A multiuser decoder based on spectrum analysis for the Brazilian Environmental Data Collecting System

Abstract

Summary The Brazilian Environmental Data Collection System (SBCDA) is an asynchronous multiuser message forwarding system based on low earth orbit (LEO) satellites with applications restricted to environmental monitoring and human life protection. This work presents a multiuser SBCDA decoder with low data memory and computational load. The decoder uses spectrum analysis to detect signal presences and upon every signal detection starts a signal decoding process with single‐user bit detection. Simulations considering an Additive White Gaussian Noise (AWGN) scenario with signal's time‐frequency positions uniformly and independently distributed and signal's powers uniformly distributed in dB within a dynamic range of 24 dB are present for different densities of user signals. Those show a frame error rate (FER) of approximately 25% for an average of six coexisting signals at every time instant, in which a missed signal was considered as a frame error. Finally, there are considerations on how to improve the performance maintaining a single‐input and single‐user bit detection strategy.

A parallel software-defined ultra-low-power receiver for a satellite message forwarding system

“…In this context, this work presents an implementation of an multi-user receiver algorithm for use with nanosatellites. For this implementation of the algorithm proposed by Duarte et al [14], fixed-point C was used. The application was embedded in the GAP8, an IoT application processor based on the PULP platform which itself implements an extended version of the open-source RISC-V instruction set [15].…”

“…Rae [18] made a status study of the SBCDA, estimated PTT signal power levels at the satellite receiver and also the number of signals coexisting in a time instant, and proposed a PTT signal detector by spectral analysis for the SBCDA/Argos-2. Duarte et al [14] proposed the detection and decoding algorithm that was used in its implementation on the EDC and that will be used in the development of this work. The authors present the frame error rate (FER) and the effect of the average number of coexisting signals in the correct detection rate.…”

“…The range of possible values is / 0 = 61.25 dB and / 0 = 43.59 dB. In [14], the authors calculate the / 0 to the receiver sensibility at 40 dB. This value was calculated for a bit error rate for a BPSK signal of 10 −5 under AWGN conditions and considering losses due to the residual carrier and losses due to the radio receiver circuit.…”

“…Since multiple PTT signals usually coexist in time at the receiver, a multi-user receiver is necessary. The authors in [14], [18] considered an average of 7 and 5 PTT signals coexisting in time, respectively.…”

“…The multi-user receiver algorithm proposed by Duarte et al [14] processes the input signal in segments of 10 ms seconds at a time. The authors defined a sample rate of 128 kilo samples per second, leading to 1280 samples per segment.…”