Tarkesh Pande

Reduced Feedback MIMO-OFDM Precoding and Antenna Selection

Transmitter precoding for multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) is an effective way of leveraging the diversity gains afforded by a multiple-transmit multiple-receive antenna system in a frequency selective environment. In the limited feedback scenario, optimal precoder representation for narrowband MIMO systems using moderately sized codebooks designed on the Grassmann manifold has been shown to perform remarkably well. In MIMO-OFDM systems, precoder matrices have to be designed for all subcarriers and the amount of feedback can get prohibitively large. This is especially true for next generation wireless local area networks and wireless metropolitan area networks which have a large number of subcarriers. In this paper, we present techniques to reduce this feedback requirement and the performance of these algorithms is numerically shown to provide improvement over existing schemes

Cyclostationary noise modeling in narrowband powerline communication for Smart Grid applications

A Smart Grid intelligently monitors and controls energy flows in an electric grid. Having up-to-date distributed readings of grid conditions helps utilities efficiently scale generation up or down to meet demand. Narrowband powerline communication (PLC) systems can provide these up-to-date readings from subscribers to the local utility over existing power lines. A key challenge in PLC systems is overcoming additive non-Gaussian noise. In this paper, we propose to use a cyclostationary model for the dominant component of additive non-Gaussian noise. The key contributions are (1) fitting measured data from outdoor narrowband PLC system field trials to a cyclostationary model, and (2) developing a cyclostationary noise generation model that fits measured data. We found that the period in the cyclostationary model matched half of the period of the main powerline frequency, which is consistent with previous work in indoor PLC additive noise modeling.

A Weighted Least Squares Approach to Precoding With Pilots for MIMO-OFDM

Next-generation wireless systems are expected to leverage multiple-antenna, commonly called multiple-input multiple-output (MIMO), technology transmitting over broadband channels via orthogonal frequency-division multiplexing (OFDM). It is now well known that MIMO systems can obtain error rate and capacity improvements by adapting the transmitter to the current channel conditions. Linear spatial precoding is a popular technique for channel adaptation where the transmitted space-time signal for each subcarrier is multiplied by a precoding matrix before transmission. Spatial precoding is complicated, however, in OFDM because channel information is often only known for a small number of pilot tones. In this correspondence, we present a subspace interpolation method for designing spatial precoders for all subcarriers by using the precoders known on pilot tones. The nonpilot precoders are solutions to a weighted least-squares design on the Grassmann manifold. Simulation results show performance benefits over existing MIMO-OFDM techniques

Design Considerations for Detecting Bicycles with Inductive Loop Detectors

Inductive loop detectors are widely used for vehicle detection. Historically, these loop detectors have been installed by saw cutting 2-m-by-2-m octagons into the top 8 cm of a pavement. New construction practices often replace the octagon loop with a preformed circular shape and place this circular loop approximately 30 cm below the paved surface. Although such installation procedures provide acceptable detection for trucks and automobiles, their performance with bicycles is less clear. This paper develops a model of loop detector-bicycle interaction, verifies the model with field measurement, and provides plots documenting the location of bicycle detection zone hot spots adjacent to loop detectors. On the basis of the model, it is concluded that the performance of circular loops in detecting bicycles is almost identical to that of similarly wound octagon loops. However, when those loops are installed under the pavement, their ability to detect bicycles is significantly degraded. Because pave-over instal...

Non-coherent demodulation for orthogonal space-time coded CPM

In this paper non-coherent receivers for orthogonal space-time coded continuous phase modulated signals transmitted over additive white Gaussian noise and quasi-static fading channels are presented. The receivers are found to perform less than 1-dB away from the corresponding coherent detectors.

Robust transceiver to combat periodic impulsive noise in narrowband powerline communications

Non-Gaussian noise/interference severely limits communication performance of narrowband powerline communication (PLC) systems. Such noise/interference is dominated by periodic impulsive noise whose statistics varies with the AC cycle. The periodic impulsive noise statistics deviate significantly from that of additive white Gaussian noise, thereby causing dramatic performance degradation in conventional narrowband PLC systems. In this paper, we propose a robust transmission scheme and corresponding receiver methods to combat periodic impulsive noise in OFDM-based narrowband PLC. Towards that end, we propose (1) a time-frequency modulation diversity scheme at the transmitter and a diversity demodulator at the receiver to improve communication reliability without decreasing data rates; and (2) a semi-online algorithm that exploits the sparsity of the noise in the frequency domain to estimate the noise power spectrum for reliable decoding at the diversity demodulator. In the simulations, compared with a narrowband PLC system using Reed-Solomon and convolutional coding, whole-packet interleaving and DBPSK/BPSK modulation, our proposed transceiver methods achieve up to 8 dB gains in Eb/N0 with convolutional coding and a smaller-sized interleaver/deinterleaver.

Time-Frequency Modulation Diversity to Combat Periodic Impulsive Noise in Narrowband Powerline Communications

Non-Gaussian noise/interference severely limits communication performance of narrowband powerline communication (PLC) systems. Such noise/interference is dominated by periodic impulsive noise whose statistics varies with the AC cycle. The periodic impulsive noise statistics deviates significantly from that of additive white Gaussian noise, thereby causing dramatic performance degradation in conventional narrowband PLC systems. In this paper, we propose a robust transmission scheme and corresponding receiver methods to combat periodic impulsive noise in OFDM-based narrowband PLC. Towards that end, we propose (1) a time-frequency modulation diversity scheme at the transmitter and a diversity demodulator at the receiver to improve communication reliability without decreasing data rates; and (2) a semi-online algorithm that exploits the sparsity of the noise in the frequency domain to estimate the noise power spectrum for reliable decoding at the diversity demodulator. In the simulations, compared with a narrowband PLC system using Reed-Solomon and convolutional coding, whole-packet interleaving and DBPSK/BPSK modulation, our proposed transceiver methods achieve up to 8 dB gains in Eb/N0 with convolutional coding and a smaller-sized interleaver/deinterleaver.

Proposed frame and preamble structure for MIMO narrowband power line communications

Narrowband power line communications (NB-PLC) operating in the 3-500 kHz frequency band is proposed as a solution to support the emerging Smart Grid applications that aim to optimize the efficiency and reliability of the power grids. PLC is attractive for Smart Grid communications as it can be deployed over the existing power grids without any additional infrastructure. However, PLC suffers from impulsive noise and frequency-selective channels which degrade the systems reliability and data rate. Multi-Input Multi-Output (MIMO) PLC is a promising technology to increase the data rate and provide robustness against the PLC interference. In this paper, we consider the design of a MIMO frame and preamble structure that can be efficiently used to perform initial receiver synchronization while ensuring backward compatibility with current NB-PLC standards.

Implementation and field test results of a software defined PLC modem

This paper presents in details the implementation and field test results of a software defined power line communication (PLC) modem using digital signal processor (DSP). The flexible software architecture using a single hardware supports multiple standard solutions, such as PRIME, G3, IEEE P1901.2. The modem software can also be configured to use different OFDM technologies to combat channel impairment specific to a particular regions grid condition. This paper describes the physical layer software architecture, complexity analysis and field test results. The field tests at multiple sites show the significant benefits of flexible software defined modem configuration to improve throughput and coverage.

Non-Coherent Receiver Performance for Orthogonal Space-Time Coded CPM in Fading Channels

In mobile communication systems where bandwidth and power efficiency are at a premium, continuous phase modulation (CPM) is a viable modulation technique. In this paper, non-coherent receivers for orthogonal space-time coded continuous phase modulated signals transmitted over two antennas are derived using a maximum likelihood (ML) approach. The performance of these receivers is numerically characterized in Rayleigh fading channels