Showing papers on "Base station published in 2009"

Pilot Contamination and Precoding in Multi-Cell TDD Systems

Abstract: This paper considers a multi-cell multiple antenna system with precoding used at the base stations for downlink transmission. For precoding at the base stations, channel state information (CSI) is essential at the base stations. A popular technique for obtaining this CSI in time division duplex (TDD) systems is uplink training by utilizing the reciprocity of the wireless medium. This paper mathematically characterizes the impact that uplink training has on the performance of such multi-cell multiple antenna systems. When non-orthogonal training sequences are used for uplink training, the paper shows that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells in an undesirable manner. This paper analyzes this fundamental problem of pilot contamination in multi-cell systems. Furthermore, it develops a new multi-cell MMSE-based precoding method that mitigate this problem. In addition to being a linear precoding method, this precoding method has a simple closed-form expression that results from an intuitive optimization problem formulation. Numerical results show significant performance gains compared to certain popular single-cell precoding methods.

Energy Efficiency Aspects of Base Station Deployment Strategies for Cellular Networks

Abstract: In the strive for lessening of the environmental impact of the information and communication industry, energy consumption of communication networks has recently received increased attention. Although cellular networks account for a rather small share of energy use, lowering their energy con- sumption appears beneficial from an economical perspective. In this regard, the deployment of small, low power base stations, alongside conventional sites is often believed to greatly lower the energy consumption of cellular radio networks. This paper investigates on the impact of deployment strategies on the power consumption of mobile radio networks. We consider layouts featuring varying numbers of micro base stations per cell in addition to conventional macro sites. We introduce the concept of area power consumption as a system performance metric and employ simulations to evaluate potential improvements of this metric through the use of micro base stations. The results suggest, that for scenarios with full traffic load, the use of micro base stations has a rather moderate effect on the area power consumption of a cellular network.

Networked MIMO with clustered linear precoding

Abstract: A clustered base transceiver station (BTS) coordination strategy is proposed for a large cellular MIMO network, which includes full intra-cluster coordination-to enhance the sum rate-and limited inter-cluster coordination-to reduce interference for the cluster edge users. Multi-cell block diagonalization is used to coordinate the transmissions across multiple BTSs in the same cluster. To satisfy per-BTS power constraints, three combined precoder and power allocation algorithms are proposed with different performance and complexity tradeoffs. For inter-cluster coordination, the coordination area is chosen to balance fairness for edge users and the achievable sum rate. It is shown that a small cluster size (about 7 cells) is sufficient to obtain most of the sum rate benefits from clustered coordination while greatly relieving channel feedback requirement. Simulations show that the proposed coordination strategy efficiently reduces interference and provides a considerable sum rate gain for cellular MIMO networks.

An unequal cluster-based routing protocol in wireless sensor networks

Abstract: Clustering provides an effective method for prolonging the lifetime of a wireless sensor network. Current clustering algorithms usually utilize two techniques; selecting cluster heads with more residual energy, and rotating cluster heads periodically to distribute the energy consumption among nodes in each cluster and extend the network lifetime. However, they rarely consider the hot spot problem in multihop sensor networks. When cluster heads cooperate with each other to forward their data to the base station, the cluster heads closer to the base station are burdened with heavier relay traffic and tend to die much faster, leaving areas of the network uncovered and causing network partitions. To mitigate the hot spot problem, we propose an Unequal Cluster-based Routing (UCR) protocol. It groups the nodes into clusters of unequal sizes. Cluster heads closer to the base station have smaller cluster sizes than those farther from the base station, thus they can preserve some energy for the inter-cluster data forwarding. A greedy geographic and energy-aware routing protocol is designed for the inter-cluster communication, which considers the tradeoff between the energy cost of relay paths and the residual energy of relay nodes. Simulation results show that UCR mitigates the hot spot problem and achieves an obvious improvement on the network lifetime.

Interference-Aware Resource Allocation for Device-to-Device Radio Underlaying Cellular Networks

Abstract: Future cellular networks such as IMT-Advanced are expected to allow underlaying direct Device-to-Device (D2D) communication for spectrally efficient support of eg rich multimedia local services Enabling D2D links in a cellular network presents a challenge in radio resource management due to the potentially severe interference it may cause to the cellular network We propose a practical and efficient scheme for generating local awareness of the interference between the cellular and D2D terminals at the base station, which then exploits the multiuser diversity inherent in the cellular network to minimize the interference System simulations demonstrate that substantial gains in cellular and D2D performance can be obtained using the proposed scheme

Orthogonal Frequency Division Multiplexing for Wireless Communications

Abstract: Orthogonal Frequency Division Multiplexing for Wireless Communications is an edited volume with contributions by leading authorities in the subject of OFDM. Its coverage consists of principles, important wireless topics (e.g. Synchronization, channel estimation, etc.) and techniques. Included is information for advancing wireless communication in a multipath environment with an emphasis on implementation of OFDM in base stations. Orthogonal Frequency Division Multiplexing for Wireless Communications provides a comprehensive introduction of the theory and practice of OFDM. Chapter 1, by G. Stber, briefly introduces the history of OFDM or multicarrier modulation and basic concepts of OFDM, Chapter 2, by Y. (G.) Li, presents design of OFDM systems for wireless communications, various impairments caused by wireless channels, and some other types of OFDM related modulation. Chapter 3 to Chapter 6 address different techniques to mitigate the impairments and to improve the performance of OFDM systems. Chapter 3, by J. Cioffi and L. Hoo, focuses on system optimization techniques, including channel partitioning, loading of parallel channels, and optimization through coding. Chapter 4, by S. Wilson and P. dling, addresses timing- and frequency-offset estimation in OFDM systems. It also briefly discusses sampling clock offset estimation and correction. Chapter 5, by Y. (G.) Li, deals with pilot aided and decision-directed channel estimation for OFDM systems. Chapter 6, by C. Tellambura and M. Friese, discusses various techniques to reduce the peak-to-average power ratio of OFDM signals. To facilitate the readers, extensive subject indices and references are given at the end of the book. Even though each chapter is written by different experts, symbols and notations in all chapters of the book are consistent.

Device-to-Device Communication Underlaying Cellular Communications Systems

Abstract: In this article we propose to facilitate local peer-to-peer communication by a Device-to-Device (D2D) radio that operates as an underlay network to an IMT-Advanced cellular network It is expected that local services may utilize mobile peer-to-peer communication instead of central server based communication for rich multimedia services The main challenge of the underlay radio in a multi-cell environment is to limit the interference to the cellular network while achieving a reasonable link budget for the D2D radio We propose a novel power control mechanism for D2D connections that share cellular uplink resources The mechanism limits the maximum D2D transmit power utilizing cellular power control information of the devices in D2D communication Thereby it enables underlaying D2D communication even in interference-limited networks with full load and without degrading the performance of the cellular network Secondly, we study a single cell scenario consisting of a device communicating with the base station and two devices that communicate with each other The results demonstrate that the D2D radio, sharing the same resources as the cellular network, can provide higher capacity (sum rate) compared to pure cellular communication where all the data is transmitted through the base station

The future of WiMAX: Multihop relaying with IEEE 802.16j

Abstract: Relaying and cooperation have re-emerged as important research topics in wireless communication over the past half-decade. Although multihop relaying for coverage extension in wireless networks is an old concept, it became practical only recently. Nowhere is this better illustrated than in the IEEE 802.16 working group, which has devoted a task group to incorporating relay capabilities in the foundation of mobile WiMAX-IEEE 802.16e-2005. Currently, this task group is in the process of finishing IEEE 802.16j, the multihop relay specification for 802.16. This amendment will be fully compatible with 802.16e-2005 mobile and subscriber stations, but a BS specific to 802.16j will be required for relays to operate. This article presents an introduction to the upcoming IEEE 802.16j amendment and provides insight about the obstacles that practical system designers face when incorporating relaying into a wireless broadband network.

Relay architectures for 3GPP LTE-advanced

Abstract: The Third Generation Partnership Project's Long Term Evolution-Advanced is considering relaying for cost-effective throughput enhancement and coverage extension. While analog repeaters have been used to enhance coverage in commercial cellular networks, the use of more sophisticated fixed relays is relatively new. The main challenge faced by relay deployments in cellular systems is overcoming the extra interference added by the presence of relays. Most prior work on relaying does not consider interference, however. This paper analyzes the performance of several emerging half-duplex relay strategies in interference-limited cellular systems: one-way, two-way, and shared relays. The performance of each strategy as a function of location, sectoring, and frequency reuse are compared with localized base station coordination. One-way relaying is shown to provide modest gains over single-hop cellular networks in some regimes. Shared relaying is shown to approach the gains of local base station coordination at reduced complexity, while two-way relaying further reduces complexity but only works well when the relay is close to the handset. Frequency reuse of one, where each sector uses the same spectrum, is shown to have the highest network throughput. Simulations with realistic channel models provide performance comparisons that reveal the importance of interference mitigation in multihop cellular networks.

Coordinated Scheduling and Power Allocation in Downlink Multicell OFDMA Networks

Abstract: We consider a multicell orthogonal frequency-division multiple-access (OFDMA) wireless network with universal frequency reuse and treat the problem of cochannel interference mitigation via base station coordination in the downlink. Assuming that coordinated access points only share channel quality measurements but not user data symbols, we propose to select the set of cochannel users and the power allocation across tones to maximize the weighted system sum rate subject to per-base-station power constraints. Since this is a nonconvex combinatorial problem, efficient suboptimal algorithms are presented and discussed, each requiring a different level of coordination among base stations and a different feedback signaling overhead. Simulation results are provided to assess the performances of the proposed strategies.

Vertical Handoff Decision Algorithms for Providing Optimized Performance in Heterogeneous Wireless Networks

Abstract: There are currently a large variety of wireless access networks, including the emerging vehicular ad hoc networks (VANETs). A large variety of applications utilizing these networks will demand features such as real-time, high-availability, and even instantaneous high-bandwidth in some cases. Therefore, it is imperative for network service providers to make the best possible use of the combined resources of available heterogeneous networks (wireless area networks (WLANs), Universal Mobile Telecommunications Systems, VANETs, Worldwide Interoperability for Microwave Access (WiMAX), etc.) for connection support. When connections need to migrate between heterogeneous networks for performance and high-availability reasons, seamless vertical handoff (VHO) is a necessary first step. In the near future, vehicular and other mobile applications will be expected to have seamless VHO between heterogeneous access networks. With regard to VHO performance, there is a critical need to develop algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a VHO decision algorithm that enables a wireless access network to not only balance the overall load among all attachment points (e.g., base stations and access points) but also maximize the collective battery lifetime of mobile nodes (MNs). In addition, when ad hoc mode is applied to 3/4G wireless data networks, VANETs, and IEEE 802.11 WLANs for a more seamless integration of heterogeneous wireless networks, we devise a route-selection algorithm for forwarding data packets to the most appropriate attachment point to maximize collective battery lifetime and maintain load balancing. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed algorithms.

Energy Efficiency Improvements through Micro Sites in Cellular Mobile Radio Networks

Abstract: Efforts to increase the energy efficiency of infor- mation and communication systems in general and cellular mobile radio networks in particular has recently gained mo- mentum. Besides positive environmental effects, lowering the energy consumption of mobile radio systems appears beneficial from an economical perspective. In this regard, the deployment of small, low power base stations, alongside conventional sites is often believed to greatly lower the energy consumption of cellular mobile radio networks. In this paper we investigate that matter in more detail from a deployment perspective. We evaluate potential improvements of the area power consumption achievable with network layouts featuring varying numbers of micro sites in addition to conventional macro sites for given system performance targets under full load conditions.

Green Mobile Access Network with Dynamic Base Station Energy Saving

Abstract: The explosive development of ICT (information and communication technology) industry has emerged as one of the major sources of world energy consumption. Therefore, this paper concerns about the BS (base station) energy saving issue, for most energy consumption of the communication network comes from the BSs and the core network. Particularly, we consider dynamically turning off certain BSs when the network traffic is low. Centralized and decentralized implementations are investigated. Simulations demonstrate the energy efficiency of the proposed algorithms and the tradeoff between energy saving and coverage guarantee.

Centralized control of peer discovery pilot transmission

Abstract: Techniques for centralized control of peer discovery pilot transmission are described. In an aspect, a designated network entity (e.g., a base station or a network controller) may control transmission of peer discovery pilots by stations located within its coverage area. In one design, the network entity may receive signaling triggering peer discovery pilot transmission. The network entity may direct each of at least one station to transmit a peer discovery pilot to allow one or more stations to detect the at least one station. The peer discovery pilot may include at least one synchronization signal or at least one reference signal. The network entity may receive pilot measurements from the one or more stations for peer discovery pilots from peer stations and/or reference signals from base stations. The network entity may determine whether or not to select peer-to-peer communication for two stations based on the pilot measurements.

Wireless base station design

Abstract: A multi-transmitter base station for wireless digital communication, having beam forming and digital pre-distortion capabilities, including a shared feedback unit for providing feedback of outgoing Radio Frequency (RF) signals for calibrating a plurality of antennas and for adapting the digital pre-distortion. Related apparatus and methods are also described.

Spectrum sharing between cellular and mobile ad hoc networks: transmission-capacity trade-off

Abstract: Spectrum sharing between wireless networks improves the efficiency of spectrum usage, and thereby alleviates spectrum scarcity due to growing demands for wireless broadband access. To improve the usual underutilization of the cellular uplink spectrum, this paper addresses spectrum sharing between a cellular uplink and a mobile ad hoc networks. These networks access either all frequency subchannels or their disjoint subsets, called spectrum underlay and spectrum overlay, respectively. Given these spectrum sharing methods, the capacity trade-off between the coexisting networks is analyzed based on the transmission capacity of a network with Poisson distributed transmitters. This metric is defined as the maximum density of transmitters subject to an outage constraint for a given signal-to-interference ratio (SIR). Using tools from stochastic geometry, the transmission-capacity trade-off between the coexisting networks is analyzed, where both spectrum overlay and underlay as well as successive interference cancellation (SIC) are considered. In particular, for small target outage probability, the transmission capacities of the coexisting networks are proved to satisfy a linear equation, whose coefficients depend on the spectrum sharing method and whether SIC is applied. This linear equation shows that spectrum overlay is more efficient than spectrum underlay. Furthermore, this result also provides insight into the effects of network parameters on transmission capacities, including link diversity gains, transmission distances, and the base station density. In particular, SIC is shown to increase the transmission capacities of both coexisting networks by a linear factor, which depends on the interference-power threshold for qualifying canceled interferers.

Video delivery systems using wireless cameras

Abstract: Systems, apparatuses, and techniques for video delivery can include one or more of the following: a wireless camera arranged in a wearable form factor comprising a battery to provide energy, and configured to generate a video feed, and a base station in wireless communication with the wireless camera and configured to receive the video feed from the wireless camera and process the video feed, and a video portal device communicatively coupled with the base station and configured to receive the processed video feed from the base station and deliver at least a portion of the processed video feed to one or more remote clients. A base station can reserve a wireless channel for the wireless camera for a video transmission.

On cellular botnets: measuring the impact of malicious devices on a cellular network core

Abstract: The vast expansion of interconnectivity with the Internet and the rapid evolution of highly-capable but largely insecure mobile devices threatens cellular networks. In this paper, we characterize the impact of the large scale compromise and coordination of mobile phones in attacks against the core of these networks. Through a combination of measurement, simulation and analysis, we demonstrate the ability of a botnet composed of as few as 11,750 compromised mobile phones to degrade service to area-code sized regions by 93%. As such attacks are accomplished through the execution of network service requests and not a constant stream of phone calls, users are unlikely to be aware of their occurrence. We then investigate a number of significant network bottlenecks, their impact on the density of compromised nodes per base station and how they can be avoided. We conclude by discussing a number of countermeasures that may help to partially mitigate the threats posed by such attacks.

Method, Apparatus and Computer Program Product for Allocating Resources in Wireless Communication Network

Abstract: The present application discloses a method, an apparatus and a computer program product for allocating resources for a Device-to-Device (D2D) direct communication user equipment in a wireless communication network, wherein the method comprise: transmitting a communication channel status report regarding Device-to-Device direct communication to a base station; receiving resource allocation instructions generated by the base station based on the communication channel status report; and performing Device-to-Device direct communication between user equipments on the allocated resources; the disclosed apparatus comprises transmitting means for transmitting a communication channel status report regarding Device-to-Device direct communication to a base station; receiving means for receiving resource allocation instructions generated by the base station based on the communication channel status report; and performing means for performing Device-to-Device direct communication between user equipments on the allocated resources. By using the method, apparatus and computer program product disclosed in the present application, resource sharing/allocation collision between the D2D user equipment and cellular user equipment can be effectively reduced and use rate of resources can be improved.

Pilot contamination problem in multi-cell TDD systems

Abstract: This paper considers a multi-cell multiple antenna system with precoding at the base stations for downlink transmission. To enable precoding, channel state information (CSI) is obtained via uplink training. This paper mathematically characterizes the impact that uplink training has on the performance of multi-cell multiple antenna systems. When non-orthogonal training sequences are used for uplink training, it is shown that the precoding matrix used by the base station in one cell becomes corrupted by the channel between that base station and the users in other cells. This problem of pilot contamination is analyzed in this paper. A multi-cell MMSE-based precoding is proposed that, when combined with frequency/time/pilot reuse techniques, mitigate this problem.

Method and apparatus for transmitting signal in wireless communication system

Abstract: A method of transmitting a signal of a base station in a wireless communication system is provided. The method includes transmitting a first signal to the relay station through the transmission period in a subframe including a transmission period and a guard time for transmission/reception switching of a relay station, and transmitting a second signal to a macro user equipment through the guard time. Accordingly, a signal can be effectively transmitted in the wireless communication system employing the relay station.

Method and apparatus for beamforming in ofdm wireless systems

Abstract: Systems and methods are disclosed for use in a wireless network that promotes simultaneous beamforming. These systems and methods include determining the Channel Quality Indicator (CQI) and Best Beam Index (BBI) for communications between a plurality of mobile stations and a base station, ranking the plurality of mobile stations in a list according to the determined CQI and BBI, and selecting a subset of the plurality of mobile stations for simultaneous beamformed communications. These systems and methods may also include verifying the selected subset of the plurality of mobile stations do not have a conflict and initiating beamformed communications. BBI is determined based on a predetermined codebook, which is function of antenna configuration as shown in equation 2 and 5. Any other codebook use equations 2 and 5 as their subset can also be applied.

Techniques for Supporting Relay Operation in Wireless Communication Systems

Abstract: Techniques for supporting operation of relay stations in wireless communication systems are described. In an aspect, a bitmap may be sent by a base station and/or a relay station to identify subframes of at least two types in multiple radio frames. For example, the bitmap may indicate whether each subframe covered by the bitmap is of a first type or a second type. UEs may use the bitmap to control their operation. For example, a UE may perform channel estimation or measurement for the subframes of the first type and may skip channel estimation and measurement for the subframes of the second type. In another aspect, a base station may transmit data and/or control information on resources not used by a relay station to transmit a reference signal. This may avoid interference to the reference signal from the relay station, which may improve performance for UEs communicating with the relay station.

EARTH — Energy Aware Radio and Network Technologies

Abstract: EARTH is a major new European research project starting in 2010 with 15 partners from 10 countries. Its main technical objective is to achieve a reduction of the overall energy consumption of mobile broadband networks by 50%. In contrast to previous efforts, EARTH regards both network aspects and individual radio components from a holistic point of view. Considering that the signal strength strongly decreases with the distance to the base station, small cells are more energy efficient than large cells. EARTH will develop corresponding deployment strategies as well as management algorithms and protocols on the network level. On the component level, the project focuses on base station optimizations as power amplifiers consume the most energy in the system. A power efficient transceiver will be developed that adapts to changing traffic load for an energy efficient operation in mobile radio systems. With these results EARTH will reduce energy costs and carbon dioxide emissions and will thus enable a sustainable increase of mobile data rates.

Dynamic allocation of subframe scheduling for time division duplex operation in a packet-based wireless communication system

Abstract: Systems and methods for enabling the dynamic allocation of certain sub frames as downlink or uplink resources in a time division duplexed over the air communications system. A base station or eNB may allocate certain subframes within a repeating radio frame of a TDD configuration as either DL or UL subframes for communicating to user equipment or UE devices to increase efficient use of system resources based on the data to be transmitted. Methods for determining the capabilities of a selected UE and based on the determining step, dynamically allocating certain subframes are disclosed. The methods and systems are compatible with user equipment that does not support the dynamic allocation of subframes.

Wireless power transfer system, power transmitter, and rectenna base station

Abstract: A wireless power transfer system includes: a plurality of power transmitters, each of which transmits a microwave; and a rectenna base station which receives the microwave to generate power. The rectenna base station includes: a rectenna; and control section which specifies an identification code for identifying each power transmitter and generates a command signal to change a phase of the power transmitter specified by identification code so as to increase a power value received at the rectenna. Each of the power transmitters comprises: a plurality of transmission antenna elements, each of which transmits the microwave to the rectenna base station; and a phase controller which makes phase change of the microwave based on the command signal from the phase monitor and control section of the rectenna base station if the identification code matches a stored identification code.

Joint Beamforming and Power Control for Multiantenna Relay Broadcast Channel With QoS Constraints

Abstract: This paper studies the two-hop relay broadcast channel (BC) for a relay-assisted wireless cellular network where the multiuser independent downlink signals from the base station (BS) are first transmitted to a fixed relay station (RS), and then forwarded by the RS to multiple mobile users. Assuming both the BS and RS are equipped with multiantennas, we study the joint optimization of linear beamforming and power control at the BS and RS so as to minimize their weighted sum-power consumption under the user minimum signal-to-interference-noise-ratio (SINR) - quality-of-service (QoS) - constraints. We apply two well-known criteria in the literature, namely, the ldquoSINR balancingrdquo and the ldquochannel-inversion,rdquo for the design of linear precoding in the traditional nonrelay-assisted multiantenna BC to the relay-assisted multiantenna BC. First, a convergence-ensured iterative SINR-balancing algorithm is proposed to successively in turn optimize the transmit parameters at one station (BS or RS) with those at the other station being fixed. Second, a joint BS and RS channel-inversion algorithm is proposed together with a novel technique, termed ldquoeigenmode switching,rdquo at the RS to reduce the power penalty of the channel inversion. Simulation results show that the proposed joint beamforming and power control schemes provide substantial power savings to achieve the assigned user QoS constraints.

Apparatus and method for communicating and processing a positioning reference signal based on identifier associated with a base station

Abstract: A base station communicates a positioning reference signal (PRS) to wireless communication devices over a downlink in a wireless communication system by encoding a PRS into a first set of transmission resources, encoding other information into a second set of transmission resources, multiplexing the two sets of resources into a subframe such that the first set of resources is multiplexed into at least a portion of a first set of orthogonal frequency division multiplexed (OFDM) symbols based on an identifier associated with the base station and the second set of resources is multiplexed into a second set of OFDM symbols, and transmitting the subframe. Upon receiving the subframe, a wireless device determines which set of transmission resources contains the PRS based on the identifier associated with the base station that transmitted the subframe and processes the set of resources containing the PRS to estimate timing (e.g., time of arrival) information.

Local Base Station Cooperation Via Finite-Capacity Links for the Uplink of Linear Cellular Networks

Abstract: Cooperative decoding at the base stations (or access points) of an infrastructure wireless network is currently well recognized as a promising approach for intercell interference mitigation, thus enabling high frequency reuse. Deployment of cooperative multicell decoding depends critically on the tolopology and quality of the available backhaul links connecting the base stations. This work studies a scenario where base stations are connected only if in adjacent cells, and via finite-capacity links. Relying on a linear Wyner-type cellular model with no fading, achievable rates are derived for the two scenarios where base stations are endowed only with the codebooks of local (in-cell) mobile stations, or also with the codebooks used in adjacent cells. Moreover, both uni- and bidirectional backhaul links are considered. The analysis sheds light on the impact of codebook information, decoding delay, and network planning (frequency reuse) on the performance of multicell decoding as enabled by local and finite-capacity backhaul links. Analysis in the high-signal-to-noise ratio (SNR) regime and numerical results validate the main conclusions.

Opportunistic spectrum sharing in cognitive MIMO wireless networks

Abstract: Cognitive radio has been recently proposed as a promising technology to improve the spectrum utilization In this paper, we consider the spectrum sharing between a large number of cognitive radio users and a licensed user in order to enhance the spectrum efficiency With the deployment of M antennas at the cognitive base station, an opportunistic spectrum sharing approach is proposed to maximize the downlink throughput of the cognitive radio system and limit the interference to the primary user In the proposed approach, cognitive users whose channels are nearly orthogonal to the primary user channel are pre-selected so as to minimize the interference to the primary user Then, M best cognitive users, whose channels are mutually near orthogonal to each other, are scheduled from the preselected cognitive users A lower bound of the proposed cognitive system capacity is derived It is then shown that opportunistic spectrum sharing approach can be extended to the multiple input/ multiple-output (MIMO) case, where a receive antenna selection is utilized in order to further reduce the computational and feedback complexity Simulation results show that our proposed approach is able to achieve a high sum-rate throughput, with affordable complexity, when considering either single or multiple antennas at the cognitive mobile terminals