Speech position

Description

In 3GPP specifications related to radio frequency (RF) exposure and Specific Absorption Rate (SAR) testing, the term 'speech position' denotes a specific test configuration where a User Equipment (UE) is placed close to a head phantom, known as a Specific Anthropomorphic Mannequin (SAM). This position simulates the typical use case of a mobile phone held against the ear during a voice call. The SAM phantom is a standardized model of the human head, defined in international standards such as IEC 62209 and IEEE 1528, and is used to measure the SAR, which is the rate at which energy is absorbed by the human body when exposed to RF electromagnetic fields. The speech position is one of several test positions specified for SAR compliance testing of mobile devices. It ensures that the device's RF emissions are within safety limits when used in close proximity to the head. The specifications 25.144 and 37.144 provide details on the speech position and related test methodologies for 3GPP terminals. The speech position is characterized by the distance and orientation of the UE relative to the SAM phantom, typically with the earpiece aligned with the ear reference point and the device tilted at a specified angle. The test is performed with the UE transmitting at maximum power in various frequency bands and modes. The results are used to certify that the device complies with regulatory SAR limits, such as 1.6 W/kg averaged over 1 gram of tissue (FCC) or 2.0 W/kg averaged over 10 grams (ICNIRP). The speech position is crucial for ensuring user safety and regulatory compliance. It is also used in the development of UE designs to optimize antenna placement and power control to minimize SAR while maintaining good communication performance. The term has been stable in 3GPP specifications, with only minor editorial changes in capitalization over releases. Understanding the speech position is essential for engineers involved in RF exposure testing, regulatory compliance, and UE design.

Purpose & Motivation

The speech position concept exists to provide a standardized, repeatable method for assessing the RF exposure of mobile devices when used in close proximity to the human head. As mobile phones became ubiquitous, concerns about potential health effects from RF radiation led to regulatory requirements for SAR testing. The speech position simulates the most common scenario: a user holding the phone to their ear during a voice call. By defining a specific phantom (SAM) and a precise positioning of the device, the test ensures that SAR measurements are consistent across different laboratories and device models. This standardization is critical for comparing results and enforcing safety limits. The speech position also helps device manufacturers design phones that meet SAR limits without compromising antenna performance. Before standardization, SAR testing methods varied, leading to inconsistent results and difficulty in comparing devices. The introduction of the SAM phantom and speech position in standards like IEEE 1528 and IEC 62209, and their adoption in 3GPP specifications, addressed this problem. The speech position remains relevant even as voice calls are increasingly made via hands-free or messaging, because regulatory compliance must cover all foreseeable use cases. Thus, the speech position is a cornerstone of RF safety testing for mobile devices.