Low-power wide-area networks (LPWANs) are wireless connectivity solutions for Internet-of-Things applications, including industrial automation. Among the several LPWAN technologies, LoRaWAN has been extensively addressed by the research community and the industry. However, the reliability and scalability of LoRaWAN are still uncertain. One of the techniques to increase the reliability of LoRaWAN is message replication, which exploits time diversity. This article proposes a novel hybrid coded message replication scheme that interleaves simple repetition and a recently proposed coded replication method. We analyze the optimization of the proposed scheme under minimum reliability requirements and show that it enhances the network performance without requiring additional transmit power compared to the competing replication techniques.

We present an improved decoding algorithm for joint turbo decoding and physical-layer network coding. Instead of decoding the individual (binary) messages separately at the relay, the proposed algorithm, from the superimposed faded signals, yields an XOR estimate of the sent messages. Moreover, we introduce a softening of the XOR values to improve the overall performance. Simulation results show that this simple idea yields gains up to 4.5 dB in a Rayleigh fading channel model when compared to a similar scheme.

A new cooperative diversity scheme with two relay stations and linear coherent detection at the destination node is proposed in this paper. We consider that a perfect CSI is available at the destination node, as well to the relay stations, allowing each relay station to perform optimal beamforming. In order to evaluate the effect of a quantized feedback link between the destination node and the relay stations, we also consider that the destination node sends, additionally, b more bits to the relays. Using these b bits, the relay stations can apply a correction factor to the detected symbol and then send it to the destination node which performs a linear coherent detection. In our proposal, the communication between the relay stations is not allowed. The performance of the proposed scheme is compared with the well known MRC receiver technique with four receive antennas in order to show that the proposed and the MRC schemes achieve the same diversity order. In addition, the influence of the number of feedback bits and the SNR between the transmit node and relay stations are also addressed.

A receiver for a MIMO OFDM communication system using direct conversion transceivers is proposed. The novel receiver takes advantage of the I/Q imbalance inherent to the direct conversion operation. It can be shown that the I/Q imbalance in multicarrier communication systems creates an additional frequency diversity. By adequately exploiting such diversity at the receiver, the overall performance can be considerably improved. Simulation results considering a MIMO OFDM system using V-BLAST show that, when exploiting the I/Q imbalance, gains of up to 5 dB at a BER of 10-4can be obtained with respect to the ideal system, without I/Q imbalance.

We present new space-time trellis codes for two transmit antennas and p-PSK modulations, where p=3. 5. 7.11. 13.17, satisfying the rank and the determinant or the trace criteria. The system utilizes a rate 1/2 convolutional encoder over GF(p), p a prime. Some encoder properties are presented that simplify the code search.

In this paper, we consider a space-time coded system composed of an encoder over GF(p), where p can be any prime number, followed by a serial-to-parallel converter, n mappers from GF(p) into a p-PSK signal constellation, and a transmitter with n antennas. The codes are designed to provide the best error performance in the quasi-static, flat Rayleigh fading channel, according to the rank and the determinant criteria derived by Tarokh et al. We present two theorems by which we can simplify the design of full diversity space-time trellis codes (STTCs), for any number of transmit antennas. A spectral efficiency of Iog/sub 2/(p) b/s/Hz is achieved. Such non-integral rates can be useful to serve a wider range of multimedia applications. New STTCs with n = 2, 3, and 4 transmit antennas are presented for the 5-PSK, 7-PSK, and 11-PSK modulations.

We consider a design procedure for achieving full 2-level diversity and coding advantage for space-time convolutional codes over GF(p), where p can be any prime number. Using a p-ary constellation (not necessarily PSK), the spectral efficiency is log/sub 2/(p) b/s/Hz. Simple conditions on the generator matrices of a rate R = 1/2 convolutional code are given so that maximum diversity is guaranteed, while reducing the computer search effort. New 2-space-time codes are presented for the 5-PSK and 7-PSK modulations. Simulation results validate the presented code design procedure.