Ranging solutions for Internet of Things (IoT) localization applications seek to provide high accuracy with low cost of implementation. Among candidate IoT technologies that may fit this criterion, Bluetooth is a desirable choice as Bluetooth low energy (BLE) support is ubiquitous in modern smartphones, providing low implementation costs and low power consumption. Recent advancements in BLE ranging technology employ the Multicarrier Phase Difference technique which takes two-way channel frequency response (CFR) measurements. However, accurate ranging with these measurements is challenging due to many closely spaced multipath components from squaring the one-way CFR, a single or low number of snapshots, and model imperfections that arise in practical scenarios. To overcome these challenges, we propose a data-driven support vector regression (SVR) approach. Using real-world BLE measurements, our proposed SVR method demonstrates decimeter-level accuracy with single antenna devices, whereas multiple signal classification (MUSIC), a popular model-based method, requires multiple antennas to obtain comparable performance. Moreover, we show robustness in different multipath environments, including indoor, outdoor, and nonline-of-sight conditions, we determine generalization capabilities with training size, and we analytically establish the reduction in computational complexity compared to MUSIC.

Vibration sensing is essential in many applications. Traditional vibration sensors are contact based. With the advance of low-cost and highly integrated CMOS radars, another class of non-contact vibration sensors is emerging. In this paper, we present detailed analysis on obtaining vibration parameters using frequency modulated continuous wave (FMCW) radars. We establish the Cramer Rao lower bounds (CRLB) of the parameter estimation problem and propose an estimation algorithm that achieves the bounds in simulations. These analysis show that vibration sensing using FMCW radars can easily achieve sub-Hertz frequency accuracy and micrometer level amplitude accuracy.

In recent decades, power line communication (PLC) has attracted considerable attention from the research community and industry, as well as from regulatory and standardization bodies. In this paper, we provide an overview of both narrowband and broadband systems, covering potential applications, regulatory and standardization efforts, and recent research advancements in channel characterization, physical layer performance, medium access, and higher layer specifications and evaluations. We also identify the areas of current and further study that will enable the continued success of PLC technology.

Welcome to the IEEE JSAC special issue on Power Line Communications and its Integration with the Networking Ecosystem. This special issue was motivated by the growth in maturity of power line communications (PLC) over the last ten years since the last JSAC special issue focusing on PLC in 2006. For this special issue, we hoped to receive papers showing the growth of PLC technology itself, and works showing applications and integration with the technology ecosystem.

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.

In orthogonal frequency division-multiple access (OFDMA) systems, the available downlink frequency is divided into subbands which are shared among users. The transmitter determines the users that are scheduled on each subband, and the data rate for each user. To enable these transmitter choices, each user feeds back a channel quality indicator (CQI), giving a compressed version of its observed signal-to-interference-noise ratio (SINR) on all subbands. In this paper, we classify existing CQI compression schemes into symmetric and asymmetric schemes. Symmetric schemes aim to accurately represent the CQI on all subbands, and are shown to be suitable when the receiver cannot accurately predict the subbands on which it will be scheduled. This happens, for instance, when the receiver is fast-moving, or when a round- robin scheduler is employed, or during low load conditions. Asymmetric schemes, on the other hand, greedily achieve accuracy only in high-SINR subbands, and are shown to perform well in high-load cellular networks with proportional fair scheduling and low-speed users. We propose one new scheme in each category. Simulation results for a 3GPP LTE cellular network show that our proposed schemes achieve similar or better performance than the current best-M feedback scheme used in LTE, with 30% less overhead.

In this paper, we investigate several possibilities to increase the efficiency of hybrid automatic retransmission request (HARQ) for multi-input multi-output (MIMO) systems. At the receiver side, two HARQ combining schemes, namely pre-combining and post-combining, are discussed and analyzed. We show that pre-combining is superior to post-combining. In addition, we propose a transmission technique, termed the basis hopping, which improves the HARQ diversity gain especially in slow fading channels. We demonstrate that the use of pre-combining in conjunction with the proposed basis hopping technique provides dramatic gain over a simplistic application of HARQ scheme for MIMO.

We assume a CDMA downlink multiuser scenario, where the base station is equipped with multiple transmit antennas, and each user has multiple receive antennas. For this setup we propose a new, computationally effective MIMO multiuser detector for frequency selective channels. We exploit the fact that the interference mainly comes from the spatial domain, while the residual interference is due to temporal dispersion and multiuser interference. This motivates us to suppress the residual interference in a linear fashion, while combating the spatial interference iteratively. This approach is an efficient performance-complexity tradeoff between fully iterative and linear detectors.

In this paper, a capacity analysis of multi-input multi-out (MIMO) channels with multipath assuming different types of sub-optimal detectors is presented. The results are instrumental for evaluating the potential of multipath MIMO channels when sub-optimal detectors are utilized. It is demonstrated that for some types of detectors, an increase in the number of paths may result in some performance loss, especially at low transmit power. In addition, it is shown that a type of iterative detector can attain near-capacity performance when highly reliable decision feedback is used.

In this paper, we study the performance of space-time block coding, also known as space-time transmit diversity (STTD) scheme for high data rate applications with 4 transmit antennas. The scheme consists of two STTD units at the transmitter and an interference-resistant detector at the receiver, termed the double-STTD (DSTTD) scheme. We compare the performance of DSTTD to general multi-input multi-output (GMIMO) signaling for a given data rate and under different channel correlation profiles. It is demonstrated that DSTTD outperforms GMIMO in all cases. In addition, additional performance gain can be attained for DSTTD in correlated channels by selectively ordering the transmit antennas to minimize the average interference terms.

Gaussian frequency shift keying modulation has been chosen as the modulation technique for the physical layer of Bluetooth. Bluetooth is a standard for low cost and low power wireless communications between various mobile devices. The optimal demodulation of a GFSK signal involves an extremely complex Viterbi decoder. Therefore designers have opted for the noncoherent detection of GFSK which uses a frequency discriminator, followed by symbol by symbol detection. We describe a decision feedback equalizer to be added after the discriminator. The DFE receiver gives gains in excess of 2 dB. We also describe how to increase the current data rate of a Bluetooth system by increasing the symbol rate and not the alphabet size.

We describe a technique to control the trade-off between the error floor and the waterfall performance of parallel concatenated trellis-coded. modulation (PCTCM), which is also known as turbo TCM, via the choice of coded-bits-to-signal mapping for a fixed component code. We demonstrate that different choice of mapping leads to different error floor and waterfall performance. One mapping may have the lowest error floor but result in poor waterfall performance, while another mapping may achieve the opposite. We then present the time-varying mixed mapping scheme for PCTCM systems. The proposed mixed mapping scheme enables us to generate a set of turbo trellis codes from two choices of coded-bits-to-signal mapping with various waterfall performance and error floor.

In this paper, a bit-error-rate (BER) analysis for closed-loop transmit diversity in a time-selective Rayleigh fading channel containing feedback delay is presented. In the absence of feedback delay, closed-loop transmit diversity always outperforms open-loop transmit for a given transmitted signal energy. This is no longer true in the presence of feedback delay. We derive closed-form expressions of the average BER for this case assuming QPSK and BPSK signaling. The results of the analysis are instrumental for comparing closed-loop with open-loop schemes under given operating conditions. In particular, we demonstrate that, for a given transmitted energy and number of transmit antennas, open-loop outperforms closed-loop at sufficiently fast channel fading. We also show that, for a given transmitted signal energy and fading rate, closed-loop outperforms open-loop for sufficiently large numbers of transmit antennas while the total average transmitted signal energy is kept constant. For some special cases, closed-form expressions for the fading rate at which the performance of open-loop is equal to closed-loop are obtained.

Multiple transmit antennas giving rise to diversity (transmit diversity) have been shown to increase the downlink (base station to the mobile) capacity in cellular systems. The third generation partnership project (3Gpp) for WCDMA FDD has chosen space time transmit diversity (STTD) as the open loop transmit diversity technique for two transmit antennas. On the other hand, the CDMA2000 has chosen space time spreading (STS) and orthogonal transmit diversity (OTD) as the open loop transmit diversity techniques. In this paper, we compare the open loop transmit diversity techniques of 3Gpp and CDMA2000. We show that STS involves a QPSK to non-QPSK constellation transformation followed by an STTD encoding of the resulting symbols. Thus, the performance of STS is the same as STTD, while the peak to average ratio (PAR) and complexity of STS is higher than STTD. We also show theoretically that the performance of STTD is 0.3-0.5 dB better than OTD. Further, STTD has another distinct advantage over OTD and STS in its application to the broadcast channels. During the power on and possibly during soft handoff, the mobile does not know the presence/absence of the diversity antenna on the primary/soft handoff base station. In this case, a blind detection of the diversity antenna is possible for STTD with a very small degradation in performance. This is not possible for OTD and STS. We thus show that STTD is a better open loop transmit diversity technique than OTD and STS.

In this paper we present a new space time block code as an antenna diversity scheme for transmit antenna diversity. The space-time-transmit-diversity (STTD) method is an open loop transmit diversity scheme, i.e. it does not require any knowledge of the channel at the transmitter. Simulations have shown that the STTD scheme significantly outperforms the case where no antenna diversity is used. In fact, it even outperforms the non-diversity (ND) case even when soft handoff is used. STTD exploits the extra path diversity afforded by the second antennas and therefore outperforms two other open loop transmit antenna diversity techniques, viz. the orthogonal transmit diversity (OTD) and the time switched time diversity (TSTD). These techniques use multiple transmit antennas to provide some interleaver time diversity against fading, particularly at low Doppler rates and when the mobile receiver does not have enough paths at the RAKE receiver. STTD has the added advantages of being a power amplifier (PA) balanced technique, is easily backward compatible with ND systems and does not need careful interleaver design.