This overview portrays the evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station's or radio port's coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment in multiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems.

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Multiuser MIMO-OFDM for Next-Generation Wireless Systems

We consider the uplink of a multiuser system where the transmitters as well as the receiver are equipped with multiple antennas. Each user multiplexes its symbols by a linear precoder through its transmit antennas. We work with the system-wide mean squared error as the performance measure and propose algorithms to find the jointly optimum linear precoders at each transmitter and linear decoders at the receiver. We first work with the case where the number of symbols to be transmitted by each user is given. We then investigate how the symbol rate should be chosen for each user with optimum transmitters and receivers. The convergence analysis of the algorithms is given, and numerical evidence that supports the analysis is presented.

/pdf/transceiver-optimization-for-multiuser-mimo-systems-5gg3s5omiv.pdf

Transceiver optimization for multiuser MIMO systems

An electronic device such as a portable electronic device has wireless communications circuitry. Antennas in the electronic device may be used in transmitting radio-frequency antenna signals. A coupler and antenna signal phase and magnitude measurement circuitry may be used to determine when external objects are in the vicinity of the antenna by making antenna impedance measurements. In-band and out-of-band phase and magnitude signal measurements may be made in determining whether external objects are present. Additional sensors such as motion sensors, light and heat sensors, acoustic and electrical sensors may produce data that can be combined with the proximity data gathered using the antenna-based proximity sensor. In response to detecting that an external object such as a user's body is within a given distance of the antenna, the electronic device may reduce transmit powers, switch antennas, steer a phased antenna array, switch communications protocols, or take other actions.

Adjustable wireless circuitry with antenna-based proximity detector

As the growing demand for mobile communications is constantly increasing, the need for better coverage, improved capacity, and higher transmission quality rises. Thus, a more efficient use of the radio spectrum is required. Smart antenna systems are capable of efficiently utilizing the radio spectrum and is a promise for an effective solution to the present wireless systems problems while achieving reliable and robust high-speed high-data-rate transmission. The purpose of this book is to provide the reader a broad view of the system aspects of smart antennas. In fact, smart antenna systems comprise several critical areas such as individual antenna array design, signal processing algorithms, space-time processing, wireless channel modeling and coding, and network performance. In this book we include an overview of smart antenna concepts, introduce some of the areas that impact smart antennas, and examine the influence of interaction and integration of these areas to Mobile Ad-Hoc Networks. In addition, the general principles and major benefits of using space-time processing are introduced, especially employing multiple-input multiple-output (MIMO) techniques.

Introduction to Smart Antennas

Energy harvesting technologies are required for autonomous sensor networks for which using a power source from a fixed utility or manual battery recharging is infeasible An energy harvesting device (eg, a solar cell) converts different forms of environmental energy into electricity to be supplied to a sensor node However, since it can produce energy only at a limited rate, energy saving mechanisms play an important role to reduce energy consumption in a sensor node In this article we present an overview of the different energy harvesting technologies and the energy saving mechanisms for wireless sensor networks The related research issues on energy efficiency for sensor networks using energy harvesting technology are then discussed To this end, we present an optimal energy management policy for a solar-powered sensor node that uses a sleep and wakeup strategy for energy conservation The problem of determining the sleep and wakeup probabilities is formulated as a bargaining game The Nash equilibrium is used as the solution of this game

Wireless sensor networks with energy harvesting technologies: a game-theoretic approach to optimal energy management

We introduce and study the use of dynamic slot allocation (DSA) in packet-switched space-division-multiple-access (SDMA) systems. In conventional SDMA, a smart antenna is used at the basestation to simultaneously communicate with multiple stations on the same frequency channel. When dynamic slot allocation is added, the basestation uses uplink channel measurements to intelligently construct future SDMA/TDMA frames. It is shown that under a simple minimum signal-to-interference-plus-noise ratio (SINR) constraint, the problem of performing optimal dynamic slot allocation is NP-complete. Heuristic slot allocation algorithms are introduced which are capable of greatly increasing SDMA/TDMA frame capacity compared with a random allocation of stations. The paper uses both theoretical results and measured data from an experimental testbed to characterize the performance of dynamic slot allocation. The experimental system operates at a carrier frequency of 1.86 GHz and uses an eight-element circular antenna array. It is demonstrated that significant increases in system capacity are possible using DSA in the indoor situations that were tested. Dynamic slot allocation requires the channel to be essentially constant from the time that channel measurements are made until the SDMA/TDMA frame is transmitted. We also present channel measurements which show the effects of channel time coherence in the presence of indoor pedestrian movement. This and other results we have taken suggest that dynamic slot allocation is possible at the frequency considered, provided turnaround times are in the low-to-mid tens of milliseconds.

Dynamic slot allocation (DSA) in indoor SDMA/TDMA using a smart antenna basestation

In the past decade, there has been a huge proliferation of wireless local area networks (WLANs) based on the IEEE 802.11 WLAN standard. As 802.11 connectivity becomes more ubiquitous, multihop communications will be increasingly used for access point range extension and coverage enhancement. In this paper, we present a design for an IEEE 802. 11 -based power saving access point (PSAP), intended for use in multihop battery and solar/battery powered applications. These types of APs have many practical applications and can be deployed very quickly and inexpensively to provide coverage enhancement in situations such as campuses, building complexes, and fast deployment scenarios. Unlike conventional wired access points, in this type of system, power saving on the AP itself is an important objective. A key design constraint is that the proposed PSAP be backward compatible to a wide range of IEEE 802.11 functionality and existing wired access points. In this paper, we introduce the protocols required to achieve this compatibility, show the constraints imposed by this restriction, and present performance results for the proposed system.

Power saving access points for IEEE 802-11 wireless network infrastructure

In the past decade there has been a huge proliferation of wireless local area networks (WLANs) based on the IEEE 802.11 WLAN standard. As 802.11 connectivity becomes more ubiquitous, multi-hop communications is increasingly used for range extension and coverage enhancement purposes. In this paper we present a design for an IEEE 802.11-based power saving access point (PSAP), intended for use in multi-hop battery and solar/battery powered applications. These types of APs have many practical applications and can be deployed very quickly and inexpensively to provide coverage enhancement in situations such as campuses, building complexes and fast deployment scenarios. Unlike conventional wired access points, in this type of system power saving on the AP itself is an important objective. A key design constraint is that the proposed PSAP be backward compatible to a wide range of legacy IEEE 802.11 end stations and existing wired access points. In this paper we describe the protocols required to achieve this compatibility, show the constraints imposed by this restriction, and present performance results for the proposed system.

Power saving access points for IEEE 802.11 wireless network infrastructure

A mobile wireless communications device may include a portable handheld housing, and a wireless transceiver carried by the housing. A pair of an antennas are positioned in side-by-side relation preferably in the upper portion of the portable handheld housing. A human interface diversity controller is connected to the wireless transceiver to preferentially operate with the plurality of antennas based upon a relative position of the portable handheld housing with respect to a hand of a human user. The device can select or weight the antennas based upon the position of the device when being held by a user.

Mobile wireless communications device with human interface diversity antenna and related methods

In this paper we consider vertical handoff for dualmode (DM) cellular/WLAN handsets. When the handset roams out of WLAN coverage, the DM's cellular interface is used to maintain the call by anchoring it through a PSTN gateway/PBX. Soft handoff can be achieved in this case if the gateway supports basic conference bridging, since a new leg of the call can be established to the conference bridge while the existing media stream path is active. Unfortunately this requires that all intraenterprise calls be routed through the gateway when the call is established. In this paper we consider conferenced dual-mode handoff and propose a much more scalable mechanism whereby active calls are handed off into the conference bridge just prior to the initiation of the vertical handoff. Results are presented which are taken from dual-mode handset simulations which characterize the scalability of the proposed mechanism.

Vytas Kezys

Papers

Dynamic slot allocation (DSA) in indoor SDMA/TDMA using a smart antenna basestation

Power saving access points for IEEE 802-11 wireless network infrastructure

Power saving access points for IEEE 802.11 wireless network infrastructure

Mobile wireless communications device with human interface diversity antenna and related methods

Dynamically Anchored Conferencing Handoff for Dual-Mode Cellular/WLAN Handsets