Design and Implementation of an Embedded System for Software Defined Radio

In this paper, developing high performance software for demanding real-time embedded systems is proposed. This software-based design will enable the software engineers and system architects in emerging technology areas like 5G Wireless and Software Defined Networking (SDN) to build their algorithms. An ADSP-21364 floating point SHARC Digital Signal Processor (DSP) running at 333 MHz is adopted as a platform for an embedded system. To evaluate the proposed embedded system, an implementation of frame, symbol and carrier phase synchronization is presented as an application. Its performance is investigated with an on line Quadrature Phase Shift keying (QPSK) receiver. Obtained results show that the designed software is implemented successfully based on the SHARC DSP which can utilized efficiently for such algorithms. In addition, it is proven that the proposed embedded system is pragmatic and capable of dealing with the memory constraints and critical time issue due to a long length interleaved coded data utilized for channel coding

Design and implementation of low complexity wake-up receiver for underwater acoustic sensor networks

This thesis designs a low-complexity dual Pseudorandom Noise (PN) scheme for identity (ID) detection and coarse frame synchronization. The two PN sequences for a node are identical and are separated by a specified length of gap which serves as the ID of different sensor nodes. The dual PN sequences are short in length but are capable of combating severe underwater acoustic (UWA) multipath fading channels that exhibit time varying impulse responses up to 100 taps. The receiver ID detection is implemented on a microcontroller MSP430F5529 by calculating the correlation between the two segments of the PN sequence with the specified separation gap. When the gap length is matched, the correlator outputs a peak which triggers the wake-up enable. The time index of the correlator peak is used as the coarse synchronization of the data frame. The correlator is implemented by an iterative algorithm that uses only one multiplication and two additions for each sample input regardless of the length of the PN sequence, thus achieving low computational complexity. The real-time processing requirement is also met via direct memory access (DMA) and two circular buffers to accelerate data transfer between the peripherals and the memory. The proposed dual PN detection scheme has been successfully tested by simulated fading channels and real-world measured channels. The results show that, in long multipath channels with more than 60 taps, the proposed scheme achieves high detection rate and low false alarm rate using maximal-length sequences as short as 31 bits to 127 bits, therefore it is suitable as a low-power wake-up receiver. The future research will integrate the wake-up receiver with Digital Signal Processors (DSP) for payload detection. --Abstract, page iv

Designing an Adaptive Acoustic Modem for Underwater Sensor Networks

Abstract-There is a growing interest in using underwater networked systems for oceanographic applications. These networks often rely on acoustic communication, which poses a number of challenges for reliable data transmission. The underwater acoustic channel is highly variable; each link can experience a vastly conditions, which change according to environmental factors as well as the locations of the communicating nodes. This makes it difficult to ensure reliable communication. Furthermore, due to the high transmit power, the energy consumed in transmitting data is substantial which is exacerbated at lower data rates. The main challenge that we address in this article is how to build a system that provides reliable and energy efficient communication in underwater sensor networks. To this end, we propose an adaptive underwater acoustic modem which changes its parameters according to the situation. We present the design of such a modem and provide supporting results from simulations and experiments

A channel aware adaptive modem for underwater acoustic communications

Acoustic underwater channels are very challenging, because of limited bandwidth, long propagation delays, extended multipath, severe attenuation, rapid time variation and large Doppler shifts. A plethora of underwater communication techniques have been developed for dealing with such a complexity, mostly tailoring specific applications scenarios which can not be considered as one-size-fits-all solutions. Indeed, the design of environment-specific solutions is especially critical for modulations with high spectral efficiency, which are very sensitive to channel characteristics. In this paper, we design and implement a software-defined modem able to dynamically estimate the acoustic channel conditions, tune the parameters of a OFDM modulator as a function of the environment, or switch to a more robust JANUS/FSK modulator in case of harsh propagation conditions. The temporal variability of the channel behavior is summarized in terms of maximum delay spread and Doppler spread. We present a very efficient solution for deriving these parameters and discuss the limit conditions under which the OFDM modulator can work. In such scenarios, we also calibrate the prefix length and the number of sub-carriers for limiting the inter-symbol interference and signal distortions due to the Doppler effect. We validate our estimation and adaptation techniques by using both a custom-made simulator for time-varying underwater channels and the well-known Watermark simulator, as well as real in field experiments. Our results show that, for many practical cases, a dynamic adjustment of the prefix length and number of sub-carriers may enable the utilization of OFDM modulations in underwater communications, while in harsher environments JANUS can be used as a fall-back modulation

A Channel-Aware Adaptive Modem for Underwater Acoustic Communications

Acoustic underwater channels are very challenging, because of limited bandwidth, long propagation delays, extended multipath, severe attenuation, rapid time variation and large Doppler shifts. A plethora of underwater communication techniques have been developed for dealing with such a complexity, mostly tailoring specific applications scenarios which can not be considered as one-size-fits-all solutions. Indeed, the design of environment-specific solutions is especially critical for modulations with high spectral efficiency, which are very sensitive to channel characteristics. In this paper, we design and implement a software-defined modem able to dynamically estimate the acoustic channel conditions, tune the parameters of a OFDM modulator as a function of the environment, or switch to a more robust JANUS/FSK modulator in case of harsh propagation conditions. The temporal variability of the channel behavior is summarized in terms of maximum delay spread and Doppler spread. We present a very efficient solution for deriving these parameters and discuss the limit conditions under which the OFDM modulator can work. In such scenarios, we also calibrate the prefix length and the number of sub-carriers for limiting the inter-symbol interference and signal distortions due to the Doppler effect. We validate our estimation and adaptation techniques by using both a custom-made simulator for time-varying underwater channels and the well-known Watermark simulator, as well as real in field experiments. Our results show that, for many practical cases, a dynamic adjustment of the prefix length and number of sub-carriers may enable the utilization of OFDM modulations in underwater communications, while in harsher environments JANUS can be used as a fall-back modulation

Adaptive Modulation Schemes for Underwater Acoustic OFDM Communication

High data rate communication is challenging in underwater acoustic (UA) communication as UA channels vary fast along with the environmental factors. A real-time Orthogonal frequency-division multiplexing (OFDM) based adaptive UA communication system is studied in this research employing the National Instruments (NI) LabVIEW software and NI CompactDAQ device. The developed adaptive modulation schemes enhance the reliability of communication, guarantee continuous connectivity, ensure maximum performance under a fixed BER at all times and boost data rate