that power ramps up and down correctly to avoid spectral splatter, interference, or gaps during transmission bursts.
  • Measurement : Setup: transmitter is commanded off/on. Signal analyzer measures power in “off” state, in “on” state, transitional period.
  • Standard requirements : Must be very low, typically many dBs below on-power; the transient time (rise/fall) must be under certain ms or µs depending on standard.

Receiver Sensitivity Test

  • Definition & Purpose : It is the minimum input signal power required for the receiver to achieve a specified performance e.g. certain BER or BLER. It reflects how well the receiver can detect and decode weak signals in low power or noisy environments.
  • Measurement : Use vector signal generator / test signal at different powers; measure bit error rate (or throughput) at each. Find the signal power at which performance metric (BER / throughput / error rate) just meets a threshold (often something like 95% throughput or certain BLER / BER).
  • Standard requirements : reference sensitivity might be approx. -94 dBm for certain RU configurations or carrier bandwidths in sub-6GHz.

Conclusion: Conformance testing is the quality gate keeper for O-RAN deployments. By validating EVM, ACLR, OBW, TAE, transmit behavior and sensitivity, operators ensure that components deliver correct performance and coexist harmoniously.