This article proposes new approximations for the bit error probability of several LoRa-based schemes, such as phase-shift keying (PSK) LoRa, in-phase and quadrature (IQ) chirp spread spectrum (CSS), discrete chirp rate keying (DCRK) CSS, and CSS with index modulation (IM). We include a new scheme that combines IQ, CSS, and IM, denoted as IQ chirp index modulation (IQCIM). Our analysis, which assumes coherent detection in additive white Gaussian noise, compares the LoRa-based schemes also in terms of spectral efficiency, computational complexity, and peak-to-average power ratio (PAPR). Noncoherent detection of CSS with IM is analyzed as well. Our performance analysis shows that the proposed IQCIM produces a significant increase of spectral efficiency (SE) compared to LoRa with similar complexity, at an energy cost of approximately 0.9 dB. When compared to the other LoRa-based schemes, for a fixed decoding latency, the SE of IQCIM is still the largest, with reduced computational cost per transmitted bit. In this context, we also propose a maximum-likelihood (ML) coherent detector for PSK-LoRa and a novel noncoherent detector for IQCSS.

Due to the growing number of devices accessing the Internet through wireless networks, the radio spectrum has become a highly contended resource. The availability of low cost radio spectrum monitoring sensors enables a geographically distributed, real-time observation of the spectrum to spot inefficiencies and to develop new strategies for its utilization. The potentially large number of sensors to be deployed and the intrinsic nature of data make this task a Big Data problem. In this work we design, implement, and validate a hardware and software architecture for wideband radio spectrum monitoring inspired to the Lambda architecture. This system offers Spectrum Sensing as a Service to let end users easily access and process radio spectrum data. To minimize the latency of services offered by the platform, we fine tune the data processing chain. From the analysis of sensor data characteristics, we design the data models for MongoDB and Cassandra, two popular NoSQL databases. A MapReduce job for spectrum visualization has been developed to show the potential of our approach and to identify the challenges in processing spectrum sensor data. We experimentally evaluate and compare the performance of the two databases in terms of application processing time for different types of queries applied on data streams with heterogeneous generation rate. Our experiments show that Cassandra outperforms MongoDB in most cases, with some exceptions depending on data stream rate.

This paper focuses on the performance of LoRa systems after channel decoding. First, we introduce a matrix model for the coded transmission and reception of LoRa signals. Second, we theoretically evaluate the probability of bit error of coherently and noncoherently detected LoRa signals, in additive white Gaussian noise (AWGN), also assuming hard decoding of the LoRa physical layer Hamming code. Simulation results confirm the correctness of the theoretical expressions. Third, we analyze by simulation the coded performance of LoRa systems, with both hard and soft decoding, assuming a multipath channel model already used in the literature. Our analysis quantifies the performance gain of channel coding with respect to uncoded transmissions, in both AWGN and multipath channels, under the assumption that the coded system uses the same bandwidth with lower bit rate.

The IEEE 802.15.4 standard, used for the Internet of Things (IoT), contains several physical layers, which also employ nonorthogonal frequency-shift keying (FSK) modulation. Herein we propose new and simple closed-form expressions for the bit-error rate (BER) of nonorthogonal FSK for the IoT. Simulation results confirm the good accuracy of the proposed expressions.

Bit-interleaved coded modulation (BICM) is at the heart of the second generation digital terrestrial television systems (DVB-T2), which achieves a large spectral efficiency by means of high-order quadrature amplitude modulation (QAM) and low-density parity-check (LDPC) codes. This paper proposes a simple but effective approximation for the log-likelihood ratio (LLR) of the bits estimated by the soft-output QAM demapper. The proposed approximation, which keeps few dominant terms of the LLR expression, needs low additional complexity with respect to the conventional Max-Log approximation. Simulation results for DVB-T2 in multipath channels show a performance gain with respect to the Max-Log approach, especially for QAM with large modulation order.

In this paper we present a technique that can be used for optimizing the streaming of Motion JPEG 2000 video when the communication channel can be abstracted as a binary symmetric channel (BSC), characterized by a certain slowly variable rate of transmission errors. The video is packetized and every packet is protected with a Reed-Solomon forward error correction (FEC) code and then sent on the communication channel. The FEC helps to recover from erased/error-affected source information bytes at the receiver-decoder. The optimized amount of error protection is chosen by using an uncomplicated mathematical expression, given the knowledge of the channel status. In particular, we show the results of simulations that outline the robustness of this technique and its clear advantage over more trivial solutions.

This paper proposes a hybrid scheme for user positioning in an urban scenario using both a Global Navigation Satellite System (GNSS) and a mobile cellular network. To maintain receiver complexity (and costs) at a minimum, the location scheme combines the time-difference-of-arrival (TDOA) technique measurements obtained from the cellular network with GNNS pseudorange measurements. The extended Kalman filter (EKF) algorithm is used as a data integration system over the time axis. Simulated results, which are obtained starting from real measurements, demonstrate that the use of cellular network data may provide increased location accuracy when the number of visible satellites is not adequate. In every case, the obtained accuracy is within the limits required by emergency location services, e.g., Enhanced 911 (E911).

In this paper, we present a theoretical method to find an optimal source and channel code allocation, by considering an embedded image compression standard such as JPEG 2000 and a memoryless transmission channel. Lagrangian optimization is used to find an optimal error correction profile, from a PSNR perspective, starting from intermediate rate-distortion traces. The resulting mathematical relationship is simple and can be computed in real time. Simulations on a binary symmetric channel show that the achieved performance, in terms of PSNR, is comparable with that of similar methods reported in literature, while keeping a lower complexity.

In this paper we present a novel implementation of the JPWL standard on a DSP device, targeted to the protection of HD video streams at 50 Mbit/s. Several investigations on computational cost have been carried out in order to find the parts that had to be optimized for DSP. The result is an implementation that uses tailored instructions for operation on Galois Field and Enhanced Direct Memory Access (EDMA) for interleaving.

The transmission of JPEG 2000 images or video over wireless channels has to cope with the high probability and burstyness of errors introduced by Gaussian noise, linear distortions, and fading. At the receiver side, there is distortion due to the compression performed at the sender side, and to the errors introduced in the data stream by the channel. Progressive source coding can also be successfully exploited to protect different portions of the data stream with different channel code rates, based upon the relative importance that each portion has on the reconstructed image. Unequal Error Protection (UEP) schemes are generally adopted, which offer a close to the optimal solution. In this paper, we present a dichotomic technique for searching the optimal UEP strategy, which lends ideas from existing algorithms, for the transmission of JPEG 2000 images and video over a wireless channel. Moreover, we also adopt a method of virtual interleaving to be used for the transmission of high bit rate streams over packet loss channels, guaranteeing a large PSNR advantage over a plain transmission scheme. These two protection strategies can also be combined to maximize the error correction capabilities.

Nonlinear devices, such as power amplifiers, typically generate spurious signal components known as inter modulations. This phenomenon is particularly important when multiple signals, allocated at different frequencies, pass through nonlinear devices simultaneously. In this paper we extend a known fast counting algorithm (FCA) of intermodulation components and compare it with other counting algorithms. The results obtained show significant improvement on the processing time. The carrier configuration is modelled by using indicator polynomials. We show that the distribution of high order intermodulation products can be computed in a reduced amount of time, by extending the algorithmic results relevant to third order intermodulations. In addition, we notice that in particular situations even order intermodulations are also important. They occupy the adjacent harmonic zones, generally allocated to other services, so that the achievable performance deteriorates. We extend an algorithm which computes the position of even and odd order intermodulations, and we make it faster and computationally more efficient. These results may improve both the optimisation of the spectrum shape and the analysis of the nonlinear effects. Comparisons with some other direct counting algorithms are made in terms of accuracy and speed.

This paper presents a Viterbi decoder (VD) architecture for a reprogrammable data transmission system, implemented using a field programmable gate array (FPGA) device. This VD has been conceived as a building block of a software defined radio (SDR) mobile transceiver, reconfigurable on user request and capable to provide agility in choosing between different standards. UMTS and GPRS standards decoding is achieved by choosing different coding rates and constraint lengths, and the possibility to switch, at run time, between them guarantees a high degree of reconfigurability. The architecture has been tested and verified with a Xilinx XC2V2000 FPGA, to provide a generalized co-simulation/co-design testbed. The results show that this decoder can sustain an uncoded data rate of about 2 Mbps, with an area occupation of 45%, due to the efficient resource reuse

In this paper, we present an overview of the JPWL standardization activity. JPWL is an extension of JPEG 2000 for the efficient transmission of JPEG 2000 images over an error-prone wireless network. More specifically, JPWL supports a set of tools for error protection and correction, including forward error correcting codes (FEC), unequal error protection (UEP), data partitioning and interleaving

Nonlinear devices such as amplifiers and electro-optical transducers introduce spurious signals known as intermodulations, especially when multiple signals at different frequencies access the system. In this paper an extension to the well known fast counting algorithm (FCA) for the intermodulations is presented and a comparison with slow counting algorithms is done. Carrier configuration is represented by means of indicator polynomials, and high-order Intermodulation products distribution can be computed in a fast way, extending the results restricted to third order intermodulations. Moreover, no particular assumption is done on the distribution of the carriers (i.e. they are not required to be equispaced). Comparisons are made in terms of accuracy and speed with slow direct counting algorithms.

This paper deals with the implementation of the sample rate conversion subsystems of the digital front-end, at intermediate frequency (IF), and of a synchronization subsystem in the framework of a software radio receiving terminal. A perviously proposed architecture is adopted and optimized for the realization of a multimodal terminal, the main operational mode of which is UMTS, but also capable to interface with GSM or IS-95. In particular, a class of multiplierless filters in conjunction with reduced complexity FIR filters is chosen for the rate conversion. The selected approach for synchronization is a modified MAX/TC algorithm that exploits dedicated sync channels, for the UMTS case. Its performance in terms of acquisition probability has been studied either in a classic AWGN channel or in a multipath environment. The algorithms have been optimized considering an FPGA based implementation, where power consumption and occupied area strongly constrain designer choices.