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PLC superimposes high-frequency data signals ranging from a few hundred Hertz to hundreds of megahertz over the low-frequency electrical power carriers to reuse the existing power lines for communication purposes. Across various indoor and outdoor PLC application scenarios, the electromagnetic compatibility restrictions and the low-pass nature of power line channels restrict the data rate gains that can be furthered by conventional means of increasing power and/ or bandwidth. In this article, we provide an overview of IBFD operation as a means to improve PLC under these constraints, by potentially doubling the spectral efficiency through simultaneous signal transmission and reception in the same frequency band and over the same power line. We summarize the recent advancements in IBFD solutions for both narrowband and broadband PLC and contrast the design considerations to those in existing IBFD methods in other communications systems. We also highlight the benefits of IBFD operation to PLC networks in easing PLC network congestion, ensuring electromagnetic compatibility of PLC across application scenarios, and obtaining added insights in the context of smartgrid monitoring and security using simultaneous bidirectional communication. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Pre-rake ultra-wideband (UWB) systems are appealing for UWB communications applications which include devices with different processing capabilities so that signal processing complexity need to be shifted from the receiver of one or more devices to the transmitter of another. Recently, basic pre-rake schemes have been extended to include full pre-equalization, multiple-antenna, and multi-user interference processing. All these design approaches for pre-rake UWB systems have relied on the availability of accurate channel state information (CSI) at the transmitter. However, uncertainties in the acquisition of CSI can drastically affect the overall system performance. Therefore, in this paper, we present robust design methods for pre-equalization filters (PEFs) for pre-rake UWB systems that take CSI uncertainties into account. We treat the general case of a broadcast (i.e., multiuser) pre-rake UWB system, which includes single-user communication often considered in literature as a special case. For this general setting, we derive new PEF designs that improve system performance with imperfect CSI. Similar to the literature on robust filter designs for multiple-input multiple output (MIMO) systems, we consider two uncertainty models, namely stochastic and bounded uncertainty, which correspond to different performance optimization paradigms, and we adjust these according to channel estimation of UWB channels. As most of previous work on (pre-rake) UWB, we focus on binary transmission. We argue that widely linear filter design should be applied in this case and thus extend the robust filter design methodology accordingly. Our numerical results for typically UWB test channels demonstrate the efficacy of the proposed design procedures to achieve reliable communication in multiuser pre-rake UWB systems. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a new differentiated successive-interference cancellation (DiffSIC) ordering technique for uplink multiple-user systems. Unlike classical successive-interference cancellation (SIC), DiffSIC is capable of differentiating users according to their priority or class of service by selecting a detection order that best fits the users' service profiles. In addition, DiffSIC is able to achieve the optimal SIC detection order that results in the best overall system performance. To develop DiffSIC, we introduce analytical methods toward finding instantaneous symbol error rates (SERs) for zero-forcing SIC (ZF-SIC) and minimum mean square error SIC (MMSE-SIC) detectors. Furthermore, we devise two procedures to reduce the computational complexity associated with the computation of SER and the enumeration of detection orders. We present a number of numerical results that clearly demonstrate the ability of DiffSIC to accomplish service differentiation and overall performance improvement in general. [ABSTRACT FROM AUTHOR]

Power line communications uses the existing power line infrastructure for communication purposes. While the majority of recent contributions have discussed PLC for high-data-rate applications like Internet access or multimedia communication serving a relatively small number of users, in this article we are concerned with PLC as an enabler for sensing, control, and automation in large systems comprising tens or even hundreds of components spread over relatively wide areas. Typical examples of such systems are energy management (Smart Grid) and facility automation systems. We provide a discussion of the communication network requirements common to such systems and present transmission concepts for PLC to make use of the existing infrastructure resources (i.e., power lines) to meet these requirements. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the performance of the Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) system for Ultra Wideband (UWB) communication in the presence of interference from IEEE 802.16 WiMAX systems operating in the 3.5 GHz band. We present an exact analysis of the uncoded bit error rate (BER) of the MB-OFDM system, based on Laplace transform techniques. We also present a simple Gaussian approximation for the WiMAX interference, and establish its relative accuracy and usefulness by means of comparison with the exact analysis and simulations. Such a Gaussian approximation is especially useful for simplified performance analysis, as well as for the design of interference mitigation techniques. Motivated by the Gaussian approximation, we propose a simple two-stage interference mitigation technique for coded MB-OFDM transmissions, consisting of interference spectrum estimation during silent periods followed by appropriate bit metric weighting during Viterbi decoding. We compare parametric and non-parametric spectrum estimation techniques for various scenarios of interest. In the presence of WiMAX interference, the two-stage interference mitigation provides substantial gains in performance in return for modest increases in complexity and without requiring any modifications to the MB-OFDM transmitter or signal structure. [ABSTRACT FROM AUTHOR]

In this paper, we investigate noncoherent detection, i.e. detection assuming the absence of channel state information at the receiver, of on-off keying in an intensity modulation and direct detection (IMIDD) free-space optical (FSO) system. To partially recover the performance loss associated with symbol- by-symbol noncoherent detection, we consider the application of multiple-symbol detection (MSD), in which block-wise decisions are made using an observation window of several bit intervals. Specifically, we develop a fast search algorithm for optimal MSD and propose a reduced-complexity decision metric suitable for suboptimal MSD; performance results confirm that the optimal and suboptimal metrics perform comparably well. Significantly, the complexity of our receiver, on a per bit-decision basis, is only logarithmically dependent on the observation window size. We also present the framework for a decision-feedback receiver and obtain performance expressions for the ideal case of error-free feedback; these expressions serve as an upper bound to the performance of MSD. Analytical and simulation results indicate that as the observation window size increases, the performance of the MSD receiver approaches that of detection with channel state information. The conclusion is reached that the proposed implementation provides an attractive low-complexity mechanism for performing noncoherent MSD in FSO systems. [ABSTRACT FROM AUTHOR]

Bluetooth is a popular short-range low-power radio standard for wireless personal area networks. Bluetooth transmitters employ Gaussian frequency shift keying (GFSK) and simple block codes for error correction. Recently, two new receiver designs for Bluetooth devices, which are the so-called modified limiter-discriminator detector with integrate-and-dump filtering (LDI) and noncoherent sequence detection (NSD), have been pro- posed in the literature. While the modified LDI receiver is a concatenation of a conventional LDI detector with an improved error-correction decoder, the NSD receiver fully takes into account the memory introduced by the GFSK. Both receivers have been shown to improve the Bluetooth system performance in terms of physical-layer metrics such as bit-error rate and packet-error rate. In this paper, we present a comprehensive performance evaluation considering practically more relevant metrics such as throughput, delay, and delay jitter at the medium-access control layer. To this end, we develop an evaluation framework, which includes the spatial distribution of Bluetooth devices, path loss, fading, realistic data traffic models, scheduling, automatic repeat request, and baseband packet selection. Our numerical and simulation results verify that the newly introduced Bluetooth receivers, especially NSD, offer a significant performance enhancement for Bluetooth systems in terms of practically relevant measures. [ABSTRACT FROM AUTHOR]

The application of trellis shaping was recently proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing (OFDM) signals. In this letter, we review the trellis-shaping schemes presented in the literature, and we introduce modifications such as a new decoding metric and the use of sequential decoding. We conduct comprehensive complexity and performance comparisons for the different schemes, and one interesting result of this work is that, in terms of PAR-reduction capability, trellis shaping with time-domain metrics is generally superior to trellis shaping with frequency-domain metrics. Furthermore, the proposed modifications enable trellis shaping for PAR reduction with a flexible performance-complexity tradeoff. [ABSTRACT FROM AUTHOR]

Several recent standards such as IEEE 802.11a/g, IEEE 802.16, and the European Computer Manufacturers Association (ECMA) Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) for High Data-Rate Ultra-Wideband em- ploy bit-interleaved convolutionally coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with nonideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure for, e.g., MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally coded interleaved multi-carrier systems employing quadrature amplitude modulation, and are also able to account for narrowband interference (modeled as a sum of tone interferers). To illustrate the application of the proposed analysis, both methods are used to study the performance of a tone-interference-impaired MB-OFDM system. [ABSTRACT FROM AUTHOR]

Differential space-time modulation (DSTM) using unitary-matrix signal constellations is an attractive solution for transmission over multiple-input multiple-output (MIMO) fading channels without requiring channel state information (CSI) at the receiver. To avoid a high error floor for DSTM in relatively fast MIMO fading channels, multiple-symbol differential detection (MSDD) has to be applied at the receiver. MSDD jointly processes blocks of several received matrix-symbols, and power efficiency improves as the blocksize increases. But since the search space of MSDD grows exponentially with the blocksize and also with the number of transmit antennas and the data rate, the complexity of MSDD quickly becomes prohibitive. In this paper, we investigate the application of tree-search algorithms to overcome the complexity limitation of MSDD. We devise a nested MSDD structure consisting of an outer and a number of inner tree-search decoders, which renders MSDD feasible for wide ranges of system parameters. Decoder designs tailored for diagonal and orthogonal DSTM codes are given, and a more power-efficient variant of MSDD, so- called subset MSDD, is proposed. Furthermore, we derive a tight symbol-error rate approximation for MSDD, which lends itself to efficient numerical evaluation. Numerical and simulation results for different DSTM constellations and fading channel scenarios show that the new tree-search MSDD achieves a significantly better performance-complexity tradeoff than benchmark decoders. [ABSTRACT FROM AUTHOR]

Direct-sequence ultra wideband (DS-UWB) transmission is a strong contender for the physical layer of high data-rate short-range UWB systems. Since long delay spreads in UWB channels cause significant intersymbol interference, DS-UWB systems require equalization. In this second part of two papers, we investigate equalization for DS-UWB with 4-ary biorthogonal keying (4BOK), which is one of the two modulation formats that was proposed for standardization by the IEEE 802.15.3a task group. To this end, we first derive expressions for the bit error rate (BER) accord- ing to the matched-filter bound for 4BOK DS-UWB, which serve as theoretical performance limits for equalization. We then devise structures and methods for filter optimization for low-complexity linear and nonlinear equalization schemes. In this context, we develop a new equivalent multiple-input multiple-output (MIMO) description of 4BOK DS-UWB, which facilitates the design of efficient equalizers using MIMO filter optimization techniques. Furthermore, we propose the application of widely linear processing to these equalizers. Simulation and semianalytical results show that MIMO equalization is greatly advantageous over more obvious non-MIMO schemes and that the proposed MIMO equalizers allow for power-efficient 4BOK DS-UWB transmission close to the theoretical limits with moderate computational complexity. [ABSTRACT FROM AUTHOR]

In this paper, we present a receiver design for Bluetooth transmission based on Laurent's decomposition of the Bluetooth transmit signal. The main features of this receiver are 1) its low complexity compared to alternative solutions; 2) its excellent performance close to the theoretical limit; and 3) its high robustness against frequency offsets, phase noise, and modulation index variations, which are characteristic for low-cost Bluetooth devices. In particular, we show that the devised noncoherent decision-feedback equalization receiver achieves a similar performance as a recently proposed two-state noncoherent sequence detector, while it is advantageous in terms of complexity. The new receiver design is therefore highly attractive for a practical implementation. [ABSTRACT FROM AUTHOR]

In this paper, we consider multiple-bit differential detection (MBDD) of differential offset quadrature phase-shift keying (DOQPSK) with conventional bit-wise differential encoding (DE). We propose two novel MBDD schemes that outperform Simon's MBDD and approach the performance of coherent detection (CD) as the observation window size N increases. The first scheme uses the full available detection window spanning N - 1 bit intervals, and is referred to as F-MBDD. A careful bit-error rate (BER) analysis shows that a significant performance improvement can be realized by reducing the detection window size to N - 3 bit intervals. The resulting improved MBDD (I-MBDD) of DOQPSK with bit-wise DE achieves a similar performance as Phoel's MBDD of DOQPSK with more complex symbol-wise DL For both F-MBDD and I-MBDD, tight upper bounds and accurate BER approximations are derived. In addition, since the complexity per bit decision of brute-force decoding of MBDD of DOQPSK grows exponentially with N, we develop optimum and suboptimum fast decoding algorithms with complexities per bit decision of orders log(N + 1) and N, respectively. [ABSTRACT FROM AUTHOR]

This letter presents an improved error-correction decoder for Bluetooth systems, employing the limiter-discriminator detector with integrate and dump filter (LDI detector) and the expurgated (15,10) binary Hamming code, which is used to protect the payload of data medium-rate packets. The proposed decoder exploits the error statistic of the LDI detector output and makes use of the single-error-correcting double-adjacent-error-correcting (SEC-DAEC) capability of the expurgated (15,10) code. As a result, notable improvements in data throughput and/or transmission range are achieved. Since the performance gains come at no additional cost in implementation, the proposed decoder is highly attractive for application in low-cost Bluetooth devices. [ABSTRACT FROM AUTHOR]

Bit-interleaved coded modulation (BICM) has become the de facto coding standard for communication systems. Recently, BICM has been cast as a mismatched decoding scheme due to the assumption of independent bit metrics. In addition to this inherent mismatch, practical demodulators may produce mismatched decoding metrics because of implementation constraints, such as clipping and metric approximation to reduce computational complexity. In this paper, we investigate BICM with such metrics. In line with recent works on this topic, we adopt the generalized mutual information (GMI) as the pertinent performance measure. First, we show that level-dependent scaling of logarithmic bit metrics can improve the BICM GMI. Second, we propose a uniform metric scaling which can lead to an improved performance of mismatched sum-product symbol-by-symbol decoding, even if the GMI is not changed. Third, we investigate general metric-mismatch correction methods and analyze their effects in terms of the GMI. By means of three application examples, we illustrate that metric-mismatch correction, including metric scaling, can significantly increase BICM rates. [ABSTRACT FROM AUTHOR]