Gautham Prasad

In-Band Full Duplex Broadband Power Line Communications

In this paper, we introduce in-band full duplexing (IBFD) for broadband power line communication (BB-PLC) systems. Inspired by the use of IBFD in digital subscriber lines, Ethernet, cable communication, and recently in wireless communication, we investigate the constraints and requirements for a successful IBFD implementation in BB-PLC. We propose a two-stage IBFD structure consisting of an initial analog isolation using an active hybrid circuit, and a simplified mixed-domain digital echo cancellation procedure to suppress the self-interference. Furthermore, we enhance the digital cancellation filter to better adapt to linear periodically time-varying channel conditions, commonly encountered in PLC scenarios. We evaluate our solution under diverse power line channel and noise conditions to examine the overall data rate gains that can be achieved. Last, we extend IBFD to multiple-input multiple-output BB-PLC systems that enable faster and/or more robust data transmission.

Enhancing transmission efficiency of broadband PLC systems with In-Band Full Duplexing

In this paper, we investigate the feasibility of In-Band Full-Duplexing (IBFD) for Broadband Power Line Communication (BB-PLC) systems, to potentially double the throughput and spectral efficiency. IBFD accomplishes this through simultaneous bidirectional communication over the same powerline in the same frequency band, by applying echo cancellation (EC) to suppress the interference caused by the self-transmitted signal. In light of various EC schemes employed in Digital Subscriber Lines, Ethernet, co-axial cables and recently in wireless systems, we investigate the specific requirements and constraints in BB-PLC, and present solutions for an effective IBFD implementation for such systems. We then use our simulated EC gain values to examine the overall data rate gains obtained by IBFD under different channel attenuations and PLC noise conditions, to determine if we truly obtain a 100% increase in throughput at all conditions.

Full-duplex spectrum sensing in broadband power line communications

We address the issue of electromagnetic interference between power line communication (PLC) and non-PLC services by using full-duplex spectrum sensing for cognitive PLC. Contemporary broadband PLC (BB-PLC) standards allow PLC devices to dynamically use idle spectra that are allotted to non-PLC services, like broadcast radio. Traditional spectrum sensing techniques operate in a half-duplex manner, and thus provide sub-optimal sensing efficiency. In this paper, we propose the use of in-band full-duplex (IBFD) operation to allow simultaneous data transmission and spectrum sensing, and eliminate all sensing-only and other wait times involved in conventional spectrum sensing operations. We first show that using the state-of-the-art IBFD solution yields inaccurate spectrum sensing performance due to non-negligible residual self-interference. We therefore propose multiple solutions to address this problem. We show through simulation results that our proposed solutions provide sufficient self-interference cancellation to achieve nearly the same spectrum sensing accuracy as that obtained in a half-duplex operation.

Analog interference cancellation for full-duplex broadband power line communications

In this paper, we present an all-analog echo cancellation solution to achieve in-band full-duplex (IBFD) operation in broadband power line communications (BB-PLC). The performance of active digital interference cancellation, as proposed previously for IBFD BB-PLC, is limited by distortion and quantization noise introduced by the analog-to-digital converter (ADC). Hence, we explore analog interference cancellation (AIC) solutions to reduce the power of the signal entering the ADC. We consider various AIC solutions for other communication media known from the literature, and show that a direct implementation of any of these solutions to a BB-PLC system renders an expensive and/or ineffective realization. Acknowledging the specific challenges encountered in BB-PLC, we propose an AIC mechanism that not only eliminates the effects of ADC distortion and quantization noise, but also provides sufficient echo cancellation gain (ECG) to function without an active digital interference cancellation module. We demonstrate through simulation results that our proposed solution provides over 80 dB of ECG, which is sufficient to reduce the echo power down to the minimum power line noise floor.

Mutual Preamble Detection for Full Duplex Broadband Power Line Communications

In this paper, we introduce a new scheme called Mutual Preamble Detection (MPD) to reduce the collision recovery time in broadband power line communication (BB-PLC) networks. Although latest BB- PLC products deliver a physical layer data rate of over 1000 Mbps, this is not efficiently translated into the medium access control (MAC) layer throughput due to several factors, including the long time intervals taken to recover from collisions. To address this, we use in-band full duplex operation to enable network nodes to transmit and simultaneously detect preambles, making them aware of a potential frame collision. With the detection of such a potential collision, we compel the network nodes to refrain from frame transmission in order to avoid the lengthy collision recovery time. The near-zero values of detection error and false alarm probabilities ensure the feasibility of our scheme in typical in-home BB-PLC networks. We present OMNeT++ simulation results to demonstrate the considerable increase in MAC efficiency obtained by using our proposed MPD scheme, over a traditional BB-PLC protocol.

Efficient Access Control for Broadband Power Line Communications in Home Area Networks

In this paper, we address the problem of improving the medium access control (MAC) layer efficiency in indoor broadband power line communication networks. Several overheads in the MAC layer, like random back-offs and collision recovery, degrade the MAC efficiency. To reduce these overheads, we apply in-band full-duplexing (IBFD), which enables medium-aware transmission at all the network nodes. Specifically, we propose two new schemes called contention-free pre-sensing and mutual preamble detection to minimize the time spent during contentions and collisions. Considering the non-idealities of IBFD, we analytically show the feasibility of our solutions. We further design a comprehensive simulation model with multiple priority data frames and Poisson network traffic arrival to emulate a real in-home network traffic. We then present numerical results for both the classical saturated network model and the comprehensive traffic model, to show through OMNeT++ simulations that our presented solutions achieve over 95% of the optimum MAC efficiency that can only be attained in the idealized case of no contentions or collisions.

CSMA/CD in PLC: Test with full G.hn and IP/UDP protocol stack

In this paper, we advocate implementing carrier sense multiple access with collision detection (CSMA/CD) in the broadband power line communication (BB-PLC) standard, G.hn, and show the gain in data rate obtained over carrier sense multiple access with collision avoidance (CSMA/CA). The use of CSMA/CD is made feasible due to the recent implementation of in-band full duplex operation in BB-PLC. We provide this implementation on a G.hn model using the NS-3 simulator, which we have made available as open-source. Our G.hn model implements physical and data link layers, including repeating function that makes it possible to simulate the long line network topologies (e.g., the network for electricity metering purpose). We also add IP/UDP layers to accomplish the higher layer protocol stack. We also provide analytical calculations of efficiency gains and validate them through our simulation results. We show that the highest achievable data rate with CSMA/CD is up to 5% higher than with CSMA/CA. Furthermore, we demonstrate that the protocol with CSMA/CD is less dependent on the number of active senders and has a smaller range of optimal contention window sizes (CW) for the same range of active senders, in comparison to CSMA/CA. This also simplifies the protocol implementation as the back-off algorithm for CSMA/CD does not vary CW as much as for CSMA/CA.

Digitally Controlled Analog Cancellation for Full Duplex Broadband Power Line Communications

Although in-band full-duplexing (IBFD) has long been implemented in various communication media, it was only recently that an IBFD solution was presented for broadband power line communications (BB-PLCs). The maximum attainable echo suppression using this solution is, however, limited by the dynamic range of the analog-to-digital converter (ADC). To counter this critical constraint, we propose echo cancellation in the analog domain, while persisting with a low-complexity frequency domain digital echo estimation. By formulating an expression for the number of ADC bits lost in IBFD over a conventional half-duplex operation, we show that the ADC dynamic range is no longer a limiting factor for our solution. We further extend our solution to present an analog cancellation method for multiple-input multiple-output IBFD BB-PLC systems. Finally, we present simulation results of echo cancellation and data rate gains obtained under realistic in-home BB-PLC settings, to demonstrate that our solution is capable of doubling bidirectional transfer rates in a large number of the tested network conditions.