As embedded in wireless signals, information of an indoor environment is captured during radio propagation, motivating the development of emerging wireless sensing technologies. In this paper, we propose a smart radio system that leverages the informative wireless radios to enable intelligent environment and extend human senses to perceive the world. In particular, owing to the time-reversal (TR) technique that captures changes in multipath profiles, the proposed TR indoor monitoring system (TRIMS) is capable of monitoring indoor events and detecting motion through walls in real time. A statistic model of intraclass TR resonance strength is developed and treated as the feature for TRIMS. Moreover, a prototype of TRIMS is implemented using commercial WiFi devices with three antennas. We investigate the performance of TRIMS in different single family houses with normal resident activities. In general, TRIMS can have a perfect detection rate with almost zero false alarm rates for seven target events, whereas during a two-week experiment TRIMS achieves a detection rate of 95.45% in the indoor multievent monitoring. The proposed TRIMS illustrates the potential of smart radio applications in smart homes, thanks to the ubiquitous WiFi.

In this paper, we present an overview of the time-reversal (TR) wireless paradigm for green Internet of Things (IoT). It is shown that the TR technique is a promising technique that focuses signal waves in both time and space domains. The unique asymmetric architecture significantly reduces the cost of the terminal devices, the total number of which is expected to be very large for IoT. The focusing effect of the TR technique can harvest the energy of all the multi-paths at the receiver, which improves the energy efficiency of the wireless transmission and thus the battery life of terminal devices in IoT. Facilitated by the high-resolution spatial focusing, the TR division multiple access scheme leverages the uniqueness of the multi-path profiles in the rich-scattering environment and maps them into location-specific signatures, so that spatial multiplexing can be achieved for multiple users operating on the same spectrum. In addition, the TR system can easily support heterogeneous terminal devices by providing various quality-of-service (QoS) options through adjusting the waveform and rate backoff factor. Finally, the unique location-specific signature in TR system can provide additional physical-layer security and thus can enhance the privacy and security of customers in IoT. All the advantages show that the TR technique is a promising paradigm for IoT.

With the explosive deployment of the information and communications technology (ICT) infrastructures, the rising cost of energy and increased environmental awareness has sparked a keen interest in the development and deployment of energy-efficient communication technologies. As a major player in the ICT sector, the energy efficiency of the mobile cellular networks can be significantly improved by switching off some base stations during off-peak periods. In this paper, we propose an energy-efficient BS switching strategy, and use cooperative communication techniques among the base stations to effectively extend network coverage. We incorporate both the path-loss and fading effects in our system model, and derive closed-form expressions for two important quality of service metrics, the call-blocking probability and the channel outage probability. The proposed scheme guarantees the quality of service of the user equipments by identifying the user equipments situated at the worst-case locations. The energy-saving performance is evaluated and compared with the conventional uni-pattern operation. Both analytical and numerical results show that the proposed energy-efficient switching strategy, facilitated by BS cooperation, can provide significant energy-saving potential for the cellular networks with guaranteed quality of service.

While demand response has achieved promising results on making the power grid more efficient and reliable, the additional dynamics and flexibility brought by demand response also increase the uncertainty and complexity of the centralized load forecast. In this paper, we propose a game theoretic demand response scheme that can transform the traditional centralized load prediction structure into a distributed load prediction system by the participation of customers. Moreover, since customers are generally rational and thus naturally selfish, they may cheat if cheating can improve their payoff. Therefore, enforcing truth-telling is crucial. We prove analytically and demonstrate with simulations that the proposed game theoretic scheme is cheat-proof, i.e., all customers are motivated to report and consume their true optimal demands and any deviation will lead to a utility loss. We also prove theoretically that the proposed demand response scheme can lead to the solution that maximizes social welfare and is proportionally fair in terms of utility function. Moreover, we propose a simple dynamic pricing algorithm for the power substation to control the total demand of all customers to meet the target demand curve. Finally, simulations are shown to demonstrate the efficiency and effectiveness of the proposed game theoretic algorithm.

The rising cost of energy and increased environmental awareness have sparked a keen interest in the development and deployment of energy-efficient communication technologies. The energy efficiency of cellular networks can be increased significantly by selectively switching off some of the base stations (BSs) during periods of low traffic load. In this paper, we propose a scalable BS switching strategy and use cooperative communications and power control to extend network coverage to the service areas of the switched-off BSs. The outage probability and the achievable power savings of the proposed scheme are analyzed, both analytically and numerically, and a potential of up to 50% power saving is observed in the numerical results.

Orthogonal designs have received considerable attention in the development of efficient modulation and coding methods for future multi-antenna wireless communication systems due to their special properties. In this paper, we propose a class of space-time block codes constructed by combining orthogonal designs with sphere packing for an arbitrary number of transmit antennas. The structure of the orthogonal designs is exploited to guarantee full diversity, and sphere packing is used to improve the coding advantage. Space-time block code construction from block-orthogonal designs is also considered: the full-diversity property is ensured by rotating the sphere packing underlying the code, and the optimal rotation angle is determined for a class of sphere packing. Code design examples are provided for two and four transmit antennas and various transmission rates. The simulation results show that by jointly designing the symbols in the orthogonal designs, the performance of the block codes can be significantly increased.

This paper addresses the problem of using a multi-node indoor wireless network as a distributed sensor network that can detect illegal intrusion/trespassing by detecting changes in the propagation environment caused by the intruder, thereby providing the functionality of an indoor surveillance system. The authors propose a detector that takes advantage of multiple scanning cycles, resulting in a very promising detection capability. The authors also investigate the theoretical performance of such systems by analyzing the asymptotic distribution of the log-likelihood ratio and provide guidelines for setting the system parameters for the desired performance. The experiments demonstrate that the theoretical results predict the detector performance very well, and they can be used for configuring the detectors.

In this paper, we propose a new family of wireless networks-the multimodal wireless networks. These networks offer multiple functionalities realized on the same infrastructure. A multimodal wireless network has two modes of operation: 1) the communication mode, when the network is used as a traditional wireless communication network, and 2) the surveillance mode, when the network is used as a distributed sensor network that can detect illegal intrusion. The surveillance functionality is realized by analyzing the properties of the received signals, and the change of the propagation environment caused by the intruder serves as the basis for intrusion detection. We derive maximum likelihood estimators and detectors based on the generalized likelihood ratio test that detects changes in the propagation environment: the single-cycle detector, which makes decisions at the end of each scanning cycle, and the multicycle detector, which combines information from multiple scanning cycles prior to detection. We also analyze the performance of these detectors by deriving the Cramer-Rao lower bound on the variance of the parameter estimators and determining the distribution of the log-likelihood ratio under both detection hypotheses. This will allow us to compare the theoretical performance of the single-cycle and the multicycle detectors and obtain analytical results to determine the decision threshold for a given probability of false alarm. To prevent performance degradation due to slowly drifting parameter values, we propose different strategies to track and update the parameter estimates. The experimental results obtained from an implemented prototype surveillance system show very promising detection capabilities. For example, the state of a door (open or closed) could be detected with a probability of 0.99 at a probability of false alarm 10-5.

Multimodal wireless networks are wireless networks that offer multiple functionalities realized on the same infrastructure. In this paper, we consider a multimodal network that has two modes of operation: the communication mode, when the network is used as a traditional wireless communication network, and the surveillance mode, when the network is used as a distributed sensor network that can detect illegal intrusion by detecting changes in the propagation environment caused by the intruder. We address the problem of distributed surveillance in a network consisting of multiple nodes: we develop a multi-sensor model for the received signal parameters of interest and derive a detector capable of detecting changes in these parameters. The experimental results demonstrate that combining the information from different nodes with the appropriate fusion function results in considerably improved detection performance compared to that of single-node detectors.

A general space-frequency (SF) block code structure is proposed that can guarantee full-rate (one channel symbol per subcarrier) and full-diversity transmission in multiple-input multiple-output-orthogonal frequency-division multiplexing (MIMO-OFDM) systems. The proposed method can be used to construct SF codes for an arbitrary number of transmit antennas, any memoryless modulation and arbitrary power-delay profiles. Moreover, assuming that the power-delay profile is known at the transmitter, we devise an interleaving method to maximize the overall performance of the code. We show that the diversity product can be decomposed as the product of the "intrinsic" diversity product, which depends only on the used signal constellation and the code design, and the "extrinsic" diversity product, which depends only on the applied interleaving method and the power delay profile of the channel. Based on this decomposition, we propose an interleaving strategy to maximize the "extrinsic" diversity product. Extensive simulation results show that the proposed SF codes outperform the previously existing codes by about 3-5 dB, and that the proposed interleaving method results in about 1-3-dB performance improvement compared to random interleaving.

We present an efficient real-time JPEG 2000 image transmission system over heterogeneous wireless networks. By exploiting the advantages of the UDP-lite protocol and cross-layer optimization, the system can utilize the limited bandwidth more efficiently. Moreover, a scalable cross-layer rate allocation (SCRA) algorithm is proposed to perform the cross-layer optimization. The algorithm can manage a large number of adjustable parameters with low complexity. The simulation results show that by using the proposed method, 1.5 dB gain in PSNR can be obtained for a fixed transmission rate of 0.5 bpp, or 30% transmission time can be saved under an end-to-end distortion constraint of 30 dB in PSNR.

In order to make the multi-antenna OFDM systems an attractive choice for practical applications, implementation issues such as decoding complexity must be addressed successfully. In this paper, we propose a computationally efficient decoding algorithm for space-frequency block codes. The central part of the algorithm is a complex-domain, modulation-independent sphere decoding framework. The simulation results demonstrate that the proposed algorithm can significantly reduce the decoding complexity. For the 64 QAM modulation, we observe up to about 73% reduction in the required FLOP count per code block compared to the previously proposed methods without noticeable performance degradation.

The initial work on an indoor infrastructure for context dependent mobile multimedia communication is presented. The aim is to enable simultaneously research and software development at the infrastructures application and service level, system software level and finally at the basis technology level. The research is carried out in a loosely coupled community of researchers mostly specializing into work at one of the levels. The infrastructure consists initially of an IEEE 802.11b WLAN coverage of a part of the IT University indoor site, a system for indoor geographical routing planning, positioning and tracking of mobile terminals, which have a general speech recognition, synthesis interface. The aim is that the infrastructure makes available Java interface to communication and positioning, and a software repository for the support of development of location based services and the multimedia signal processing functions needed for these. The paper describes the initial experiences on the implementation and application of the infrastructure on a part of the university indoor site of approx. 1200 m/sup 2/.

A general space-frequency block code structure is proposed that can guarantee full-rate and full-diversity transmission in MIMO-OFDM systems. The proposed method can be used to construct space-frequency codes for an arbitrary number of transmit antennas, any memoryless modulation and arbitrary power delay profiles. Moreover, assuming that the power delay profile is known at the transmitter, we devise an interleaving method to maximize the overall performance of the code. The simulation results show that under the simulated environment, the proposed SF codes outperform the existing SF codes from orthogonal designs by about 3-5 dB, and that the proposed interleaving method results in about 1-3 dB performance improvement compared to random interleaving.

The potential for capacity increase in multiple-antenna wireless communication systems has drawn considerable attention to space-time codes. However, most of the existing space-time code construction methods have assumed ideal channel models: either quasi-static fading or fast fading. In this work, we propose a systematic space-time trellis code construction method for correlated fading channels. We derive the performance criteria that take into account both spatial and temporal channel correlation, assuming that the space-time correlation matrix is of full rank. Moreover, we introduce a new design criterion and analyze the properties of the space-time trellis codes satisfying the proposed criterion. Using the design criterion, we develop a code construction procedure that jointly considers diversity advantage and coding advantage for an arbitrary number of transmit antennas and any memoryless modulation. The flexibility of the proposed code construction method is demonstrated by designing space-time trellis codes for two, three, and four transmit antennas with quaternary phase-shift keying (QPSK), 8PSK (phase-shift keying), and 4ASK (amplitude-shift keying) modulations. The simulation results demonstrate that not only can our method generate new codes for an arbitrary number of antennas, but in some special cases, where previously proposed codes exist, our codes also perform very well.

Most space-time codes in the literature were proposed based on two ideal channel conditions: either quasistatic or rapid fading. However, these codes may suffer performance degradation due to temporal correlation caused by the movement of the mobile terminal or imperfect interleaving. In this correspondence, we provide a novel analytical framework for the diversity analysis of space-time modulation in time-correlated fading environment. We show that the space-time signals of square size achieving full diversity in quasistatic fading channels also achieve full diversity in time-correlated fading channels, independently of the time correlation matrix. Consequently, various classes of space-time signals designed for quasistatic fading channels can also be used for full-diversity transmission over time-correlated fading channels. Moreover, we show that if the time correlation matrix is of full rank, the design criteria for time-correlated fading channels are the same as those for rapid fading channels. To illustrate the theoretical results, some simulations were also performed under various temporal fading conditions.

The potential for capacity increase in multiantenna wireless communication systems has drawn considerable attention to space-time codes. However, most of the existing space-time code construction methods have assumed ideal channel models: either quasi-static fading of fast fading. In this work, we derive the performance criteria for space-time coded wireless communications systems taking into account both spatial and temporal channel correlation. We show that if the space-time correlation matrix is of full rank, the space-time code design problem for fast fading channels can be reduced to the code design problem for fast fading channels. Some simulation results are also presented to support the theory.

The existing construction of space-time codes or modulation has mainly focused on two ideal situations: either quasi-static or rapid fading channels. In this paper, we consider the design of robust space-time modulation for time-correlated Rayleigh fading channels. We show that the space-time signals of square size achieving full diversity in quasi-static fading channels can also achieve the full diversity in time-correlated fading channels irrespectively of the time correlation matrix. Moreover, we propose a space-time signal construction method by combining orthogonal designs with sphere packings. The simulation results show that our scheme outperforms the previously existing methods. For example, we observe a coding gain of about 1.5 dB over the conventional orthogonal design, about 2 dB over the parametric code, and about 4 dB over the cyclic code under certain fading conditions.

The need for bandwidth- and power-efficient wireless communication systems has raised considerable interest in space-time codes. In this work, we propose a systematic space-time code construction procedure for fast fading channels. The method can be used to design space-time codes for an arbitrary number of transmit antennas and any memoryless modulation. We introduce a new design criterion that ensures full spatial diversity and develop the code design method based on this criterion. The flexibility of the proposed approach is demonstrated by designing space-time trellis codes for 2, 3 and 4 transmit antennas with QPSK, 8PSK and 4ASK modulations.

Space-time codes have been developed to answer the need for high data rates in future wireless communication systems. In this work, we propose a systematic code construction method that provides full diversity advantages for any number of transmit antennas, any number of encoder states, and any constellation. Our approach is to exploit the properties of the state transitions in the trellis to force the desired structure on the channel symbol difference matrix. The design rules do not specify the space-time codes completely, leaving room for further optimization for coding advantage.

The potential for a capacity increase in multi-antenna wireless communication systems has drawn considerable attention to space-time codes. In this work, we propose a systematic code construction method that jointly considers diversity advantage and coding advantage for an arbitrary number of transmit antennas and any memoryless constellation. Due to the special structure of the channel symbol difference matrix, the code construction problem is reduced to a combinatorial optimization problem and a computationally efficient suboptimal solution is proposed. The simulations show that our design procedure results in codes that outperform the ones constructed by previously existing methods. In certain cases, as much as 2-2.5 dB coding gain can be observed.