Description
EP1 is a specific test condition defined in 3GPP specification TS 46.055 for evaluating the performance of GSM speech codecs and the associated channel coding under controlled interference. It is not a signaling procedure but a standardized reference point for performance characterization. The condition is defined by a Carrier-to-Interference (C/I) ratio of 10 decibels (dB) and a target Gross Bit Error Rate (GBER) of 5%. The C/I ratio is a key metric in cellular networks, representing the strength of the desired signal (Carrier) relative to the sum of interfering signals (Interference) from other cells using the same frequency.
In practical terms, a C/I of 10 dB represents a relatively high-quality radio link. This ratio indicates that the desired signal power is ten times stronger than the interfering power. Under these conditions, the channel coding and interleaving schemes in GSM are designed to correct most transmission errors, resulting in a Gross Bit Error Rate of 5% before channel decoding. The 'Gross' BER is measured on the encoded bitstream after demodulation but before the application of forward error correction (FEC). A 5% GBER at this C/I level is considered acceptable, as the subsequent channel decoder (e.g., for a Full-Rate or Enhanced Full-Rate speech traffic channel) can successfully recover the original speech frames, providing good voice quality.
The definition of EP1 serves as a benchmark. Equipment manufacturers and network planners use this condition to verify that a mobile station (MS) or base station subsystem (BSS) meets minimum performance requirements for operation in non-critical areas of a cell. When a device is tested 'at EP1,' it means its receiver performance is evaluated with a test signal that simulates this specific interference environment. Performance metrics like Frame Erasure Rate (FER) or speech quality Mean Opinion Score (MOS) are then measured to ensure compliance. This allows for consistent and comparable performance testing across different hardware implementations.
Purpose & Motivation
EP1 was created to provide a standardized, repeatable test condition for quantifying the robustness of GSM voice services against co-channel interference. Before such standardized reference points, it was difficult to objectively compare the performance of different mobile handsets or network infrastructure equipment. By defining a specific C/I and expected GBER, 3GPP established a common benchmark that all vendors must meet, ensuring a baseline level of voice quality for subscribers located in areas with good signal conditions.
It addresses the problem of performance verification in a controlled, laboratory-like environment that correlates to real-world network conditions. 'Well inside a cell' is a typical operating point for many users. Defining this condition allows engineers to isolate and test the performance of the speech codec, channel coding, and demodulator without the extreme stress of cell-edge conditions. It ensures that the fundamental link budget and receiver sensitivity calculations for network planning are based on a universally accepted performance criterion.
Historically, these types of performance points became crucial with the dense frequency reuse patterns of GSM networks, where interference from neighboring cells using the same frequency (co-channel interference) is a primary capacity limiter. EP1, along with EP2, provides a two-point model for system performance, covering both good and poor coverage scenarios. This was motivated by the need to guarantee service quality and drive improvements in receiver technology, directly impacting network capacity and user experience.
Key Features
- Defines a reference Carrier-to-Interference (C/I) ratio of 10 dB
- Specifies a target Gross Bit Error Rate (GBER) of 5%
- Models radio conditions 'well inside a cell'
- Used for conformance testing of GSM speech channel performance
- Provides a benchmark for receiver sensitivity under moderate interference
- Enables comparable performance evaluation across different vendors' equipment
Evolution Across Releases
Introduced in the context of GSM/EDGE radio access network (GERAN) performance testing specifications. Established as a fixed reference point (C/I=10 dB, 5% GBER) for testing the performance of legacy GSM speech traffic channels and associated channel coding schemes in a controlled interference environment.
Defining Specifications
| Specification | Title |
|---|---|
| TS 46.055 | 3GPP TR 46.055 |