In previous work we have studied the use of sequential second price auctions for sharing a wireless resource, such as bandwidth or power. The resource is assumed to be managed by a spectrum broker (auctioneer), who collects bids and allocates discrete units of the resource. It is well known that a second price auction for a single indivisible good has an efficient dominant strategy equilibrium; this is no longer the case when multiple units of a homogeneous good are sold in repeated iterations. Previous work attempted to bound this inefficiency loss for two users with non-increasing marginal valuations and full information. This work was based on studying a setting in which one agent's valuation for each resource unit is strictly larger than any of the other agent's valuations and assuming a certain property of the price paid by such a dominant user in any sub-game. Using this assumption it was shown that the worst-case efficiency loss was no more than e(-1). However, here we show that this assumption is not satisfied for all non-increasing marginals with this dominance property. In spite of this, we show that it is always true for the worst-case marginals for any number of goods and so the worst-case efficiency loss for any non-increasing marginal valuations is still bounded by e(-1).

We study a sequential second price auction mechanism for sharing wireless resources among competing transmitters. It is well known that a second price auction for a single indivisible good has an efficient dominant strategy equilibrium; this is no longer the case when multiple units of a homogeneous good are sold in repeated iterations. Nevertheless, in the wireless industry there are pragmatic reasons to prefer mechanisms that are, in effect, equivalent to sequential auctions. Our objective is to study the equilibrium outcomes in these settings and assess their performance. To focus our study on the strategic implications, setting aside issues such as beliefs, incomplete information and collusion, we assume bidders have full information on the mutual valuations. Our results show that, regardless of the number of bidders, there always exists a pure strategy equilibrium. For the two users case, we show that this equilibrium is unique and could result in loss of efficiency. We give bounds on the loss and characterize the worst cases under various constraints. We conclude with some numerical results for losses in the average case.

It has been suggested that light regulation in the form of etiquette protocols, device design and bargaining amongst users will suffice to mitigate a tragedy of the commons in unlicensed spectrum. In this paper we propose a game theoretic model to examine this claim. In this game, each user decides whether or not to set up an access point, which operates on a particular (single) band. The effect of regulation is modeled in reduced form through transfers. A user who sets up an access point, provides payments to each neighbor who does not and suffers a disutility depending on the number of interfering access points. A user who does not set up an access point, receives payments from each neighbor that does. For a suitable model of payoffs, the game is a potential game and best response updates converge to a Nash equilibrium of the game. For any interference parameters, there is a suitable transfer resulting in a Nash equilibrium which is efficient. However, all Nash equilibria may not be efficient.

It has been widely recognized that the current under-utilization of spectrum across many bands could be alleviated through the application of spectrum markets. So far, discussions of market mechanisms for spectrum allocations have focused primarily on secondary markets, which are managed by licensees. Here we explore the consequences of lifting current restrictions on allocations and ownership, and allowing more extensive markets for allocating spectrum across locations, times, and diverse sets of applications (e.g., broadcast, cellular, broadband data, emergency, etc). To motivate our discussion we first estimate the achievable rate per user that could be provided by sharing a large portion of the spectrum suitable for cellular and broadcast types of services. Our results suggest that in general the demand for spectrum may exceed supply implying that market mechanisms are needed to avoid a tragedy of the commons (i.e., associated with an alternative commons model). We then discuss a two- tier spectrum market structure for wireless services in which licenses for spectrum assets at particular locations are traded as commodities. Spectrum owners can choose to rent or lease their spectrum assets via spot markets at particular locations. Such an approach may lower barriers to entry into the wireless services market thereby facilitating competition and the introduction of new services.

A multihop relay extension for IEEE 802.16e systems is the subject of ongoing standardization activities within the IEEE 802.16j Task Group. The emerging IEEE 802.16J standard enhances the 802.16e PHY and MAC to enable support of multihop routes between a mobile station and a base station through intermediate relay stations. Since it is believed that the capacity of a single-hop 802.16e system is uplink-limited, this paper evaluates potential capacity gains attained with the relay enhancement of the 802.16e uplink. The capacity here denotes either cumulative throughput for data traffic or total number of users for voice traffic supported, under certain system-specific constrains detailed below. We first develop a simplified one-dimensional model of a relay-enhanced 802.16e system and estimate the capacity gains via analysis and numerical optimization. Motivated by the capacity gains predicted by this first-order analysis, simulation results obtained from a full two-dimensional simulator modeling a realistic deployment of a relay-enhanced system are then presented. Based on the simulation results, a parametric analysis of relay deployment cost vs. the capacity gain is also presented.

This thesis focuses on resource allocation in wireless communication and networking. Resource allocation has been studied widely, for example, to maximize the system-wide throughput or to minimize the average delay per user. Moreover, the utility-based framework is becoming an important tool for addressing fairness and Quality-of-Service (QoS) for individual users. With this framework, therefore, we study wireless resource allocation for relay extensions in a cellular network and dynamic spectrum sharing among non-cooperative agents.In the first part of the thesis, we study the centralized resource allocation problems among cooperative agents. Especially, the relay extension in a cellular network is focused on, including in-band relays in IEEE 802.16j and out-of-band relays with Wi-Fi access points. Here, the base station optimizes the time or power allocation such that total throughput for data traffic or total number of active users for voice traffic is maximized. For the cases considered, a significant gain for both data traffic and voice traffic is obtained.In the second part of the thesis, dynamic spectrum sharing with distributed resource allocation is considered with an emphasis on the development of mechanisms and their performance. First, we consider an "AP deployment" game in the commons model and show that there exists a Nash equilibrium which is efficient. In addition, we address the limitations of the commons model when interference is severe. Second, we study two auction mechanisms for resource allocation in a peer-to-peer network: The sequential second-price auction and the "Fallback" auction. For the sequential auction, the resource is divided into n units and each unit is auctioned off sequentially according to a second-price auction. The worst-case efficiency of the sequential auction is shown to be lower bounded by 1 - e-1 for a bandwidth allocation and upper bounded by 1/n for a power allocation. Because of the low worst-case efficiency for power allocation and the impracticality of the complete information assumption in the sequential auction, we discuss a Fallback auction, which modifies Ausubel's ascending auction. With an increasing convex utility of one agent due to interference, we show that the Fallback auction for power allocation achieves a stable outcome with minimum revenue to the seller in the core.

We study an implementation problem for settings where some of the participants have non concave valuations. These valuations are common in the wireless industry in cases where primary users with property rights on a spectrum band would like to lease some of it to low power users. The non concavity void the efficiency results for standard designs of dynamic auctions. Moreover, policy concerns in such settings is often to prevent collusion and fraudulent bidding, therefore static Vickrey mechanisms do not provide the right incentives. We present an alternative mechanism that selects a core outcome that minimizes seller revenue. Such an allocation is efficient in equilibrium, limits the incentives to use shills, maximizes incentives for truthful bidding, and gives a Vickrey outcome whenever the latter is in the core.

We study a sequential auction for sharing a wireless resource (bandwidth or power) among competing transmitters. The resource is assumed to be managed by a spectrum broker (auctioneer), who collects bids and allocates discrete units of the resource via a sequential second-price auction. It is well known that a second price auction for a single indivisible good has an efficient dominant strategy equilibrium; this is no longer the case when multiple units of a homogeneous good are sold in repeated iterations. For two users with full information, we show that such an auction has a unique equilibrium allocation. The worst-case efficiency of this allocation is characterized under the following cases: (i) both bidders have a concave valuation for the spectrum resource, and (ii) one bidder has a concave valuation and the other bidder has a convex valuation (e.g., for the other useriquests power). Although the worst-case efficiency loss can be significant, numerical results are presented, which show that for randomly placed transmitter-receiver pairs with rate utility functions, the sequential second-price auction typically achieves the efficient allocation. For more than two users it is shown that this mechanism always has a pure strategy equilibrium, but in general there may be multiple equilibria. We give a constructive procedure for finding one equilibrium; numerical results show that when all users have concave valuations the efficiency loss decreases with an increase in the number of users.

We study a sequential second-price auction for allocating wireless resources between two non-cooperative users. This mechanism requires relatively little computation and information exchange among agents, but does not always achieve an efficient allocation. This is a continuation of previous work in which the worst-case efficiency is evaluated, assuming each user has full knowledge of the other user's utility function. Here we assume that the users are randomly placed within a region, and evaluate the associated efficiency via simulation. Sequential auctions for bandwidth (with fixed power) and for power (with fixed bandwidth) are considered, where each user utility is the achievable rate, and interference is treated as background noise. Our results show that the sequential auction typically achieves the efficient (utility-maximizing) allocation. We also relate observed improvements in the worst-case efficiency to constraints on the size of the marginal utilities associated with each resource.

Market-based mechanisms such as auctions have been widely considered for various network resource allocation problems. We consider such a mechanism motivated by dynamic spectrum sharing applications. In this model multiple homogeneous units of a given resource are to be allocated to two agents. We study a sequential second price auction for allocating these resource units. It is well known that such auctions can have inefficient equilibria. For the case of two bidders, we show that the value of the allocation obtained in the unique subgame perfect equilibrium is at least 1 - e-1 of the value of the efficient allocation. Furthermore, we show that this bound is asymptotically tight as the number of goods increases.

We study the design of a dynamic auction for sharing wireless spectrum between a primary high power user and one or more secondary low power users. In this market, the good being auctioned is transmission power which can be either allocated to the secondary users for transmission or bought by the primary user to reduce her interference. In this setting, the primary user may have a non-concave valuation, which prohibits applying standard designs of dynamic auctions. Moreover, a policy concern in such settings is often to prevent collusion and fraudulent bidding. Hence, Vickrey mechanisms may not provide the right incentives. We present a mechanism that selects a core outcome that minimizes the seller revenue. Such an allocation is efficient in equilibrium, limits the incentives to use shills, maximizes incentives for truthful bidding, and is incentive compatible when the Vickrey outcome is in the core.

We study the downlink coverage of a base station terminal (BST), which has access to a relay node. Continuing a previous study in which the BST is assumed to provide a variable-rate data service, here we assume that each active user requires a target data rate, corresponding to a voice type of service. The relay is assumed to serve a separate set of (non- cellular) users, corresponding to a WiFi Access Point (AP). A one-dimensional model is considered in which cellular and non- cellular users are uniformly distributed along a line. The BST and AP jointly allocate available power across users and the BST-AP link to maximize the total number of users served. We characterize the optimized set of active cellular users served by the BST directly and the AP relay, and the non-cellular users served by the AP. We also give a closed-form upper bound on the increase in the total number of users provided by the relay as a function of user densities and path loss exponents. Our results show that depending on the distance between the BST and the AP, the addition of a relay gives a modest increase in the total number of active users.

The coverage of a base station terminal (BST) in a cellular network can generally be increased through the use of a relay node within the cell boundary. We consider the downlink for a single, one-dimensional cell with a relay node, or access point (AP), which serves a separate set of (non-cellular) users (e.g., corresponding to a WiFi system). The BST and AP jointly allocate available power across users and the BST-AP link to maximize the sum data rate across all cellular and AP users. Two relay schemes are considered: (i) the information flows to the cellular users served by the relay are jointly encoded and transmitted from the BST to the AP; and (ii) the preceding information flows are transmitted in parallel from the BST to the AP. We give an upper bound on the increase in rate provided by the AP, which depends on the relative powers and bandwidths available to the BST and AP. Although the increase in total rate provided by sharing AP resources is typically modest, it can provide a more equitable rate distribution across cellular users, and extend the coverage of the BST.

We have studied the effects of remote hydrogen plasma treatment on the defect characteristics in single crystal ZnO. Temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence spectra reveal that H-plasma exposure of ZnO effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a relative increase in intensity of the I4 (3.363 eV) peak, thought to be related to a neutral donor bound exciton, and a peak feature at 3.366 eV with a distinctly small thermal activation energy. Hydrogenation also produces a violet 100 meV wide peak centered at ∼3.15 eV. Remote plasma hydrogenation yields similar changes in room-temperature depth-dependent cathodoluminescence spectra: the emission intensity increases with hydrogenation mostly in the violet and near-ultraviolet range. Subsequent annealing at 450 °C within the same plasma environment completely restores both the photoluminescence and cathodoluminescence spectra in the subband gap range. The appearance of another bound-exciton feature at 3.366 eV and a relative intensity increase of the donor-bound exciton at line I4 with H-plasma exposure, and the reversibility with annealing of the spectral changes, indicate a direct link between hydrogen indiffusion and appearance of a shallow donor.

The authors report the most recent progress in Type II InAs/GaSb superlattice materials and photovoltaic detectors developed for focal plane array applications with a cutoff wavelength of similar to8 mum. No turn-on of tunneling current was observed even at a reverse bias of -3 V for a 3 mum thick p-i-n photodiodes. The thermally-limited zero bias detectivity under 300 K 2 pi FOV was 2similar to3x10(11) cm(.)Hz(1/2)/W at liquid nitrogen temperature, with a current responsivity of 2similar to3 A/W and a mean quantum efficiency of similar to50%. Initial passivation using SiO2 has shown to decrease the dark current by similar to30% at a reverse bias of -1 V. The same detector structure was used for focal plane arrays with silicon readout integrated circuit. Concept proof of imaging was demonstrated with a format of 256x256 at liquid nitrogen temperature.

We report the most recent advance in the area of type II InAs/GaSb superlattices that have cutoff wavelength of ∼3.7 μm. With GaxIn1−x type interface engineering techniques, the mismatch between the superlattices and the GaSb (001) substrate has been reduced to <0.1%. There is no evidence of dislocations using the best examination tools of x-ray, atomic force microscopy, and transmission electron microscopy. The full width half maximum of the photoluminescence peak at 11 K was ∼4.5 meV using an Ar+ ion laser (514 nm) at fluent power of 140 mW. The integrated photoluminescence intensity was linearly dependent on the fluent laser power from 2.2 to 140 mW at 11 K. The temperature-dependent photoluminescence measurement revealed a characteristic temperature of one T1=245 K at sample temperatures below 160 K with fluent power of 70 mW, and T1=203 K for sample temperatures above 180 K with fluent power of 70 and 420 mW.