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The commercial deployment of LTE Release 8 is gaining significant momentum all over the globe, and LTE is evolving to LTE-Advanced, which offers various new features to meet or exceed IMT-Advanced requirements. Since LTE-Advanced targets ambitious spectral efficiency and peak throughput, it poses tremendous system design challenges to operators and manufacturers, especially for mobile terminals. This article discusses modem design issues related to carrier aggregation, enhanced ICIC for HetNet, detection of eight-layer transmission, reference signals for enhanced multi-antenna support, and HARQ buffer management. We provide an overview of technical challenges and sketch the perspectives for tackling them to exploit the full benefits of the LTE-Advanced system.

Almost all mobile communication systems today use spectrum in the range of 300 MHz-3 GHz. In this article, we reason why the wireless community should start looking at the 3-300 GHz spectrum for mobile broadband applications. We discuss propagation and device technology challenges associated with this band as well as its unique advantages for mobile communication. We introduce a millimeter-wave mobile broadband (MMB) system as a candidate next generation mobile communication system. We demonstrate the feasibility for MMB to achieve gigabit-per-second data rates at a distance up to 1 km in an urban mobile environment. A few key concepts in MMB network architecture such as the MMB base station grid, MMB interBS backhaul link, and a hybrid MMB + 4G system are described. We also discuss beamforming techniques and the frame structure of the MMB air interface.

Practical application of superposition coding in multiplexing broadcast and unicast for OFDM-based mobile cellular systems is discussed. Superposition coding, whose gain is increased as the superposed signals have larger difference in signal-to interference-plus-noise ratio, is well matched for unicast and broadcast in a single-frequency network configuration. Combined with interference cancellation technique, broadcast signals from multiple base stations can be cancelled in a single step, minimizing the interference from broadcast to unicast. Issues related with scheduling and strategy for time, frequency and power resource sharing between broadcast and unicast are discussed. The application of superposed broadcast and unicast is then extended to MIMO systems. Simulation results in a practical mobile cellular environment are also provided, showing significant throughput gain of superposed broadcast and unicast.

The rapid growth of Internet-based applications calls for design of a high-speed wireless packet data communication system. This anticipated increase in future mobile wireless packet data services has challenged the current 3G standardization bodies to respond with evolved 3G system specifications capable of providing increased data throughput. In response to such a need, 3GPP2 recently completed the enhanced reverse link standardization effort of the CDMA technology flagship, cdma2000/spl reg/ by completing the definition of the 1/spl times/EV-DV 1/spl times/ system. 1/spl times/EV-DV achieves higher data throughput while simultaneously providing coexisting and backward-compatible voice services within the same spectrum. This feature of 1/spl times/EV-DV allows wireless operators to manage the voice and data loading in their system more efficiently. This article describes the physical layer reverse link enhancements in cdma2000 revision D that are necessary to support 1/spl times/EV-DV.

The problems of blind timing acquisition and channel estimation for DS-CDMA signals in multipath fading channels are investigated. Using only the spreading code of the desired user, methods based on QR decompositions are proposed. These methods perform comparably or even better than subspace based methods with an order lower complexity. Furthermore, the methods exhibit significantly more robustness to channel order mismatch. Based on the acquired timing information, channel estimation algorithms are also developed which are competitive with the previously proposed subspace based channel estimation algorithms. In addition, a channel order estimation algorithm is proposed for the scenario where the order is unknown. Performance of the proposed algorithms is evaluated through simulation and comparison to asymptotic Cramer-Rao bounds.

Non-intrusive load monitoring (NILM) is an important topic in smart-grid and smart-home. Many energy disaggregation algorithms have been proposed to detect various individual appliances from one aggregated signal observation. However, few works studied the energy disaggregation of plug-in electric vehicle (EV) charging in the residential environment since EVs charging at home has emerged only recently. Recent studies showed that EV charging has a large impact on smart-grid especially in summer. Therefore, EV charging monitoring has become a more important and urgent missing piece in energy disaggregation. In this paper, we present a novel method to disaggregate EV charging signals from aggregated real power signals. The proposed method can effectively mitigate interference coming from air-conditioner (AC), enabling accurate EV charging detection and energy estimation under the presence of AC power signals. Besides, the proposed algorithm requires no training, demands a light computational load, delivers high estimation accuracy, and works well for data recorded at the low sampling rate 1/60 Hz. When the algorithm is tested on real-world data recorded from 11 houses over about a whole year (total 125 months worth of data), the averaged error in estimating energy consumption of EV charging is 15.7 kwh/month (while the true averaged energy consumption of EV charging is 208.5 kwh/month), and the averaged normalized mean square error in disaggregating EV charging load signals is 0.19., Comment: Accepted by The 40th Annual Conference of the IEEE Industrial Electronics Society (IECON 2014)

Heart rate monitoring using wrist-type photoplethysmographic (PPG) signals during subjects' intensive exercise is a difficult problem, since the signals are contaminated by extremely strong motion artifacts caused by subjects' hand movements. So far few works have studied this problem. In this work, a general framework, termed TROIKA, is proposed, which consists of signal decomposiTion for denoising, sparse signal RecOnstructIon for high-resolution spectrum estimation, and spectral peaK trAcking with verification. The TROIKA framework has high estimation accuracy and is robust to strong motion artifacts. Many variants can be straightforwardly derived from this framework. Experimental results on datasets recorded from 12 subjects during fast running at the peak speed of 15 km/hour showed that the average absolute error of heart rate estimation was 2.34 beat per minute (BPM), and the Pearson correlation between the estimates and the ground-truth of heart rate was 0.992. This framework is of great values to wearable devices such as smart-watches which use PPG signals to monitor heart rate for fitness., Matlab codes and data are available at: https://sites.google.com/site/researchbyzhang/

Energy consumption is an important issue in continuous wireless telemonitoring of physiological signals. Compressed sensing (CS) is a promising framework to address it, due to its energy-efficient data compression procedure. However, most CS algorithms have difficulty in data recovery due to non-sparsity characteristic of many physiological signals. Block sparse Bayesian learning (BSBL) is an effective approach to recover such signals with satisfactory recovery quality. However, it is time-consuming in recovering multichannel signals, since its computational load almost linearly increases with the number of channels. This work proposes a spatiotemporal sparse Bayesian learning algorithm to recover multichannel signals simultaneously. It not only exploits temporal correlation within each channel signal, but also exploits inter-channel correlation among different channel signals. Furthermore, its computational load is not significantly affected by the number of channels. The proposed algorithm was applied to brain computer interface (BCI) and EEG-based driver's drowsiness estimation. Results showed that the algorithm had both better recovery performance and much higher speed than BSBL. Particularly, the proposed algorithm ensured that the BCI classification and the drowsiness estimation had little degradation even when data were compressed by 80%, making it very suitable for continuous wireless telemonitoring of multichannel signals., Comment: Codes are available at: https://sites.google.com/site/researchbyzhang/stsbl

We develop a new tractable model for K-tier cellular networks, where each base station (BS) is solely powered by a self-contained energy harvesting module instead of a conventional power-line source. The BSs across tiers differ in terms of the energy harvesting rate, energy storage capacity, transmit power and deployment density. Since a BS may not always have enough energy, it may need to be kept OFF and allowed to recharge while its load is served by the neighboring BSs that are ON. Using tools from random walk theory and stochastic geometry, we characterize the fraction of time each type of BS can be kept ON, termed availability, for general uncoordinated strategies, where each BS toggles its ON/OFF state independently of the others. As a part of our analysis, we model the temporal dynamics of the energy level at each BS as a birth-death process, derive energy utilization rate for each BS class, and use hitting/stopping time analysis to study availabilities. We prove that there is a fundamental limit on the availabilities, which cannot be surpassed by any uncoordinated strategy. As a part of the proof, we construct the strategy that achieves this limit.

In this paper, we present a novel FPGA-based high-throughput beamforming MIMO receiver for millimeter wave mobile communication. With vast spectrum and small antenna element size, millimeter wave communication becomes very attractive and promising to support next generation mobile communication (5G). However, the high data rate requirement challenges both algorithm and architecture. In order to support the high data rate and to reduce the overhead of selecting the best beam pair, we propose a novel beamforming synchronization scheme more suitable for mobile communication. By further optimizing the algorithm and the architecture, we present a complete mobile receiver based on FPGA, which includes RF frontend, ADC, beamforming control, synchronization, channel estimator, soft MAP detector, and channel decoder. The design operates at 28 GHz carrier frequency with 500 MHz bandwidth. The throughput can reach 1.52 Gbps. We also performed the indoor and outdoor over-the-air transmission field tests. This work provides a platform for future millimeter wave mobile communication research.

We present the design and development of the first fully integrated, two stage Doherty power amplifier (DPA) in the Ka-Band. The DPA is fabricated in a 0.15-μm GaAs pseudomorphic high electron mobility transistor (pHEMT) process. At 26.4 GHz, the amplifier achieves measured small signal gain of 10.3 dB, output power at 1-dB compression point (P1dB) of 25.1 dBm, peak power added efficiency (PAE) of 38%, and PAE of 27% at 6 dB back-off power. To the best of the author's knowledge, this Doherty circuit is the first fully integrated millimeter-wave amplifier that achieves the highest power and a recorded 27% PAE at 6-dB back-off and each unit amplifier has 2 stages.

Heterogeneous networks are usually operated in the interference limited regime due to the overlaid coverage areas of various base stations, so radio resource management and interference management are of critical importance to the success of heterogeneous networks. In this chapter we discuss these two issues in details mainly under the LTE‐Advanced standard. Specifically, we discuss various deployment scenarios and corresponding interference management categories for heterogeneous networks. For multi‐carrier scenarios, carrier partitioning, power control and carrier aggregation based approaches are introduced. For co‐channel scenarios, both time‐domain solution and the power setting solutions are discussed.

The spectacular growth of mobile data traffic calls for drastic improvement in mobile network capacity beyond current 3G/4G networks. In this paper, we describe a millimeter-wave mobile broadband (MMB) system that taps the vast spectrum in 3 – 300 GHz to meet that demand. We discuss the unique advantages of millimeter waves such as spectrum availability and massive antenna arrays in small form factors. We also describe a practical MMB system design that provides Gbps data rate at distance up to 500 meters and supports mobility up to 350 kmph. We show in system simulation that an MMB system with basic configuration achieves more than 30 times cell throughput and cell-edge performance than a 20-MHz LTE system.

In order to meet the spectacular growth in mobile data traffic, one of the technologies is heterogeneous network, where small cells overlaid by large cells can be deployed. With such, base stations (BSs) can be of heterogeneous characteristics in bandwidth, capacity, load, backhaul delay, etc. Meanwhile, the traffic of diverse applications of a mobile station (MS) can be of heterogeneous quality of service (QoS) in rate, delay, etc. This paper proposes a framework to solve the problem of how to efficiently deliver heterogeneous traffic with heterogeneous QoS requirements in heterogeneous networks. We formulate optimization problems, to associate traffic flows with different QoS requirements of an MS to multiple BSs, so that QoS requirements can be satisfied, where the BS backhaul conditions are taken into account. Algorithms are proposed based on analysis. Numerical results show our framework can provide more efficiency in delay stringent and delay astringent traffic delivery.

Millimeter wave (mmWave) systems must overcome the heavy attenuation at high frequency to support high-throughput wireless communication. The small wavelength in mmWave systems enables beamforming using large antenna arrays to combat path loss with large array gain. Beamforming in traditional microwave systems is often done at baseband for maximum flexibility. Such baseband processing requires a dedicated transceiver chain per antenna element. The high cost of radio frequency (RF) chains in mmWave systems, however, makes supporting each antenna with a dedicated RF chain expensive. This mismatch between the number of antennas and transceiver chains makes baseband processing infeasible; thus mmWave systems typically rely on a traditional approach known as beam steering which can be done at RF using inexpensive phase shifters. Unlike baseband precoding, however, traditional beam steering is not explicitly designed to achieve the capacity of the mmWave channel. In this paper, we consider both beamforming and multi-stream precoding in single user systems with large mmWave antenna arrays at both transmitter and receiver. Using a realistic channel model, we show that the unconstrained capacity-achieving precoding solutions converge to simple beam steering solutions. Therefore, in large mmWave systems, no rate loss is incurred by adopting the traditional lower-complexity solution.

Almost all cellular mobile communications including first generation analog systems, second generation digital systems, third generation WCDMA, and fourth generation OFDMA systems use Ultra High Frequency (UHF) band of radio spectrum with frequencies in the range of 300MHz-3GHz. This band of spectrum is becoming increasingly crowded due to spectacular growth in mobile data and other related services. More recently, there have been proposals to explore mmWave spectrum (3-300GHz) for commercial mobile applications due to its unique advantages such as spectrum availability and small component sizes. In this paper, we discuss system design aspects such as antenna array design, base station and mobile station requirements. We also provide system performance and SINR geometry results to demonstrate the feasibility of an outdoor mmWave mobile broadband communication system. We note that with adaptive antenna array beamforming, multi-Gbps data rates can be supported for mobile cellular deployments.

Evolution beyond 4G (LTE and mobile WiMAX) is crucial in keeping up with the exponential growth of mobile data traffic. In this paper, we describe a millimeter-wave mobile broadband (MMB) system that utilizes frequencies in the 3–300 GHz spectrum as a candidate for next generation mobile communication. A few key concepts in MMB network architecture such as the MMB inter-BS backhaul link, MMB base station grid, and hybrid MMB + 4G system are described. We demonstrate the feasibility of using millimeter waves to provide Giga bps data rate at a distance up to 1 km for mobility up to 350 kmph. We also discuss a few aspects of MMB air interface design such as beamforming, multiple access, and adaptive modulation and coding.

Almost all cellular mobile communications including first generation analog systems, second generation digital systems, third generation WCDMA, and fourth generation OFDMA systems use Ultra High Frequency (UHF) band of radio spectrum with frequencies in the range of 300MHz-3GHz. This band of spectrum is becoming increasingly crowded due to spectacular growth in mobile data and other related services. The portion of the RF spectrum above 3GHz has largely been uxexploited for commercial mobile applications. In this paper, we reason why wireless community should start looking at 3–300GHz spectrum for mobile broadband applications. We discuss propagation and device technology challenges associated with this band as well as its unique advantages such as spectrum availability and small component sizes for mobile applications.

Relays are used to forward data from the source to the destination. There are scenarios wherein a relay is the only means for the data to reach the destination. In this paper, we will focus on scenarios wherein one or more relays are used to forward data to the destinations when the destination is already in the coverage area of the source. This latter scenario has been studied under the term cooperative relaying, as a scheme that primarily aids in improving the throughput within a given coverage area. Our goal is to take previously postulated studies and evaluate achievable cooperative relaying gains in more realistic settings. In discussing the gains, we first identify the practical constraints and study the implications of adding such constraints on the gains that can be extracted from cooperative relaying.