# Technical Program

## Paper Detail

Paper Title Capacity per Unit-Energy of Gaussian Many-Access Channels FR2.R8.2 Jithin Ravi, Tobias Koch, Universidad Carlos III de Madrid, Spain Energy Efficient Communications Conseil, Level 5 Friday, 12 July, 11:40 - 13:00 Friday, 12 July, 12:00 - 12:20 Click here to download the manuscript We consider a Gaussian multiple-access channel where the number of transmitters grows with the blocklength \$n\$. For this setup, the maximum number of bits that can be transmitted reliably per unit-energy is analyzed. We show that if the number of users is of an order strictly above \$n/\log n\$, then the users cannot achieve any positive rate per unit-energy. In contrast, if the number of users is of order strictly below \$n/\log n\$, then each user can achieve the single-user capacity per unit-energy \$(\log e)/N_0\$ (where \$N_0/ 2\$ is the noise power) by using an orthogonal access scheme such as time division multiple access. We further demonstrate that orthogonal codebooks, which achieve the capacity per unit-energy when the number of users is bounded, can be strictly suboptimal.