Code Acquisition at Low SINR in Spread Spectrum Communications

Abstract—We consider the problem of code acquisition at low signal to interference and noise ratio (SINR) in packet-based spread spectrum communications, where a centralized “pilot ” synchronization signal and high-precision oscillators are not available. Such problems arise in the context of ad-hoc networks, for example, which require fast code acquisition times and gradual degradation of the network with decreasing SINR. We motivate the use of the “postdetection integration ” ap-proach, which utilizes the energy of multiple bits in a packet, for code acquisition at low SINR. We present the implementation of a fully parallel architecture which simultaneously looks at all possible code alignments over multiple bits. This leads to a drastic reduction in acquisition time compared to serial search based methods. We report some preliminary simulation and experimental results from a hardware prototype of a transceiver on which the code acquisition algorithm was implemented. I

MLlib: Machine learning in Apache Spark

Apache Spark is a popular open-source platform for large-scale data processing that is well-suited for iterative machine learning tasks. In this paper we present MLLIB, Spark's open-source distributed machine learning library. MLLIB provides efficient functionality for a wide range of learning settings and includes several underlying statistical, optimization, and linear algebra primitives. Shipped with Spark, MLLIB supports several languages and provides a high-level API that leverages Spark's rich ecosystem to simplify the development of end-to-end machine learning pipelines. MLLIB has experienced a rapid growth due to its vibrant open-source community of over 140 contributors, and includes extensive documentation to support further growth and to let users quickly get up to speed

Synchronization at low SNR in MIMO communications

A key requirement for the increased reliability, range and throughput of the wireless communications is the ability to synchronize in a low signal-to-noise ratio (SNR) environment. It is particularly important in multiple- input and multiple-output (MIMO) communications, where a separate synchronization needs to be performed for each transmit-receive antenna pair. Moreover, the SNR for synchronization in MIMO communications is generally lower than in the single-input and single-output (SISO) case, since the transmit power is distributed amongst the multiple transmit antennas for a fixed total transmit power. Thus, the synchronization is a potential bottleneck for performance improvements in future wireless communications. This dissertation presents a synchronization architecture for packet-based MIMO communications. Specifically, it describes a direct- sequence spread-spectrum (DSSS) based synchronization system for improving the synchronization performance at low SNR, utilizing a parallel code acquisition scheme. This dissertation presents the performance analysis for the packet-based SISO communications as well as for the pilot and packet-based MIMO communications. It proposes a staggered transmission strategy for the parallel code acquisition in systems with multiple transmitter antennas, and also presents the proof for its optimality. Furthermore, it describes an architecture for the parallel code acquisition and presents the implementation of the SISO acquisition system (which is a basic building block for the MIMO acquisition system) on a radio prototype. Finally, it reports the experimental results that confirm the reliable operation at low SNR. The parallel code acquisition forms the backbone of the proposed MIMO synchronization system. This dissertation presents the performance analysis for the SISO synchronization system (which is a basic building block for the MIMO synchronization system) and describes its implementation on a radio prototype. Digital and RF tests verify the accurate translation of the synchronization system into hardware. Calibrations in the lab and experiments conducted at outdoor test sites confirm the ability to synchronize at low SN

Synchronization at low SNR in MIMO communications

A key requirement for the increased reliability, range and throughput of the wireless communications is the ability to synchronize in a low signal-to-noise ratio (SNR) environment. It is particularly important in multiple- input and multiple-output (MIMO) communications, where a separate synchronization needs to be performed for each transmit-receive antenna pair. Moreover, the SNR for synchronization in MIMO communications is generally lower than in the single-input and single-output (SISO) case, since the transmit power is distributed amongst the multiple transmit antennas for a fixed total transmit power. Thus, the synchronization is a potential bottleneck for performance improvements in future wireless communications. This dissertation presents a synchronization architecture for packet-based MIMO communications. Specifically, it describes a direct- sequence spread-spectrum (DSSS) based synchronization system for improving the synchronization performance at low SNR, utilizing a parallel code acquisition scheme. This dissertation presents the performance analysis for the packet-based SISO communications as well as for the pilot and packet-based MIMO communications. It proposes a staggered transmission strategy for the parallel code acquisition in systems with multiple transmitter antennas, and also presents the proof for its optimality. Furthermore, it describes an architecture for the parallel code acquisition and presents the implementation of the SISO acquisition system (which is a basic building block for the MIMO acquisition system) on a radio prototype. Finally, it reports the experimental results that confirm the reliable operation at low SNR. The parallel code acquisition forms the backbone of the proposed MIMO synchronization system. This dissertation presents the performance analysis for the SISO synchronization system (which is a basic building block for the MIMO synchronization system) and describes its implementation on a radio prototype. Digital and RF tests verify the accurate translation of the synchronization system into hardware. Calibrations in the lab and experiments conducted at outdoor test sites confirm the ability to synchronize at low SN