Energy-Efficient Vector OFDM PLC Systems with Dynamic Peak-Based Threshold Estimation

© 2013 IEEE. Power line communication (PLC) has made remarkable strides to become a key enabler of smart grid and its applications. Existing PLC systems are based on orthogonal frequency division multiplexing (OFDM), which has a high peak-to-average power ratio (PAPR). This paper presents vector OFDM (VOFDM) with advanced signal processing at the receiver to improve the energy efficiency of the PLC system. Results show that, due to its low PAPR properties, VOFDM is less sensitive to impulsive noise and provides a reduction of 5.8 dB in transmit power requirement relative to conventional OFDM. Furthermore, unlike the existing impulsive noise cancellation methods, the adopted signal processing technique also improves the SNR at the receiver by 2.1 dB, which further reduces the power requirement of the PLC transceiver. Together, these can simplify design, reduce cost, and improve energy efficiency of future PLC transceivers

Cross-layer energy efficiency of plc systems for smart grid applications

Though opinions are still divided over the specific choices of technology for smart grid, there is a consensus that heterogeneous communications network is most appropriate. Power line communication (PLC) is promising because it is readily available and it aligns with the natural topology of power distribution network. One of the emerging realities is that the communication system enabling smart grid must be energy-efficient. This thesis employs a cross-layer approach to address energy efficiency of PLC networks in different smart grid scenarios. At network layer, this work exploits the topology of a PLC-enabled advanced metering infrastructure (AMI) to improve the probability of successful packet delivery across the network. The technique, termed AMI clustering, leverages the traditional structure of the low voltage (LV) network by organising the smart meters into clusters and locally aggregating their readings. Improvement in packet delivery inherently reduces energy wastage. Next, the adaptation layer exploits the low data rate transmission techniques to reduce the energy requirements of PLC nodes. To achieve that, this work developed a network model in NS-3 (an open-source network simulator) that considers PLC transceivers as resource-constrained devices and interconnects them to emulate home energy management system (HEMS). The model was validated with experimental results which showed that in the home area network (HAN), low-rate applications such as energy management can be supported over low-power PLC networks. Furthermore, at physical layer, this thesis proposes a more energy-efficient multi-carrier modulation scheme than the orthogonal frequency division multiplexing (OFDM) used in most of the current PLC systems. OFDM is widely known for its high peak-to-average-power ratio (PAPR) which degrades energy efficiency of the systems. This thesis found that by employing vector- OFDM (V-OFDM), power requirements of PLC transmitter can be reduced. The results also showed the energy efficiency can be further improved by using a dynamic noise cancellation technique such as dynamic peak-based threshold estimation (DPTE) at the receiver. By applying the proposed methods, packet delivery can be improved by 3% at network layer (which conserves energy) and reduced data rate can save about 2.6014 dB in transmit power. Finally, at physical layer, V-OFDM and DPTE can respectively provide 5.8 dB and 2.1 dB reduction in power requirements of the PLC transceivers. These signify that if V-OFDM is combined with DPTE, future PLC modems could benefit from energy-efficient power amplifiers at reduced cost

Vector OFDM Transmission over Non-Gaussian Power Line Communication Channels

Most of the recent power line communication (PLC) systems and standards, both narrow-band and broadband, are based on orthogonal frequency-division multiplexing (OFDM). This multiplexing scheme, however, suffers from the high peak-to-average power ratio (PAPR), which can considerably impact the energy efficiency, size, and cost of PLC modems as well as cause electromagnetic compatibility (EMC) issues. This paper investigates the performance of vector OFDM (VOFDM), which has inherently better PAPR properties, over non-Gaussian broadband PLC channels equipped with two nonlinear preprocessors at the receiver. In addition, the low PAPR property of the VOFDM system is exploited to further enhance the efficiency of the nonlinear preprocessors. The achievable gains are studied in terms of the complementary cumulative distribution function of the PAPR, probability of noise detection error, and the signal-to-noise ratio at the output of the nonlinear preprocessors. For comparison’s sake, the performance of conventional OFDM systems is also presented throughout this paper. Results reveal that the proposed system is able to provide up to 2-dB saving in the transmit power relative to the conventional OFDM under same system conditions, which eventually also translates into a system that is more resilient to EMC limits, reduced cost, and size of PLC modems. It is also shown that the achievable gains become more significant as the vector block size of the VOFDM system is increased

Masreliez-Equalized VOFDM in Non-Gaussian Channels: Power Line Communication Systems

In this paper, we derive a non-linear equalizer for a fading channel with non-Gaussian noise. In particular, we look into the effects of non-Gaussian noise over power line channels that severely affect communication signals. Unlike most existing work based on orthogonal frequency-division multiplexing (OFDM) in the literature, we investigate the performance of vector OFDM (VOFDM) over multi-path power line communication (PLC) channels contaminated with Middleton Class-A noise. To reduce the impact of impulsive noise we propose a novel filter to equalize the output of the channel. The performance of the equalizer is evaluated in terms of bit error rate (BER), and the impact of several impulsive noise parameters are examined at the receiver. Results show that the proposed system can considerably improve the BER performance in comparison to the conventional OFDM scheme. In addition, it is shown that increasing the number of vector blocks of the VOFDM system will enhance the BER performance under the same condition. The proposed non-linear equalizer improves the performance of VOFDM system successfully at low signal-to-noise ratios (SNRs), at some instances it nearly halved the probability of error with respect to linear filter

Modeling and Optimization of Next-Generation Wireless Access Networks

The ultimate goal of the next generation access networks is to provide all network users, whether they are fixed or mobile, indoor or outdoor, with high data rate connectivity, while ensuring a high quality of service. In order to realize this ambitious goal, delay, jitter, error rate and packet loss should be minimized: a goal that can only be achieved through integrating different technologies, including passive optical networks, 4th generation wireless networks, and femtocells, among others. This thesis focuses on medium access control and physical layers of future networks. In this regard, the first part of this thesis discusses techniques to improve the end-to-end quality of service in hybrid optical-wireless networks. In these hybrid networks, users are connected to a wireless base station that relays their data to the core network through an optical connection. Hence, by integrating wireless and optical parts of these networks, a smart scheduler can predict the incoming traffic to the optical network. The prediction data generated herein is then used to propose a traffic-aware dynamic bandwidth assignment algorithm for reducing the end-to-end delay. The second part of this thesis addresses the challenging problem of interference management in a two-tier macrocell/femtocell network. A high quality, high speed connection for indoor users is ensured only if the network has a high signal to noise ratio. A requirement that can be fulfilled with using femtocells in cellular networks. However, since femtocells generate harmful interference to macrocell users in proximity of them, careful analysis and realistic models should be developed to manage the introduced interference. Thus, a realistic model for femtocell interference outside suburban houses is proposed and several performance measures, e.g., signal to interference and noise ratio and outage probability are derived mathematically for further analysis. The quality of service of cellular networks can be degraded by several factors. For example, in industrial environments, simultaneous fading and strong impulsive noise significantly deteriorate the error rate performance. In the third part of this thesis, a technique to improve the bit error rate of orthogonal frequency division multiplexing systems in industrial environments is presented. This system is the most widely used technology in next-generation networks, and is very susceptible to impulsive noise, especially in fading channels. Mathematical analysis proves that the proposed method can effectively mitigate the degradation caused by impulsive noise and significantly improve signal to interference and noise ratio and bit error rate, even in frequency-selective fading channels

Constant Envelope DCT- and FFT- based Multicarrier Systems

Discrete Cosine Transform (DCT)- and Fast Fourier Transform (FFT)- based Orthogonal Frequency Division Multiplexing (OFDM) systems with a variety of angle modulations are considered for data transmission. These modulations are used with the purpose of achieving Constant Envelope (CE) transmitted signals, for superior power efficiency with nonlinear High Power Amplifier (HPA), typically used at the transmitter in OFDM systems. Specifically, four angle modulations are considered: i) Phase Modulation (PM); ii) Frequency Modulation (FM); iii) Continuous Phase Modulation (CPM); and iv) Continuous Phase Chirp Modulation (CPCM). Descriptions of DCT- and FFT- based OFDM systems with M-ary Pulse Amplitude Modulation (MPAM) mapper, with these modulations, are given and expressions for transmitted signals are developed. The detection of these signals in Additive White Gaussian Noise (AWGN) and multipath fading channels is addressed. The receiver structure consists of arctangent demodulator followed by the optimum OFDM receiver for memoryless PM and FM modulations. However, for CPM and CPCM modulations that have inherent memory, arctangent demodulator followed by correction with oversampling technique is used prior to the optimum OFDM receiver. Closed-form expressions for Bit Error Rate (BER) have been derived and are function of: i) Signal-to-Noise Ratio, (Eb/N0); ii) Modulation parameters; iii) Number of amplitude levels of M-PAM mapper; and iv) parameters of multipath fading environment. It is shown that, in general, BER performance of CE-DCT-OFDM system is superior compared to that of conventional DCT-OFDM system, when the effect of HPA in the system is taken into account. Also, it is observed that CE-DCT-OFDM system outperforms CE-FFT-OFDM system by nearly 3 dB. The DCT- and FFT- OFDM systems with CPM and CPCM modulations are superior in BER performance compared to PM and FM modulations in these systems. The use of CPCM in OFDM systems can provide attractive trade off between bandwidth and BER performance. The performance of CE-DCT-OFDM and CE-FFT-OFDM systems over Rayleigh and Rician frequency non-selective slowly-varying fading channels are illustrated as a function of channel parameters and the penalty in SNR that must be paid as consequence of the fading is determined