TH-PPM with non-coherent detection for multiple access in electromagnetic wireless nanocommunications

Terahertz band (0.1-10 THz)-based electromagnetic nanocommunications could advance several nanotechnology applications in the biomedical, environmental, and military fields. One of the fundamental challenges with nanocommunications is the need for an appropriate modulation and channel access mechanism. In multi-user nanocommunications, detrimental effects of path loss and interference could pose a significant problem for multiple nano-devices trying to access the channel concurrently. This would result in retransmissions, which is barely affordable at the nano-level due to the minute size and energy constraints of nano-devices. In this paper, time-hopping (TH) combined with M-ary pulse position modulation (PPM) is proposed as a modulation and multiple access scheme for multi-user nanocommunications systems. PPM, being the most energy-efficient modulation scheme, with TH would allow nano-devices to communicate simultaneously with greater efficiency. Decoding at the receiver is done after non-coherent detection. The symbol-error rate (SER) in the presence of multi-user interference is evaluated in terms of signal-energy-to-noise ratio and the number of interfering users. Moreover, capacity of the system is also evaluated in terms of bits per symbol for different design parameters. Numerical results show that the SER and capacity of the system can be improved by choosing appropriate TH-PPM parameters for a given network condition. The comparisons of simulation results for TH-PPM with another existing scheme witnesses an improved energy efficiency and reduced computational complexity.