Spectrum Engineering

Version three of Advanced Wireless Services (AWS 3) radio systems will soon use spectrum that is adjacent to bands currently used by airborne telemetry links at U.S. government test and training ranges (TTRs). Spectrum sharing analyses need to be performed to determined how much off-tuning (number of megahertz) and distance separation (number of kilometers) are needed between AWS 3 transmitters and telemetry receiver stations to avoid harmful interference to those receivers. To complete these studies, detailed wide dynamic range emission spectrum measurements of representative models of the soon-to-be-deployed AWS 3 transmitters have been performed. This report describes those measurements, and the method used to obtain them. These measurements have been performed with over 100 decibels (dB) of dynamic range. The measurements have been collected in a variety of resolution bandwidths, transmitter modulations, and types of transmitter loading (i.e., number of resource blocks used) for two measurement detector modes. In general, AWS 3 eNB and UE transmitted emission spectra are found to be insensitive to variations in transmitter configurations. The measured power spectra of the eNBs and UEs vary in direct proportion to measurement (or receiver) bandwidth (i.e., as 10 log measurement bandwidth) with an approximate offset of about 10 dB between peak and average levels. The measurement results indicate that AWS 3 eNB and UE power spectra are suppressed by at least 100 dB in the adjacent telemetry bands for the devices tested. These results can now be factored into EMC analyses for AWS 3 transmitters operating in proximity to telemetry receivers.

The work described in this report was performed by the National Advanced Spectrum and Communications Test Network (NASCTN). Results were published simultaneously as NASCTN Report 4, NTIA Technical Report TR-18-528, and NIST Technical Note TN 1980.

Keywords: band sharing; emission spectrum; spectrum sharing; spectrum measurements; interference analysis; out-of-band (OOB) emissions; 1755-1780 MHz; 2155-2180 MHz; AWS-3; aeronautical mobile telemetry (AMT); Band 66; band sharing analysis; eNodeB (eNB); telemetry links; user equipment (UE)

• TR-18-528

Frame erasures and background noise are two factors that can interact with speech coding to reduce speech intelligibility and thus impair public safety mission-critical voice communications. We conducted two tests of intelligibility in the face of these factors. The tests covered five adaptive multi-rate (AMR) and enhanced voice services (EVS) speech coding modes, each using a bit rate near 13 kb/s. Two EVS Channel Aware (CA) modes were included. Both tests use the Modified Rhyme Test (MRT) protocol and together they comprise over 150,000 trials. The first test used frame erasures targeted at critical consonants for maximum sensitivity and the second used frame erasures generated at random by a two-state Gauss-Markov model. By using these large numbers of MRT trials we found that the CA codec modes offer small but statistically significant speech intelligibility improvements in numerous frame-erasure environments.

Keywords: noise; speech coding; speech quality; modified rhyme test (MRT); packet loss; speech intelligibility; frame erasures; AMR; EVS; channel aware; frame loss

• TR-18-529 

Spectrum is a limited resource upon which the world makes continually increasing demands. It is therefore natural and compelling to study the efficiency with which radio systems use spectrum. Spectrum efficiency studies reveal how future systems can make better use of radio spectrum, and allow spectrum engineers and managers to make better allocation and sharing decisions. This report provides a 53-year historical review of previous domestic and international spectrum efficiency studies. Based on this review, we recommend possible future spectrum efficiency work to extend the state of knowledge in this area.

Keywords: spectrum efficiency; band sharing; spectrum utilization; spectrum sharing; out-of-band (OOB) emissions; spurious emissions; frequency bandwidth; spectrum efficiency metrics

• TR-18-530